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1.
The potential energy profile of the reaction between dimethyl disulfide and OH? radicals is explored by utilizing ab initio and hybrid meta density functional theory methods. Having the energies and structural data of the stationary points, statistical rate theories, such as transition state theory and variable reaction coordinate-transition state theory, are employed to compute the overall rate constants, and discuss the mechanism and product channels. On the basis of the calculations, the overall rate coefficient is predicted to be 2.49?×?10?10?cm3?molecule?1?s?1 at 298?K. It is found that in the most favorable pathway, the reaction proceeds via formation of the relatively unstable intermediate CH3S?(OH)SCH3 decomposing rapidly to yield CH3S?+CH3SOH. 相似文献
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Hyun Kyu Suh 《Fuel》2008,87(6):925-932
This paper investigates the effect of injection parameters on the characteristics of dimethyl ether (DME) as an alternative fuel in a diesel engine with experimental and analytical models based on empirical equations. In order to study macroscopic and microscopic characteristics of DME fuel, this work focuses on the atomization characteristics of DME and compares experimental and predicted results for spray development obtained by empirical models for diesel and DME fuel. Detailed comparisons of spray tip penetration from three different empirical correlations and from visualization experiments of diesel and DME fuels were conducted under various fuel injection conditions. In comparison with the results of different empirical equations for measured spray tip penetration, the experimental results of this study provide good agreement with the calculation results based on empirical equations, except during the earliest stage of the injected spray sequence. The results of atomization characteristics indicate that DME showed better spray characteristics than conventional diesel fuel. Also, the fuel injection delay and maximum injection rate of DME fuel are shorter and lower than those of diesel fuel at the same injection conditions, respectively. 相似文献
4.
A combined technique of the rapid freezing, freeze substitution–fixation method and the osmium–DMSO-osmium method was devised. By this combined method we clearly observed the architecture of intracellular components in three dimensions. Morphological characteristics were generally similar to those of tissue prepared by the osmium–DMSO-osmium method but different in some respects. Mucigen droplets in intestinal goblet cells, for example, appeared as separated spheres, while in specimens prepared by chemical fixation they were observed as a mass of fused droplets. In the Golgi complex, all cisternae were extremely flat, although they usually dilated on the cis side after chemical fixation. Particles on the mitochondrial tubules of liver cells were well distinguished. They were mushroom shaped, as are those observed by negative staining. The combined method, that is, the rapid freezing, osmium–DMSO-osmium method, is thought to be effective for studying the true structure of intracellular components by scanning electron microscopy. 相似文献
5.
Troy A. Semelsberger Kevin C. Ott Rodney L. Borup Howard L. Greene 《Applied catalysis. B, Environmental》2006,65(3-4):291-300
Homogeneous physical mixtures containing a commercial Cu/ZnO/Al2O3 catalyst and a solid–acid catalyst were used to examine the acidity effects on dimethyl ether hydrolysis and their subsequent effects on dimethyl ether steam reforming (DME-SR). The acid catalysts used were zeolites Y [Si/Al = 2.5 and 15: denoted Y(Si/Al)], ZSM-5 [Si/Al = 15, 25, 40, and 140: denoted Z(Si/Al)] and other conventional catalyst supports (ZrO2, and γ-Al2O3). The homogeneous physical mixtures contained equal amounts, by volume, of the solid–acid catalyst and the commercial Cu/ZnO/Al2O3 catalyst (BASF K3-110, denoted as K3). The steam reforming of dimethyl ether was carried out in an isothermal packed-bed reactor at ambient pressure.
The most promising physical mixtures for the low-temperature production of hydrogen from DME contained ZSM-5 as the solid–acid catalyst, with hydrogen yields exceeding 90% (T = 275 °C, S/C = 1.5, τ = 1.0 s and P = 0.78 atm) and hydrogen selectivities exceeding 94%, comparable to those observed for methanol steam reforming (MeOH-SR) over BASF K3-110, with values equaling 95% and 99%, respectively (T = 225 °C, S/C = 1.0, τ = 1.0 s and P = 0.78 atm). Large production rates of hydrogen were directly related to the type of acid catalyst used. The hydrogen production activity trend as a function of physical mixture was
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Nirvana Delgado Otalvaro Pembe Gül Bilir Karla Herrera Delgado Stephan Pitter Jörg Sauer 《化学,工程师,技术》2021,93(5):754-761
Artificial neural networks (ANNs) are designed and implemented to model the direct synthesis of dimethyl ether (DME) from syngas over a commercial catalyst system. The predictive power of the ANNs is assessed by comparison with the predictions of a lumped model parameterized to fit the same data used for ANN training. The ANN training converges much faster than the parameter estimation of the lumped model, and the predictions show a higher degree of accuracy under all conditions. Furthermore, the simulations show that the ANN predictions are also accurate even at some conditions beyond the validity range. 相似文献
9.
In general, peptides do not exhibit a well-defined conformational profile in solution. However, despite the experimental blurred picture associated with their structure, compelling spectroscopic evidence shows that peptides exhibit local order. The conformational profile of a peptide is the result of a balance between intramolecular interactions between different atoms of the molecule and intermolecular interactions between atoms of the molecule and the solvent. Accordingly, the conformational profile of a peptide will change upon the properties of the solvent it is soaked. To get insight into the balance between intra- and intermolecular interactions on the conformational preferences of the peptide backbone we have studied the conformational profile of the alanine dipeptide in diverse solvents using molecular dynamics as sampling technique. Solvents studied include chloroform, methanol, dimethyl sulfoxide, water and N-methylacetamide. Different treatments of the solvent have been studied in the present work including explicit solvent molecules, a generalized Born model and using the bulk dielectric constant of the solvent. The diverse calculations identify four major conformations with different populations in the diverse solvents: the C7eq only sampled in chloroform; the C5 or extended conformation; the polyproline (PII) conformation and the right-handed α-helix conformation (αR). The results of present calculations permit to analyze how the balance between intra- and intermolecular interactions explains the populations of the diverse conformations observed. 相似文献
10.
21世纪的"绿色燃料"--二甲醚 总被引:9,自引:0,他引:9
被称为 2 1世纪“绿色燃料”的二甲醚具有清洁、低毒性、低蒸气压和优良的燃烧性能 ,因而成为多种产品的替代品 ,如环境友好的民用燃料、柴油和制冷剂 ,而且具有较好的市场潜力。本文主要介绍了二甲醚的生产方法、用途和国内外的发展状况 相似文献