全文获取类型
收费全文 | 877篇 |
免费 | 21篇 |
国内免费 | 100篇 |
专业分类
化学 | 194篇 |
力学 | 9篇 |
综合类 | 2篇 |
数学 | 729篇 |
物理学 | 64篇 |
出版年
2023年 | 9篇 |
2022年 | 17篇 |
2021年 | 13篇 |
2020年 | 19篇 |
2019年 | 14篇 |
2018年 | 12篇 |
2017年 | 13篇 |
2016年 | 16篇 |
2015年 | 16篇 |
2014年 | 17篇 |
2013年 | 61篇 |
2012年 | 57篇 |
2011年 | 63篇 |
2010年 | 56篇 |
2009年 | 85篇 |
2008年 | 68篇 |
2007年 | 88篇 |
2006年 | 69篇 |
2005年 | 37篇 |
2004年 | 27篇 |
2003年 | 25篇 |
2002年 | 25篇 |
2001年 | 36篇 |
2000年 | 30篇 |
1999年 | 28篇 |
1998年 | 19篇 |
1997年 | 20篇 |
1996年 | 9篇 |
1995年 | 8篇 |
1994年 | 12篇 |
1993年 | 2篇 |
1992年 | 5篇 |
1989年 | 4篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 6篇 |
1984年 | 1篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 1篇 |
排序方式: 共有998条查询结果,搜索用时 15 毫秒
981.
In this paper we develop a network location model that combines the characteristics of ordered median and gradual cover models resulting in the Ordered Gradual Covering Location Problem (OGCLP). The Gradual Cover Location Problem (GCLP) was specifically designed to extend the basic cover objective to capture sensitivity with respect to absolute travel distance. The Ordered Median Location problem is a generalization of most of the classical locations problems like p-median or p-center problems. The OGCLP model provides a unifying structure for the standard location models and allows us to develop objectives sensitive to both relative and absolute customer-to-facility distances. We derive Finite Dominating Sets (FDS) for the one facility case of the OGCLP. Moreover, we present efficient algorithms for determining the FDS and also discuss the conditional case where a certain number of facilities is already assumed to exist and one new facility is to be added. For the multi-facility case we are able to identify a finite set of potential facility locations a priori, which essentially converts the network location model into its discrete counterpart. For the multi-facility discrete OGCLP we discuss several Integer Programming formulations and give computational results. 相似文献
982.
Anisse Kasraoui 《Journal of Combinatorial Theory, Series A》2009,116(3):539-563
[E. Steingrímsson, Statistics on ordered partitions of sets, arXiv: math.CO/0605670] introduced several hard statistics on ordered set partitions and conjectured that their generating functions are related to the q-Stirling numbers of the second kind. In a previous paper, half of these conjectures have been proved by Ishikawa, Kasraoui and Zeng using the transfer-matrix method. In this paper, we shall give bijective proofs of all the conjectures of Steingrímsson. Our basic idea is to encode ordered set partitions by a kind of path diagrams and explore the rich combinatorial properties of the latter structure. As a bonus of our approach, we derive two new σ-partition interpretations of the p,q-Stirling numbers of the second kind introduced by Wachs and White. We also discuss the connections with MacMahon's theorem on the equidistribution of the inversion number and major index on words and give a partition version of his result. 相似文献
983.
Wolfgang A. Schmid 《Journal of Number Theory》2009,129(5):990-999
Text
By a result of G. Freiman and A. Geroldinger [G. Freiman, A. Geroldinger, An addition theorem and its arithmetical application, J. Number Theory 85 (1) (2000) 59-73] it is known that the set of lengths of factorizations of an algebraic integer (in the ring of integers of an algebraic number field), or more generally of an element of a Krull monoid with finite class group, has a certain structure: it is an almost arithmetical multiprogression for whose difference and bound only finitely many values are possible, and these depend just on the class group. We establish a sort of converse to this result, showing that for each choice of finitely many differences and of a bound there exists some number field such that each almost arithmetical multiprogression with one of these difference and that bound is up to shift the set of lengths of an algebraic integer of that number field. Moreover, we give an explicit sufficient condition on the class group of the number field for this to happen.Video
For a video summary of this paper, please visit http://www.youtube.com/watch?v=c61xM-5D6Do. 相似文献984.
Sydney Bulman-Fleming 《Semigroup Forum》2009,78(1):27-33
If S is a monoid, a right S-act A S is a set A, equipped with a “right S-action” A×S→A sending the pair (a,s)∈ A×S to as, that satisfies the conditions (i) a(st)=(as)t and (ii) a1=a for all a∈A and s,t∈S. If, in addition, S is equipped with a compatible partial order and A is a poset, such that the action is monotone (when A×S is equipped with the product order), then A S is called a right S-poset. Left S-acts and S-posets are defined analogously. For a given S-act (resp. S-poset) a tensor product functor A S ?? from left S-acts to sets (resp. left S-posets to posets) exists, and A S is called pullback flat or equalizer flat (resp. subpullback flat or subequalizer flat) if this functor preserves pullbacks or equalizers (resp. subpullbacks or subequalizers). By analogy with the Lazard-Govorov Theorem for R-modules, B. Stenström proved in 1971 that an S-act is isomorphic to a directed colimit of finitely generated free S -acts if and only if it is both pullback flat and equalizer flat. Some 20 years later, the present author showed that, in fact, pullback flatness by itself is sufficient. (A new, more direct proof of that result is contained in the present article.) In 2005, Valdis Laan and the present author obtained a version of the Lazard-Govorov Theorem for S-posets, in which subpullbacks and subequalizers now assume the role previously played by pullbacks and equalizers. The question of whether subpullback flatness implies subequalizer flatness remained unsolved. The present paper provides a negative answer to this question. 相似文献
985.
The study of flatness properties of pomonoids acting on posets was initiated by S.M. Fakhruddin in the 1980s. This work has
recently been continued by various authors (see references). The Rees factor S-posets are investigated in S. Bulman-Fleming, D. Gutermuth, A. Gilmour and M. Kilp, Flatness properties of
S
-posets (Commun. Algebra 34:1291–1317, 2006). In the present article, we investigate the homological classification problems of pomonoids by their Rees factor S-posets.
Supported by Research Supervisor Program of Education Department of Gansu Province (0801-03) and nwnu-kjcxgc-03-51. 相似文献
986.
987.
在四值非线性序集逻辑系统L24中,给出了随机相似度和随机逻辑伪距离的基本性质。然后在随机逻辑度量空间中提出了理论的随机发散度,指出全体原子公式之集在随机逻辑度量空间中未必是全发散的,其是否全发散取决于给定的四值概率分布序列。 相似文献
988.
989.
990.