全文获取类型
收费全文 | 4003篇 |
免费 | 215篇 |
国内免费 | 139篇 |
专业分类
化学 | 87篇 |
晶体学 | 1篇 |
力学 | 12篇 |
综合类 | 33篇 |
数学 | 4021篇 |
物理学 | 203篇 |
出版年
2024年 | 14篇 |
2023年 | 62篇 |
2022年 | 88篇 |
2021年 | 74篇 |
2020年 | 119篇 |
2019年 | 116篇 |
2018年 | 126篇 |
2017年 | 115篇 |
2016年 | 82篇 |
2015年 | 69篇 |
2014年 | 140篇 |
2013年 | 302篇 |
2012年 | 174篇 |
2011年 | 199篇 |
2010年 | 199篇 |
2009年 | 363篇 |
2008年 | 344篇 |
2007年 | 250篇 |
2006年 | 236篇 |
2005年 | 156篇 |
2004年 | 134篇 |
2003年 | 126篇 |
2002年 | 108篇 |
2001年 | 98篇 |
2000年 | 81篇 |
1999年 | 86篇 |
1998年 | 76篇 |
1997年 | 71篇 |
1996年 | 50篇 |
1995年 | 33篇 |
1994年 | 32篇 |
1993年 | 27篇 |
1992年 | 24篇 |
1991年 | 19篇 |
1990年 | 19篇 |
1989年 | 15篇 |
1988年 | 14篇 |
1987年 | 4篇 |
1986年 | 7篇 |
1985年 | 22篇 |
1984年 | 16篇 |
1983年 | 10篇 |
1982年 | 14篇 |
1981年 | 8篇 |
1980年 | 15篇 |
1979年 | 4篇 |
1978年 | 9篇 |
1977年 | 4篇 |
1970年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有4357条查询结果,搜索用时 187 毫秒
991.
In this article, we consider the maximum cocliques of the 211: M24 ‐graph Λ. We show that the maximum cocliques of size 24 of Λ can be obtained from two Hadamard matrices of size 24, and that there are exactly two maximum cocliques up to equivalence. We verify that the two nonisomorphic designs with parameters 5‐(24,9,6) can be constructed from the maximum cocliques of Λ, and that these designs are isomorphic to the support designs of minimum weights of the ternary extended quadratic residue and Pless symmetry [24,12,9] codes. Further, we give a new construction of Λ from these 5‐(24,9,6) designs. © 2009 Wiley Periodicals, Inc. J Combin Designs 17: 323–332, 2009 相似文献
992.
Mykhaylo Tyomkyn 《Discrete Mathematics》2009,309(20):5963-5967
Bonato and Tardif [A. Bonato, C. Tardif, Mutually embeddable graphs and the tree alternative conjecture, J. Combinatorial Theory, Series B 96 (2006), 874-880] conjectured that the number of isomorphism classes of trees mutually embeddable with a given tree T is either 1 or infinite. We prove the analogue of their conjecture for rooted trees. We also make some progress towards the original conjecture for locally finite trees and state some new conjectures. 相似文献
993.
994.
Daniel Wachsmuth 《Journal of Mathematical Analysis and Applications》2006,319(1):228-247
In this article sufficient optimality conditions are established for optimal control problems with pointwise convex control constraints. Here, the control is a function with values in Rn. The constraint is of the form u(x)∈U(x), where U is a set-valued mapping that is assumed to be measurable with convex and closed images. The second-order condition requires coercivity of the Lagrange function on a suitable subspace, which excludes strongly active constraints, together with first-order necessary conditions. It ensures local optimality of a reference function in an L∞-neighborhood. The analysis is done for a model problem namely the optimal distributed control of the instationary Navier-Stokes equations. 相似文献
995.
Pinar Heggernes 《Discrete Mathematics》2006,306(3):297-317
Any given graph can be embedded in a chordal graph by adding edges, and the resulting chordal graph is called a triangulation of the input graph. In this paper we study minimal triangulations, which are the result of adding an inclusion minimal set of edges to produce a triangulation. This topic was first studied from the standpoint of sparse matrices and vertex elimination in graphs. Today we know that minimal triangulations are closely related to minimal separators of the input graph. Since the first papers presenting minimal triangulation algorithms appeared in 1976, several characterizations of minimal triangulations have been proved, and a variety of algorithms exist for computing minimal triangulations of both general and restricted graph classes. This survey presents and ties together these results in a unified modern notation, keeping an emphasis on the algorithms. 相似文献
996.
The first step toward developing complete cell circuitry is to build quantitative networks for enzyme reactions. The conventional King-Altman-Hill (KAH) algorithm for topological analysis of enzyme networks, adapted from electrical networks, is based on “Reaction Graphs” that, unlike electrical circuits, are not quantitative, being straightforward renderings of conventional schematics of reaction mechanisms. Therefore, we propose the use of “Reaction Route (RR) Graphs” instead, as a more suitable graph-theoretical representation for topological analysis of enzyme reaction networks. The RR Graphs are drawn such that they are not only useful for visualizing the various reaction routes or pathways, but unlike Reaction Graphs possess network properties consistent with requisite kinetic, mass balance, and thermodynamic constraints. Therefore, they are better than the conventional Reaction Graphs for topological representation and analysis of enzyme reactions, both via the KAH methodology as well as via numerical matrix inversion. The difference between the two is highlighted based on the example of a single enzyme reaction network for the conversion of 7,8-dihydrofolate and NADPH into 5,6,7,8-tetrahydrofolate and NADP+, catalyzed by the enzyme dihydrofolate reductase. 相似文献
997.
Zsolt Katona 《Random Structures and Algorithms》2006,29(2):194-207
Consider the random graph model of Barabási and Albert, where we add a new vertex in every step and connect it to some old vertices with probabilities proportional to their degrees. If we connect it to only one of the old vertices the graph will be a tree. These graphs have been shown to have power law degree distributions, the same as observed in some large real‐world networks. We show that the degree distribution is the same on every sufficiently high level of the tree. © 2005 Wiley Periodicals, Inc. Random Struct. Alg., 2006 相似文献
998.
999.
Robert M. Freund 《Mathematical Programming》2006,106(3):527-545
There is a natural norm associated with a starting point of the homogeneous self-dual (HSD) embedding model for conic convex
optimization. In this norm two measures of the HSD model's behavior are precisely controlled independent of the problem instance:
(i) the sizes of ɛ-optimal solutions, and (ii) the maximum distance of ɛ-optimal solutions to the boundary of the cone of the HSD variables. This norm is also useful in developing a stopping-rule
theory for HSD-based interior-point solvers such as SeDuMi. Under mild assumptions, we show that a standard stopping rule
implicitly involves the sum of the sizes of the ɛ-optimal primal and dual solutions, as well as the size of the initial primal and dual infeasibility residuals. This theory
suggests possible criteria for developing starting points for the homogeneous self-dual model that might improve the resulting
solution time in practice.
This research has been partially supported through the MIT-Singapore Alliance. 相似文献
1000.
Ying Ying TAN Yi Zheng FAN 《数学学报(英文版)》2008,24(1):139-146
Let G be a mixed glaph which is obtained from an undirected graph by orienting some of its edges. The eigenvalues and eigenvectors of G are, respectively, defined to be those of the Laplacian matrix L(G) of G. As L(G) is positive semidefinite, the singularity of L(G) is determined by its least eigenvalue λ1 (G). This paper introduces a new parameter edge singularity εs(G) that reflects the singularity of L(G), which is the minimum number of edges of G whose deletion yields that all the components of the resulting graph are singular. We give some inequalities between εs(G) and λ1 (G) (and other parameters) of G. In the case of εs(G) = 1, we obtain a property on the structure of the eigenvectors of G corresponding to λ1 (G), which is similar to the property of Fiedler vectors of a simple graph given by Fiedler. 相似文献