全文获取类型
收费全文 | 2553篇 |
免费 | 305篇 |
国内免费 | 78篇 |
专业分类
化学 | 48篇 |
晶体学 | 1篇 |
力学 | 250篇 |
综合类 | 26篇 |
数学 | 274篇 |
物理学 | 330篇 |
无线电 | 2007篇 |
出版年
2024年 | 11篇 |
2023年 | 26篇 |
2022年 | 67篇 |
2021年 | 83篇 |
2020年 | 61篇 |
2019年 | 49篇 |
2018年 | 59篇 |
2017年 | 83篇 |
2016年 | 79篇 |
2015年 | 127篇 |
2014年 | 178篇 |
2013年 | 169篇 |
2012年 | 162篇 |
2011年 | 156篇 |
2010年 | 129篇 |
2009年 | 131篇 |
2008年 | 173篇 |
2007年 | 164篇 |
2006年 | 174篇 |
2005年 | 128篇 |
2004年 | 113篇 |
2003年 | 105篇 |
2002年 | 73篇 |
2001年 | 86篇 |
2000年 | 63篇 |
1999年 | 51篇 |
1998年 | 43篇 |
1997年 | 46篇 |
1996年 | 42篇 |
1995年 | 31篇 |
1994年 | 17篇 |
1993年 | 9篇 |
1992年 | 7篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 8篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1957年 | 2篇 |
排序方式: 共有2936条查询结果,搜索用时 31 毫秒
81.
For the low computing speed of reconciliation for current continuous variable quantum key distribution, CPU&GPU-parallel reconciliation algorithms was designed based on LDPC of SEC protocol to speed up decoding computing.In order to raise decoding speed without sacrifice reconciliation efficiency,a static two-way cross linked list to efficiently store large scale sparse parity matrix was employed.The simulation experimental results show that the speed of the decoding rate reaches 16.4 kbit/s when the channel SNR is over 4.9 dB and the reliability of the 2×105continuous variable quantum sequence,with reconciliation efficiency of 91.71%.The experimental based on the Geforce GT 650 MB GPU and the 2.5 GHz and 8 GB memory CPU hardware platform.Relative to the only CPU platform,computing speed increased by more than 15 times. 相似文献
82.
83.
采用显微形貌、微观结构和元素成分分析等物理分析方法,以不同类型的化镍浸金(electroless nickel/immersion gold,ENIG)基板为对象,分析了其焊点在不同情形下的失效模式和失效机理,阐述了"黑盘"缺陷的主要失效特征,研究了具有黑盘缺陷的化镍浸金基板的重工工艺.研究结果显示,Ni层断裂表面单一的高P含量或轻微Ni层腐蚀不能作为黑盘缺陷的唯一依据,已形成良好金属间化合物(intermetallic compound,IMC)层的Ni层腐蚀位置的焊接界面仍具有良好的机械结合强度,采用喷锡工艺(hot air solder level,HASL)对具有黑盘缺陷的化镍浸金基板进行重新处理切实可行. 相似文献
84.
A new and efficient class of nonlinear receivers is introduced for digital communication systems. These iterated-decision receivers use optimized multipass algorithms to successively cancel interference from a block of received data and generate symbol decisions whose reliability increases monotonically with each iteration. Two variants of such receivers are discussed: the iterated-decision equalizer and the iterated-decision multiuser detector. Iterated-decision equalizers, designed to equalize intersymbol interference (ISI) channels, asymptotically achieve the performance of maximum-likelihood sequence detection (MLSD), but only have a computational complexity on the order of a linear equalizer (LE). Even more importantly, unlike the decision-feedback equalizer (DFE), iterated-decision equalizers can be readily used in conjunction with error-control coding. Similarly, iterated-decision multiuser detectors, designed to cancel multiple-access interference (MAI) in typical wireless environments, approach the performance of the optimum multiuser detector in uncoded systems with a computational complexity comparable to a decorrelating detector or a linear minimum mean-square error (MMSE) multiuser detector. 相似文献
85.
Eero Hyry 《Compositio Mathematica》2002,130(3):319-343
Let A be a local ring, and let I
1,...,I
r
A be ideals of positive height. In this article we compare the Cohen–Macaulay property of the multi–Rees algebra R
A
(I
1,...,I
r
) to that of the usual Rees algebra R
A
(I
1 ··· I
r
) of the product I
1 ··· I
r
. In particular, when the analytic spread of I
1 ··· I
r
is small, this leads to necessary and sufficient conditions for the Cohen–Macaulayness of R
A
(I
1,...,I
r
). We apply our results to the theory of joint reductions and mixed multiplicities. 相似文献
86.
Starting with an initial vector λ = (λ(κ))κ∈z ∈ ep(Z), the subdivision scheme generates asequence (Snaλ)∞n=1 of vectors by the subdivision operator Saλ(κ) = ∑λ(j)a(k - 2j), k ∈ Z. j∈zSubdivision schemes play an important role in computer graphics and wavelet analysis. It is very interesting tounderstand under what conditions the sequence (Snaλ)∞n=1 converges to an Lp-function in an appropriate sense.This problem has been studied extensively. In this paper we show that the subdivision scheme converges forany initial vector in ep(Z) provided that it does for one nonzero vector in that space. Moreover, if the integertranslates of the refinable function are stable, the smoothness of the limit function corresponding to the vectorλ is also independent of λ. 相似文献
87.
JIN Yi-dan WU Wei-ling School of Information Engineering Beijing University of Posts Telecommunications Beijing China ZHANG Feng Institue of China Mobile Beijing China 《中国邮电高校学报(英文版)》2006,13(4):24-28
1 Introduction Recently space–time coding (STC) techniques [1] are designed to combat fading in wireless links by utilizing multiple antenna systems, in which transmit diversity and coding gains can be exploited without sacrificing additional power and b… 相似文献
88.
Soft-Decision Decoding of Punctured Convolutional Codes in Asynchronous-CDMA Communications Under Perfect Phase-Tracking Conditions 总被引:1,自引:0,他引:1
Vidhyacharan Bhaskar 《International Journal of Wireless Information Networks》2006,13(3):229-237
In this paper, the performance of punctured convolutional codes of short constraint lengths is discussed. The punctured codes are used to provide error protection to a particular user in an asynchronous CDMA system. A perfect phase reference is assumed to be available throughout this paper. A slow fading Rician channel is assumed. Maximum likelihood decoding through a Viterbi algorithm is used to decode the information symbols. Soft-decision decoding of punctured convolutional codes is considered in this paper. The upper bounds with Viterbi decoding are derived and plotted for the various punctured codes considered. The simulated results are found to agree very well with their upper and lower bounds. 相似文献
89.
90.
主要研究卫星通信协议IESS 309协议中的系统卷积码的编码及其序列译码的计算机模拟。用C语言实现了码率为1/2的36位的系统卷积码的编码,然后模拟高斯噪声信道生成一个Fano度量表,最后用Fano算法实现该卷积码的软判决序列译码,并进行了性能分析,为以后的工程应用打下一个良好的基础。 相似文献