全文获取类型
收费全文 | 5171篇 |
免费 | 339篇 |
国内免费 | 501篇 |
专业分类
化学 | 405篇 |
晶体学 | 4篇 |
力学 | 284篇 |
综合类 | 120篇 |
数学 | 4871篇 |
物理学 | 327篇 |
出版年
2024年 | 5篇 |
2023年 | 60篇 |
2022年 | 84篇 |
2021年 | 100篇 |
2020年 | 108篇 |
2019年 | 113篇 |
2018年 | 130篇 |
2017年 | 130篇 |
2016年 | 133篇 |
2015年 | 102篇 |
2014年 | 202篇 |
2013年 | 356篇 |
2012年 | 225篇 |
2011年 | 287篇 |
2010年 | 259篇 |
2009年 | 353篇 |
2008年 | 346篇 |
2007年 | 326篇 |
2006年 | 325篇 |
2005年 | 259篇 |
2004年 | 225篇 |
2003年 | 262篇 |
2002年 | 223篇 |
2001年 | 204篇 |
2000年 | 173篇 |
1999年 | 171篇 |
1998年 | 176篇 |
1997年 | 153篇 |
1996年 | 91篇 |
1995年 | 68篇 |
1994年 | 55篇 |
1993年 | 48篇 |
1992年 | 36篇 |
1991年 | 25篇 |
1990年 | 19篇 |
1989年 | 13篇 |
1988年 | 13篇 |
1987年 | 11篇 |
1986年 | 9篇 |
1985年 | 24篇 |
1984年 | 20篇 |
1983年 | 12篇 |
1982年 | 21篇 |
1981年 | 16篇 |
1980年 | 18篇 |
1979年 | 5篇 |
1978年 | 6篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1974年 | 3篇 |
排序方式: 共有6011条查询结果,搜索用时 15 毫秒
911.
Let G be a graph of order n and maximum degree Δ(G) and let γt(G) denote the minimum cardinality of a total dominating set of a graph G. A graph G with no isolated vertex is the total domination vertex critical if for any vertex v of G that is not adjacent to a vertex of degree one, the total domination number of G−v is less than the total domination number of G. We call these graphs γt-critical. For any γt-critical graph G, it can be shown that n≤Δ(G)(γt(G)−1)+1. In this paper, we prove that: Let G be a connected γt-critical graph of order n (n≥3), then n=Δ(G)(γt(G)−1)+1 if and only if G is regular and, for each v∈V(G), there is an A⊆V(G)−{v} such that N(v)∩A=0?, the subgraph induced by A is 1-regular, and every vertex in V(G)−A−{v} has exactly one neighbor in A. 相似文献
912.
本文在二阶锥上引入一类新的映射,称之为笛卡尔P_*(κ)映射,它是单调映射的推广.文中讨论涉及这类映射的二阶锥互补问题的解的存在性和解集的有界性.主要结论为:如果所考虑的互补问题是严格可行的,那么它的解集是非空有界的. 相似文献
913.
914.
Verena Bögelein 《Annali di Matematica Pura ed Applicata》2009,188(1):61-122
In the present paper we provide a broad survey of the regularity theory for non-differentiable higher order parabolic systems
of the type
Initially, we prove a partial regularity result with the method of A-polycaloric approximation, which is a parabolic analogue of the harmonic approximation lemma of De Giorgi. Moreover, we prove
better estimates for the maximal parabolic Hausdorff-dimension of the singular set of weak solutions, using fractional parabolic
Sobolev spaces. Thereby, we also consider different situations, which yield a better dimension reduction result, including
the low dimensional case and coefficients A(z, D
m
u), independent of the lower order derivatives of u.
相似文献
915.
Corrugated paper is produced by gluing three types of papers of the same breadth. Given a set of orders, we first assign each order to one of the standard breadths, and then sequence those assigned to each standard breadth so that they are continuously manufactured from the three rolls of the specified standard breadth equipped in the machine called corrugator. Here we are asked to achieve multi-goals of minimizing total length of roll papers, total loss of papers caused by the differences between standard breadths and real breadths of the orders, and the number of machine stops needed during production. We use integer programming to assign orders to standard breadths, and then develop a special purpose algorithm to sequence the orders assigned to each standard breadth. This is a first attempt to handle scheduling problems of the corrugator machine. 相似文献
916.
Rough set approach to multiple criteria classification with imprecise evaluations and assignments 总被引:2,自引:0,他引:2
Krzysztof Dembczyński Salvatore Greco Roman Słowiński 《European Journal of Operational Research》2009
Dominance-based Rough Set Approach (DRSA) has been introduced to deal with multiple criteria classification (also called multiple criteria sorting, or ordinal classification with monotonicity constraints), where assignments of objects may be inconsistent with respect to dominance principle. In this paper, we consider an extension of DRSA to the context of imprecise evaluations of objects on condition criteria and imprecise assignments of objects to decision classes. The imprecisions are given in the form of intervals of possible values. In order to solve the problem, we reformulate the dominance principle and introduce second-order rough approximations. The presented methodology preserves well-known properties of rough approximations, such as rough inclusion, complementarity, identity of boundaries and precisiation. Moreover, the meaning of the precisiation property is extended to the considered case. The paper presents also a way to reduce decision tables and to induce decision rules from rough approximations. 相似文献
917.
Yonghui Huang 《Journal of Mathematical Analysis and Applications》2009,359(1):404-140
This paper studies the risk minimization problem in semi-Markov decision processes with denumerable states. The criterion to be optimized is the risk probability (or risk function) that a first passage time to some target set doesn't exceed a threshold value. We first characterize such risk functions and the corresponding optimal value function, and prove that the optimal value function satisfies the optimality equation by using a successive approximation technique. Then, we present some properties of optimal policies, and further give conditions for the existence of optimal policies. In addition, a value iteration algorithm and a policy improvement method for obtaining respectively the optimal value function and optimal policies are developed. Finally, two examples are given to illustrate the value iteration procedure and essential characterization of the risk function. 相似文献
918.
Qiao-Xing Li 《Journal of Mathematical Analysis and Applications》2009,359(2):514-526
A system whose information is partially known and partially unknown is named as a grey system and it is general situation in reality. On the basis of grey number/matrix and their covered operation, some definitions of grey functions are enumerated. Combining grey system theory with traditional dynamic input-output analysis, we propose the grey dynamic input-output analysis. It has two types, i.e., the continuous and the disperse. The most important results are the computational formulas of the matrix-covered set of inverse grey investment coefficient matrix. By using them, we can forecast and control the economic system under the uncertain situation. For the calculation of the matrix-covered set of inverse grey matrices, we obtain the desired formulas, which can be applied to general grey matrices. The formulas can greatly promote the development of grey theory and enrich the applied fields of uncertain mathematics. The modified case illustrates our method. 相似文献
919.
We prove the existence of certain spanning subgraphs of graphs embedded in the torus and the Klein bottle. Matheson and Tarjan proved that a triangulated disc with n vertices can be dominated by a set of no more than n/3 of its vertices and thus, so can any finite graph which triangulates the plane. We use our existence theorems to prove results closely allied to those of Matheson and Tarjan, but for the torus and the Klein bottle. 相似文献
920.
Wiesaw Kubi 《Journal of Mathematical Analysis and Applications》2009,350(2):758-257
A projectional skeleton in a Banach space is a σ-directed family of projections onto separable subspaces, covering the entire space. The class of Banach spaces with projectional skeletons is strictly larger than the class of Plichko spaces (i.e. Banach spaces with a countably norming Markushevich basis). We show that every space with a projectional skeleton has a projectional resolution of the identity and has a norming space with similar properties to Σ-spaces. We characterize the existence of a projectional skeleton in terms of elementary substructures, providing simple proofs of known results concerning weakly compactly generated spaces and Plichko spaces. We prove a preservation result for Plichko Banach spaces, involving transfinite sequences of projections. As a corollary, we show that a Banach space is Plichko if and only if it has a commutative projectional skeleton. 相似文献