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   336385篇
  免费   38845篇
  国内免费   146篇
  375376篇
  2018年   3074篇
  2016年   4200篇
  2015年   5885篇
  2014年   6877篇
  2013年   9673篇
  2012年   10955篇
  2011年   11022篇
  2010年   7454篇
  2009年   6723篇
  2008年   9608篇
  2007年   10058篇
  2006年   9337篇
  2005年   9071篇
  2004年   9067篇
  2003年   8731篇
  2002年   8605篇
  2001年   14474篇
  2000年   14475篇
  1999年   11692篇
  1998年   4254篇
  1997年   4305篇
  1996年   4079篇
  1995年   3921篇
  1994年   3927篇
  1993年   3814篇
  1992年   9928篇
  1991年   9501篇
  1990年   9345篇
  1989年   9064篇
  1988年   8450篇
  1987年   8093篇
  1986年   7280篇
  1985年   7405篇
  1984年   6150篇
  1983年   5373篇
  1982年   4253篇
  1981年   3761篇
  1980年   3571篇
  1979年   6156篇
  1978年   4598篇
  1977年   4317篇
  1976年   4009篇
  1975年   4323篇
  1974年   4685篇
  1973年   4744篇
  1972年   4377篇
  1971年   4084篇
  1970年   3453篇
  1969年   3349篇
  1968年   2986篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
961.
Immunocytological investigations have been performed on semi-thin sections of human fetal pituitaries ranging in fetal age from 6 to 26 weeks. Corticotrophs can be revealed by anti-ACTH (1-24), anti-ACTH (17-39) and anti-beta MSH but not by anti-alpha MSH immunesera from the 8th week. Somatotrophs are revealed with anti-human STH from 9th week. Differentiating cells containing only alpha subunits of glycoproteic hormones are present from 8th to 12th week. At 13th week beta subunits of TSH can be revealed immunocytologically in thyreotrophs. Beta subunits of LH or FSH can be detected in same gonadotrophic cells only from 15th week.  相似文献   
962.
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   
963.
964.
965.
966.
967.
968.
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   
969.
970.
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   
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