全文获取类型
收费全文 | 4821篇 |
免费 | 251篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 68篇 |
综合类 | 2篇 |
化学工业 | 1313篇 |
金属工艺 | 154篇 |
机械仪表 | 93篇 |
建筑科学 | 118篇 |
矿业工程 | 12篇 |
能源动力 | 150篇 |
轻工业 | 553篇 |
水利工程 | 10篇 |
石油天然气 | 10篇 |
无线电 | 150篇 |
一般工业技术 | 754篇 |
冶金工业 | 1085篇 |
原子能技术 | 22篇 |
自动化技术 | 582篇 |
出版年
2023年 | 26篇 |
2022年 | 112篇 |
2021年 | 194篇 |
2020年 | 96篇 |
2019年 | 86篇 |
2018年 | 157篇 |
2017年 | 148篇 |
2016年 | 181篇 |
2015年 | 134篇 |
2014年 | 172篇 |
2013年 | 292篇 |
2012年 | 200篇 |
2011年 | 265篇 |
2010年 | 173篇 |
2009年 | 160篇 |
2008年 | 148篇 |
2007年 | 159篇 |
2006年 | 111篇 |
2005年 | 92篇 |
2004年 | 85篇 |
2003年 | 78篇 |
2002年 | 79篇 |
2001年 | 43篇 |
2000年 | 36篇 |
1999年 | 40篇 |
1998年 | 195篇 |
1997年 | 219篇 |
1996年 | 158篇 |
1995年 | 116篇 |
1994年 | 59篇 |
1993年 | 78篇 |
1992年 | 25篇 |
1991年 | 16篇 |
1990年 | 22篇 |
1989年 | 20篇 |
1988年 | 25篇 |
1987年 | 31篇 |
1986年 | 25篇 |
1985年 | 41篇 |
1984年 | 43篇 |
1983年 | 31篇 |
1982年 | 55篇 |
1981年 | 55篇 |
1980年 | 66篇 |
1979年 | 38篇 |
1978年 | 39篇 |
1977年 | 123篇 |
1976年 | 239篇 |
1975年 | 21篇 |
1973年 | 14篇 |
排序方式: 共有5076条查询结果,搜索用时 31 毫秒
71.
72.
An emitting, absorbing, and anisotropically scattering plain medium containing a suspension of ZnO particles is considered, in which the particles are directly exposed to high-flux irradiation and undergo shrinkage during their endothermic dissociation into Zn(g) and O2 at above 2100 K. The unsteady energy equation that links the rate of radiative heat transfer to the rate of the chemical reaction is formulated and solved numerically by the finite volume technique and the explicit Euler time-integration scheme. The path-length Monte Carlo method is applied for modeling the radiative transfer within the suspension using the absorption/scattering coefficients and the scattering phase function obtained from the Mie theory. It is found that the particle suspension can be heated rapidly from its initial 300 K to over 1800 K in less than 0.1 s, resulting in a more uniform temperature profile as the reaction progresses, particles shrink, and the suspension becomes optically thinner. The chemical conversion increases with decreasing initial particle diameter and volume fraction due to the efficient radiative absorption. 相似文献
73.
Ionic liquids as electrolytes 总被引:5,自引:0,他引:5
Salts having a low melting point are liquid at room temperature, or even below, and form a new class of liquids usually called room temperature ionic liquids (RTIL). Information about RTILs can be found in the literature with such key words as: room temperature molten salt, low-temperature molten salt, ambient-temperature molten salt, liquid organic salt or simply ionic liquid. Their physicochemical properties are the same as high temperature ionic liquids, but the practical aspects of their maintenance or handling are different enough to merit a distinction. The class of ionic liquids, based on tetraalkylammonium cation and chloroaluminate anion, has been extensively studied since late 1970s of the XX century, following the works of Osteryoung. Systematic research on the application of chloroaluminate ionic liquids as solvents was performed in 1980s. However, ionic liquids based on aluminium halides are moisture sensitive. During the last decade an increasing number of new ionic liquids have been prepared and used as solvents. The general aim of this paper was to review the physical and chemical properties of RTILs from the point of view of their possible application as electrolytes in electrochemical processes and devices. The following points are discussed: melting and freezing, conductivity, viscosity, temperature dependence of conductivity, transport and transference numbers, electrochemical stability, possible application in aluminium electroplating, lithium batteries and in electrochemical capacitors. 相似文献
74.
Julian Chojnowski Slawomir Rubinsztajn Witold Fortuniak Jan Kurjata 《Journal of Inorganic and Organometallic Polymers and Materials》2007,17(1):173-187
Summary Reactions of hexamethylcyclotrisiloxane, D3, with 1,1,3,3-tetramethyldisiloxane, HMMH, 1,1,1,3,3-pentamethyldisiloxane, HMM, phenyldimethylsilane and phenylmethylsilane catalyzed by tris(pentafluorophenyl)borane were studied. These reactions lead
to ring opening of D3 by the SiH reactant producing open chain oligomers with hydrosilane functionality at one or both chain ends. The reactivity
of the hydrosilanes toward D3 decreases in the series: PhMeSiH2 > HMMH > PhMe2SiH > HMM. Competitive self-oligomerization of HMMH and HMM also occurs. Primary products of these processes are able to enter into reactions with the SiH and D3 reactants; some also undergo cyclization. Thus, consecutive and competitive processes lead to a series of various oligohomologues.
Gas chromatography in conjunction with chemical ionization mass spectroscopy permitted identification of structure and determination
of the basic directions of these oligomerization processes. Polysiloxanes of higher molecular weight may be also formed in
some of these systems. The reactions, which occur in the systems studied, are rationalized on the basis of the mechanism involving
the hydride transfer from silicon to trivalent boron. This includes the transient formation of tertiary trisilyloxonium borate
which decomposes by the hydride transfer to one of the silicon atoms of the trisilyloxonium center.
Footnote: This paper is dedicated to Professor Ian Manners in recognition of his significant contributions to the field of
organometallic polymers. 相似文献
75.
Beata Biaobok Janusz Trawczyski Wodzimierz Mita Mirosaw Zawadzki 《Applied catalysis. B, Environmental》2007,72(3-4):395-403
Ce- or Sr-doped LaCoO3 bulk perovskites were prepared by citric acid method as well as 10 wt.% of LaCoO3 was deposited on alumina carrier stabilized with lanthanum. Properties of prepared materials were characterized by determination of surface area, acid-basic properties and XRD, XPS, TPDO2, H2-TPR measurements as well as catalytic activity and selectivity for ethanol combustion was tested. It was found that substitution of La in LaCoO3 with either Sr or Ce has only small effect on its activity in ethanol combustion. Strontium inserted into LaCoO3 structure increases basic character of the perovskite surface as well as selectivity to acetaldehyde (ACA). Substitution of La with cerium has no effect on the concentration of basic sites and does not affect the selectivity to ACA. Activity of LaCoO3-based catalysts in ethanol combustion and their selectivity to ACA formation can be explained on the basis of the presence of both -oxygen species and sites with basic character on the material surface.
Acid-basic properties of supported LaCoO3 are dominated by acidic character of the carrier. Results of XPS and H2-TPR measurements of LaCoO3 supported on La–Al2O3 suggest that perovskite remains in strong interaction with carrier and probably is partially decomposed. Deposition of perovskite on stabilized carrier significantly increases the rate of ethanol combustion. 相似文献
76.
Changes in transparency and color as well as GHCl values of hard PVC foils exposed to gamma radiation were investigated while using different amounts of the stabilizers ethylene glycol bis-β-aminocrotonate (I), calcium/zinc laurate + epoxy compounds (II), and magnesium/zinc stearate + sorbitol + epoxy compounds (III), and plasticizers dioctyl phthalate (DOP) (IV), dioctyl sebacate (V), propylene glycol polyadipate + octyl alcohol composition (VI), and diisotridecyl phthalate (VII). A strong synergistic effect was observed in systems containing both plasticizer and stabilizer. Best results were obtained for the I + II + IV, I + II + V, and I + III + V systems. 相似文献
77.
Friction and wear resistance are two vital tribological properties of polymer-based materials but optimization of both is rarely attempted. We have investigated blends of 70 wt% poly(vinylidene fluoride) (PVDF)+30% ultra high molecular weight polyethylene, the latter either un-irradiated or else γ-irradiated. Each sample contained varying amounts of carbon black (CB) and also had a varied degree of crosslinking and irradiation dose. We have determined static and dynamic friction, scratch resistance, and sliding wear in multiple scratching tests. Effects of the irradiation dose and CB concentration have been quantified. The electric conductivity threshold is reflected in a drop of static friction; formation of a continuous phase of the lubricant affects tribology as well as electrical properties—both for irradiated and for un-irradiated samples. The scratch resistance as represented by the residual (healing) depth is affected by crosslinking, by the stage at which irradiation is applied (before or after blending) and by CB addition. Crosslinking by moderate amounts of irradiation provides shallower residual depths while higher doses cause adverse results. Similarly, the CB lubricant can either improve or worsen the scratch resistance. A combination of both approaches produces either better or else worse results than crosslinking alone. Lower friction seems accompanied by higher scratch resistance. A combination of a specific irradiation dose and an optimized CB concentration lowers the sliding wear significantly. Strain hardening in sliding wear determination takes place for all materials studied, irrespective of the extent or radiation-induced crosslinking and of the presence and concentration of carbon black. 相似文献
78.
Witold Brostow Ligia Gargallo Andrea Hormazabal Magdalena Jaklewicz Kevin P Menard Alejandra Opazo Deodato Radic 《Polymer International》2004,53(4):460-464
We have studied blends of a polymer liquid crystal (PLC) with poly(cyclohexylethyl methacrylate) (PCHEMA) or poly(cyclohexylpropyl methacrylate) (PCHPMA). The PLC is PET/0.6PHB where PET = poly(ethylene terephthalate), PHB = p-hydroxybenzoic acid and 0.6 is the mole fraction of the latter in the copolymer. The microstructure was studied by scanning electron microscopy (SEM). PCHEMA + PLC (20 wt% of the latter, blend E) has a fine texture with LC islands evenly distributed in the matrix and good adhesion between the phases resulting from their partial miscibility. The PCHPMA + PLC (20 wt% of the latter, blend P) shows only limited compatibility. The SEM results are confirmed by values of the glass transition temperatures Tg determined via thermal mechanical analysis. The Tg value of the blend E is shifted towards the Tg of PLC; Tg of blend P is practically equal to that of PCHPMA. The linear isobaric expansivity αL values for both blends are lower than the respective values for pure PCHPMA and PCHEMA. Thermal stabilities of the blends determined by thermogravimetry are also better than those of pure polymethacrylates. The temperature of 50% weight degradation for blend E is higher than that for pure PCHEMA by more than 60 K Copyright © 2004 Society of Chemical Industry 相似文献
79.
Rajmund S. Dybczyński Marta Pyszynska Krzysztof Kulisa Anna Bojanowska-Czajka 《分离科学与技术》2020,55(7):1364-1379
ABSTRACTNew ion interaction chromatographic (IIC) method employing Kromasil 100 C18 column and tetra-n-butylammonium hydroxide (TBAOH) as an ion interaction reagent (IIR) is able to separate yttrium from Rare Earth Elements (REE) as anionic complexes with nitrilotriacetic acid (NTA). New method for the chromatographic determination of Y in REE mixture was devised and validated by the analysis of the certified reference material (CRM). Potential possibilities of the new chromatographic system for larger scale applications including macro-micro events were demonstrated. 相似文献
80.
Szymkowski Maciej Jasiński Piotr Saeed Khalid 《Innovations in Systems and Software Engineering》2021,17(3):309-317
Innovations in Systems and Software Engineering - One of the most important modules of computer systems is the one that is responsible for user safety. It was proven that simple passwords and... 相似文献