全文获取类型
收费全文 | 389篇 |
免费 | 0篇 |
专业分类
系统科学 | 6篇 |
教育与普及 | 2篇 |
现状及发展 | 91篇 |
研究方法 | 50篇 |
综合类 | 229篇 |
自然研究 | 11篇 |
出版年
2020年 | 2篇 |
2018年 | 2篇 |
2017年 | 2篇 |
2016年 | 3篇 |
2014年 | 3篇 |
2013年 | 7篇 |
2012年 | 14篇 |
2011年 | 23篇 |
2010年 | 7篇 |
2009年 | 2篇 |
2008年 | 16篇 |
2007年 | 17篇 |
2006年 | 18篇 |
2005年 | 14篇 |
2004年 | 16篇 |
2003年 | 12篇 |
2002年 | 17篇 |
2001年 | 17篇 |
2000年 | 7篇 |
1999年 | 8篇 |
1998年 | 2篇 |
1996年 | 2篇 |
1992年 | 7篇 |
1991年 | 9篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 11篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 9篇 |
1978年 | 8篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 8篇 |
1972年 | 2篇 |
1971年 | 6篇 |
1970年 | 11篇 |
1969年 | 8篇 |
1968年 | 14篇 |
1967年 | 8篇 |
1966年 | 4篇 |
1965年 | 9篇 |
1960年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有389条查询结果,搜索用时 109 毫秒
21.
22.
Non-indigenous African honey bees have invaded most of South and Central America in just over 30 years. The genetic composition of this population and the means by which it rapidly colonizes new territory remain controversial. In particular, it has been unclear whether this 'Africanized' population has resulted from interbreeding between African and domestic European bees, or is an essentially pure African population. Also, it has not been known whether this population expanded primarily by female or by male migration. Restriction site mapping of 62 mitochondrial DNAs of African bees from Brazil, Venezuela and Mexico reveals that 97% were of African (Apis mellifera scutellata) type. Although neotropical European apiary populations are rapidly Africanized by mating with neotropical African males, there is little reciprocal gene flow to the neotropical African population through European females. These are the first genetic data to indicate that the neotropical African population could be expanding its range by female migration. 相似文献
23.
A structural change in the kinesin motor protein that drives motility 总被引:34,自引:0,他引:34
Rice S Lin AW Safer D Hart CL Naber N Carragher BO Cain SM Pechatnikova E Wilson-Kubalek EM Whittaker M Pate E Cooke R Taylor EW Milligan RA Vale RD 《Nature》1999,402(6763):778-784
Kinesin motors power many motile processes by converting ATP energy into unidirectional motion along microtubules. The force-generating and enzymatic properties of conventional kinesin have been extensively studied; however, the structural basis of movement is unknown. Here we have detected and visualized a large conformational change of an approximately 15-amino-acid region (the neck linker) in kinesin using electron paramagnetic resonance, fluorescence resonance energy transfer, pre-steady state kinetics and cryo-electron microscopy. This region becomes immobilized and extended towards the microtubule 'plus' end when kinesin binds microtubules and ATP, and reverts to a more mobile conformation when gamma-phosphate is released after nucleotide hydrolysis. This conformational change explains both the direction of kinesin motion and processive movement by the kinesin dimer. 相似文献
24.
Regulation of non-muscle myosin assembly by calmodulin-dependent light chain kinase 总被引:33,自引:0,他引:33
The presence of actin and myosin in non-muscle cells suggests that they may be involved in a wide range of cellular contractile activities. The generally accepted view is that interaction between actin and myosin in these cells and in vertebrate smooth muscle, is regulated by the level of phosphorylation of the 20,000-molecular weight (MW) light chain. In the absence of calcium, this light chain is not phosphorylated and the myosin cannot interact with actin. Calcium activates a specific calmodulin-dependent kinase which phosphorylates the light chain, initiating actin-myosin interaction. Although most studies on the role of phosphorylation have concentration on the regulation of actin-activated myosin Mg-ATPase activity, phosphorylation of the light chain also seems to control the assembly of smooth muscle myosin into filaments. Using purified smooth muscle light chain kinase, we have confirmed this observation. We report here studies of myosins isolated from the two non-muscle sources, thymus cells and platelets. We observed that these myosins are assembled into filaments at physiological ionic strength and Mg-ATP concentrations, only when the 20,000-MW light chain is phosphorylated. 相似文献
25.
26.
Effect of chloroform on charge movement in the nerve membrane 总被引:2,自引:0,他引:2
27.
Hygroscopic food: a source of water for desert antelopes? 总被引:2,自引:0,他引:2
C R Taylor 《Nature》1968,219(5150):181-182
28.
29.
30.
Phosphorus nuclear magnetic resonance of perfused working rat hearts. 总被引:16,自引:0,他引:16