全文获取类型
收费全文 | 70800篇 |
免费 | 6260篇 |
国内免费 | 3734篇 |
专业分类
电工技术 | 5263篇 |
综合类 | 5506篇 |
化学工业 | 11612篇 |
金属工艺 | 7618篇 |
机械仪表 | 4145篇 |
建筑科学 | 6124篇 |
矿业工程 | 1744篇 |
能源动力 | 4346篇 |
轻工业 | 4566篇 |
水利工程 | 1678篇 |
石油天然气 | 3556篇 |
武器工业 | 631篇 |
无线电 | 5944篇 |
一般工业技术 | 8031篇 |
冶金工业 | 5046篇 |
原子能技术 | 1337篇 |
自动化技术 | 3647篇 |
出版年
2024年 | 302篇 |
2023年 | 993篇 |
2022年 | 1881篇 |
2021年 | 2260篇 |
2020年 | 2397篇 |
2019年 | 1932篇 |
2018年 | 1824篇 |
2017年 | 2444篇 |
2016年 | 2586篇 |
2015年 | 2674篇 |
2014年 | 4139篇 |
2013年 | 4374篇 |
2012年 | 5123篇 |
2011年 | 5558篇 |
2010年 | 3854篇 |
2009年 | 4039篇 |
2008年 | 3596篇 |
2007年 | 4622篇 |
2006年 | 4239篇 |
2005年 | 3453篇 |
2004年 | 3046篇 |
2003年 | 2611篇 |
2002年 | 2164篇 |
2001年 | 1926篇 |
2000年 | 1581篇 |
1999年 | 1255篇 |
1998年 | 1014篇 |
1997年 | 881篇 |
1996年 | 789篇 |
1995年 | 599篇 |
1994年 | 531篇 |
1993年 | 375篇 |
1992年 | 367篇 |
1991年 | 318篇 |
1990年 | 241篇 |
1989年 | 161篇 |
1988年 | 134篇 |
1987年 | 81篇 |
1986年 | 84篇 |
1985年 | 70篇 |
1984年 | 67篇 |
1983年 | 49篇 |
1982年 | 37篇 |
1981年 | 22篇 |
1980年 | 29篇 |
1979年 | 18篇 |
1977年 | 10篇 |
1975年 | 4篇 |
1959年 | 13篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
Mayank Kashyap 《Powder Technology》2008,183(3):441-453
The effect of electric field on the hydrodynamics of nanoparticles was studied in a fluidized rectangular bed, with electrodes attached to two parallel walls. It was shown that the electric field of the order of 3 times the gravity markedly decreased the bed expansion and increased the solids volume fraction of nanoparticles fluidized by air. In these experiments, a light diode assembly was utilized to infer the local solids volume fractions within a rectangular bed of 10 nm silica particles. These experimental measurements yielded a two dimensional solids volume fraction distribution within the rectangular bed. The experimental results provided some new insights into the distribution of solids within the bed. The agglomerate diameters were computed using a momentum balance with the drag given by the Ergun equation and the empirical Richardson-Zaki method. Both methods yielded agglomerate diameters of the order of 100 μm and showed dependence on the strength of the electric field. The electric field decreased the granular temperature of the nanoparticles. 相似文献
12.
A model is presented for drying of a single porous particle with superheated steam and humid air. Experimental data for spherical porous ceramic particle reported in the literature were used for the validation of the model. An inversion temperature at which the evaporation rates within superheated steam and humid air are equal was predicted. The effect of thermophysical properties of the particle (permeability 10-14 - 10-17 m2, diameter 3 × 10-3 - 10 × 10-3 m) and operating variables (gas mass flux 0.26 - 0.78 kg m-2 s-1, drying agent temperature 120-200°C) is tested. The inversion temperature is shown to be affected by the thermophysical properties of the porous particle and of the drying agent. 相似文献
13.
14.
M. Jayasankar 《Materials Letters》2007,61(3):790-793
Formation of aluminium titanate (AT) has been achieved at low temperature through sol-gel process using boehmite and titanium hydroxide as precursors by controlling the particle size at nanoscale followed by in-situ peptisation. The formations of AT phase, particle size distributions, sintering and thermal expansion characteristics, and microstructural features have been reported. DTA and XRD analysis have been performed to confirm the formation of AT. A 94% relative density was obtained for aluminium titanate sintered at 1550 °C with controlled grain size in the range of 2-3 μm. 相似文献
15.
Jules Sadefo Kamdem 《Computing and Visualization in Science》2007,10(4):197-210
In this paper, we generalize the Linear VaR method from portfolios with normally distributed risk factors to portfolios with
mixture of elliptically distributed ones. We treat both the Expected Shortfall and the Value-at-Risk of such portfolios. Special
attention is given to the particular case of a mixture of multivariate t-distributions.
This is a part of J. SADEFO-KAMDEM PhD Thesis[12] of the Université de Reims, France . It has been presented at the workshop
on modelling and computation in Financial Engineering at Bad Herrenalb, Germany May 6-8, 2003. The author is an associate
professor at the Department of mathematics, université d’Evry Val d’Essonne. 相似文献
16.
17.
18.
Aboubakar Sako Kenneth G. MacLeod Catherine M. O’Reilly 《Journal of Great Lakes research》2007,33(4):806-815
In this study, we measured growth trends in oxygen and carbon isotopic ratios in whole sagittal otoliths from three adult centropomid fish (Lates stappersii) from each of three sub-basins of Lake Tanganyika, East Africa. Sampling density was 20 to 50 samples per otolith. Both δ18O and δ13C values increase with age. The δ18O data suggest that otoliths were precipitated near the expected equilibrium with the ambient environment (ca. +3.5‰) and support a migration pattern from surface waters during larval stages to deeper waters (40 to 80 m) for mature fish. Relatively high δ18O values in the southern sub-basin are consistent with cooler temperatures in the region during seasonal upwelling. The δ13C increase from otolith core to edge is large (up to 4‰) and is interpreted as due to ontogenetic changes in diet and contributions from a decrease in the proportion of respired CO2 incorporated into otolith carbonate as metabolic rates of the fish dropped with maturity. The data seem to successfully reveal life strategy and migration patterns of L. stappersii, document regional differences in lake conditions, and provide a record of temperature within the water column during which the fish lived. Higher resolution studies and analyses of historical samples could be used to constrain modern and past growth patterns, and to reconstruct past temperature gradients and productivity patterns in the lake. 相似文献
19.
Shunsuke Ohashi 《Electrical Engineering in Japan》2005,150(1):71-77
Magnetic bearing using pinning force of a permanent magnet and a high‐temperature superconductor has been developed. Additional permanent magnet is introduced to increase the levitation force of the magnetic bearing. In this hybrid magnetic bearing system, levitation force is mainly given by the repulsive force of the permanent magnets, and stability for the lateral direction is given by pinning force of the superconductor. The experimental device is developed. A ring‐type superconductor and a bulk one are examined. Levitation characteristics of the hybrid magnetic bearing are measured. The bulk superconductor shows better characteristics of both levitation and lateral stability than the ring one. Levitation force of the hybrid system becomes about twice as large as that of the nonhybrid one. Although, the repulsive force of the permanent magnet decreases the lateral stability of the system, its influence becomes small by choosing an adequate position of the permanent magnets and the superconductor. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(1): 71–77, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10350 相似文献
20.