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   234478篇
  免费   2820篇
  国内免费   1062篇
电工技术   3883篇
综合类   2493篇
化学工业   35218篇
金属工艺   10434篇
机械仪表   7913篇
建筑科学   6540篇
矿业工程   933篇
能源动力   5037篇
轻工业   20870篇
水利工程   2382篇
石油天然气   960篇
武器工业   5篇
无线电   29640篇
一般工业技术   44903篇
冶金工业   26465篇
原子能技术   2596篇
自动化技术   38088篇
  2019年   842篇
  2018年   15380篇
  2017年   14362篇
  2016年   11122篇
  2015年   1665篇
  2014年   2023篇
  2013年   6766篇
  2012年   6280篇
  2011年   13861篇
  2010年   11728篇
  2009年   9591篇
  2008年   11286篇
  2007年   12514篇
  2006年   4470篇
  2005年   5292篇
  2004年   5106篇
  2003年   5055篇
  2002年   4457篇
  2001年   4078篇
  2000年   3921篇
  1999年   3753篇
  1998年   6733篇
  1997年   5278篇
  1996年   4523篇
  1995年   3730篇
  1994年   3376篇
  1993年   3200篇
  1992年   2802篇
  1991年   2714篇
  1990年   2635篇
  1989年   2618篇
  1988年   2476篇
  1987年   2172篇
  1986年   2120篇
  1985年   2558篇
  1984年   2318篇
  1983年   2199篇
  1982年   2069篇
  1981年   1993篇
  1980年   1863篇
  1979年   1879篇
  1978年   1772篇
  1977年   2093篇
  1976年   2569篇
  1975年   1587篇
  1974年   1433篇
  1973年   1453篇
  1972年   1196篇
  1971年   1115篇
  1970年   948篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
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   
102.
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   
103.
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   
104.
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   
105.
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   
106.
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   
107.
108.
Group communication supports information transfer between a set of participants. It is becoming more and more relevant in distributed environments. For distributed or replicated data, it provides efficient communication without overloading the network. For some types of multimedia applications, it is the only way to control data transmission to group members. This paper surveys protocol functions and mechanisms for data transmission within a group, from multicast routing problems up to end-to-end multipoint transmission control. We provide a bibliography which is organized by topic  相似文献   
109.
Nuclear magnetic resonance imaging (MRI), calorimetry, and temperature measurements were used to monitor cylindrical potato sections frozen at -11C and -42C. MRI showed the advance of the nonsymmetric freezing zone and loss of signal intensity as liquid water turned to ice. Differential calorimetry was used to follow heat removal during transient freezing. Measured times to 95% enthalpy change were 24 min (-42C) and 49 min (-11C), as compared to modeled values of 29 min (-42C) and 100 min (-11C). Times to 95% change in the NMR signal, integrated over the area of the image, were 21 min (-42C) and 56 min (-11C). Changes in NMR signal intensity could be correlated with the amount of unfrozen water remaining after a steady-state had been reached. At -42C, NMR indicated 25% unfrozen water remaining as compared to 26% by calorimetry, and 22% by modeling. At -11C, NMR measured 67% unfrozen water remaining as compared to 48% by calorimetry, and 25% by equilibrium modeling.  相似文献   
110.
The authors describe and discuss the new technique, multistep adaptive flux interpolation (MAFI), and its application to image data for coding. When applied to an image, MAFI produces an output which is also in an image form, but which has a more uniform feature density and a greatly reduced size. MAFI warps the input image by removing those rows and columns which contain a majority of redundant pixels. The side information required for reconstruction is minimal, and the image can be further compressed using conventional coders, making the compression ratio even higher. Because of its warped nature, the MAFI output's statistics are also more consistent with the properties assumed by block-based discrete cosine transform (DCT) methods  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