全文获取类型
收费全文 | 14775篇 |
免费 | 1209篇 |
国内免费 | 1329篇 |
专业分类
化学 | 2150篇 |
晶体学 | 27篇 |
力学 | 836篇 |
综合类 | 297篇 |
数学 | 10660篇 |
物理学 | 3343篇 |
出版年
2024年 | 27篇 |
2023年 | 147篇 |
2022年 | 221篇 |
2021年 | 300篇 |
2020年 | 340篇 |
2019年 | 409篇 |
2018年 | 387篇 |
2017年 | 443篇 |
2016年 | 501篇 |
2015年 | 347篇 |
2014年 | 618篇 |
2013年 | 1713篇 |
2012年 | 574篇 |
2011年 | 807篇 |
2010年 | 734篇 |
2009年 | 846篇 |
2008年 | 944篇 |
2007年 | 966篇 |
2006年 | 847篇 |
2005年 | 766篇 |
2004年 | 701篇 |
2003年 | 678篇 |
2002年 | 640篇 |
2001年 | 489篇 |
2000年 | 466篇 |
1999年 | 391篇 |
1998年 | 371篇 |
1997年 | 335篇 |
1996年 | 251篇 |
1995年 | 188篇 |
1994年 | 125篇 |
1993年 | 117篇 |
1992年 | 98篇 |
1991年 | 95篇 |
1990年 | 48篇 |
1989年 | 58篇 |
1988年 | 43篇 |
1987年 | 24篇 |
1986年 | 36篇 |
1985年 | 33篇 |
1984年 | 32篇 |
1983年 | 16篇 |
1982年 | 21篇 |
1981年 | 20篇 |
1980年 | 16篇 |
1979年 | 21篇 |
1978年 | 13篇 |
1977年 | 16篇 |
1976年 | 8篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
1.
2.
3.
4.
5.
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
6.
In this paper, the deformation of the Heisenberg algebra, consistent with both the generalized uncertainty principle and doubly special relativity, has been analyzed. It has been observed that, though this algebra can give rise to fractional derivative terms in the corresponding quantum mechanical Hamiltonian, a formal meaning can be given to them by using the theory of harmonic extensions of function. Depending on this argument, the expression of the propagator of the path integral corresponding to the deformed Heisenberg algebra, has been obtained. In particular, the consistent expression of the one dimensional free particle propagator has been evaluated explicitly. With this propagator in hand, it has been shown that, even in free particle case, normal generalized uncertainty principle and doubly special relativity show very much different result. 相似文献
7.
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
8.
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
9.
Summary This paper is concerned with the problem of developing numerical integration algorithms for differential equations that, when
viewed as equations in some Euclidean space, naturally evolve on some embedded submanifold. It is desired to construct algorithms
whose iterates also evolve on the same manifold. These algorithms can therefore be viewed as integrating ordinary differential
equations on manifolds. The basic method “decouples” the computation of flows on the submanifold from the numerical integration
process. It is shown that two classes of single-step and multistep algorithms can be posed and analyzed theoretically, using
the concept of “freezing” the coefficients of differential operators obtained from the defining vector field. Explicit third-order
algorithms are derived, with additional equations augmenting those of their classical counterparts, obtained from “obstructions”
defined by nonvanishing Lie brackets. 相似文献
10.