全文获取类型
收费全文 | 9839篇 |
免费 | 1886篇 |
国内免费 | 383篇 |
专业分类
电工技术 | 359篇 |
综合类 | 968篇 |
化学工业 | 253篇 |
金属工艺 | 30篇 |
机械仪表 | 562篇 |
建筑科学 | 280篇 |
矿业工程 | 41篇 |
能源动力 | 58篇 |
轻工业 | 680篇 |
水利工程 | 131篇 |
石油天然气 | 39篇 |
武器工业 | 215篇 |
无线电 | 5886篇 |
一般工业技术 | 374篇 |
冶金工业 | 212篇 |
原子能技术 | 54篇 |
自动化技术 | 1966篇 |
出版年
2024年 | 67篇 |
2023年 | 221篇 |
2022年 | 333篇 |
2021年 | 326篇 |
2020年 | 467篇 |
2019年 | 510篇 |
2018年 | 418篇 |
2017年 | 433篇 |
2016年 | 412篇 |
2015年 | 512篇 |
2014年 | 685篇 |
2013年 | 629篇 |
2012年 | 837篇 |
2011年 | 830篇 |
2010年 | 670篇 |
2009年 | 640篇 |
2008年 | 575篇 |
2007年 | 703篇 |
2006年 | 548篇 |
2005年 | 410篇 |
2004年 | 382篇 |
2003年 | 333篇 |
2002年 | 283篇 |
2001年 | 200篇 |
2000年 | 142篇 |
1999年 | 100篇 |
1998年 | 68篇 |
1997年 | 64篇 |
1996年 | 65篇 |
1995年 | 72篇 |
1994年 | 43篇 |
1993年 | 26篇 |
1992年 | 22篇 |
1991年 | 19篇 |
1990年 | 19篇 |
1989年 | 10篇 |
1988年 | 14篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1972年 | 1篇 |
1963年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 500 毫秒
21.
22.
改进型遗传算法在加载天线设计中的运用 总被引:5,自引:2,他引:3
遗传算法是一种全新的优化搜索方法,可以用来解决各种复杂的实际问题。针对简单型遗传算法的一些不足之处,介绍了一种改进型的遗传算法,并阐述了其在短波宽带集总加载天线优化设计中的运用。 相似文献
23.
An adaptive antenna array is incorporated into a decorrelatingmulti-user detector to effectively increase the DS-CDMA system capacity.Capacity improvement is due to beamforming gain, spatial diversity gain(assuming large angle spread), and the decorrelating effect. Thereceiver has been analyzed for the cases of sufficiently andinsufficiently spaced receiving antennas. The receiver consists of afront-end beamformer for every user in the cell and has knowledge of allusers' signature sequences. The beamformer estimates the desired userchannel vector, enhancing its signal and reducing the co-channelinterference from other directions. The multi-user detection, exploitingknowledge of other users, rejects those interferers whose arrival anglesare close to that of the desired user. The average uncoded Bit ErrorRate (BER) as a function of the number of in-beam active users, theaverage antenna Signal-to-Noise Ratio (SNR), and the number of receivingantennas is examined in both single-path and multi-path Rayleigh fadingchannels. Analysis shows an increase in system capacity proportional tothe number of receiving antennas. 相似文献
24.
本文从小卫星、星座飞速发展以及对测控通信系统新的要求出发,介绍了综合基带、连续波多波束相控阵天线的功能、特点及工作原理,提出了建立新型多功能智能化测控通信站的设想。 相似文献
25.
26.
Finkel Melinda J.; Storaasli Ragnar D.; Bandele Anthony; Schaefer Vivian 《Canadian Metallurgical Quarterly》2003,34(5):555
How can psychologists and graduate students become more affirmative of lesbian, gay, bisexual, and transgender (LGBT) issues? Safe Zone is a diversity-training program to increase sensitivity toward, knowledge of, and advocacy for LGBT populations and issues that affect them. In this exploratory study, the implementation of Safe Zone is described within a school of professional psychology; its effectiveness was assessed by self-reported behavioral and attitudinal changes and from participant evaluations. Results were encouraging with regard to the goals of Safe Zone and its adaptation to institutions interested in improving relations with the LGBT community, but additional empirical studies are needed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
27.
本文提出一种多输入多输出(MIMO)天线系统中简单的扩展空时块编码(SSTBC)分集技术,采用沃尔什码来区分各天线发送数据子流。采用这种方法,在系统带宽一定时,不降低发送信息速率,同时接收机简单。不同天线的发送信息经过了所有收一发天线对之间的空间子信道,获得了所有路径的部分空间分集增益,仿真结果表明,这种增益的获得不受限于接收分集阶数,并且随发射天线的增加以一定的线性关系增加。 相似文献
28.
CAO Wei-feng WANG Wen-boBeijing University of Posts Telecommunications Beijing P.R. China 《中国邮电高校学报(英文版)》2005,12(4)
1IntroductionCurrently,smart antenna technology can greatly en-hance system performance and i mprove the system ca-pacity so that it has been considered as a keytechnologyinthe third generation wireless communicationsystems .The researches on channel model , beamforming algo-rithms and receive algorithms have been widely carriedout and a great many of proposition have beensubmittedtothe 3th Generation Project Partner (3GPP) . Fromthe viewpoint of link-level and system-level research,many asp… 相似文献
29.
Business publications and the popular press have stressed the importance of creating conditions for meaningful employee expression in work roles, also known as engagement. Few empirical studies, however, have examined how individual or situational factors relate to engagement. Consequently, this study examines the interplay between employee age, perceived coworker age composition, and satisfaction with older (older than 55) and younger (younger than 40) coworkers on engagement using a sample of 901 individuals employed in the United Kingdom. Results indicated that satisfaction with one's coworkers related significantly to engagement. Moreover, perceived age similarity was associated with higher levels of engagement among older workers when they were highly satisfied with their coworkers over 55 and lower levels of engagement when they were not. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
30.
Carlos Fernandes Agostinho C. Rosa 《Soft Computing - A Fusion of Foundations, Methodologies and Applications》2008,12(10):955-979
Mate selection plays a crucial role in both natural and artificial systems. While traditional Evolutionary Algorithms (EA)
usually engage in random mating strategies, that is, mating chance is independent of genotypic or phenotypic distance between
individuals, in natural systems non-random mating is common, which means that somehow this mechanism has been favored during
the evolutionary process. In non-random mating, the individuals mate according to their parenthood or likeness. Previous studies
indicate that negative assortative mating (AM)—also known as dissortative mating—, which is a specific type of non-random mating, may improve EAs performance by maintaining the genetic diversity of the
population at a higher level during the search process. In this paper we present the Variable Dissortative Mating Genetic Algorithm (VDMGA). The algorithm holds a mechanism that varies the GA’s mating restrictions during the run by means of simple rule
based on the number of chromosomes created in each generation and indirectly influenced by the genetic diversity of the population.
We compare VDMGA not only with traditional Genetic Algorithms (GA) but also with two preceding non-random mating EAs: the
CHC algorithm and the negative Assortative Mating Genetic Algorithm (nAMGA). We intend to study the effects of the different methods in the performance of GAs and verify the reliability of
the proposed algorithm when facing an heterogeneous set of landscapes. In addition, we include the positive Assortative Mating Genetic Algorithm (pAMGA) in the experiments in order test both negative and positive AM mechanisms, and try to understand if and when negative
AM (or DM) speeds up the search process or enables the GAs to escape local optima traps. For these purposes, an extensive
set of optimization test problems was chosen to cover a variety of search landscapes with different characteristics. Our results
confirm that negative AM is effective in leading EAs out of local optima traps, and show that the proposed VDMGA is at least
as efficient as nAMGA when applied to the range of our problems, being more efficient in very hard functions were traditional
GAs usually fail to escape local optima. Also, scalability tests have been made that show VDMGA ability to decrease optimal
population size, thus reducing the amount of evaluations needed to attain global optima. We like to stress that only two parameters
need to be hand-tuned in VDMGA, thus reducing the tuning effort present in traditional GAs and nAMGA. 相似文献