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   241860篇
  免费   16697篇
  国内免费   60篇
  258617篇
  2021年   2271篇
  2019年   1973篇
  2018年   3491篇
  2017年   3316篇
  2016年   4184篇
  2015年   4073篇
  2014年   5344篇
  2013年   7552篇
  2012年   8971篇
  2011年   9409篇
  2010年   6552篇
  2009年   5608篇
  2008年   8239篇
  2007年   8496篇
  2006年   8097篇
  2005年   7577篇
  2004年   7625篇
  2003年   7306篇
  2002年   7253篇
  2001年   9449篇
  2000年   9094篇
  1999年   7149篇
  1998年   2270篇
  1997年   2077篇
  1996年   1922篇
  1992年   5570篇
  1991年   5771篇
  1990年   5740篇
  1989年   5700篇
  1988年   5297篇
  1987年   4930篇
  1986年   4506篇
  1985年   4759篇
  1984年   3781篇
  1983年   3084篇
  1982年   2085篇
  1981年   1791篇
  1979年   3413篇
  1978年   2625篇
  1977年   2430篇
  1976年   2391篇
  1975年   2893篇
  1974年   3165篇
  1973年   3136篇
  1972年   2781篇
  1971年   2648篇
  1970年   2245篇
  1969年   2207篇
  1968年   2065篇
  1967年   1829篇
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
11.
The immunization of mice with the protein fraction of B. pertussis strain 305 has made it possible to obtain hybridomas producing monoclonal antibodies to B. pertussis antigens. Ascitic fluids containing monoclonal antibodies react in the ELISA in high titers and actively agglutinate B. pertussis strains 305 and 475.  相似文献   
12.
The study of the specific epidemiological and clinical features of Q fever revealed the existence of an active focus of infection among humans due to their contacts with agricultural animals in one of the districts of the region. The focus was manifested by group morbidity among the cattle-tending personnel of a dairy farm. The source of this infection was cattle. The infection was transferred mainly through the air. The disease took a moderately severe course. The study of the rickettsial contamination of humans, animals and ticks suggested the presence of the active epidemic process and made it possible to work out concrete antiepidemic measures.  相似文献   
13.
14.
Mutants of Bacillus amyloliquefaciens resistant to at least 10 micrograms/ml of tunicamycin were isolated and shown to be pleiotropic. The mutants were more resistant to streptomycin, chloramphenicol, kanamycin and neomycin than was the parent strain but less resistant to penicillin G and tetracycline. They were more autolytic, presumably due to an altered cell wall. The mutants produced reduced levels of amylase, penicillinase and both metal and serine protease besides having an enhanced sporulation frequency and being more motile.  相似文献   
15.
The content of neurospecific proteins S-100, GFA and D2 was measured in malignant cerebral tumors by electrophoresis with the use of monospecific antisera. Concomitant measurement of proteins S-100 and GFA is a more reliable diagnostic criterion as to the tumor histogenesis than study of each protein alone. D2 protein appeared to be the most stable specific marker.  相似文献   
16.
17.
18.
The paper presents data on a change in lysozyme content in tissues of spleen, liver and heart in fry of the Lena River sturgeon exposed to the presence of sublethal concentrations of Hg2+, Cd2+, and Cu2+ under conditions of chronic experiment. It has been shown that the lysozyme content in fish tissues varies and has a phasic character. The amplitude of fluctuations of this parameter depends on the moment of sampling, nature of the toxicant, and structural-functional organization of the studied organs.  相似文献   
19.
20.
An agar-degrading marine bacterium identified as a Microscilla species was isolated from coastal California marine sediment. This organism harbored a single 101-kb circular DNA plasmid designated pSD15. The complete nucleotide sequence of pSD15 was obtained, and sequence analysis indicated a number of genes putatively encoding a variety of enzymes involved in polysaccharide utilization. The most striking feature was the occurrence of five putative agarase genes. Loss of the plasmid, which occurred at a surprisingly high frequency, was associated with loss of agarase activity, supporting the sequence analysis results.  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