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   51222篇
  免费   4668篇
  国内免费   2994篇
  2024年   78篇
  2023年   1101篇
  2022年   1022篇
  2021年   1979篇
  2020年   1931篇
  2019年   2404篇
  2018年   1993篇
  2017年   1482篇
  2016年   1548篇
  2015年   1922篇
  2014年   2890篇
  2013年   3693篇
  2012年   2065篇
  2011年   2618篇
  2010年   1952篇
  2009年   2274篇
  2008年   2309篇
  2007年   2420篇
  2006年   2166篇
  2005年   2040篇
  2004年   1799篇
  2003年   1616篇
  2002年   1546篇
  2001年   1278篇
  2000年   1070篇
  1999年   986篇
  1998年   916篇
  1997年   834篇
  1996年   726篇
  1995年   756篇
  1994年   710篇
  1993年   642篇
  1992年   626篇
  1991年   581篇
  1990年   441篇
  1989年   451篇
  1988年   405篇
  1987年   350篇
  1986年   286篇
  1985年   371篇
  1984年   461篇
  1983年   261篇
  1982年   357篇
  1981年   337篇
  1980年   261篇
  1979年   238篇
  1978年   187篇
  1977年   136篇
  1976年   133篇
  1974年   55篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
《Cell reports》2020,30(4):1152-1163.e4
  1. Download : Download high-res image (170KB)
  2. Download : Download full-size image
  相似文献   
2.
Plant somatic cells have the capability to switch their cell fates from differentiated to undifferentiated status under proper culture conditions, which is designated as totipotency. As a result, plant cells can easily regenerate new tissues or organs from a wide variety of explants. However, the mechanism by which plant cells have such remarkable regeneration ability is still largely unknown. In this study, we used a set of meristem-specific marker genes to analyze the patterns of stem cell differentiation in the processes of somatic embryogenesis as well as shoot or root organogenesis in vitro. Our studies furnish preliminary and important information on the patterns of the de novo stem cell differentiation during various types of in vitro organogenesis.  相似文献   
3.
4.
《Cell reports》2020,30(1):112-123.e4
  1. Download : Download high-res image (131KB)
  2. Download : Download full-size image
  相似文献   
5.
1. Because L-asparagine augments insulin release evoked by L-leucine, the metabolism of these two amino acids was investigated in rat pancreatic islets. 2. L-Leucine inhibited the uptake and deamidation of L-asparagine, but failed to exert any obvious primary effect upon the further catabolism of aspartate derived from exogenous asparagine. 3. L-Asparagine augmented the oxidation of L-leucine, and effect possibly attributable to activaion of 2-ketoisocaproate dehydrogenase. 4. The association of L-asparagine and L-leucine exerted a sparing action on the utilization of endogenous amino acids, so that the integrated rate of nutrients oxidation was virtually identical in the sole presence of L-leucine and simultaneous presence of L-asparagine and L-leucine, respectively. 5. It is proposed that the enhancing action of L-asparagine upon insulin release evoked by L-leucine is attributable to an increased generation rate of cytosolic NADPH rather than any increase in nutrients oxidation.  相似文献   
6.
In C. elegans, cell death can be readily studied at the cellular, genetic, and molecular levels. Two types of death have been characterized in this nematode: (1) programmed cell death, which occurs as a normal component in development; and (2) pathological cell death which occurs aberrantly as a consequence of mutation. Analysis of mutations that disrupt programmed cell death in various ways has defined a genetic pathway for programmed cell death which includes genes that perform such functions as the determination of which cells die, the execution of cell death, the engulfment of cell corpses, and the digestion of DNA from dead cells. Molecular analysis is providing insightinto the nature of the molecules that function in these aspects of programmed cell death. Characterization of some genes that mutate to induce abnormal cell death has defined a novel gene family called degenerins that encode putative membrane proteins. Dominant alleles of at least two degenerin genes, mec-4 and deg-1, can cause cellular swelling and late onset neurodegeneration of specific groups of cells. © 1992 John Wiley & Sons, Inc.  相似文献   
7.
THE TIMING OF DIVISION IN CHLAMYDOMONAS   总被引:3,自引:2,他引:1  
  相似文献   
8.
The effects of 5-hydroxytryptamine and 5-hydroxytryptophan on 86Rb+ efflux from prelabelled ob/ob-mouse islets were studied to better understand the cellular mechanisms underlying the effects of 5-hydroxytryptamine and 5-hydroxytryptophan on insulin release. 5-Hydroxytryptophan (4 mM) had no effect on 86Rb+ efflux either at a low (3 mM) or at a high (20 mM) d-glucose concentration, whereas 5-hydroxytryptamine (4 mM) stimulated 86Rb+ efflux at both glucose concentrations. These results indicate that 5-hydroxytryptamine may reduce glucose-induced insulin release by inhibiting early steps in the β-cell stimulus-secretion coupling.  相似文献   
9.
In this paper very simple nonparametric classification rule for mixtures of discrete and continuous random variables is described. It is based on the method of nearest neighbor proposed by Cover and Hart (1967). The bounds on the limit of the nearest neighbor rule risks are given. Both lower and upper bound depend on the Bayes risk and the loss function. Finally the method is compared with other existing methods on some practical data set.  相似文献   
10.
《Cell reports》2020,30(1):98-111.e5
  1. Download : Download high-res image (124KB)
  2. Download : Download full-size image
  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