全文获取类型
收费全文 | 593488篇 |
免费 | 6831篇 |
国内免费 | 1911篇 |
专业分类
电工技术 | 11291篇 |
综合类 | 750篇 |
化学工业 | 87035篇 |
金属工艺 | 24479篇 |
机械仪表 | 20205篇 |
建筑科学 | 14315篇 |
矿业工程 | 2902篇 |
能源动力 | 14588篇 |
轻工业 | 49040篇 |
水利工程 | 5837篇 |
石油天然气 | 9914篇 |
武器工业 | 50篇 |
无线电 | 70819篇 |
一般工业技术 | 118720篇 |
冶金工业 | 104003篇 |
原子能技术 | 12556篇 |
自动化技术 | 55726篇 |
出版年
2021年 | 4026篇 |
2019年 | 3863篇 |
2018年 | 13281篇 |
2017年 | 13659篇 |
2016年 | 10582篇 |
2015年 | 5064篇 |
2014年 | 8019篇 |
2013年 | 24042篇 |
2012年 | 15124篇 |
2011年 | 24665篇 |
2010年 | 20563篇 |
2009年 | 21639篇 |
2008年 | 22205篇 |
2007年 | 23762篇 |
2006年 | 14820篇 |
2005年 | 16619篇 |
2004年 | 14950篇 |
2003年 | 14343篇 |
2002年 | 13139篇 |
2001年 | 12946篇 |
2000年 | 12338篇 |
1999年 | 12774篇 |
1998年 | 30790篇 |
1997年 | 22202篇 |
1996年 | 17298篇 |
1995年 | 13357篇 |
1994年 | 11931篇 |
1993年 | 11768篇 |
1992年 | 8718篇 |
1991年 | 8445篇 |
1990年 | 8144篇 |
1989年 | 8029篇 |
1988年 | 7667篇 |
1987年 | 6657篇 |
1986年 | 6822篇 |
1985年 | 7757篇 |
1984年 | 7114篇 |
1983年 | 6664篇 |
1982年 | 6093篇 |
1981年 | 6271篇 |
1980年 | 5973篇 |
1979年 | 5762篇 |
1978年 | 5613篇 |
1977年 | 6511篇 |
1976年 | 8371篇 |
1975年 | 4809篇 |
1974年 | 4685篇 |
1973年 | 4707篇 |
1972年 | 3941篇 |
1971年 | 3491篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
891.
A technique is proposed for introducing microdoses (10?5–10?10 g) of germanium and indium metals into semiconductor compounds by coulometric titration in a solid electrolyte cell. The solid electrolytes that are reversible with respect to germanium cations (the GeSe-GeI2 system containing 5 mol % GeI2) and indium cations (the InCl3-MgCl2 system containing 15 mol % MgCl2, the InCl3-CdCl2 system containing 1.5 mol % CdCl2, and the In2S3-InCl3 system containing 5 mol % InCl3) are chosen, and their electric transport properties are characterized. The optimum conditions for electrochemical doping (temperature, current density), under which the current efficiency reaches 90–100%, are determined. The doping with germanium and indium is performed for nonstoichiometric compounds, such as lead monotelluride, indium sulfide, and ternary chalcogenide spinel Cd1 ± δCr2Se4. The doping efficiency is controlled by measuring the electromotive force of the corresponding electrochemical cells and the Hall effect, as well as using the electrical conductivity method. The solid electrolytes that are reversible with respect to indium are used to determine the standard Gibbs energies of formation of a number of indium-containing semiconductors. 相似文献
892.
Becker-Gomez A. Lakshmi Viswanathan T. Viswanathan T.R. 《Circuits and Systems II: Express Briefs, IEEE Transactions on》2008,55(7):609-613
893.
Chaves R. Kuzmanov G. Sousa L. Vassiliadis S. 《Very Large Scale Integration (VLSI) Systems, IEEE Transactions on》2008,16(8):999-1008
894.
V. N. Jmerik A. M. Mizerov T. V. Shubina A. V. Sakharov A. A. Sitnikova P. S. Kop’ev S. V. Ivanov E. V. Lutsenko A. V. Danilchyk N. V. Rzheutskii G. P. Yablonskii 《Semiconductors》2008,42(12):1420-1426
Features of plasma-assisted molecular-beam epitaxy of AlGaN compounds at relatively low temperatures of the substrate (no higher than 740°C) and various stoichiometric conditions for growth of the nitrogen- and metal-enriched layers are studied. Discrete submonolayer epitaxy for formation of quantum wells and n-type blocking layers without varying the fluxes of components was used for the first time in the case of molecular- beam epitaxy with plasma activation of nitrogen for the nanostructures with the Al x Ga1 ? x N/Al y Ga1 ? y N quantum wells. Structural and optical properties of the Al x Ga1 ? x N layers in the entire range of compositions (x = 0–1) and nanostructures based on these layers are studied; these studies indicate that there is photoluminescence at room temperature with minimum wavelength of 230 nm. Based on the analysis of the photoluminescence spectra for bulk layers and nanoheterostructures and their temperature dependences, it is concluded that there are localized states in quantum wells. Using the metal-enriched layers grown on the c-Al2O3 substrates, heterostructures for light-emitting diodes with Al x Ga1 ? x N/Al y Ga1 ? y N quantum wells (x = 0.4–0.5, y = x + 0.15) were obtained and demonstrated electroluminescence in the ultraviolet region of the spectrum at the wavelength of 320 nm. 相似文献
895.
896.
J.A. Giroto A.C.S.C. Teixeira C.A.O. Nascimento R. Guardani 《Chemical Engineering and Processing: Process Intensification》2008,47(12):2361-2369
This paper presents the results of experiments carried out in a laboratory-scale photochemical reactor on the photodegradation of different polymers in aqueous solutions by the photo-Fenton process. Solutions of three polymers, polyethyleneglicol (PEG), polyacrylamide (PAM), and polyvinylpyrrolidone (PVP), were tested under different conditions. The reaction progress was evaluated by sampling and analyzing the total organic carbon concentration in solution (TOC) along the reaction time. The behavior of the different polymers is discussed, based on the evolution of the TOC–time curves. Under specific reaction conditions, the formation and coalescence of solid particles was visually observed. Solids formation occurred simultaneously to a sharp decrease in the TOC of the liquid phase. This may be favorable for the treatment of industrial wastewater containing polymers, since the photodegradation process can be coupled with solid separation systems, which may reduce the treatment cost. 相似文献
897.
Vjacheslav V. Zuev 《Journal of Polymer Research》2008,15(5):351-356
Functionalized polyanilines containing biphenyl, terphenyl, carbazole, anthracene, and 4-n-hexylphenyl moieties were synthesized though the reaction of polyaniline in emeraldine base form with sodium salt of corresponding
vinylketoaromatics with quantitative yields. Polymers were characterized with Fourier transform infrared spectroscopy, proton
nuclear magnetic resonance spectroscopy, and thermogravimetry. The emission characteristics of these polymers in N-methyl-2-pyrrolidone solution were examined. The functionalized polyanilines exhibited an intense green emission. 相似文献
898.
P. M. Solozhenkin E. A. Deliyanni V. N. Bakoyannakis A. I. Zouboulis K. A. Matis 《Journal of Mining Science》2003,39(3):287-296
The original method is developed for producing the new inorganic sorption material of akaganeite bgr-FeO(OH). The material in question is characterized relative to arsenic contained in aqua. The possibility is established for removing arsenate ions from water by contemporary physicochemical methods. 相似文献
899.
The results of computer simulations demonstrate the possibility of light energy transmission through band gaps of a one-dimensional photonic crystal with fluctuating lengths of individual layers. In the case of weak (±5%) fluctuations, the light pulse energy partly penetrates in depth a photonic crystal. If fluctuations of the layer length are strong (±20%), the light pulse energy can be partly transmitted through the crystal. 相似文献
900.
P. Provenzano 《Computer-Aided Civil and Infrastructure Engineering》2003,18(6):391-411
Abstract: Uncertainty often recurs in structural system characterization as well as in choosing the mechanical model and in calibrating it. When analyzing a structure founded in cohesionless soils, the uncertainty in system modeling comes from soil inherent variability, site conditions, construction tolerance, and failure mechanisms. In this research, a Fuzzy-Neural Network method to predict the behavior of structures built on complex cohesionless soils is proposed. The method is based on an Artificial-Neural Network (ANN) for modeling the soil-foundation interaction. Its learning process analyzes over 200 records of building foundations, tanks, and embankments settlements on sand and gravel. Once validated, ANN is introduced in the soil-foundation-sovrastructure interaction model. Using fuzzy sets to define vague and ambiguous variables, the Fuzzy-Neural Network method predicts the system behavior and quantifies the uncertainty of its response. A numerical example shows the method effectiveness in the case of uncertainty in soil parameters and gives suggestions for successive applications. 相似文献