全文获取类型
收费全文 | 189039篇 |
免费 | 22077篇 |
国内免费 | 13942篇 |
专业分类
电工技术 | 15854篇 |
技术理论 | 4篇 |
综合类 | 21933篇 |
化学工业 | 17436篇 |
金属工艺 | 7158篇 |
机械仪表 | 13724篇 |
建筑科学 | 19785篇 |
矿业工程 | 7364篇 |
能源动力 | 5137篇 |
轻工业 | 11777篇 |
水利工程 | 6816篇 |
石油天然气 | 7047篇 |
武器工业 | 2713篇 |
无线电 | 20538篇 |
一般工业技术 | 21426篇 |
冶金工业 | 6349篇 |
原子能技术 | 2730篇 |
自动化技术 | 37267篇 |
出版年
2024年 | 1111篇 |
2023年 | 3098篇 |
2022年 | 5539篇 |
2021年 | 6248篇 |
2020年 | 6677篇 |
2019年 | 5566篇 |
2018年 | 5157篇 |
2017年 | 6597篇 |
2016年 | 7198篇 |
2015年 | 7710篇 |
2014年 | 12359篇 |
2013年 | 11399篇 |
2012年 | 14832篇 |
2011年 | 15192篇 |
2010年 | 11698篇 |
2009年 | 11947篇 |
2008年 | 11300篇 |
2007年 | 13556篇 |
2006年 | 11606篇 |
2005年 | 9813篇 |
2004年 | 7858篇 |
2003年 | 6683篇 |
2002年 | 5458篇 |
2001年 | 4407篇 |
2000年 | 3857篇 |
1999年 | 3299篇 |
1998年 | 2618篇 |
1997年 | 2229篇 |
1996年 | 1906篇 |
1995年 | 1663篇 |
1994年 | 1371篇 |
1993年 | 1024篇 |
1992年 | 922篇 |
1991年 | 660篇 |
1990年 | 545篇 |
1989年 | 511篇 |
1988年 | 383篇 |
1987年 | 217篇 |
1986年 | 188篇 |
1985年 | 91篇 |
1984年 | 92篇 |
1983年 | 58篇 |
1982年 | 58篇 |
1981年 | 75篇 |
1980年 | 45篇 |
1979年 | 42篇 |
1978年 | 23篇 |
1976年 | 17篇 |
1975年 | 20篇 |
1959年 | 31篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
This study develops a mathematical model for coupled heat and mass transfer in an unsaturated porous slab exposed to a flowing hot gas. Effects of the initial saturation conditions on associated variables, i.e., total pressure, temperature, moisture content, and multiphase flow, are studied. The Newton-Raphson method based on a finite volume technique is applied. This study emphasizes the influence of initial saturation level and gravitational effect in heat and multiphase flow phenomena associated with this system. Gravity enhances the downward flow of liquid within the porous slab. Pressure buildup occurs near the interface between the wet and the dry zone. However, it appears that the order of magnitude to the total pressure is small. This study explains the fundamental mechanism of multiphase flow that involves heat and mass transfer in a heated unsaturated porous slab. 相似文献
72.
We present a numerical study of the packing of uniform spheres under three-dimensional vibration using the discrete element method (DEM), focusing on the effects of vibration condition (amplitude and frequency) and inter-particle frictions (sliding and rolling frictions). The results are analysed in terms of packing density, coordination number (CN), radial distribution function (RDF) and pore structure. It is shown that increasing either the vibration amplitude or frequency causes packing density to increase initially to a maximum and then decrease. Both vibration frequency and amplitude should be considered to characterize the effect of vibration process on packing structure. The sliding and rolling frictions between particles can decrease packing density since they dissipate energy, although the effect of rolling friction is less significant. In line with the change of packing density, microstructural properties such as CN, RDF and pore distribution also change: a looser packing often corresponds to smaller CN, less peaked RDF and larger but more widely distributed pores. 相似文献
73.
The present study is an investigation on the behaviors of concrete-filled thin-walled steel tubular members subjected to combined loading, such as compression and torsion, bending and torsion, compression, bending and torsion. ABAQUS software is used in this paper for the finite element analysis (FEA). A comparison of results calculated using this modeling shows generally good agreement with test results. The FEA modeling is then used to investigate the influence of important parameters that determine the ultimate strength of the composite members under combined loading, such as compression and torsion, bending and torsion, compression, bending and torsion. The parametric studies provide information for the development of formulae for calculating the ultimate strength of the composite members subjected to combined loading. 相似文献
74.
Conceptual damage-sensitive features for structural health monitoring: Laboratory and field demonstrations 总被引:2,自引:0,他引:2
F. Necati Catbas Mustafa Gul Jason L. Burkett 《Mechanical Systems and Signal Processing》2008,22(7):1650-1669
The use of damage-sensitive features to evaluate structural condition or health is a very critical aspect of structural health monitoring. The purpose of this paper is to investigate the potential of two different damage-sensitive features for detecting damage. Different damage scenarios are simulated on a large-scale laboratory structure and a three-span highway bridge for demonstration. The features presented in this paper are the modal flexibility-based deflection and curvature both of which are obtained directly from dynamic properties. In the literature, flexibility associated with mode shapes and mode shapes curvatures have been mostly explored. In this study, multi-input–multi-output dynamic data are used to obtain modal flexibility, which is a close approximation to the actual flexibility. A main novelty is that the curvature is calculated from the deflected shapes using the modal flexibility as opposed to using modal vectors. In this paper, the theory of the methodology is explained and then experimental studies and results are presented. For the experimental studies, the laboratory specimen and the three-span bridge were gradually damaged. It is shown that both deflection and curvature are conceptual and physically meaningful features for damage detection and localization. The issues and the requirements for these features to perform successfully are also presented. 相似文献
75.
A. Benhamida I. Djeran-Maigre H. Dumontet S. Smaoui 《International Journal of Rock Mechanics and Mining Sciences》2005,42(7-8):996-1005
The modelling of hydromechanical behavior of clayey sediments by homogenization theory is described. The rheological model of clays buried in depth requires a three-dimensional approach and laboratory experiments to quantify the model parameters. An iterative process which can be coupled to any homogenization method is used to model the porous media behavior. Hydromechanical compaction results from oedometric experiments are simulated with the proposed model. 相似文献
76.
The effect of pressure on combustion and heat transfer is analyzed. The research is based on the basic combustion and heat
transfer theorem. A correction for the heat calculation method for pressurized furnace is made on the basis of the normal
pressure case. The correction takes the effect of pressurizing into account. The results show that the correction is reasonable
and the method is applicable to combustion and heat transfer of the marine supercharged boiler. 相似文献
77.
LaNiO3 was synthesized by sol-gel method in which lanthanum nitrate and nickel nitrate were used as start materials and citric acid was used as complex for gel formation.The precursor was dried and subsequently heated at elevated temperature to form the desired product.XRD analysis shows that pure LaNiO3 was synthesized.Electrical conductivity and electrochemical performance of the material were tested.The electrical conductivity decreases from 34.5that there are current peaks in the curve, which is the evidence of the electrochemical activity of LaNiO3. 相似文献
78.
讨论了直流法在线测量钯氢化物电极电阻时的电化学效应,计算了电解液的共导、测量电流与电解电流引起的浓差电池效应以及电极作为集流体引起的电阻贡献。结果表明:当电极具有高的长度与半径比值、粗糙的表面、高的溶液电导以及大的电解电流时容易引起显著的附加电阻。 相似文献
79.
应用功率控制、波束赋形和多用户检测可以有效地消除和减少CDMA系统中的干扰。本文结合波束赋形和多用户检测的特性,提出一种应用波束赋形增益和多用户相关矩阵的解相关算法。基于算法的复杂性,提出一种区分聚集用户进行多用户检测的的算法。由于波束赋形能够消减主瓣波束之外的多用户干扰,对聚集移动台采用解相关检测达到减少运算量和消除多用户干扰的目的。对算法进行了仿真分析,证明了本算法的优越性。 相似文献
80.
Using boundary element based three dimensional modelling for linear fracture mechanics, we present an analysis of cracking in a homogeneous medium subject to contact load. The proposed iterative solution procedure allows a simultaneous treatment of a reasonable number of partially closed cracks. It is shown that the most probable direction of propagation of a vertical internal crack is strongly dependent on its size compared to the contact radius and its location with respect to the axis of maximum normal load. 相似文献