全文获取类型
收费全文 | 36336篇 |
免费 | 3387篇 |
国内免费 | 1878篇 |
专业分类
电工技术 | 10205篇 |
技术理论 | 1篇 |
综合类 | 2827篇 |
化学工业 | 5673篇 |
金属工艺 | 1974篇 |
机械仪表 | 1883篇 |
建筑科学 | 1531篇 |
矿业工程 | 1137篇 |
能源动力 | 2398篇 |
轻工业 | 1273篇 |
水利工程 | 487篇 |
石油天然气 | 1240篇 |
武器工业 | 321篇 |
无线电 | 2380篇 |
一般工业技术 | 4537篇 |
冶金工业 | 1888篇 |
原子能技术 | 296篇 |
自动化技术 | 1550篇 |
出版年
2024年 | 186篇 |
2023年 | 713篇 |
2022年 | 1012篇 |
2021年 | 1176篇 |
2020年 | 1322篇 |
2019年 | 1129篇 |
2018年 | 1070篇 |
2017年 | 1278篇 |
2016年 | 1160篇 |
2015年 | 1216篇 |
2014年 | 2256篇 |
2013年 | 2031篇 |
2012年 | 2621篇 |
2011年 | 2740篇 |
2010年 | 1845篇 |
2009年 | 2003篇 |
2008年 | 1863篇 |
2007年 | 2327篇 |
2006年 | 2143篇 |
2005年 | 1840篇 |
2004年 | 1594篇 |
2003年 | 1511篇 |
2002年 | 1129篇 |
2001年 | 992篇 |
2000年 | 804篇 |
1999年 | 673篇 |
1998年 | 527篇 |
1997年 | 405篇 |
1996年 | 349篇 |
1995年 | 314篇 |
1994年 | 249篇 |
1993年 | 155篇 |
1992年 | 171篇 |
1991年 | 130篇 |
1990年 | 103篇 |
1989年 | 108篇 |
1988年 | 83篇 |
1987年 | 61篇 |
1986年 | 50篇 |
1985年 | 33篇 |
1984年 | 53篇 |
1983年 | 60篇 |
1982年 | 43篇 |
1981年 | 19篇 |
1980年 | 15篇 |
1979年 | 8篇 |
1978年 | 3篇 |
1975年 | 4篇 |
1955年 | 3篇 |
1951年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
The compositions (1 −x)Ag2SO4−(x)BaSO4, wherex=0·01 to 0·6, were prepared by slow cooling of the melt. The extent of the solid solubility of Ba2+ in Ag2SO4 was determined by X-ray powder diffraction and scanning electron microscopy. The bulk conductivity of each sample was obtained
using a detailed impedance analysis. The partial substitution of Ba2+ results in the enhancement of conductivity in compliance with the classical aliovalent doping theory. A simplistic model
based on lattice distortion (expansion) due to partial substitution of Ag+ by the bigger Ba2+ has been considered to explain enhanced conductivity. Beyond solid-solubility limit (5·27 mole%) the BaSO4-dispersed Ag2SO4 conductivity follows the usual trend seen in binary systems. An increase in conductivity in this case is discussed in the
light of interfacial reactions and surface defect chemistry. The maximum conductivity in 20 mole% BaSO4 dispersed Ag2SO4 is due to percolation threshold. 相似文献
102.
A restructured electricity system may undervalue renewable energy. We remain wary of unregulated markets, but urge the renewable energy community to begin considering how they could adapt to increasing customer choice. 相似文献
103.
国内外电雷管电引火元件现状及改进思路 总被引:1,自引:1,他引:0
文章分析了目前国内外电引火元件的现状,列举了国外著名火炸药公司典型的几种电引火元件结构及电火参数,提出了改进我国电引火元件的技术构思。 相似文献
104.
文中介绍了利用硫磺盖帽电探针测定工业炸药爆轰压力的方法,并对煤炭工业常的4类11个品种炸药的爆轰压力进行了实际测量。 相似文献
105.
Transport properties of 1,1-difluoroethane (R152a) 总被引:2,自引:0,他引:2
R. Krauss V. C. Weiss T. A. Edison J. V. Sengers K. Stephan 《International Journal of Thermophysics》1996,17(4):731-757
Based on reliable. carefully selected data sets. equations for the thermal conductivity and the viscosity of the refrigerant R 112a are presented. They are valid at temperatures from 240 to 440 K, pressures up to 20 MPa. and densities up to 1050 kg · m–3. including the critical region. 相似文献
106.
介绍了非稳态法测试液体在低温下(-100~50℃)的热导率的测试原理、方法,测试了全氟三乙胺的低温热导率。为了提高测试的重复性,采用了相对比较法,并给出了测试装置及测试结果和误差分析。 相似文献
107.
108.
F. Cœuret E. Oliveira Vilar E. Bezerra Cavalcanti 《Journal of Applied Electrochemistry》2002,32(10):1175-1182
The paper deals with carbon fibre cloth electrodes, employed in the fabrication of composite materials. The electrical conductivity of single bundles, groups of bundles and cloth is studied. Ohm's law applies to the electrical conduction in the direction of the fibre length, but bundle conductivity decreases with the number of fibres in the bundle. Electrochemical mass transfer between a flowing electrolyte and a cloth arranged as a flow-through or a flow-by porous electrode indicates the existence of double porosity in the material. Due to double porosity, only the external surface of the cloth works as an electrode. This finding shows that the material is not suitable for such an application. 相似文献
109.
110.
Evolution of the capillary network in a reactive powder concrete during hydration process 总被引:7,自引:0,他引:7
V. Morin F. Cohen-Tenoudji A. Feylessoufi P. Richard 《Cement and Concrete Research》2002,32(12):1907-1914
Ultrasonic waves in echographic mode, combined with autogenous shrinkage measurements, were used to study the evolution of the capillary network of reactive powder concrete (RPC) from the time after the mixing. Two characteristic porous classes have been identified: the first, between 10 and 20 nm, begins when the material reaches its solid hyperstatic state, and the second about 1 or 2 nm. The first class is associated with the porous space between the C-S-H hydrate clusters and the second with the internal porosity of the hydrate. The evolution of the active capillary radius as a function of the degree of hydration allows us to understand the strong interaction between the capillary network size and the chemical activity given by the dissipated calorimetric power curve. Indeed, the maximum point of the chemical activity marks the transition of the first class of pores to the second one. Finally, measurements of electrical conductivity through RPC samples show that after the maximum of the dissipated power, the curve of this electrical conductivity presents the same evolution as the capillary radius. As the electrical conductivity clearly depends on the evolution of the capillary network, the similarity between the results confirms our analysis in pore classes. 相似文献