全文获取类型
收费全文 | 324712篇 |
免费 | 4049篇 |
国内免费 | 741篇 |
专业分类
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 |
出版年
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.
M. Reza Ziai
Dileep R. Sule
《Computers & Industrial Engineering》1991,21(1-4):385-389The 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.
M Soncini F Casazza R Mattioli C Bonfardeci A Motta C Cimminiello 《Canadian Metallurgical Quarterly》1997,88(12):501-505
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.
Jenghwa Chang Graber H.L. Ping Chen Koo Aronson R. Barbour S.-L.S. Barbour R.L. 《IEEE transactions on medical imaging》1997,16(1):68-77
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