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   3466461篇
  免费   244173篇
  国内免费   8728篇
耳鼻咽喉   46818篇
儿科学   113700篇
妇产科学   96141篇
基础医学   491025篇
口腔科学   99262篇
临床医学   318048篇
内科学   678089篇
皮肤病学   81205篇
神经病学   283758篇
特种医学   131440篇
外国民族医学   980篇
外科学   507313篇
综合类   69966篇
现状与发展   8篇
一般理论   1482篇
预防医学   276763篇
眼科学   77780篇
药学   251691篇
  12篇
中国医学   6927篇
肿瘤学   186954篇
  2021年   27999篇
  2019年   28638篇
  2018年   39810篇
  2017年   30497篇
  2016年   34465篇
  2015年   39258篇
  2014年   54109篇
  2013年   81098篇
  2012年   108830篇
  2011年   115539篇
  2010年   68510篇
  2009年   65479篇
  2008年   107022篇
  2007年   113862篇
  2006年   114600篇
  2005年   110848篇
  2004年   106640篇
  2003年   102428篇
  2002年   97796篇
  2001年   157843篇
  2000年   161466篇
  1999年   136480篇
  1998年   39835篇
  1997年   35524篇
  1996年   35966篇
  1995年   34515篇
  1994年   31853篇
  1993年   29920篇
  1992年   107197篇
  1991年   104026篇
  1990年   100703篇
  1989年   97264篇
  1988年   89729篇
  1987年   87927篇
  1986年   82875篇
  1985年   78999篇
  1984年   59438篇
  1983年   50686篇
  1982年   30219篇
  1979年   53483篇
  1978年   38221篇
  1977年   32460篇
  1976年   29978篇
  1975年   32170篇
  1974年   38286篇
  1973年   36951篇
  1972年   34743篇
  1971年   32309篇
  1970年   30112篇
  1969年   28744篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
23.
24.
Sinus venosus atrial septal defect (SV‐ASD) usually coexists with partial anomalous pulmonary vein connection (PAPVC). It is a difficult diagnosis in transthoracic echocardiography (TTE) due to eccentric position of defects. We present a rare case of atypical anatomical variation in PAPVC, which was never described before. Two right pulmonary veins drained into superior vena cava, which overrode SV‐ASD and interatrial septum, a third pulmonary vein into the right atrium. Complete diagnosis could not be set after TTE, nor transesophageal echocardiography, whereas angio‐CT was finally conclusive. This diagnostic approach allowed the surgical planning.  相似文献   
25.
26.
In the current immunosuppressive therapy era, vessel thrombosis is the most common cause of early graft loss after renal transplantation. The prevalence of IgA anti–β2-glycoprotein I antibodies (IgA-aB2GPI-ab) in patients on dialysis is elevated (>30%), and these antibodies correlate with mortality and cardiovascular morbidity. To evaluate the effect of IgA-aB2GPI-ab in patients with transplants, we followed all patients transplanted from 2000 to 2002 in the Hospital 12 de Octubre prospectively for 10 years. Presence of IgA-aB2GPI-ab in pretransplant serum was examined retrospectively. Of 269 patients, 89 patients were positive for IgA-aB2GPI-ab (33%; group 1), and the remaining patients were negative (67%; group 2). Graft loss at 6 months post-transplant was significantly higher in group 1 (10 of 89 versus 3 of 180 patients in group 2; P=0.002). The most frequent cause of graft loss was thrombosis of the vessels, which was observed only in group 1 (8 of 10 versus 0 of 3 patients in group 2; P=0.04). Multivariate analysis showed that the presence of IgA-aB2GPI-ab was an independent risk factor for early graft loss (P=0.04) and delayed graft function (P=0.04). There were no significant differences regarding patient survival between the two groups. Graft survival was similar in both groups after 6 months. In conclusion, patients with pretransplant IgA-aB2GPI-ab have a high risk of early graft loss caused by thrombosis and a high risk of delayed graft function. Therefore, pretransplant IgA-aB2GPI-ab may have a detrimental effect on early clinical outcomes after renal transplantation.  相似文献   
27.
Animal and human studies suggest fish oil and green tea may have protective effect on prostate cancer. Fatty acid synthase (FAS) has been hypothesized to be linked to chemoprotective effects of both compounds. This study evaluated the independent and joint effects of fish oil (FO) and green tea supplement (epigallocatechin-3-gallate, EGCG) on FAS and Ki-67 levels in prostate tissue. Through a double-blinded, randomized controlled trial with 2 × 2 factorial design, 89 men scheduled for repeat prostate biopsy following an initial negative prostate biopsy were randomized into either FO alone (1.9 g DHA + EPA/day), EGCG alone (600 mg/day), a combination of FO and EGCG, or placebo. We used linear mixed-effects models to test the differences of prostate tissue FAS and Ki-67 by immunohistochemistry between pre- and post-intervention within each group, as well as between treatment groups. Results did not show significant difference among treatment groups in pre-to-post-intervention changes of FAS (P = 0.69) or Ki-67 (P = 0.26). Comparing placebo group with any of the treatment groups, we did not find significant difference in FAS or Ki-67 changes (all P > 0.05). Results indicate FO or EGCG supplementation for a short duration may not be sufficient to produce biologically meaningful changes in FAS or Ki-67 levels in prostate tissue.  相似文献   
28.
29.
30.
Analyzing functional species’ characteristics (species traits) that represent physiological, life history and morphological characteristics of species help understanding the impacts of various stressors on aquatic communities at field conditions. This research aimed to study the combined effects of pesticides and other environmental factors (temperature, dissolved oxygen, dissolved organic carbon, floating macrophytes cover, phosphate, nitrite, and nitrate) on the trait modality distribution of aquatic macrofauna communities. To this purpose, a field inventory was performed in a flower bulb growing area of the Netherlands with significant variation in pesticides pressures. Macrofauna community composition, water chemistry parameters and pesticide concentrations in ditches next to flower bulb fields were determined. Trait modalities of nine traits (feeding mode, respiration mode, locomotion type, resistance form, reproduction mode, life stage, voltinism, saprobity, maximum body size) likely to indicate pesticides impacts were analyzed. According to a redundancy analysis, phosphate -and not pesticides- constituted the main factor structuring the trait modality distribution of aquatic macrofauna. The functional composition could be ascribed for 2–4 % to pesticides, and for 3–11 % to phosphate. The lack of trait responses to pesticides may indicate that species may have used alternative strategies to adapt to ambient pesticides stress. Biomass of animals exhibiting trait modalities related to feeding by predation and grazing, presence of diapause form or dormancy, reproduction by free clutches and ovoviviparity, life stage of larvae and pupa, was negatively correlated to the concentration of phosphate. Hence, despite the high pesticide pollution in the area, variation in nutrient-related stressors seems to be the dominant driver of the functional composition of aquatic macrofauna assembly in agricultural ditches.  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