全文获取类型
收费全文 | 391443篇 |
免费 | 3686篇 |
国内免费 | 785篇 |
专业分类
电工技术 | 6604篇 |
综合类 | 217篇 |
化学工业 | 61015篇 |
金属工艺 | 21056篇 |
机械仪表 | 14227篇 |
建筑科学 | 7348篇 |
矿业工程 | 4755篇 |
能源动力 | 7880篇 |
轻工业 | 20936篇 |
水利工程 | 5913篇 |
石油天然气 | 16122篇 |
武器工业 | 41篇 |
无线电 | 36831篇 |
一般工业技术 | 91876篇 |
冶金工业 | 59031篇 |
原子能技术 | 13973篇 |
自动化技术 | 28089篇 |
出版年
2021年 | 4039篇 |
2019年 | 3933篇 |
2018年 | 7426篇 |
2017年 | 7676篇 |
2016年 | 8152篇 |
2015年 | 4490篇 |
2014年 | 7645篇 |
2013年 | 16489篇 |
2012年 | 11032篇 |
2011年 | 13950篇 |
2010年 | 11313篇 |
2009年 | 12609篇 |
2008年 | 12847篇 |
2007年 | 12393篇 |
2006年 | 10349篇 |
2005年 | 9323篇 |
2004年 | 8859篇 |
2003年 | 8610篇 |
2002年 | 8341篇 |
2001年 | 8247篇 |
2000年 | 8005篇 |
1999年 | 7523篇 |
1998年 | 16273篇 |
1997年 | 12014篇 |
1996年 | 9128篇 |
1995年 | 7077篇 |
1994年 | 6395篇 |
1993年 | 6684篇 |
1992年 | 5377篇 |
1991年 | 5452篇 |
1990年 | 5383篇 |
1989年 | 5200篇 |
1988年 | 5109篇 |
1987年 | 4797篇 |
1986年 | 4754篇 |
1985年 | 5191篇 |
1984年 | 4964篇 |
1983年 | 4761篇 |
1982年 | 4429篇 |
1981年 | 4459篇 |
1980年 | 4517篇 |
1979年 | 4706篇 |
1978年 | 4827篇 |
1977年 | 5026篇 |
1976年 | 5767篇 |
1975年 | 4445篇 |
1974年 | 4461篇 |
1973年 | 4555篇 |
1972年 | 4051篇 |
1971年 | 3701篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
31.
N. P. Mandal S. C. Agarwal 《Journal of Materials Science: Materials in Electronics》2003,14(10-12):797-798
Exposure to ammonia (NH3) increases the dark current (DC) in nanocrystalline silicon. Light soaking (LS) for short periods also enhances the dark current, which remains at a high value for a long time. Pumping alone is unable to restore the initial annealed state, but annealing brings it back. The final state obtained by LS and NH3 exposure depends on the order in which they are performed. Evaporated selenium (Se) deposited on nanocrystalline silicon decreases the DC. These effects cannot be explained entirely by the presence of a-Si : H alone, in our sample. DC and photoluminescence (PL) measurements indicate the presence of two types of center in our sample, which behave differently when exposed to NH3. 相似文献
32.
A method of measuring and identifying the static parameters of a bipolar transistor is considered. The characteristic of the transistor, from which the parameters of the model are determined, is chosen depending on what group the calculated parameters belong to. The characteristics are measured in such a way that the equations of the model describing them can be reduced to the simplest form. 相似文献
33.
A. V. Butko A. A. Klimov S. A. Nikitov Yu. A. Filimonov 《Journal of Communications Technology and Electronics》2006,51(8):944-947
The magneto-optical Kerr effect for red (628 nm) and green (532 nm) light is used to study magnetization processes in 2D magnonic crystals obtained by etching pits with the diameter D ≈ 32 μm to a depth of t ≤ 2 μm in a 16.1-μm-thick film of yttrium iron garnet (YIG). Hysteresis loops obtained in the case of the inplane crystal magnetization at 628 nm are characterized by lower saturation fields H s and higher remanent magnetizations than those obtained at 532 nm, a result that is attributed to different absorption coefficients of the YIG film at these wavelengths. This difference between the magnetization curves reflects the fact that the magnonic-crystal surface probed with the green light makes a greater contribution to the magneto-optical Kerr effect. Therefore, the green light is more sensitive to the demagnetizing fields, which govern magnetization processes in the magnonic crystals. 相似文献
34.
R. Murgan F. Razak D. R. Tilley T. Y. Tan J. Osman M. N. A. Halif 《Computational Materials Science》2004,30(3-4):468-473
We derive an expression for transmittivity (TSHG) of second harmonic generation (SHG) signals from a ferroelectric (FE) film. Intensities of up and down fields in the medium are investigated in relation to TSHG. The derivations are made based on undepletion of input fields and nonlinear wave equation derived from the Maxwell equations. We present two cases: film without mirrors and with partial mirrors. Expressions for the newly derived nonlinear susceptibility coefficients of SHG for real crystal symmetry [J. Opt. Soc. Am. B 19 (2002) 2007] are used to get more realistic results. Variations in TSHG with respect to film thickness are illustrated. 相似文献
35.
The electrical properties and microstructure of (Ba,Y)TiO3 PTCR ceramics were studied. The results indicate that the Mn ions increase the intergranular barrier height and produce a high-resistance layer on the grain surface. The temperature-dependent resistances of the grain bulk, surface layer, and grain boundaries, the temperature coefficient of resistance, and the magnitude of the varistor effect were assessed as a function of Mn content. 相似文献
36.
37.
The microstructure evolution in nonstoichiometric titanium carbide is studied during high-temperature deformation at high strain rates and low strains (shock compression) and at slow strain rates and high strains (superplastic regime). The results demonstrate that high-temperature deformation in a broad range of strain rates offers a means of controlling the microstructure of titanium carbide. By varying deformation conditions, one can obtain materials differing in microstructure and chemical composition, in particular, with equilibrium and nonequilibrium microstructures. Accordingly, the physicochemical properties of such materials also differ. 相似文献
38.
K. N. Subramanian J. G. Lee 《Journal of Materials Science: Materials in Electronics》2004,15(4):235-240
Properties of body centered tetragonal tin are highly anisotropic. As a consequence large stresses can develop at the tin grain boundaries due to coefficient of thermal expansion mismatch during temperature excursions. A modeling approach to evaluate the 3D stress states that develop at grain boundaries during thermomechanical fatigue in tin-based solder is presented. Development of significant amounts of stresses in the plane of the grain boundary can cause grain-boundary sliding and surface-relief effects, while those normal to the grain boundary can cause grain-boundary decohesion and cracking. 相似文献
39.
S. V. Doronin 《Chemical and Petroleum Engineering》2006,42(7-8):461-464
Current features are considered in the calculation of carrying capacities for constructions in engineering plant (EP). Methods
and algorithms are described for EP calculations with comprehensive incorporation of the effects from technological and working
defects on the behavior of structures under standard and emergency conditions.
__________
Translated from Khimicheskoe i Neftegazovoe Mashinostroenie, No. 8, pp. 38–40, August, 2006. 相似文献
40.
V. N. Pavlechko 《Journal of Engineering Physics and Thermophysics》2004,77(1):115-120
Relations for determining a motive force in a complex model of mass transfer as applied to concurrent, countercurrent, and cross motion of the vapor and liquid phases have been introduced. These forces have been compared for different forms of organization of the flow, and their comparison with similar quantities from the known Murphree and Hausen models is presented. 相似文献