全文获取类型
收费全文 | 244600篇 |
免费 | 2964篇 |
国内免费 | 1243篇 |
专业分类
电工技术 | 4836篇 |
综合类 | 264篇 |
化学工业 | 35558篇 |
金属工艺 | 10870篇 |
机械仪表 | 7075篇 |
建筑科学 | 6337篇 |
矿业工程 | 485篇 |
能源动力 | 6299篇 |
轻工业 | 24213篇 |
水利工程 | 1849篇 |
石油天然气 | 1336篇 |
武器工业 | 3篇 |
无线电 | 31125篇 |
一般工业技术 | 45040篇 |
冶金工业 | 50499篇 |
原子能技术 | 3877篇 |
自动化技术 | 19141篇 |
出版年
2021年 | 1572篇 |
2019年 | 1427篇 |
2018年 | 2330篇 |
2017年 | 2235篇 |
2016年 | 2455篇 |
2015年 | 1914篇 |
2014年 | 3170篇 |
2013年 | 10841篇 |
2012年 | 5471篇 |
2011年 | 7820篇 |
2010年 | 6305篇 |
2009年 | 7001篇 |
2008年 | 7591篇 |
2007年 | 7681篇 |
2006年 | 7078篇 |
2005年 | 6545篇 |
2004年 | 6274篇 |
2003年 | 6287篇 |
2002年 | 6263篇 |
2001年 | 6388篇 |
2000年 | 5820篇 |
1999年 | 6446篇 |
1998年 | 16648篇 |
1997年 | 11651篇 |
1996年 | 8995篇 |
1995年 | 6726篇 |
1994年 | 5934篇 |
1993年 | 5755篇 |
1992年 | 4073篇 |
1991年 | 4013篇 |
1990年 | 3598篇 |
1989年 | 3518篇 |
1988年 | 3455篇 |
1987年 | 2923篇 |
1986年 | 2849篇 |
1985年 | 3430篇 |
1984年 | 3061篇 |
1983年 | 2759篇 |
1982年 | 2567篇 |
1981年 | 2587篇 |
1980年 | 2447篇 |
1979年 | 2292篇 |
1978年 | 2238篇 |
1977年 | 2822篇 |
1976年 | 4201篇 |
1975年 | 1909篇 |
1974年 | 1805篇 |
1973年 | 1789篇 |
1972年 | 1465篇 |
1971年 | 1322篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
161.
A new technique for mixing optical waves to generate microwave-frequency signals using an injection laser diode and a fibre-optic interferometer is reported. A beat signal is produced by interfering light from the laser with light from the same laser emitted earlier at a different frequency. The interferometer consists of an evanescent-field fibre coupler joined to a length of single-mode optical fibre. The laser is tuned by pulsed or bipolar current waveforms superimposed on a DC bias current. Feedback from an external cavity stabilises the laser frequency and reduces its linewidth. Efficient mixing at difference frequencies from 250 MHz to 2 GHz is obtained, with spectral widths of less than 1% of the centre frequency. 相似文献
162.
In the development of a novel freeze-drying technique in a fluidized bed at atmospheric pressure, a parallel study was undertaken using a conventional vacuum equipment. Two kinetically distinct phases were observed during freeze drying of representative Pood samples:
(1) a period during which the rate of drying was constant and (2) a second period during which the drying rate sufferedcontinual reduction. This paper focused attention on the primary drying period which corresponded with the kinetics of sublimation of pure 相似文献
(1) a period during which the rate of drying was constant and (2) a second period during which the drying rate sufferedcontinual reduction. This paper focused attention on the primary drying period which corresponded with the kinetics of sublimation of pure 相似文献
163.
164.
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
165.
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
166.
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
167.
Effect of misalignment on electrical characteristics of ACF joints for flip chip on flex applications 总被引:1,自引:0,他引:1
The effect of misalignment on the electrical properties of anisotropic conductive film (ACF) joints is investigated in this work. It is found that along with the increase of misalignment, the connection resistance of ACF joints increases. When the misalignment in x-direction is less than 5 μm, the increase rate of connection resistance is quite large. Then, along with the severity of misalignment, the increase rate becomes smaller. Finally, when the misalignment is close to 20 μm, the increase rate rises again. The Holm's electric contact theory is used for understanding the connection resistance variation. On the other hand, with the increase of misalignment in x-direction, the insulation resistance between ACF joints decreases. If the misalignment exceeded 10 μm, the decrease is prominent for the Ni particle ACF joints. This phenomenon can be explained by the effect of dielectric damage of the epoxy.Computer programs are also developed to calculate the variation of the probability of open and shorting after misalignment and predicate the maximum misalignment tolerance. The results show that the open and shorting probability increase abruptly after misalignment. On the view of pad parameters, the open probability is mainly related to the pad area, while the pads gap is critical to the shorting probability. Large pads gap (small pad width) can reduce the shorting probability obviously. On the other hand, enlarging the pad area by increasing pad length decreases the open probability significantly. So comparing to square shape pad, rectangle shape pad can reduce the failure probability greatly. 相似文献
168.
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
169.
170.