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   281032篇
  免费   18741篇
  国内免费   60篇
  299833篇
  2021年   2661篇
  2020年   2058篇
  2019年   2406篇
  2018年   4975篇
  2017年   4607篇
  2016年   5646篇
  2015年   5787篇
  2014年   7103篇
  2013年   9855篇
  2012年   11686篇
  2011年   11802篇
  2010年   8188篇
  2009年   6887篇
  2008年   10108篇
  2007年   10288篇
  2006年   9971篇
  2005年   9077篇
  2004年   9247篇
  2003年   8714篇
  2002年   8530篇
  2001年   10623篇
  2000年   10177篇
  1999年   8024篇
  1998年   2634篇
  1997年   2321篇
  1996年   2200篇
  1995年   2015篇
  1992年   6073篇
  1991年   6232篇
  1990年   6121篇
  1989年   6081篇
  1988年   5637篇
  1987年   5267篇
  1986年   4823篇
  1985年   5055篇
  1984年   4001篇
  1983年   3269篇
  1982年   2228篇
  1979年   3660篇
  1978年   2794篇
  1977年   2560篇
  1976年   2511篇
  1975年   3016篇
  1974年   3339篇
  1973年   3304篇
  1972年   2944篇
  1971年   2790篇
  1970年   2404篇
  1969年   2343篇
  1968年   2208篇
排序方式: 共有10000条查询结果,搜索用时 15 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