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   318989篇
  免费   37310篇
  国内免费   137篇
  356436篇
  2018年   2763篇
  2016年   3752篇
  2015年   5082篇
  2014年   6011篇
  2013年   8664篇
  2012年   9592篇
  2011年   9771篇
  2010年   6605篇
  2009年   5898篇
  2008年   8544篇
  2007年   8975篇
  2006年   8388篇
  2005年   8092篇
  2004年   8175篇
  2003年   7907篇
  2002年   7810篇
  2001年   14294篇
  2000年   14322篇
  1999年   11475篇
  1998年   4021篇
  1997年   4132篇
  1996年   3929篇
  1995年   3799篇
  1994年   3802篇
  1993年   3690篇
  1992年   9806篇
  1991年   9388篇
  1990年   9212篇
  1989年   8941篇
  1988年   8348篇
  1987年   7985篇
  1986年   7211篇
  1985年   7319篇
  1984年   6047篇
  1983年   5301篇
  1982年   4175篇
  1981年   3691篇
  1980年   3511篇
  1979年   6094篇
  1978年   4548篇
  1977年   4272篇
  1976年   3968篇
  1975年   4295篇
  1974年   4651篇
  1973年   4715篇
  1972年   4357篇
  1971年   4065篇
  1970年   3435篇
  1969年   3334篇
  1968年   2962篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
942.
943.
Immunological investigation of four patients with meningococcal meningitis who developed arthritis or cutaneous lesions showed circulating meningococcal antigen at the time of presentation in each patient. It was cleared from the circulation over the next few days. Circulating antibody was detectable in three of the four patients about a week after the onset of the illness. A marked fall in the serum C3 level occurred in two patients at about that time. Deposits of meningococcal antigen, immunoglobulin, and C3 were detected in the synovial fluid white cells of the two patients studied and in one of three skin biopsies examined. These findings suggest that the arthritis and cutaneous lesions of meningococcal meningitis may be due to immune complex formation.  相似文献   
944.
Species composition and ecological structure of ground beetle population was studied in northern taiga meadows of the Arkhangelsk Region. Meadows in the northern forest zone proved to harbor 91 ground beetle species. Carabid complexes formed in the intrazonal biocenoses of the northern forest zone can be as rich as the family topical groups in the southern forest zone by the number of species and ecological diversity. Ecological properties of the fauna and ground beetle population proved similar in different parts of the forest zone. The proportion of stenobiotic meadow species proved to decrease while that of ecologically plastic ones increased from south to north. The proportion of the genus Harpalus decreased in the ground beetle population while the number of Amara species remained unaltered and their abundance increased. The changes in the species composition caused no transformation of the ecological structure of ground beetle population since they were limited to a single life form or guild.  相似文献   
945.
Colonies of Thelohania apodemi in fresh preparations of the brain of the field mouse show an intense fluorescence with ultra violet radiation. This phenomenon is undoubtedly due to the presence of chitin in the spore envelope. It is to our knowledge the first time that such a phenomenon of fluorescence has been described in the Microsporida.  相似文献   
946.
In two different strains of cholera vibrios two recA-dependent plasmids, pVib I (1.9-2.2 Md) and pVib II (5.2-5.8 Md), have been detected. These plasmids determine the synthesis of vibriocin, coagulase and fibrinolysin, which has been established by the cotransformation of the DNA of plasmids pVib I and pBR322 and by the transfer mobilization with the use of plasmid RP4.  相似文献   
947.
The authors describe the results obtained on rats by a method of four channel telemetric recording system. The transmitter with a range of a few meters, has a pass band from 0,3 to 400 Hz, weighs 4 grams and can operate autonomously for a minimum of 10 days.  相似文献   
948.
949.
950.
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