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排序方式: 共有306条查询结果,搜索用时 15 毫秒
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Nano-Structured Carbide-Derived Carbon Films and Their Tribology 总被引:3,自引:0,他引:3
Michael McNallan Daniel Ersoy Ranyi Zhu Allen Lee Christopher White Sascha Welz Yury Gogotsi Ali Erdemir Andriy Kovalchenko 《清华大学学报》2005,10(6):699-703
Carbide-derived carbon (CDC) is a form of carbon produced by reacting metal carbides, such as SiC or TiC, with halogens at temperatures high enough to produce fast kinetics, but too low to permit the rearrangement of the carbon atoms into an equilibrium graphitic structure. The structure of CDC is derivative of the original carbide structure and contains nanoscale porosity and both sp2 and sp3 bonded carbon in a variety of nanoscale structures. CDC can be produced as a thin film on hard carbides to improve their tribological performance. CDC coatings are distinguished by their low friction coefficients and high wear resistance in many important industrial environments and by their resistance to spallation and delamination. The tribology of CDC coatings on SiC surfaces is described in detail. 相似文献
46.
Springel V White SD Frenk CS Navarro JF Jenkins A Vogelsberger M Wang J Ludlow A Helmi A 《Nature》2008,456(7218):73-76
Dark matter is the dominant form of matter in the Universe, but its nature is unknown. It is plausibly an elementary particle, perhaps the lightest supersymmetric partner of known particle species. In this case, annihilation of dark matter in the halo of the Milky Way should produce gamma-rays at a level that may soon be observable. Previous work has argued that the annihilation signal will be dominated by emission from very small clumps (perhaps smaller even than the Earth), which would be most easily detected where they cluster together in the dark matter haloes of dwarf satellite galaxies. Here we report that such small-scale structure will, in fact, have a negligible impact on dark matter detectability. Rather, the dominant and probably most easily detectable signal will be produced by diffuse dark matter in the main halo of the Milky Way. If the main halo is strongly detected, then small dark matter clumps should also be visible, but may well contain no stars, thereby confirming a key prediction of the cold dark matter model. 相似文献
47.
Mullighan CG Miller CB Radtke I Phillips LA Dalton J Ma J White D Hughes TP Le Beau MM Pui CH Relling MV Shurtleff SA Downing JR 《Nature》2008,453(7191):110-114
48.
Domingues CM Church JA White NJ Gleckler PJ Wijffels SE Barker PM Dunn JR 《Nature》2008,453(7198):1090-1093
Changes in the climate system's energy budget are predominantly revealed in ocean temperatures and the associated thermal expansion contribution to sea-level rise. Climate models, however, do not reproduce the large decadal variability in globally averaged ocean heat content inferred from the sparse observational database, even when volcanic and other variable climate forcings are included. The sum of the observed contributions has also not adequately explained the overall multi-decadal rise. Here we report improved estimates of near-global ocean heat content and thermal expansion for the upper 300 m and 700 m of the ocean for 1950-2003, using statistical techniques that allow for sparse data coverage and applying recent corrections to reduce systematic biases in the most common ocean temperature observations. Our ocean warming and thermal expansion trends for 1961-2003 are about 50 per cent larger than earlier estimates but about 40 per cent smaller for 1993-2003, which is consistent with the recognition that previously estimated rates for the 1990s had a positive bias as a result of instrumental errors. On average, the decadal variability of the climate models with volcanic forcing now agrees approximately with the observations, but the modelled multi-decadal trends are smaller than observed. We add our observational estimate of upper-ocean thermal expansion to other contributions to sea-level rise and find that the sum of contributions from 1961 to 2003 is about 1.5 +/- 0.4 mm yr(-1), in good agreement with our updated estimate of near-global mean sea-level rise (using techniques established in earlier studies) of 1.6 +/- 0.2 mm yr(-1). 相似文献
49.
Big data: The future of biocuration 总被引:2,自引:0,他引:2
Howe D Costanzo M Fey P Gojobori T Hannick L Hide W Hill DP Kania R Schaeffer M St Pierre S Twigger S White O Rhee SY 《Nature》2008,455(7209):47-50
50.
Complete genome sequence of a multiple drug resistant Salmonella enterica serovar Typhi CT18. 总被引:33,自引:0,他引:33
J Parkhill G Dougan K D James N R Thomson D Pickard J Wain C Churcher K L Mungall S D Bentley M T Holden M Sebaihia S Baker D Basham K Brooks T Chillingworth P Connerton A Cronin P Davis R M Davies L Dowd N White J Farrar T Feltwell N Hamlin A Haque T T Hien S Holroyd K Jagels A Krogh T S Larsen S Leather S Moule P O'Gaora C Parry M Quail K Rutherford M Simmonds J Skelton K Stevens S Whitehead B G Barrell 《Nature》2001,413(6858):848-852
Salmonella enterica serovar Typhi (S. typhi) is the aetiological agent of typhoid fever, a serious invasive bacterial disease of humans with an annual global burden of approximately 16 million cases, leading to 600,000 fatalities. Many S. enterica serovars actively invade the mucosal surface of the intestine but are normally contained in healthy individuals by the local immune defence mechanisms. However, S. typhi has evolved the ability to spread to the deeper tissues of humans, including liver, spleen and bone marrow. Here we have sequenced the 4,809,037-base pair (bp) genome of a S. typhi (CT18) that is resistant to multiple drugs, revealing the presence of hundreds of insertions and deletions compared with the Escherichia coli genome, ranging in size from single genes to large islands. Notably, the genome sequence identifies over two hundred pseudogenes, several corresponding to genes that are known to contribute to virulence in Salmonella typhimurium. This genetic degradation may contribute to the human-restricted host range for S. typhi. CT18 harbours a 218,150-bp multiple-drug-resistance incH1 plasmid (pHCM1), and a 106,516-bp cryptic plasmid (pHCM2), which shows recent common ancestry with a virulence plasmid of Yersinia pestis. 相似文献