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   3156543篇
  免费   234304篇
  国内免费   8758篇
耳鼻咽喉   43921篇
儿科学   102013篇
妇产科学   88402篇
基础医学   445938篇
口腔科学   88546篇
临床医学   285700篇
内科学   617283篇
皮肤病学   73771篇
神经病学   259090篇
特种医学   122622篇
外国民族医学   892篇
外科学   476595篇
综合类   69048篇
现状与发展   7篇
一般理论   1163篇
预防医学   243516篇
眼科学   72035篇
药学   232052篇
  8篇
中国医学   6410篇
肿瘤学   170593篇
  2018年   33754篇
  2017年   26026篇
  2016年   30076篇
  2015年   34185篇
  2014年   47299篇
  2013年   71459篇
  2012年   94606篇
  2011年   99932篇
  2010年   60135篇
  2009年   57535篇
  2008年   93541篇
  2007年   99836篇
  2006年   101301篇
  2005年   97477篇
  2004年   94214篇
  2003年   91145篇
  2002年   87822篇
  2001年   147562篇
  2000年   150893篇
  1999年   127583篇
  1998年   37255篇
  1997年   33280篇
  1996年   33246篇
  1995年   32109篇
  1994年   29629篇
  1993年   27794篇
  1992年   100792篇
  1991年   97259篇
  1990年   94437篇
  1989年   91300篇
  1988年   83982篇
  1987年   82468篇
  1986年   77515篇
  1985年   74180篇
  1984年   55734篇
  1983年   47434篇
  1982年   28622篇
  1981年   25760篇
  1979年   50808篇
  1978年   36258篇
  1977年   30727篇
  1976年   28432篇
  1975年   30477篇
  1974年   36406篇
  1973年   34713篇
  1972年   32758篇
  1971年   30341篇
  1970年   28249篇
  1969年   27240篇
  1968年   25008篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
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   
102.
103.
104.
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   
105.
106.
107.
108.
109.
110.
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