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   4884614篇
  免费   374468篇
  国内免费   15233篇
耳鼻咽喉   68292篇
儿科学   157067篇
妇产科学   130224篇
基础医学   736750篇
口腔科学   133749篇
临床医学   446459篇
内科学   887934篇
皮肤病学   118174篇
神经病学   402457篇
特种医学   188472篇
外国民族医学   919篇
外科学   740498篇
综合类   139017篇
现状与发展   24篇
一般理论   2805篇
预防医学   408610篇
眼科学   115824篇
药学   343445篇
  26篇
中国医学   13207篇
肿瘤学   240362篇
  2021年   56642篇
  2019年   59117篇
  2018年   75843篇
  2017年   58124篇
  2016年   64464篇
  2015年   76803篇
  2014年   111383篇
  2013年   176864篇
  2012年   142265篇
  2011年   151395篇
  2010年   131529篇
  2009年   130959篇
  2008年   136549篇
  2007年   146780篇
  2006年   154409篇
  2005年   149353篇
  2004年   149158篇
  2003年   138690篇
  2002年   127262篇
  2001年   187027篇
  2000年   183541篇
  1999年   165296篇
  1998年   74777篇
  1997年   69642篇
  1996年   67764篇
  1995年   62991篇
  1994年   57030篇
  1993年   52844篇
  1992年   119947篇
  1991年   115735篇
  1990年   111291篇
  1989年   108428篇
  1988年   99963篇
  1987年   97833篇
  1986年   92120篇
  1985年   90244篇
  1984年   73949篇
  1983年   65507篇
  1982年   50389篇
  1981年   46739篇
  1980年   43881篇
  1979年   64957篇
  1978年   51554篇
  1977年   44952篇
  1976年   42091篇
  1975年   42741篇
  1974年   47836篇
  1973年   45898篇
  1972年   43201篇
  1971年   40235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