全文获取类型
收费全文 | 24502篇 |
免费 | 2236篇 |
国内免费 | 1402篇 |
专业分类
化学 | 1660篇 |
晶体学 | 29篇 |
力学 | 2866篇 |
综合类 | 255篇 |
数学 | 18634篇 |
物理学 | 4696篇 |
出版年
2024年 | 47篇 |
2023年 | 229篇 |
2022年 | 230篇 |
2021年 | 385篇 |
2020年 | 598篇 |
2019年 | 620篇 |
2018年 | 621篇 |
2017年 | 664篇 |
2016年 | 704篇 |
2015年 | 569篇 |
2014年 | 1042篇 |
2013年 | 2391篇 |
2012年 | 1061篇 |
2011年 | 1346篇 |
2010年 | 1140篇 |
2009年 | 1517篇 |
2008年 | 1532篇 |
2007年 | 1479篇 |
2006年 | 1366篇 |
2005年 | 1137篇 |
2004年 | 1007篇 |
2003年 | 945篇 |
2002年 | 976篇 |
2001年 | 826篇 |
2000年 | 780篇 |
1999年 | 745篇 |
1998年 | 603篇 |
1997年 | 546篇 |
1996年 | 437篇 |
1995年 | 332篇 |
1994年 | 291篇 |
1993年 | 236篇 |
1992年 | 199篇 |
1991年 | 169篇 |
1990年 | 140篇 |
1989年 | 112篇 |
1988年 | 87篇 |
1987年 | 93篇 |
1986年 | 76篇 |
1985年 | 111篇 |
1984年 | 146篇 |
1983年 | 65篇 |
1982年 | 98篇 |
1981年 | 81篇 |
1980年 | 73篇 |
1979年 | 79篇 |
1978年 | 63篇 |
1977年 | 46篇 |
1976年 | 35篇 |
1974年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
This work is concerned with the maximum principle for optimal control problem governed by magnetohydrodynamic equations, which describe the motion of a viscous incompressible conducting fluid in a magnetic field and consist of a subtle coupling of the Navier-Stokes equation of viscous incompressible fluid flow and the Maxwell equation of electromagnetic field. An integral type state constraint is considered. 相似文献
152.
This paper develops a theory for the global solution of nonconvex optimization problems with parameter-embedded linear dynamic systems. A quite general problem formulation is introduced and a solution is shown to exists. A convexity theory for integrals is then developed to construct convex relaxations for utilization in a branch-and-bound framework to calculate a global minimum. Interval analysis is employed to generate bounds on the state variables implied by the bounds on the embedded parameters. These bounds, along with basic integration theory, are used to prove convergence of the branch-and-bound algorithm to the global minimum of the optimization problem. The implementation of the algorithm is then considered and several numerical case studies are examined thoroughly 相似文献
153.
Nguyen Minh Chuong Bui Kien Cuong 《Proceedings of the American Mathematical Society》2004,132(12):3589-3597
A class of Cauchy problems for interesting complicated periodic pseudodifferential equations is considered. By the Galerkin-wavelet method and with weak solutions one can find sufficient conditions to establish convergence estimates of weak Galerkin-wavelet solutions to a Cauchy problem for this class of equations.
154.
On Covariant Phase Space and the Variational Bicomplex 总被引:1,自引:0,他引:1
Enrique G. Reyes 《International Journal of Theoretical Physics》2004,43(5):1267-1286
The notion of a phase space in classical mechanics is well known. The extension of this concept to field theory however, is a challenging endeavor, and over the years numerous proposals for such a generalization have appeared in the literature. In this paper We review a Hamiltonian formulation of Lagrangian field theory based on an extension to infinite dimensions of J.-M. Souriau's symplectic approach to mechanics. Following G. Zuckerman, we state our results in terms of the modern geometric theory of differential equations and the variational bicomplex. As an elementary example, we construct a phase space for the Monge–Ampere equation. 相似文献
155.
156.
In this paper, based on the Lame function and Jacobi elliptic function, the perturbation method is appliedto some nonlinear evolution equations to derive their multi-order solutions. 相似文献
157.
Some previous works show that symmetric fixed- and variable-stepsize linear multistep methods for second-order systems which do not have any parasitic root in their first characteristic polynomial give rise to a slow error growth with time when integrating reversible systems. In this paper, we give a technique to construct variable-stepsize symmetric methods from their fixed-stepsize counterparts, in such a way that the former have the same order as the latter. The order and symmetry of the integrators obtained is proved independently of the order of the underlying fixed-stepsize integrators. As this technique looks for efficiency, we concentrate on explicit linear multistep methods, which just make one function evaluation per step, and we offer some numerical comparisons with other one-step adaptive methods which also show a good long-term behaviour.
158.
L. D. Popov 《Central European Journal of Mathematics》2004,2(1):76-86
For a linear complementarity problem with inconsistent system of constraints a notion of quasi-solution of Tschebyshev type
is introduced. It’s shown that this solution can be obtained automatically by Lemke’s method if the constraint matrix of the
original problem is copositive plus or belongs to the intersection of matrix classes P
0 and Q
0. 相似文献
159.
We initiate the study of a new measure of approximation. This measure compares the performance of an approximation algorithm to the random assignment algorithm. This is a useful measure for optimization problems where the random assignment algorithm is known to give essentially the best possible polynomial time approximation. In this paper, we focus on this measure for the optimization problems Max‐Lin‐2 in which we need to maximize the number of satisfied linear equations in a system of linear equations modulo 2, and Max‐k‐Lin‐2, a special case of the above problem in which each equation has at most k variables. The main techniques we use, in our approximation algorithms and inapproximability results for this measure, are from Fourier analysis and derandomization. © 2004 Wiley Periodicals, Inc. Random Struct. Alg., 2004 相似文献
160.