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   1903308篇
  免费   195352篇
  国内免费   1712篇
  2021年   18673篇
  2018年   19921篇
  2017年   18575篇
  2016年   30002篇
  2015年   44307篇
  2014年   52531篇
  2013年   78908篇
  2012年   56685篇
  2011年   49378篇
  2010年   50005篇
  2009年   49461篇
  2008年   45391篇
  2007年   44740篇
  2006年   46306篇
  2005年   46692篇
  2004年   45787篇
  2003年   42927篇
  2002年   40728篇
  2001年   63994篇
  2000年   62413篇
  1999年   53965篇
  1998年   29500篇
  1997年   29467篇
  1996年   28337篇
  1995年   26519篇
  1994年   26183篇
  1993年   25775篇
  1992年   46062篇
  1991年   44267篇
  1990年   42979篇
  1989年   42996篇
  1988年   39498篇
  1987年   38206篇
  1986年   35756篇
  1985年   37130篇
  1984年   33684篇
  1983年   29505篇
  1982年   26540篇
  1981年   24837篇
  1980年   23413篇
  1979年   30818篇
  1978年   26364篇
  1977年   24520篇
  1976年   23412篇
  1975年   24194篇
  1974年   25520篇
  1973年   25618篇
  1972年   22440篇
  1971年   20755篇
  1970年   18028篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
A double antibody radioimmunoassay technique is described for the measurement of anti-zona antibodies in the peripheral plasma of marmosets actively immunized against intact cow zonae pellucidae. The method has been shown to be a reliable, repeatable indicator of antibody titer, enabling direct comparison of the response obtained between marmosets. This is the first report of a procedure describing the active immunization of a primate against zona antigens, and the first time a radioimmunoassay technique has been used to monitor profiles of anti-cow zona antibody production following active immunization. The method should prove to be a useful tool in the evaluation of zona antigens as agents for immunocontraception.  相似文献   
992.
993.
994.
995.
A microcomputer mainframe linked system is described which allows video camera data capture and storage of one-dimensional whole-cell protein electrophoresis gel images, processing of normalized traces to produce a similarity matrix, and analysis of the matrix using the commercial cluster analysis program CLUSTAN. A new similarity coefficient is introduced which takes into account both band position and intensity. Forty-five strains of Haemophilus influenzae, including the eight biotypes and six serotypes, were analyzed using this system. Results demonstrated groupings which are consistent with known genetic relationships.  相似文献   
996.
1. Nile crocodiles, reared in fresh water and exposed acutely to seawater, suffer marked dehydration and hypernatraemia. Cloacal urine osmolarity and potassium concentration increased markedly but urine sodium remains low. 2. Hypernatraemia is increased when secretion from the lingual salt glands is prevented. 3. C. niloticus appears not to drink seawater. 4. Similarities in osmoregulatory response between estuarine and Nile crocodiles suggest that the lingual salt glands of C. niloticus are functional in salt water, playing an important role in sodium balance. 5. Significant differences in the function of the renal/cloacal complex of Alligator and Crocodylus emphasize further the differences between these two groups of crocodilian and provide support for the postulated marine ancestry of many or all of the Crocodylidae.  相似文献   
997.
Oligonucleotide analogs consisting exclusively of alpha-anomeric deoxynucleoside units bridged with phosphorothioate linkages have been synthesized and tested in vitro as antiviral agents against human immunodeficiency virus (HIV) in human T cells. Two 28-mers, an homopolymer alpha-S-dC28 and an oligomer alpha-S-anti-rev complementary to the initiation site of the regulatory viral gene rev exhibited antiviral activities comparable to those reported for the corresponding beta-anomeric phosphorothioate analogs. In contrast, a nuclease-resistant homopolymer, alpha-dC28 was inactive. Their preliminary results would indicate that the origin of oligonucleotide phosphorothioate anti-HIV activity is not exclusively correlated with their higher nuclease resistance.  相似文献   
998.
An apparently novel human plasma and urinary protein of low molecular weight was isolated from several highly purified preparations of protein HC by gel chromatography and high voltage electrophoresis with a yield of about 8 mg/g. The protein has a molecular weight of about 20,000, neutral electrophoretic mobility at pH 6.5 and a high content of half-cystine. It is associated with a yellow-brown chromophore like protein HC and could be demonstrated in all investigated preparations of isolated human, rabbit and guinea-pig protein HC and alpha 1-microglobulin.  相似文献   
999.
1000.
The photoacoustic spectroscopic studies of purple pigmented leaves revealed the occurrence of anthocyanins and betalains in some local weed species growing on soils with low moisture levels. The pigmentation intensities were higher in C4 plants than in C3 plants. An inverse correlation was observed between pigmentation intensities and soil moisture levels. This work is a part of the UNEP Research Project granted to Prof. D. O. Hall, UNEP Coordinator, Department of Plant Sciences, King’s College; London.  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