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   1488199篇
  免费   147758篇
  国内免费   3368篇
耳鼻咽喉   19733篇
儿科学   50630篇
妇产科学   41807篇
基础医学   215213篇
口腔科学   42352篇
临床医学   137744篇
内科学   306082篇
皮肤病学   39418篇
神经病学   128692篇
特种医学   56044篇
外国民族医学   464篇
外科学   223750篇
综合类   32877篇
现状与发展   3篇
一般理论   513篇
预防医学   114625篇
眼科学   32904篇
药学   104204篇
  1篇
中国医学   4324篇
肿瘤学   87945篇
  2021年   12162篇
  2020年   11479篇
  2019年   21518篇
  2018年   24984篇
  2017年   22283篇
  2016年   24461篇
  2015年   26063篇
  2014年   32633篇
  2013年   44051篇
  2012年   49343篇
  2011年   51693篇
  2010年   35920篇
  2009年   31825篇
  2008年   46489篇
  2007年   48098篇
  2006年   48630篇
  2005年   46894篇
  2004年   44852篇
  2003年   42728篇
  2002年   41293篇
  2001年   73987篇
  2000年   75490篇
  1999年   62114篇
  1998年   17182篇
  1997年   15566篇
  1996年   15741篇
  1995年   14924篇
  1994年   13535篇
  1993年   12715篇
  1992年   46100篇
  1991年   43756篇
  1990年   41736篇
  1989年   39841篇
  1988年   36414篇
  1987年   35580篇
  1986年   33057篇
  1985年   31526篇
  1984年   24001篇
  1983年   20177篇
  1982年   12338篇
  1979年   20861篇
  1978年   14695篇
  1977年   12177篇
  1976年   11440篇
  1975年   11717篇
  1974年   14097篇
  1973年   13620篇
  1972年   12724篇
  1971年   11542篇
  1970年   10987篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
2.
3.
Direct peroral cholangioscopy (POC) using an ultra‐slim upper endoscope is one modality of POC for intraductal endoscopic evaluation and treatment of the bile duct. Choledochoduodenostomy (CDS) is one modality of biliary bypass surgery that provides a new route to the bile duct. We carried out direct POC using an ultra‐slim upper endoscope without the use of accessories in 10 patients (four sump syndromes, three bile duct strictures and three intrahepatic duct stones) previously undergoing surgical CDS. Direct POC was successful in all patients. The use of an intraductal balloon catheter was required in one patient for advancement of the endoscope into the bile duct. Distal bile ducts with sump syndromes were cleared using baskets and water irrigation under direct POC. Cholangiocarcinoma was diagnosed in one patient with hilar bile duct stricture after cholangioscopic evaluation and a targeting forceps biopsy under direct POC. Intrahepatic duct stones were successfully extracted after intraductal fragmentation under direct POC. Oozing bleeding occurred during intraductal lithotripsy but stopped spontaneously. Direct POC using an ultra‐slim upper endoscope without the assistance of accessories can easily be carried out in patients undergoing CDS.  相似文献   
4.
5.
6.
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   
7.
8.
9.
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   
10.
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