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   406384篇
  免费   36398篇
  国内免费   22913篇
电工技术   28061篇
技术理论   66篇
综合类   49388篇
化学工业   45246篇
金属工艺   12417篇
机械仪表   21019篇
建筑科学   52751篇
矿业工程   20880篇
能源动力   13157篇
轻工业   24162篇
水利工程   29827篇
石油天然气   19610篇
武器工业   3630篇
无线电   31972篇
一般工业技术   26409篇
冶金工业   19725篇
原子能技术   4328篇
自动化技术   63047篇
  2024年   1711篇
  2023年   5122篇
  2022年   9485篇
  2021年   11201篇
  2020年   11684篇
  2019年   9407篇
  2018年   8718篇
  2017年   10825篇
  2016年   12388篇
  2015年   13491篇
  2014年   24445篇
  2013年   22468篇
  2012年   28663篇
  2011年   29855篇
  2010年   23247篇
  2009年   23943篇
  2008年   22510篇
  2007年   28645篇
  2006年   26440篇
  2005年   23329篇
  2004年   19309篇
  2003年   17329篇
  2002年   14332篇
  2001年   11901篇
  2000年   9985篇
  1999年   8028篇
  1998年   6015篇
  1997年   5146篇
  1996年   4598篇
  1995年   3914篇
  1994年   3357篇
  1993年   2535篇
  1992年   2221篇
  1991年   1669篇
  1990年   1408篇
  1989年   1247篇
  1988年   982篇
  1987年   706篇
  1986年   553篇
  1985年   471篇
  1984年   443篇
  1983年   315篇
  1982年   262篇
  1981年   198篇
  1980年   169篇
  1979年   138篇
  1978年   74篇
  1977年   85篇
  1976年   67篇
  1975年   63篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
21.
What has become known as Community Operational Research has been around in the UK for many years. The election of Jonathan Rosenhead as President of the UK OR Society in 1986–87 was the catalyst for bringing together and expanding activities which had been carried out largely by individuals working in isolation on a voluntary basis. The following five years have seen the establishment of the Community OR Unit at Northern College, the Centre for Community OR at Hull University and the Community OR Network, which supports the activities of volunteer OR workers across the UK. This paper reviews the range and types of work which have been undertaken by various practitioners. An assessment of the success of community OR is made and a number of issues which have arisen are discussed. Finally, given the diverse nature of community OR, its practice and practitioners, there is some discussion about the future of the area.  相似文献   
22.
The hydrolysis of isocyanic acid in the gaseous phase has been investigated at temperatures between 553 and 613 K by mass spectrometry and evaluated to obtain the corresponding kinetic data. The reaction order and reaction constant have been determined. Finally, the influence of water on the catalysed formation of melamine from isocyanic acid under the operating conditions employed has been investigated in order to determine whether there is a need to try the process gas.  相似文献   
23.
24.
In order to control a project, construction management requires project information. This is obtained through accounting, estimating, cost management and scheduling functions which produce project reports. These reports are best obtained by subdividing the project into small parts. The ways in which each of these functions subdivides a project in order to produce its reports is discussed, together with a means of interrelating this information with a technique known as the work breakdown structure.  相似文献   
25.
26.
One hundred and twenty-five pairs of chicken drumsticks were randomly allocated to one of five dose rates: 5, 10, 15, 20 or 600 kGyh-. The highest dose rate was obtained using a linear accelerator whilst the remaining dose rates were provided using a 60Co gamma source. Each batch of 25 pairs was further divided into groups five of which were stored at 4°C for 0, 7, 14, 21 or 28 days. ESR spectroscopy was used to measure the intensity of the radiation-induced signal. There was a quadratic relationship between ESR signal strength and dose rate, which although statistically significant is unlikely to be of practical importance. The magnitude of the ESR signal declined by about 20% over the first 14 days of storage at 4°C and thereafter the decrease was minimal.  相似文献   
27.
With a view to evaluate the effects of hydraulic retention time and volatile solids loading rate on methane production using water hyacinth, experiments were conducted in a 160 dm3 capacity, well-mixed continuous digestion unit at ambient temperature. The optimal design of biogas plant using water hyacinth was elucidated, to provide a unit giving a maximum methane yield of 0.16 nm3 kg?1 volatile solids added, which was 60% greater than the conventional plant using cowdung. The calculations of optimal design factors were based on reactor size, hydraulic retention time and volatile solids loading rate; considerations were made of capital cost, running costs and operational revenue.  相似文献   
28.
支气管上皮靶细胞形态学参数对计算受氡子体照射的支气管的剂量是很重要的。本文介绍利用奥尔新兰-PAS 染色的外科切除人肺组织切片,测量基底细胞粘液细胞和的胞核深度与数目。结果表明,叶、段和小支气管的粘液细胞核深度分别为相应节段基底细胞的61%、69%和73%;此三节段粘液细胞的数目分别为基底细胞的53%、29%和28%,平均为37%。  相似文献   
29.
30.
A method of approximate channel identification is proposed that is based on a simplification of the correlation estimator. Despite the numerical simplification (no multiplications or additions are required, only comparisons and an accumulator), the performance of the proposed estimator is not significantly worse than that of the standard correlation estimator. A free (user selectable) parameter moves ‘smoothly’ from a situation with small sum‐squared channel estimation error but hard‐to‐identify channel peaks, to one with a larger sum‐squared estimation error but easy‐to‐identify channel peaks. The proposed estimator is shown to be biased and its behaviour is analysed in a number of situations. Applications of the proposed estimator to sparsity detection, symbol timing recovery and to the initialization of blind equalizers are suggested. Copyright © 2002 John Wiley & Sons, Ltd.  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