全文获取类型
收费全文 | 245967篇 |
免费 | 2714篇 |
国内免费 | 430篇 |
专业分类
电工技术 | 4353篇 |
综合类 | 260篇 |
化学工业 | 40142篇 |
金属工艺 | 9460篇 |
机械仪表 | 7480篇 |
建筑科学 | 5568篇 |
矿业工程 | 1425篇 |
能源动力 | 5220篇 |
轻工业 | 25168篇 |
水利工程 | 2509篇 |
石油天然气 | 5121篇 |
武器工业 | 33篇 |
无线电 | 25682篇 |
一般工业技术 | 45360篇 |
冶金工业 | 46595篇 |
原子能技术 | 5976篇 |
自动化技术 | 18759篇 |
出版年
2021年 | 2140篇 |
2019年 | 2045篇 |
2018年 | 3541篇 |
2017年 | 3465篇 |
2016年 | 3733篇 |
2015年 | 2269篇 |
2014年 | 3970篇 |
2013年 | 10452篇 |
2012年 | 6267篇 |
2011年 | 8441篇 |
2010年 | 6652篇 |
2009年 | 7361篇 |
2008年 | 7732篇 |
2007年 | 7888篇 |
2006年 | 7036篇 |
2005年 | 6167篇 |
2004年 | 5935篇 |
2003年 | 5729篇 |
2002年 | 5782篇 |
2001年 | 5666篇 |
2000年 | 5482篇 |
1999年 | 5437篇 |
1998年 | 12893篇 |
1997年 | 9125篇 |
1996年 | 7020篇 |
1995年 | 5463篇 |
1994年 | 4855篇 |
1993年 | 4738篇 |
1992年 | 3748篇 |
1991年 | 3471篇 |
1990年 | 3671篇 |
1989年 | 3533篇 |
1988年 | 3366篇 |
1987年 | 2934篇 |
1986年 | 2973篇 |
1985年 | 3423篇 |
1984年 | 3266篇 |
1983年 | 2939篇 |
1982年 | 2786篇 |
1981年 | 2873篇 |
1980年 | 2771篇 |
1979年 | 2669篇 |
1978年 | 2719篇 |
1977年 | 3004篇 |
1976年 | 3864篇 |
1975年 | 2422篇 |
1974年 | 2272篇 |
1973年 | 2405篇 |
1972年 | 2004篇 |
1971年 | 1879篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
162.
P. E. Donovan 《Journal of Materials Science》1989,24(2):523-535
The geometry of plastic flow under spherical and Vickers indentors in Pd40Ni40P20 metallic glass has been investigated by sectioning and etching. The surface pile-ups and slip lines around the indentations are found to be only a small part of the total deformation. Beneath the surface extensive plastic zones are formed in which material is moved radially away from the indentor, but this movement is produced by slip on surfaces of high shear stress rather than by direct radial flow or compaction. Networks of cracks or incipient cracks also form around an indentation but are not normally visible until the material is etched. 相似文献
163.
L. B. Getsov A. Ya. Madorskii N. N. Mozzhukhina A. G. Tereshchenko E. E. Yushchenkov 《Strength of Materials》1989,21(1):92-98
Leningrad. Translated from Problemy Prochnosti, No. 1, pp. 71–76, January, 1989. 相似文献
164.
A model of the electronic structure of graphite-like carbon films, describing the semiconductor properties of this material, is presented. Spectra of optical constants of microcrystalline carbon films in the region λ = 0.4–8.0 μm were studied by the spectral ellipsometry and IR reflection methods. A number of distinctive features of the spectra, associated with both the appearance of C---C- and C---Hn-type bonds and direct energy gaps, were found. Analysis of the optical data using the proposed model makes possible a common interpretation of our results and literature data. Values of a parameter Θ, which is an averaged qualitative parameter of structural distortions within carbon microcrystallites as compared with crystalline graphite, are determined from comparison of theoretical results and experimental data. 相似文献
165.
This paper derives the governing equations for the thermomechanical behaviour of composites. When the basic equations for the thermoelastic behaviour of solids were first derived in the nineteenth century several approximations were made. The effect of these assumptions are discussed and illustrated by the results of a simple laboratory test. The implications of this work on the analysis of impact damaged laminates are then discussed. 相似文献
166.
R. Morena P. E. Lockwood L. Evans C. W. Fairhurst 《Journal of the American Ceramic Society》1986,69(4):75-C-
The effect on mechanical behavior of ZrO2 additions to a dental porcelain was investigated. The ZrO2 was introduced into the glassy matrix phase of the porcelain by refritting the all-glass porcelain constituent. X-ray diffraction indicated that a sizeable fraction of the ZrO2 was retained in the tetragonal form after the porcelain was fired. Zirconia additions to the porcelain produced substantial improvements in fracture toughness, strength, and thermal shock resistance. 相似文献
167.
168.
169.
E St?lberg S St?lberg M Melander K Arimura 《Computer methods and programs in biomedicine》1991,34(2-3):219-227
Programs for rule based electromyography (EMG) interpretation and reporting are described. A number of parameters are obtained during an EMG investigation. The combination of these data leads to a neurophysiological conclusion. Knowledge from the literature, research and experience is the basis for rule development. Rules have been developed for 14 of the most commonly used classifications of an EMG. The syntax is relatively easy and the user may change the rules, add rules or apply the system for other types of data. The results are displayed in a new graphical way. The system presented here is part of an integrated EMG laboratory with administrative routines, distributed databases for storage of results and routines for automatic report generation. 相似文献
170.
Seo K. Heiblum M. Knoedler C.M. Oh J.E. Pamulapati J. Bhattacharya P. 《Electron Device Letters, IEEE》1989,10(2):73-75
A high-gain ballistic hot-electron device is described. The GaAs-AlGaAs heterostructure device, with a 21-mm-thick pseudomorphic In 0.12Ga0.88As base, had a current gain of 27 at 77 K and 41 at 4.2 K. As characteristically seen in ballistic devices, transfer into the L valley limited the maximum gain. The Γ-L valley separation in the strained In0.12Ga0.88As was estimated to be about 380 meV 相似文献