全文获取类型
收费全文 | 25183篇 |
免费 | 2584篇 |
国内免费 | 1279篇 |
专业分类
电工技术 | 1556篇 |
技术理论 | 1篇 |
综合类 | 1540篇 |
化学工业 | 3747篇 |
金属工艺 | 1534篇 |
机械仪表 | 1617篇 |
建筑科学 | 1551篇 |
矿业工程 | 661篇 |
能源动力 | 823篇 |
轻工业 | 1994篇 |
水利工程 | 494篇 |
石油天然气 | 803篇 |
武器工业 | 221篇 |
无线电 | 3823篇 |
一般工业技术 | 3369篇 |
冶金工业 | 1226篇 |
原子能技术 | 365篇 |
自动化技术 | 3721篇 |
出版年
2024年 | 151篇 |
2023年 | 447篇 |
2022年 | 889篇 |
2021年 | 1352篇 |
2020年 | 927篇 |
2019年 | 734篇 |
2018年 | 890篇 |
2017年 | 937篇 |
2016年 | 877篇 |
2015年 | 1127篇 |
2014年 | 1549篇 |
2013年 | 1819篇 |
2012年 | 1920篇 |
2011年 | 2066篇 |
2010年 | 1650篇 |
2009年 | 1591篇 |
2008年 | 1615篇 |
2007年 | 1426篇 |
2006年 | 1240篇 |
2005年 | 1042篇 |
2004年 | 710篇 |
2003年 | 552篇 |
2002年 | 518篇 |
2001年 | 429篇 |
2000年 | 355篇 |
1999年 | 283篇 |
1998年 | 370篇 |
1997年 | 226篇 |
1996年 | 209篇 |
1995年 | 199篇 |
1994年 | 159篇 |
1993年 | 151篇 |
1992年 | 90篇 |
1991年 | 73篇 |
1990年 | 59篇 |
1989年 | 51篇 |
1988年 | 38篇 |
1987年 | 51篇 |
1986年 | 31篇 |
1985年 | 26篇 |
1984年 | 29篇 |
1983年 | 25篇 |
1982年 | 25篇 |
1981年 | 16篇 |
1980年 | 27篇 |
1979年 | 9篇 |
1977年 | 11篇 |
1976年 | 16篇 |
1975年 | 10篇 |
1974年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
We propose a new service for digital mobile communication systems. The service enables two or more users to hold a secure conference. Two requirements must be considered: privacy and authentication. Privacy involves ensuring that an eavesdropper cannot intercept the conversations of the parties holding the conference. Authentication involves ensuring that service is not obtained fraudulently in order to avoid usage charges. We present two new conference key distribution schemes for digital mobile communication systems. In these schemes, a group of users can generate a common secret keg over a public channel so that they may hold a secure conference 相似文献
43.
The paper addresses the design of two-level power system stabilizers using an optimal reduced order model whose state variables are torque angles and speeds. The reduced order model retains their physical meaning and is used to design a two-level linear feedback controller that takes into account the realities and constraints of electrical power systems. The two-level control strategy is used, and a global control signal is generated from the output variables to minimize the effect of interactions. The effectiveness of this controller is evaluated and a multimachine system is given as an example to illustrate the advantages of the proposed method. Responses of the system with a two-level scheme and an optimal reduced order scheme are included for comparative analysis. 相似文献
44.
Mathews V.K. Maddox R.L. Fazan P.C. Rosato J. Hwang H. Lee J. 《Electron Device Letters, IEEE》1992,13(12):648-650
Nitrided gate oxides offer several electrical and reliability advantages over conventional oxides and also provide a good barrier against impurity diffusion. Oxidation in nitrous oxide (N2O) has been very successful in overcoming some of the problems associated with nitridation in ammonia. The authors have observed that the extent of N2O oxidation has a strong detrimental effect on the drain leakage current of MOS transistors in the off state. This phenomenon has been identified to be caused by an increase in the active area junction leakage current 相似文献
45.
粉煤灰在混凝土中的作用举足轻重,该文主要从水泥脆性系数、弹性模量、温度、混凝土干缩及徐变等角度,分析了粉煤灰对碾压混凝土的抗裂影响。 相似文献
46.
Hwang H.-K. Lee L.-S. Chen S.-H. 《Selected Areas in Communications, IEEE Journal on》1989,7(9):1450-1461
Multi-H phase-coded modulation (MHPM) is a bandwidth-efficient modulation scheme which offers substantial coding gain over conventional digital modulation schemes. MHPM with asymmetric modulation indices corresponding to the bipolar data +1 and -1 is considered, and numerical results for the minimum Euclidean distances are provided. It is shown that performance improvements on the error probability over conventional MHPM are gained with essentially the same bandwidth and a very slight modification in implementation. The upper bounds on the error probabilities as functions of observation intervals and received E b/N 0 are also investigated in detail. It is concluded that the concept of asymmetric modulation indices for MHPM is attractive for bandwidth and power-efficient modulation 相似文献
47.
信息时代的大学生素质教育是高等院校面临的一项重要任务,本文从素质教育的重要性出发,对大学生思想道德素质、科学文化素质、健康素质,以及创新精神和实践能力等有关方面的内容进行了探讨. 相似文献
48.
This study examines the comfort criteria of ASHRAE Standard 55-2004 for their applicability in hospital environments. Through an extensive field survey conducted in a university hospital in Taiwan, 927 sets of data have been collected. Above half of the measured samples failed to meet the specifications of Standard 55 comfort zone due to improper humidity control. Acceptability votes by patients exceeded the Standard's 80% criterion, regardless of whether the physical conditions were in or out of the comfort zone. Thermal neutrality, preference and comfort range are compared with other studies conducted in office environments and Standard 55 criteria. Results of chi-square tests revealed that patients’ physical strength significantly effected their thermal requirements. The net effect of health yields a marked difference in thermal neutrality and preference, and also in the comfortable temperature range. 相似文献
49.
The popularity regarding wireless communications is such that more and more WAP sites have been developed with wireless markup language (WML). Meanwhile, to translate hypertext markup language (HTML) pages into proper WML ones becomes imperative since it is difficult for WAP users to read most contents designed for PC users via their mobile phone screens. However, for those sites that have been maintained with hypertext markup language (HTML), considerable time and manpower costs will be incurred to rebuild them with WML. In this paper, we propose an intelligent WAP site management system to cope with these problems. With the help of the intelligent management system, the original contents of HTML Web sites can be automatically translated to proper WAP content in an efficient way. As a consequence, the costs associated with maintaining WAP sites could be significantly reduced. The management system also allows the system manager to define the relevance of numerals and keywords for removing unimportant or meaningless contents. The original contents will be reduced and reorganized to fit the size of mobile phone screens, thus reducing the communication cost and enhancing readability. Numerical results gained through various experiments have evinced the effective performance of the WAP management system. 相似文献
50.
Keon Woo Kang Jaemin Ann Hwang Soo Lee 《Electronics letters》1994,30(25):2153-2154
The authors propose a method to estimate the synchronisation offset for orthogonal frequency division multiplexing (OFDM) frame alignment without resort to pilot tones. A decision-directed maximum-likelihood estimation of frame synchronisation offset is derived, and the performance of the proposed scheme is confirmed by computer simulation for QAM systems 相似文献