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   4864篇
  免费   321篇
  国内免费   6篇
  5191篇
  2023年   32篇
  2022年   51篇
  2021年   89篇
  2020年   88篇
  2019年   59篇
  2018年   163篇
  2017年   140篇
  2016年   192篇
  2015年   231篇
  2014年   236篇
  2013年   343篇
  2012年   352篇
  2011年   350篇
  2010年   223篇
  2009年   169篇
  2008年   275篇
  2007年   270篇
  2006年   231篇
  2005年   218篇
  2004年   208篇
  2003年   218篇
  2002年   162篇
  2001年   77篇
  2000年   77篇
  1999年   62篇
  1998年   42篇
  1997年   31篇
  1996年   26篇
  1995年   31篇
  1994年   32篇
  1993年   16篇
  1992年   32篇
  1991年   26篇
  1990年   36篇
  1989年   33篇
  1988年   22篇
  1987年   18篇
  1986年   21篇
  1985年   19篇
  1984年   41篇
  1983年   21篇
  1982年   19篇
  1981年   27篇
  1980年   19篇
  1979年   17篇
  1978年   11篇
  1977年   11篇
  1975年   10篇
  1972年   11篇
  1971年   11篇
排序方式: 共有5191条查询结果,搜索用时 15 毫秒
1.
2.
3.
The A(280)/A(260) ratio of a purified protein is frequently used as an indication of the purity of the preparation with respect to nucleic acids. We show here that for low-molecular-weight recombinant proteins purified from Escherichia coli, a low A(280)/A(260) ratio can also result from contamination with UDP-linked murein precursors derived from bacterial cell wall metabolism. Although these precursors are small molecules of molecular weight 1000-1200, they comigrate in gel filtration with recombinant human FKBP (MW 11,820). This gel filtration behavior, which is distinct from that of unmodified mononucleotides, does not reflect binding interactions with FKBP, but is an intrinsic property of these precursors. Therefore, these molecules would be expected to copurify with other low-molecular-weight proteins, especially in the abbreviated purification protocols made possible by freeze-thaw release of recombinant proteins from E. coli (Johnson, B. H., and Hecht, M. H. (1994) BioTechnology 12, 1357-1360). Several alternative strategies are discussed for integrating these findings into the design of improved purification procedures for low-molecular-weight recombinant proteins.  相似文献   
4.
5.
Triacylglycerol lipase activity with a pH optimum of 5 was present in homogenates of myocardial cells from rat heart. Acid lipase activity was inhibited by serum, heparin, and increased ionic strength. Methylamine, a lysosomotropic agent, did not inhibit the basal or isoproterenol-stimulated rate of endogenous lipolysis as measured by glycerol output from control myocytes. Similarly, accelerated rates of glycerol output that are a consequence of an elevation in the intracellular stores of triacylglycerols in myocytes from diabetic rat hearts and from myocytes prepared with free fatty acids in the isolation solutions were not reduced by methylamine. Therefore, the acid lysosomal triacylglycerol lipase must not be involved in the mobilization of endogenous triacylglycerols in myocardial cells from rat heart.  相似文献   
6.
7.
We describe a calcium transport that is sensitive to ruthenium red in liposomes reconstituted with mitochondrial extracts. This system is able to build an internally negative membrane potential, which allows the electrogenic influx of Ca2+ and Sr2+. Proteins with molecular weights higher than 35 kDa were incorporated to the vesicles, and enhanced the accumulation of the cation in an energy-dependent fashion.  相似文献   
8.
9.
That the uptake of glucose by the parasitic amoeba Entamoeba histolytica occurs by an equilibrative transport system is supported by the following observations. 1. The rate of glucose uptake is several orders of magnitude greater than the uptake by pinocytosis. 2. The uptake of glucose exhibits saturation kinetics, with K(m)=1.6mm and V(max.) ranging from 2 to 5mumol/min per ml of cells at 37 degrees C. 3. The glucose analogues 2-deoxyglucose, 3-O-methylglucose and d-xylose are transported by the glucose system although with much less affinity. Competitive inhibition was observed between pairs of substrates, with K(i) values for any sugar closely coincident with the corresponding K(m). 4. d-Xylose, a sugar not metabolized by the cells, equilibrated with 80% of the amoebal cell water. 5. Cells equilibrated with xylose exhibited countertransport of this sugar against its concentration gradient when another substrate was added to the medium. 6. Blocking of glycolysis by iodoacetate or F(-) has no immediate effect on transport. The presence of a glucose-transport system in E. histolytica contrasts with the situation found in the non-parasitic amoeba, where pinocytosis seems to be the only mechanism of solute uptake.  相似文献   
10.
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