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   324712篇
  免费   4049篇
  国内免费   741篇
电工技术   6384篇
综合类   571篇
化学工业   49507篇
金属工艺   10602篇
机械仪表   9087篇
建筑科学   8542篇
矿业工程   922篇
能源动力   8953篇
轻工业   31986篇
水利工程   2665篇
石油天然气   3754篇
武器工业   9篇
无线电   40727篇
一般工业技术   60656篇
冶金工业   60734篇
原子能技术   5591篇
自动化技术   28812篇
  2021年   2447篇
  2019年   2281篇
  2018年   3817篇
  2017年   3633篇
  2016年   3771篇
  2015年   2760篇
  2014年   4750篇
  2013年   15131篇
  2012年   7834篇
  2011年   10718篇
  2010年   8354篇
  2009年   9618篇
  2008年   10158篇
  2007年   10082篇
  2006年   9002篇
  2005年   8328篇
  2004年   8166篇
  2003年   7830篇
  2002年   7659篇
  2001年   7790篇
  2000年   7467篇
  1999年   7812篇
  1998年   18518篇
  1997年   13357篇
  1996年   10519篇
  1995年   8170篇
  1994年   7508篇
  1993年   7192篇
  1992年   5493篇
  1991年   5234篇
  1990年   5109篇
  1989年   5005篇
  1988年   4855篇
  1987年   4073篇
  1986年   4199篇
  1985年   4920篇
  1984年   4486篇
  1983年   4184篇
  1982年   3758篇
  1981年   3888篇
  1980年   3587篇
  1979年   3559篇
  1978年   3351篇
  1977年   3982篇
  1976年   5073篇
  1975年   2887篇
  1974年   2779篇
  1973年   2778篇
  1972年   2298篇
  1971年   2019篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
142.
The paper describes a computerized facility layout designer, COMLAD II, for plant layout development. Besides developing an efficient layout, COMLAD II has useful features which allow fixing the departments, changing the shape of the departments and changing the length and width dimensions of the overall layout.  相似文献   
143.
The IBM RISC System/6000, a superscalar microprocessor, is presented. The architecture of this processor has its instruction set specifically designed for a superscalar machine containing three independent units-branch, fixed-point, and floating-point. The design also emphasizes high-performance floating-point operations. The design principles are to offer maximum overlap of the three functional units, avoid dead cycles, and define instructions that can (for the most part) be completed at a rate of one per cycle. The branch cycle, fixed- and floating-point units, cache management, and performance are described. Benchmark results are given  相似文献   
144.
Pull-out experiments have been carried out on single production fibres under carefully controlled conditions. Four parameters were determined. The interfacial yield stresses, of about 9–14 MPa, were very much smaller than the shear strengths of the bulk polymers in the case of an epoxy, whether post-cured or not, and a non-post-cured polyester. Values for the work of fracture of the interface varied from 140 to 300 Jm?2, and again were less than those of the polymer. Interface failure sometimes took place in the epoxy rather than at the fibre surface, whereas with the polyester it always took place at the fibre surface. After interface failure, pull-out was governed by friction, with maximum shear stresses of 7–10 MPa for polyester, and 21–34 MPa for epoxy, the higher values being obtained for the post-cured resins. Average frictional shear stresses were sometimes less than a half of the maximum shear stress, indicating that the fibre Poisson's shrinkage was playing an important role in the pull-out process. A silicone release agent reduced the frictional shear stresses to 2·5 MPa, with both resins.  相似文献   
145.
146.
147.
BACKGROUND: We have studied 64 patients with congestive heart failure, half of them also with chronic nonvalvular atrial fibrillation (AF). Patients were also stratified according to a history of prior stroke. METHODS: The generation of thrombin was investigated by means of the molecular markers prothrombin fragment 1 + 2 (F1 + 2) and thrombin-antithrombin III complex (TAT), because AF patients may have a hypercoagulable state. There was only a trend toward higher values of TAT and F1 + 2 for AF patients, while subjects with previous stroke (irrespective of AF) had increased levels of the markers of thrombin generation (TAT stroke+ 18.95 +/- 5.15 vs TAT stroke- 8.34 +/- 2.41; F1 + 2 stroke+ 2.22 +/- 0.29 vs F1 + 2 stroke- 1.32 +/- 0.12). The presence of spontaneous echo contrast (SEC) within left atrium was also investigated in 32 AF patients by transesophageal echocardiography. RESULTS: TAT were significantly higher in subjects (n = 11) with SEC (TAT sec+ 37.5 +/- 13.41 vs TAT sec- 8.7 +/- 2.51, p = 0.008). CONCLUSIONS: Finally, when we grouped into 1) those with both AF and stroke, 2) AF alone, 3) stroke alone and 4) sinus rhythm without stroke, levels of F1 + 2 were higher (and marginally higher TAT) in patients with AF and stroke than in those without stroke, revealing that there is a true clotting activation state in these subjects.  相似文献   
148.
Presents a model suitable for computing images of absorption cross sections of thick tissue structures illuminated at near infrared (NIR) wavelengths from tomographic projection data. Image reconstruction is accomplished by solving a system of linear equations derived from transport theory. Reconstruction results using different algebraic solvers are shown for anatomical maps of the breast, derived from magnetic resonance imaging data, containing two simulated pathologies, in which case qualitatively good reconstructions were obtained. Evaluation of magnetic resonance (MR) data to optimize NIR optical tomographic imaging methods and to assess the feasibility of a combined MR-optical measurement scheme is discussed  相似文献   
149.
The design and application of an apparatus for measuring pain threshold by controlling the conditions of an experiment carefully and measuring stimulus and response parameters precisely are described. Heat generated by an incandescent source, focused on a small area of the subject's forehead, was used as the stimulus to determine the cutaneous pain threshold. The equipment was in different experiments in which the threshold of thermocutaneous pain was evaluated with and without the use of an analgesic. The analgesic Pirazolane was found to reduce thermocutaneous pain threshold and to diminish the average duration of alpha rhythm blockade and the response of galvanic skin resistance. The results of these experiments with constituents of marijuana indicated that canabidiol provokes and increases the sensibility of pain reactions while both Δ9 THC and canabinol do not modify the pain threshold  相似文献   
150.
A survey of perceptions of IS personnel – managers, technical specialists and programmer/analysts – was conducted by the Association for Technical Information in Spain, using the JDS/DP, a modification of the job diagnostic survey instrument. Data were collected on fifteen job variables, related to four motivation aspects: job components, satisfaction levels, need for growth/achievement and goal participation/feedback. The results were compared with those of a similar survey for the same job types in Finland. Results were also compared with the norms developed for computer personnel in the USA. The survey revealed that personnel attracted to the computer field have a high need for growth and a low need for social interaction. It also revealed that the work itself was ranked highest among eleven motivating factors. For both Spain and Finland, the technical specialist job had a mis-match between the job's motivating potential and the employee's need for growth, compared with similar personnel in the USA. By examining the core job dimensions, managers can redesign the job to produce a match between these two major components of motivation.  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