全文获取类型
收费全文 | 260336篇 |
免费 | 4648篇 |
国内免费 | 1796篇 |
专业分类
电工技术 | 5406篇 |
技术理论 | 5篇 |
综合类 | 1148篇 |
化学工业 | 42013篇 |
金属工艺 | 11015篇 |
机械仪表 | 7745篇 |
建筑科学 | 6609篇 |
矿业工程 | 1656篇 |
能源动力 | 5601篇 |
轻工业 | 25827篇 |
水利工程 | 2886篇 |
石油天然气 | 5954篇 |
武器工业 | 243篇 |
无线电 | 27767篇 |
一般工业技术 | 49233篇 |
冶金工业 | 47163篇 |
原子能技术 | 5632篇 |
自动化技术 | 20877篇 |
出版年
2021年 | 2475篇 |
2019年 | 2104篇 |
2018年 | 3379篇 |
2017年 | 3340篇 |
2016年 | 3672篇 |
2015年 | 2799篇 |
2014年 | 4566篇 |
2013年 | 11353篇 |
2012年 | 7698篇 |
2011年 | 10213篇 |
2010年 | 8128篇 |
2009年 | 8680篇 |
2008年 | 9486篇 |
2007年 | 9610篇 |
2006年 | 8438篇 |
2005年 | 7395篇 |
2004年 | 6662篇 |
2003年 | 6211篇 |
2002年 | 6214篇 |
2001年 | 6322篇 |
2000年 | 5914篇 |
1999年 | 5886篇 |
1998年 | 12863篇 |
1997年 | 9541篇 |
1996年 | 7278篇 |
1995年 | 5533篇 |
1994年 | 5086篇 |
1993年 | 4955篇 |
1992年 | 3945篇 |
1991年 | 3755篇 |
1990年 | 3827篇 |
1989年 | 3775篇 |
1988年 | 3530篇 |
1987年 | 3021篇 |
1986年 | 3053篇 |
1985年 | 3407篇 |
1984年 | 3322篇 |
1983年 | 3076篇 |
1982年 | 2701篇 |
1981年 | 2906篇 |
1980年 | 2642篇 |
1979年 | 2840篇 |
1978年 | 2736篇 |
1977年 | 2842篇 |
1976年 | 3695篇 |
1975年 | 2457篇 |
1974年 | 2290篇 |
1973年 | 2321篇 |
1972年 | 1982篇 |
1971年 | 1785篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
191.
L. B. Knayz'kov 《Journal of Infrared, Millimeter and Terahertz Waves》2003,24(11):1931-1938
Variants are considered of palarizational frequency-selective multipath interference devices for millimetric- and submillimetric- wave receivers. Main expressions are presented that describe their characteristics. Advantages are pointed out of the devices as compared with Fabry-Perot interferometers when solving problems of received frequency-band shaping, heterodyne noise rejection, and signal- and heterodyne-radiation transfer to mixer. 相似文献
192.
L. V. Kuzmin V. A. Morozov S. O. Starkov B. A. Khadzhi 《Journal of Communications Technology and Electronics》2006,51(11):1283-1289
The models of indoor multipath propagation of wideband and ultrawideband (UWB) signals are considered. Application of these models is recommended by an IEEE working group. In the framework of one of the models corresponding to the line-of-sight conditions, the algorithms for reception of UWB chaotic signals in the presence of reflection from multiple surfaces (echo signals) are proposed and analyzed. The efficiency of reception techniques is estimated from the viewpoint of the error probabilities. Limitations caused by the specific properties of echo signals are revealed, and the methods for improvement of reception quality are discussed. 相似文献
193.
Marks L D Ciston J Deng B Rondinelli J 《电子显微学报》2006,25(B08):1-2
Many areas of structure analysis have focused on finding the locations of the atoms. If, instead of the atoms, we knew the positions of the electrons we would in fact know much more, and in most respects knowing where the nuclei are is not important. There is a long history of measurements using precise electron diffraction or X-ray diffraction of the average charge density in materials, but extending beyond to local charge density is, as yet, an unexplored area. 相似文献
194.
Systematic assessment of anger among people with developmental disabilities has been lacking, especially for hospital inpatients. Reliability and validity of anger self-report psychometric scales were investigated with 129 male patients, mostly forensic. Anger prevalence and its relationship to demographic, cognitive, and personality variables and to hospital assaultive behavior were examined. High internal and intermeasure consistency, and some concurrent validity with staff ratings, were found. Retrospective validity regarding physically assaultive behavior in the hospital was obtained. Hierarchical regressions revealed that patient-reported anger was a significant predictor of assaults postadmission, controlling for age, length of stay, IQ, violence offense history, and personality variables. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
195.
D. Vignolles D. Smirnov G. Rikken B. Raquet H. Rakoto C. Proust M. Nardone J. Léotin F. Lecouturier M. Goiran O. Drachenko J. M. Broto L. Brossard A. Audouard 《Journal of Low Temperature Physics》2003,133(1-2):97-120
An overview over past and present activities and future developments at the Toulouse pulsed magnetic field facility is given, both as far as technical developments of the infrastructure, as well as low temperature physics performed at the LNCMP are concerned. 相似文献
196.
Hybrid monolithic materials were prepared through polymerisation of 2-hydroxyethyl methacrylate (HEMA) mixed with zirconium alkoxides (Zr(OBun)4, Zr(OPrn)4 and Zr(OEt)4), modified by acetylacetonate groups. The molar ratio HEMA/Zr varied between 1 and 4. Thermo-Gravimetry coupled with Mass Spectroscopy (TG-MS) analyses, 13C MAS NMR and Dynamical Mechanical Thermal Analysys (DMTA) indicated the polymeric chains were interconnected by the inorganic component.The presence of zirconium alkoxides modified substantially the poly-HEMA properties. Glass transition temperature of hybrid materials derived from butoxy and propoxy was found in the range 50-80 °C, depending on the composition. The typical swelling of p-HEMA in the water, was suppressed by the presence of zirconium compounds. After immersion in distilled water, hybrid polymers showed an initial slight weight increase, followed by a small mass loss, which increases proportionally to the length of alkoxyl group (ethoxide(propoxide(butoxide) and reaches a constant value after about 40 days. The hybrids remained always rigid and transparent. Flexural modulus and strength of about 400-900 and 4-8 MPa were measured. 相似文献
197.
Beebe-Frankenberger Margaret; Bocian Kathleen M.; MacMillan Donald L.; Gresham Frank M. 《Canadian Metallurgical Quarterly》2004,96(2):204
A cohort of 2nd-grade students provided comparisons of academic and social competence based on school retention/promotion decisions. Sample groups were (a) retained, (b) at risk for retention, (c) special education, and (d) promoted. Findings suggested most children with academic deficiencies are identified by schools early and are sorted into educational treatments differing in intensity that represent a continuum of competence. The authors provide empirical evidence counter to the assumptions that retained students have the requisite ability to catch up and have more problem behaviors than other low-achieving students. The relevance of high-stakes test scores for promotion/retention decisions and the parallels between schools' implementation of retention policy and implementation of regulations for identifying children with disabilities are included in the discussion. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
198.
Three different vanadium-modified Pd/Al2O3 catalysts were prepared and tested as catalysts for the deep oxidation of methane. Vanadium was added to the palladium catalyst by incipient wetness of palladium catalyst in order to modify its properties and improve its thermal stability and thioresistance. The behaviour of vanadium-modified catalysts depends on the concentration of this compound, being 0.5 wt.% the optimum amount. However, when strong catalyst poisons are present in the gas (SO2), these modified catalysts do not show a better performance than unmodified catalyst. Bimetallic catalysts were tested with and without further reduction, being observed that reduced bimetallic catalysts perform worse than the non-reduced ones. 相似文献
199.
200.
The selector activated sludge (SAS) systems are known to prevent excessive growth of filamentous microorganisms responsible for bulking sludge, but these systems were hardly ever modelled. This study aimed to develop a model capable of predicting rapid substrate removal in the SAS systems. For this purpose, the Activated Sludge Model No. 3 (ASM3) was extended with three processes (adsorption, direct growth on the adsorbed substrate under aerobic or anoxic conditions). The modified ASM3 was tested against the results of batch experiments with the biomass originating from two full-scale SAS systems in Germany. The endogenous biomass was mixed with various readily biodegradable substrates (acetate, peptone, glucose and wastewater) and the utilisation of substrate (expresses as COD) and oxygen uptake rates (OURs) were measured during the experiments. In general, model predictions fitted to the experimental data, but a considerable number of kinetic (5) and stoichiometric (2) parameters needed to be adjusted during model calibration. The simulation results revealed that storage was generally a dominating process compared to direct growth in terms of the adsorbed substrate utilisation. The contribution of storage ranged from 65-71% (Plant A) and 69-92% (Plant B). 相似文献