全文获取类型
收费全文 | 2176篇 |
免费 | 81篇 |
国内免费 | 123篇 |
专业分类
化学 | 280篇 |
晶体学 | 2篇 |
力学 | 30篇 |
综合类 | 29篇 |
数学 | 1774篇 |
物理学 | 265篇 |
出版年
2023年 | 28篇 |
2022年 | 17篇 |
2021年 | 22篇 |
2020年 | 47篇 |
2019年 | 67篇 |
2018年 | 62篇 |
2017年 | 59篇 |
2016年 | 66篇 |
2015年 | 25篇 |
2014年 | 75篇 |
2013年 | 238篇 |
2012年 | 58篇 |
2011年 | 100篇 |
2010年 | 70篇 |
2009年 | 140篇 |
2008年 | 135篇 |
2007年 | 119篇 |
2006年 | 126篇 |
2005年 | 105篇 |
2004年 | 86篇 |
2003年 | 77篇 |
2002年 | 79篇 |
2001年 | 58篇 |
2000年 | 77篇 |
1999年 | 56篇 |
1998年 | 56篇 |
1997年 | 52篇 |
1996年 | 40篇 |
1995年 | 26篇 |
1994年 | 24篇 |
1993年 | 27篇 |
1992年 | 20篇 |
1991年 | 9篇 |
1990年 | 12篇 |
1989年 | 8篇 |
1988年 | 11篇 |
1987年 | 15篇 |
1986年 | 10篇 |
1985年 | 11篇 |
1984年 | 11篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 8篇 |
1980年 | 8篇 |
1979年 | 6篇 |
1978年 | 7篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1973年 | 2篇 |
1972年 | 2篇 |
排序方式: 共有2380条查询结果,搜索用时 15 毫秒
151.
This article derives from first principles a definition of equivalence for higher‐dimensional Hadamard matrices and thereby a definition of the automorphism group for higher‐dimensional Hadamard matrices. Our procedure is quite general and could be applied to other kinds of designs for which there are no established definitions for equivalence or automorphism. Given a two‐dimensional Hadamard matrix H of order ν, there is a Product Construction which gives an order ν proper n‐dimensional Hadamard matrix P(n)(H). We apply our ideas to the matrices P(n)(H). We prove that there is a constant c > 1 such that any Hadamard matrix H of order ν > 2 gives rise via the Product Construction to cν inequivalent proper three‐dimensional Hadamard matrices of order ν. This corrects an erroneous assertion made in the literature that ”P(n)(H) is equivalent to “P(n)(H′) whenever H is equivalent to H′.” We also show how the automorphism group of P(n)(H) depends on the structure of the automorphism group of H. As an application of the above ideas, we determine the automorphism group of P(n)(Hk) when Hk is a Sylvester Hadamard matrix of order 2k. For ν = 4, we exhibit three distinct families of inequivalent Product Construction matrices P(n)(H) where H is equivalent to H2. These matrices each have large but non‐isomorphic automorphism groups. © 2008 Wiley Periodicals, Inc. J Combin Designs 16: 507–544, 2008 相似文献
152.
Chi-Kwong Li Yiu-Tung Poon Nung-Sing Sze 《Proceedings of the American Mathematical Society》2005,133(2):369-377
We characterize linear maps between different rectangular matrix spaces preserving Ky Fan norms.
153.
本文在[1]的基础上研究由特殊微分算子确定的一类再生核的计算,指出这类再生核的特例与以往通常采用的再生核是相似的,但其计算与以往的再生核相比却得到了极大的简化.文中还给出了这类再生核系数的迭代算法. 相似文献
154.
主要研究随机矩阵逆特征值问题.特别是对称双随机矩阵和列随机矩阵逆特征值问题.对参考文献[1]与[2]的结论作了一些推广.并给出了—个数值例子. 相似文献
155.
Mireille Bousquet-Mélou Svante Linusson Eran Nevo 《Journal of Algebraic Combinatorics》2008,27(4):423-450
The enumeration of independent sets of regular graphs is of interest in statistical mechanics, as it corresponds to the solution
of hard-particle models. In 2004, it was conjectured by Fendley et al., that for some rectangular grids, with toric boundary conditions, the alternating number of independent sets is extremely simple. More precisely, under a coprimality condition on the sides of the rectangle,
the number of independent sets of even and odd cardinality always differ by 1. In physics terms, this means looking at the
hard-particle model on these grids at activity −1. This conjecture was recently proved by Jonsson.
Here we produce other families of grid graphs, with open or cylindric boundary conditions, for which similar properties hold
without any size restriction: the number of independent sets of even and odd cardinality always differ by 0, ±1, or, in the
cylindric case, by some power of 2.
We show that these results reflect a stronger property of the independence complexes of our graphs. We determine the homotopy
type of these complexes using Forman’s discrete Morse theory. We find that these complexes are either contractible, or homotopic
to a sphere, or, in the cylindric case, to a wedge of spheres.
Finally, we use our enumerative results to determine the spectra of certain transfer matrices describing the hard-particle
model on our graphs at activity −1. These results parallel certain conjectures of Fendley et al., proved by Jonsson in the toric case. 相似文献
156.
Luis Velázquez 《Journal of Functional Analysis》2008,254(4):954-986
We present an operator theoretic approach to orthogonal rational functions based on the identification of a suitable matrix representation of the multiplication operator associated with the corresponding orthogonality measure. Two alternatives are discussed, leading to representations which are linear fractional transformations with matrix coefficients acting on infinite Hessenberg or five-diagonal unitary matrices. This approach permits us to recover the orthogonality measure throughout the spectral analysis of an infinite matrix depending uniquely on the poles and the parameters of the recurrence relation for the orthogonal rational functions. Besides, the zeros of the orthogonal and para-orthogonal rational functions are identified as the eigenvalues of matrix linear fractional transformations of finite Hessenberg or five-diagonal matrices. As an application we use operator perturbation theory results to obtain new relations between the support of the orthogonality measure and the location of the poles and parameters of the recurrence relation for the orthogonal rational functions. 相似文献
157.
The paper provides a combinatorial method to decide when the space of local systems with nonvanishing first cohomology on the complement to an arrangement of lines in a complex projective plane has as an irreducible component a subgroup of positive dimension. Partial classification of arrangements having such a component of positive dimension and a comparison theorem for cohomology of Orlik–Solomon algebra and cohomology of local systems are given. The methods are based on Vinberg–Kac classification of generalized Cartan matrices and study of pencils of algebraic curves defined by mentioned positive dimensional components. 相似文献
158.
Eric S. Key 《Journal of Theoretical Probability》1990,3(3):477-488
Upper bounds for the maximal Lyapunov exponent,E, of a sequence of matrix-valued random variables are easy to come by asE is the infimum of a real-valued sequence. We shall show that under irreducibility conditions similar to those needed to prove the Perron-Frobenius theorem, one can find sequences which increase toE. As a byproduct of the proof we shall see that we may replace the matrix norm with the spectral radius when computingE in such cases. Finally, a sufficient condition for transience of random walk in a random environment is given. 相似文献
159.
Summary Further properties are derived for a class of invariant polynomials with several matrix arguments which extend the zonal polynomials.
Generalized Laguerre polynomials are defined, and used to obtain expansions of the sum of independent noncentral Wishart matrices
and an associated generalized regression coefficient matrix. The latter includes thek-class estimator in econometrics. 相似文献
160.
We consider C=A+B where A is selfadjoint with a gap (a,b) in its spectrum and B is (relatively) compact. We prove a general result allowing B of indefinite sign and apply it to obtain a (δV)d/2 bound for perturbations of suitable periodic Schrödinger operators and a (not quite) Lieb–Thirring bound for perturbations of algebro-geometric almost periodic Jacobi matrices. 相似文献