全文获取类型
收费全文 | 14659篇 |
免费 | 1548篇 |
国内免费 | 973篇 |
专业分类
化学 | 2361篇 |
晶体学 | 36篇 |
力学 | 1516篇 |
综合类 | 291篇 |
数学 | 9176篇 |
物理学 | 3800篇 |
出版年
2024年 | 23篇 |
2023年 | 137篇 |
2022年 | 191篇 |
2021年 | 277篇 |
2020年 | 394篇 |
2019年 | 397篇 |
2018年 | 367篇 |
2017年 | 442篇 |
2016年 | 549篇 |
2015年 | 362篇 |
2014年 | 699篇 |
2013年 | 1458篇 |
2012年 | 648篇 |
2011年 | 864篇 |
2010年 | 772篇 |
2009年 | 864篇 |
2008年 | 882篇 |
2007年 | 965篇 |
2006年 | 813篇 |
2005年 | 752篇 |
2004年 | 658篇 |
2003年 | 652篇 |
2002年 | 573篇 |
2001年 | 479篇 |
2000年 | 460篇 |
1999年 | 397篇 |
1998年 | 352篇 |
1997年 | 266篇 |
1996年 | 260篇 |
1995年 | 189篇 |
1994年 | 156篇 |
1993年 | 126篇 |
1992年 | 125篇 |
1991年 | 127篇 |
1990年 | 62篇 |
1989年 | 57篇 |
1988年 | 43篇 |
1987年 | 37篇 |
1986年 | 38篇 |
1985年 | 46篇 |
1984年 | 40篇 |
1983年 | 22篇 |
1982年 | 25篇 |
1981年 | 30篇 |
1980年 | 16篇 |
1979年 | 20篇 |
1978年 | 16篇 |
1977年 | 18篇 |
1976年 | 10篇 |
1974年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
2.
G. Peruginelli 《代数通讯》2018,46(11):4724-4738
We classify the maximal subrings of the ring of n×n matrices over a finite field, and show that these subrings may be divided into three types. We also describe all of the maximal subrings of a finite semisimple ring, and categorize them into two classes. As an application of these results, we calculate the covering number of a finite semisimple ring. 相似文献
3.
《Discrete Mathematics》2021,344(12):112589
Let be the set of positive integers. For a nonempty set A of integers and every integer u, denote by the number of with such that . For a sequence S of positive integers, let be the counting function of S. The set is called a perfect difference set if for every positive integer u. In 2008, Cilleruelo and Nathanson (2008) [4] constructed dense perfect difference sets from dense Sidon sets. In this paper, as a main result, we prove that: let be an increasing function satisfying for any positive integer n, then for every Sidon set B and every function , there exists a set such that for every positive integer u and for all . 相似文献
4.
In this paper, we study the existence of the uniformly minimum risk equivariant (UMRE) estimators of parameters in a class
of normal linear models, which include the normal variance components model, the growth curve model, the extended growth curve
model, and the seemingly unrelated regression equations model, and so on. The necessary and sufficient conditions are given
for the existence of UMRE estimators of the estimable linear functions of regression coefficients, the covariance matrixV and (trV)α, where α > 0 is known, in the models under an affine group of transformations for quadratic losses and matrix losses, respectively.
Under the (extended) growth curve model and the seemingly unrelated regression equations model, the conclusions given in literature
for estimating regression coefficients can be derived by applying the general results in this paper, and the sufficient conditions
for non-existence of UMRE estimators ofV and tr(V) are expanded to be necessary and sufficient conditions. In addition, the necessary and sufficient conditions that there
exist UMRE estimators of parameters in the variance components model are obtained for the first time. 相似文献
5.
施国勇 《宁波大学学报(理工版)》1998,(2)
提出了一个线性双向联想存储器的模型,一组有限个向量对由一线性算子建立起双向联想关系,此线性算于是一个网络的联结权重矩阵。该权矩阵由最小二乘法决定。由权矩阵的解导出一特殊类型的Lyapunov矩阵方程.本文提供了这种Lyapunov矩阵方程的解。 相似文献
6.
In circuit-switched networks call streams are characterized by their mean and peakedness (two-moment method). The GI/M/C/0 system is used to model a single link, where the GI-stream is determined by fitting moments appropriately. For the moments of the overflow traffic of a GI/M/C/0 system there are efficient numerical algorithms available. However, for the moments of the freed carried traffic, defined as the moments of a virtual link of infinite capacity to which the process of calls accepted by the link (carried arrival process) is virtually directed and where the virtual calls get fresh exponential i.i.d. holding times, only complex numerical algorithms are available. This is the reason why the concept of the freed carried traffic is not used. The main result of this paper is a numerically stable and efficient algorithm for computing the moments of freed carried traffic, in particular an explicit formula for its peakedness. This result offers a unified handling of both overflow and carried traffics in networks. Furthermore, some refined characteristics for the overflow and freed carried streams are derived. 相似文献
7.
8.
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
9.
10.
Wei Gengping~ Shen Jianhua~ 《高校应用数学学报(英文版)》2006,21(3):320-326
This paper studies the nonautonomous nonlinear system of difference equationsΔx(n)=A(n)x(n)+f(n,x(n)),n∈Z,(*) where x(n)∈R~N,A(n)=(a_(ij)(n))N×N is an N×N matrix,with a-(ij)∈C(R,R) for i,j= 1,2,3,...,N,and f=(f_1,f_2,...,f_N)~T∈C(R×R~N,R~N),satisfying A(t+ω)=A(t),f(t+ω,z)=f(t,z) for any t∈R,(t,z)∈R×R~N andωis a positive integer.Sufficient conditions for the existence ofω-periodic solutions to equations (*) are obtained. 相似文献