全文获取类型
收费全文 | 20757篇 |
免费 | 2330篇 |
国内免费 | 104篇 |
专业分类
电工技术 | 1609篇 |
综合类 | 539篇 |
化学工业 | 9283篇 |
金属工艺 | 447篇 |
机械仪表 | 483篇 |
建筑科学 | 791篇 |
矿业工程 | 264篇 |
能源动力 | 184篇 |
轻工业 | 2211篇 |
水利工程 | 184篇 |
石油天然气 | 153篇 |
武器工业 | 2篇 |
无线电 | 567篇 |
一般工业技术 | 3607篇 |
冶金工业 | 316篇 |
原子能技术 | 68篇 |
自动化技术 | 2483篇 |
出版年
2023年 | 634篇 |
2022年 | 386篇 |
2021年 | 753篇 |
2020年 | 731篇 |
2019年 | 637篇 |
2018年 | 674篇 |
2017年 | 527篇 |
2016年 | 775篇 |
2015年 | 912篇 |
2014年 | 963篇 |
2013年 | 1681篇 |
2012年 | 717篇 |
2011年 | 662篇 |
2010年 | 936篇 |
2009年 | 1064篇 |
2008年 | 535篇 |
2007年 | 490篇 |
2006年 | 371篇 |
2005年 | 434篇 |
2004年 | 330篇 |
2003年 | 328篇 |
2002年 | 278篇 |
2001年 | 189篇 |
1999年 | 162篇 |
1998年 | 255篇 |
1997年 | 190篇 |
1996年 | 247篇 |
1995年 | 213篇 |
1994年 | 184篇 |
1993年 | 257篇 |
1992年 | 178篇 |
1990年 | 172篇 |
1989年 | 215篇 |
1987年 | 177篇 |
1986年 | 191篇 |
1985年 | 181篇 |
1984年 | 189篇 |
1983年 | 190篇 |
1982年 | 170篇 |
1981年 | 222篇 |
1980年 | 174篇 |
1979年 | 187篇 |
1977年 | 161篇 |
1976年 | 178篇 |
1975年 | 215篇 |
1974年 | 208篇 |
1973年 | 398篇 |
1972年 | 218篇 |
1971年 | 157篇 |
1968年 | 165篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
The paper presents a computational approach and numerical data which facilitate the use of the smeared-tip method for cohesive fracture in large enough structures. In the recently developed K-version of the smeared tip method, the large-size asymptotic profile of the stress intensity factor density along a cohesive crack is considered as a material characteristic, which is uniquely related to the softening stress-displacement law of the cohesive crack. After reviewing the K-version, an accurate and efficient numerical algorithm for the computation of this asymptotic profile is presented. The algorithm is based on solving a singular Abel's integral equation. The profiles corresponding to various typical softening stress-displacement laws of the cohesive crack model are computed, tabulated and plotted. The profiles for a certain range of other typical softening laws can be approximately obtained by interpolation from the tables. Knowing the profile, one can obtain with the smeared-tip method an analytical expression for the large-size solution to fracture problems, including the first two asymptotic terms of the size effect law. Consequently, numerical solutions of the integral equations of the cohesive crack model as well as finite element simulations of the cohesive crack are made superfluous. However, when the fracture process zone is attached to a notch or to the body surface and the cohesive zone ends with a stress jump, the solution is expected to be accurate only for large-enough structures. 相似文献
82.
83.
T. Jing M. Sc. Ir. P. H. F. Moshuis Prof. Dr. Ir. F. H. Kreuger 《Electrical Engineering (Archiv fur Elektrotechnik)》1991,74(4):315-319
Contents Surface charge accumulation and its decay at a GIS spacer are studied at atmospheric conditions employing a two step-calibration method. The results show that the accumulation saturates within 30 minutes; the dominant mechanism of surface charge accumulation is the drift of charged particles via air, while that of the decay is surface conduction. The characteristics are similar at both polarities.
Sättigungskonzentration und Abklingverhalten der Oberflächenladung an einem mit Gleichspannung beanspruchten Abstandshalter unter atmosphärischen Bedingungen
Übersicht Die Konzentration und das Abklingen von Oberflächenladungen an einem GIS Abstandshalter wurden unter atmosphärischen Bedingungen mit Hilfe eines zweistufigen Kalibrierungsverfahrens untersucht. Die Ergebnisse zeigen eine Sättigung der Ladungskonzentration innerhalb von 30 Minuten. Als Hauptursache der Ladungskonzentration ist die Drift geladener Teilchen in Luft anzusehen, während das Abklingen auf die Oberflächenleitung zurückzuführen ist. Ähnliche Charakteristiken ergeben sich mit beiden Polaritäten.相似文献
84.
Dipl.-Ing. Gerhard Sauer 《Forschung im Ingenieurwesen》1995,61(5):134-140
Zusammenfassung Eine einfache Formel zur n?herungsweisen Berechnung der Axialspannungen eines Rohres infolge der von einer Temperaturschichtung
im Rohrinnern hervorgerufenen Temperaturfelder wird vorgestellt. Die Formel basiert auf der konventionellen Balkentheorie.
Durch Vergleiche der von der N?herungsformel gelieferten Axialspannungen mit den Axialspannungen, die mit Hilfe von Finite-Elemente-Rechnungen
erhalten werden, wird gezeigt, da? die N?herungsformel die maximalen Axialspannungen ausreichend genau wiedergibt. 相似文献
85.
Three-dimensional, turbulent fluid flow analysis with computational methods has emerged as a viable tool in the design process
of engine components for passenger cars. If applied in the early stages of the component development such analysis can help
reduce the product development time drastically, and may support the design engineer to evaluate several competing design
aspects before product completion. However the grid generation for complex geometries still poses a difficult and time consuming
taks which strongly influences the accuracy of the numerical solution. The present paper studies the numerical solution of
the flow in an inlet-manifold of a five-cylinder engine with two intake-ports for each cylinder. A fast and reliable grid
generation technique is discussed in detail. The finite volume based Navier-Stokes solver with schemes of first and second
order accuracy for the convective terms is used. Numerical results at several mass flow rates and different boundary conditions
at the intake ports are compared with measurements. Finally, the computational results are discussed with respect to their
applicability to support the design process of an inlet-manifold. 相似文献
86.
IT/Business alignment 总被引:3,自引:2,他引:1
Dr. Alexander Teubner 《WIRTSCHAFTSINFORMATIK》2006,48(5):368-371
87.
88.
Dr. A. N. Danilenko V. Yu. Vetrov A. P. Dmitrochenko A. L. Leontiev E. E. Braudo V. B. Tolstoguzov 《Molecular nutrition & food research》1992,36(2):105-111
Thermodynamic properties of aqueous solutions of both native and modified legumin of broad beans (Vicia faba L.) have been examined. A restricted trypsin-induced proteolysis was used to modify protein structure. Evaluation of protein affinity to ficoll in aqueous solutions showed that modified protein possessed higher hydrophilicity. Thermodynamic properties of diluted solutions were used to predict the phase behaviour in concentrated systems containing protein and ficoll. At specific concentrations of native legumin, the system can separate in two phases, whereas in the case of modified protein the single-phase behaviour of the system was predicted for any concentrations of both components. The experimental data obtained in concentrated systems confirmed predictions of thermodynamic analysis of diluted solutions. 相似文献
89.
C. Schönbauer Dipl.-Ing. 《e & i Elektrotechnik und Informationstechnik》2003,120(10):304-306
The new law for the support of electricity produced by renewable sources in Austria (Ökostromgesetz) which came into force with the beginning of 2003, shows its impacts already after the first months. Investments into wind power have increased considerably. These will be accompanied by activities for electricity production by biomass and biogas. The 4%-target quota will probably be reached earlier than the 2008 target period of the law. 相似文献
90.
A. Stelzer Univ.-Ass. Ing. Dipl.-Ing. Dr. techn. A. Springer A. Univ.-Prof. Dipl.-Ing. Dr. techn. 《e & i Elektrotechnik und Informationstechnik》2003,120(3):98-101
This contribution reviews the research work performed at the Johannes Kepler University of Linz, Austria, on the development of oscillators for the microwave and millimeter wave frequency range. This work, performed by the Microelectronics Institute and the Institute for Communications and Information Engineering, covers the range from low GHz frequencies up to 61 GHz and is devoted to applications like mobile communications and sensing. The active devices are based on gallium arsenide (GaAs), silicon germanium (SiGe), and Silicon (Si) and include Gunn-devices, bipolar transistors, and CMOS-technology. 相似文献