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   8634篇
  免费   480篇
  国内免费   122篇
耳鼻咽喉   137篇
儿科学   152篇
妇产科学   84篇
基础医学   1453篇
口腔科学   148篇
临床医学   707篇
内科学   1815篇
皮肤病学   483篇
神经病学   645篇
特种医学   520篇
外科学   1036篇
综合类   22篇
现状与发展   1篇
一般理论   1篇
预防医学   315篇
眼科学   193篇
药学   845篇
中国医学   146篇
肿瘤学   533篇
  2024年   7篇
  2023年   76篇
  2022年   249篇
  2021年   351篇
  2020年   183篇
  2019年   233篇
  2018年   286篇
  2017年   236篇
  2016年   333篇
  2015年   418篇
  2014年   516篇
  2013年   491篇
  2012年   803篇
  2011年   790篇
  2010年   413篇
  2009年   381篇
  2008年   512篇
  2007年   441篇
  2006年   352篇
  2005年   384篇
  2004年   273篇
  2003年   229篇
  2002年   234篇
  2001年   175篇
  2000年   184篇
  1999年   130篇
  1998年   48篇
  1997年   27篇
  1996年   35篇
  1995年   15篇
  1994年   32篇
  1993年   16篇
  1992年   41篇
  1991年   44篇
  1990年   37篇
  1989年   49篇
  1988年   28篇
  1987年   30篇
  1986年   25篇
  1985年   22篇
  1984年   10篇
  1983年   6篇
  1981年   9篇
  1980年   14篇
  1979年   15篇
  1978年   7篇
  1977年   9篇
  1971年   4篇
  1970年   4篇
  1967年   4篇
排序方式: 共有9236条查询结果,搜索用时 0 毫秒
71.
The potential for adipose‐derived stem cells to differentiate into keratinocyte‐like cells has recently been receiving attention, stemming from the hypothesis that a bioengineered skin may be manufactured from these readily available mesenchymal stem cells. This study was conducted to evaluate the influence of human keratinocyte non‐contact coculture on hADSCs. Human epidermal keratinocytes and hADSCs obtained by lipoaspiration were cultured in keratinogenic growth media, which were divided into the following groups: human adipose‐derived stem cell (hADSC) monoculture, non‐contact coculture of hADSCs and human keratinocytes and keratinocyte monoculture. Cell proliferation was assessed, and keratogenicity was analysed through immunocytochemistry and polymerase chain reaction of early, intermediate and late keratogenic markers. hADSCs cocultured with keratinocytes displayed enhanced proliferation compared with the monoculture group. After a 7‐day coculture period, immunohistochemistry and polymerase chain reaction findings revealed the presence of specific keratinocyte markers in the coculture group. This study demonstrates that hADSCs cocultured with keratinocytes have the capacity to transdifferentiate into keratinocyte lineage cells, and suggests that adipose tissue may be a source of keratinocytes that may further be used in structuring the bioengineered skin.  相似文献   
72.
OBJECTIVE. We compared the soft-copy images produced by a digital chest radiography system that uses a flat-panel X-ray detector based on amorphous selenium with images produced by a storage phosphor radiography system for the visualization of anatomic regions of the chest. MATERIALS AND METHODS. Two chest radiologists and two residents analyzed 46 pairs of posteroanterior chest radiographs on high-resolution video monitors (2560 x 2048 x 8 bits). In each pair, one radiograph was obtained with a storage phosphor radiography system, and the other radiograph was obtained with a selenium-based flat-panel detector radiography system. Each pair of radiographs was obtained at the same exposure settings. The interpreter rated the visibility and radiographic quality of 11 different anatomic regions. Each pair of images was ranked on a five-point scale (1 = prefer image A, 3 = no preference, 5 = prefer image B) for preference of technique. Statistical significance of preference was determined using the Wilcoxon's signed rank test. RESULTS. The interpreters had a statistically significant preference for the selenium-based radiography system in six (unobscured lung, hilum, rib, minor fissure, heart border, and overall appearance) of 11 anatomic regions (p<0.001) and for the storage phosphor system in two regions (proximal airway and thoracic spine) (p<0.05). Chest radiologists strongly preferred selenium-based images in eight regions, and they did not prefer storage phosphor images in any region. CONCLUSION. The soft-copy images produced by the selenium-based radiography system were perceived as equal or superior to those produced by the storage phosphor system in most but not all anatomic regions.  相似文献   
73.
The "High-Riding" superior pericardial recess: CT findings   总被引:3,自引:0,他引:3  
OBJECTIVE. We recently observed patients in whom the superior pericardial recess extended cephalad ("high-riding") into the right paratracheal region. In these patients, differentiation from mediastinal lymphadenopathy or mass was difficult. The purpose of this study was to assess the prevalence and CT features of the high-riding superior pericardial recess. CONCLUSION. Narrow-collimation CT with multiplanar reformations was useful for confidently diagnosing a high-riding superior pericardial recess and for distinguishing it from pathologic lesions.  相似文献   
74.
Vascular smooth muscle cell (VSMC) proliferation and extracellular matrix (ECM) accumulation play key roles in the development and the progression of vascular remodeling such as transplant arteriosclerosis and restenosis. The present study examined the effects of sirolimus (SRL) on platelet-derived growth factor (PDGF)-induced fibronectin secretion, collagen synthesis, and the related signaling pathways including reactive oxygen species (ROS) and mitogen-activated protein kinases (MAPK) in rat VSMCs. Primary rat VSMCs were isolated from male Sprague-Dawley rats. Growth arrested, synchronized cells were treated with various concentrations of SRL before the addition of PDGF at 10 ng/mL. Proliferating cell nuclear antigen expression, fibronectin secretion, and the activation of extracellular signal-regulated protein kinase (ERK) and p38 MAPK were assessed by Western blot analysis, collagen synthesis by [(3)H]-proline incorporation, and cellular ROS by flow cytometry. PDGF (10 ng/mL) increased VSMC proliferation by 1.7-fold, fibronectin secretion by 1.5-fold, collagen synthesis by 2.1-fold, cellular ROS by 1.6-fold, and activation of ERK and p38 MAPK by 3.3- and 3.9-fold compared to controls. SRL above 1 nmol/L inhibited PDGF-induced VSMC proliferation and collagen synthesis but not PDGF-induced fibronectin secretion, cellular ROS, and activation of ERK and p38 MAPK. These data demonstrated that PDGF increased ECM synthesis as well as proliferation through cellular ROS and subsequent MAPK activation and that SRL inhibited PDGF-induced VSMC proliferation and collagen synthesis in a cellular ROS- and MAPK activation-independent way.  相似文献   
75.
BACKGROUND: We performed a retrospective analysis to evaluate the usefulness of combined spinal epidural anesthesia (CSEA) in emergency cesarean section compared with conventional spinal anesthesia. METHODS: A retrospective chart analysis of patients who had undergone emergency cesarean section over a 7 year period was performed. We extracted at random 150 patients planned by spinal anesthesia, and 150 patients planned by separate-needle CSEA. Patient's data were gathered and analyzed according to the anesthetic technique used. RESULTS: There were no significant differences between the two groups in age, weight, and BMI. Although the time to incision and the time to delivery were significantly faster in spinal anesthesia group than in CSEA group, there was no significant difference in Apgar score between the groups. Moreover, failure of anesthesia and post-dural puncture headache were higher in spinal group than in CSEA group. CONCLUSIONS: CSEA is useful as anesthesia for an emergency cesarean section.  相似文献   
76.

OBJECTIVE

To evaluate the long‐term results and predictive risk factors for efficacy after the tension‐free vaginal tape (TVT) procedure for treating female stress urinary incontinence (SUI).

PATIENTS AND METHODS

Inall, 306 women (mean age 50.7 years, sd 8.7) who had a TVT procedure for SUI were selected and followed ≥7 years (mean 92.3 months, range 84–110) after surgery. We analysed the long‐term results, the variables predictive of cure rates, and patient satisfaction.

RESULTS

The overall 7‐year cure rate was 84.6%, with a satisfaction rate of 69.3%. The cure rates were lower in patients with high‐grade SUI (50% in grade III, 82.8% in grade II and 90.7% in grade I; P < 0.001). On multivariate analysis, there were no independent risk factors related to cure rate, and urgency was the only factor independently associated with patient satisfaction (P = 0.008; odds ratio 2.47). Seventy‐one patients (23.2%) had complications at the 1‐month follow‐up after surgery, but only eight (2.6%) had complications at the 7‐year follow‐up, including mesh exposure in six and de novo urgency in two.

CONCLUSION

The absence of long‐term adverse events associated with the TVT procedure, and high subjective and objective 7‐year success rates with no independent predictive factors affecting the long‐term cure rate, make the TVT procedure a recommendable surgical treatment for female SUI.  相似文献   
77.
78.
A 74-year-old woman was diagnosed with hilar bile duct cancer, and underwent a curative resection of the bile duct and the left and caudate lobes of the liver in 1995. Ten years later (April 2005), she noted a small mass in the abdominal wall. The mass slowly enlarged to reach 4 cm in diameter by January 2007. With a diagnosis of a possible recurrence of bile duct cancer, a laparotomy was thus performed. The abdominal wall tumor was buried in the rectus abdominis muscle and was tightly attached to the ileum. The lesion was resected en bloc with the associated rectus muscle and ileocecal region. A histopathological examination of the resected specimen revealed tubular adenocarcinoma that closely resembled the original primary bile duct cancer. In addition, the immunohistochemical staining pattern of the abdominal tumor was identical to that of the original bile duct cancer. This indicated that the abdominal tumor represented a local recurrence (probably due to peritoneal implantation) at 12 years after the resection of the hilar bile duct cancer. This case emphasizes that long-time surveillance is required for patients with bile duct cancer, even if they have survived without recurrence for more than 5 years after a curative resection.  相似文献   
79.

Background

A web-based survey was conducted among colorectal surgeons who represented members of both SAGES and ASCRS to find out how they define conversion for laparoscopic colorectal surgery.

Methods

Questionnaires were designed based on MCQs, including three parts: surgeon information, different definitions for conversion, and four different clinical scenarios. Surgeons were asked to choose the best definition(s).

Results

325 (28.5%) of 1,140 surgeons, 28.5% responded; approximately half of them were part of private-based practices. Fifty-three percent had more than 10 years experience; 35.9% performed more than 50 laparoscopic colon cases per year, 12% performed more than 25 laparoscopic rectal cases per year, and 60% less than 10. The majority (68.4%) agreed that any incision made earlier than planned is conversion. Whereas 81.4% felt that incision >5 cm is not a conversion, only 53.4% considered incision >10 cm a conversion, and 37% did not. Neither extracorporeal vessel ligation (73.8%), bowel resection (81.2%), anastomosis (77%), or incision made for specimen retrieval (91.1%) was counted as conversion. In clinical case scenarios, 62% found an incision made to facilitate phlegmon dissection after laparoscopically mobilizing the left colon up to and around the splenic flexure to be laparoscopic-assisted. A 10-cm incision required for fistula take down after finishing laparoscopic dissection was defined as conversion (55.6%). A 10-cm incision made for the rectal dissection in rectopexy was described as conversion in 51% and laparoscopic-assisted in 48%. Increasing a 5–12-cm for specimen extraction, 49.3% was declared a laparoscopic-assisted case.

Conclusions

It was considered clear that any incision made earlier than planned a conversion, whereas extra corporeal vessel ligation, bowel resection and anastomosis were not. However, there seem to be many views of conversion regarding incision length, and some clinical situations that might influence outcome among different centers.  相似文献   
80.
OBJECTIVES: The purpose of this study is to evaluate the correlation of the perfusion parameters of 3-dimensional, contrast-enhanced magnetic resonance (MR) imaging (3D CEMRI) with pulmonary function test (PFT) and quantitative computed tomography (CT) parameters in patients with chronic obstructive pulmonary disease (COPD). MATERIALS AND METHODS: In 14 patients with COPD, 3D CEMRI was performed. From the signal intensity-time curves, pulmonary blood flow (PBF), pulmonary blood volume (PBV), and mean transit time of each pixel was calculated. From the volumetric CT data, the quantitative parameters including the volume fraction of the lung below -950 Housefield Units (V(-950)) and mean lung density were assessed. The correlation between the MR perfusion parameters and the parameters from quantitative CT and PFT was assessed using Spearman correlation analysis. The correspondence of the regional impairment of perfusion on MR perfusion maps to the areas of emphysema on quantitative CT maps in each patient was assessed qualitatively using a 4-class visual scoring method by 2 readers. RESULTS: All 3D CEMRI examinations were successfully completed and MR perfusion parameters were obtained in all patients. The Spearman correlation test showed that PBF positively correlated with forced expiratory volume in 1 second (FEV(1))/forced vital capacity (FVC) (R = 0.49, P = 0.044), PBV positively correlated with FEV(1)/FVC (R = 0.69, P = 0.006) and negatively correlated with V-950 (R = -0.61, P = 0.020), and mean transit time positively correlated with FEV(1) (R = 0.63, P = 0.017) and FEV(1)/FVC (R = 0.76, P = 0.002). The areas of perfusion impairment on PBF and PBV maps were relatively well correlated with the areas of emphysema on CT maps [very good or good: PBF 71.5% (reader 1) and 64.3% (reader 2) of the patients, kappa = 0.47 (P < 0.001); PBV 78.6% (reader 1) and 78.6% (reader 2) of the patients, kappa = 0.89 (P < 0.001)]. CONCLUSIONS: This study shows that the deterioration of perfusion parameters measured on MR in patients with COPD, correlates with worsening of airflow limitation on PFT and emphysema index on CT. Regional heterogeneity of emphysema on CT matches with the decreased perfusion on MR.  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