首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2124篇
  免费   98篇
  国内免费   69篇
耳鼻咽喉   19篇
儿科学   24篇
妇产科学   29篇
基础医学   365篇
口腔科学   46篇
临床医学   197篇
内科学   345篇
皮肤病学   56篇
神经病学   105篇
特种医学   82篇
外科学   310篇
综合类   12篇
一般理论   1篇
预防医学   106篇
眼科学   12篇
药学   208篇
中国医学   12篇
肿瘤学   362篇
  2023年   15篇
  2022年   56篇
  2021年   75篇
  2020年   34篇
  2019年   54篇
  2018年   55篇
  2017年   44篇
  2016年   71篇
  2015年   115篇
  2014年   141篇
  2013年   165篇
  2012年   226篇
  2011年   186篇
  2010年   96篇
  2009年   94篇
  2008年   117篇
  2007年   140篇
  2006年   84篇
  2005年   103篇
  2004年   57篇
  2003年   57篇
  2002年   44篇
  2001年   36篇
  2000年   36篇
  1999年   32篇
  1998年   22篇
  1997年   16篇
  1996年   8篇
  1995年   12篇
  1994年   5篇
  1993年   11篇
  1992年   11篇
  1991年   10篇
  1990年   15篇
  1989年   9篇
  1988年   11篇
  1987年   5篇
  1986年   3篇
  1985年   5篇
  1984年   2篇
  1983年   3篇
  1982年   1篇
  1981年   1篇
  1979年   1篇
  1976年   1篇
  1975年   1篇
  1974年   1篇
  1954年   1篇
  1948年   2篇
  1947年   1篇
排序方式: 共有2291条查询结果,搜索用时 15 毫秒
71.
Recently, applications for lithium-ion batteries (LIBs) have expanded to include electric vehicles and electric energy storage systems, extending beyond power sources for portable electronic devices. The power sources of these flexible electronic devices require the creation of thin, light, and flexible power supply devices such as flexile electrolytes/insulators, electrode materials, current collectors, and batteries that play an important role in packaging. Demand will require the progress of modern electrode materials with high capacity, rate capability, cycle stability, electrical conductivity, and mechanical flexibility for the time to come. The integration of high electrical conductivity and flexible buckypaper (oxidized Multi-walled carbon nanotubes (MWCNTs) film) and high theoretical capacity silicon materials are effective for obtaining superior high-energy-density and flexible electrode materials. Therefore, this study focuses on improving the high-capacity, capability-cycling stability of the thin-film Si buckypaper free-standing electrodes for lightweight and flexible energy-supply devices. First, buckypaper (oxidized MWCNTs) was prepared by assembling a free stand-alone electrode, and electrical conductivity tests confirmed that the buckypaper has sufficient electrical conductivity (10−4(S m−1) in LIBs) to operate simultaneously with a current collector. Subsequently, silicon was deposited on the buckypaper via magnetron sputtering. Next, the thin-film Si buckypaper freestanding electrodes were heat-treated at 600 °C in a vacuum, which improved their electrochemical performance significantly. Electrochemical results demonstrated that the electrode capacity can be increased by 27/26 and 95/93 μAh in unheated and heated buckypaper current collectors, respectively. The measured discharge/charge capacities of the USi_HBP electrode were 108/106 μAh after 100 cycles, corresponding to a Coulombic efficiency of 98.1%, whereas the HSi_HBP electrode indicated a discharge/charge capacity of 193/192 μAh at the 100th cycle, corresponding to a capacity retention of 99.5%. In particular, the HSi_HBP electrode can decrease the capacity by less than 1.5% compared with the value of the first cycle after 100 cycles, demonstrating excellent electrochemical stability.  相似文献   
72.
Background/AimsAlthough localized lymphoid hyperplasia (LLH) of the rectum is occasionally observed, its clinical implications are unclear. This study aimed to investigate the clinical course and significance of LLH of the rectum.MethodsWe identified 65 patients diagnosed with LLH of the rectum using a histopathologic examination and who received follow-up endoscopies between January 2009 and June 2015. Patients with a history of inflammatory bowel disease, lymphoma, familial adenomatous polyposis, or uncontrolled malignancy and patients who underwent scar biopsy after endoscopic resection or surgery were excluded. Endoscopic findings and clinical courses were analyzed.ResultsDuring the median follow-up of 31 months (interquartile range, 19 to 40 months), 81.5% (53/65) of LLHs of the rectum were resolved. Clinically significant diseases, including ulcerative colitis (UC, n=5) and mucosa-associated lymphoid tissue (MALT) lymphoma (n=1), were diagnosed in 9.2% of patients (6/65). The other six patients showed no significant changes in the lesion (n=3) or a waxing and waning appearance (n=3). According to endoscopic findings, all of the 47 polypoid types showed resolution or waxing and waning patterns. Five of the 11 nodular types (45.5%) developed into UC. One of the seven submucosal tumor (SMT)-like types (14.3%) developed into MALT lymphoma.ConclusionsLLH of the rectum with persistent symptoms or the endoscopic appearance of the nodular or SMT-like type may lead to clinically significant disease. Risk stratification according to endoscopic findings and careful surveillance are required for these lesions.  相似文献   
73.
Peroxisome proliferator-activated receptor-gamma (PPARgamma) is a ligand-activated nuclear receptor expressed in all of the major cell types found in atherosclerotic lesions: monocytes/macrophages, endothelial cells, and smooth muscle cells. In vitro, PPARgamma ligands inhibit cell proliferation and migration, 2 processes critical for vascular lesion formation. In contrast to these putative antiatherogenic activities, PPARgamma has been shown in vitro to upregulate the CD36 scavenger receptor, which could promote foam cell formation. Thus, it is unclear what impact PPARgamma activation will have on the development and progression of atherosclerosis. This issue is important because thiazolidinediones, which are ligands for PPARgamma, have recently been approved for the treatment of type 2 diabetes, a state of accelerated atherosclerosis. We report herein that the PPARgamma ligand, troglitazone, inhibited lesion formation in male low density lipoprotein receptor-deficient mice fed either a high-fat diet, which also induces type 2 diabetes, or a high-fructose diet. Troglitazone decreased the accumulation of macrophages in intimal xanthomas, consistent with our in vitro observation that troglitazone and another thiazolidinedione, rosiglitazone, inhibited monocyte chemoattractant protein-1-directed transendothelial migration of monocytes. Although troglitazone had some beneficial effects on metabolic risk factors (in particular, a reduction of insulin levels in the diabetic model), none of the systemic cardiovascular risk factors was consistently improved in either model. These observations suggest that the inhibition of early atherosclerotic lesion formation by troglitazone may result, at least in part, from direct effects of PPARgamma activation in the artery wall.  相似文献   
74.

Aims/Introduction

Many studies have reported that high levels of glycated hemoglobin (HbA1c) are strongly associated with an increased risk of cardiovascular disease. Many researchers have not studied the association of HbA1c with various subclinical atherosclerosis phenotypes. We evaluated the impact of HbA1c on arterial stiffness and atherosclerosis in healthy Korean healthy men.

Materials and Methods

The study population included healthy adult men who participated in health check‐ups. All participants fasted for at least 8 h before taking the blood sample for fasting blood glucose, HbA1c, total cholesterol, high‐density lipoprotein cholesterol, low‐density lipoprotein cholesterol and triglyceride. Arterial stiffness was measured using brachial‐ankle pulse wave velocity. Hierarchical regression analysis allowed us to determine the relationship between brachial‐ankle pulse wave velocity (baPWV) and potential risk factors for cardiovascular disease.

Results

Age and HbA1c were significantly related to baPWV, in model 1. In model 2, blood pressure was added to model 1. Systolic blood pressure was a more significant variable, which was more affected on baPWV than diastolic blood pressure. In the case of model 3, we included all variables regarding arterial stiffness. According to model 3, the most explainable variable was age, and then systolic blood pressure, body mass index and triglyceride, respectively.

Conclusions

We analyzed the associations between HbA1c, which is one of the risk factors, and arterial stiffness independently. An arterial stiffness measurement using baPWV can show the level of severity of the arteriosclerosis. When the level of stiffness has been increased, we could assume that the risk of arteriosclerosis would be increased. It can also be related to the increase of the risk of cardiovascular disease.  相似文献   
75.

Objective

Chronic pain frequently coexists with psychiatric symptoms in patients diagnosed with complex regional pain syndrome (CRPS). Previous studies have shown a relationship between CRPS and the risk of suicide. The purpose of this study was to assess risk factors for suicidal ideation in patients with CRPS.

Methods

Based on criteria established by the International Association for the Study of Pain, 39 patients diagnosed with CRPS Type 1 or Type 2 were enrolled in this study. Suicidal ideation was assessed using item 3 of the Hamilton Depression Rating Scale (HAMD), and symptoms of pain were evaluated using the short form of the McGill Pain Questionnaire (SF-MPQ). Psychiatric symptoms were assessed in using the Structured Clinical Interview for DSM-IV Disorders (SCID-I, SCID-II), the HAMD, the Hamilton Anxiety Rating Scale (HAMA), the Global Assessment of Functioning Scale (GAF), and the Pittsburgh Sleep Quality Index (PSQI).

Results

Twenty-nine patients (74.4%) were at high risk and 10 (25.6%) were at low risk for suicidal ideation. Risk factors significantly associated with suicidal ideation included depression (p=0.002), severity of pain (p=0.024), and low scores on the GAF (p=0.027). No significant correlations were found between suicidal ideation and anxiety or quality of sleep.

Conclusion

Significant risk factors for suicidal ideation in patients with CRPS include severity of pain, depressive symptoms, and decreased functioning. These results suggest that psychiatric evaluation and intervention should be included in the treatment of CRPS.  相似文献   
76.
77.
Brilliant animal colors often are produced from light interacting with intricate nano-morphologies present in biological materials such as butterfly wing scales. Surveys across widely divergent butterfly species have identified multiple mechanisms of structural color production; however, little is known about how these colors evolved. Here, we examine how closely related species and populations of Bicyclus butterflies have evolved violet structural color from brown-pigmented ancestors with UV structural color. We used artificial selection on a laboratory model butterfly, B. anynana, to evolve violet scales from UV brown scales and compared the mechanism of violet color production with that of two other Bicyclus species, Bicyclus sambulos and Bicyclus medontias, which have evolved violet/blue scales independently via natural selection. The UV reflectance peak of B. anynana brown scales shifted to violet over six generations of artificial selection (i.e., in less than 1 y) as the result of an increase in the thickness of the lower lamina in ground scales. Similar scale structures and the same mechanism for producing violet/blue structural colors were found in the other Bicyclus species. This work shows that populations harbor large amounts of standing genetic variation that can lead to rapid evolution of scales’ structural color via slight modifications to the scales’ physical dimensions.Organisms produce colors in two basic ways: by synthesizing pigments that selectively absorb light of certain spectral bands so that only light outside the absorption bands is backscattered (chemical color) or by developing nanomorphologies that enhance the reflection of light of certain wavelengths by interference (physical color or structural color). Structural colors play major roles in natural and sexual selection in many species (1) and have a broad range of applications in color display, paint, cosmetics, and textile industries (2). Structural color surveys across widely divergent species have revealed a large diversity of color-producing mechanisms (39). However, there has been a lack of systematic study and comparison of how different colors from closely related species or within populations of a single species evolve, even though these colors can vary dramatically. By examining how these species/populations evolve different colors, it is possible to identify the minimal amount of morphological change that results in significant color variation. Furthermore, this research may serve as an inspiration for future application of similar evolutionary principles to the design of photonic devices for color tuning, light trapping, or beam steering (2, 1020). From an evolutionary biology point of view, we are curious to examine how structural colors respond to selection pressure and whether there is sufficient standing genetic variation in natural populations to allow the rapid evolution of novel colors. Here we focus on determining the morphological changes and the physical mechanisms that cause the evolution of violet structural color in populations of a single species and also across different species within a single genus of butterflies.We focus on the genus Bicyclus (Lepidoptera: Nymphalidae), composed of more than 80 species that predominantly exhibit brown color along with marginal eyespots. Some Bicyclus species, however, have independently evolved transverse bands of bright violet/blue structural color on the dorsal surface of the forewings (black asterisks in Fig. 1A) (21, 22). One species, Bicyclus anynana, has become a model species amenable to laboratory rearing, and multiple aspects of its marginal eyespots (size, relative width of the color rings, shape) have been altered by artificial selection (2327). However, change of color (hue), either pigmentary or structural, via artificial selection has not been reported. B. anynana does not exhibit bright violet coloration on its wings and therefore provides an excellent opportunity for investigating whether there is genetic potential to produce violet color upon directed selection. We investigated this potential by performing an artificial selection experiment in B. anynana that targeted the color of the specific dorsal wing region that evolved violet/blue coloration in other members of the genus (Fig. 1 BG).Open in a separate windowFig. 1.Structural color in Bicyclus butterflies and basic wing scale morphology. (A) A phylogenetic estimate of Bicyclus butterfly relationships (modified from ref. 41) illustrating the evolution of color in the genus. The black asterisks mark two clades that evolved violet/blue color independently, represented here by B. sambulos and B. medontias. (BD) Dorsal wing images of B. sambulos, B. anynana (the region used for artificial selection is marked by white asterisk), and B. medontias. (EG) Graphs of reflectance spectra of the blue/violet wing band showing reflectance peaks in the 400–450 nm range and in the brown-colored homologous region in B. anynana with a UV reflectance peak centered at 300 nm (colored arrows). (H) 3D illustration of the wing and scales in the selected wing area of B. anynana. (I) Magnified view of the ripped region in H showing how cover (c; brown) and ground (g; green) scales are attached to the wing membrane (m, pink) and alternate along rows. Scales on the other (ventral) side of the wing membrane are visible also. (J) Cross-sectional view of a single scale showing the trabeculae (T) connecting the lower lamina (LL) to the upper lamina that includes ridges (R), microribs (Mr), and crossribs (Cr). Windows (W) are the spaces between the ridges and crossribs. Cover and ground scales have the same basic morphology. [llustrations in HJ courtesy of Katerina Evangelou (Central Saint Martin’s College, London).]B. anynana, like other butterflies, has two types of scales, cover and ground, which alternate within a row with cover scales partially covering the ground scales and the point where both scales attach to the wing membrane (Fig. 1 H and I and Fig. S1) (28). Both cover and ground scales contain a lower lamina with a continuous smooth surface below a region composed of longitudinal ridges and crossribs, collectively referred to as the “upper lamina” and connected to the lower lamina via pillars called “trabeculae” (Fig. 1J and Fig. S1) (6). Previous studies on butterflies showed that structural color can be produced by interference with light reflected from the overlapping lamella that build the longitudinal ridges, from microribs protruding from the sides of the longitudinal ridges, or from the lower lamina, which can vary in thickness and patterning (Fig. 1J) (29, 30). However, it is not clear how the violet/blue color is produced in members of the two Bicyclus clades that separately evolved this color, whether B. anynana can be made to evolve the same violet/blue color via artificial selection, and whether it will generate the color in the same way as the other species. To answer these questions, we conducted detailed optical characterization and structural analysis of butterfly wing scales from three separate species and artificially evolved populations of Bicyclus to illustrate how color is generated and how it has evolved.  相似文献   
78.

Background

Completion total gastrectomy for remnant gastric cancer (RGC) is technically challenging, especially using the minimally invasive approach. Only a few small case series have reported the technical feasibility of completion total gastrectomy by minimally invasive surgery (MIS). The aim of this study was to compare the efficacy and safety of MIS and open surgery for RGC.

Methods

We retrospectively analyzed 76 completion total gastrectomies for RGC between 2005 and 2012. Indications for MIS were limited to no evidence of serosa invasion or lymph node metastasis to extraperigastric areas on preoperative evaluation. We compared patient characteristics, intraoperative factors, post-operative outcomes, and survival for the MIS and open surgery groups.

Results

Eighteen patients underwent completion total gastrectomy with MIS (10 laparoscopic, 8 robotic) and 58 patients underwent open surgery. Operation time was longer in the MIS than the open group (266 vs. 203 min, P = 0.004), but the groups had similar estimated blood loss, frequency of unplanned other organ resection, and number of retrieved lymph nodes. The MIS group had a significantly earlier initiation of soft diet, shorter hospital stay, and fewer pain medication injections. Complication rates, recurrence, and overall 5-year survival were similar for the two groups. When we compared laparoscopy with robotic, similar result was shown in all parameters except operation time.

Conclusions

Compared to open surgery, MIS for RGC demonstrated better short-term outcome and comparable oncologic results. MIS for RGC is feasible and safe and maintains advantages of minimal invasiveness. Both laparoscopic and robotic approaches are reasonable to the management of RGC.  相似文献   
79.

Purpose

Wrist fracture is considered a typical initiating trauma for complex regional pain syndrome type I (CRPS I). However, few studies have comprehensively evaluated factors associated with the occurrence of CRPS I after the surgical treatment of a distal radius fracture (DRF). This study evaluates the factors influencing the occurrence of CRPS I after the surgical treatment of a DRF.

Methods

A total of 477 patients with a DRF who had been treated surgically were enrolled in this prospective observational study. Patients were followed for 6 months after surgery, and CRPS I was diagnosed using the Budapest diagnostic criteria for research. The factors assessed for the development of CPRS I were age, gender, the body mass index, the type of fracture, the energy of trauma, the number of trial reductions, the type of surgery, and the duration of immobilization. A multivariate logistic regression analysis was conducted to identify independent predictors of the occurrence of CRPS I.

Results

Among the 477 patients, 42 (8.8 %) satisfied the Budapest criteria for CRPS I within 6 months of surgery. Female patients developed CRPS I more frequently, and the patients who developed CRPS I were older and more likely to sustain a high energy injury or have a comminuted fracture. According to the multivariate analysis, female patients and those with a high energy trauma or severe fracture type were significantly more likely to develop CRPS I (p = 0.02, 0.01, and 0.01, respectively).

Conclusions

High energy injuries, severe fractures, and the female gender contribute to the development of CRPS I after the surgical treatment of DRF. The results have important implications for physicians who wish to identify patients at high risk for CRPS I after operative fixation for DRF and instigate treatment accordingly.  相似文献   
80.
Resistance of glioblastoma to the chemotherapeutic compound temozolomide is associated with the presence of glioblastoma stem cells in glioblastoma and is a key obstacle for the poor prognosis of glioblastoma. Here, we show that phospholipase D1 is elevated in CD44High glioblastoma stem cells and in glioblastoma, especially recurring glioblastoma. Phospholipase D1 elevation positively correlated with the level of CD44 and poor prognosis in glioblastoma patients. Temozolomide significantly upregulated the expression of phospholipase D1 in the low and moderate CD44 populations of glioblastoma stem cells, but not in the CD44High population in which phospholipase D1 is highly expressed. Phospholipase D1 conferred resistance to temozolomide in CD44High glioblastoma stem cells and increased their self-renewal capacity and maintenance. Phospholipase D1 expression significantly correlated with levels of temozolomide resistance factors, which were suppressed by microRNA-320a and -4496 induced by phospholipase D1 inhibition. Genetic and pharmacological targeting of phospholipase D1 attenuated glioblastoma stem cell-derived intracranial tumors of glioblastoma using the microRNAs, and improved survival. Treatment solely with temozolomide produced no benefits on the glioblastoma, whereas in combination, phospholipase D1 inhibition sensitized glioblastoma stem cells to temozolomide and reduced glioblastoma tumorigenesis. Together, these findings indicate that phospholipase D1 inhibition might overcome resistance to temozolomide and represents a potential treatment strategy for glioblastoma. © 2020 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号