全文获取类型
收费全文 | 15366篇 |
免费 | 1576篇 |
国内免费 | 1580篇 |
专业分类
化学 | 2151篇 |
晶体学 | 34篇 |
力学 | 854篇 |
综合类 | 255篇 |
数学 | 12261篇 |
物理学 | 2967篇 |
出版年
2024年 | 39篇 |
2023年 | 183篇 |
2022年 | 174篇 |
2021年 | 288篇 |
2020年 | 335篇 |
2019年 | 386篇 |
2018年 | 396篇 |
2017年 | 453篇 |
2016年 | 516篇 |
2015年 | 377篇 |
2014年 | 669篇 |
2013年 | 1203篇 |
2012年 | 710篇 |
2011年 | 768篇 |
2010年 | 712篇 |
2009年 | 908篇 |
2008年 | 987篇 |
2007年 | 1048篇 |
2006年 | 940篇 |
2005年 | 882篇 |
2004年 | 740篇 |
2003年 | 662篇 |
2002年 | 702篇 |
2001年 | 599篇 |
2000年 | 550篇 |
1999年 | 559篇 |
1998年 | 444篇 |
1997年 | 400篇 |
1996年 | 314篇 |
1995年 | 218篇 |
1994年 | 188篇 |
1993年 | 143篇 |
1992年 | 133篇 |
1991年 | 109篇 |
1990年 | 83篇 |
1989年 | 66篇 |
1988年 | 64篇 |
1987年 | 59篇 |
1986年 | 53篇 |
1985年 | 80篇 |
1984年 | 77篇 |
1983年 | 29篇 |
1982年 | 54篇 |
1981年 | 31篇 |
1980年 | 42篇 |
1979年 | 39篇 |
1978年 | 26篇 |
1977年 | 24篇 |
1976年 | 18篇 |
1974年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Ieva
Dauickait Amos S. Lawless Jennifer A. Scott Peter Jan van Leeuwen 《Numerical Linear Algebra with Applications》2020,27(5)
We consider the large sparse symmetric linear systems of equations that arise in the solution of weak constraint four‐dimensional variational data assimilation, a method of high interest for numerical weather prediction. These systems can be written as saddle point systems with a 3 × 3 block structure but block eliminations can be performed to reduce them to saddle point systems with a 2 × 2 block structure, or further to symmetric positive definite systems. In this article, we analyse how sensitive the spectra of these matrices are to the number of observations of the underlying dynamical system. We also obtain bounds on the eigenvalues of the matrices. Numerical experiments are used to confirm the theoretical analysis and bounds. 相似文献
12.
G. Montero L. Gonzlez E. Flrez M. D. García A. Surez 《Numerical Linear Algebra with Applications》2002,9(3):239-247
Parallel preconditioners are presented for the solution of general linear systems of equations. The computation of these preconditioners is achieved by orthogonal projections related to the Frobenius inner product. So, minM∈??∥AM?I∥ F and matrix M0∈?? corresponding to this minimum (?? being any vectorial subspace of ??n(?)) are explicitly computed using accumulative formulae in order to reduce computational cost when subspace ?? is extended to another one containing it. Every step, the computation is carried out taking advantage of the previous one, what considerably reduces the amount of work. These general results are illustrated with the subspace of matrices M such that AM is symmetric. The main application is developed for the subspace of matrices with a given sparsity pattern which may be constructed iteratively by augmenting the set of non‐zero entries in each column. Finally, the effectiveness of the sparse preconditioners is illustrated with some numerical experiments. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
13.
SPECTRUM-PRESERVING ELEMENTARY OPERATORS ON B(X) 总被引:4,自引:0,他引:4
Hou Jinchuan 《数学年刊B辑(英文版)》1998,19(4):511-516
1.IntroductionLetXbeaninfinitedimensionalcomplexBanachspaceandB(X)theBanachalgebraofallboundedlinearoperatorsonX.ForTEB(X),a(T),asusual,willdenotethespectrumofT.Let4bealinearmapfromB(X)intoitself.4isspectrum-preservingifa(di(T))=a(T)forallTEB(X);4isspectrum-compressingifa(4(T))ga(T)forallTEB(X).Itisclearthatif4isunital(i.e.,ac(I)=I),thenacisspectrum-preserving(spectrum-compressing)ifandonlyif4preservesinvertibilityinbothdirections(preservesinvertibility),i.e.,4(T)isinvertibleifando… 相似文献
14.
本文是文[1-7]的继续,研究变权综合问题,从确定变权的经验公式入手引出了变权原理,给出了变权的公理化定义,讨论了与之有关的均衡函数及其梯度向量。 相似文献
15.
The theory of tree-growing (RECPAM approach) is developed for outcome variables which are distributed as the canonical exponential family. The general RECPAM approach (consisting of three steps: recursive partition, pruning and amalgamation), is reviewed. This is seen as constructing a partition with maximal information content about a parameter to be predicted, followed by simplification by the elimination of ‘negligible’ information. The measure of information is defined for an exponential family outcome as a deviance difference, and appropriate modifications of pruning and amalgamation rules are discussed. It is further shown how the proposed approach makes it possible to develop tree-growing for situations usually treated by generalized linear models (GLIM). In particular, Poisson and logistic regression can be tree-structured. Moreover, censored survival data can be treated, as in GLIM, by observing a formal equivalence of the likelihood under random censoring and an appropriate Poisson model. Three examples are given of application to Poisson, binary and censored survival data. 相似文献
16.
Zhong Yin Xiao 《International Journal of Infrared and Millimeter Waves》2006,27(6):847-855
A new compact bandpass filter composed of two coupled linear tapered line resonators (LTLRs) is designed. The two resonators
are arranged in different layers. The filter has two transmission zeros on both sides of the passband. It has small size and
steep response below its passband. It is also shown that this filter has 0.6 dB low insertion loss at the centre frequency
and 10.5% 3dB bandwidth.
This work was supported by the Development Foundation of Shanghai Educational Committee (217608) and Shanghai Leading Academic
Discipline Project (T0102). 相似文献
17.
WANG Libin 《数学年刊B辑(英文版)》2002,23(4):439-454
The author gets a blow-up result of C1 solution to the Cauchy problem for a first order quasilinear non-strictly hyperbolic system in one space dimension. 相似文献
18.
Stefan Nörtemann 《Applied Categorical Structures》2002,10(4):417-429
The Hahn–Banach Theorem for partially ordered totally convex modules [3] and a necessary and sufficient condition for the existence of an extension of a morphism from a submodule C
0 of a partially ordered totally convex module C (with the ordered unit ball of the reals as codomain) to C, are proved. Moreover, the categories of partially ordered positively convex and superconvex modules are introduced and for both categories the Hahn–Banach Theorem is proved. 相似文献
19.
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
20.
Eva Lesanska 《Applications of Mathematics》2002,47(5):411-426
The problem is to determine nonsensitiveness regions for threshold ellipsoids within a regular mixed linear model. 相似文献