全文获取类型
收费全文 | 146184篇 |
免费 | 14591篇 |
国内免费 | 9247篇 |
专业分类
电工技术 | 11786篇 |
技术理论 | 2篇 |
综合类 | 18511篇 |
化学工业 | 16002篇 |
金属工艺 | 6332篇 |
机械仪表 | 10753篇 |
建筑科学 | 18908篇 |
矿业工程 | 6658篇 |
能源动力 | 4841篇 |
轻工业 | 7894篇 |
水利工程 | 6544篇 |
石油天然气 | 6198篇 |
武器工业 | 2066篇 |
无线电 | 10031篇 |
一般工业技术 | 18722篇 |
冶金工业 | 5753篇 |
原子能技术 | 2323篇 |
自动化技术 | 16698篇 |
出版年
2024年 | 605篇 |
2023年 | 1699篇 |
2022年 | 3285篇 |
2021年 | 3850篇 |
2020年 | 4383篇 |
2019年 | 3796篇 |
2018年 | 3677篇 |
2017年 | 4648篇 |
2016年 | 5176篇 |
2015年 | 5397篇 |
2014年 | 8821篇 |
2013年 | 8421篇 |
2012年 | 11224篇 |
2011年 | 11345篇 |
2010年 | 8808篇 |
2009年 | 9121篇 |
2008年 | 8416篇 |
2007年 | 10465篇 |
2006年 | 9192篇 |
2005年 | 7772篇 |
2004年 | 6359篇 |
2003年 | 5453篇 |
2002年 | 4565篇 |
2001年 | 3817篇 |
2000年 | 3389篇 |
1999年 | 2934篇 |
1998年 | 2316篇 |
1997年 | 2025篇 |
1996年 | 1691篇 |
1995年 | 1520篇 |
1994年 | 1283篇 |
1993年 | 938篇 |
1992年 | 842篇 |
1991年 | 593篇 |
1990年 | 486篇 |
1989年 | 486篇 |
1988年 | 354篇 |
1987年 | 202篇 |
1986年 | 166篇 |
1985年 | 68篇 |
1984年 | 70篇 |
1983年 | 39篇 |
1982年 | 42篇 |
1981年 | 56篇 |
1980年 | 29篇 |
1979年 | 37篇 |
1978年 | 17篇 |
1975年 | 16篇 |
1973年 | 13篇 |
1959年 | 30篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
结合兰州市的水泥标准稠度用水量方法测定 (代用法 )的实例 ,分析代用法测定标准稠度用水量的缺点 ,并对此方法提出了一些改进措施 相似文献
102.
通过低应变反射波法与钻孔抽芯 2种检测方法的结果对比分析 ,验证低应变反射波法检测基桩的缺陷及位置的准确性 ,积累波形判别的经验。 相似文献
103.
A method is considered to solve a conditional optimization problem with a linear-fractional objective function over permutations.
The performance of sub algorithms to solve this problem is evaluated. The practical efficiency of the algorithm is analyzed
by conducting numerical experiments.
__________
Translated from Kibernetika i Sistemnyi Analiz, No. 4, pp. 133–146, July–August 2007. 相似文献
104.
孔颖 《数字社区&智能家居》2007,(3):1429-1429,1438
针对C语言程序设计课程本身的特点,分析学习过程中存在的问题,强调实践的必要性。结合一些学校课程改革和实践的经验.提出面向应用的,科学的学习内容、方法和模式。同时提高学习者的专业动手能力。 相似文献
105.
Arash Sarhangi Fard Navid M. Famili Patrick D. Anderson 《Computers & Chemical Engineering》2008,32(7):1471-1481
The main objective of the present work is to modify the traditional mapping method for the simulation of distributive mixing of multiphase flows in geometries involving moving parts such as, internal mixers or twin-screw extruders without a limitation on their geometrical periodicity. The periodicity condition, limits the results of traditional mapping method to tracking mapping mesh between specific discrete time intervals or distances for that geometry is repeated, hence, result is only for fixed orientation of rotors. Imaginary domain method is introduced to track mapping mesh from one state to the next free of geometrical periodicity limitations. In this work the method is introduced and its applicability and accuracy is discussed in details. A two-dimensional (2D) simulation of mixing of two Newtonian fluids with different viscosities in an intermeshing internal mixer is used as a test case study. In this example the key issues of ability to predict mixing state in details for all orientations of rotors is presented. To reduce diffusion errors of mapping method in the boundaries of the rotors, mapping mesh refinement technique that relies upon one single reference mesh is also presented. 相似文献
106.
风管摩擦阻力的直接计算方法 总被引:2,自引:1,他引:1
提出用高精度的反映密度、黏度和温度关系的经验公式和Colebrook公式计算风管摩擦阻力系数的方法。分析和算例表明,用该方法计算,计算结果比采用常用工程设计方法更为准确,为应用计算机进行风道设计提供了直接、简便的方法。 相似文献
107.
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
108.
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
109.
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
110.
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