全文获取类型
收费全文 | 1984篇 |
免费 | 43篇 |
国内免费 | 18篇 |
专业分类
化学 | 1415篇 |
晶体学 | 26篇 |
力学 | 31篇 |
数学 | 273篇 |
物理学 | 300篇 |
出版年
2023年 | 8篇 |
2021年 | 22篇 |
2020年 | 22篇 |
2019年 | 11篇 |
2018年 | 12篇 |
2017年 | 9篇 |
2016年 | 30篇 |
2015年 | 31篇 |
2014年 | 26篇 |
2013年 | 85篇 |
2012年 | 85篇 |
2011年 | 122篇 |
2010年 | 66篇 |
2009年 | 74篇 |
2008年 | 130篇 |
2007年 | 141篇 |
2006年 | 127篇 |
2005年 | 111篇 |
2004年 | 101篇 |
2003年 | 102篇 |
2002年 | 103篇 |
2001年 | 41篇 |
2000年 | 47篇 |
1999年 | 28篇 |
1998年 | 22篇 |
1997年 | 24篇 |
1996年 | 43篇 |
1995年 | 17篇 |
1994年 | 18篇 |
1993年 | 15篇 |
1992年 | 26篇 |
1991年 | 15篇 |
1990年 | 11篇 |
1989年 | 13篇 |
1988年 | 10篇 |
1987年 | 10篇 |
1986年 | 14篇 |
1985年 | 19篇 |
1984年 | 16篇 |
1983年 | 9篇 |
1982年 | 23篇 |
1981年 | 34篇 |
1980年 | 18篇 |
1979年 | 22篇 |
1978年 | 21篇 |
1977年 | 14篇 |
1976年 | 16篇 |
1975年 | 23篇 |
1974年 | 11篇 |
1973年 | 11篇 |
排序方式: 共有2045条查询结果,搜索用时 468 毫秒
1.
2.
3.
4.
I. P. Kuranova K. M. Polyakov E. A. Smirnova W. E. Höhne V. S. Lamzin R. Meijer 《Crystallography Reports》2003,48(6):953-958
Crystals of Saccharomyces cerevisiae inorganic pyrophosphatase suitable for X-ray diffraction study were grown by cocrystallization of the enzyme with cobalt chloride and imidodiphosphate. Saccharomyces cerevisiae is a metal-dependent enzyme which catalyzes hydrolysis of inorganic pyrophosphate to orthophosphate. The three-dimensional structure of this enzyme was solved by the molecular-replacement method and refined at 1.8 Å resolution to an R factor of 19.5%. Cobalt and phosphate ions were revealed in the active centers of both identical subunits (A and B) of the pyrophosphatase molecule. In subunit B, a water molecule was found between two cobalt ions. It is believed that this water molecule acts as an attacking nucleophile in the enzymatic cleavage of the pyrophosphate bond. It was demonstrated that cobalt ions and a phosphate group occupy only part of the potential binding sites (two chemically identical and crystallographically independent subunits have different binding sites). The arrangement of ligands and the structure of the nucleophile-binding site are discussed in relation to the mechanism of action of the enzyme and the nature of the metal activator. 相似文献
5.
6.
Bart M. J. M. Suijkerbuijk Duncan M. Tooke Anthony L. Spek Gerard van Koten Robertus J. M. Klein Gebbink Prof. Dr. 《无机化学与普通化学杂志》2007,633(15):2649-2653
A tin(IV) porphyrin was combined with two axial NCN‐pincer platinum(II) fragments by utilizing the oxophilicity of the apical positions on the tin atom and the acidic nature of the NCN‐pincer platinum derived benzoic acid. The solid‐state structure determined by X‐ray crystallography revealed some close contacts between the pincer complexes and the meso‐p‐tolyl subsitutents of the porphyrin. It was shown by 1H NMR spectroscopy that these close contacts were not present in solution and that this compound can potentially act as a novel building block for supramolecular architectures. 相似文献
7.
T. Peprnicek A. Kalendova J. Simonik J.F. Gerard 《Polymer Degradation and Stability》2006,91(12):3322-3329
The paper concentrates on poly(vinyl chloride) - PVC - from the point of nanocomposite characterisation through thermal degradation of samples, evolution of the changes caused by elevating temperature using TGA, FTIR and Congo Red methods combined with morphological characterisation by XRD and TEM analyses. A novel method of PVC-paste/nanocomposite preparation while processing was used. During preparation, PVC plasticizer was mixed with clay, both natural and organophilic, and the suspension was then compounded with the other components. Two factors were followed: effect of shearing alone, and in combination with temperature. As is presented, the type of nano-filler and its chemical modifier have obvious influence on final properties either thermal or morphological. Presented contribution follows previous part of investigation and brings further information from PVC-paste/nanocomposite field. 相似文献
8.
9.
Robert Andreu Gerard Lligadas Joan Carles Ronda Marina Galià Virginia Cádiz 《Journal of polymer science. Part A, Polymer chemistry》2007,45(21):4965-4973
A new oxazolidine derivative was obtained from phenol, 2‐amino‐2‐methylpropane‐1,3‐diol and paraformaldehyde. The reaction of this novel oxazolidine diol with phenylisocyanate lead to a urethane model compound which can be polymerized thermally by oxazolidine ring opening to give a Mannich bridge structure. Linear segmented polyurethanes were prepared by reaction of different ratios of oxazolidine diol and commercial polyethylenglycol (Mw ~ 400) with 4,4′‐methylenbis (cyclohexylisocyanate) (HMDI, 90% isomers mixture). The polyurethanes were thermally characterized and crosslinked by oxazolidine ring opening to obtain materials which showed improved thermal stability. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4965–4973, 2007 相似文献
10.
We study the structure of the most common type of Riemannian submersions, namely those whose fibers are given by the orbits
of an isometric group action on a Riemannian manifold. Special emphasis is given to the case where the ambient space has nonnegative
curvature.
The first author was supported by research grant MTM2004-04794-MEC. Most of this work was done during a visit of the second
author to Madrid, financed in part by funds of the aforementioned grant. 相似文献