全文获取类型
收费全文 | 326330篇 |
免费 | 3317篇 |
国内免费 | 1281篇 |
专业分类
电工技术 | 5993篇 |
综合类 | 261篇 |
化学工业 | 47481篇 |
金属工艺 | 18458篇 |
机械仪表 | 13172篇 |
建筑科学 | 6456篇 |
矿业工程 | 3137篇 |
能源动力 | 6797篇 |
轻工业 | 19428篇 |
水利工程 | 4514篇 |
石油天然气 | 10134篇 |
武器工业 | 61篇 |
无线电 | 33039篇 |
一般工业技术 | 73911篇 |
冶金工业 | 49435篇 |
原子能技术 | 9507篇 |
自动化技术 | 29144篇 |
出版年
2021年 | 2734篇 |
2019年 | 2602篇 |
2018年 | 11455篇 |
2017年 | 11902篇 |
2016年 | 9227篇 |
2015年 | 3404篇 |
2014年 | 5094篇 |
2013年 | 11784篇 |
2012年 | 9617篇 |
2011年 | 16199篇 |
2010年 | 14225篇 |
2009年 | 14007篇 |
2008年 | 14168篇 |
2007年 | 15643篇 |
2006年 | 7414篇 |
2005年 | 9407篇 |
2004年 | 7801篇 |
2003年 | 7486篇 |
2002年 | 6373篇 |
2001年 | 5952篇 |
2000年 | 5746篇 |
1999年 | 5587篇 |
1998年 | 13466篇 |
1997年 | 9468篇 |
1996年 | 7248篇 |
1995年 | 5527篇 |
1994年 | 4834篇 |
1993年 | 5070篇 |
1992年 | 3845篇 |
1991年 | 3880篇 |
1990年 | 3781篇 |
1989年 | 3688篇 |
1988年 | 3619篇 |
1987年 | 3181篇 |
1986年 | 3256篇 |
1985年 | 3579篇 |
1984年 | 3310篇 |
1983年 | 3163篇 |
1982年 | 2841篇 |
1981年 | 2816篇 |
1980年 | 2866篇 |
1979年 | 2883篇 |
1978年 | 2882篇 |
1977年 | 3136篇 |
1976年 | 3711篇 |
1975年 | 2652篇 |
1974年 | 2513篇 |
1973年 | 2609篇 |
1972年 | 2327篇 |
1971年 | 2118篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
L. N. Dmitruk S. Kh. Batygov L. V. Moiseeva O. B. Petrova M. N. Brekhovskikh V. A. Fedorov 《Inorganic Materials》2007,43(7):793-796
We have studied the effect of In3+, Pb2+, Gd3+, and Cl (heavier ions) substitutions for Al3+, Ba2+, La3+, and F? on the crystallization stability and UV/IR optical properties of HBLAN fluorohafnatc glasses (HfF4-BaF2-LaF3-AlF3-NaF system). We obtained stable glasses containing InF3 and BaCl2 instead of AlF3 and BaF2, respectively, and offering increased IR transmission. The presence of CCl4 in the process atmosphere and the removal of oxygen-containing impurities via directional solidification are shown to have an advantageous effect on the optical quality of the glasses. The fluoride-chloride glasses are capable of accommodating about 1.5 times higher levels of rare-earth activators in comparison with their fluoride analogs. 相似文献
992.
Yen-Cho ChenJ.N. Chung 《Computers & Fluids》2003,32(6):795-822
This study intends to provide an increased understanding of the laminar-turbulent transition phenomena for the buoyancy-assisted heated vertical channel flow during the early transient stage. The spectral method with weak formulation is applied in the direct numerical simulation. Initial disturbances consist of the finite-amplitude two-dimensional TS wave and a pair of three-dimensional oblique waves for the K-type disturbances. The results from the harmonic energy competitions of different wave modes show that for the buoyancy-assisted heated flow, the (kx=1, kz=1) or (1,1) and (1,0) modes would gain energy immediately and start to rise at almost the same rate. This phenomenon is different from that of the buoyancy-opposed flow, where the (1,1) mode decays slowly in the beginning until other modes gain enough energy and then it begins to grow quickly and overtakes the (1,0) mode after a short time period. These different transition patterns match with the experimental results that the flow transition is supercritical and subcritical for the buoyancy-assisted and -opposed flows, respectively. Buoyancy-assisted heated flow transition follows the general trend of an isothermal flow in the beginning, but the thermal-buoyant force is crucial in accelerating the instability and also causing notable differences during the subsequent transition process. All of the results for the vortex structures development, kinetic energy budget of the disturbances, flow visualization by tagged fluid particles, and the local temperature fluctuations are consistent in pointing to a clear pattern for the buoyancy-assisted heated flow transition. 相似文献
993.
We determine the temperature fields and stresses formed in a long hollow conducting cylinder under the action of pulsed electromagnetic fields specified by the values of the axial component of the vector of intensity of a uniform magnetic field on the inner and outer surfaces. We consider the case where the electromagnetic action obeys the law of damped sinusoid on the inner and outer surfaces of the cylinder. 相似文献
994.
Terahertz characterisation of building materials 总被引:1,自引:0,他引:1
Piesiewicz R. Kleine-Ostmann T. Krumbholz N. Mittleman D. Koch M. Kurner T. 《Electronics letters》2005,41(18):1002-1004
To obtain realistic models for propagation channels in future pico-cellular indoor terahertz communication systems it is necessary to know the reflective properties of building materials found in a typical office environment. The angular dependent reflection coefficients of different building materials were determined using terahertz time-domain spectroscopy in transmission geometry and Fresnel's equations. This approach is more efficient than a set of measurements in reflection geometry for different angles. Verification of the method with a set of such reflection measurements shows an excellent agreement. 相似文献
995.
Cinematic primitives for multimedia 总被引:5,自引:0,他引:5
The development of robust frameworks in interactive multimedia for representing story elements to the machine so that they can be retrieved in multiple contexts is addressed. Interactive multimedia is discussed as a user-directed form of storytelling, and the nature of cinematic storytelling is examined. It is proposed that content can be represented in layers. This model for layered information will allow programs to take advantage of the relation between cinematic sequences and the world they represent. The collection of content by the camera and microphone is considered in this context. The use of the methodology to build meaningful, context-rich sequences is discussed 相似文献
996.
This paper analyses the load influence on a d.c. drive motor servo system for all six degrees of freedom of industrial robots with an articulated configuration. Through the analyses, the analytical equations of total inertia and gravitation moments of an industrial robot servo system for external coordinate function were obtained. A mathematical model of an electro-mechanical industrial robot system was also developed. 相似文献
997.
The fabrication process of a low-temperature poly-Si thin-film transistor (TFT) with a storage capacitor was studied. The atmospheric-pressure chemical-vapour deposited SiO2 protected the buried indium tin oxide (ITO) from reduction by a pure H2 plasma treatment that was essential for the effective improvement of the poly-Si TFT characteristics. Thus, a storage capacitor with an ITO (picture electrode)-SiO2-ITO (buried common electrode) structure was successfully fabricated. The poly-Si TFT with a channel width/length W/L ratio of 5 drove a 3 pF storage capacitor in 2 μs, and it showed superior driverability for LCD use. The TFT also had good hold characteristics under illumination for the realization of grey-scale representation. 相似文献
998.
999.
Convective burning in channels and cracks in solid propellants 总被引:1,自引:0,他引:1
N. N. Smirnov 《Combustion, Explosion, and Shock Waves》1985,21(5):531-538
1000.