全文获取类型
收费全文 | 291篇 |
免费 | 2篇 |
国内免费 | 2篇 |
专业分类
教育与普及 | 3篇 |
理论与方法论 | 4篇 |
现状及发展 | 40篇 |
研究方法 | 53篇 |
综合类 | 160篇 |
自然研究 | 35篇 |
出版年
2020年 | 1篇 |
2016年 | 1篇 |
2015年 | 1篇 |
2014年 | 1篇 |
2013年 | 9篇 |
2012年 | 14篇 |
2011年 | 58篇 |
2010年 | 9篇 |
2009年 | 1篇 |
2008年 | 17篇 |
2007年 | 28篇 |
2006年 | 19篇 |
2005年 | 27篇 |
2004年 | 25篇 |
2003年 | 15篇 |
2002年 | 26篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1996年 | 2篇 |
1994年 | 1篇 |
1992年 | 2篇 |
1990年 | 3篇 |
1988年 | 1篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1978年 | 1篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1971年 | 2篇 |
1970年 | 5篇 |
1969年 | 4篇 |
1968年 | 3篇 |
1967年 | 1篇 |
1966年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有295条查询结果,搜索用时 31 毫秒
81.
Polymer electrolytes consist of salts dissolved in polymers (for example, polyethylene oxide, PEO), and represent a unique class of solid coordination compounds. They have potential applications in a diverse range of all-solid-state devices, such as rechargeable lithium batteries, flexible electrochromic displays and smart windows. For 30 years, attention was focused on amorphous polymer electrolytes in the belief that crystalline polymer:salt complexes were insulators. This view has been overturned recently by demonstrating ionic conductivity in the crystalline complexes PEO6:LiXF6 (X = P, As, Sb); however, the conductivities were relatively low. Here we demonstrate an increase of 1.5 orders of magnitude in the conductivity of these materials by replacing a small proportion of the XF6- anions in the crystal structure with isovalent N(SO2CF3)2- ions. We suggest that the larger and more irregularly shaped anions disrupt the potential around the Li+ ions, thus enhancing the ionic conductivity in a manner somewhat analogous to the AgBr(1-x)I(x) ionic conductors. The demonstration that doping strategies can enhance the conductivity of crystalline polymer electrolytes represents a significant advance towards the technological exploitation of such materials. 相似文献
82.
Nanoscale hydrodynamics: enhanced flow in carbon nanotubes 总被引:3,自引:0,他引:3
Nanoscale structures that could mimic the selective transport and extraordinarily fast flow possible in biological cellular channels would have a wide range of potential applications. Here we show that liquid flow through a membrane composed of an array of aligned carbon nanotubes is four to five orders of magnitude faster than would be predicted from conventional fluid-flow theory. This high fluid velocity results from an almost frictionless interface at the carbon-nanotube wall. 相似文献
83.
Reich D Patterson N De Jager PL McDonald GJ Waliszewska A Tandon A Lincoln RR DeLoa C Fruhan SA Cabre P Bera O Semana G Kelly MA Francis DA Ardlie K Khan O Cree BA Hauser SL Oksenberg JR Hafler DA 《Nature genetics》2005,37(10):1113-1118
Multiple sclerosis is a common disease with proven heritability, but, despite large-scale attempts, no underlying risk genes have been identified. Traditional linkage scans have so far identified only one risk haplotype for multiple sclerosis (at HLA on chromosome 6), which explains only a fraction of the increased risk to siblings. Association scans such as admixture mapping have much more power, in principle, to find the weak factors that must explain most of the disease risk. We describe here the first high-powered admixture scan, focusing on 605 African American cases and 1,043 African American controls, and report a locus on chromosome 1 that is significantly associated with multiple sclerosis. 相似文献
84.
The structure of a protein depends critically on the complex interactions among its amino acid residues. It has long been hypothesized that interacting residues might tend to coevolve, but it is not known whether such coevolution is a general phenomenon across the proteome. Here, we describe a novel methodology called phylogeny-aided structural analysis, which uncovers robust signals of interacting-residue coevolution in mammalian proteomes. Furthermore, this new method allows the magnitude of coevolution to be quantified. Finally, it facilitates a comprehensive evaluation of various factors that affect interacting-residue coevolution, such as the physicochemical properties of the interactions between residues, solvent accessibility of the residues and their secondary structure context. 相似文献
85.
Zusammenfassung Untersuchungen an Laboratoriums-FledermäusenMyotis lucifugus während aller Phasen der Winterschlaflethargie zeigen, dass Unbeweglichkeit der Tiere entscheidend auf den Verlust an Knochenmineralien wirkt. Die Vermehrung an Osteoklasten sowie die Hyperkalzemie und die Hypophosphatemie bei winterschlafenden Fledermäusen weisen ebenfalls in Richtung der Resorptionsvorgänge im Knochen. 相似文献
86.
87.
Amino-acid composition of soluble and membranous lipoproteins 总被引:3,自引:0,他引:3
88.
89.
Minocycline inhibits cytochrome c release and delays progression of amyotrophic lateral sclerosis in mice 总被引:56,自引:0,他引:56
Zhu S Stavrovskaya IG Drozda M Kim BY Ona V Li M Sarang S Liu AS Hartley DM Wu DC Gullans S Ferrante RJ Przedborski S Kristal BS Friedlander RM 《Nature》2002,417(6884):74-78
Minocycline mediates neuroprotection in experimental models of neurodegeneration. It inhibits the activity of caspase-1, caspase-3, inducible form of nitric oxide synthetase (iNOS) and p38 mitogen-activated protein kinase (MAPK). Although minocycline does not directly inhibit these enzymes, the effects may result from interference with upstream mechanisms resulting in their secondary activation. Because the above-mentioned factors are important in amyotrophic lateral sclerosis (ALS), we tested minocycline in mice with ALS. Here we report that minocycline delays disease onset and extends survival in ALS mice. Given the broad efficacy of minocycline, understanding its mechanisms of action is of great importance. We find that minocycline inhibits mitochondrial permeability-transition-mediated cytochrome c release. Minocycline-mediated inhibition of cytochrome c release is demonstrated in vivo, in cells, and in isolated mitochondria. Understanding the mechanism of action of minocycline will assist in the development and testing of more powerful and effective analogues. Because of the safety record of minocycline, and its ability to penetrate the blood-brain barrier, this drug may be a novel therapy for ALS. 相似文献
90.
IFNgamma and lymphocytes prevent primary tumour development and shape tumour immunogenicity 总被引:51,自引:0,他引:51
Shankaran V Ikeda H Bruce AT White JM Swanson PE Old LJ Schreiber RD 《Nature》2001,410(6832):1107-1111
Lymphocytes were originally thought to form the basis of a 'cancer immunosurveillance' process that protects immunocompetent hosts against primary tumour development, but this idea was largely abandoned when no differences in primary tumour development were found between athymic nude mice and syngeneic wild-type mice. However, subsequent observations that nude mice do not completely lack functional T cells and that two components of the immune system-IFNgamma and perforin-help to prevent tumour formation in mice have led to renewed interest in a tumour-suppressor role for the immune response. Here we show that lymphocytes and IFNgamma collaborate to protect against development of carcinogen-induced sarcomas and spontaneous epithelial carcinomas and also to select for tumour cells with reduced immunogenicity. The immune response thus functions as an effective extrinsic tumour-suppressor system. However, this process also leads to the immunoselection of tumour cells that are more capable of surviving in an immunocompetent host, which explains the apparent paradox of tumour formation in immunologically intact individuals. 相似文献