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   84647篇
  免费   1034篇
  国内免费   419篇
电工技术   806篇
综合类   2321篇
化学工业   11621篇
金属工艺   4802篇
机械仪表   3067篇
建筑科学   2214篇
矿业工程   563篇
能源动力   1180篇
轻工业   3680篇
水利工程   1289篇
石油天然气   365篇
无线电   9322篇
一般工业技术   16420篇
冶金工业   2652篇
原子能技术   260篇
自动化技术   25538篇
  2023年   40篇
  2022年   48篇
  2021年   93篇
  2020年   87篇
  2019年   98篇
  2018年   14523篇
  2017年   13454篇
  2016年   10021篇
  2015年   655篇
  2014年   313篇
  2013年   332篇
  2012年   3201篇
  2011年   9466篇
  2010年   8308篇
  2009年   5571篇
  2008年   6785篇
  2007年   7783篇
  2006年   127篇
  2005年   1208篇
  2004年   1130篇
  2003年   1173篇
  2002年   533篇
  2001年   96篇
  2000年   177篇
  1999年   59篇
  1998年   56篇
  1997年   33篇
  1996年   46篇
  1995年   9篇
  1994年   14篇
  1993年   8篇
  1992年   12篇
  1991年   25篇
  1988年   10篇
  1969年   24篇
  1968年   43篇
  1967年   33篇
  1966年   42篇
  1965年   44篇
  1964年   11篇
  1963年   28篇
  1962年   22篇
  1961年   18篇
  1960年   30篇
  1959年   35篇
  1958年   37篇
  1957年   36篇
  1956年   34篇
  1955年   63篇
  1954年   68篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
82.
83.
In this paper, we argue that successful integration of knowledge across work domains in the short-term can mask the generation of long-term consequences. We explore a setting, the introduction of environmental considerations into semiconductor manufacturing, where the eventual adoption of common measurement artifacts and associated practices enabled knowledge integration, but failed to address significant underlying consequences. Drawing from observational, interview, and archival data we develop an understanding of the work practices of the Tech and EnviroTech groups as structured by the material world and broader collective conventions. We introduce the concept of knowledge regime to outline the differences in knowledge across these work domains. More specifically, we find that differences in the causal specificity and developmental time horizon of knowledge and the measurement artifacts that result contribute to the relative power of one knowledge regime over another. Understanding these sources of incompatibility provides insight into the design requirements of information systems as boundary objects for knowledge integration, but also specifies the potential limits to any design effort.  相似文献   
84.
85.
86.
87.
Understanding consumer behaviour is of vital importance to consumer-oriented e-business models today. In this paper, we study the relationships between consumer perceptions of risk and trust and the attitude towards purchasing at a consumer-to-consumer electronic marketplace (EM). Typical for EM settings is that consumer behaviour is subject to perceptions of the selling party as well as of the institutional structures of the intermediary that is operating the EM. Building upon the well-established literature of trust, we consider the concepts of intermediary trust and seller trust. We extend this categorisation by introducing the concepts of intermediary risk and seller risk. We developed measurement instruments for intermediary risk and seller risk. All measurement scales have acceptable alphas and are unidimensional. An empirical study is conducted to explore the relationships between the risk and trust types and consumer purchase attitude. The results reveal significant, direct effects of seller trust and seller risk. Second-order effects of intermediary trust and intermediary risk are investigated and reported. The paper concludes with general observations and recommendations for research and practice.  相似文献   
88.
89.
DC resistivity, dielectric constant, dielectric loss and positron annihilation spectra of (Ba1−x Ho x )TiO3 ceramics have been measured as a function of holmium concentration x. It has been found that the DC resistivity of (Ba1−x Ho x )TiO3 is strongly dependent on the Ho content: it decreases three orders of magnitude and reaches a minimum at x = 0.4%. Doping with 0.6% holmium increases the permittivity of BaTiO3 by approximately three times (from ∼1,300 to ∼4,000), with only a slight increase in the corresponding dielectric loss. The local electron density and defect concentration estimated using positron annihilation technique conforms well to the features found in the dielectric and resistivity measurements. The results have been discussed in terms of a mixed compensation model.  相似文献   
90.
Document caching and connection caching are extensively studied problems. In document caching, one has to maintain caches containing documents accessible in a network. In connection caching, one has to maintain a set of open network connections that handle data transfer. Previous work investigated these two problems separately while in practice the problems occur together: In order to load a document, one has to establish a connection between network nodes if the required connection is not already open. In this paper we present the first study that integrates document and connection caching. We first consider a very basic model in which all documents have the same size and the cost of loading a document or establishing a connection is equal to 1. We present deterministic and randomized online algorithms that achieve nearly optimal competitive ratios unless the size of the connection cache is extremely small. We then consider general settings where documents have varying sizes. We investigate a FAULT model in which the loading cost of a document is 1 as well as a BIT model in which the loading cost is equal to the size of the document.  相似文献   
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