全文获取类型
收费全文 | 527333篇 |
免费 | 6684篇 |
国内免费 | 1622篇 |
专业分类
化学 | 285343篇 |
晶体学 | 8008篇 |
力学 | 22663篇 |
综合类 | 18篇 |
数学 | 60595篇 |
物理学 | 159012篇 |
出版年
2021年 | 4092篇 |
2020年 | 4645篇 |
2019年 | 4960篇 |
2018年 | 6288篇 |
2017年 | 6171篇 |
2016年 | 9743篇 |
2015年 | 6263篇 |
2014年 | 9476篇 |
2013年 | 23834篇 |
2012年 | 18026篇 |
2011年 | 22293篇 |
2010年 | 15445篇 |
2009年 | 15076篇 |
2008年 | 20304篇 |
2007年 | 20319篇 |
2006年 | 19015篇 |
2005年 | 17233篇 |
2004年 | 15930篇 |
2003年 | 14066篇 |
2002年 | 13886篇 |
2001年 | 15681篇 |
2000年 | 11832篇 |
1999年 | 9437篇 |
1998年 | 7876篇 |
1997年 | 7629篇 |
1996年 | 7417篇 |
1995年 | 6722篇 |
1994年 | 6472篇 |
1993年 | 6306篇 |
1992年 | 7105篇 |
1991年 | 7162篇 |
1990年 | 6840篇 |
1989年 | 6742篇 |
1988年 | 6708篇 |
1987年 | 6619篇 |
1986年 | 6282篇 |
1985年 | 8201篇 |
1984年 | 8411篇 |
1983年 | 6769篇 |
1982年 | 7092篇 |
1981年 | 6937篇 |
1980年 | 6592篇 |
1979年 | 6992篇 |
1978年 | 7263篇 |
1977年 | 7069篇 |
1976年 | 7016篇 |
1975年 | 6552篇 |
1974年 | 6436篇 |
1973年 | 6602篇 |
1972年 | 4546篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
961.
962.
In 1983, a preconditioner was proposed [J. Comput. Phys. 49 (1983) 443] based on the Laplace operator for solving the discrete Helmholtz equation efficiently with CGNR. The preconditioner is especially effective for low wavenumber cases where the linear system is slightly indefinite. Laird [Preconditioned iterative solution of the 2D Helmholtz equation, First Year's Report, St. Hugh's College, Oxford, 2001] proposed a preconditioner where an extra term is added to the Laplace operator. This term is similar to the zeroth order term in the Helmholtz equation but with reversed sign. In this paper, both approaches are further generalized to a new class of preconditioners, the so-called “shifted Laplace” preconditioners of the form Δφ−k2φ with
. Numerical experiments for various wavenumbers indicate the effectiveness of the preconditioner. The preconditioner is evaluated in combination with GMRES, Bi-CGSTAB, and CGNR. 相似文献
963.
We analyse a model for equilibrium configurations of composite systems of nematic liquid crystal with polymer inclusions, in the presence of an external magnetic field. We assume that the system has a periodic structure, and consider the relaxed problem on the unit length constraint of the nematic director field. The relaxation of the Oseen–Frank energy functional is carried out by including bulk as well as surface energy penalty terms, rendering the problem fully non‐linear. We employ two‐scale convergence methods to obtain effective configurations of the system, as the size of the polymeric inclusions tends to zero. We discuss the minimizers of the effective energies for, both, the constrained as well as the unconstrained models. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
964.
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
965.
L. E. Payne P. W. Schaefer J. C. Song 《Mathematical Methods in the Applied Sciences》2004,27(17):2045-2053
Energy bounds are derived for Dirichlet type boundary value problems for the Navier–Stokes and Stokes equations when a combination of the solution values initially and at a later time is prescribed. The bounds are obtained by means of a differential inequality and imply uniqueness and continuous data dependence of the solutions for a range of values of the parameter in the non‐standard auxiliary condition. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
966.
967.
Matveeva E. D. Podrugina T. A. Grishin Yu. K. Tkachev V. V. Zhdankin V. V. Aldoshin S. M. Zefirov N. S. 《Russian Journal of Organic Chemistry》2003,39(4):536-541
A mixed phosphonium-iodonium ylide, phenyliodoniumethoxycarbonylmethylenetriphenylphosphorane borofluoride, was synthesized. Its structure was established by means of X-ray diffraction analysis. Temperature dependence of 1H, 13C, and 31P spectra of the ylide synthesized was investigated. A dynamic equilibrium between Z and E-isomers was observed. 相似文献
968.
969.
M. S. Nikol'skii 《Differential Equations》2003,39(11):1603-1608
970.
Stephen M. Robinson 《Mathematical Programming》2003,97(1-2):245-265
This is an expository paper about the analysis of variational conditions over sets defined in finite-dimensional spaces by
fairly smooth functions satisfying a constraint qualification. The primary focus is on results that can provide quantitative
and computable sensitivity information for particular instances of the problems under study, and our objective is to give
a personal view of the state of current knowledge in this area and of gaps in that knowledge that require future work. The
writing style is informal, in keeping with the objective of focusing the reader's attention on the basic concepts and the
relationships between them, rather than on details of the particular results themselves.
Received: December 1, 2002 / Accepted: April 25, 2003
Published online: May 28, 2003
Key words. variational condition – variational inequality – complementarity – sensitivity – stability – nondegeneracy
Mathematics Subject Classification (2000): Primary: 90C31. Secondary: 47J20, 49J40, 49J53, 90C33 相似文献