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   175955篇
  免费   2498篇
  国内免费   687篇
电工技术   3412篇
综合类   199篇
化学工业   29379篇
金属工艺   6262篇
机械仪表   5358篇
建筑科学   5484篇
矿业工程   653篇
能源动力   4513篇
轻工业   18860篇
水利工程   1328篇
石油天然气   834篇
武器工业   5篇
无线电   22057篇
一般工业技术   32475篇
冶金工业   29224篇
原子能技术   2569篇
自动化技术   16528篇
  2021年   1151篇
  2019年   1142篇
  2018年   1468篇
  2017年   1475篇
  2016年   1720篇
  2015年   1418篇
  2014年   2351篇
  2013年   8032篇
  2012年   4042篇
  2011年   5701篇
  2010年   4428篇
  2009年   5038篇
  2008年   5678篇
  2007年   5852篇
  2006年   5232篇
  2005年   4873篇
  2004年   4682篇
  2003年   4531篇
  2002年   4547篇
  2001年   4420篇
  2000年   4086篇
  1999年   4086篇
  1998年   7034篇
  1997年   5613篇
  1996年   4882篇
  1995年   4101篇
  1994年   3768篇
  1993年   3580篇
  1992年   3177篇
  1991年   2930篇
  1990年   2992篇
  1989年   2965篇
  1988年   2758篇
  1987年   2539篇
  1986年   2433篇
  1985年   2941篇
  1984年   2735篇
  1983年   2546篇
  1982年   2398篇
  1981年   2261篇
  1980年   2119篇
  1979年   2198篇
  1978年   2036篇
  1977年   2295篇
  1976年   2761篇
  1975年   1803篇
  1974年   1621篇
  1973年   1653篇
  1972年   1342篇
  1971年   1214篇
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
91.
Zage  W.M. Zage  D.M. 《Software, IEEE》1993,10(4):75-81
Design-quality metrics that are being developed for predicting the potential quality and complexity of the system being developed are discussed. The goal of the metrics is to provide timely design information that can guide a developer in producing a higher quality product. The metrics were tested on projects developed in a university setting with client partners in industry. To further validate the metrics, they were applied to professionally developed systems to test their predictive qualities. The results of applying two design metrics and a composite metric to data from a large-scale industrial project are presented  相似文献   
92.
93.
It is pointed out that strength value of rock samples changes with time after sample excavation from a quarry. Three main stages of strength variability with time are distinguished: 1-the stage of hardening connected with increase in the compression strength; 2-stage of equilibrium of the antagonistic processes: hardening and mechanical fatigue; 3-stage of manifestation of mechanical fatigue. Mechanical fatigue is favorable to the manifestation latent weakness surface to new crack formation and at last to total disintegration in rock samples.  相似文献   
94.
The management of innovation inevitably implies the management of uncertainty. Research and practise clearly indicate that judgements about the size and the nature of this are often inaccurate. This can result in poor performance against expectations and in some cases in complete failure. In this paper it is argued that prior analysis of the type of uncertainty can help to improve the success rate and/or reduce the time to completion. Early signs that discontinuation, or a significant change in direction, might be called for are also highlighted by this analysis.  相似文献   
95.
The rapid advances in molecular biology have begun to shift many of the bottlenecks in genome research from the laboratory to the data analysis facility. The pace at which this has occurred creates a situation in which software development always has to catch up with the flow of data. Since such large-scale processes were not anticipated, the analysis infrastructure has not been fully established. Furthermore, most systems that have been built were designed by the biologists who collected the data. More recently, computer scientists, mathematicians, and engineers have taken an interest in this problem. This has had a positive effect, since it has created a tight synergy between the informatics and the biology. Several principles affected the design of the system developed at TIGR. Each of the sample preparation, sequencing, and analysis steps had to be managed, scheduled, and tracked. This information had to be made readily available to those who needed it for carrying out their tasks. Different skill levels of the users had to be taken into account. The degree of human intervention at each step had to be evaluated and built into the design. A mixed processing environment of Macintosh and Unix platforms had to be integrated. Most importantly, the system had to save time, reduce error, and ensure uniformity of the analysis and quality of the results. In the authors' experience, the tools they have built work well because of their early decisions as to which systems to use for development. The authors settled on a robust relational database management system (Sybase) and a portable development environment (C, C++)  相似文献   
96.
Pulse oximetry is increasingly used to assess hypoxaemia in respiratory illnesses. Six children presenting with acute asthma and prolonged falls in oxygen saturation values after treatment with salbutamol are described who were subsequently shown to have pneumonic consolidation on chest radiography.  相似文献   
97.
In this article the direct boundary element formulations of stretching and bending plate problems are combined together to solve thin walled structures and other similar frames. The final system is obtained by assuming each individual plane structural element as a subregion. After the necessary transforms of these equations they can be combined together taking into account the displacement compatibility and equilibrium conditions.  相似文献   
98.
The Kyoto Protocol to the United Nationsl Framework Convention on Climate Change gives a target for the reduction of greenhouse gases in the EU and most associated states of 8% from 1990 levels to 2010. The European Commissions Whitebook on Renewable Energy is setting a target of doubling the share of Renewable Energy from 6% now to 12% in 2010 for the European Union. There is no contradiction between these targets.  相似文献   
99.
An improved accelerated cable life test is described. Through the use of programmable logic controllers (PLCs), very precise and consistent control of the accelerated aging process has been achieved. A computer has been utilized to make continuous real-time acquisition and storage of key operating parameters possible. This precise control and monitoring methodology has permitted the study of the synergistic effects of voltage and temperature on the accelerated aging of full-sized cables in the laboratory  相似文献   
100.
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