全文获取类型
收费全文 | 1060篇 |
免费 | 56篇 |
国内免费 | 97篇 |
专业分类
化学 | 93篇 |
晶体学 | 2篇 |
力学 | 74篇 |
综合类 | 20篇 |
数学 | 700篇 |
物理学 | 208篇 |
无线电 | 116篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 19篇 |
2021年 | 22篇 |
2020年 | 19篇 |
2019年 | 26篇 |
2018年 | 23篇 |
2017年 | 30篇 |
2016年 | 11篇 |
2015年 | 22篇 |
2014年 | 33篇 |
2013年 | 114篇 |
2012年 | 38篇 |
2011年 | 43篇 |
2010年 | 41篇 |
2009年 | 54篇 |
2008年 | 69篇 |
2007年 | 64篇 |
2006年 | 58篇 |
2005年 | 81篇 |
2004年 | 47篇 |
2003年 | 53篇 |
2002年 | 60篇 |
2001年 | 37篇 |
2000年 | 30篇 |
1999年 | 33篇 |
1998年 | 28篇 |
1997年 | 23篇 |
1996年 | 19篇 |
1995年 | 21篇 |
1994年 | 13篇 |
1993年 | 13篇 |
1992年 | 10篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有1213条查询结果,搜索用时 913 毫秒
1.
2.
An oriented tetrahedron defined on four vertices is a set of four cyclic triples with the property that any ordered pair of vertices is contained in exactly one of the cyclic triples. A tetrahedral quadruple system of order with index , denoted by , is a pair , where is an ‐set and is a set of oriented tetrahedra (blocks) such that every cyclic triple on is contained in exactly members of . A is pure if there do not exist two blocks with the same vertex set. When , the spectrum of a pure TQS has been completely determined by Ji. In this paper, we show that there exists a pure if and only if and . A corollary is that a simple also exists if and only if and . 相似文献
3.
A (w,r) cover‐free family is a family of subsets of a finite set such that no intersection of w members of the family is covered by a union of r others. A (w,r) superimposed code is the incidence matrix of such a family. Such a family also arises in cryptography as the concept of key distribution pattern. In the present paper, we give some new results on superimposed codes. First we construct superimposed codes from super‐simple designs which give us results better than superimposed codes constructed by other known methods. Next we prove the uniqueness of the (1,2) superimposed code of size 9 × 12, the (2,2) superimposed code of size 14 × 8, and the (2,3) superimposed code of size 30 × 10. Finally, we improve numerical values of upper bounds for the asymptotic rate of some (w,r) superimposed codes. © 2004 Wiley Periodicals, Inc. 相似文献
4.
We show that the LF-algebra considered by Akkar and Nacir in [1] is topologically simple. 相似文献
5.
Cao H. P. Chen G. Grechkoseeva M. A. Mazurov V. D. Shi W. J. Vasil'ev A. V. 《Siberian Mathematical Journal》2004,45(6):1031-1035
The spectrum of a finite group is the set of its element orders. A finite group G is said to be recognizable by spectrum, if every finite group with the same spectrum as G is isomorphic to G. The purpose of the paper is to prove that for every natural m the finite simple Chevalley group F
4(2
m
) is recognizable by spectrum. 相似文献
6.
7.
Wujie Shi 《Frontiers of Mathematics in China》2007,2(1):123-125
Let G be a finite group, and let π
e
(G) be the set of all element orders of G. In this short paper we prove that π
e
(B
n
(q)) ≠ π
e
(C
n
(q)) for all odd q.
相似文献
8.
9.
用线性插值法求单摆运动周期的近似解 总被引:6,自引:1,他引:5
利用线性插值的方法,提出了一个任意摆角条件下的单摆运动周期的近似公式.并利用Mathematica软件将该公式与精确解进行了比较,还与其他近似公式进行了对比.结果表明,该公式的近似程度相当好. 相似文献
10.
We present a Bayesian theory of object identification. Here, identifying an object means selecting a particular observation from a group of observations (variants), this observation (the regular variant) being characterized by a distributional model. In this sense, object identification means assigning a given model to one of several observations. Often, it is the statistical model of the regular variant, only, that is known. We study an estimator which relies essentially on this model and not on the characteristics of the “irregular” variants. In particular, we investigate under what conditions this variant selector is optimal. It turns out that there is a close relationship with exchangeability and Markovian reversibility. We finally apply our theory to the case of irregular variants generated from the regular variant by a Gaussian linear model. 相似文献