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   27948篇
  免费   1371篇
  国内免费   165篇
耳鼻咽喉   376篇
儿科学   406篇
妇产科学   500篇
基础医学   3459篇
口腔科学   745篇
临床医学   1994篇
内科学   7489篇
皮肤病学   438篇
神经病学   2203篇
特种医学   855篇
外科学   4760篇
综合类   124篇
一般理论   2篇
预防医学   794篇
眼科学   561篇
药学   1824篇
中国医学   48篇
肿瘤学   2906篇
  2023年   130篇
  2022年   282篇
  2021年   533篇
  2020年   297篇
  2019年   363篇
  2018年   511篇
  2017年   387篇
  2016年   490篇
  2015年   486篇
  2014年   669篇
  2013年   824篇
  2012年   1331篇
  2011年   1404篇
  2010年   800篇
  2009年   723篇
  2008年   1344篇
  2007年   1374篇
  2006年   1325篇
  2005年   1252篇
  2004年   1269篇
  2003年   1239篇
  2002年   1236篇
  2001年   932篇
  2000年   960篇
  1999年   842篇
  1998年   348篇
  1997年   247篇
  1996年   239篇
  1995年   225篇
  1994年   193篇
  1993年   174篇
  1992年   628篇
  1991年   640篇
  1990年   544篇
  1989年   548篇
  1988年   536篇
  1987年   503篇
  1986年   437篇
  1985年   442篇
  1984年   327篇
  1983年   242篇
  1979年   232篇
  1978年   141篇
  1977年   141篇
  1974年   130篇
  1973年   122篇
  1972年   138篇
  1971年   129篇
  1969年   138篇
  1967年   128篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
Treatment of moving targets with scanned particle beams results in local over- and under-dosage due to interplay of beam and target motion. To mitigate the impact of respiratory motion, a motion tracking system has been developed and integrated in the therapy control system at Gesellschaft für Schwerionenforschung. The system adapts pencil beam positions as well as the beam energy according to target motion to irradiate the planned position. Motion compensation performance of the tracking system was assessed by measurements with radiographic films and a 3D array of 24 ionization chambers. Measurements were performed for stationary detectors and moving detectors using the tracking system. Film measurements showed comparable homogeneity inside the target area. Relative differences of 3D dose distributions within the target volume were 1 +/- 2% with a maximum of 4%. Dose gradients and dose to surrounding areas were in good agreement. The motion tracking system successfully preserved dose distributions delivered to moving targets and maintained target conformity.  相似文献   
992.
BACKGROUND: Japanese cedar (Cryptomeria japonica) pollinosis is the most prevalent allergy in Japan. Recently, the Japanese cedar pollen allergen Cry j 3 was cloned as a homologue of Jun a 3, which is a major allergen from mountain cedar (Juniperus ashei) pollen. However, native Cry j 3 has not been isolated and there are no reports on its allergenic activity. The aims of this study were to isolate native Cry j 3 and assess its immunoglobulin E (IgE)-binding capacity in patients with Japanese cedar pollinosis. METHODS: Native Cry j 3 was purified from Japanese cedar pollen by multidimensional chromatography. We assessed the IgE-binding capacity using sera from patients allergic to Japanese cedar pollen by immunoblot analysis and ELISA. Moreover, we assayed the capacity of Cry j 3 to induce histamine release from the patients' leukocytes. We cloned cDNA corresponding to purified Cry j 3 from a cDNA library of Japanese cedar pollen. RESULTS: We isolated native Cry j 3 as a 27-kDa protein. The IgE-binding frequency of Cry j 3 from the sera of patients allergic to Japanese cedar pollen was estimated as 27% (27/100) by ELISA. Cry j 3 induced the release of histamine from leukocytes. We cloned the cDNA and named it Cry j 3.8. Cry j 3.8 cDNA encoded 225 amino acids and had significant homology with thaumatin-like proteins. CONCLUSIONS: Cry j 3 is a causative allergen in Japanese cedar pollinosis and may play crucial roles in the cross-reactivity with oral allergy syndrome.  相似文献   
993.
Regulation of the adhesion of mononuclear cells to endothelial cells is considered to be a critical step for the treatment of inflammatory diseases, including autoimmune diseases. K-13182 was identified as a novel inhibitor for these adhesions. K-13182 inhibited the expression of vascular cell adhesion molecule-1 (VCAM-1, CD106) on human umbilical vein endothelial cells (HUVECs) and on mouse vascular endothelial cell line (MAECs) induced by tumour necrosis factor (TNF)-α. K-13182 also inhibited the adhesion of mononuclear cells to these HUVECs and MAECs, indicating that K-13182 suppressed these adhesions mediated by cellular adhesion molecules including VCAM-1. To evaluate the therapeutic effect in autoimmune disease model mice, K-13182 was orally administered to non-obese diabetic (NOD) mice as Sjögren''s syndrome (SS) model mice. Severe destructive inflammatory lesions were observed in the lacrimal glands of vehicle-treated control mice; however, 8-week administration of K-13182 inhibited the mononuclear cell infiltration into the inflammatory lesions of the lacrimal glands. In K-13182-treated mice, the decrease in tear secretion was also prevented compared to the control mice. In addition, the apoptosis and the expression of FasL (CD178), perforin, and granzyme A was suppressed in the lacrimal glands of K-13182-treated mice. Therefore, K-13182 demonstrated the possibility of therapeutic efficacy for the inflammatory region of autoimmune disease model mice. These data reveal that VCAM-1 is a promising target molecule for the treatment of autoimmune diseases as a therapeutic strategy and that K-13182 has the potential as a new anti-inflammatory drug for SS.  相似文献   
994.
Contact hypersensitivity (CHS) is a cutaneous immune reaction mediated mainly by antigen-specific effector T cells and is regarded as a model for Th1/Tc1-mediated inflammation. However, recent reports have suggested pivotal roles of B cells in CHS. CD19 serves as a positive B-cell response regulator that defines signaling thresholds critical for B-cell responses. In the current study, we assessed the role of the B-cell-specific surface molecule CD19 on the development of CHS by examining CD19-deficient mice. Although CD19-deficient mice are hyposensitive to a variety of transmembrane signals, CD19 loss resulted in increased and prolonged reaction of CHS, suggesting an inhibitory role of CD19 expression in CHS. Sensitized lymph nodes and elicited ear lesions from CD19-deficient mice exhibited Th1/Tc1-shifted cytokine profile with increased interferon-gamma expression and decreased interleukin-10 expression. Adoptive transfer experiments revealed that CD19 expression in recipient mice was required for optimal suppression of CHS response, indicating its role in the elicitation phase. Furthermore, spleen B cells, especially marginal zone B cells, from wild-type mice were able to normalize exaggerated CHS reactions in CD19-deficient mice. Thus, CD19 expression in B cells is critical for termination of CHS responses, possibly through the function of regulatory B cells.  相似文献   
995.
Oncogenic role of JC virus in lung cancer   总被引:1,自引:0,他引:1  
The JC virus (JCV) infects a large proportion of the population world wide and can cause progressive multifocal leucoencephalopathy in the context of immunodeficiency. Recent reports provide evidence that it may also be oncogenic. Here, JCV was examined by targeting its T-antigen in lung carcinomas (n=103) and normal lung tissues (n=18) by nested-PCR followed by Southern blot, real-time PCR, immunohistochemistry, in situ hybridization and in situ PCR. Additionally, expression of Ki-67, caspase-3, beta-catenin, p53, and Rb was analysed by immunohistochemistry on tissue microarrays of lung carcinomas. Copy numbers of JCV were compared with clinicopathological features. Normal lung tissue was positive significantly less frequently, and contained a lower copy number of JCV than lung carcinomas (p<0.05), and copies were lower in lung adenocarcinomas than in squamous, small or large cell carcinomas (p<0.05). In situ PCR and immunolabelling revealed JCV positivity in the nuclei of lung carcinoma cells. The JCV copy number correlated closely with sex, and expression of Ki-67 and membrane beta-catenin (p<0.05), but not with age, tumour size, pleural invasion, lymph node metastasis, expression of caspase-3, cytoplasmic beta-catenin, p53 or Rb, prognosis, smoking or cancer family history (p>0.05). Age and UICC staging were independent prognostic factors for lung carcinoma patients. These data suggest that JCV may be involved in lung carcinogenesis, especially in tumour types other than adenocarcinoma. Lung carcinomas with higher JCV copy numbers display high proliferation and down-regulation of cell adhesion mediated by membrane beta-catenin.  相似文献   
996.
The smooth pursuit system and the vestibular system interact to keep the retinal target image on the fovea by matching the eye velocity in space to target velocity during head and/or whole body movement. The caudal part of the frontal eye fields (FEF) in the fundus of the arcuate sulcus contains pursuit-related neurons and the majority of them respond to vestibular stimulation induced by whole body movement. To understand the role of FEF pursuit neurons in the interaction of vestibular and pursuit signals, we examined the latency and time course of discharge modulation to horizontal whole body rotation during different vestibular task conditions in head-stabilized monkeys. Pursuit neurons with horizontal preferred directions were selected, and they were classified either as gaze-velocity neurons or eye/head-velocity neurons based on the previous criteria. Responses of these neurons to whole body step-rotation at 20 degrees/s were examined during cancellation of the vestibulo-ocular reflex (VOR), VOR x1, and during chair steps in complete darkness without a target (VORd). The majority of pursuit neurons tested (approximately 70%) responded during VORd with latencies <80 ms. These initial responses were basically similar in the three vestibular task conditions. The shortest latency was 20 ms and the modal value was 24 ms. These responses were also similar between gaze-velocity neurons and eye/head-velocity neurons, indicating that the initial responses (<80 ms) were vestibular responses induced by semicircular canal inputs. During VOR cancellation and x1, discharge of the two groups of neurons diverged at approximately 90 ms following the onset of chair rotation, consistent with the latencies associated with smooth pursuit. The shortest latency to the onset of target motion during smooth pursuit was 80 ms and the modal value was 95 ms. The time course of discharge rate difference of the two groups of neurons between VOR cancellation and x1 was predicted by the discharge modulation associated with smooth pursuit. These results provide further support for the involvement of the caudal FEF in integration of vestibular inputs and pursuit signals.  相似文献   
997.
Lymphocyte proliferation is regulated by signals through antigen receptors, co-stimulatory receptors, and other positive and negative modulators. Several membrane tetraspanning molecules are also involved in the regulation of lymphocyte growth and death. We cloned a new B cell-specific tetraspanning (BTS) membrane molecule, which is similar to CD20 in terms of expression, structure and function. BTS is specifically expressed in the B cell line and its expression is increased after the pre-B cell stage. BTS is expressed in intracellular granules and on the cell surface. Overexpression of BTS in immature B cell lines induces growth retardation through inhibition of cell cycle progression and cell size increase without inducing apoptosis. This inhibitory function is mediated predominantly by the N terminus of BTS. The development of mature B cells is inhibited in transgenic mice expressing BTS, suggesting that BTS is involved in the in vivo regulation of B cells. These results indicate that BTS plays a role in the regulation of cell division and B cell growth.  相似文献   
998.
Bisphenol A (BPA), 4‐nonylphenol (NP) and butyl benzyl phthalate (BBP), termed endocrine‐disrupting chemicals, are known to mimic estrogen activity. The effects of these chemicals on 17β‐estradiol (E2) metabolism in vivo in rats were examined. Male and female rats were given NP (250 mg kg–1 day–1), BPA (250 μg kg–1 day–1) or BBP (500 mg kg–1 day–1) by gavage for 14 days, followed by a single intraperitoneal injection of E2 (5 mg kg–1) on the final day. The urinary excretion over 72 hours of 2‐hydroxyestrone 1‐N‐acetylcysteine thioether, 2‐hydroxyestrone 4‐N‐acetylcysteine thioether, 4‐hydroxyestrone 2‐N‐acetylcysteine thioether, 2‐hydroxy‐17β‐estradiol (2‐OHE2), 2‐hydroxyestrone (2‐OHE1), 4‐hydroxy‐17β‐estradiol, 4‐hydroxyestrone, 15α‐hydroxyestriol (E4), 15α‐hydroxy‐17β‐estradiol and 15α‐hydroxyestrone was measured. Increases in urinary excretion of 2‐OHE1 and decreases in E4 were observed in males treated with NP or BBP. Decreases in urinary excretion of 2‐OHE2 and E4 were observed in males treated with BPA. Decreases in urinary excretion of 2‐OHE1 and 2‐OHE2 were observed in females treated with BBP. Normalized liver and weights were increased in both sexes treated with NP or BBP. Histologic observations revealed marked changes in the distal tubules and collecting ducts in the kidneys of rats exposed to NP and BBP, and hypertrophy in the hepatocytes of the centrilobular zone of the liver. No BPA‐related effects on organ weight and on liver or kidney histopathology were found. These results suggest that the 14 day oral dosing of NP and BBP disrupted E2 metabolism, resulting from marked morphological and functional alterations in the liver and kidneys. In addition, BPA could induce metabolic and endocrine disruption.  相似文献   
999.
1000.

Purpose

We investigated the association between reproductive history and mortality from all and major causes among Japanese women.

Methods

A large-scale population-based cohort study in Japan included 40,149 eligible women aged 40–69 years in 1990–1994. A total of 4788 deaths were reported during follow-up (average 20.9 years). A Cox proportional hazards regression model was used to estimate the hazard ratios (HRs) and 95% confidence intervals (95% CI) for all-cause and major causes of mortality, adjusting for potential confounders.

Results

Inverse associations with all-cause mortality were found in parous women (0.74 [0.67–0.82]), women with two or three births compared with a single birth (2 births: 0.88 [0.78–0.99]; 3 births: 0.83 [0.74–0.94]), parous women who breastfed (0.81 [0.75–0.87]), women who were older at menopause (0.88 [0.80–0.97]; p-trend: <0.01), and women who had a longer fertility span (0.85 [0.76–0.95]; p-trend: <0.01). A positive association was seen between all-cause mortality and later age at first birth (≥30 years) than early childbearing (≤22 years).

Conclusions

Our study suggests that parous, two or three births, breastfeeding, late age at menopause, and longer reproductive span are associated with lower risk of all-cause of mortality.  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