全文获取类型
收费全文 | 168425篇 |
免费 | 1328篇 |
国内免费 | 193篇 |
专业分类
电工技术 | 2553篇 |
综合类 | 120篇 |
化学工业 | 26629篇 |
金属工艺 | 9471篇 |
机械仪表 | 5717篇 |
建筑科学 | 3009篇 |
矿业工程 | 1887篇 |
能源动力 | 2709篇 |
轻工业 | 8818篇 |
水利工程 | 2729篇 |
石油天然气 | 8692篇 |
武器工业 | 12篇 |
无线电 | 14497篇 |
一般工业技术 | 38273篇 |
冶金工业 | 27797篇 |
原子能技术 | 6933篇 |
自动化技术 | 10100篇 |
出版年
2018年 | 2980篇 |
2017年 | 3091篇 |
2016年 | 3345篇 |
2015年 | 1674篇 |
2014年 | 2957篇 |
2013年 | 6339篇 |
2012年 | 4313篇 |
2011年 | 5402篇 |
2010年 | 4420篇 |
2009年 | 4896篇 |
2008年 | 4943篇 |
2007年 | 4872篇 |
2006年 | 4143篇 |
2005年 | 3821篇 |
2004年 | 3637篇 |
2003年 | 3522篇 |
2002年 | 3451篇 |
2001年 | 3463篇 |
2000年 | 3361篇 |
1999年 | 3213篇 |
1998年 | 7020篇 |
1997年 | 5150篇 |
1996年 | 3821篇 |
1995年 | 2916篇 |
1994年 | 2593篇 |
1993年 | 2720篇 |
1992年 | 2255篇 |
1991年 | 2307篇 |
1990年 | 2409篇 |
1989年 | 2315篇 |
1988年 | 2313篇 |
1987年 | 2190篇 |
1986年 | 2246篇 |
1985年 | 2292篇 |
1984年 | 2206篇 |
1983年 | 2136篇 |
1982年 | 1980篇 |
1981年 | 2197篇 |
1980年 | 2055篇 |
1979年 | 2269篇 |
1978年 | 2431篇 |
1977年 | 2430篇 |
1976年 | 3095篇 |
1975年 | 2244篇 |
1974年 | 2307篇 |
1973年 | 2342篇 |
1972年 | 2155篇 |
1971年 | 1911篇 |
1970年 | 1701篇 |
1969年 | 1632篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A new and simple compensated structure for a vertically installed planar (VIP) 3 dB directional coupler has been studied theoretically as well as experimentally by combining an improved 2-D-general finite difference (2-D-GFD) design procedure with a three-dimensional finite difference time domain (3-D-FDTD) method. The obtained full wave analysis results agree well with the measured ones. The investigations have shown that with this planar compensated structure, a better performance of the VIP coupler in the L-band can be realized by only using the same kind of dielectric substrate for its vertical and horizontal one 相似文献
992.
The behavior of the components of an inseparable mixture of processing wastes containing polyamide, polyacrylonitrile, and cellulose fibres was investigated. The possibility of using them in production of wood—polymer composites if cyclization in the structure of PAN and chemical reaction of basic and acid functional groups play the determining role in intensification of the interfacial interaction in the composite and correspondingly in increasing the strength properties of the final product, was demonstrated. The parameters of the process were optimized, and this allowed for obtaining materials with a static bending strength of up to 80 MPa, water absorption of up to 11%, and a degree of swelling of up to 8.3% according to GOST, which satisfies the requirements for brand STs-500 ultrahard board materials.St. Petersburg State University of Technology and Design. Wood Technology Academy, St. Petersburg. Translated from Khimicheskie Volokna, No. 6, pp. 39–44, November–December, 1996. 相似文献
993.
994.
Polarisation insensitive semiconductor optical amplifier withintegrated electroabsorption modulators
Koren U. Miller B.I. Young M.G. Chien M. Raybon G. Brenner T. Ben-Michael R. Dreyer K. Capik R.J. 《Electronics letters》1996,32(2):111-112
The authors demonstrate a 1.55 μm wavelength multiquantum well semiconductor optical amplifier, integrated with bulk layer electroabsorption modulators and passive waveguide beam expanders at the input and output ports. The device has a fibre to fibre gain of 9 dB, an extinction ratio of 15 dB per modulator, a spectral range >35 nm, and polarisation sensitivity <1 dB 相似文献
995.
996.
Models for the elastic deformation of honeycombs 总被引:8,自引:0,他引:8
A theoretical model has been developed for predicting the elastic constants of honeycombs based on the deformation of the honeycomb cells by flexure, stretching and hinging. This is an extension of earlier work based on flexure alone. The model has been used to derive expressions for the tensile moduli, shear moduli and Poisson's ratios. Examples are given of structures with a negative Poisson's ratio. It is shown how the properties can be tailored by varying the relative magnitudes of the force constants for the different deformation mechanisms. Off-axis elastic constants are also calculated and it is shown how the moduli and Poisson's ratios vary with applied loading direction. Depending on the geometry of the honeycomb the properties may be isotropie (for regular hexagons) or extremely anisotropic. Again, the degree of anisotropy is also affected by the relative magnitude of the force constants for the three deformation mechanisms. 相似文献
997.
A justification is given for the conversion of pointer-reading manual gear measuring instruments to digital ones. The BV-5126
digital gear tooth micrometer and BV-5126 pitch gauge, both developed at NII-izmerieniya, are described. These instruments,
while retaining the advantages of mechanical manual instruments, are more convenient in use, and have smaller errors. Computer
software is also described which considerably widens the functional possibilities of the manual instruments.
Translated from Izmeritel'naya Tekhnika, No. 6, pp. 31–33, June, 1996. 相似文献
998.
It is shown that plastic deformations of metals govern the kinetics of hydrogen release (by decreasing the work function of escape of an electron into solution) and are a controlling factor in the processes of hydrogenation and crack growth by a hydrogen mechanism.Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 29, No. 6, pp. 16–22, November–December, 1993. 相似文献
999.
Ufa Petroleum Institute, Ufa. Translated from Fiziko-Khimicheskaya Mekhanika Materialov. Vol. 29, No. 5, pp. 97–98, September–October, 1993. 相似文献
1000.
An intrinsic guanine nucleotide exchange inhibitor in Gi2 alpha. Significance of G-protein self-suppression which antagonizes receptor signal 总被引:1,自引:0,他引:1
T Okamoto Y Murayama SM Strittmatter T Katada S Asano E Ogata I Nishimoto 《Canadian Metallurgical Quarterly》1994,269(19):13756-13759
The alpha subunit of Gi2 (Gi2 alpha) is a member of the heterotrimeric G protein family, which transduces receptor signals as a proto-oncogene product. We have found a novel self-suppressive region in Gi2 alpha near its C terminus. A polypeptide consisting of residues 338-352 of Gi2 alpha (Gi2 alpha-339-352) antagonizes receptor- and receptor peptide-stimulated Gi2 alpha activation, without affecting basal activity. Antagonism by Gi2 alpha-338-352 is attributable to an interaction with activated Gi2 alpha, which is not competitive with receptor polypeptides. Combined with the reports suggesting the presence of self-suppressive domains in a juxta-C-terminal portion of Gi2 alpha and G(o) alpha, this study supports the hypothesis that Gi2 alpha-338-352 constitutes an intrinsic guanine nucleotide exchange inhibitor, which in turn antagonizes receptor stimulation, suggesting that G proteins are activated by receptors through relaxation of a self-suppressive conformation. 相似文献