全文获取类型
收费全文 | 2720篇 |
免费 | 210篇 |
国内免费 | 153篇 |
专业分类
化学 | 314篇 |
晶体学 | 1篇 |
力学 | 114篇 |
综合类 | 79篇 |
数学 | 2087篇 |
物理学 | 488篇 |
出版年
2024年 | 5篇 |
2023年 | 31篇 |
2022年 | 90篇 |
2021年 | 75篇 |
2020年 | 81篇 |
2019年 | 73篇 |
2018年 | 68篇 |
2017年 | 83篇 |
2016年 | 85篇 |
2015年 | 67篇 |
2014年 | 106篇 |
2013年 | 188篇 |
2012年 | 106篇 |
2011年 | 119篇 |
2010年 | 136篇 |
2009年 | 167篇 |
2008年 | 180篇 |
2007年 | 172篇 |
2006年 | 155篇 |
2005年 | 101篇 |
2004年 | 119篇 |
2003年 | 121篇 |
2002年 | 93篇 |
2001年 | 100篇 |
2000年 | 88篇 |
1999年 | 74篇 |
1998年 | 68篇 |
1997年 | 48篇 |
1996年 | 43篇 |
1995年 | 26篇 |
1994年 | 30篇 |
1993年 | 20篇 |
1992年 | 23篇 |
1991年 | 18篇 |
1990年 | 18篇 |
1989年 | 10篇 |
1988年 | 6篇 |
1987年 | 9篇 |
1986年 | 11篇 |
1985年 | 11篇 |
1984年 | 13篇 |
1983年 | 2篇 |
1982年 | 13篇 |
1981年 | 6篇 |
1980年 | 11篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1973年 | 2篇 |
1971年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有3083条查询结果,搜索用时 0 毫秒
1.
2.
Searching in trees 总被引:1,自引:0,他引:1
Frank Recker 《Discrete Applied Mathematics》2004,140(1-3):169-183
In (Discrete Math. 17 (1977)181) Rivest introduced the search complexity of binary trees and proved that among all binary trees with a fixed search complexity the smallest ones are the so-called Fibonacci trees. This result is extended for q-trees. The structure of the smallest q-trees is again Fibonacci-like but more complicated than in the binary case. In addition an upper bound for the asymptotic growth of these trees is given. 相似文献
3.
In this paper, we study the stability conditions of the MMAP[K]/G[K]/1/LCFS preemptive repeat queue. We introduce an embedded Markov chain of matrix M/G/1 type with a tree structure and identify conditions for the Markov chain to be ergodic. First, we present three conventional methods for the stability problem of the queueing system of interest. These methods are either computationally demanding or do not provide accurate information for system stability. Then we introduce a novel approach that develops two linear programs whose solutions provide sufficient conditions for stability or instability of the queueing system. The new approach is numerically efficient. The advantages and disadvantages of the methods introduced in this paper are analyzed both theoretically and numerically. 相似文献
4.
5.
应用七级目测法对浙江中部地区27个夏熟作物田样点的杂草进行了优势等级调查,将所得数据转换成重要值,以杂草在27个样点中的重要值为运算指标,应用主成分分析法和图论聚类中的最小生成树法,对24种杂草的生态学相似性进行了比较,指出了长期使用单一的除草剂导致农田杂草种群迅速更迭的原因:杂草对除草剂的敏感性差异及不同杂草间的生态学特性的差异。 相似文献
6.
Bounds are given on the size of the parameter-space decomposition induced by multiple sequence alignment problems where phylogenetic information may be given or inferred. It is shown that many of the usual formulations of these problems fall within the same integer parametric framework, implying that the number of distinct optima obtained as the parameters are varied across their ranges is polynomially bounded in the length and number of sequences. 相似文献
7.
Alexander Zimmermann 《Algebras and Representation Theory》2004,7(1):19-34
In an earlier paper, Raphaël Rouquier and the author introduced the group of self-equivalences of a derived category. In the case of a Brauer tree algebra, we determined a nontrivial homomorphism of the Artin braid group to this group of self-equivalences. The class of Brauer tree algebras include blocks of finite group rings over a large enough field with cyclic defect groups. In the present paper we give an integral version of this homomorphism. Moreover, we identify some interesting arithmetic subgroups with natural groups of self-equivalences of the derived category. 相似文献
8.
Marco Pretti 《Journal of statistical physics》2003,111(3-4):993-1015
In this article we deal with the variational approach to cactus trees (Husimi trees) and the more common recursive approach, that are in principle equivalent for finite systems. We discuss in detail the conditions under which the two methods are equivalent also in the analysis of infinite (self-similar) cactus trees, usually investigated to the purpose of approximating ordinary lattice systems. Such issue is hardly ever considered in the literature. We show (on significant test models) that the phase diagram and the thermodynamic quantities computed by the variational method, when they deviates from the exact bulk properties of the cactus system, generally provide a better approximation to the behavior of a corresponding ordinary system. Generalizing a property proved by Kikuchi, we also show that the numerical algorithm usually employed to perform the free energy minimization in the variational approach is always convergent. 相似文献
9.
David M. Evans 《组合设计杂志》2004,12(6):459-465
For all ‘reasonable’ finite t, k, and s, we construct a t‐(?0, k, 1) design and a group of automorphisms which is transitive on blocks and has s orbits on points. In particular, there is a 2‐(?0, 4, 1) design with a block‐transitive group of automorphisms having two point orbits. This answers a question of P. J. Cameron and C. E. Praeger. The construction is presented in a purely combinatorial way, but is a by‐product of a new way of looking at a model‐theoretic construction of E. Hrushovski. © 2004 Wiley Periodicals, Inc. 相似文献
10.