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   76779篇
  免费   6532篇
  国内免费   39篇
  2022年   388篇
  2021年   944篇
  2020年   567篇
  2019年   721篇
  2018年   926篇
  2017年   871篇
  2016年   1449篇
  2015年   2403篇
  2014年   2739篇
  2013年   3755篇
  2012年   4607篇
  2011年   4760篇
  2010年   3138篇
  2009年   2833篇
  2008年   4193篇
  2007年   4313篇
  2006年   4121篇
  2005年   4089篇
  2004年   4188篇
  2003年   3774篇
  2002年   3786篇
  2001年   869篇
  2000年   610篇
  1999年   888篇
  1998年   1189篇
  1997年   854篇
  1996年   786篇
  1995年   761篇
  1994年   738篇
  1993年   686篇
  1992年   625篇
  1991年   603篇
  1990年   579篇
  1989年   615篇
  1988年   528篇
  1987年   509篇
  1986年   459篇
  1985年   593篇
  1984年   743篇
  1983年   638篇
  1982年   760篇
  1981年   795篇
  1980年   720篇
  1979年   499篇
  1978年   557篇
  1977年   527篇
  1976年   525篇
  1975年   402篇
  1974年   498篇
  1973年   452篇
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
901.
902.
(1) The proportion of infected B. megatherium cells which develop lysogenic colonies depends on the number and kind of infecting virus particles and on the culture medium in which the cells are growing. (2) Cells infected with 100 or more T virus particles (from megatherium 899) in yeast extract peptone disintegrate, produce very few virus particles, and less than one lysogenic colony per 107 infected cells. Cells infected with one or a few particles produce 500 to 1000 virus particles each and about 30 lysogenic colonies per 107 infected colonies. (3) T phage obtained from lysogenic magatherium KM cultures produces many more lysogenic cells than does the original megatherium 899 virus. (4) Cells infected with megatherium 899 T virus in peptone medium and then transferred to asparagine medium give rise to 106 lysogenic colonies per 107 infected cells and this transformation will occur even after the infected cells have been in peptone for 60 to 90 minutes and are beginning to produce virus particles. (5) Continued growth of KM strain with either C or T virus from megatherium 899 for several hundred generations in the steady state apparatus results in a lysogenic strain which produces several different types of virus.  相似文献   
903.
Voltage clamp measurements of the sodium potential have been made on the resting squid giant axon to study the effect of variations in external divalent ion concentration upon net sodium flux. From these measurements the intracellular sodium concentration and the net sodium inflow were calculated using the Nernst relation and constant activity coefficients. While an axon bathed in artificial sea water shows a slow increase in internal sodium concentration, the rate of sodium accumulation is increased about two times by reducing external calcium and magnesium concentrations to 0.1 times their normal values. The mean inward net sodium flux increases from a mean control value of 97 pmole/cm2 sec. to 186 pmole/cm2 sec. in low divalent solution. Associated with these effects of external divalent ion reduction are a marked decrease in action potential amplitude, little or no change in resting potential, and a shift along the voltage axis of the curve relating peak sodium conductance to membrane potential similar to that obtained by Frankenhaeuser and Hodgkin (1957). These results implicate divalent ions in long term (minutes to hours) sodium permeability.  相似文献   
904.
905.
906.
907.
908.
909.
John McLeish 《Chromosoma》1959,10(1-6):686-710
Summary Photometric measurements have been made of the amounts of stain formed in the Feulgen (DNA) and Sakaguchi (arginine) reactions in plant nuclei of differing ploidy.In nuclei of diploid and tetraploid plants of Tradescantia ohioensis and of diploid, triploid and tetraploid plants of Ranunculus ficaria, both Feulgen and Sakaguchi values gave ratios which agreed closely with the ratios of the number of chromatids known to be present. The Feulgen/ Sakaguchi ratio for each of the different types of nuclei measured was very similar both within and between these two species.In the interphase nuclei of five different species, both Feulgen and Sakaguchi values gave bimodal distributions. In the nuclei of differentiating cells, the proportions of values falling into each of the 2C, 4C or 8C classes were the same for both stains.Measurements of the amounts of both stains were made in sequence on the same individual nuclei and a positive correlation found between the two sets of values.In nuclei from differentiating cells of Vicia faba primary roots, the Feulgen/Sakaguchi ratio decreased with increasing distance from the apex.The following suggestions were made from the results: (a) that there is some degree of quantitative constancy of nuclear arginine which parallels that of DNA; (b) that the amount of nuclear arginine, like that of DNA, is doubled during synthesis in interphase; (c) that the syntheses of DNA and arginine in interphase, if not simultaneous, at least occur within the same relatively short period; (d) that there may be a difference in the DNA/arginine ratio between the nuclei of meristematic and differentiating cells.  相似文献   
910.
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