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   340857篇
  免费   37718篇
  国内免费   219篇
  2018年   3264篇
  2017年   3011篇
  2016年   4305篇
  2015年   5816篇
  2014年   6823篇
  2013年   9491篇
  2012年   10762篇
  2011年   10634篇
  2010年   7204篇
  2009年   6455篇
  2008年   9251篇
  2007年   9693篇
  2006年   8949篇
  2005年   8629篇
  2004年   8275篇
  2003年   7976篇
  2002年   7970篇
  2001年   18229篇
  2000年   18442篇
  1999年   14165篇
  1998年   4276篇
  1997年   4403篇
  1996年   4182篇
  1995年   4032篇
  1994年   3959篇
  1993年   3798篇
  1992年   11508篇
  1991年   11154篇
  1990年   10714篇
  1989年   10268篇
  1988年   9512篇
  1987年   8863篇
  1986年   8104篇
  1985年   7984篇
  1984年   6414篇
  1983年   5578篇
  1982年   4122篇
  1981年   3608篇
  1980年   3361篇
  1979年   6117篇
  1978年   4576篇
  1977年   4132篇
  1976年   3778篇
  1975年   4343篇
  1974年   4503篇
  1973年   4399篇
  1972年   4094篇
  1971年   3501篇
  1970年   3174篇
  1969年   2973篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
A method for the extraction and quantitative determination of both the mass and radioactivity of glycolic acid from -14C-labeled leaf tissue is described. The recoveries of both mass and radioactivity from standard [1-14C]glycolic acid solutions averaged 98 percent, and recovery of radioactivity added to plant samples as [1-14C]glycolic acid was over 90 percent after the complete procedure. The method was reliable with total samples containing as little as 130 nmol of glycolic acid. The mass of glycolic acid recovered from sunflower leaf tissue was proportional to the amount of tissue extracted. In experiments with different plant material, the amount of glycolic acid varied between 530 and 1120 nmol/dm-2 of leaf tissue. The specific radioactivity of the glycolic acid in sunflower leaf tissue during photosynthesis in -14CO(2) was never more than 20 percent of the specific radioactivity of the -14CO(2) supplied.  相似文献   
992.
993.
Intermittent illumination increased H2 and C2H4 yields per unit of light from growing cells and from nitrogren-starved cells by 1.7- and 1.35-fold, respectively, as compared with continuous illumination.  相似文献   
994.
The release of alanine by rat diaphragm muscle in vitro.   总被引:13,自引:10,他引:3       下载免费PDF全文
Z discs were isolated from Lethocerus flight muscle by removing the contractile proteins from myofibrils with a solution of high ionic strength. The protein composition of the Z discs was analysed by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis; the major proteins were alpha-actinin, actin and tropomyosin. Z lines were selectively removed from intact myofibrils by digestion with crude lipase and chymotrypsin, but not by purified lipase.  相似文献   
995.
996.
997.
Anaerobic rupture of the benzoic acid ring was investigated. Carbon 4 was converted primarily to carbon dioxide. Following ring rupture during methane fermentation, propanoic acid is an intermediate, and carbon 4 of benzoate becomes its carboxyl.Contribution No. 1285-j, Division of Biology, Kansas State University, Manhattan, KS 66506. This work was supported in part by funds from the Kansas Agricultural Experiment Station, Kansas State University, Manhattan, KS 66506. Paper II of this series is Fina and Fiskin (1960)  相似文献   
998.
Bac. subtilis 168 (BD-25) cells were infected with DNA of plasmide R1drd19 isolated from E. coli strain; transformants resistant to streptomycin (500 microgram/ml) and kanamycin (40 microgram/ml) appeared with the frequency of 2.10(-6). These transformants retained resistance to the mentioned antibiotics stably. A satellite DNA peak was revealed in centrifugation in the density gradient of cesium chloride with ethidium bromide. It was possible to infect cells of Bac. subtilis 168 (BD-25) with plasmide DNA isolated from the transformants. Plasmide transduction with the aid of phages AR9 and PBSI multiplied on the transformant strains was also effected. Physico-chemical analysis of the transformed plasmide DNA was conducted; its molecular weight was determined.  相似文献   
999.
1000.
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