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   396663篇
  免费   18014篇
  国内免费   412篇
耳鼻咽喉   4978篇
儿科学   13790篇
妇产科学   11766篇
基础医学   57123篇
口腔科学   8062篇
临床医学   30345篇
内科学   76159篇
皮肤病学   6788篇
神经病学   31045篇
特种医学   16148篇
外国民族医学   46篇
外科学   64329篇
综合类   8532篇
现状与发展   1篇
一般理论   160篇
预防医学   29103篇
眼科学   7957篇
药学   26033篇
中国医学   793篇
肿瘤学   21931篇
  2018年   15138篇
  2017年   12093篇
  2016年   14389篇
  2015年   3895篇
  2014年   4880篇
  2013年   7490篇
  2012年   12244篇
  2011年   19694篇
  2010年   14227篇
  2009年   11614篇
  2008年   19442篇
  2007年   22807篇
  2006年   9596篇
  2005年   11106篇
  2004年   11353篇
  2003年   12258篇
  2002年   10516篇
  2001年   13657篇
  2000年   14217篇
  1999年   11651篇
  1998年   3228篇
  1997年   3063篇
  1996年   2802篇
  1995年   2711篇
  1994年   2533篇
  1993年   2361篇
  1992年   8459篇
  1991年   8605篇
  1990年   8414篇
  1989年   8210篇
  1988年   7430篇
  1987年   7216篇
  1986年   6837篇
  1985年   6633篇
  1984年   4839篇
  1983年   4194篇
  1982年   2565篇
  1979年   4529篇
  1978年   3297篇
  1977年   2752篇
  1976年   2577篇
  1975年   2838篇
  1974年   3389篇
  1973年   3373篇
  1972年   3118篇
  1971年   2950篇
  1970年   2864篇
  1969年   2619篇
  1968年   2563篇
  1967年   2373篇
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
11.
12.
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   
13.
14.
15.
16.
Pharmaceutical Chemistry Journal - Three extracts were produced from the above-ground part of the meadowsweet Filipendula ulmaria (L.) Maxim. using water, 40% ethanol, and 70% ethanol. Comparative...  相似文献   
17.
18.
19.
20.
In the 6th Basic Plan for Long-Term Electricity Supply and Demand (6th BPE) for Korea, for the first time, the environmental costs of air pollution caused by oxides of sulfur (SOx), oxides of nitrogen (NOx), and particulate matters (PM) from power plants were estimated and included. However, several deficiencies in evaluating the environmental costs were found. In this study, (1) the validity of the environmental costs used in the 6th BPE was assessed, (2) a systematic approach was suggested and used to improve the environmental costs estimation, and (3) the sensitivity of the cost of generating electricity to the environmental costs by fuel type with the proposed approach was discussed. We found that the applied environmental costs used in the 6th BPE did not fully include the demographic characteristics of Korea. By applying more realistic parameter values, it was found that the newly estimated environmental cost was about 23 times higher than the cost estimated in the original 6th BPE for coal-fired power plants and about 1.5 times higher for liquefied natural gas (LNG)-fired power plants, suggesting that LNG-fired power plants are more economical if using more realistic environmental costs. Thus, it is critical to check the validity of parameter values when calculating environmental costs.  相似文献   
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