全文获取类型
收费全文 | 1948篇 |
免费 | 187篇 |
国内免费 | 111篇 |
专业分类
化学 | 169篇 |
晶体学 | 1篇 |
力学 | 78篇 |
综合类 | 41篇 |
数学 | 1379篇 |
物理学 | 578篇 |
出版年
2024年 | 3篇 |
2023年 | 35篇 |
2022年 | 68篇 |
2021年 | 58篇 |
2020年 | 75篇 |
2019年 | 68篇 |
2018年 | 63篇 |
2017年 | 66篇 |
2016年 | 64篇 |
2015年 | 45篇 |
2014年 | 87篇 |
2013年 | 274篇 |
2012年 | 63篇 |
2011年 | 95篇 |
2010年 | 67篇 |
2009年 | 116篇 |
2008年 | 138篇 |
2007年 | 112篇 |
2006年 | 123篇 |
2005年 | 93篇 |
2004年 | 93篇 |
2003年 | 53篇 |
2002年 | 62篇 |
2001年 | 66篇 |
2000年 | 40篇 |
1999年 | 53篇 |
1998年 | 32篇 |
1997年 | 24篇 |
1996年 | 21篇 |
1995年 | 12篇 |
1994年 | 19篇 |
1993年 | 7篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1990年 | 7篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1971年 | 2篇 |
1969年 | 1篇 |
排序方式: 共有2246条查询结果,搜索用时 15 毫秒
71.
72.
In present times, barcode decoders on mobile phones can extract the data content of QR codes. However, this convenience raises concerns about security issues when using QR codes to transmit confidential information, such as e-tickets, coupons, and other private data. Moreover, current secret hiding techniques are unsuitable for QR code applications since QR codes are module-oriented, which is different from the pixel-oriented hiding manner. In this article, we propose an algorithm to conceal confidential information by changing the modules of the QR Code. This new scheme designs the triple module groups based on the concept of the error correction capability. Additionally, this manner can conceal two secret bits by changing only one module, and the amount of hidden confidential information can be twice the original amount. As a result, the ordinary data content (such as URL) can be extracted correctly from the generated QR code by any barcode decoders, which does not affect the readability of scanning. Furthermore, only authorized users with the secret key can further extract the concealed confidential information. This designed scheme can provide secure and reliable applications for the QR system. 相似文献
73.
The minimum number of rows in covering arrays (equivalently, surjective codes) and radius-covering arrays (equivalently, surjective codes with a radius) has been determined precisely only in special cases. In this paper, explicit constructions for numerous best known covering arrays (upper bounds) are found by a combination of combinatorial and computational methods. For radius-covering arrays, explicit constructions from covering codes are developed. Lower bounds are improved upon using connections to orthogonal arrays, partition matrices, and covering codes, and in specific cases by computation. Consequently for some parameter sets the minimum size of a covering array is determined precisely. For some of these, a complete classification of all inequivalent covering arrays is determined, again using computational techniques. Existence tables for up to 10 columns, up to 8 symbols, and all possible strengths are presented to report the best current lower and upper bounds, and classifications of inequivalent arrays. 相似文献
74.
Thái Hoàng Lê 《Journal of Number Theory》2010,130(8):1705-1717
Intersective polynomials are polynomials in Z[x] having roots every modulus. For example, P1(n)=n2 and P2(n)=n2−1 are intersective polynomials, but P3(n)=n2+1 is not. The purpose of this note is to deduce, using results of Green and Tao (2006) [8] and Lucier (2006) [16], that for any intersective polynomial h, inside any subset of positive relative density of the primes, we can find distinct primes p1,p2 such that p1−p2=h(n) for some integer n. Such a conclusion also holds in the Chen primes (where by a Chen prime we mean a prime number p such that p+2 is the product of at most 2 primes). 相似文献
75.
本设计为一种便携式条形码阅读译码器(简称阅读器),它采用INTEL8031CPU微处理器为主芯片,辅以其它大规模集成电路芯片,构成一智能化系统,阅读及识别采用Code39码编制的条形码,并能完成条形码信息的存储、数目统计及与微机进行串行通信功能。 相似文献
76.
Xiang-dong Hou 《Journal of Combinatorial Theory, Series A》2007,114(3):522-544
Let Ψn be the number of inequivalent self-dual codes in . We prove that , where . Let Δn be the number of inequivalent doubly even self-dual codes in . We also prove that . 相似文献
77.
A. R. Nasr-Isfahani 《代数通讯》2013,41(11):4461-4469
For a ring R, endomorphism α of R and positive integer n we define a skew triangular matrix ring T n (R, α). By using an ideal theory of a skew triangular matrix ring T n (R, α) we can determine prime, primitive, maximal ideals and radicals of the ring R[x; α]/ ? x n ?, for each positive integer n, where R[x; α] is the skew polynomial ring, and ? x n ? is the ideal generated by x n . 相似文献
80.
Harvey Dubner. 《Mathematics of Computation》2002,71(238):833-835
The Repunit R is a probable prime. In order to prove primality R49080 must be approximately 33.3% factored. The status of this factorization is included.