全文获取类型
收费全文 | 3833篇 |
免费 | 53篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 85篇 |
综合类 | 1篇 |
化学工业 | 404篇 |
金属工艺 | 20篇 |
机械仪表 | 39篇 |
建筑科学 | 48篇 |
矿业工程 | 2篇 |
能源动力 | 25篇 |
轻工业 | 107篇 |
水利工程 | 10篇 |
石油天然气 | 5篇 |
无线电 | 332篇 |
一般工业技术 | 393篇 |
冶金工业 | 1823篇 |
原子能技术 | 29篇 |
自动化技术 | 564篇 |
出版年
2021年 | 27篇 |
2020年 | 17篇 |
2019年 | 28篇 |
2018年 | 29篇 |
2017年 | 30篇 |
2016年 | 17篇 |
2015年 | 26篇 |
2014年 | 23篇 |
2013年 | 137篇 |
2012年 | 66篇 |
2011年 | 82篇 |
2010年 | 86篇 |
2009年 | 86篇 |
2008年 | 93篇 |
2007年 | 71篇 |
2006年 | 87篇 |
2005年 | 67篇 |
2004年 | 47篇 |
2003年 | 74篇 |
2002年 | 77篇 |
2001年 | 72篇 |
2000年 | 56篇 |
1999年 | 106篇 |
1998年 | 431篇 |
1997年 | 267篇 |
1996年 | 193篇 |
1995年 | 150篇 |
1994年 | 135篇 |
1993年 | 136篇 |
1992年 | 66篇 |
1991年 | 54篇 |
1990年 | 76篇 |
1989年 | 62篇 |
1988年 | 65篇 |
1987年 | 48篇 |
1986年 | 63篇 |
1985年 | 66篇 |
1984年 | 40篇 |
1983年 | 49篇 |
1982年 | 45篇 |
1981年 | 47篇 |
1980年 | 37篇 |
1979年 | 27篇 |
1978年 | 39篇 |
1977年 | 56篇 |
1976年 | 103篇 |
1975年 | 24篇 |
1974年 | 30篇 |
1972年 | 20篇 |
1970年 | 17篇 |
排序方式: 共有3887条查询结果,搜索用时 0 毫秒
81.
82.
83.
84.
Uri Cohen 《Journal of Electronic Materials》1977,6(6):607-643
Electrodeposition of both epitaxial and polycrystalline continuous films of dense, coherent, and well-adherent silicon coatings
was achieved from molten fluorides. A dissolving Si anode and an operating temperature of about 750 C were utilized. Silicon
electrocrystallization epitaxy (ECE) produced films with the (111) orientation on Si substrates of the same orientation. The
unintentionally doped films were of p-type character with a resistivity in the range 0.05 - 0.10 Ω-cm. Polycrystalline Si
films were similarly electroplated onto various polycrystalline metal substrates. Uniform coherent, and well-adherent coatings
with grain diameters as large as 40 – 50 μm were obtained. The useful rate of electrodeposition of Si could be significantly
increased by the application of an alternating square wave pulse (ASWP)2technique. Cathodic current pulses as high as 300 mA/cm2 (growth rate of about 5 μm/min) were demonstrated. The cathodic current efficiencies, for all modes of growth, were about
70 – 100%. The effects of the various operating parameters, and some prospective applications to the fabrication of solar
cells, are discussed.
This was paper A-6 in the 18th Annual Electronic Materials Conference, Salt Lake City, June 23–25, 1976. 相似文献
85.
Suzanne Varet Sidonie Lefebvre Gérard Durand Antoine Roblin Serge Cohen 《Computer Physics Communications》2012,183(12):2535-2541
Many problems require the computation of a high dimensional integral, typically with a few tens of input factors, with a low number of integrand evaluations. To avoid the curse of dimensionality, we reduce the dimension before applying the Quasi-Monte Carlo method. We will show how to reduce the dimension by computing approximate Sobol indices of the variables with a two-levels fractional factorial design. Then, we will use the Sobol indices to define the effective discrepancy, which turns out to be correlated with the QMC error and thus enables one to choose a good sequence for the integral estimation. 相似文献
86.
A continuous-wave hybrid AlGaInAs-silicon evanescent laser 总被引:1,自引:0,他引:1
A.W. Fang Hyundai Park R. Jones O. Cohen M.J. Paniccia J.E. Bowers 《Photonics Technology Letters, IEEE》2006,18(10):1143-1145
We report a novel laser architecture, the hybrid silicon evanescent laser (SEL), that utilizes offset AlGaInAs quantum wells (QWs) bonded to a silicon waveguide. The silicon waveguide is fabricated on a silicon-on-insulator wafer using a complimentary metal-oxide-semiconductor-compatible process, and is subsequently bonded with the AlGaInAs QW structure using low temperature O/sub 2/ plasma-assisted wafer bonding. The optical mode in the SEL is predominantly confined in the passive silicon waveguide and evanescently couples into the III-V active region providing optical gain. The SEL lases continuous wave (CW) at 1568 nm with a threshold of 23 mW. The maximum temperature for CW operation is 60/spl deg/C. The maximum single-sided fiber-coupled CW output power at room temperature is 4.5 mW. 相似文献
87.
Fred Cohen 《Network Security》2003,2003(6):18-20
Networks dominate today's computing landscape and commercial technical protection is lagging behind attack technology. As a result, protection programme success depends more on prudent management decisions than on the selection of technical safeguards. Managing Network Security takes a management view of protection and seeks to reconcile the need for security with the limitations of technology. 相似文献
88.
Maurie J. Cohen 《突发事故与危机管理杂志》2003,11(2):78-85
Disaster preparedness and emergency response in the United States have become increasingly decentralised with state and local governments assuming a larger share of these responsibilities. Policy planners generally view these as positive developments because of the presumed greater adaptability of lower levels of government rapidly evolving crisis conditions. The terrorist incidents of September 11, 2001 required disaster managers across the country to take charge of a situation of an unanticipated type and magnitude. During the events' aftermath public attention was transfixed on activities at the World Trade Center in New York and the Pentagon outside of Washington, DC. However, emergency responders nation‐wide were simultaneously taking preventative measures to secure nuclear power plants, water resources, and other exposed facilities. This analysis highlights the immediate response activities implemented in New Jersey under the aegis of the state's Department of Environmental Protection (NJDEP). The discussion also considers several of the longer‐term initiatives carried out in the state during the subsequent period due to on‐going threat vulnerability assessments and actual events such as anthrax contamination. The conclusion assesses the implications of the September 11 incidents on emergency preparedness at the state level. 相似文献
89.
Scaling Gross Primary Production (GPP) over boreal and deciduous forest landscapes in support of MODIS GPP product validation 总被引:1,自引:0,他引:1
David P. Turner William D. RittsWarren B. Cohen Stith T. GowerMaosheng Zhao Steve W. RunningSteven C. Wofsy Shawn UrbanskiAllison L. Dunn J.W. Munger 《Remote sensing of environment》2003,88(3):256-270
The Moderate Resolution Imaging Radiometer (MODIS) is the primary instrument in the NASA Earth Observing System for monitoring the seasonality of global terrestrial vegetation. Estimates of 8-day mean daily gross primary production (GPP) at the 1 km spatial resolution are now operationally produced by the MODIS Land Science Team for the global terrestrial surface using a production efficiency approach. In this study, the 2001 MODIS GPP product was compared with scaled GPP estimates (25 km2) based on ground measurements at two forested sites. The ground-based GPP scaling approach relied on a carbon cycle process model run in a spatially distributed mode. Land cover classification and maximum annual leaf area index, as derived from Landsat ETM+ imagery, were used in model initiation. The model was driven by daily meteorological observations from an eddy covariance flux tower situated at the center of each site. Model simulated GPPs were corroborated with daily GPP estimates from the flux tower. At the hardwood forest site, the MODIS GPP phenology started earlier than was indicated by the scaled GPP, and the summertime GPP from MODIS was generally lower than the scaled GPP values. The fall-off in production at the end of the growing season was similar to the validation data. At the boreal forest site, the GPP phenologies generally agreed because both responded to the strong signal associated with minimum temperature. The midsummer MODIS GPP there was generally higher than the ground-based GPP. The differences between the MODIS GPP products and the ground-based GPPs were driven by differences in the timing of FPAR and the magnitude of light use efficiency as well as by differences in other inputs to the MODIS GPP algorithm—daily incident PAR, minimum temperature, and vapor pressure deficit. Ground-based scaling of GPP has the potential to improve the parameterization of light use efficiency in satellite-based GPP monitoring algorithms. 相似文献
90.
Kraut Robert; Olson Judith; Banaji Mahzarin; Bruckman Amy; Cohen Jeffrey; Couper Mick 《Canadian Metallurgical Quarterly》2004,59(2):105
As the Internet has changed communication, commerce, and the distribution of information, so too it is changing psychological research. Psychologists can observe new or rare phenomena online and can do research on traditional psychological topics more efficiently, enabling them to expand the scale and scope of their research. Yet these opportunities entail risk both to research quality and to human subjects. Internet research is inherently no more risky than traditional observational, survey, or experimental methods. Yet the risks and safeguards against them will differ from those characterizing traditional research and will themselves change over time. This article describes some benefits and challenges of conducting psychological research via the Internet and offers recommendations to both researchers and institutional review boards for dealing with them. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献