全文获取类型
收费全文 | 7359篇 |
免费 | 653篇 |
国内免费 | 943篇 |
专业分类
化学 | 2809篇 |
晶体学 | 30篇 |
力学 | 694篇 |
综合类 | 102篇 |
数学 | 3714篇 |
物理学 | 1606篇 |
出版年
2024年 | 10篇 |
2023年 | 87篇 |
2022年 | 89篇 |
2021年 | 171篇 |
2020年 | 204篇 |
2019年 | 230篇 |
2018年 | 209篇 |
2017年 | 208篇 |
2016年 | 255篇 |
2015年 | 213篇 |
2014年 | 356篇 |
2013年 | 589篇 |
2012年 | 332篇 |
2011年 | 365篇 |
2010年 | 331篇 |
2009年 | 454篇 |
2008年 | 498篇 |
2007年 | 487篇 |
2006年 | 453篇 |
2005年 | 368篇 |
2004年 | 389篇 |
2003年 | 344篇 |
2002年 | 329篇 |
2001年 | 273篇 |
2000年 | 287篇 |
1999年 | 193篇 |
1998年 | 198篇 |
1997年 | 158篇 |
1996年 | 152篇 |
1995年 | 134篇 |
1994年 | 116篇 |
1993年 | 82篇 |
1992年 | 79篇 |
1991年 | 63篇 |
1990年 | 36篇 |
1989年 | 22篇 |
1988年 | 26篇 |
1987年 | 32篇 |
1986年 | 25篇 |
1985年 | 20篇 |
1984年 | 20篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1981年 | 11篇 |
1980年 | 10篇 |
1979年 | 12篇 |
1978年 | 8篇 |
1976年 | 6篇 |
1959年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有8955条查询结果,搜索用时 31 毫秒
41.
Alexander Kolokolov Nikolay Kosarev 《Journal of Mathematical Modelling and Algorithms》2006,5(2):189-199
In this paper the algorithms for solving the p-median problem based on the Benders decomposition are investigated. A family of problems hard for solving with such algorithms is constructed and then generalized to a special NP-hard case of the p-median problem. It is shown that the effectiveness of the considered algorithms depends on the choice of the optimal values of the dual variables used in Benders cuts. In particular, the depth of the cuts can be equal to one. 相似文献
42.
设(X,d)是一个可分的度量空间,Cu(X,d)是由全体一致连续函数所组成的C(X,d)的子空间,T是定义在X上的一致Lipschitz映射,那么对f∈Cu(X),1/n n∑k=1 Uk If在Cu(X)上收敛.从这个基本结果出发,利用Cu(X,d)的共扼空间的表示定理,得到了相空间的Yosida型遍历分解;利用空间的嵌入技术证明了非一致Lipschitz映射的大数法则. 相似文献
43.
This paper has demonstrated that the Schwartz alternating process must converge if D-N alternating process has converged. Its technique is that the overlapping regions in Schwartz alternating process are considered as independent domains, then Schwartz alternating process could be transformed into D-N alter-nating process. Finally the convergence estimation of Schwartz alternating process could be obtained. The results show that its convergence rate is same as that of D-N alternating process. 相似文献
44.
We show that the tensor product B-spline basis and the triangular Bernstein basis are in some sense best conditioned among all nonnegative bases for the spaces of tensor product splines and multivariate polynomials, respectively. We also introduce some new condition numbers which are analogs of component-wise condition numbers for linear systems introduced by Skeel. 相似文献
45.
A cube factorization of the complete graph on n vertices, Kn, is a 3‐factorization of Kn in which the components of each factor are cubes. We show that there exists a cube factorization of Kn if and only if n ≡ 16 (mod 24), thus providing a new family of uniform 3‐factorizations as well as a partial solution to an open problem posed by Kotzig in 1979. © 2004 Wiley Periodicals, Inc. 相似文献
46.
Gabriela Jeronimo Teresa Krick Juan Sabia Martín Sombra 《Foundations of Computational Mathematics》2004,4(1):41-117
We present a bounded probability algorithm for the computation of the
Chowforms of the equidimensional components of an algebraic variety. In particular,
this gives an alternative procedure for the effective equidimensional decomposition
of the variety, since each equidimensional component is characterized by its Chow
form.
The expected complexity of the algorithm is polynomial in the size and the geometric
degree of the input equation system defining the variety. Hence it improves (or
meets in some special cases) the complexity of all previous algorithms for computing Chow forms. In addition to this, we clarify the probability and uniformity aspects,
which constitutes a further contribution of the paper.
The algorithm is based on elimination theory techniques, in line with the geometric
resolution algorithm due to M. Giusti, J. Heintz, L. M. Pardo, and their collaborators.
In fact, ours can be considered as an extension of their algorithm for zero-dimensional
systems to the case of positive-dimensional varieties. The key element for dealing
with positive-dimensional varieties is a new Poisson-type product formula. This
formula allows us to compute the Chow form of an equidimensional variety from a
suitable zero-dimensional fiber.
As an application, we obtain an algorithm to compute a subclass of sparse resultants,
whose complexity is polynomial in the dimension and the volume of the input
set of exponents. As another application, we derive an algorithm for the computation
of the (unique) solution of a generic overdetermined polynomial equation system. 相似文献
47.
Thomas Wanner 《Transactions of the American Mathematical Society》2004,356(6):2251-2279
Many interesting and complicated patterns in the applied sciences are formed through transient pattern formation processes. In this paper we concentrate on the phenomenon of spinodal decomposition in metal alloys as described by the Cahn-Hilliard equation. This model depends on a small parameter, and one is generally interested in establishing sharp lower bounds on the amplitudes of the patterns as the parameter approaches zero. Recent results on spinodal decomposition have produced such lower bounds. Unfortunately, for higher-dimensional base domains these bounds are orders of magnitude smaller than what one would expect from simulations and experiments. The bounds exhibit a dependence on the dimension of the domain, which from a theoretical point of view seemed unavoidable, but which could not be observed in practice.
In this paper we resolve this apparent paradox. By employing probabilistic methods, we can improve the lower bounds for certain domains and remove the dimension dependence. We thereby obtain optimal results which close the gap between analytical methods and numerical observations, and provide more insight into the nature of the decomposition process. We also indicate how our results can be adapted to other situations.
48.
We show that there is a threshold in energy for the onset of chaos in cosmology for the Universe described as a dynamical system derived from the Einstein equations of General Relativity (GR). In the case of the mixmaster model (homogeneous and anisotropic cosmology with a Bianchi IX metric), the chaos occurs precisely at the prescribed necessary value H
vac=0 of the GR for the energy of the Universe while the system is found to be regular for H<0 and chaotic for H>0 with respect to its pure vacuum part. In the case of generalized scalar tensor theories within the Bianchi IX model, we show using the ADM formalism and a conformal transformation that the energy of the dynamical system as compared to vacuum lies below the zero energy threshold. The system is thus not exhibiting chaos and the conclusion still holds in the presence of ordinary matter as well. The suppression of chaos occurs in a similar way for stiff matter alone. 相似文献
49.
Bogdan Nita 《General Relativity and Gravitation》2003,35(10):1865-1868
Algebraically special gravitational fields are described using algebraic and differential invariants of the Weyl tensor. A type III invariant is also given and calculated for Robinson-Trautman spaces. 相似文献
50.
Lá szló L. Stachó Borut Zalar 《Proceedings of the American Mathematical Society》2004,132(10):3019-3025
We prove that every JB* triple with rank one bicircular projection is a direct sum of two ideals, one of which is isometrically isomorphic to a Hilbert space.