全文获取类型
收费全文 | 60209篇 |
免费 | 6892篇 |
国内免费 | 4037篇 |
专业分类
电工技术 | 7425篇 |
技术理论 | 3篇 |
综合类 | 5722篇 |
化学工业 | 9110篇 |
金属工艺 | 2841篇 |
机械仪表 | 4603篇 |
建筑科学 | 2716篇 |
矿业工程 | 1692篇 |
能源动力 | 5085篇 |
轻工业 | 1241篇 |
水利工程 | 5186篇 |
石油天然气 | 4059篇 |
武器工业 | 847篇 |
无线电 | 4957篇 |
一般工业技术 | 5058篇 |
冶金工业 | 2952篇 |
原子能技术 | 1770篇 |
自动化技术 | 5871篇 |
出版年
2024年 | 56篇 |
2023年 | 826篇 |
2022年 | 1507篇 |
2021年 | 1838篇 |
2020年 | 1971篇 |
2019年 | 1637篇 |
2018年 | 1486篇 |
2017年 | 2072篇 |
2016年 | 2218篇 |
2015年 | 2384篇 |
2014年 | 3302篇 |
2013年 | 3938篇 |
2012年 | 4147篇 |
2011年 | 4794篇 |
2010年 | 3366篇 |
2009年 | 3602篇 |
2008年 | 3483篇 |
2007年 | 4138篇 |
2006年 | 3797篇 |
2005年 | 3371篇 |
2004年 | 2737篇 |
2003年 | 2467篇 |
2002年 | 1973篇 |
2001年 | 1680篇 |
2000年 | 1375篇 |
1999年 | 1146篇 |
1998年 | 947篇 |
1997年 | 814篇 |
1996年 | 767篇 |
1995年 | 701篇 |
1994年 | 592篇 |
1993年 | 456篇 |
1992年 | 377篇 |
1991年 | 244篇 |
1990年 | 249篇 |
1989年 | 183篇 |
1988年 | 130篇 |
1987年 | 89篇 |
1986年 | 68篇 |
1985年 | 40篇 |
1984年 | 45篇 |
1983年 | 33篇 |
1982年 | 23篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1979年 | 15篇 |
1978年 | 5篇 |
1977年 | 4篇 |
1974年 | 3篇 |
1959年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
《Advanced Powder Technology》2022,33(8):103664
Powder transport systems are ubiquitous in various industries, where they can encounter single powder flow, two-phase flow with solids carried by gas or liquid, and gas–solid–liquid three-phase flow. System geometry, operating conditions, and particle properties have significant impacts on the flow behavior, making it difficult to achieve good transportation of granular materials. Compared to experimental trials and theoretical studies, the numerical approach provides unparalleled advantages over the investigation and prediction of detailed flow behavior, of which the discrete element method (DEM) can precisely capture complex particle-scale information and attract a plethora of research interests. This is the first study to review recent progress in the DEM and coupled DEM with computational fluid dynamics for extensive powder transport systems, including single-particle, gas–solid/solid–liquid, and gas–solid–liquid flows. Some important aspects (i.e., powder electrification during pneumatic conveying, pipe bend erosion, non-spherical particle transport) that have not been well summarized previously are given special attention, as is the application in some new-rising fields (ocean mining, hydraulic fracturing, and gas/oil production). Studies involving important large-scale computation methods, such as the coarse grained DEM, graphical processing unit-based technique, and periodic boundary condition, are also introduced to provide insight for industrial application. This review study conducts a comprehensive survey of the DEM studies in powder transport systems. 相似文献
2.
An analytical model for gas leakage through contact interface in proton exchange membrane fuel cells
《International Journal of Hydrogen Energy》2022,47(75):32273-32286
Sealing performance between two contacting surfaces is of significant importance to stable operation of proton exchange membrane (PEM) fuel cells. In this work, an analytical micro-scale approach is first established to predict the gas leakage in fuel cells. Gas pressure and uneven pressure distribution at the interface are also included in the model. At first, the micro tortuous leakage path at the interface is constructed by introducing contact modelling and fractal porous structure theory. In order to obtain the leakage at the entire surface, contact pressure distribution is predicted based on bonded elastic layer model. The gas leakage through the discontinuous interface can be obtained with consideration of convection and diffusion. Then, experiments are conducted to validate the numerical model, and good agreement is obtained between them. Finally, influences of surface topology, gasket compression and gasket width on leakage are studied based on the model. The results show that gas leakage would be greatly amplified when the asperity standard deviation of surface roughness exceeds 1.0 μm. Gaskets with larger width and smaller thickness are beneficial to sealing performance. The model is helpful to understand the gas leakage behavior at the interface and guide the gasket design of fuel cells. 相似文献
3.
为探究高水头大幅变化对混流式水轮机尾水管涡带的演化及对压力脉动的影响,以国内运行水头变幅最大的紫坪铺水电站水轮机为例,通过三维建模及定常和非定常条件的CFD分析,研究混流式水轮机在相同开度下最大水头、设计水头和最小水头三种工况的流动特点。结果表明,最小水头工况下尾水管内部流态较乱,尾水管中存在螺旋型空腔涡带,主要分布在直锥段。最大水头工况下尾水管的柱状涡带直径较大,且分布在直锥段和弯肘段,对机组振动和空化影响较大。研究结果阐明了非定常流动的特性,揭示了尾水管内压力脉动与涡带发展形态变化的规律,可为水轮机的安全可靠运行提供技术保障。 相似文献
4.
5.
6.
为了减轻因流动加速腐蚀(FAC)引起的锅炉结垢加速、汽水系统管道厚度减小甚至爆裂现象,对超临界机组发生流动加速腐蚀的机理及其主要影响因素进行了研究,并讨论了管壁内表面粗糙度、蒸汽含汽率、pH值、溶氧量对FAC的影响,以及温度与pH值、温度与流速、pH值与溶解氧量、溶解氧量与氢电导率等影响因素之间的相互作用关系,最后结合实际电厂的运行数据验证了分析结果。研究表明:减小工质流速、管壁粗糙度和氢电导率,增大给水的pH值和溶解氧含量可以使FAC的腐蚀速率减小,超临界加氧处理时pH值应在8.9~9.2之间,溶解氧量范围为45~100μg/L,氢电导率的期望值在0.1μS/cm以下。由于各影响因素之间的作用十分复杂,本文只给出了大致范围和趋势,并未给出准确数据。 相似文献
7.
8.
In this study, the optimal homotopy analysis (OHAM) technique has been examined to solve the laminar magnetohydrodynamic flow (MHD flow) on the upper-convected Maxwell fluid on an isothermal porous stretch surface. A study on the effects of parameters like the relaxation time, suction/injection velocity, as well as the magnetic number on velocity over a sheet was conducted and these results are compared to the corresponding previously available results. It was observed that the thickness of the boundary layer is lowered by enhancing , , and values. Opposing this, it was observed that large values increase the magnituIIde. It is found that OHAM is an efficient method capable of giving a greater degree of accuracy in numerical values of flow parameters even after fewer approximations. 相似文献
9.
Hybrid nanofluid boundary layer flow past a stretching surface with zero mass flux boundary condition is explored in this article. The main aim of this article is to analyze the electromagnetohydrodynamic role in a hybrid nanofluid containing silver and molybdenum disulfide nanoparticles. The self-similar solution is embedded to reduce the governing partial differential equation into algebraic equations and a shooting algorithm is applied to obtain the solution of the resultant boundary value problem. Variation in momentum, energy, and nanoparticle concentration is explained through graphical profiles. Nusselt number and drag force coefficients are computed for various flow parameters and their impact on the nanofluid and hybrid nanofluid is computed and presented and explained in a comparative fashion. It is observed that the velocity profile shows the opposite nature with respect to the electric field and magnetic field. For electric field parameter velocity accelerates whereas for magnetic parameter velocity diminishes. Nusselt number increases with electric field parameter and nanoparticle volume fraction. 相似文献
10.
We considered the magnetohydrodynamic (MHD) free convective flow of an incompressible electrically conducting viscous fluid past an infinite vertical permeable porous plate with a uniform transverse magnetic field, heat source and chemical reaction in a rotating frame taking Hall current effects into account. The momentum equations for the fluid flow during absorbent medium are controlled by the Brinkman model. Through the undisturbed state, both the plate and fluid are in a rigid body rotation by the uniform angular velocity perpendicular to an infinite vertical plate. The perpendicular surface is subject to the homogeneous invariable suction at a right angle to it and the heat on the surface varies about a non-zero unvarying average whereas the warmth of complimentary flow is invariable. The systematic solutions of the velocity, temperature, and concentration distributions are acquired systematically by utilizing the perturbation method. The velocity expressions consist of steady-state and fluctuating situations. It is revealed that the steady part of the velocity field has a three-layer characteristic while the oscillatory part of the fluid field exhibits a multi-layer characteristic. The influence of various governing flow parameters on the velocity, temperature, and concentration are analyzed graphically. We also discuss computational results for the skin friction, Nusselt number, and Sherwood number in the tabular forms. 相似文献