全文获取类型
收费全文 | 1000篇 |
免费 | 2篇 |
国内免费 | 6篇 |
专业分类
系统科学 | 6篇 |
丛书文集 | 1篇 |
教育与普及 | 3篇 |
理论与方法论 | 32篇 |
现状及发展 | 365篇 |
研究方法 | 121篇 |
综合类 | 457篇 |
自然研究 | 23篇 |
出版年
2018年 | 8篇 |
2017年 | 11篇 |
2016年 | 11篇 |
2015年 | 5篇 |
2014年 | 9篇 |
2013年 | 9篇 |
2012年 | 56篇 |
2011年 | 66篇 |
2010年 | 20篇 |
2009年 | 7篇 |
2008年 | 30篇 |
2007年 | 35篇 |
2006年 | 48篇 |
2005年 | 27篇 |
2004年 | 45篇 |
2003年 | 40篇 |
2002年 | 25篇 |
2001年 | 32篇 |
2000年 | 30篇 |
1999年 | 34篇 |
1996年 | 5篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1990年 | 8篇 |
1989年 | 11篇 |
1988年 | 18篇 |
1987年 | 12篇 |
1986年 | 14篇 |
1985年 | 21篇 |
1984年 | 15篇 |
1983年 | 13篇 |
1982年 | 11篇 |
1981年 | 6篇 |
1980年 | 16篇 |
1979年 | 21篇 |
1978年 | 16篇 |
1977年 | 17篇 |
1976年 | 8篇 |
1975年 | 16篇 |
1974年 | 24篇 |
1973年 | 16篇 |
1972年 | 21篇 |
1971年 | 12篇 |
1970年 | 17篇 |
1969年 | 15篇 |
1968年 | 24篇 |
1967年 | 14篇 |
1966年 | 13篇 |
1965年 | 14篇 |
1964年 | 7篇 |
排序方式: 共有1008条查询结果,搜索用时 93 毫秒
71.
72.
73.
74.
75.
76.
A radiation hybrid map of mouse genes 总被引:13,自引:0,他引:13
Hudson TJ Church DM Greenaway S Nguyen H Cook A Steen RG Van Etten WJ Castle AB Strivens MA Trickett P Heuston C Davison C Southwell A Hardisty R Varela-Carver A Haynes AR Rodriguez-Tome P Doi H Ko MS Pontius J Schriml L Wagner L Maglott D Brown SD Lander ES Schuler G Denny P 《Nature genetics》2001,29(2):201-205
A comprehensive gene-based map of a genome is a powerful tool for genetic studies and is especially useful for the positional cloning and positional candidate approaches. The availability of gene maps for multiple organisms provides the foundation for detailed conserved-orthology maps showing the correspondence between conserved genomic segments. These maps make it possible to use cross-species information in gene hunts and shed light on the evolutionary forces that shape the genome. Here we report a radiation hybrid map of mouse genes, a combined project of the Whitehead Institute/Massachusetts Institute of Technology Center for Genome Research, the Medical Research Council UK Mouse Genome Centre, and the National Center for Biotechnology Information. The map contains 11,109 genes, screened against the T31 RH panel and positioned relative to a reference map containing 2,280 mouse genetic markers. It includes 3,658 genes homologous to the human genome sequence and provides a framework for overlaying the human genome sequence to the mouse and for sequencing the mouse genome. 相似文献
77.
'Inverse' melting of a vortex lattice 总被引:1,自引:0,他引:1
Avraham N Khaykovich B Myasoedov Y Rappaport M Shtrikman H Feldman DE Tamegai T Kes PH Li M Konczykowski M van der Beek K Zeldov E 《Nature》2001,411(6836):451-454
Inverse melting is the process in which a crystal reversibly transforms into a liquid or amorphous phase when its temperature is decreased. Such a process is considered to be very rare, and the search for it is often hampered by the formation of non-equilibrium states or intermediate phases. Here we report the discovery of first-order inverse melting of the lattice formed by magnetic flux lines in a high-temperature superconductor. At low temperatures, disorder in the material pins the vortices, preventing the observation of their equilibrium properties and therefore the determination of whether a phase transition occurs. But by using a technique to 'dither' the vortices, we were able to equilibrate the lattice, which enabled us to obtain direct thermodynamic evidence of inverse melting of the ordered lattice into a disordered vortex phase as the temperature is decreased. The ordered lattice has larger entropy than the low-temperature disordered phase. The mechanism of the first-order phase transition changes gradually from thermally induced melting at high temperatures to a disorder-induced transition at low temperatures. 相似文献
78.
Vanhove M Zakhem M Devreese B Franceschini N Anne C Bebrone C Amicosante G Rossolini GM Van Beeumen J Frère JM Galleni M 《Cellular and molecular life sciences : CMLS》2003,60(11):2501-2509
The CphA metallo--lactamase produced by Aeromonas hydrophila exhibits two zinc-binding sites. Maximum activity is obtained upon binding of one zinc ion, whereas binding of the second zinc ion results in a drastic decrease in the hydrolytic activity. In this study, we analyzed the role of Asn116 and Cys221, two residues of the active site. These residues were replaced by site-directed mutagenesis and the different mutants were characterized. The C221S and C221A mutants were seriously impaired in their ability to bind the first, catalytic zinc ion and were nearly completely inactive, indicating a major role for Cys221 in the binding of the catalytic metal ion. By contrast, the binding of the second zinc ion was only slightly affected, at least for the C221S mutant. Mutation of Asn116 did not lead to a drastic decrease in the hydrolytic activity, indicating that this residue does not play a key role in the catalytic mechanism. However, the substitution of Asn116 by a Cys or His residue resulted in an approximately fivefold increase in the affinity for the second, inhibitory zinc ion. Together, these data suggested that the first zinc ion is located in the binding site involving the Cys221 and that the second zinc ion binds in the binding site involving Asn116 and, presumably, His118 and His196.Received 3 March 2003; received after revision 4 August 2003; accepted 25 August 2003 相似文献
79.
van der Marel D Molegraaf HJ Zaanen J Nussinov Z Carbone F Damascelli A Eisaki H Greven M Kes PH Li M 《Nature》2003,425(6955):271-274
Quantum criticality is associated with a system composed of a nearly infinite number of interacting quantum degrees of freedom at zero temperature, and it implies that the system looks on average the same regardless of the time- and length scale on which it is observed. Electrons on the atomic scale do not exhibit such symmetry, which can only be generated as a collective phenomenon through the interactions between a large number of electrons. In materials with strong electron correlations a quantum phase transition at zero temperature can occur, and a quantum critical state has been predicted, which manifests itself through universal power-law behaviours of the response functions. Candidates have been found both in heavy-fermion systems and in the high-transition temperature (high-T(c)) copper oxide superconductors, but the reality and the physical nature of such a phase transition are still debated. Here we report a universal behaviour that is characteristic of the quantum critical region. We demonstrate that the experimentally measured phase angle agrees precisely with the exponent of the optical conductivity. This points towards a quantum phase transition of an unconventional kind in the high-T(c) superconductors. 相似文献
80.
Hurlstone AF Haramis AP Wienholds E Begthel H Korving J Van Eeden F Cuppen E Zivkovic D Plasterk RH Clevers H 《Nature》2003,425(6958):633-637
Truncation of the tumour suppressor adenomatous polyposis coli (Apc) constitutively activates the Wnt/beta-catenin signalling pathway. Apc has a role in development: for example, embryos of mice with truncated Apc do not complete gastrulation. To understand this role more fully, we examined the effect of truncated Apc on zebrafish development. Here we show that, in contrast to mice, zebrafish do complete gastrulation. However, mutant hearts fail to loop and form excessive endocardial cushions. Conversely, overexpression of Apc or Dickkopf 1 (Dkk1), a secreted Wnt inhibitor, blocks cushion formation. In wild-type hearts, nuclear beta-catenin, the hallmark of activated canonical Wnt signalling, accumulates only in valve-forming cells, where it can activate a Tcf reporter. In mutant hearts, all cells display nuclear beta-catenin and Tcf reporter activity, while valve markers are markedly upregulated. Concomitantly, proliferation and epithelial-mesenchymal transition, normally restricted to endocardial cushions, occur throughout the endocardium. Our findings identify a novel role for Wnt/beta-catenin signalling in determining endocardial cell fate. 相似文献