全文获取类型
收费全文 | 4896篇 |
免费 | 335篇 |
国内免费 | 36篇 |
专业分类
电工技术 | 135篇 |
综合类 | 65篇 |
化学工业 | 1257篇 |
金属工艺 | 156篇 |
机械仪表 | 152篇 |
建筑科学 | 166篇 |
矿业工程 | 23篇 |
能源动力 | 241篇 |
轻工业 | 842篇 |
水利工程 | 65篇 |
石油天然气 | 45篇 |
无线电 | 369篇 |
一般工业技术 | 708篇 |
冶金工业 | 372篇 |
原子能技术 | 38篇 |
自动化技术 | 633篇 |
出版年
2024年 | 23篇 |
2023年 | 61篇 |
2022年 | 150篇 |
2021年 | 264篇 |
2020年 | 209篇 |
2019年 | 210篇 |
2018年 | 231篇 |
2017年 | 235篇 |
2016年 | 223篇 |
2015年 | 155篇 |
2014年 | 238篇 |
2013年 | 362篇 |
2012年 | 301篇 |
2011年 | 341篇 |
2010年 | 235篇 |
2009年 | 251篇 |
2008年 | 201篇 |
2007年 | 138篇 |
2006年 | 141篇 |
2005年 | 94篇 |
2004年 | 105篇 |
2003年 | 161篇 |
2002年 | 168篇 |
2001年 | 132篇 |
2000年 | 79篇 |
1999年 | 54篇 |
1998年 | 102篇 |
1997年 | 71篇 |
1996年 | 56篇 |
1995年 | 47篇 |
1994年 | 28篇 |
1993年 | 36篇 |
1992年 | 22篇 |
1991年 | 17篇 |
1990年 | 21篇 |
1989年 | 12篇 |
1988年 | 21篇 |
1987年 | 8篇 |
1986年 | 13篇 |
1985年 | 12篇 |
1984年 | 3篇 |
1982年 | 2篇 |
1980年 | 3篇 |
1979年 | 5篇 |
1977年 | 5篇 |
1976年 | 9篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1950年 | 1篇 |
排序方式: 共有5267条查询结果,搜索用时 0 毫秒
11.
V. Anjos M.J.V. Bell E.F. da Silva Jr. R.W.A. Franco I.A. Esquef 《Microelectronics Journal》2005,36(11):977-980
In this paper we report the use of photothermal techniques such as Thermal lens (TL) spectrometry, Photoacoustic and heat capacity, ρcp, to determine the thermo-optical parameters, such as thermal conductivity (K), thermal diffusivity (D), specific heat (cp) and the optical path dependence with temperature (ds/dT), of an undoped polycrystalline 3C-SiC. To our knowledge, this is the first time that Thermal lens technique is used for wide band-gap systems. Results obtained for the polycrystalline sample with TL technique indicates that ds/dT is negative at room temperature. Moreover, the obtained values of thermal diffusivity and thermal conductivity are in good agreement with that found in the literature, indicating that the phototermal techniques can be used to obtain the referred parameters in circumstances where other techniques cannot be used, for example, in harsh environments. 相似文献
12.
Daniel X. Gouveia Odair P. Ferreira Antonio G. Souza Filho M. G. da Silva J. A. C. de Paiva Oswaldo L. Alves Josué Mendes Filho 《Journal of Materials Science》2007,42(2):534-538
The thermal decomposition properties of Mg–Fe hydrotalcites were studied through in situ 57Fe Mössbauer spectroscopy and in situ X-ray diffraction. Abrupt changes in the quadrupolar splitting measured in the Mössbauer spectra revealed a phase transition from the starting lamellar structure to a new crystalline arrangement. By analyzing the Mössbauer parameters we show that the material is highly disordered in the 300–400 °C temperature range. This hypothesis is confirmed by the X-ray results whose diffractograms indicated the collapse of the lamellar structure and the formation of a solid solution. 相似文献
13.
Fbio Gomes Costa Elias Andrade Braga Soraia Teixeira Brando Alexandre de Freitas Espeleta Zênis Novais da Rocha Lílian Maria Tosta Simplício Emerson Andrade Sales 《Applied Catalysis A: General》2005,290(1-2):221-226
Infrared and UV–vis studies of metallocene immobilization on silica are reported here. The results have indicated changes in the Zr coordination sphere of metallocene depending on the immobilization route used. The reaction of [(Cp)2ZrCl2] with silica formed [(Cp)2ZrCl]+[SiO]− species. The same metallocene, reacting with TMA modified silica, formed monomethylated and dimethylated species by the substitution of chloro for methyl ligands, stabilized on the surface by interaction with “MAO-like” species (methylaluminoxane, MAO). These monomethylated and dimethylated cationic zirconium species are the active centers for the polymerization reaction. Different order of TMA addition in the silica modification step generated surface species of a similar nature, differing in their relative quantities. The highest amount of these active species was obtained when the support was added to the TMA solution rather than adding the TMA solution to the silica support. This was the most significant parameter affecting catalytic activity in ethylene polymerization. 相似文献
14.
15.
da Costa D.B. Yacoub M.D. Filho J.C.S.S. Fraidenraich G. Mendes J.R. 《Communications Letters, IEEE》2006,10(1):13-15
This paper provides simple, exact, new closed-form expressions for the generalized phase crossing rate of Nakagami-m fading channels. Sample numerical results obtained by simulation are presented that validate the formulations developed here. A special case of this formulation is the Rayleigh case, whose result agrees with that obtained elsewhere in the literature. In passing, several new closed-form results concerning the statistics of the envelope, its in-phase and quadrature components, phase, and their time derivatives are obtained. 相似文献
16.
X-ray photoelectron spectroscopy (XPS) applied to the study of fluorinated polymer surfaces presents several problems related both to peak assignment and to degradation. In this work, we analyse extensively the question of XPS peak assignments in this kind of surfaces. We conclude that in this kind of surfaces using binding energy differences between fluorine and carbon is better than using absolute binding energies. Also a useful relation between fluorine photoelectron energy vs. polymer composition expressed through the atomic ratio fluorine/carbon (F/C) was found. A protocol for data treatment is proposed and applied to a XPS study of the degradation induced by X-ray on high-density polyethylene surfaces modified by direct fluorination. Results obtained for the degradation, namely the atomic ratio F/C obtained by two different methods, combined with angle resolved X-ray photoelectron spectroscopy (ARXPS) were used to study the fluorine concentration profile in depth, producing self-consistent results. 相似文献
17.
AF da Silva P McCollum T Szymanska L de Cossart 《Canadian Metallurgical Quarterly》1996,83(10):1370-1372
A total of 700 patients who had carotid endarterectomy (CEA) in the UK and Ireland during a 6-month interval between March and August 1994 were studied prospectively. Some 108 patients (15.4 per cent) had a contralateral internal carotid artery occlusion. Previous reports have shown an associated stroke rate of about 10 per cent in these patients. This study assessed complications and outcome for patients undergoing CEA with contralateral internal carotid artery occlusion compared with those without. The indications for surgery were comparable between the two groups although the patients with occlusion had a slightly higher incidence of arrhythmia and stroke. Intraoperative shunts were used in a significantly higher proportion of those with occlusion (83.3 versus 64.7 per cent, P = 0.0001). The combined death and stroke rate for patients with occlusion was 5.6 per cent compared with 2.4 per cent for the remainder (P not significant). On the basis of the present data, CEA with a contralateral carotid artery occlusion carries only a slight increase in the rate of postoperative stroke and death. This increase was not statistically significant and is lower than that reported previously. 相似文献
18.
B. Herreros G. Lifante A. Kling J.C. Soares M.F. da Silva P.D. Townsend P.J. Chandler J. Olivares J.M. Cabrera 《Optical Materials》1996,6(4):281-286
We present a structural study of two Nd3+/MgO codoped LiNbO3 waveguides fabricated by two different methods: ion-implantation and proton-exchange. Rutherford backscattering spectrometry in combination with channelling was used to study the influence of the waveguide fabrication method on the possible modification of the LiNbO3 crystal structure within the waveguiding layer. The results show that the ion-implanted waveguide mainly maintains the same properties as the virgin crystal, apart from a deterioration of a thin surface layer, whilst the proton-exchanged waveguide exhibits a quite different behaviour, although its surface is less damaged. 相似文献
19.
A semianalytical method to estimate the bit-error rate performance of nonsynchronous ASK and FSK optical heterodyne systems is presented. This approach takes into account numerous system details with an accuracy similar to Monte-Carlo simulation, but with a computation time reduced by several orders of magnitude. An analytical approximation, based on a closed-form expression for the decision variable moment generating function, is also presented. The results obtained with the semianalytical method and the analytical approximation are compared to Monte-Carlo simulation results and to measurements obtained on a practical FSK system 相似文献
20.