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   4643075篇
  免费   367648篇
  国内免费   15890篇
耳鼻咽喉   66268篇
儿科学   145126篇
妇产科学   121117篇
基础医学   702959篇
口腔科学   129826篇
临床医学   423631篇
内科学   841266篇
皮肤病学   110841篇
神经病学   388984篇
特种医学   183735篇
外国民族医学   970篇
外科学   704855篇
综合类   135198篇
现状与发展   23篇
一般理论   2662篇
预防医学   391492篇
眼科学   110267篇
药学   328709篇
  25篇
中国医学   12894篇
肿瘤学   225765篇
  2021年   56234篇
  2019年   58982篇
  2018年   74512篇
  2017年   56976篇
  2016年   63244篇
  2015年   76334篇
  2014年   111085篇
  2013年   176463篇
  2012年   127002篇
  2011年   132420篇
  2010年   126545篇
  2009年   128091篇
  2008年   119031篇
  2007年   127447篇
  2006年   135818篇
  2005年   130635篇
  2004年   131463篇
  2003年   121676篇
  2002年   112293篇
  2001年   174320篇
  2000年   170887篇
  1999年   155956篇
  1998年   73643篇
  1997年   69234篇
  1996年   67071篇
  1995年   62811篇
  1994年   56886篇
  1993年   52777篇
  1992年   116357篇
  1991年   112242篇
  1990年   107487篇
  1989年   104853篇
  1988年   97277篇
  1987年   95506篇
  1986年   90639篇
  1985年   88470篇
  1984年   73187篇
  1983年   64734篇
  1982年   50366篇
  1981年   46856篇
  1980年   44071篇
  1979年   64997篇
  1978年   51619篇
  1977年   45332篇
  1976年   42406篇
  1975年   42566篇
  1974年   48074篇
  1973年   45903篇
  1972年   43108篇
  1971年   39614篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
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   
52.
53.
54.
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   
55.
56.
57.
58.
59.
60.
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