全文获取类型
收费全文 | 55140篇 |
免费 | 5259篇 |
国内免费 | 2542篇 |
专业分类
电工技术 | 3507篇 |
技术理论 | 1篇 |
综合类 | 4338篇 |
化学工业 | 7863篇 |
金属工艺 | 2445篇 |
机械仪表 | 3669篇 |
建筑科学 | 8741篇 |
矿业工程 | 1235篇 |
能源动力 | 3699篇 |
轻工业 | 5847篇 |
水利工程 | 812篇 |
石油天然气 | 2454篇 |
武器工业 | 702篇 |
无线电 | 3235篇 |
一般工业技术 | 5218篇 |
冶金工业 | 2485篇 |
原子能技术 | 356篇 |
自动化技术 | 6334篇 |
出版年
2024年 | 286篇 |
2023年 | 1010篇 |
2022年 | 1948篇 |
2021年 | 2242篇 |
2020年 | 2304篇 |
2019年 | 1946篇 |
2018年 | 1885篇 |
2017年 | 2162篇 |
2016年 | 2265篇 |
2015年 | 2292篇 |
2014年 | 3593篇 |
2013年 | 3531篇 |
2012年 | 4074篇 |
2011年 | 4211篇 |
2010年 | 3118篇 |
2009年 | 3180篇 |
2008年 | 2797篇 |
2007年 | 3561篇 |
2006年 | 3029篇 |
2005年 | 2586篇 |
2004年 | 2081篇 |
2003年 | 1750篇 |
2002年 | 1417篇 |
2001年 | 1168篇 |
2000年 | 880篇 |
1999年 | 691篇 |
1998年 | 470篇 |
1997年 | 402篇 |
1996年 | 375篇 |
1995年 | 268篇 |
1994年 | 229篇 |
1993年 | 168篇 |
1992年 | 125篇 |
1991年 | 123篇 |
1990年 | 92篇 |
1989年 | 73篇 |
1988年 | 52篇 |
1987年 | 40篇 |
1986年 | 21篇 |
1985年 | 35篇 |
1984年 | 45篇 |
1983年 | 34篇 |
1982年 | 29篇 |
1980年 | 47篇 |
1965年 | 19篇 |
1964年 | 28篇 |
1963年 | 26篇 |
1961年 | 22篇 |
1956年 | 18篇 |
1955年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
Christos Bouras Agisilaos Konidaris 《International Journal of Communication Systems》2005,18(2):119-142
Redundant data transfers over the Web, can be mainly attributed to the repeated transfers of unchanged data. Web caches and Web proxies are some of the solutions that have been proposed, to deal with the issue of redundant data transfers. In this paper we focus on the efficient estimation and reduction of redundant data transfers over the Web. We first prove that a vast amount of redundant data is transferred in Web pages that are considered to carry fresh data. We show this by following an approach based on Web page fragmentation and manipulation. Web pages are broken down to fragments, based on specific criteria. We then deal with these fragments as independent constructors of the Web page and study their change patterns independently and in the context of the whole Web page. After the fragmentation process, we propose solutions for dealing with redundant data transfers. This paper has been based on our previous work on ‘Web Components’ but also on related work by other researchers. It utilises a proxy based, client/server architecture, and imposes changes to the algorithms executed on the Proxy server and on clients. We show that our proposed solution can considerably reduce the amount of redundant data transferred on the Web. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
102.
Dunn Barnaby D.; Dalgleish Tim; Lawrence Andrew D.; Ogilvie Alan D. 《Canadian Metallurgical Quarterly》2007,116(1):1
The accuracy with which dysphoric (Study 1) and clinically depressed (Study 2) individuals make self-regulatory judgments about their own performance in the absence of external feedback and the extent to which this relates to trait self-focused attention (SFA) were examined. Relative to objective criteria, both dysphoric and depressed participants showed a positive judgment bias, overestimating the number of trials they had performed correctly. Relative to control participants, the dysphoric and depressed groups showed a reduction in the extent of this positive bias in that they judged error trials more accurately and correct trials less accurately. Although the dysphoric and depressed groups both reported elevated trait SFA, this did not correlate significantly with accuracy of self-judgment on the performance-monitoring task. Implications for self-regulation models of depression are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
103.
混凝土早期收缩开裂是加剧混凝土劣化并导致最终失效的一个重要因素.分析混凝土早期的自由收缩量值是进行收缩开裂研究的基础。为此,基于湿度扩散理论建立了混凝士早期的自生收缩与干燥收缩计算分析模型,经实例验证,计算结果与试验结果有较好的一致性。 相似文献
104.
对一台火花点火式两缸天然气发动机进行了缸内示功图、进气压力波、空燃比、缸盖及活塞温度场和排放等项目的测试。试验和分析表明,两缸进气道中存在着明显的压力波动,波动程度取决于发动机工况。两缸混合气的质和量都不均匀,一缸空燃比偏浓,燃烧不完全,后燃倾向大;二缸空燃比较合适,燃烧过程较完善。两缸的尾气排放量相差不大。据此,可应用稀燃、快燃技术,以提高燃烧速度,改善燃烧过程;同时调整进气系统特性,将两缸混合气的质和量的不均匀性降到最低限度。 相似文献
105.
106.
107.
由进口电性能仪配上自制的高温系统,计算机自动采集数据,配置成一套高低温电性参数测定装置,该装置的特点是,升温快,炉体小巧,炉芯可更换盛液氮装置,屏蔽良好,等温区长,温工及参数测量精确可靠。 相似文献
108.
109.
网络的性能与可靠性已分别得到广泛的研究,然而,怎样分析具有容错机制的环网的性能仍属有待开拓的研究领域,本文提出了一种分析具有自修复机制的多环网络系统的方法,并给出了报文传输时间分布的拉氏变换式,平均等待时间及平均队列长度公式,分析结果可用于评估故障与修复过程对实时令牌环网的实时响应特性的影响,对基于LAN的分布式实时系统设计具有指导意义。 相似文献
110.
Since electronic switching systems usually require very strict reliability requirements as well as good performance objectives, we need to jointly analyse the performance and reliability of switching systems. In this paper, we compare conventional time–space–time switches with single space switches with those with multiple separated space switches, from the viewpoints of reliability and performance. We consider time–space–time switching networks which consist of N incoming time switches, i.e. one NxN space switch, two (N/2)x(N/2) space switches, and four (N/4)x(N/4) space switches. We introduce a Markov reliability model to study the effect of failures and analyse the reliability and performance of three different types of switching networks in terms of average blocking probability and the mean time to unreliable operation, as we vary the offered traffic. As a result, T–S–T switching networks with multiple separated space switches exhibit better performance and reliability than those with single space switches. 相似文献