全文获取类型
收费全文 | 5541篇 |
免费 | 351篇 |
国内免费 | 299篇 |
专业分类
电工技术 | 263篇 |
综合类 | 673篇 |
化学工业 | 33篇 |
金属工艺 | 6篇 |
机械仪表 | 87篇 |
建筑科学 | 37篇 |
矿业工程 | 54篇 |
能源动力 | 8篇 |
轻工业 | 10篇 |
水利工程 | 25篇 |
石油天然气 | 8篇 |
武器工业 | 19篇 |
无线电 | 3637篇 |
一般工业技术 | 145篇 |
冶金工业 | 45篇 |
原子能技术 | 4篇 |
自动化技术 | 1137篇 |
出版年
2024年 | 6篇 |
2023年 | 23篇 |
2022年 | 28篇 |
2021年 | 48篇 |
2020年 | 77篇 |
2019年 | 48篇 |
2018年 | 58篇 |
2017年 | 66篇 |
2016年 | 77篇 |
2015年 | 110篇 |
2014年 | 244篇 |
2013年 | 238篇 |
2012年 | 300篇 |
2011年 | 371篇 |
2010年 | 309篇 |
2009年 | 422篇 |
2008年 | 386篇 |
2007年 | 394篇 |
2006年 | 399篇 |
2005年 | 346篇 |
2004年 | 285篇 |
2003年 | 365篇 |
2002年 | 319篇 |
2001年 | 251篇 |
2000年 | 215篇 |
1999年 | 158篇 |
1998年 | 132篇 |
1997年 | 112篇 |
1996年 | 101篇 |
1995年 | 78篇 |
1994年 | 45篇 |
1993年 | 12篇 |
1992年 | 9篇 |
1991年 | 11篇 |
1990年 | 20篇 |
1989年 | 16篇 |
1988年 | 12篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 10篇 |
1984年 | 13篇 |
1983年 | 12篇 |
1982年 | 17篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1964年 | 6篇 |
1961年 | 3篇 |
1960年 | 3篇 |
排序方式: 共有6191条查询结果,搜索用时 15 毫秒
31.
有近20年历史的爱立信AXE10交换机在信息时代到来之际再放异彩,目前,它作为公共平台广泛应用于PSTN、ISDN、IN,PLMN、信令网和商务通信等。 相似文献
32.
首先从CDMA1X网络结构进行详细分析,引出CDMA1X网络安全风险分析。根据网络安全原理,联系江西联通现在CDMA1X网络结构,采取对每层安全进行预防,提出较详细的网络安全解决方案,最后对现网进行安全评估。 相似文献
33.
本文提出了一种宽线性共轭梯度算法,分析了算法在均值意义下的收敛性,并给出了算法稳定条件。仿真表明,新算法应用于码分多址系统多址干扰抑制时的性能优于Yin(2003)及Schober(2004)所提出的算法。 相似文献
34.
Paulo S. André António L. Teixeira Armando N. Pinto Lara P. Pellegrino Berta B. Neto José F. Rocha Joäo L. Pinto Paulo N. Monteiro 《ETRI Journal》2006,28(2):257-259
In this letter, we will evaluate the performance degradation of a 40 km high‐speed (40 Gb/s) optical system, induced by optical fiber variations of the chromatic dispersion induced by temperature changes. The chromatic dispersion temperature sensitivity will be estimated based on the signal quality parameters. 相似文献
35.
36.
Costas Chaikalis 《Wireless Personal Communications》2007,41(1):77-97
Reconfiguration concept represents reconfigurable functionalities of the radio interface for mobile radio systems. Particularly
for the physical layer, some possible reconfigurable architectures can be identified. We focus on outer interleaving for turbo
codes, which can improve their performance in flat Rayleigh fading environment. The larger the number of columns in the outer
interleaver, the better is the performance, but with the penalty of more complexity and delay. Furthermore, an incorrect choice
of the number of columns can increase the bit and frame error rates. Therefore, it would be advantageous to reconfigure the
outer interleaver in different operating environments with the optimum number of columns. Using two different data frame lengths,
in this contribution simulation results are presented for the four possible outer block interleaver configurations specified
for the 3GPP mobile standard in the case of flat Rayleigh fading channel. It is shown that different operating environments
require an optimum number of columns in terms of bit error rate and frame error rate performance. Finally, frame fade duration
is considered and the effect of the product of the Doppler frequency with the frame duration on the performance for the four
different 3GPP outer block interleaver configurations is discussed.
Costas Chaikalis was born in Athens, Greece, on March 7, 1973. He received the B.Sc. degree in electrical engineering in 1995 from Technological
Educational Institute of Lamia, Greece. He also received the M.Sc. and Ph.D. degrees from Department of Electronics and Telecommunications,
University of Bradford, Bradford, UK in 1999 and 2003, respectively. During his doctoral studies he worked as a Research Assistant
for Mobile Virtual Center of Excellence (Mobile VCE), Terminals Group, UK. Since 2003, he is a lecturer in the Department
of Electrical Engineering, Technological Educational Institute of Lamia, Greece. His research interests are in all areas of
mobile communications but especially in forward error correction coding, reconfigurable (software radio) architectures, cross
layer architectures and DSP applications. 相似文献
37.
Huayi Wu Xiaohua Jia Yanxiang He Chuanhe Huang 《International Journal of Communication Systems》2005,18(9):803-816
This paper investigates the issues of QoS routing in CDMA/TDMA ad hoc networks. Since the available bandwidth is very limited in ad hoc networks, a QoS request between two nodes will be blocked if there does not exist a path that can meet the QoS requirements, even though there is enough free bandwidth in the whole system. In this paper, we propose a new scheme of using multiple paths between two nodes as the route for a QoS call. The aggregate bandwidth of the multiple paths can meet the bandwidth requirement of the call and the delays of these paths are within the required bound of the call. We also propose three strategies by which to choose a set of paths as the route, namely, shortest path first (SPF), largest bandwidth first (LBF), and largest hop‐bandwidth first (LHBF). Extensive simulations have been conducted to evaluate the performance of the three strategies in comparison with a traditional single path routing algorithm. The simulation results show that the proposed multiple paths routing scheme significantly reduces the system blocking rates in various network environments, especially when the network load is heavy. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
38.
中国光纤通信技术的研究、应用和发展 总被引:1,自引:0,他引:1
主要从光纤光缆、光器件与组件、光传输设备与系统、光网络建设等方面论述光纤通信技术在我国的研究、应用发展历程,并对我国光纤通信技术的未来发展进行展望。 相似文献
39.
分析了现有移动通信网络存在的问题,阐述了第2代移动通信核心网向第3代移动通信核心网演进的必然性:讨论了第2代移动通信核心网向第3代移动通信核心网演进所采用的演进策略,介绍了两种可供选择的全IP核心网络的参考结构。 相似文献
40.