全文获取类型
收费全文 | 95788篇 |
免费 | 7953篇 |
国内免费 | 4362篇 |
专业分类
电工技术 | 5610篇 |
技术理论 | 11篇 |
综合类 | 6483篇 |
化学工业 | 15969篇 |
金属工艺 | 4977篇 |
机械仪表 | 5637篇 |
建筑科学 | 7492篇 |
矿业工程 | 2723篇 |
能源动力 | 2656篇 |
轻工业 | 7711篇 |
水利工程 | 1816篇 |
石油天然气 | 5366篇 |
武器工业 | 723篇 |
无线电 | 10939篇 |
一般工业技术 | 11300篇 |
冶金工业 | 4705篇 |
原子能技术 | 1024篇 |
自动化技术 | 12961篇 |
出版年
2024年 | 447篇 |
2023年 | 1646篇 |
2022年 | 2933篇 |
2021年 | 4002篇 |
2020年 | 3068篇 |
2019年 | 2482篇 |
2018年 | 2842篇 |
2017年 | 3015篇 |
2016年 | 2884篇 |
2015年 | 3735篇 |
2014年 | 4771篇 |
2013年 | 5639篇 |
2012年 | 6113篇 |
2011年 | 6781篇 |
2010年 | 5672篇 |
2009年 | 5429篇 |
2008年 | 5409篇 |
2007年 | 5025篇 |
2006年 | 4789篇 |
2005年 | 4211篇 |
2004年 | 3027篇 |
2003年 | 2629篇 |
2002年 | 2430篇 |
2001年 | 2162篇 |
2000年 | 2280篇 |
1999年 | 2570篇 |
1998年 | 2142篇 |
1997年 | 1798篇 |
1996年 | 1714篇 |
1995年 | 1423篇 |
1994年 | 1249篇 |
1993年 | 857篇 |
1992年 | 685篇 |
1991年 | 473篇 |
1990年 | 402篇 |
1989年 | 344篇 |
1988年 | 266篇 |
1987年 | 181篇 |
1986年 | 123篇 |
1985年 | 88篇 |
1984年 | 74篇 |
1983年 | 49篇 |
1982年 | 58篇 |
1981年 | 40篇 |
1980年 | 40篇 |
1979年 | 15篇 |
1977年 | 9篇 |
1976年 | 13篇 |
1974年 | 11篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 12 毫秒
11.
Jing Wang Walker D.M. Xiang Lu Majhi A. Kruseman B. Gronthoud G. Villagra L.E. van de Wiel P.J.A. Eichenberger S. 《Design & Test of Computers, IEEE》2007,24(3):226-234
Excessive power supply noise during test can cause overkill. This article discusses two models for supply noise in delay testing and their application to test compaction. The proposed noise models avoid complicated power network analysis, making them much faster than existing power noise analysis tools. can cause performance degradation and 相似文献
12.
Spectral slope (S), describing the exponential decrease of the absorption spectrum over a given wavelength range, is an important parameter in the study of of chromophoric dissolved organic matter (CDOM) dynamics, and also an essential input parameter in remote sensing models. Furthermore, S is often used as a proxy for CDOM composition, including the ratio of fulvic to humic acids and molecular weight. The relative broad range in S values reported in the literature can be explained by the different spectral ranges and fitting methods used. A single exponential model is used to fit the S values for 17 investigations involving 458 samples in Lake Taihu from January to October in 2004. The average S value was 15.18 ± 1.39 μm−1 for the range of 280–500 nm, which fell within the range reported in the literature. The frequency distribution of S value basically obeyed a normal distribution. Significant differences in S values between summer and other seasons showed that phytoplankton degradation was one of the important sources of CDOM in summer, whereas CDOM mainly came from the river input in other seasons. Furthermore, the estimated S value decreased with increasing wavelength range used in regression. The maximum and minimum values derived from the regression were 17.89 ± 1.25 μm−1 and 13.62 ± 2.11 μm−1 for the wavelength ranges of 280–380 nm and 400–500 nm, respectively, a decrease of 23.9%. S values significantly decreased with the increase of CDOM absorption coefficients. CDOM absorption coefficients could be more appropriately estimated from exponential model introducing the variation of S with absorption coefficients, making them useful for a remote sensing bio-optical model of Lake Taihu. DOC-specific absorption coefficient a*(λ) and the parameter M describing molecular size of the humic molecules could also be used as a proxy for the sources and types of CDOM. A general relationship was found between S and a*(λ), and M values. S increased with the decrease of DOC-specific absorption coefficient and the increase of M corresponding to the decrease of molecular weight. 相似文献
13.
A jet-printed digital-lithographic method, in place of conventional photolithography, was used to fabricate 64 /spl times/ 64 pixel (300 /spl mu/m pitch) matrix addressing thin-film transistor (TFT) arrays. The average hydrogenated amorphous silicon TFT device within an array had a threshold voltage of /spl sim/3.5 V, carrier mobility of 0.7 cm/sup 2//V/spl middot/s, subthreshold slope of 0.76 V/decade, and an on/off ratio of 10/sup 8/. 相似文献
14.
4G mobile communications: toward open wireless architecture 总被引:2,自引:0,他引:2
15.
Zhen-Qiu Lu Yan-Yun Zhang 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1996,43(2):296-302
Reconstruction algorithms and their numerical examples of acoustical tomography based on the second-order Born transform perturbation approximation are presented. The reconstruction algorithms in the second-order Born approximation are similar in form to those in the first-order Born approximation. Replacing the angular spectrum of the scattered wave in the first-order case by the result of applying a first-order operator to the angular spectrum of the scattered wave or applying a second-order operator to the angular spectrum of the incident wave leads to the second-order reconstruction algorithms. Also, comparisons of reconstruction algorithms of the first- and second-order Born approximations are given, and they show that the second-order Born approximation algorithms have a distinct advantage over the first-order approximations in many cases 相似文献
16.
17.
The effect of the atomic mobility on a film surface has been studied by using a three-dimensional atomistic thin-film deposition model which simulates three-dimensional thin-film images, surface profiles and cross-sectional area pictures. In addition, quantitative results of surface RMS roughness, average film thickness, atomic coordination number and its distribution, and solid fraction of the deposited thin films, were obtained from the simulations. When the film surface mobility increased from 0.3 to 3.0, RMS roughness decreased from 6.5 to 1.1, solid fraction increased from 0.27 to 0.56 and average film thickness decreased from 40 to 28, due to the reduction of the voids within the film. The full-width half magnitude of the atomic coordination distribution became narrower indicating the increased degree of crystallization. With increase in surface mobility crossing the boundary to 1.5, the film evolved from a porous or loose columnar structure with voids, to a densely packed fibrous grain structure which can be categorized by the zone structure models. 相似文献
18.
19.
20.