全文获取类型
收费全文 | 7964篇 |
免费 | 1079篇 |
国内免费 | 497篇 |
学科分类
工业技术 | 9540篇 |
出版年
2024年 | 56篇 |
2023年 | 268篇 |
2022年 | 204篇 |
2021年 | 342篇 |
2020年 | 316篇 |
2019年 | 304篇 |
2018年 | 285篇 |
2017年 | 324篇 |
2016年 | 330篇 |
2015年 | 282篇 |
2014年 | 352篇 |
2013年 | 687篇 |
2012年 | 508篇 |
2011年 | 476篇 |
2010年 | 330篇 |
2009年 | 423篇 |
2008年 | 365篇 |
2007年 | 422篇 |
2006年 | 378篇 |
2005年 | 341篇 |
2004年 | 350篇 |
2003年 | 318篇 |
2002年 | 289篇 |
2001年 | 250篇 |
2000年 | 196篇 |
1999年 | 183篇 |
1998年 | 164篇 |
1997年 | 128篇 |
1996年 | 127篇 |
1995年 | 104篇 |
1994年 | 78篇 |
1993年 | 71篇 |
1992年 | 71篇 |
1991年 | 34篇 |
1990年 | 40篇 |
1989年 | 39篇 |
1988年 | 29篇 |
1987年 | 14篇 |
1986年 | 11篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 11篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1959年 | 2篇 |
1951年 | 6篇 |
排序方式: 共有9540条查询结果,搜索用时 15 毫秒
1.
Navab SinghAuthor Vitae Moitreyee Mukherjee-RoyAuthor VitaeSohan Singh MehtaAuthor Vitae 《Microelectronics Journal》2003,34(4):237-245
The patterning of contact holes by selecting out-of-focus image plane (defocus) using attenuated phase shift masks (APSM) has been studied. Defocus is found to enhance the image modulation at low partial coherence for contact holes with negative local average of mask function. Semi-dense holes up to 130 nm in 8% APSM have been printed by 0.5 μm defocus at a partial coherence of 0.31 using KrF scanner with highest numerical aperture of 0.68. However, these holes were closed with in-focus imaging. Defocus is also found to be beneficial for patterning the pitches that have extensive side lobes with in-focus imaging. 相似文献
2.
Heat transfer of highly consistent shear-thinning fluids flowing in a horizontal cylindrical channel has been investigated numerically and experimentally when the outer channel wall is subjected to a constant convective heat exchange. The case considered being cooling, a possible ice deposit must be taken into account. The variation of the rheological properties with temperature must be considered as well. 相似文献
3.
Theoretical analysis of heat transfer in laminar pulsating flow 总被引:2,自引:0,他引:2
H.N. HemidaM.N. Sabry A. Abdel-RahimH. Mansour 《International Journal of Heat and Mass Transfer》2002,45(8):1767-1780
Pulsation effect on heat transfer in laminar incompressible flow, which led to contradictory results in previous studies, is theoretically investigated in this work starting from basic principles in an attempt to eliminate existing confusion at various levels. First, the analytical solution of the fully developed thermal and hydraulic profiles under constant wall heat flux is obtained. It eliminates the confusion resulting from a previously published erroneous solution. The physical implications of the solution are discussed. Also, a new time average heat transfer coefficient for pulsating flow is carefully defined such as to produce results that are both useful from the engineering point of view, and compliant with the energy balance. This rationally derived average is compared with intuitive averages used in the literature. New results are numerically obtained for the thermally developing region with a fully developed velocity profile. Different types of thermal boundary conditions are considered, including the effect of wall thermal inertia. The effects of Reynold and Prandtl numbers, as well as pulsation amplitude and frequency on heat transfer are investigated. The mechanism by which pulsation affects the developing region, by creating damped oscillations along the tube length of the time average Nusselt number, is explained. 相似文献
4.
Critical heat fluxes (CHFs) were measured for two types of rectangular ducts containing horizontal flat plate heaters. One has the flat plate heater of 6 mm wide and 20 mm long located on the inner lower wall at 50 mm from the inlet. The other duct has two horizontal flat plates of 6 mm wide and 20 mm long on inner upper and lower walls at 50 mm from the inlet. The equation of CHF for the forced convection containing a new nondimensional-parameter m introduced in order to calculate cross-sectionally averaged liquid temperature at the center of the duct was derived based on two fluid model, ordinary convection theorem and experimental results. It was confirmed that this correlation can describe not only the author's data on the duct but also other worker's data for channels with different shapes and sizes. 相似文献
5.
6.
Wenwei He Wuping Liao Weiwei Wang Deqian Li Chunji Niu 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(9):1314-1320
BACKGROUND: Thermodynamics and kinetics data are both important to explain the extraction property. In order to develop a novel separation technology superior to current extraction systems, many promising extractants have been developed including calixarene carboxylic acids. The extraction thermodynamics behavior of calix[4]arene carboxylic acids has been reported extensively. In this study, the mass transfer kinetics of neodymium(III) and the interfacial behavior of calix[4]arene carboxylic acid were investigated. RESULTS: The rate constant (Kao) becomes constant when the stirring speed was controlled between 250 rpm and 400 rpm. The activation energy (Ea) was calculated to be 21·41 kJ mol?1 or 88·17 kJ mol?1 (dependent on temperature) from the slope of log Kao against 1000/T. The linear relationship between the specific area and the extraction rate is the characteristic of an interfacial reaction control. The minimum bulk concentration of the extractant necessary to saturate the interface (Cmin) is lower than 4·19 × 10?4 mol L?1. CONCLUSION: The effect of stirring speed, temperature, and species concentration on the extraction rate demonstrates that the extraction regime depends on the extraction conditions. The chemical reaction control governs the extraction regime at temperatures below 303 K and a mixed control regime occurs when the temperature is between 303 K and 318 K. The probable locale for the chemical reaction is at the liquid–liquid interface and the rate equation is deduced to be: ? d[Nd3+](a)/dt = kf[Nd3+](a)[H4A](o)0·727[H+](a)?0·978. The rate‐controlling step was suggested by the analysis of the experimental results. Copyright © 2008 Society of Chemical Industry 相似文献
7.
螺旋翅片管的换热计算 总被引:1,自引:0,他引:1
本文引入区域平均表面传热系数的概念。在实验研究的基础上进行了肋基和肋端温度分布预测及肋片换热数值计算。 相似文献
8.
9.
10.
The phenomena of natural convection caused by a concentration gradient usually creates currents as a result of buoyancy forces. These forces are formed from the combined effect of a fluid density gradient and the body force (gravitational force). The above phenomenon was studied experimentally in a circular glass column of 0.08 m diameter and 1 m length. This column was erected vertically and filled with distilled water with a salt bag placed on top of it and partially immersed in water. The dissolution mechanism was then modelled and a finite difference method was used to solve the formulated equations by using the implicit scheme of MacCormack (Anderson et al., 1984). The experimental results and the numerical predictions are represented graphically and give compatible agreement. 相似文献