首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   327587篇
  免费   4525篇
  国内免费   837篇
电工技术   6484篇
综合类   588篇
化学工业   50856篇
金属工艺   10862篇
机械仪表   9405篇
建筑科学   8248篇
矿业工程   908篇
能源动力   9946篇
轻工业   32209篇
水利工程   2679篇
石油天然气   3746篇
武器工业   9篇
无线电   41829篇
一般工业技术   62340篇
冶金工业   57879篇
原子能技术   5603篇
自动化技术   29358篇
  2022年   2377篇
  2021年   3395篇
  2020年   2529篇
  2019年   3040篇
  2018年   4755篇
  2017年   4355篇
  2016年   4417篇
  2015年   3126篇
  2014年   5216篇
  2013年   15692篇
  2012年   8196篇
  2011年   11133篇
  2010年   8716篇
  2009年   9887篇
  2008年   10271篇
  2007年   10130篇
  2006年   8934篇
  2005年   8229篇
  2004年   8005篇
  2003年   7717篇
  2002年   7525篇
  2001年   7700篇
  2000年   7348篇
  1999年   7693篇
  1998年   17900篇
  1997年   13020篇
  1996年   10270篇
  1995年   8009篇
  1994年   7333篇
  1993年   7031篇
  1992年   5371篇
  1991年   5172篇
  1990年   5023篇
  1989年   4862篇
  1988年   4744篇
  1987年   3976篇
  1986年   4075篇
  1985年   4787篇
  1984年   4334篇
  1983年   4091篇
  1982年   3663篇
  1981年   3835篇
  1980年   3505篇
  1979年   3449篇
  1978年   3252篇
  1977年   3841篇
  1976年   4875篇
  1975年   2788篇
  1974年   2667篇
  1973年   2683篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
Irvin  D.R. 《IEEE network》1993,7(1):40-45
It is argued that the technology needed to support the emerging broadband integrated services digital network technology (B-ISDN) is on the horizon, but the deployment of this technology in the telecommunication plant will not be sufficient to make B-ISDN a commercial success. Two corequisites for ensuring the long-term success of the emerging B-ISDN include stimulating the demand for bandwidth by inventing and promoting new telecommunication applications, and enabling the interconnection or convergence of the emerging high-speed network and the existing cable television infrastructure. The author believes that this is necessary because no alternative seems to offer a workable base for financing the transition to B-ISDN and for reaching the needed economy of scale, and because the intrinsic value of the public network grows combinatorially with the number of subscribers  相似文献   
962.
Data access cost evaluation is fundamental in the design and management of database systems. When some data items have duplicates, a clustering effect that can heavily influence access costs is observed. The availability of a finite amount of buffer memory in real systems has an even more dramatic impact. A comprehensive cost model for clustered data retrieval by an index using a finite buffer is presented. The approach combines and extends previous models based either on finite buffer or on uniform data clustering assumptions. The computational costs of the formulas proposed are independent of the data size or of the query cardinality and need only a single statistics per search key, the clustering factor, to be maintained by the system. The predictive power and the accuracy of the model are shown in comparison with actual costs resulting from simulations  相似文献   
963.
964.
The influence of prior austenite grain size on the transformation behaviour and microstructural development of C-Mn-Ni weld metals was investigated. It was found that increasing the grain size depressed the start temperature of grain-boundary ferrite and slightly increased the acicular ferrite start temperature. The microstructural products also changed from a boundary-dominated effect in the small grain sizes, to an intragranular-dominated effect in the large grain sizes, and at the same time, the morphology of the acicular ferrite was seen to change to a larger aspect ratio.  相似文献   
965.
The most influential study of the person–environment (P–E) fit approach to stress was conducted by J. R. French et al (1982). Unfortunately, this study operationalized fit using various transformations of difference scores, thereby introducing numerous substantive and methodological problems. In the present study, the authors reanalyze data from French et al, using a procedure described by J. R. Edwards (in press) that avoids problems with difference scores and captures the underlying 3-dimensional relationship between environment, person, and strain. Results resolve ambiguities in the French et al findings and identify relationships between environment, person, and strain that, although consistent with P–E fit theory, cannot be adequately represented by fit measures such as those used by French et al. Implications for P–E fit research are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
966.
Surface forces nonuniformity within the volume of a capillary system for a given structure has been examined in terms of its effect on a wetting fluid distribution. This approach enables the distribution for a porous body with a uniform structure to be quantified using a specific function for the pore volume size distribution. The surface forces nonuniformity effect is illustrated using a fibrous structure impregnated with molten copper.Institute of Materials Science Problems, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, No. 8(368), pp. 66–69, August, 1993.  相似文献   
967.
We isolated a mutant defective in C-terminal farnesyl cysteine:carboxyl methyltransferase activity from a screen for mutations causing a -specific sterility. A genomic fragment was cloned from a yeast multi-copy library that restored mating. Both the cloned gene and the sterile mutation were allelic to the STE14 gene. A ste14-complementing 2·17 kb BamHI fragment subclone was sequenced and found to encode a 239 amino acid protein with a molecular weight of 27,887 Daltons. The hydrophobicity profile of the methyltransferase reveals the presence of at least five potential transmembrane domains. In comparisons of the C-terminal methyltransferase amino acid sequence with those in the PIR and Swiss protein databases, no significantly similar sequences were found nor were conserved regions from other methyltransferases present.  相似文献   
968.
969.
970.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号