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   341086篇
  免费   26401篇
  国内免费   96篇
  367583篇
  2021年   3589篇
  2019年   3048篇
  2018年   4816篇
  2017年   4569篇
  2016年   6212篇
  2015年   7517篇
  2014年   9315篇
  2013年   12268篇
  2012年   15322篇
  2011年   15587篇
  2010年   10536篇
  2009年   9479篇
  2008年   13705篇
  2007年   14046篇
  2006年   13260篇
  2005年   12615篇
  2004年   12539篇
  2003年   12090篇
  2002年   11758篇
  2001年   11018篇
  2000年   10470篇
  1999年   8634篇
  1998年   3743篇
  1997年   3158篇
  1996年   2946篇
  1995年   2683篇
  1993年   2556篇
  1992年   6730篇
  1991年   6787篇
  1990年   6763篇
  1989年   6768篇
  1988年   6226篇
  1987年   5875篇
  1986年   5302篇
  1985年   5793篇
  1984年   4803篇
  1983年   3990篇
  1982年   3088篇
  1981年   2690篇
  1980年   2678篇
  1979年   4123篇
  1978年   3390篇
  1977年   3075篇
  1976年   3005篇
  1975年   3430篇
  1974年   3824篇
  1973年   3772篇
  1972年   3244篇
  1971年   3057篇
  1970年   2621篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
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   
12.
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