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   796918篇
  免费   82488篇
  国内免费   244篇
  879650篇
  2018年   7946篇
  2017年   7596篇
  2016年   10652篇
  2015年   13474篇
  2014年   16061篇
  2013年   23160篇
  2012年   26008篇
  2011年   26778篇
  2010年   18298篇
  2009年   16897篇
  2008年   23937篇
  2007年   24897篇
  2006年   23275篇
  2005年   22384篇
  2004年   22165篇
  2003年   21321篇
  2002年   20836篇
  2001年   34743篇
  2000年   34197篇
  1999年   27573篇
  1998年   10179篇
  1997年   10269篇
  1996年   9842篇
  1995年   9058篇
  1994年   8720篇
  1993年   8752篇
  1992年   22336篇
  1991年   21916篇
  1990年   21370篇
  1989年   20816篇
  1988年   19084篇
  1987年   18323篇
  1986年   17092篇
  1985年   16955篇
  1984年   13938篇
  1983年   12183篇
  1982年   9232篇
  1981年   8360篇
  1980年   7755篇
  1979年   12942篇
  1978年   10203篇
  1977年   9194篇
  1976年   8803篇
  1975年   9818篇
  1974年   10485篇
  1973年   10355篇
  1972年   9478篇
  1971年   8457篇
  1970年   7384篇
  1969年   7256篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Coordination polymers of HEAP-ED with La(III), Pr(III), Nd(III), Sm(III), Gd(III), Tb(III) and Dy(III) metal ions have been synthesized and characterized by elemental analyses, electronic spectra, magnetic susceptibilities, FTIR, NMR, scanning electronic microscopy (SEM) and thermogravimetric analyses. Catalytic activity of selected coordination polymers was examined for pharmaceutical important organic synthesis. Antimicrobial activity of isolated Ln(III) coordination polymers against Escherichia coli, Bacillus subtilis, Staphylococcus aureus (bacteria) and Saccharomyces cerevisiae (yeast) were measured. It was observed from the study that the Ln(III) coordination polymers acted as an efficient and effective catalysts and antimicrobial agents.  相似文献   
992.
993.
Mitochondrial DNA variation was examined in one of the southem most populations of domestic reindeer, inhabiting Tyva Republic (Tuva). In Tuvinian population sequence polymorphism of the mitochondrial DNA D-loop region was demonstrated. In a sample of 29 individuals 7 mitotypes were distinguished, pointing to the preservation of rather high level of genetic diversity in this population.  相似文献   
994.
995.
The ECF™ lateral flow assay test is marketed to detect non-pregnancy in mares. The objectives of the present study were to determine the accuracy of the ECF test, the accuracy of the electronic reader accompanying the ECF test, and agreement between two human readers and the electronic reader. Serum samples were collected from anestrus, cycling but not inseminated, and inseminated mares, and were evaluated with the ECF™ test (EDP Biotech Company, Knoxville, TN, USA) at The Ohio State University and at the EDP Biotech Laboratory. Specificity ranged from 0.07 to 0.16, the negative predictive value ranged from 0.15 to 0.33, and accuracy ranged from 0.43 to 0.52. The electronic reader did not add improve the accuracy or predictive values of the test. Based on the electronic reader, 80.0% of the serum samples collected from the anestrus mares were false positives; Readers 1 and 2 had 60.0 and 33.3% false positives, respectively. For samples collected during the estrous cycle, 83.9% were false positives by the electronic reader, whereas Readers 1 and 2 had 43.7 and 26.4% false positives. We concluded that, regardless of whether the test strips were evaluated by a human or electronic reader, this assay was not accurate for determination of the non-pregnant mare.  相似文献   
996.
997.
998.
999.
In the experiments on redox potential measurement for a series of identical samples of purified and presettled water it was found that the response to ultraviolet irradiation varies appreciably within a few days after treatment, including stepwise changes. In a few hours after exposure, leading to a higher content of reactive oxygen species as compared with the equilibrium values, long-term changes including variations in redox potential and optical system parameters are recorded in water and diluted aqueous media. We propose a heuristic organization model of the water-gas system with an increased content of reactive oxygen species.  相似文献   
1000.
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