全文获取类型
收费全文 | 989篇 |
免费 | 4篇 |
国内免费 | 1篇 |
专业分类
系统科学 | 6篇 |
理论与方法论 | 12篇 |
现状及发展 | 535篇 |
研究方法 | 97篇 |
综合类 | 342篇 |
自然研究 | 2篇 |
出版年
2018年 | 13篇 |
2017年 | 13篇 |
2016年 | 9篇 |
2014年 | 12篇 |
2013年 | 12篇 |
2012年 | 46篇 |
2011年 | 47篇 |
2010年 | 23篇 |
2009年 | 12篇 |
2008年 | 50篇 |
2007年 | 47篇 |
2006年 | 45篇 |
2005年 | 39篇 |
2004年 | 28篇 |
2003年 | 31篇 |
2002年 | 40篇 |
2001年 | 28篇 |
2000年 | 26篇 |
1999年 | 11篇 |
1994年 | 10篇 |
1990年 | 7篇 |
1989年 | 10篇 |
1988年 | 9篇 |
1987年 | 8篇 |
1986年 | 10篇 |
1985年 | 13篇 |
1984年 | 11篇 |
1980年 | 10篇 |
1979年 | 18篇 |
1978年 | 12篇 |
1977年 | 13篇 |
1976年 | 14篇 |
1975年 | 13篇 |
1974年 | 12篇 |
1973年 | 23篇 |
1972年 | 10篇 |
1971年 | 21篇 |
1970年 | 16篇 |
1969年 | 19篇 |
1968年 | 9篇 |
1967年 | 16篇 |
1966年 | 23篇 |
1965年 | 10篇 |
1962年 | 8篇 |
1961年 | 7篇 |
1960年 | 8篇 |
1957年 | 8篇 |
1956年 | 7篇 |
1955年 | 11篇 |
1946年 | 7篇 |
排序方式: 共有994条查询结果,搜索用时 46 毫秒
81.
82.
Ceci M Gaviraghi C Gorrini C Sala LA Offenhäuser N Marchisio PC Biffo S 《Nature》2003,426(6966):579-584
The assembly of 80S ribosomes requires joining of the 40S and 60S subunits, which is triggered by the formation of an initiation complex on the 40S subunit. This event is rate-limiting for translation, and depends on external stimuli and the status of the cell. Here we show that 60S subunits are activated by release of eIF6 (also termed p27BBP). In the cytoplasm, eIF6 is bound to free 60S but not to 80S. Furthermore, eIF6 interacts in the cytoplasm with RACK1, a receptor for activated protein kinase C (PKC). RACK1 is a major component of translating ribosomes, which harbour significant amounts of PKC. Loading 60S subunits with eIF6 caused a dose-dependent translational block and impairment of 80S formation, which were reversed by expression of RACK1 and stimulation of PKC in vivo and in vitro. PKC stimulation led to eIF6 phosphorylation, and mutation of a serine residue in the carboxy terminus of eIF6 impaired RACK1/PKC-mediated translational rescue. We propose that eIF6 release regulates subunit joining, and that RACK1 provides a physical and functional link between PKC signalling and ribosome activation. 相似文献
83.
Pellegata NS Dieguez-Lucena JL Joensuu T Lau S Montgomery KT Krahe R Kivelä T Kucherlapati R Forsius H de la Chapelle A 《Nature genetics》2000,25(1):91-95
Specialized collagens and small leucine-rich proteoglycans (SLRPs) interact to produce the transparent corneal structure. In cornea plana, the forward convex curvature is flattened, leading to a decrease in refraction. A more severe, recessively inherited form (CNA2; MIM 217300) and a milder, dominantly inherited form (CNA1; MIM 121400) exist. CNA2 is a rare disorder with a worldwide distribution, but a high prevalence in the Finnish population. The gene mutated in CNA2 was assigned by linkage analysis to 12q (refs 4, 5), where there is a cluster of several SLRP genes. We cloned two additional SLRP genes highly expressed in cornea: KERA (encoding keratocan) in 12q and OGN (encoding osteoglycin) in 9q. Here we report mutations in KERA in 47 CNA2 patients: 46 Finnish patients are homozygous for a founder missense mutation, leading to the substitution of a highly conserved amino acid; and one American patient is homozygous for a mutation leading to a premature stop codon that truncates the KERA protein. Our data establish that mutations in KERA cause CNA2. CNA1 patients had no mutations in these proteoglycan genes. 相似文献
84.
85.
Progress in the field of superconductivity is often linked to the discovery of new classes of materials, with the layered copper oxides being a particularly impressive example. The superconductors known today include a wide spectrum of materials, ranging in complexity from simple elemental metals, to alloys and binary compounds of metals, to multi-component compounds of metals and chalcogens or metalloids, doped fullerenes and organic charge-transfer salts. Here we present a new class of superconductors: insulating organic molecular crystals that are made metallic through charge injection. The first examples are pentacene, tetracene and anthracene, the last having the highest transition temperature, at 4 K. We anticipate that many other organic molecular crystals can also be made superconducting by this method, which will lead to surprising findings in the vast composition space of molecular crystals. 相似文献
86.
Hobmayer B Rentzsch F Kuhn K Happel CM von Laue CC Snyder P Rothbächer U Holstein TW 《Nature》2000,407(6801):186-189
87.
Superconductivity at 52 K in hole-doped C60 总被引:4,自引:0,他引:4
Superconductivity in electron-doped C60 was first observed almost ten years ago. The metallic state and superconductivity result from the transfer of electrons from alkaline or alkaline-earth ions to the C60 molecule, which is known to be a strong electron acceptor. For this reason, it is very difficult to remove electrons from C60--yet one might expect to see superconductivity at higher temperatures in hole-doped than in electron-doped C60, because of the higher density of electronic states in the valence band than in the conduction band. We have used the technique of gate-induced doping in a field-effect transistor configuration to introduce significant densities of holes into C60. We observe superconductivity over an extended range of hole density, with a smoothly varying transition temperature Tc that peaks at 52 K. By comparison with the well established dependence of Tc on the lattice parameter in electron-doped C60, we anticipate that Tc values significantly in excess of 100 K should be achievable in a suitably expanded, hole-doped C60 lattice. 相似文献
88.
The most striking feature of the Sun's magnetic field is its cyclic behaviour. The number of sunspots, which are dark regions of strong magnetic field on the Sun's surface, varies with a period of about 11 years. Superposed on this cycle are secular changes that occur on timescales of centuries and events like the Maunder minimum in the second half of the seventeenth century, when there were very few sunspots. A part of the Sun's magnetic field reaches out from the surface into interplanetary space, and it was recently discovered that the average strength of this interplanetary field has doubled in the past 100 years. There has hitherto been no clear explanation for this doubling. Here we present a model describing the long-term evolution of the Sun's large-scale magnetic field, which reproduces the doubling of the interplanetary field. The model indicates that there is a direct connection between the length of the sunspot cycle and the secular variations. 相似文献
89.
Ernst Gäumann 《Cellular and molecular life sciences : CMLS》1945,1(5):153-157
Summary For the initiation of an epidemic with a tendency to become wide-spread, various conditions must be fulfilled in the vegetable kingdom. Factors which can lead to such an epidemic are the same as in epidemic diseases in humans and concern the host, causative agents and environmental factors. 相似文献
90.