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   1031460篇
  免费   112521篇
  国内免费   706篇
  1144687篇
  2018年   9524篇
  2017年   8940篇
  2016年   12963篇
  2015年   17930篇
  2014年   20930篇
  2013年   29795篇
  2012年   33341篇
  2011年   33698篇
  2010年   22965篇
  2009年   20852篇
  2008年   29811篇
  2007年   30750篇
  2006年   28937篇
  2005年   27848篇
  2004年   27467篇
  2003年   26452篇
  2002年   25790篇
  2001年   48092篇
  2000年   48478篇
  1999年   38477篇
  1998年   13445篇
  1997年   14004篇
  1996年   13211篇
  1995年   12343篇
  1994年   12066篇
  1993年   11810篇
  1992年   31712篇
  1991年   30909篇
  1990年   30011篇
  1989年   29158篇
  1988年   27075篇
  1987年   25399篇
  1986年   23590篇
  1985年   23452篇
  1984年   19387篇
  1983年   16382篇
  1982年   12415篇
  1981年   11133篇
  1980年   10433篇
  1979年   17949篇
  1978年   13841篇
  1977年   12537篇
  1976年   11363篇
  1975年   12760篇
  1974年   13551篇
  1973年   13390篇
  1972年   12076篇
  1971年   10888篇
  1970年   9443篇
  1969年   9073篇
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
871.
The evaluation of growth by dry weight determination of fungus mycelium for agar plates was examined. The data obtained were statistically analyzed. This method was shown to be sufficiently accurate to be used as an investigative tool.  相似文献   
872.
873.
874.
875.
876.
Heat treatment (37 degrees C) of transgenic tobacco (Nicotiana tabacum) plants led to a reversible reduction or complete loss of transgene-encoded activities in about 40% of 10 independent transformants carrying the luciferase-coding region fused to the 355 cauliflower mosaic virus or the soybean small subunit promoter and the nopaline synthase promoter driving the neomycin phosphotransferase gene, whereas the other lines had temperature-tolerant activities. Temperature sensitivity or tolerance of transgene-encoded activities was heritable. In some of the lines, temperature sensitivity of the transgene-encoded activities depended on the stage of development, occurring in either seedlings (40% luciferase and 50% neomycin phosphotransferase) or adult plants (both 40%). The phenomenon did not correlate with copy numbers or the homo- or hemizygous state of the transgenes. In lines harboring a temperature-sensitive luciferase activity, reduction of bioluminescence was observed after 2 to 3 h at 37 degrees C. Activity was regained after 2 h of subsequent cultivation at 25 degrees C. Irrespective of the reaction to the heat treatment, the level of luciferase RNA was slightly increased at 37 degrees C. Only in lines showing temperature sensitivity of transgene-encoded activities was the amount of luciferase and neomycin phosphotransferase strongly reduced. In sterile culture, heat treatment for 15 d did not cause visible damage or changes in plant morphology. In all plants tested a slight induction of the heat-shock response was observed at 37 degrees C.  相似文献   
877.
878.
879.
Little is known regarding the role of androgenic hormones in the maintenance of myosin heavy chain (MHC) composition of rodent masticatory muscles. Because the masseter is the principal jaw closer in rodents, we felt it was important to characterize the influence of androgenic hormones on the MHC composition of the masseter. To determine the extent of sexual dimorphism in the phenotype of masseter muscle fibers of adult (10-mo-old) C57 mice, we stained tissue sections with antibodies specific to type IIa and IIb MHC isoforms. Females contain twice as many fibers containing the IIa MHC as males, and males contain twice as many fibers containing the IIb MHC as females. There is a modest amount of regionalization of MHC phenotypes in the mouse masseter. The rostral portions of the masseter are composed mostly of type IIa fibers, whereas the midsuperficial and caudal regions contain mostly type IIb fibers. Using immunoblots, we showed that castration results in an increase in the expression of type IIa MHC fibers in males. Ovariectomy has no effect on the fiber type composition in females. We conclude that testosterone plays a role in the maintenance of MHC expression in the adult male mouse masseter.  相似文献   
880.
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