全文获取类型
收费全文 | 462175篇 |
免费 | 6082篇 |
国内免费 | 1209篇 |
专业分类
电工技术 | 8710篇 |
综合类 | 580篇 |
化学工业 | 70909篇 |
金属工艺 | 18074篇 |
机械仪表 | 14415篇 |
建筑科学 | 10823篇 |
矿业工程 | 2325篇 |
能源动力 | 10779篇 |
轻工业 | 42939篇 |
水利工程 | 4689篇 |
石油天然气 | 8166篇 |
武器工业 | 98篇 |
无线电 | 54455篇 |
一般工业技术 | 86859篇 |
冶金工业 | 86810篇 |
原子能技术 | 10200篇 |
自动化技术 | 38635篇 |
出版年
2021年 | 3773篇 |
2019年 | 3661篇 |
2018年 | 6284篇 |
2017年 | 6290篇 |
2016年 | 6669篇 |
2015年 | 4221篇 |
2014年 | 7219篇 |
2013年 | 19924篇 |
2012年 | 11588篇 |
2011年 | 15781篇 |
2010年 | 12495篇 |
2009年 | 13959篇 |
2008年 | 14890篇 |
2007年 | 14956篇 |
2006年 | 13488篇 |
2005年 | 12103篇 |
2004年 | 11670篇 |
2003年 | 11343篇 |
2002年 | 11114篇 |
2001年 | 10963篇 |
2000年 | 10587篇 |
1999年 | 10609篇 |
1998年 | 25069篇 |
1997年 | 17859篇 |
1996年 | 14014篇 |
1995年 | 10911篇 |
1994年 | 9725篇 |
1993年 | 9494篇 |
1992年 | 7531篇 |
1991年 | 6998篇 |
1990年 | 7015篇 |
1989年 | 6690篇 |
1988年 | 6448篇 |
1987年 | 5633篇 |
1986年 | 5578篇 |
1985年 | 6445篇 |
1984年 | 6096篇 |
1983年 | 5497篇 |
1982年 | 5206篇 |
1981年 | 5400篇 |
1980年 | 5095篇 |
1979年 | 4914篇 |
1978年 | 4805篇 |
1977年 | 5509篇 |
1976年 | 6906篇 |
1975年 | 4346篇 |
1974年 | 4204篇 |
1973年 | 4351篇 |
1972年 | 3560篇 |
1971年 | 3302篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
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
992.
A voltage-controlled oscillator (VCO) with sine wave output has been built using a tunable inductor along with a tunable capacitor to operate at frequencies ranging from 100 kHz to over 20 MHz. The method of tuning the inductor by changing the permeability of its ferrite core and the ability to extend the frequency response of the core are discussed. Dynamic characteristics of the VCO are explained with examples of a parallel and series tank implementation 相似文献
993.
994.
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
995.
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
996.
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
997.
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
998.
Graduates of clinical training programs were surveyed to determine the degree to which they have found various graduate school experiences useful in their professional work. Samples of academic clinical psychologists and practicing clinical psychologists reported time allocation and preference for various professional activities, perceived usefulness of various theoretical orientations, and the influence on their current professional work of 19 different graduate training topics. Results suggest that where differences exist, academic clinical psychologists are generally more satisfied with Boulder-model-inspired scientific training than are clinical practitioners. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
999.
Shokooh-Saremi M. Ta'eed V.G. Littler I.C.M. Moss D.J. Eggleton B.J. Ruan Y. Luther-Davies B. 《Electronics letters》2005,41(13):738-739
The first ultra-strong, near-perfect, raised-apodised Bragg gratings in As/sub 2/S/sub 3/ chalcogenide rib waveguides using /spl lambda/=532 nm light and a modified Sagnac holographic writing setup are demonstrated. Good agreement is achieved between the experimental results and the numerical modelling of the gratings using the transfer matrix analysis for thin film structures. 相似文献
1000.