全文获取类型
收费全文 | 372608篇 |
免费 | 1887篇 |
国内免费 | 646篇 |
专业分类
化学 | 161091篇 |
晶体学 | 5431篇 |
力学 | 23269篇 |
综合类 | 20篇 |
数学 | 63284篇 |
物理学 | 122046篇 |
出版年
2021年 | 3196篇 |
2020年 | 3559篇 |
2019年 | 4380篇 |
2018年 | 11981篇 |
2017年 | 12449篇 |
2016年 | 10885篇 |
2015年 | 4142篇 |
2014年 | 7180篇 |
2013年 | 12474篇 |
2012年 | 13444篇 |
2011年 | 20671篇 |
2010年 | 14951篇 |
2009年 | 15250篇 |
2008年 | 18983篇 |
2007年 | 21385篇 |
2006年 | 10342篇 |
2005年 | 12558篇 |
2004年 | 10413篇 |
2003年 | 10359篇 |
2002年 | 9405篇 |
2001年 | 7998篇 |
2000年 | 6484篇 |
1999年 | 4653篇 |
1998年 | 4413篇 |
1997年 | 4245篇 |
1996年 | 4022篇 |
1995年 | 3508篇 |
1994年 | 3546篇 |
1993年 | 3560篇 |
1992年 | 3573篇 |
1991年 | 3982篇 |
1990年 | 3983篇 |
1989年 | 4014篇 |
1988年 | 3735篇 |
1987年 | 3820篇 |
1986年 | 3515篇 |
1985年 | 4074篇 |
1984年 | 4334篇 |
1983年 | 3707篇 |
1982年 | 3911篇 |
1981年 | 3560篇 |
1980年 | 3335篇 |
1979年 | 3864篇 |
1978年 | 3961篇 |
1977年 | 4033篇 |
1976年 | 4178篇 |
1975年 | 3897篇 |
1974年 | 3769篇 |
1973年 | 3966篇 |
1972年 | 3402篇 |
排序方式: 共有10000条查询结果,搜索用时 828 毫秒
941.
942.
V E Krivonozhko O B Utkin A V Volodin I A Sablin M Patrin 《The Journal of the Operational Research Society》2004,55(10):1049-1058
The aim of the paper is to present and substantiate a technique to visualize DEA modelling results without any loss of mathematical rigour. The proposed family of parametric optimization methods allows one to construct an intersection of the multidimensional frontier with a two-dimensional plane determined by any pair of given directions. This approach reduces the efficiency analysis of production units to the investigation of well-known functions in economics. We also propose constructive methods to calculate marginal rates of substitution, marginal rates of transformation and so on. 相似文献
943.
We construct the polynomial quantization on the space G/H where G=SL(n,R),H=GL(n–1,R). It is a variant of quantization in the spirit of Berezin. In our case covariant and contravariant symbols are polynomials on G/H. We introduce a multiplication of covariant symbols, establish the correspondence principle, study transformations of symbols (the Berezin transform) and of operators. We write a full asymptotic decomposition of the Berezin transform. 相似文献
944.
In this note we show how 1-factors in the middle two layers of the discrete cube can be used to construct 2-factors in the
Odd graph (the Kneser graph of (k − 1)-sets from a (2k − 1)-set). In particular, we use the lexical matchings of Kierstead and Trotter, and the modular matchings of Duffus, Kierstead
and Snevily, to give explicit constructions of two different 2-factorisations of the Odd graph.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
945.
946.
M. A. Efendiev J. Fuhrmann S. V. Zelik 《Mathematical Methods in the Applied Sciences》2004,27(8):907-930
For the Boussinesq approximation of the equations of coupled heat and fluid flow in a porous medium we show that the corresponding system of partial differential equations possesses a global attractor. We give lower and upper bounds of the Hausdorff dimension of the attractor depending on a physical parameter of the system, namely the Rayleigh number of the flow. Numerical experiments confirm the theoretical findings and raise new questions on the structure of the solutions of the system. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
947.
948.
Petro P Onys'ko Olena A SuvalovaYuliya V Rassukana Tetyana I ChudakovaAnatolii D Sinitsa 《Tetrahedron letters》2003,44(9):1855-1857
The reaction of alkyl trifluoro(organylsulfonylimino)propionates with phosphites occurs with NC transfer of the RSO2 group and leads to sulfonyl-substituted trifluoroalanine derivatives. The novel rearrangement is interpreted as cheletropic 1,4-cycloaddition of the phosphite and subsequent 1,2-shift of the sulfonyl group in the intermediate cyclic phosphorane. 相似文献
949.
Dmitri V Sevenard Vyacheslav Ya SosnovskikhAlexander A Kolomeitsev Martin H KönigsmannGerd-Volker Röschenthaler 《Tetrahedron letters》2003,44(41):7623-7627
In a convenient and efficient procedure, the nucleophilic 1,4-trifluoromethylation of several α,β-enones using (trifluoromethyl)trimethylsilane was achieved. The high regioselectivity of the reaction has been reached by blocking the carbonyl moiety of the electrophile with a bulky aluminum-centered Lewis acid. 相似文献
950.
Aldehydes undergo smooth conjugate addition to α,β-unsaturated ketones in the presence of 5-(2-hydroxyethyl)-1,3-thiazolium halides and DBU adsorbed onto the surface of basic alumina under microwave irradiation and solvent-free conditions to afford 1,4-diketones in enhanced yields and reduced reaction times compared to conventional methods. 相似文献