全文获取类型
收费全文 | 650篇 |
免费 | 19篇 |
国内免费 | 51篇 |
专业分类
化学 | 167篇 |
晶体学 | 2篇 |
力学 | 6篇 |
综合类 | 3篇 |
数学 | 388篇 |
物理学 | 154篇 |
出版年
2023年 | 4篇 |
2022年 | 13篇 |
2021年 | 7篇 |
2020年 | 19篇 |
2019年 | 17篇 |
2018年 | 17篇 |
2017年 | 12篇 |
2016年 | 12篇 |
2015年 | 11篇 |
2014年 | 24篇 |
2013年 | 65篇 |
2012年 | 28篇 |
2011年 | 42篇 |
2010年 | 39篇 |
2009年 | 66篇 |
2008年 | 51篇 |
2007年 | 49篇 |
2006年 | 34篇 |
2005年 | 26篇 |
2004年 | 23篇 |
2003年 | 18篇 |
2002年 | 20篇 |
2001年 | 15篇 |
2000年 | 18篇 |
1999年 | 20篇 |
1998年 | 11篇 |
1997年 | 10篇 |
1996年 | 9篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 6篇 |
1992年 | 10篇 |
1991年 | 5篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有720条查询结果,搜索用时 203 毫秒
691.
An alternative perspective to evaluate networks and network evolution is introduced, based on the notion of covering. For a particular node in a network covering captures the idea of being outperformed by another node in terms of, for example, visibility and possibility of information gathering. In this paper, we focus on networks where these subdued network positions do not exist. We call these networks stable. Within this set we identify the minimal stable networks, which frequently have a ‘bubble-like’ structure. Severing a link in such a network results in at least one of the nodes being covered. In a minimal stable network therefore all nodes cooperate to avoid that one of the nodes ends up in a subdued position. Our results can be applied to, for example, the design of (covert) communication networks and the dynamics of social and information networks. 相似文献
692.
Jiong Sheng LI Jian Hua YIN 《数学学报(英文版)》2006,22(4):1133-1138
Let σ(k, n) be the smallest even integer such that each n-term positive graphic sequence with term sum at least σ(k, n) can be realized by a graph containing a clique of k + 1 vertices. Erdos et al. (Graph Theory, 1991, 439-449) conjectured that σ(k, n) = (k - 1)(2n- k) + 2. Li et al. (Science in China, 1998, 510-520) proved that the conjecture is true for k 〉 5 and n ≥ (k2) + 3, and raised the problem of determining the smallest integer N(k) such that the conjecture holds for n ≥ N(k). They also determined the values of N(k) for 2 ≤ k ≤ 7, and proved that [5k-1/2] ≤ N(k) ≤ (k2) + 3 for k ≥ 8. In this paper, we determine the exact values of σ(k, n) for n ≥ 2k+3 and k ≥ 6. Therefore, the problem of determining σ(k, n) is completely solved. In addition, we prove as a corollary that N(k) -= [5k-1/2] for k ≥6. 相似文献
693.
694.
695.
696.
Let G be a graph of order n and k a positive integer. A set of subgraphs H={H1,H2,…,Hk} is called a k-degenerated cycle partition (abbreviated to k-DCP) of G if H1,…,Hk are vertex disjoint subgraphs of G such that and for all i, 1≤i≤k, Hi is a cycle or K1 or K2. If, in addition, for all i, 1≤i≤k, Hi is a cycle or K1, then H is called a k-weak cycle partition (abbreviated to k-WCP) of G. It has been shown by Enomoto and Li that if |G|=n≥k and if the degree sum of any pair of nonadjacent vertices is at least n−k+1, then G has a k-DCP, except G≅C5 and k=2. We prove that if G is a graph of order n≥k+12 that has a k-DCP and if the degree sum of any pair of nonadjacent vertices is at least , then either G has a k-WCP or k=2 and G is a subgraph of K2∪Kn−2∪{e}, where e is an edge connecting V(K2) and V(Kn−2). By using this, we improve Enomoto and Li’s result for n≥max{k+12,10k−9}. 相似文献
697.
Zsolt Lengvarszky 《Discrete Mathematics》2009,309(12):4171-4175
We consider the problem of how the assembly process of an origami model, made up of similar pieces, can be completed given that at each step there are several choices. A result is given in the language of graphs that provides a sufficient condition under which assembly of the model will never fail. 相似文献
698.
Kiyoshi Ando 《Discrete Mathematics》2009,309(22):6359-6367
An edge of a 5-connected graph is said to be contractible if the contraction of the edge results in a 5-connected graph. A 5-connected graph with no contractible edge is said to be contraction critically 5-connected. Let G be a contraction critically 5-connected graph and let H be a component of the subgraph induced by the set of degree 5 vertices of G. Then it is known that |V(H)|≥4. We prove that if |V(H)|=4, then , where stands for the graph obtained from K4 by deleting one edge. Moreover, we show that either |NG(V(H))|=5 or |NG(V(H))|=6 and around H there is one of two specified structures called a -configuration and a split -configuration. 相似文献
699.
Eyal Loz 《Discrete Mathematics》2009,309(10):3125-3130
We derive an upper bound on the number of vertices in regular graphs of given degree and diameter arising as regular coverings of dipoles over abelian groups. 相似文献
700.
Mohamed A. Ramadan Mokhtar A. Abdel Naby Ahmed M.E. Bayoumi 《Mathematical and Computer Modelling》2009,50(9-10):1400-1408
In this paper, we consider the explicit solutions of two matrix equations, namely, the Yakubovich matrix equation V−AVF=BW and Sylvester matrix equations AV−EVF=BW,AV+BW=EVF and AV−VF=BW. For this purpose, we make use of Kronecker map and Sylvester sum as well as the concept of coefficients of characteristic polynomial of the matrix A. Some lemmas and theorems are stated and proved where explicit and parametric solutions are obtained. The proposed methods are illustrated by numerical examples. The results obtained show that the methods are very neat and efficient. 相似文献