全文获取类型
收费全文 | 512978篇 |
免费 | 5407篇 |
国内免费 | 1086篇 |
专业分类
电工技术 | 9167篇 |
综合类 | 495篇 |
化学工业 | 76436篇 |
金属工艺 | 27571篇 |
机械仪表 | 19016篇 |
建筑科学 | 10682篇 |
矿业工程 | 4806篇 |
能源动力 | 10215篇 |
轻工业 | 31903篇 |
水利工程 | 6813篇 |
石油天然气 | 15397篇 |
武器工业 | 91篇 |
无线电 | 54517篇 |
一般工业技术 | 115021篇 |
冶金工业 | 76432篇 |
原子能技术 | 15106篇 |
自动化技术 | 45803篇 |
出版年
2021年 | 4185篇 |
2019年 | 4170篇 |
2018年 | 12720篇 |
2017年 | 13174篇 |
2016年 | 11660篇 |
2015年 | 5113篇 |
2014年 | 8406篇 |
2013年 | 19679篇 |
2012年 | 14065篇 |
2011年 | 21193篇 |
2010年 | 17861篇 |
2009年 | 18352篇 |
2008年 | 19442篇 |
2007年 | 20371篇 |
2006年 | 13084篇 |
2005年 | 13615篇 |
2004年 | 12627篇 |
2003年 | 12360篇 |
2002年 | 11217篇 |
2001年 | 10673篇 |
2000年 | 10458篇 |
1999年 | 9870篇 |
1998年 | 20252篇 |
1997年 | 15235篇 |
1996年 | 11938篇 |
1995年 | 9551篇 |
1994年 | 8684篇 |
1993年 | 8738篇 |
1992年 | 7286篇 |
1991年 | 7095篇 |
1990年 | 7036篇 |
1989年 | 6714篇 |
1988年 | 6449篇 |
1987年 | 6027篇 |
1986年 | 5878篇 |
1985年 | 6485篇 |
1984年 | 6218篇 |
1983年 | 5752篇 |
1982年 | 5453篇 |
1981年 | 5566篇 |
1980年 | 5403篇 |
1979年 | 5485篇 |
1978年 | 5542篇 |
1977年 | 5910篇 |
1976年 | 6958篇 |
1975年 | 5105篇 |
1974年 | 5146篇 |
1973年 | 5228篇 |
1972年 | 4467篇 |
1971年 | 4108篇 |
排序方式: 共有10000条查询结果,搜索用时 531 毫秒
951.
New fundamental solutions which automatically satisfy boundary conditions at the interfaces of an elastic plate perfectly bonded to two elastic halfspaces are implemented in a 3-D boundary element method (BEM) for crack problems. The BEM features a new integration scheme for highly singular kernels. The capability is achieved through a part analytic and part numerical integration procedure, such that the analytic part of the integration is similar for all slip/opening variations, ‘Part-through’ elliptic cracks in an elastic plate with traction-free surfaces are analysed and the stress intensity factor (SIF) values along the crack front are found to compare favourably with widely accepted numerically obtained SIF results by Raju and Newman.1 相似文献
952.
953.
954.
R. M. Pillai S. G. K. Pilhii A. D. Damodaran 《JOM Journal of the Minerals, Metals and Materials Society》2002,54(10):12-16
Indian artisans and craftsmen have long been masters at extracting and shaping metals and alloys, as proven by archaeological
finds from the 2nd—3rd millennia B.C. For example, two well-known artifacts, castings of the dancing girl of Mohenjo Daro
and the Mother Goddess of Adichanallur, Tamilnadu, depict a high degree of metallurgical knowledge. Those castings were formed
by the lost wax process, which later was modified and became known as investment casting. In various parts of India, this
age-old casting process is still being practiced, without any major modifications. This paper discusses details of the process
used by the Indian artisans of Swamimalai, Tamilnadu, and Mannar, Kerala, South India in shaping copper-base alloys into icons
and utensils, bells, and lamps. 相似文献
955.
M. M. Rahman M. M. Hossain D. G. Crosby M. K. Rahman S. S. Rahman 《Journal of Petroleum Science and Engineering》2002,35(3-4)
This paper presents results of a comprehensive study involving analytical, numerical and experimental investigations into transverse fracture propagation from horizontal wells. The propagation of transverse hydraulic fractures from horizontal wells is simulated and investigated in the laboratory using carefully designed experimental setups. Closed-form analytical theories for Mode I (opening) stress intensity factors for idealized fracture geometries are reviewed, and a boundary element-based model is used herein to investigate non-planar propagation of fractures. Using the mixed mode fracture propagation criterion of the model, a reasonable agreement is found with respect to fracture geometry, net fracture pressures and fracture propagation paths between the modeled fractures and the laboratory tested fractures. These results suggest that the propagation of multiple fractures requires higher net pressures than a single fracture, the underlying reason of which is theoretically justified on the basis of local stress distribution. 相似文献
956.
957.
958.
T.J. ChungJ.H. Park C.K. Choi D.-Y. Yoon 《International Journal of Heat and Mass Transfer》2002,45(14):3061-3064
The onset of convective instability in a fluid-saturated porous layer between the two horizontal plates heated isothermally from below has been analyzed theoretically by using propagation theory. In the analysis the thermal dispersion coefficient is assumed to be proportional to the streamwise velocity. The results show that both inertia and thermal dispersion stabilize the system. 相似文献
959.
R.V.R. PandyaF. Mashayek 《International Journal of Heat and Mass Transfer》2002,45(24):4753-4759
In this paper, effects of particles on the subgrid scales of turbulence are properly accounted for during the modeling of subgrid scale stresses in the large-eddy simulation (LES) of fluid phase. In doing so, we propose closed filtered kinetic equations for phase space density of the particle. The various moments of these equations give the `fluid' equations which can be considered as the LES equations for the particle phase. The influence of subgrid scales motion on the particles is included in these `fluid' equations. 相似文献
960.
The influence of pressure on the onset of flocculation of asphaltenes was calculated in the region from 1 to 300 bar and from 50 to 100°C. These calculations are the counterpart to our experimental data which, recently, have been reported in part 1 of an equally titled article [9]. As gas component methane and as precipitant i-octane were used. The asphaltene flocculation was considered to be a liquid-liquid equilibrium. For modelling the van der Waals equation of state (vdW-EOS) in the framework of continuous thermodynamics was applied. The composition of the crude oil was described by a continuous distribution function with respect to the solubility parameter δ of the Scatchard-Hildebrand theory. Within the distribution the asphaltenes represent the species with the highest δ-values. For oils with a very low content of asphaltenes the model developed describes the experimental flocculation data reasonably. In accordance to the experimental data the model predicts that, in the considered pressure range, without addition of i-octane asphaltene flocculation does not occur. However, on contrary to the experimental results, the model predicts the asphaltenes to show a higher flocculation tendency with increasing asphaltene content of the crude oil. For very high asphaltene contents the model even completely fails. Probably, the reason of this lack is the disregarding of asphaltene association. 相似文献