全文获取类型
收费全文 | 452547篇 |
免费 | 5429篇 |
国内免费 | 1336篇 |
专业分类
电工技术 | 8802篇 |
综合类 | 658篇 |
化学工业 | 68924篇 |
金属工艺 | 16905篇 |
机械仪表 | 12857篇 |
建筑科学 | 11574篇 |
矿业工程 | 1674篇 |
能源动力 | 12372篇 |
轻工业 | 43308篇 |
水利工程 | 3967篇 |
石油天然气 | 6258篇 |
武器工业 | 10篇 |
无线电 | 55077篇 |
一般工业技术 | 85138篇 |
冶金工业 | 84478篇 |
原子能技术 | 8929篇 |
自动化技术 | 38381篇 |
出版年
2021年 | 3314篇 |
2019年 | 3131篇 |
2018年 | 5272篇 |
2017年 | 5132篇 |
2016年 | 5341篇 |
2015年 | 3853篇 |
2014年 | 6607篇 |
2013年 | 20676篇 |
2012年 | 11003篇 |
2011年 | 15236篇 |
2010年 | 12032篇 |
2009年 | 13958篇 |
2008年 | 14318篇 |
2007年 | 14257篇 |
2006年 | 12568篇 |
2005年 | 11621篇 |
2004年 | 11317篇 |
2003年 | 10807篇 |
2002年 | 10635篇 |
2001年 | 10749篇 |
2000年 | 10270篇 |
1999年 | 10743篇 |
1998年 | 26066篇 |
1997年 | 18775篇 |
1996年 | 14685篇 |
1995年 | 11309篇 |
1994年 | 10103篇 |
1993年 | 9776篇 |
1992年 | 7319篇 |
1991年 | 7069篇 |
1990年 | 6872篇 |
1989年 | 6746篇 |
1988年 | 6576篇 |
1987年 | 5625篇 |
1986年 | 5675篇 |
1985年 | 6661篇 |
1984年 | 6064篇 |
1983年 | 5602篇 |
1982年 | 5115篇 |
1981年 | 5330篇 |
1980年 | 4917篇 |
1979年 | 4895篇 |
1978年 | 4672篇 |
1977年 | 5556篇 |
1976年 | 7100篇 |
1975年 | 4031篇 |
1974年 | 3932篇 |
1973年 | 3998篇 |
1972年 | 3327篇 |
1971年 | 3014篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
231.
The behavior of two series of concrete slabs exposed to sulfate-bearing soils was investigated by a numerical model called
STADIUM. In addition to the diffusion of ions and moisture, the model also accounts for the effects of dissolution/precipitation
reactions on the transport mechanisms. The simulations yielded by the model were compared to the actual degradation of the
slabs after 8 years of exposure. The microstructural alterations of concrete resulting from the penetration of magnesium,
chloride and sulfate ions were studied by backscatter mode scanning electron microscope observations and energy-dispersive
X-ray analyses. The comparison of both series of data indicates that the model can reliably predict the various features of
the microstructural alterations of concrete.
Editorial Note Laval University (Canada) is a RILEM Titular Member. Prof. J. Marchand was awarded the 2000 Robert L'Hermite Medal. He is Editor in Chief for Concrete Science and Engineering and Associate Editor for Materials and Structures. He participates in RILEM TC 186-ISA ‘Internal Sulfate attack’. 相似文献
Résumé Le comportement de deux séries de dalles sur sol en béton exposées à des sols chimiquement agressifs a été étudié à l'aide d'un code de calcul numérique appelé STADIUM. Ce modèle permet de décrire le transport couplé de l'eau et des ions dans des matériaux poreux non-saturés en prenant en considération l'influence des réactions chimiques. Les résultats des simultations de la dégradation du béton après huit ans d'exposition à des ions chlore, sulfate et magnésium. Les observations ont été réalisées par microscopie électronique à balayage. Des analyses par dispersion des rayons X ont également été effectuées. Les données démontrent clairement que le modèle perment de prédire avec précision le comportement du béton soumis à différents types d'agression chimique.
Editorial Note Laval University (Canada) is a RILEM Titular Member. Prof. J. Marchand was awarded the 2000 Robert L'Hermite Medal. He is Editor in Chief for Concrete Science and Engineering and Associate Editor for Materials and Structures. He participates in RILEM TC 186-ISA ‘Internal Sulfate attack’. 相似文献
232.
The failure of the conductor of the 460 kV overhead transmission line located along the crossing of the Paraná River was investigated. As a result of this failure, a blackout took place in the southern states of Brazil in January of 2002, reaching approximately 67 million inhabitants. Investigation of the external aluminium layer of the ACSR conductor near the fracture showed typical static deformation marks and dynamic fretting wear tangential marks, both associated with the presence of Al2O3 debris. Additionally, encrusted silicon particles were observed on the external surface of the strands. The internal Al layer showed elliptical deformation marks also associated with Al2O3 debris. Both Al2O3 and Si particles are efficient abrasive material, which associated with slight relative motion of metallic surfaces (clamp/strand and strand/strand) can promote fretting wear. Two types of fracture surface of the Al strands were identified: 45° and quasi-normal surfaces, the former being the predominant type. Delamination and particle detachment were the mechanisms of superficial degradation observed on the Al strands, indicating that the rupture of the strands occurred under a gross slip fretting regime induced by sub-conductor oscillation. Inspection of the internal surface of as-cast Al–10%Si spacer clamps revealed different stages of intense circumferential wear caused by the preferential cracking and particle detachment of the eutectic constituent of the as-cast microstructure. This intense wear reduces the clamping contact pressure, which allows higher displacement amplitude and leads to the critical fretting regime. Finally, a few suggestions are discussed to minimise the occurrence of future failures. 相似文献
233.
Coarse filters for shape matching 总被引:3,自引:0,他引:3
Corney J. Rea H. Clark D. Pritchard J. Breaks M. Macleod R. 《Computer Graphics and Applications, IEEE》2002,22(3):65-74
This article describes the coarse shape filters that support the 3D, Internet-based search engine ShapeSifter, which aims to locate parts already in production that have a shape similar to a desired new part. The search engine analyzes the target model's shape characteristics and performs a similarity match on the database's contents. Our main challenge is identifying shape metrics that produce effective characterizations of 3D models for similarity comparison. We focus on using three novel convex hull-based indices to carry out a preliminary coarse filtering of candidates prior to more detailed analysis. We also describe the crucial role played by two databases of benchmark objects. Unlike other shape-matching systems, we chose ShapeSifter's architecture (multistep query), 3D representation (triangulated mesh), and implementation (Java3D) to allow deployment online once it matures 相似文献
234.
235.
236.
Nichols M.A. Siegel H.J. Dietz H.G. Quong R.W. Nation W.G. 《Parallel and Distributed Systems, IEEE Transactions on》1991,2(3):290-303
Efficient data layout is an important aspect of the compilation process. A model for the creation of perfect memory maps for large-scale parallel machines capable of user-controlled partitionable single-instruction-multiple data/single-program-multiple data (SIMD/SPMD) operation is developed. The term perfect implies that no memory fragmentation occurs and ensures that the memory map size is kept to a minimum. A major constraint on solving this problem is based on the single program nature of both the SIMD and SPMD modes of parallelism. It is assumed that all processors within the same submachine used identical addresses to access corresponding data items in each of their local memories. Necessary and sufficient conditions are derived for being able to create perfect memory maps, and results are applied to several partitionable interconnection networks 相似文献
237.
238.
M. Polák M. Majoro F. Hanic J. Pitel M. Kedrová P. Kottman J. Talapa L. Vencel 《Journal of Superconductivity》1989,2(2):219-233
A method for contactless measurement of the shielding critical current density and its dependence on the external magnetic field is described and analyzed. The obtained values are compared with those measured resistively on two different samples. It is shown that the shielding critical current densityJ
cs
and the intergranular transport current densityJ
cr
are identical if the measurement conditions are similar. A degradation ofJ
cs
measured in the external field with AC ripple has been observed. 相似文献
239.
240.
Containment structures have several regions in which the continuity of the cylindrical pressure boundary is interrupted, e.g., shell penetrations, discontinuous stiffeners, and changes in the shell thickness. Significant strain concentrations can occur in these areas of discontinuity. The Sandia National Laboratories 1:8-scale steel containment equipment hatch was analyzed as an example of an eccentricity at a stiffener intersection.A portion of the as-built 1:8-scale model was modeled with the ANSYS general purpose finite element program using triangular, thin shell finite elements. The overall size of the model was determined from Saint-Venant type considerations of the stress field around the hatch. Shell elements were used to model the ring and formed stiffeners. Geometric and material nonlinear behavior were included. The model was loaded using discrete load steps up to a pressure of 165 psig. At this pressure, the maximum strain was 19.7 percent in the formed stiffener near its intersection with the ring stiffener. The finite element solution demonstrated the very localized nature of the strain field near the ring/formed stiffener intersection.In an attempt to reduce analysis costs, a small portion of the 1:8-scale model immediately surrounding the ring/formed stiffener intersection was selected for further analysis. Two smaller models, a ring/formed stiffener intersection and a ring/circular stiffener intersection, were studied. The models were significantly smaller than the regions used previously. A comparison of the two intersection models showed that the circular stiffener is a more efficient configuration. 相似文献