全文获取类型
收费全文 | 17121篇 |
免费 | 212篇 |
国内免费 | 23篇 |
专业分类
电工技术 | 188篇 |
综合类 | 3篇 |
化学工业 | 2005篇 |
金属工艺 | 362篇 |
机械仪表 | 342篇 |
建筑科学 | 514篇 |
矿业工程 | 60篇 |
能源动力 | 307篇 |
轻工业 | 1214篇 |
水利工程 | 89篇 |
石油天然气 | 118篇 |
无线电 | 1509篇 |
一般工业技术 | 2343篇 |
冶金工业 | 6744篇 |
原子能技术 | 159篇 |
自动化技术 | 1399篇 |
出版年
2021年 | 101篇 |
2019年 | 102篇 |
2018年 | 135篇 |
2017年 | 101篇 |
2016年 | 94篇 |
2015年 | 107篇 |
2014年 | 225篇 |
2013年 | 572篇 |
2012年 | 307篇 |
2011年 | 406篇 |
2010年 | 332篇 |
2009年 | 336篇 |
2008年 | 450篇 |
2007年 | 439篇 |
2006年 | 432篇 |
2005年 | 386篇 |
2004年 | 323篇 |
2003年 | 364篇 |
2002年 | 308篇 |
2001年 | 322篇 |
2000年 | 316篇 |
1999年 | 469篇 |
1998年 | 1975篇 |
1997年 | 1178篇 |
1996年 | 840篇 |
1995年 | 548篇 |
1994年 | 491篇 |
1993年 | 529篇 |
1992年 | 288篇 |
1991年 | 261篇 |
1990年 | 282篇 |
1989年 | 232篇 |
1988年 | 243篇 |
1987年 | 211篇 |
1986年 | 208篇 |
1985年 | 262篇 |
1984年 | 208篇 |
1983年 | 211篇 |
1982年 | 208篇 |
1981年 | 182篇 |
1980年 | 208篇 |
1979年 | 129篇 |
1978年 | 140篇 |
1977年 | 278篇 |
1976年 | 425篇 |
1975年 | 136篇 |
1974年 | 125篇 |
1973年 | 108篇 |
1972年 | 78篇 |
1970年 | 83篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Granularity is a well known concept in parallel processing. While intuitively, the distinction between coarse-grain and fine-grain paralellism is clear, there is no rigorous definition. This paper develops two notions of granularity, each defined formally and represented by a single rational number. The two notions are compared and contrasted with each other and with previously proposed definitions of granularity.Supported, in part, by NSA OCREAE Grant MDA904-85-H-0002. Currently on leave at the National Science Foundation. 相似文献
103.
104.
105.
We have performed Nuclear Quadrupole Resonance (NQR) experiments on an alloy of scandium and yttrium. We find that the characteristic resonance frequencies in zero external field are 50 percent larger than in pure scandium. This increase in frequency makes the Sc-Y alloy a better candidate for absolute thermometry below 500 µK. However, the spin-lattice relaxation time of this alloy is more than an order of magnitude longer than in the pure scandium. In addition, we have observed an abrupt increase in the Korringa constant for temperatures below 5mK. 相似文献
106.
107.
Approximations commonly used to determine the effective indexes of the guided modes of optical waveguides formed using multiple quantum well (MQW) materials are compared to the exact solutions in the slab waveguide model. Modeling the quantum well region as a single homogeneous layer with an average index of refraction is shown to produce results in close agreement with exact values of the effective index. A geometrically weighted average of the indexes provides the most accurate approximation for typical values of index and layer thickness of GaAs-AlxGa1-xAs quantum well waveguides 相似文献
108.
Gesbert D. Shafi M. Da-shan Shiu Smith P.J. Naguib A. 《Selected Areas in Communications, IEEE Journal on》2003,21(3):281-302
This paper presents an overview of progress in the area of multiple input multiple output (MIMO) space-time coded wireless systems. After some background on the research leading to the discovery of the enormous potential of MIMO wireless links, we highlight the different classes of techniques and algorithms proposed which attempt to realize the various benefits of MIMO including spatial multiplexing and space-time coding schemes. These algorithms are often derived and analyzed under ideal independent fading conditions. We present the state of the art in channel modeling and measurements, leading to a better understanding of actual MIMO gains. Finally, the paper addresses current questions regarding the integration of MIMO links in practical wireless systems and standards. 相似文献
109.
Solid polymer electrolytes (SPEs) synthesized by the sol-gel process and designated as di-ureasils have been prepared through the incorporation of lithium perchlorate, LiClO4, into the d-U(2000) organic-inorganic hybrid network. Electrolytes with lithium salt compositions of n (where n indicates the number of oxyethylene units per Li+ ion) between ∞ and 0.5 were characterized by conductivity measurements, cyclic voltammetry at a gold microelectrode, thermal analysis and Fourier transform Raman (FT-Raman) spectroscopy. The conductivity results obtained suggest that this system offers a quite significant improvement over previously characterized analogues doped with lithium triflate [S.C. Nunes, V. de Zea Bermudez, D. Ostrovskii, M.M. Silva, S. Barros, M.J. Smith, R.A. Sá Ferreira, L.D. Carlos, J. Rocha, E. Morales, J. Electrochem. Soc. 152 (2) (2005), A429]. “Free” perchlorate ions, detected in all the samples examined, are identified as the main charge carriers in the sample that yields the highest room temperature conductivity (n = 20). In the di-ureasils with n ≤ 10 ionic association is favoured and the ionic conductivity drops. 相似文献
110.