全文获取类型
收费全文 | 33379篇 |
免费 | 4578篇 |
国内免费 | 1739篇 |
专业分类
电工技术 | 2149篇 |
技术理论 | 5篇 |
综合类 | 2825篇 |
化学工业 | 10020篇 |
金属工艺 | 1147篇 |
机械仪表 | 1504篇 |
建筑科学 | 2487篇 |
矿业工程 | 387篇 |
能源动力 | 4666篇 |
轻工业 | 1183篇 |
水利工程 | 668篇 |
石油天然气 | 1018篇 |
武器工业 | 253篇 |
无线电 | 2498篇 |
一般工业技术 | 4114篇 |
冶金工业 | 1224篇 |
原子能技术 | 779篇 |
自动化技术 | 2769篇 |
出版年
2024年 | 177篇 |
2023年 | 645篇 |
2022年 | 1025篇 |
2021年 | 1182篇 |
2020年 | 1207篇 |
2019年 | 1124篇 |
2018年 | 1011篇 |
2017年 | 1101篇 |
2016年 | 1198篇 |
2015年 | 1253篇 |
2014年 | 1833篇 |
2013年 | 2278篇 |
2012年 | 2104篇 |
2011年 | 2435篇 |
2010年 | 1808篇 |
2009年 | 1847篇 |
2008年 | 1787篇 |
2007年 | 2048篇 |
2006年 | 1902篇 |
2005年 | 1814篇 |
2004年 | 1439篇 |
2003年 | 1376篇 |
2002年 | 1137篇 |
2001年 | 905篇 |
2000年 | 789篇 |
1999年 | 607篇 |
1998年 | 585篇 |
1997年 | 501篇 |
1996年 | 432篇 |
1995年 | 378篇 |
1994年 | 285篇 |
1993年 | 257篇 |
1992年 | 245篇 |
1991年 | 167篇 |
1990年 | 159篇 |
1989年 | 138篇 |
1988年 | 101篇 |
1987年 | 74篇 |
1986年 | 66篇 |
1985年 | 48篇 |
1984年 | 63篇 |
1983年 | 40篇 |
1982年 | 25篇 |
1981年 | 11篇 |
1980年 | 10篇 |
1979年 | 4篇 |
1974年 | 3篇 |
1966年 | 7篇 |
1959年 | 15篇 |
1951年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
光盘用光学头物镜性能的综合评估 总被引:1,自引:0,他引:1
论述了采用波象差均方根、点扩展函数、光学传递函数对高次旋转对称非球面光学头物镜性能进行综合评估的方法。作者在正则坐标理论基础〔1〕上编制了光学头物镜性能综合评估软件。给出了评估实例。 相似文献
72.
73.
A study on the prediction of heat transfer coefficient (HTC) and pressure drop of refrigerant mixtures is reported. HTCs and pressure drops of prospective mixtures to replace R12 and R22 are predicted on the same cooling capacity basis. Results indicate that nucleate boiling is suppressed at qualities greater than 20.0% for all mixtures and evaporation becomes the main heat transfer mechanism. For the same capacity, some mixtures containing R32 and R152a show 8.0–10.0% increase in HTCs. Some mixtures with large volatility difference exhibit as much as 55.0% reduction compared with R12 and R22, caused by mass transfer resistance and property degradation due to mixing (32.0%) and reduced mass flow rates (23.0%). Other mixtures with moderate volatility difference exhibit 20.0–30.0% degradation due mainly to reduced mass flow rates. The overall impact of heat transfer degradation, however, is insignificant if major heat transfer resistance exists in the heat transfer fluid side (air system). If the resistance in the heat transfer fluid side is of the same order of magnitude as that on the refrigerant side (water system), considerable reduction in overall HTC of up to 20% is expected. A study of the effect of uncertainties in transport properties on heat transfer shows that transport properties of liquid affect heat transfer more than other properties. Uncertainty of 10.0% in transport properties causes a change of less than 6% in heat transfer prediction. 相似文献
74.
75.
77.
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
78.
Mao Ze yu Chen Chang zhi Department of Hydraulic Engineering Tsinghua University Beijing P.R.China 《水动力学研究与进展(B辑)》1999,(3)
1. INTRODUCTIONThesimulationofstreamwatertemperatureissignificantlyimportantforthestudyofnumericalmodelingofrivericeprocesses[1] .Historically,themathematicalmodelingofthetransportandfateofheatinawaterbodyhasbeenthesubjectofextensivestudyforvariousre… 相似文献
79.
80.
Optical measurements of thermal diffusivity of a material 总被引:2,自引:0,他引:2
The measurement of thermal diffusivity of a material (in particular, a thin film) is important for various reasons, e.g., to predict the heat transfer in the solid subjected to a thermal process, to monitor surface composition or morphology, or to detect invisible subsurface defects like delaminations. This measurement can be done in a noncontact manner using various photothermal methods. Such methods typically involve pulsed heating of the surface by small amounts using a laser source; the decay of the surface temperature after this pulsed photothermal heating is then probed to provide the thermal diffusivity. Various probing methods have been developed in the literature, including the probing of reflection, refraction, and diffraction from the pulsed heated area, infrared thermal radiometry, and surface deformation. This paper provides an overview of such techniques and some examples of their applications. 相似文献