全文获取类型
收费全文 | 400584篇 |
免费 | 38027篇 |
国内免费 | 20906篇 |
专业分类
电工技术 | 27758篇 |
技术理论 | 35篇 |
综合类 | 40940篇 |
化学工业 | 44202篇 |
金属工艺 | 16608篇 |
机械仪表 | 27457篇 |
建筑科学 | 49495篇 |
矿业工程 | 19004篇 |
能源动力 | 15366篇 |
轻工业 | 29153篇 |
水利工程 | 17354篇 |
石油天然气 | 19857篇 |
武器工业 | 5169篇 |
无线电 | 27478篇 |
一般工业技术 | 33279篇 |
冶金工业 | 18861篇 |
原子能技术 | 4082篇 |
自动化技术 | 63419篇 |
出版年
2024年 | 1854篇 |
2023年 | 5333篇 |
2022年 | 10429篇 |
2021年 | 12944篇 |
2020年 | 13015篇 |
2019年 | 10179篇 |
2018年 | 9713篇 |
2017年 | 12041篇 |
2016年 | 14521篇 |
2015年 | 15493篇 |
2014年 | 26471篇 |
2013年 | 24818篇 |
2012年 | 29117篇 |
2011年 | 32188篇 |
2010年 | 23544篇 |
2009年 | 24030篇 |
2008年 | 22370篇 |
2007年 | 26933篇 |
2006年 | 23910篇 |
2005年 | 20567篇 |
2004年 | 17250篇 |
2003年 | 14908篇 |
2002年 | 12133篇 |
2001年 | 9888篇 |
2000年 | 8476篇 |
1999年 | 6856篇 |
1998年 | 5327篇 |
1997年 | 4565篇 |
1996年 | 3737篇 |
1995年 | 3114篇 |
1994年 | 2684篇 |
1993年 | 1983篇 |
1992年 | 1721篇 |
1991年 | 1221篇 |
1990年 | 1048篇 |
1989年 | 935篇 |
1988年 | 658篇 |
1987年 | 467篇 |
1986年 | 408篇 |
1985年 | 416篇 |
1984年 | 405篇 |
1983年 | 381篇 |
1982年 | 276篇 |
1981年 | 187篇 |
1980年 | 188篇 |
1979年 | 119篇 |
1978年 | 90篇 |
1977年 | 87篇 |
1976年 | 76篇 |
1959年 | 56篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Many approaches have been proposed to enhance software productivity and reliability. These approaches typically fall into three categories: the engineering approach, the formal approach and the knowledge-based approach. But the optimal gain in software productivity cannot be obtained if one relies on only one of these approaches. This paper describes the work in knowledge-based software engineering conducted by the authors for the past 10 years. The final goal of the research is to develop a paradigm for software engineering which integrates the three approaches mentioned above. A knowledge-based tool which can support the whole process of software development is provided in this paper. 相似文献
32.
33.
A. F. Kurbatskii 《High Temperature》2004,42(1):79-87
The difference in the turbulent diffusion between the active (heat) and passive (mass) scalars in a thermally stably stratified medium is investigated. The axisymmetric problem is treated on the formation of a turbulent circulation flow above a heated disk and on the turbulent diffusion of a passive scalar (impurity) from a continuous surface source in a stably stratified medium. The results indicate that the thermal stratification causes appreciable differences in the coefficients of turbulent transfer between the active (heat) and passive (mass) scalars. This means that the assumption of the identity of the coefficient of turbulent diffusion of heat and mass, employed in conventional models of turbulence, produces significant errors in estimating the heat and mass transfer in a thermally stably stratified medium. 相似文献
34.
This paper describes an effective analysis of magnetic shielding based on homogenization. The analyses become time‐consuming if the problems include the magnetic substances having fine structure. The homogenization of the structure makes it possible to analyze effectively the magnetic fields. The authors introduce a method to estimate the effective permeability of the homogenized substance. This method can be applied to any periodic structure made of magnetic substance. The magnetic shielding effects by the structures against direct‐current (DC) fields generated by electric railways are analyzed by using the present method. As a result, it is found that the overhead way and the protective fence near the railway work as a magnetic shield, whose effects can be improved by appropriate arrangement of those constructions. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(4): 7–15, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20310 相似文献
35.
Huai Wen-xin Wuhan University of Hydraulic & Electric Engineering Wuhan Hubei P.R.China Prof.Li Wei 《水动力学研究与进展(B辑)》1993,(3)
Turbulence represents an essential aspect in atmospheric and oceanic circulations.In particu-lar,it is a preponderant factor in the dispersion of pollutants of artificial or natural origin.Thevertical turbulent jets,plumes and buoyant jets discharging into static environment is one of themost important and basic flow patterns related with the environment pollution.These flows havenumerous important applications,for example,thrust augmentors,waste disposal plumes fromstacks and combustion systems,and significant problems of turbulent diffusion. 相似文献
36.
ETRⅠ-30调速器是瑞士爱舍维斯工厂生产的具有PID调节规律的电液调速器。本文对其液压控制系统作了较详细的介绍,供有关人员参考。 相似文献
37.
Recently, a demand for small-capacity generators has been increasing as electric sources in small ships and automobiles or as portable electric sources driven by engines. It is desired that the structure of small-capacity generators be simple and robust, and that the generators be highly reliable, easily maintained and controlled. This paper describes an analysis of the original brushless synchronous generator without exciter. The output voltage can be adjusted in the wide range by controlling the stator dc current. To analyze the characteristics of this generator, the finite element method is applied. It is found that the results of theoretical analysis agree well with the experimental results. 相似文献
38.
Poly(ethylene aspartate) [PEA] was synthesized by the melt condensation of D,L-aspartic acid and ethylene glycol. PEA containing pendent amino and carbonyl groups in its repeating chain was used as the polymeric ligand for complexation with transition metal ions, viz. Co(II), Ni(II), Cu(II), Mn(II), Zn(II), Cd(II), Ca(II), Mg(II), Pb(II) and Hg(II). Complexation was found to be most effective in DMSO. The resulting polyester-metal complexes were solid coloured materials which have been characterized by IR spectroscopy, elemental analysis and magnetic susceptibility measurements. The thermal stability of the polyester-metal complexes was investigated by thermogravimetric analysis (TGA). On the basis of the physico-chemical studies, an oxygen and nitrogen coordinated structure for the polyester-metal complexes is proposed. 相似文献
39.
V. P. Naumenko 《Strength of Materials》1996,28(1):10-18
The adoption of unified fracture mechanics terminology (UFMT) will promote efficient communication between specialists in different fields of fracture research, harmonization of national and international standards relating to fracture mechanics, and last but not least improvement of the existing methodology for teaching and education in fatigue and fracture. In this paper the definitions of some basic and related terms included in different standards on fracture mechanics terminology are confronted with one another. Alternative definitions of the same terms are offered. By this strategy the author tries to show that the definitions of basic and related terms appropriate for the UFMT should emerge as a consequence of harmonizing a crack model with an actual crack and then both taken together with a fracture model, laboratory test methods, and failure assessment codes.Published in Problemy Prochonsti, No. 1, pp. 17–29, January, 1996.This paper is published as a matter of discussion. 相似文献
40.
Since electronic switching systems usually require very strict reliability requirements as well as good performance objectives, we need to jointly analyse the performance and reliability of switching systems. In this paper, we compare conventional time–space–time switches with single space switches with those with multiple separated space switches, from the viewpoints of reliability and performance. We consider time–space–time switching networks which consist of N incoming time switches, i.e. one NxN space switch, two (N/2)x(N/2) space switches, and four (N/4)x(N/4) space switches. We introduce a Markov reliability model to study the effect of failures and analyse the reliability and performance of three different types of switching networks in terms of average blocking probability and the mean time to unreliable operation, as we vary the offered traffic. As a result, T–S–T switching networks with multiple separated space switches exhibit better performance and reliability than those with single space switches. 相似文献