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   4865890篇
  免费   381853篇
  国内免费   15834篇
耳鼻咽喉   69371篇
儿科学   153223篇
妇产科学   129497篇
基础医学   730359篇
口腔科学   137444篇
临床医学   447927篇
内科学   884002篇
皮肤病学   114297篇
神经病学   409864篇
特种医学   191747篇
外国民族医学   1128篇
外科学   729634篇
综合类   140185篇
现状与发展   24篇
一般理论   2861篇
预防医学   415063篇
眼科学   115504篇
药学   344477篇
  28篇
中国医学   12397篇
肿瘤学   234545篇
  2021年   56231篇
  2019年   58933篇
  2018年   74951篇
  2017年   57377篇
  2016年   63716篇
  2015年   76512篇
  2014年   111306篇
  2013年   176742篇
  2012年   135443篇
  2011年   142320篇
  2010年   128507篇
  2009年   129525篇
  2008年   128991篇
  2007年   138406篇
  2006年   145878篇
  2005年   141200篇
  2004年   141465篇
  2003年   131646篇
  2002年   121990篇
  2001年   181082篇
  2000年   178128篇
  1999年   161869篇
  1998年   74416篇
  1997年   69894篇
  1996年   68019篇
  1995年   63679篇
  1994年   57888篇
  1993年   53659篇
  1992年   121901篇
  1991年   117549篇
  1990年   112500篇
  1989年   109373篇
  1988年   101845篇
  1987年   99974篇
  1986年   95118篇
  1985年   92579篇
  1984年   76385篇
  1983年   67828篇
  1982年   51737篇
  1981年   48031篇
  1980年   45146篇
  1979年   68891篇
  1978年   54468篇
  1977年   47569篇
  1976年   44346篇
  1975年   44676篇
  1974年   51192篇
  1973年   49366篇
  1972年   46562篇
  1971年   42978篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
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   
62.
63.
64.
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   
65.
66.
67.
68.
69.
70.
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