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   93045篇
  免费   20184篇
  国内免费   1771篇
  115000篇
  2023年   402篇
  2022年   1089篇
  2021年   1983篇
  2020年   3032篇
  2019年   4781篇
  2018年   5177篇
  2017年   5158篇
  2016年   5894篇
  2015年   7100篇
  2014年   7292篇
  2013年   8175篇
  2012年   7292篇
  2011年   6721篇
  2010年   6180篇
  2009年   4626篇
  2008年   4822篇
  2007年   4099篇
  2006年   3704篇
  2005年   3399篇
  2004年   3197篇
  2003年   2896篇
  2002年   2564篇
  2001年   2079篇
  2000年   1882篇
  1999年   1513篇
  1998年   660篇
  1997年   559篇
  1996年   462篇
  1995年   447篇
  1994年   359篇
  1993年   334篇
  1992年   689篇
  1991年   550篇
  1990年   506篇
  1989年   504篇
  1988年   420篇
  1987年   404篇
  1986年   334篇
  1985年   341篇
  1984年   278篇
  1983年   229篇
  1982年   194篇
  1981年   165篇
  1980年   163篇
  1979年   225篇
  1978年   199篇
  1977年   183篇
  1976年   173篇
  1974年   199篇
  1972年   157篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
Rabbit alveolar macrophages exhibit a chemiluminescent response which is associated with phagocytosis of zymosan and polystyrene-butadiene particles. The chemiluminescence reaches a peak in 15 to 25 minutes and then gradually diminishes over the next 1 to 3 hours. During the time of maximal light emission there appears to be no actual uptake of particles, but the response is dependent upon the particle concentration. The metabolic inhibitor, DNP (2,4-dinitrophenol), causes a rapid inhibition of the chemiluminescent response. The addition of ATP to the medium prior to exposure of the cells to particles causes the chemiluminescent response to be greatly diminished, i.e., 0.3mM ATP virtually abolishes the response. These experiments suggest that some metabolic response of the cell to phagocytosis is responsible for the chemiluminescence.  相似文献   
62.
How Can the Eco‐efficiency of a Region be Measured and Monitored?   总被引:2,自引:0,他引:2  
The concept of eco-efficiency is commonly referred to as a business link to sustainable development. In this article, ecoefficiency is examined at a regional level as an approach to promoting the competitiveness of economic activities in the Finnish Kymenlaakso region and mitigating their harmful impacts on the environment. The aim is to develop appropriate indicators for monitoring changes in the eco-efficiency of the region. A starting point is to produce indicators for the environmental and economic dimensions of regional development and use them for measuring regional eco-efficiency. The environmental impact indicators are based on a life-cycle assessment method, producing different types of environmental impact indicators: pressure indicators (e.g., emissions of CO2), impact category indicators (e.g., CO2 equivalents in the case of climate change), and a total impact indicator (aggregating different impact category indicator results into a single value). Environmental impact indicators based on direct material input, total material input, and total material requirement of the Kymenlaakso region are also assessed. The economic indicators used are the gross domestic product, the value added, and the output of the main economic sectors of Kymenlaakso. In the eco-efficiency assessment, the economic and environmental impact indicators are monitored in the same graph. In a few cases eco-efficiency ratios can also be calculated (the economic indicators are divided by the environmental indicators). Output (= value added + intermediate consumption) is used as an economic indicator related to the environmental impact indicators, which also cover the upstream processes of the region's activities. In the article, we also discuss the strengths and weaknesses of using the different environmental impact indicators.  相似文献   
63.
Rapid and reproducible method is described here for the purification of the 43 kDa fimbrial protein from P. gingivalis by preferential fractionation in the presence of 1% SDS and 0.2M of a bivalent cation at pH 6.5. Homogeneity of the purified 43 kDa was confirmed by SDS-PAGE and Western blot analysis using monoclonal and polyclonal antibodies raised against this protein. Amino acid composition and the amino acid sequence of the first 30 amino acid residues of the purified fimbriae are consistent with the composition and sequence predicted from the cloned gene of the fimbrial subunit. Circular dichroism spectra shows high levels of beta-sheet structure. The purified 43 kDa polymer shows fimbriae-like morphology under the electron microscope. Ultrastructural localization of the 43 kDa protein by the immunogold technique revealed specific labeling of the fimbriae with a diameter of approximately 3.5 to 5.0 nm. Localization of this protein suggest that the 43 kDa component is a fimbrial subunit.  相似文献   
64.
Avian oviductal fluids contain phosphorylating-dephosphorylating enzymes that might function in sperm-oocyte interactions. Phosphorprotein phosphatase and protein kinase have been purified 20-fold and 40-fold, respectively. The latter easily aggregates and is highly labile. Other properties are comparable to those of holoenzymes.  相似文献   
65.
66.
67.
68.
69.
70.
88 rice and 75 soybean samples were collected from 8 provinces of Korea from March through September in 1988. The Fusarium mycotoxins, zearalenone was analyzed by direct competitive enzyme linked immunosorbent assay. 10.2% of rice and 9.3 % of soybean samples contained detectable zearalenone. The average levels of zearalenone of rice and soybean samples were 11.78μg/kg and 7.70μ/kg, respectively.  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