全文获取类型
收费全文 | 352188篇 |
免费 | 6568篇 |
国内免费 | 753篇 |
专业分类
电工技术 | 6787篇 |
综合类 | 661篇 |
化学工业 | 56128篇 |
金属工艺 | 11286篇 |
机械仪表 | 9676篇 |
建筑科学 | 10396篇 |
矿业工程 | 1032篇 |
能源动力 | 9624篇 |
轻工业 | 35546篇 |
水利工程 | 2904篇 |
石油天然气 | 3848篇 |
武器工业 | 11篇 |
无线电 | 42639篇 |
一般工业技术 | 67484篇 |
冶金工业 | 61448篇 |
原子能技术 | 5755篇 |
自动化技术 | 34284篇 |
出版年
2021年 | 3240篇 |
2020年 | 2396篇 |
2019年 | 2927篇 |
2018年 | 4786篇 |
2017年 | 4616篇 |
2016年 | 4974篇 |
2015年 | 3782篇 |
2014年 | 5956篇 |
2013年 | 17266篇 |
2012年 | 9535篇 |
2011年 | 12878篇 |
2010年 | 10004篇 |
2009年 | 11092篇 |
2008年 | 11950篇 |
2007年 | 11783篇 |
2006年 | 10312篇 |
2005年 | 9371篇 |
2004年 | 9078篇 |
2003年 | 8676篇 |
2002年 | 8512篇 |
2001年 | 8316篇 |
2000年 | 7901篇 |
1999年 | 8190篇 |
1998年 | 18231篇 |
1997年 | 13393篇 |
1996年 | 10633篇 |
1995年 | 8388篇 |
1994年 | 7674篇 |
1993年 | 7373篇 |
1992年 | 5715篇 |
1991年 | 5361篇 |
1990年 | 5285篇 |
1989年 | 5121篇 |
1988年 | 4965篇 |
1987年 | 4206篇 |
1986年 | 4292篇 |
1985年 | 5105篇 |
1984年 | 4643篇 |
1983年 | 4324篇 |
1982年 | 3899篇 |
1981年 | 4047篇 |
1980年 | 3701篇 |
1979年 | 3652篇 |
1978年 | 3448篇 |
1977年 | 3979篇 |
1976年 | 5024篇 |
1975年 | 2975篇 |
1974年 | 2806篇 |
1973年 | 2822篇 |
1972年 | 2305篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
This article offers a quantitative model for site selection by high technology manufacturing firms. In the past, site selection studies have usually been qualitative in nature, and very subjective. This is an attempt to introduce a more objective quantitative approach. The site selection factors most important to high technology manufacturing firms were identified, ranked and weighted based on a US Joint Economic Committe survey of such firms. The eight most important factors were: the availability of technical and professional workers, labor costs, tax climate, academic institutions, cost of living, transportation for people, and access to markets. Demographic data on these factors were collected and analyzed for 32 developing high technology areas in the United States. By using the quantitative model, a score was developed for each area, allowing them to be ranked as R & D manufacturing environments. This model should prove a useful tool for both regional planners and high-tech companies seeking to relocate. 相似文献
993.
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
994.
Canham R.O. Smith S.L. Tyrrell A.M. 《Vision, Image and Signal Processing, IEE Proceedings -》2005,152(6):741-749
Complex and highly distorted line drawings are produced by subjects attempting the Rey Complex Figure test, a clinical test of neuropsychological assessment. However, the marking scheme conventionally employed can be subjective and unreliable. In this paper, the first stages in automating this scoring system are investigated using a robust technique to locate a reduced set of scoring sections and a knowledge-based system that employs spatial metrics and fuzzy approximation techniques. Testing the technique using clinical data produced encouraging results that support the argument that this is a feasible approach for implementing a fully automated system, and that in its current state, can be immediately applied in a semi-automated system. 相似文献
995.
996.
997.
The solid phase crystallization kinetics of chemically vapour-deposited amorphous silicon films were studied by in situ X-ray diffraction. We determined the crystalline volume directly from the Bragg peak intensities at various times during isothermal annealing in the temperature range 578 °C < T < 658 °C. From these experiments we deduced that the crystallization was due to nucleation predominantly at the substrate-film interface followed by crystal growth perpendicular to this interface. The crystal growth rate was thermally activated with an activation energy Ev of 3.1 eV. A strong 〈111〉 preferred orientation of the growing polycrystal was observed and the grain size remained constant at about 60 nm. Evidence of stresses at the amorphous-crystalline interface during the early stages of crystallization was observed. A comparison with previous conductivity measurements is also carried out. 相似文献
998.
999.
Ramirez-Angulo J. Sawant M.S. Lopez-Martin A. Carvajal R.G. 《Electronics letters》2005,41(10):570-572
A high-performance compact current mirror implementation with very low input resistance, very high output resistance, high copying accuracy, low input and output voltage supply requirements and high bandwidth is proposed. The circuit characteristics are validated with simulations in 0.5 /spl mu/m CMOS technology and with experimental results. 相似文献
1000.
CHING-HUA Su YI-GAO Sha S. L Lehoczky F. R Szofran D. C Gillies S. D Cobb R. N Scripa 《Journal of Materials Science》1997,32(14):3765-3768
A series of Hg0.84Zn0.16 Te crystal ingots have been grown from pseudobinary melts by the Bridgmam–Stockbarger type directional solidification using
a Marshall Space Flight Center/Space Science Laboratory heat-pipe furnace and the ground control experiment laboratory furnace
of the crystal growth furnace which was flown on the first United States Microgravity Mission. A number of translation rates
and a series of hot- and cold-zone temperatures were employed to assess the influence of growth parameters on the crystal
properties for the purpose of optimizing the in-flight growth conditions.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献