全文获取类型
收费全文 | 18213篇 |
免费 | 1429篇 |
国内免费 | 674篇 |
专业分类
电工技术 | 790篇 |
技术理论 | 11篇 |
综合类 | 2305篇 |
化学工业 | 296篇 |
金属工艺 | 378篇 |
机械仪表 | 557篇 |
建筑科学 | 9338篇 |
矿业工程 | 330篇 |
能源动力 | 441篇 |
轻工业 | 54篇 |
水利工程 | 844篇 |
石油天然气 | 63篇 |
武器工业 | 57篇 |
无线电 | 2085篇 |
一般工业技术 | 627篇 |
冶金工业 | 570篇 |
原子能技术 | 14篇 |
自动化技术 | 1556篇 |
出版年
2024年 | 104篇 |
2023年 | 278篇 |
2022年 | 444篇 |
2021年 | 579篇 |
2020年 | 603篇 |
2019年 | 531篇 |
2018年 | 354篇 |
2017年 | 587篇 |
2016年 | 599篇 |
2015年 | 569篇 |
2014年 | 1421篇 |
2013年 | 1322篇 |
2012年 | 1333篇 |
2011年 | 1490篇 |
2010年 | 1222篇 |
2009年 | 1130篇 |
2008年 | 1134篇 |
2007年 | 1102篇 |
2006年 | 1046篇 |
2005年 | 843篇 |
2004年 | 645篇 |
2003年 | 561篇 |
2002年 | 530篇 |
2001年 | 463篇 |
2000年 | 372篇 |
1999年 | 227篇 |
1998年 | 149篇 |
1997年 | 128篇 |
1996年 | 105篇 |
1995年 | 90篇 |
1994年 | 66篇 |
1993年 | 36篇 |
1992年 | 42篇 |
1991年 | 22篇 |
1990年 | 28篇 |
1989年 | 26篇 |
1988年 | 16篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1985年 | 11篇 |
1984年 | 14篇 |
1983年 | 13篇 |
1982年 | 20篇 |
1981年 | 7篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1964年 | 7篇 |
1961年 | 3篇 |
1960年 | 3篇 |
1955年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
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
22.
星间激光通信技术进展与趋势 总被引:3,自引:3,他引:0
较详细地评述了目前国外卫星间光通信技术研究的现状.根据关键单元技术的进展情况,总结了未来星间光通信系统的发展趋势。 相似文献
23.
Thai Binh Wan Rachel Seneviratne Aruna Rakotoarivelo Thierry 《Mobile Networks and Applications》2003,8(1):27-36
The high expectations and demand for users to access the Internet from anywhere at anytime has made user mobility an important part of the design and development of the next generation mobile communications and computing. Traditionally user mobility has been divided into two areas: Terminal Mobility and Personal Mobility. In recent years terminal mobility has focused on the movement of the terminal and developed extensions to IP protocols such as Mobile IP. In contrast, personal mobility has only received limited attention, and is somewhat lagging behind. This research has either focussed on personal mobility in communications or personalisation of operating environments. As a result, to date no framework for providing true personal mobility has emerged. In this paper, we introduce a new personal mobility framework called IPMoA (Integrated Personal Mobility Architecture), which integrates both aspects of personal mobility to provide a complete personal mobility solution, and illustrate the viability of this approach through a proof-of-concept implementation. 相似文献
24.
Claudio Sacchi Gianluca Gera Carlo S. Regazzoni 《International Journal of Satellite Communications and Networking》2004,22(2):193-215
This paper aims at focusing on the aspects concerning the physical layer design for an innovative satellite communication experiment. Such an experiment, denoted by the acronym DAVID–DCE (Data and Video Interactive Distribution—Data Collection Experiment) is based on the exploitation of the W‐band (75–110 GHz) for high‐bit‐rate satellite transmission. The potential advantages of using of the W‐band are mainly related to the great bandwidth availability, and to the absence of interference. Moreover, an expected result of the experiment is a substantive improvement in the communication system's performances in the presence of meteorological phenomena (e.g. rain) as compared with the more conventional Ka‐band satellite transmission. On the other hand, problems to be faced concern the non‐ideal behaviours of hardware devices employed for high‐frequency digital transmission. In particular, carrier recovery and timing recovery are the most crucial signal‐processing tasks to be carefully considered in the design of the physical level of the system, because they considerably suffer from hardware impairments. The purpose of this work is to illustrate the proposed solutions in terms of the most critical modulation, demodulation and synchronization design issues, together with the effects of non‐ideal behaviours of hardware components on BER performances. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
25.
Research on the Handover of a Novel Cellular Architecture in Wireless Personal Communication Systems
ZHANG Zu-fan~ 《中国邮电高校学报(英文版)》2003,10(4)
1 IntroductionHandoverbetweencellsisplayinganimportantroleincellularcommunicationsystems[1~ 1 2 ] .Thehandoverprocedureanditseffectivenessareseriouslylimitedbythecellulararchitectureasaresultofmar ketplanning .Basedonthehexagonalcellulararchi tecture,manyhandoverprocedureshavebeendis cussedandevaluated ,andmostoftheimprovementproposedonthemleadstotheintroductionofsector ingcellularorlayeredcellularmodel.Otherwise ,abetterhandoverprocedureisessentialinmaintainingacallinprogressbutitreflectshi… 相似文献
26.
27.
热浸镀铝护栏的生产通过除油→除锈→烘干→热浸镀→精整等过程完成,最佳热浸镀温度为730~750℃,保温时间3~8min,护栏提升速度1m/s 相似文献
28.
29.
The results of the measurements of the concentrations of freons (F-11 and F-113), chloroform (CHCl3), trichloroethane (CH3CCl3) and carbon tetrachloride (CCl4) in air are presented. The data concern concentration measurements that have been conducted in Krakow since half way through 1997 to the end of 1999. The mean monthly values of these concentrations have been compared with the data from Mace Head, the station situated at a similar longitude as Krakow. It has been concluded that, in the observed period of time, the concentrations of the pollutants in Krakow are higher than in Mace Head. The mean monthly concentrations of F-11 and CCl4 decrease in Krakow faster than in Mace Head (2.5 and 3.3 times, respectively). The concentrations of CHCl3 and CH3CCl3 decrease at both locations, but the change is greater in Krakow. In Krakow, the observed increase of F-113 is 0.13 ppt/month and has an opposite trend than in the same period at Mace Head. 相似文献
30.
Between 1998 and 2002, surface water samples were collected from several sites in the Don River and Humber River watersheds, both tributaries to Lake Ontario, and analyzed for a variety of pesticides, including those used for urban lawn care. Analyses included 152 pesticide active ingredients and eight metabolites. Samples were collected during base flow periods (i.e., dry events) and rainfall events (i.e., wet events). The objectives of the study were to determine which pesticides were detectable, whether there was a difference in the detection frequency between the two watersheds and between upstream and downstream in each river, and whether precipitation influenced the frequency of detection. Eleven pesticides and one metabolite were detected in surface waters of the Don and Humber rivers or their tributaries, with approximately 72% of samples containing at least one pesticide attributable to lawn care use. The pesticides and pesticide metabolite detected in this study included 2,4-D, atrazine, bromacil, carbofuran, chlorpyrifos, cypermethrin, diazinon, dicamba, MECOPROP, metolachlor, metribuzin, and an atrazine metabolite (des-ethyl atrazine). Four pesticides exceeded federal or provincial water quality guidelines/objectives. Diazinon exceeded the provincial water quality objective in 28% of the samples taken. For the three other pesticides (atrazine, carbofuran and chlorpyrifos) exceedance of a water quality criteria occurred in less than 1% of the samples. 相似文献