全文获取类型
收费全文 | 485750篇 |
免费 | 14271篇 |
国内免费 | 2613篇 |
专业分类
化学 | 282366篇 |
晶体学 | 6839篇 |
力学 | 19560篇 |
综合类 | 13篇 |
数学 | 55219篇 |
物理学 | 138637篇 |
出版年
2021年 | 4152篇 |
2020年 | 5684篇 |
2019年 | 7187篇 |
2018年 | 7242篇 |
2017年 | 6772篇 |
2016年 | 12519篇 |
2015年 | 9151篇 |
2014年 | 12085篇 |
2013年 | 25027篇 |
2012年 | 19563篇 |
2011年 | 22695篇 |
2010年 | 16810篇 |
2009年 | 16418篇 |
2008年 | 21048篇 |
2007年 | 20290篇 |
2006年 | 18626篇 |
2005年 | 17000篇 |
2004年 | 15545篇 |
2003年 | 13627篇 |
2002年 | 13972篇 |
2001年 | 14960篇 |
2000年 | 11532篇 |
1999年 | 8451篇 |
1998年 | 6768篇 |
1997年 | 6461篇 |
1996年 | 6314篇 |
1995年 | 5617篇 |
1994年 | 5558篇 |
1993年 | 5405篇 |
1992年 | 6016篇 |
1991年 | 6033篇 |
1990年 | 5768篇 |
1989年 | 5561篇 |
1988年 | 5572篇 |
1987年 | 5452篇 |
1986年 | 5164篇 |
1985年 | 6688篇 |
1984年 | 6797篇 |
1983年 | 5386篇 |
1982年 | 5461篇 |
1981年 | 5436篇 |
1980年 | 5017篇 |
1979年 | 5414篇 |
1978年 | 5547篇 |
1977年 | 5441篇 |
1976年 | 5385篇 |
1975年 | 4966篇 |
1974年 | 4927篇 |
1973年 | 4942篇 |
1972年 | 3487篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
951.
Many real problems can be modelled as robust shortest path problems on interval digraphs, where intervals represent uncertainty about real costs and a robust path is not too far from the shortest path for each possible configuration of the arc costs.A branch and bound algorithm for this problem is presented. 相似文献
952.
The essential self-adjointness on a natural domain of the sharp-time Wick powers of the relativistic free field in two space-time dimension is proven. Other results on Wick powers are reviewed and discussed. 相似文献
953.
This work consists of two parts. In Part I, we shall give a systematic study of Lorentz conformal structure from structural viewpoints. We study manifolds with split-complex structure. We apply general results on split-complex structure for the study of Lorentz surfaces.In Part II, we study the conformal realization of Lorentz surfaces in the Minkowski 3-space via conformal minimal immersions. We apply loop group theoretic Weierstrass-type representation of timelike constant mean curvature for timelike minimal surfaces. Classical integral representation formula for timelike minimal surfaces will be recovered from loop group theoretic viewpoint. 相似文献
954.
For any chain Γ the ring NT(Γ,K) of all finitary Γ-matrices ‖a ij ‖ i,jεΓ over an associative ring K with zeros on and above the main diagonal is locally nilpotent and hence radical. If R′=NT(Γ′,K′),R=NT(Γ,K) and either |Γ|<∞ or K is a ring with no zero-divisors, then isomorphisms between rings R and R′, their adjoint groups and associated Lie rings are described. 相似文献
955.
956.
Anna Dbiska‐Nagrska Andrzej Just Zdzisaw Stempie 《Mathematical Methods in the Applied Sciences》2004,27(2):221-230
This paper presents the Galerkin approximation of the optimization problem of a system governed by non‐linear second‐order evolution equation where a non‐linear operator depends on derivative of the state of the system. The control is acting on a non‐linear equation. After giving some results on the existence of optimal control we shall prove the existence of the weak and strong condensation points of a set of solutions of the approximate optimization problems. Each of these points is a solution of the initial optimization problem. Finally we shall give a simple example using the obtained results. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
957.
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
958.
A. Bourgeat O. Gipouloux E. Marui‐Paloka 《Mathematical Methods in the Applied Sciences》2004,27(4):381-403
In this paper, we study the global behaviour of an underground waste disposal in order to have an accurate upscaled model suitable for the computations involved in safety assessment processes. We start from a detailed model describing the transport of pollutant leaking from a high number of units. Using the method of homogenization, going to the limit, we obtain first a macroscopic model where the sources are now appearing globally. Then we compute a first‐order matched asymptotic expansion and we give the error estimates for this approximation. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
959.
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
960.
Mari Grobbelaar‐Van Dalsen 《Mathematical Methods in the Applied Sciences》2004,27(11):1301-1315
This paper is concerned with well‐posedness results for a mathematical model for the transversal vibrations of a two‐dimensional hybrid elastic structure consisting of a rectangular Reissner–Mindlin plate with a Timoshenko beam attached to its free edge. The model incorporates linear dynamic feedback controls along the interface between the plate and the beam. Classical semigroup methods are employed to show the unique solvability of the coupled initial‐boundary‐value problem. We also show that the energy associated with the system exhibits the property of strong stability. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献