全文获取类型
收费全文 | 72104篇 |
免费 | 6409篇 |
国内免费 | 4324篇 |
专业分类
化学 | 38674篇 |
晶体学 | 348篇 |
力学 | 4746篇 |
综合类 | 1045篇 |
数学 | 19020篇 |
物理学 | 19004篇 |
出版年
2024年 | 110篇 |
2023年 | 692篇 |
2022年 | 1227篇 |
2021年 | 2197篇 |
2020年 | 1818篇 |
2019年 | 1824篇 |
2018年 | 1541篇 |
2017年 | 1956篇 |
2016年 | 2279篇 |
2015年 | 2220篇 |
2014年 | 2669篇 |
2013年 | 4514篇 |
2012年 | 3368篇 |
2011年 | 3580篇 |
2010年 | 3257篇 |
2009年 | 4380篇 |
2008年 | 4529篇 |
2007年 | 4666篇 |
2006年 | 3795篇 |
2005年 | 2812篇 |
2004年 | 2534篇 |
2003年 | 2570篇 |
2002年 | 4855篇 |
2001年 | 2241篇 |
2000年 | 1725篇 |
1999年 | 1492篇 |
1998年 | 1416篇 |
1997年 | 1068篇 |
1996年 | 1107篇 |
1995年 | 952篇 |
1994年 | 890篇 |
1993年 | 820篇 |
1992年 | 777篇 |
1991年 | 612篇 |
1990年 | 484篇 |
1989年 | 414篇 |
1988年 | 382篇 |
1987年 | 324篇 |
1986年 | 321篇 |
1985年 | 444篇 |
1984年 | 322篇 |
1983年 | 203篇 |
1982年 | 380篇 |
1981年 | 528篇 |
1980年 | 496篇 |
1979年 | 538篇 |
1978年 | 421篇 |
1977年 | 330篇 |
1976年 | 291篇 |
1973年 | 162篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
In this paper we give a realization of some symmetric space G/K as a closed submanifold P of G. We also give several equivalent representations of the submanifold P. Some properties of the set gK∩P are also discussed, where gK is a coset space in G. 相似文献
62.
P.A. Ramachandran 《Numerical Methods for Partial Differential Equations》2006,22(4):831-846
Time‐dependent differential equations can be solved using the concept of method of lines (MOL) together with the boundary element (BE) representation for the spatial linear part of the equation. The BE method alleviates the need for spatial discretization and casts the problem in an integral format. Hence errors associated with the numerical approximation of the spatial derivatives are totally eliminated. An element level local cubic approximation is used for the variable at each time step to facilitate the time marching and the nonlinear terms are represented in a semi‐implicit manner by a local linearization at each time step. The accuracy of the method has been illustrated on a number of test problems of engineering significance. © 2005 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 2006 相似文献
63.
超尺寸物品装箱问题及其算法 总被引:3,自引:0,他引:3
本文探讨一类新装箱问题-超尺寸物品装箱问题。针对实际解决该问题的两涉法,我们提出了一个评价效率更高的目标函数,证明了在此目标函数下两步法的渐近最坏比不小于2,并给出了渐近量坏比与拆分次数的关系。最后本文提出了一种不同于两步法的新在线算法MA,证明了在新目标函数下其渐近最坏比不超过7/4。 相似文献
64.
Necessary conditions for the Gâteaux differentiability of the distance function to a set are considered. A series of characterizing results is obtained. 相似文献
65.
Mathematical Notes - 相似文献
66.
A. B. Mazo 《Fluid Dynamics》2002,37(6):913-918
Plane ideal incompressible flow in a rectangular channel partitioned by a thin permeable barrier (lattice) is considered. In flowing through the lattice the stream suddenly (jumpwise) changes direction and loses energy. The flow is assumed to be vortical; the vorticity is discontinuous on the lattice. A mathematical formulation of the problem for the stream function is proposed in the form of a nonlinear elliptic equation with coefficients discontinuous on the lattice line. A numerical solution is constructed using the finite-element iteration method. The results of the numerical simulation show how the flow velocity profile in the channel can be controlled by means of permeable barriers. 相似文献
67.
一类机器人系统的最优控制 总被引:1,自引:1,他引:0
王辉 《数学的实践与认识》2002,32(3):455-459
本文通过把结构阻尼系数当作控制变量来讨论一类弹性机器人系统的最优控制问题 ,并利用Banach空间几何性质证明了最优控制元的存在唯一性 相似文献
68.
We consider a resource management problem in which the management objective is to minimize fluctuations in resource stocks. Stabilizing management policies constitute the designing of memoryless state feedback control strategies for a discrete time resource model which contains unknown but bounded fluctuations. We also show that the problem of maximizing sustainable yield in an uncertain fishery can be considered as the problem of stabilizing of the stock level.The paper corresponds to an invited talk at the 14th Symposium on Operations Research, Ulm, September 6–8, 1989.The support by Yrjö Jahnsson Foundation is gratefully acknowledged.This work was supported by NSF and AFOSR under grant ECS 8602524. 相似文献
69.
Summary In 1980 Dahmen-DeVore-Scherer introduced a modulus of continuity which turns out to reflect invariance properties of compound cubature rules effectively. Accordingly, sharp error bounds are derived, the existence of relevant counterexamples being a consequence of a quantitative resonance principle, established previously. 相似文献
70.
Boban Marinković 《Mathematical Methods of Operations Research》2006,63(3):513-524
We present local sensitivity analysis for discrete optimal control problems with varying endpoints in the case when the customary regularity of boundary conditions can be violated. We study the behavior of the optimal solutions subject to parametric perturbations of the problem. 相似文献