全文获取类型
收费全文 | 263244篇 |
免费 | 4111篇 |
国内免费 | 1297篇 |
专业分类
电工技术 | 5099篇 |
综合类 | 284篇 |
化学工业 | 40048篇 |
金属工艺 | 11636篇 |
机械仪表 | 8268篇 |
建筑科学 | 6620篇 |
矿业工程 | 487篇 |
能源动力 | 7095篇 |
轻工业 | 25835篇 |
水利工程 | 1880篇 |
石油天然气 | 1351篇 |
武器工业 | 3篇 |
无线电 | 34302篇 |
一般工业技术 | 48901篇 |
冶金工业 | 51494篇 |
原子能技术 | 4104篇 |
自动化技术 | 21245篇 |
出版年
2021年 | 2237篇 |
2020年 | 1510篇 |
2019年 | 1902篇 |
2018年 | 2997篇 |
2017年 | 2858篇 |
2016年 | 3190篇 |
2015年 | 2484篇 |
2014年 | 4051篇 |
2013年 | 12086篇 |
2012年 | 6832篇 |
2011年 | 9456篇 |
2010年 | 7471篇 |
2009年 | 8193篇 |
2008年 | 8647篇 |
2007年 | 8464篇 |
2006年 | 7743篇 |
2005年 | 7114篇 |
2004年 | 6776篇 |
2003年 | 6776篇 |
2002年 | 6744篇 |
2001年 | 6798篇 |
2000年 | 6161篇 |
1999年 | 6780篇 |
1998年 | 17162篇 |
1997年 | 11952篇 |
1996年 | 9297篇 |
1995年 | 6907篇 |
1994年 | 6039篇 |
1993年 | 5852篇 |
1992年 | 4133篇 |
1991年 | 4078篇 |
1990年 | 3642篇 |
1989年 | 3577篇 |
1988年 | 3503篇 |
1987年 | 2963篇 |
1986年 | 2885篇 |
1985年 | 3446篇 |
1984年 | 3077篇 |
1983年 | 2764篇 |
1982年 | 2571篇 |
1981年 | 2589篇 |
1980年 | 2454篇 |
1979年 | 2282篇 |
1978年 | 2238篇 |
1977年 | 2830篇 |
1976年 | 4201篇 |
1975年 | 1913篇 |
1974年 | 1806篇 |
1973年 | 1790篇 |
1972年 | 1465篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
The effect of secondary scattering that is produced by the induced current in an infinitely long, finitely conducting wire over a plane, finitely conducting earth from an incident electromagnetic pulse is investigated. This is accomplished by finding the field of a Hertzian dipole over the earth and identifying the part that is due to secondary scattering. Frequency-domain results for the overall induced current require that certain infinite integrals be numerically evaluated. Fourier inversion to the time domain in turn requires the numerical evaluation of another infinite integral. When the results are compared to those obtained when secondary scattering is ignored, it is found that secondary scattering slightly increases the current for the case of broadside incidence and reduces it for the case of grazing incidence by as much as two orders of magnitude. Peak currents are much smaller than previously thought. These general results hold for all of the earth parameters that were used in the study 相似文献
103.
W Seilmeier H Wieser H D Belitz 《Zeitschrift für Lebensmittel-Untersuchung und -Forschung》1987,185(6):487-489
Reduced glutenin is separated by gel permeation high-performance liquid chromatography into three major and five minor fractions, which significantly differ in their amino acid compositions. By reversed-phase high performance liquid chromatography, about 20 glutenin components are obtained. These can be classified into three groups according to their amino acid compositions: a hydrophilic group with relatively high values of Glx and Phe, a more hydrophobic group with a high content of Gly, and a strongly hydrophobic group with higher values of Val and Leu. Groups 1, 2 and 3 contain middle-, high- and low-molecular-weight (MMW-, HMW-, LMW-) subunits respectively. 相似文献
104.
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
105.
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
106.
107.
Flame structure and NO emission characteristics in counterflow diffusion flame of blended fuel of H2/CO2/Ar have been numerically simulated with detailed chemistry. The combination of H2, CO2 and Ar as fuel is selected to clearly display the contribution of hydrocarbon products to flame structure and NO emission characteristics due to the breakdown of CO2. A radiative heat loss term is involved to correctly describe the flame dynamics especially at low strain rates. The detailed chemistry adopts the reaction mechanism of GRI 2.11, which consists of 49 species and 279 elementary reactions. All mechanisms including thermal, NO2, N2O and Fenimore are taken into account to separately evaluate the effects of CO2 addition on NO emission characteristics. The increase of added CO2 quantity causes flame temperature to fall since at high strain rates a diluent effect is prevailing and at low strain rates the breakdown of CO2 produces relatively populous hydrocarbon products and thus the existence of hydrocarbon products inhibits chain branching. It is also found that the contribution of NO production by N2O and NO2 mechanisms are negligible and that thermal mechanism is concentrated on only the reaction zone. As strain rate and CO2 quantity increase, NO production is remarkably augmented. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
108.
109.
This letter further discusses the difference between different definitions of voltage unbalance. Contrary to an earlier letter (see P. Pillay et al., ibid., vol.5, p.50-1, 2001), it is concluded that different definitions may give significantly different results. The two IEEE definitions that were not discussed in the earlier letter give different results and both deviate significantly from the true value (ratio of negative, and positive-sequence voltage) when a zero-sequence component is present. 相似文献
110.