全文获取类型
收费全文 | 20028篇 |
免费 | 1900篇 |
国内免费 | 1150篇 |
专业分类
电工技术 | 711篇 |
综合类 | 1522篇 |
化学工业 | 2213篇 |
金属工艺 | 1913篇 |
机械仪表 | 835篇 |
建筑科学 | 2270篇 |
矿业工程 | 854篇 |
能源动力 | 1580篇 |
轻工业 | 503篇 |
水利工程 | 808篇 |
石油天然气 | 1567篇 |
武器工业 | 148篇 |
无线电 | 3072篇 |
一般工业技术 | 2608篇 |
冶金工业 | 580篇 |
原子能技术 | 196篇 |
自动化技术 | 1698篇 |
出版年
2024年 | 83篇 |
2023年 | 293篇 |
2022年 | 478篇 |
2021年 | 622篇 |
2020年 | 651篇 |
2019年 | 587篇 |
2018年 | 507篇 |
2017年 | 715篇 |
2016年 | 702篇 |
2015年 | 756篇 |
2014年 | 1162篇 |
2013年 | 1196篇 |
2012年 | 1447篇 |
2011年 | 1641篇 |
2010年 | 1158篇 |
2009年 | 1173篇 |
2008年 | 1125篇 |
2007年 | 1280篇 |
2006年 | 1263篇 |
2005年 | 992篇 |
2004年 | 835篇 |
2003年 | 780篇 |
2002年 | 625篇 |
2001年 | 571篇 |
2000年 | 498篇 |
1999年 | 387篇 |
1998年 | 293篇 |
1997年 | 258篇 |
1996年 | 206篇 |
1995年 | 178篇 |
1994年 | 124篇 |
1993年 | 130篇 |
1992年 | 106篇 |
1991年 | 65篇 |
1990年 | 47篇 |
1989年 | 40篇 |
1988年 | 27篇 |
1987年 | 18篇 |
1986年 | 11篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 8篇 |
1980年 | 1篇 |
1979年 | 7篇 |
1978年 | 1篇 |
1976年 | 2篇 |
1959年 | 2篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
A detailed numerical three-dimensional (3D) model for a planar solid oxide fuel cell (SOFC) is developed in this paper. The 3D model takes into account detailed processes including transport, chemical and electrochemical processes taking place in the cell. Moreover, effects of the composite electrodes are taken into account by considering an electrochemically active layer of finite thickness in each of the electrodes. The developed model is applied to a repeating unit of an anode-supported SOFC working under direct internal reforming conditions. Detailed results for chemical species, temperature, current density and electric potential distribution are presented and discussed. It was found that the temperature distribution across the cell is more uniform in the interconnects than in the inner part of the cell. However, only small differences in the electric potential between the electrode and the corresponding interconnect are found. The current density in the electrodes is found to be high near the electrolyte and low deep into the electrochemically active layer. The current density is also low under the ribs of the interconnects. 相似文献
992.
993.
The heat transfer of pool boiling in bead packed porous layers was experimentally investigated to analyze the effects of the bead material, bead diameter and the layer number of the porous bed on the transport of flux and the heat transfer coefficients. The glass and copper bead, the bead sizes of 4 mm and 6 mm as well as the bead packed porous structures ranging from one to three layers were chosen in the experiments. The pool boiling heat transfer in the bead packed porous structures and that on the plain surface were compared to analyze the enhancement of pool boiling heat transfer while the bead packed porous layers were employed. The maximum relative error between the collected experimental data of the pure water on a plain surface and the theoretical prediction of pool boiling using the Rohsenow correlation was less than 12%. Besides, the boiling bubble generation, integration and departure have a great effect on the pool boiling and were recorded with a camera in the bead stacked porous structures of the different layers and materials at different heat flux. All these results should be taken into account for the promotion and application of bead packed porous structures in pool boiling to enhance the heat transfer. 相似文献
994.
We study the influence of boundary layer stability on the near‐surface wind speed, especially for high‐wind conditions. An analysis of the wind speed ratio between two vertical levels observed at tall masts in the North Sea and The Netherlands demonstrates that over sea non‐neutral conditions commonly occur, even when the 10 m wind speed is 7 Bft or higher (at least 13.9 ms?1). Over land, stability conditions are always close to neutral for these strong wind conditions. This is because over land, large vertical temperature differences are rare in these conditions. An analysis of 30 years of station data shows that even in storm conditions the ratio of the 10 m wind speed between sea and land depends systematically on the difference between the air temperature and the sea surface temperature. The observational results are reproduced by HARMONIE, a state‐of‐the‐art Numerical Weather Prediction model, although the impact of stability is smaller than in the observations. A model sensitivity analysis for a severe storm shows that the near‐surface wind speed over sea can vary by 10% depending on the difference between the air temperature and the sea surface temperature. The results presented in this study indicate that even in conditions that are usually classified as ‘(near) neutral’, small variations in stability may have a significant impact on the wind profile. They also indicate that for high wind speeds, the sea‐to‐land wind speed ratio is dominated by the stability over sea as in these conditions the stability over land is close to neutral. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
995.
In this study, we consider the frictional sliding contact problem between a functionally graded magnetoelectroelastic (MEE) layer resting on a perfectly insulated rigid half plane and a perfectly conducting rigid flat punch with frictional heat generation. The punch is subjected to magnetoelectromechanical loads. The graded layer is modeled as a nonhomogeneous medium with a transversely isotropic stress–strain law and an exponential variation of the magnetoelectrothermoelastic properties along the thickness direction. Neglecting inertia effects and assuming a constant friction coefficient, the solution is obtained within the framework of steady-state plane magnetoelectrothermoelasticity under plane strain conditions. The heat equation is first solved using Fourier transform to yield the temperature field in the layer which is then substituted in the MEE governing equations. These equations are solved analytically using the same transform leading to three coupled Cauchy-type singular integral equations in which the main unknowns are the normal contact stress, the electric displacement, and the magnetic induction. These equations are then solved numerically to obtain the distributions of the normal contact stress, electric displacement, and magnetic induction at the surface of the graded medium. The main objective of this paper is to study the effect of the nonhomogeneity parameter; the friction coefficient; and the elastic, electric, and magnetic coefficients on the surface contact pressure, electric displacement, and magnetic induction distributions for the case of flat punch profile. 相似文献
996.
以高岭石-甲醇(K-M)复合物为前驱体,利用置换法于常温下制备了3种高岭石-氨基硅烷插层复合物。用X射线衍射、Fourier变换红外光谱仪、透射电子显微镜、热分析仪等对复合物进行了表征。结果表明:3种高岭石-氨基硅烷插层复合物的层间距均扩大至2nm以上,插层率都大于95%。3种氨基硅烷分子均和K-M前驱体的甲氧基共同存在于高岭石层间,均呈两层倾斜排列,倾斜程度不同。氨基硅烷的插入破坏了高岭石层间的氢键,加剧了高岭石自身结构中硅氧四面体片层与铝氧八面体片层之间的错位,使得复合物片层出现不同程度的卷曲变形。3种高岭石-氨基硅烷插层复合物的热分解过程均分三步进行:表面水的蒸发及层间甲氧基的脱嵌分解、插层剂氨基硅烷分子的脱嵌、高岭石脱羟基。 相似文献
997.
Jeff T. Gostick Marios A. IoannidisMichael W. Fowler Mark D. Pritzker 《Journal of power sources》2007
A pore network model of the gas diffusion layer (GDL) in a polymer electrolyte membrane fuel cell is developed and validated. The model idealizes the GDL as a regular cubic network of pore bodies and pore throats following respective size distributions. Geometric parameters of the pore network model are calibrated with respect to porosimetry and gas permeability measurements for two common GDL materials and the model is subsequently used to compute the pore-scale distribution of water and gas under drainage conditions using an invasion percolation algorithm. From this information, the relative permeability of water and gas and the effective gas diffusivity are computed as functions of water saturation using resistor-network theory. Comparison of the model predictions with those obtained from constitutive relationships commonly used in current PEMFC models indicates that the latter may significantly overestimate the gas phase transport properties. Alternative relationships are suggested that better match the pore network model results. The pore network model is also used to calculate the limiting current in a PEMFC under operating conditions for which transport through the GDL dominates mass transfer resistance. The results suggest that a dry GDL does not limit the performance of a PEMFC, but it may become a significant source of concentration polarization as the GDL becomes increasingly saturated with water. 相似文献
998.
Lessons from Rotor 37 总被引:12,自引:0,他引:12
J.D. Denton 《热科学学报(英文版)》1997,6(1):1-13
INTanDUCTIONhi1992theturbomachinerycommittee0ftheIoter-nationalGasTurbineInstitute(IGTI)decidedtosetuPatestcaseforCFDcalculations.Aftersomedebateitwasdecidedthatthetestcasesh0uldbecalculated'blind',i.e.thattheexperimentalresultssh0uldn0tbemadeawilableulltilafterthesolutionshadbeensubndtted.NASA(LewisResearchCenter)offeredasuitabletestca-seintheformofahighlyloadedtransoniccompressorrot0rwhichwasthenbeingtestedwitheXtensiveuseoflaseranemometrytomeasuretheiliternalflow.Themeasurementsw… 相似文献
999.
1000.