全文获取类型
收费全文 | 7806篇 |
免费 | 667篇 |
国内免费 | 518篇 |
专业分类
化学 | 2285篇 |
晶体学 | 27篇 |
力学 | 680篇 |
综合类 | 125篇 |
数学 | 4113篇 |
物理学 | 1761篇 |
出版年
2024年 | 14篇 |
2023年 | 91篇 |
2022年 | 134篇 |
2021年 | 141篇 |
2020年 | 202篇 |
2019年 | 178篇 |
2018年 | 176篇 |
2017年 | 207篇 |
2016年 | 211篇 |
2015年 | 184篇 |
2014年 | 293篇 |
2013年 | 433篇 |
2012年 | 277篇 |
2011年 | 326篇 |
2010年 | 338篇 |
2009年 | 427篇 |
2008年 | 522篇 |
2007年 | 522篇 |
2006年 | 465篇 |
2005年 | 390篇 |
2004年 | 294篇 |
2003年 | 320篇 |
2002年 | 423篇 |
2001年 | 292篇 |
2000年 | 245篇 |
1999年 | 245篇 |
1998年 | 248篇 |
1997年 | 173篇 |
1996年 | 185篇 |
1995年 | 150篇 |
1994年 | 116篇 |
1993年 | 115篇 |
1992年 | 93篇 |
1991年 | 78篇 |
1990年 | 48篇 |
1989年 | 43篇 |
1988年 | 41篇 |
1987年 | 41篇 |
1986年 | 40篇 |
1985年 | 42篇 |
1984年 | 32篇 |
1983年 | 19篇 |
1982年 | 36篇 |
1981年 | 40篇 |
1980年 | 23篇 |
1979年 | 26篇 |
1978年 | 19篇 |
1977年 | 6篇 |
1976年 | 9篇 |
1973年 | 6篇 |
排序方式: 共有8991条查询结果,搜索用时 15 毫秒
31.
We give a Gray code and constant average time generating algorithm for derangements, i.e., permutations with no fixed points. In our Gray code, each derangement is transformed into its successor either via one or two transpositions or a rotation of three elements. We generalize these results to permutations with number of fixed points bounded between two constants. 相似文献
32.
多小波子空间上的单小波表示 总被引:1,自引:0,他引:1
本文在较弱的条件下,建立了2重多小波子空间与单小波子空间的关系.即由2重多小波构造出单小波.一方面,这种单小波的平移伸缩与2重多小波的平移伸缩生成的子空间是完全相同的;另一方面,它具有插值性.因此通过构造出的单小波建立了多小波子空间上的Shannon型采样定理. 相似文献
33.
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
34.
工程施工中运输网络优化方案 总被引:5,自引:0,他引:5
施工工地运输方案的优化设计可以归结为 :按施工期要求设计运输线路或验证已有线路通行能力 ,计算总线路中影响提高流量的关键路段 ,取得最小费用最大流 .本文运用图论理论这一数学工具把实际问题抽象为有向网络 ,进而建立数学模型 .此方法理论上严密 ,解题步聚直观清晰 ,对水利、公路、水路、铁路等其它运输系统有普遍意义 . 相似文献
35.
Mean value in invexity analysis 总被引:1,自引:0,他引:1
In this paper, a generalization of the mean value theorem is considered in the case of functions defined on an invex set with respect to η (which is not necessarily connected). 相似文献
36.
Tsonka Stefanova Baicheva 《Designs, Codes and Cryptography》1998,13(3):223-227
The covering radius of all ternary cyclic codes of length up to 25 is given. Some of the results were obtained by computer
and for others mathematical reasonings were applied. The minimal distances of all codes were recalculated. 相似文献
37.
1 Introduction Moderndigitalcommunicationsystemsoftenrequireerror freetransmission .Errorcontrolcodingtechnologyhasbeenusedwidelyincommunicationsystem .Andithasbeenimprovingtheperformanceofcommunicationsystem greatly ,especiallyinwirelesscommunicationss… 相似文献
38.
Fusion-evaporation cross-sections for the α-induced reactions upon197Au,193Ir,191Ir,185Re,181Ta,121Sb and69Ga nuclei at bombarding energies near the Coulomb barrier have been measured by off-line observation of the γ-rays emitted
in the radioactive decay of the residual nuclei using stacked foil technique. The total fusion cross-section for the systems
have been compared with simple statistical model calculations using the code ALICE/91 as well as with the coupled channel
calculations that include the β2 and ν4 slatic deformations and dynamic couplings of the vibrational/rotational states of the target and the projet tile using the
code CCDEF. 相似文献
39.
Recently extremal double circulant self-dual codes have been classified for lengths n ≤ 62. In this paper, a complete classification
of extremal double circulant self-dual codes of lengths 64 to 72 is presented. Almost all of the extremal double circulant
singly-even codes given have weight enumerators for which extremal codes were not previously known to exist. 相似文献
40.
Ross Anderson Cunsheng Ding Tor Helleseth Torleiv Klove 《Designs, Codes and Cryptography》1998,15(2):111-124
Previous researchers have designed shared control schemes with a view to minimising the likelihood that participants will conspire to perform an unauthorised act. But, human nature being what it is, systems inevitably fail; so shared control schemes should also be designed so that the police can identify conspirators after the fact. This requirement leads us to search for schemes with sparse access structures. We show how this can be done using ideas from coding theory. In particular, secret sharing schemes based on geometric codes whose dual [n,k,d] codes have d and n as their only nonzero weights are suitable. We determine their access structures and analyse their properties. We have found almost all of them, and established some relations among codes, designs and secret-sharing schemes. 相似文献