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   368590篇
  免费   41816篇
  国内免费   169篇
  410575篇
  2018年   3420篇
  2017年   3260篇
  2016年   4782篇
  2015年   6762篇
  2014年   7862篇
  2013年   11102篇
  2012年   12686篇
  2011年   12921篇
  2010年   8655篇
  2009年   7749篇
  2008年   11198篇
  2007年   11700篇
  2006年   10998篇
  2005年   10650篇
  2004年   10629篇
  2003年   10207篇
  2002年   10021篇
  2001年   14871篇
  2000年   14835篇
  1999年   12118篇
  1998年   4732篇
  1997年   4681篇
  1996年   4408篇
  1995年   4221篇
  1994年   4197篇
  1993年   4130篇
  1992年   10310篇
  1991年   9856篇
  1990年   9684篇
  1989年   9379篇
  1988年   8772篇
  1987年   8356篇
  1986年   7610篇
  1985年   7735篇
  1984年   6522篇
  1983年   5705篇
  1982年   4654篇
  1981年   4190篇
  1980年   3915篇
  1979年   6437篇
  1978年   4898篇
  1977年   4601篇
  1976年   4320篇
  1975年   4551篇
  1974年   4950篇
  1973年   5024篇
  1972年   4565篇
  1971年   4246篇
  1970年   3601篇
  1969年   3493篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
981.
Cytogenetic studies were done on bone marrow cells and peripheral lymphocytes of four patients (three with acute nonlymphocytic leukemia, one with aplastic anemia) at various intervals up to 861 days after total-body X irradiation (TBI) at doses between 4.5 and 10 Gy (450-1000 rad) followed by syngeneic or allogeneic bone marrow transplantation. Whereas no radiation-induced aberrations could be found in the bone marrow, apart from a transient finding in the patient with the lowest radiation dose, aberrant metaphases were seen in the peripheral lymphocytes of three patients in the range from 2.5 to 46% even at 861 days after the exposure. There were no demonstrable aberrations related to TBI in the only patient developing graft-versus-host disease. The dicentric yield as determined in the aberrant metaphases with 46 centromeres ranged between 3.4 +/- 1.3 and 4.9 +/- 0.4. In one patient it was demonstrated by BUdR-labeling that after 10 Gy (1000 rad) TBI the surviving and heavily damaged lymphocytes can go into cell cycle and reach at least the third mitosis. The percentage of aberrant cells diminished by about 25% at each mitotic division.  相似文献   
982.
983.
984.
985.
986.
987.
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   
988.
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   
989.
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   
990.
Prostaglandins E1, F and A2 were covalently joined to the surface of Sepharose as carboxamide linkages. The insolubilized prostaglandins were shown to function effectively in the purification of 15(S) -hydroxyprostaglandin dehydrogenase.  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