全文获取类型
收费全文 | 1409篇 |
免费 | 68篇 |
国内免费 | 64篇 |
专业分类
化学 | 8篇 |
晶体学 | 3篇 |
力学 | 11篇 |
综合类 | 20篇 |
数学 | 1282篇 |
物理学 | 217篇 |
出版年
2024年 | 2篇 |
2023年 | 41篇 |
2022年 | 57篇 |
2021年 | 59篇 |
2020年 | 59篇 |
2019年 | 44篇 |
2018年 | 30篇 |
2017年 | 34篇 |
2016年 | 40篇 |
2015年 | 31篇 |
2014年 | 56篇 |
2013年 | 88篇 |
2012年 | 26篇 |
2011年 | 53篇 |
2010年 | 37篇 |
2009年 | 91篇 |
2008年 | 108篇 |
2007年 | 81篇 |
2006年 | 93篇 |
2005年 | 46篇 |
2004年 | 44篇 |
2003年 | 54篇 |
2002年 | 72篇 |
2001年 | 55篇 |
2000年 | 50篇 |
1999年 | 63篇 |
1998年 | 44篇 |
1997年 | 37篇 |
1996年 | 21篇 |
1995年 | 6篇 |
1994年 | 2篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1991年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有1541条查询结果,搜索用时 828 毫秒
201.
It has been shown by Bogdanova and Boukliev [1] that there exist a ternary [38,5,24] code and a ternary [37,5,23] code. But it is unknown whether or not there exist a ternary [39,6,24] code and a ternary [38,6,23] code. The purpose of this paper is to prove that (1) there is no ternary [39,6,24] code and (2) there is no ternary [38,6,23] code using the nonexistence of ternary [39,6,24] codes. Since it is known (cf. Brouwer and Sloane [2] and Hamada and Watamori [14]) that (i) n3(6,23) = 38> or 39 and d3(38,6) = 22 or 23 and (ii) n3(6,24) = 39 or 40 and d3(39,6) = 23 or 24, this implies that n3(6,23) = 39, d3(38,6) = 22, n3(6,24) = 40 and d3(39,6) = 23, where n3<>(k,d) and d<>3(n,k) denote the smallest value of n and the largest value of d, respectively, for which there exists an [n,k,d] code over the Galois field GF(3). 相似文献
202.
We characterize the finite Veronesean
of all Hermitian varieties of PG(n,q2) as the unique representation of PG(n,q2) in PG(d,q), d n(n+2), where points and lines of PG(n,q2) are represented by points and ovoids of solids, respectively, of PG(d,q), with the only condition that the point set of PG(d,q) corresponding to the point set of PG(n,q2) generates PG(d,q). Using this result for n=2, we show that
is characterized by the following properties: (1)
; (2) each hyperplane of PG(8,q) meets
in q2+1, q3+1 or q3+q2+1 points; (3) each solid of PG(8,q) having at least q+3 points in common with
shares exactly q2+1 points with it.51E24 相似文献
203.
The rank of a q-ary code C is the dimension of the subspace spanned by C. The kernel of a q-ary code C of length n can be defined as the set of all translations leaving C invariant. Some relations between the rank and the dimension of the kernel of q-ary 1-perfect codes, over
as well as over the prime field
, are established. Q-ary 1-perfect codes of length n=(qm − 1)/(q − 1) with different kernel dimensions using switching constructions are constructed and some upper and lower bounds for the dimension of the kernel, once the rank is given, are established.Communicated by: I.F. Blake 相似文献
204.
XOR-based Visual Cryptography Schemes 总被引:2,自引:0,他引:2
P.?TuylsEmail author H.?D.?L.?Hollmann J.?H.?Van?Lint L.?Tolhuizen 《Designs, Codes and Cryptography》2005,37(1):169-186
A recent publication introduced a Visual Crypto (VC) system, based on the polarisation of light. This VC system has goodresolution, contrast and colour properties.Mathematically, the VC system is described by the XOR operation (modulo two addition). In this paper we investigate Threshold Visual Secret Sharing schemes associated to XOR-based VC systems. Firstly, we show that n out of n schemes with optimal resolution and contrast exist, and that (2,n) schemes are equivalent to binary codes. It turns out that these schemes have much better resolution than their OR-based counterparts. Secondly, we provide two explicit constructions for general k out of n schemes. Finally, we derive bounds on the contrast and resolution of XOR-based schemes. It follows from these bounds that for k<n, the contrast is strictly smaller than one. Moreover, the bounds imply that XOR-based k out of n schemes for even k are fundamentally different from those for odd k.AMS Classification: 94A60 相似文献
205.
In this paper we show how to strengthen public-key cryptosystems against known attacks, together with the reduction of the public-key. We use properties of subcodes to mask the structure of the codes used by the conceiver of the system. We propose new parameters for the cryptosystems and even a modified Niederreiter cryptosystem in the case of Gabidulin codes, with a public-key size of less than 4000 bits.Communicated by: P. WildAMS Classification: 11T71 相似文献
206.
This is a first step toward the determination of the parameters of two-point codes on a Hermitian curve. We describe the dimension of such codes and determine the minimum distance of some two-point codes.AMS Classification: 94B27, 14H50, 11T71, 11G20Masaaki Homma - Partially supported by Grant-in-Aid for Scientific Research (15500017), JSPS.Seon Jeong Kim - Partially supported by Korea Research Foundation Grant (KRF-2002-041-C00010). 相似文献
207.
LU ZhiXin YU Li LI Kang LIU BingCan LIN JianGui JIAO RongZhen & YANG BoJun School of Science Beijing University of Posts Telecommunications Beijing China Key Laboratory of Information Photonics Optical Communication Ministry of Education 《中国科学:物理学 力学 天文学(英文版)》2010,(1)
An efficient and practical post-processing technique based on reverse reconciliation for continuous variable quantum key distribution is proposed and simulated with low-density parity check (LDPC) codes. MultiLevel Coding/ MultiStage Decoding, which fully utilizes optimization technique such as vector quantization and iterative decoding and the optimal channel coding most close to the Shannon limit, was used to realize efficient reverse reconciliation algorithm. Simulation results showed that the proposed m... 相似文献
208.
For q = p
m
and m ≥ 1, we construct systematic authentication codes over finite field using Galois rings. We give corrections of the construction of [2]. We generalize corresponding systematic authentication codes of [6] in various ways. 相似文献
209.
We determine the structure of cyclic codes over
for arbitrary even length giving the generator polynomial for these codes. We determine the number of cyclic codes for a
given length. We describe the duals of the cyclic codes, describe the form of cyclic codes that are self-dual and give the
number of these codes. We end by examining specific cases of cyclic codes, giving all cyclic self-dual codes of length less
than or equal to 14.
San Ling - The research of the second named author is partially supported by research Grants MOE-ARF R-146-000-029-112 and
DSTA R-394-000-011-422. 相似文献
210.
《Discrete Mathematics》2018,341(10):2708-2719