全文获取类型
收费全文 | 13571篇 |
免费 | 1053篇 |
国内免费 | 1157篇 |
专业分类
化学 | 383篇 |
晶体学 | 1篇 |
力学 | 1304篇 |
综合类 | 245篇 |
数学 | 11969篇 |
物理学 | 1879篇 |
出版年
2024年 | 19篇 |
2023年 | 137篇 |
2022年 | 157篇 |
2021年 | 170篇 |
2020年 | 314篇 |
2019年 | 309篇 |
2018年 | 294篇 |
2017年 | 374篇 |
2016年 | 333篇 |
2015年 | 298篇 |
2014年 | 619篇 |
2013年 | 1054篇 |
2012年 | 505篇 |
2011年 | 819篇 |
2010年 | 661篇 |
2009年 | 803篇 |
2008年 | 948篇 |
2007年 | 920篇 |
2006年 | 824篇 |
2005年 | 779篇 |
2004年 | 621篇 |
2003年 | 652篇 |
2002年 | 540篇 |
2001年 | 453篇 |
2000年 | 411篇 |
1999年 | 412篇 |
1998年 | 411篇 |
1997年 | 357篇 |
1996年 | 245篇 |
1995年 | 176篇 |
1994年 | 162篇 |
1993年 | 117篇 |
1992年 | 102篇 |
1991年 | 89篇 |
1990年 | 69篇 |
1989年 | 51篇 |
1988年 | 57篇 |
1987年 | 42篇 |
1986年 | 48篇 |
1985年 | 58篇 |
1984年 | 55篇 |
1983年 | 30篇 |
1982年 | 48篇 |
1981年 | 52篇 |
1980年 | 32篇 |
1979年 | 33篇 |
1978年 | 35篇 |
1977年 | 24篇 |
1976年 | 22篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
In this paper we consider a wavelet algorithm for the piecewise constant collocation method applied to the boundary element solution of a first kind integral equation arising in acoustic scattering. The conventional stiffness matrix is transformed into the corresponding matrix with respect to wavelet bases, and it is approximated by a compressed matrix. Finally, the stiffness matrix is multiplied by diagonal preconditioners such that the resulting matrix of the system of linear equations is well conditioned and sparse. Using this matrix, the boundary integral equation can be solved effectively. 相似文献
12.
We examine two criteria for balance of a gain graph, one based on binary cycles and one on circles. The graphs for which each criterion is valid depend on the set of allowed gain groups. The binary cycle test is invalid, except for forests, if any possible gain group has an element of odd order. Assuming all groups are allowed, or all abelian groups, or merely the cyclic group of order 3, we characterize, both constructively and by forbidden minors, the graphs for which the circle test is valid. It turns out that these three classes of groups have the same set of forbidden minors. The exact reason for the importance of the ternary cyclic group is not clear. © 2005 Wiley Periodicals, Inc. J Graph Theory 相似文献
13.
Algebra matrix and similarity classification of operators 总被引:1,自引:0,他引:1
ZHANG Zilong & LI Yucheng Department of Mathematics Hebei Normal University Shijiazhuang China 《中国科学A辑(英文版)》2006,49(3):398-409
In this paper, by the Gelfand representation theory and the Silov idempotents theorem, we first obtain a central decomposition theorem related to a unital semi-simple n-homogeneous Banach algebra, and then give a similarity classification of two strongly irreducible Cowen-Douglas operators using this theorem. 相似文献
14.
Paul Bankston 《Archive for Mathematical Logic》2006,45(1):97-112
The Chang-Łoś-Suszko theorem of first-order model theory characterizes universal-existential classes of models as just those
elementary classes that are closed under unions of chains. This theorem can then be used to equate two model-theoretic closure
conditions for elementary classes; namely unions of chains and existential substructures. In the present paper we prove a
topological analogue and indicate some applications. 相似文献
15.
根据生产任务选择加工设备进行制造资源重组是实现可重构制造系统的关键问题之一,由于设备的选择涉及到多种因素,既有定量指标,又有定性指标,传统的依靠人工经验的方法显得力不从心。本文首先结合实际情况,提出了一套设备选择评价体系,通过对模糊判断矩阵采用最小对数二乘法确定各评价因素的权重系数,针对定性指标和定量指标采用不同的方法确定其性能指标值,通过模糊积分对评判指标进行综合评判,最后进行了实例研究。所提出的方法有效地简化了决策过程,为可重构制造系统设备选择提供了一套行之有效的方法。 相似文献
16.
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
17.
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
18.
We present a new approach to study the convergence of Newton's method in Banach spaces, which relax the conditions appearing in the usual studies. The approach is based on the bound required for the second derivative of the operator involved. An application to a nonlinear integral equation is presented. 相似文献
19.
设函数f(w)为凸区域D内的单叶解析函数,对于2≤n≤8和所有w∈D,本文得到估计式|f(n)(w)/f'(w)|的精确上界.这个结果推广了一些已知的结论. 相似文献
20.
This paper solves the problem of the duration of the total eclipseof a satellite of a body, provided that (a) the body is sphericalin shape and the mass distribution inside the body is sphericallysymmetrical; (b) the satellite is a very small object; (c) thesatellite's orbit around a body is circular and the satellitecan pass through the centre of its shadow; (d) a source of lightis the source of the conical body's shadow (umbra) and it doesnot change its apparent position in the sky; (e) there are noperturbations on the satellite's orbit. The solution presentedrepresents the general discussion of the problem based on utilizationof some parts of the theory of contraction mappings. 相似文献