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排序方式: 共有2606条查询结果,搜索用时 15 毫秒
81.
Christoph Schmerbauch Jesus Gonzalez‐Julian Robert Röder Carsten Ronning Olivier Guillon 《Journal of the American Ceramic Society》2014,97(6):1728-1735
We report the sintering behavior of nanocrystalline zinc oxide under external AC electric field between 0 and 160 V/cm. In situ acquisition of density by means of laser dilatometry, evaluation of specimen temperature, real‐time measurement of electric field and current help analyze this peculiar behavior. Field strength and blocking electrodes significantly affect densification and microstructure, which was evaluated in the vicinity of the flash event and for the fully sintered material. High current densities flow through the sample at high electric fields, entailing a sudden increment of the temperature estimated to several hundreds of K and an exaggerated grain growth. In contrast, low current density flows through the sample at lower electric fields, which guarantees normal grain growth and highest final density. Macroscopic photoluminescence measurements give insights into the development of the defect structure. Electric fields are expected to enhance defect mobility, explaining the high densification rates observed during the sintering process. 相似文献
82.
Jana P. Parras Chen Cao Zheng Ma Robert Mücke Lei Jin Rafal Dunin-Borkowski Olivier Guillon Roger A. De Souza 《Journal of the American Ceramic Society》2020,103(3):1755-1764
Weakly acceptor-doped ceria ceramics were characterized structurally and compositionally with advanced transmission electron microscopy (TEM) techniques and electrically with electrochemical impedance spectroscopy (EIS). The grain boundaries studied with TEM were found to be free of second phases. The impedance spectra, acquired in the range 703 ≤ T/K ≤ 893 in air, showed several arcs that were analyzed in terms of bulk, grain-boundary, and electrode responses. We ascribed the grain-boundary resistance to the presence of space-charge layers. Continuum-level simulations were used to calculate charge-carrier distributions (of acceptor cations, oxygen vacancies, and electrons) in these space-charge layers. The acceptor cations were assumed to be mobile at high (sintering) temperatures but immobile at the temperatures of the EIS measurements. Space-charge formation was assumed to be driven by the segregation of oxygen vacancies to the grain-boundary core. Comparisons of data from the simulations and from the EIS measurements yielded space-charge potentials and the segregation energy of vacancies to the grain-boundary core. The space-charge potentials from the simulations are compared with values obtained by applying the standard, analytical (Mott–Schottky and Gouy–Chapman) expressions. The importance of modelling space-charge layers from the thermodynamic level is demonstrated. 相似文献
83.
Yifan Deng Bruno Faivre Dr. Olivier Back Dr. Murielle Lombard Dr. Ludovic Pecqueur Prof. Dr. Marc Fontecave 《Chembiochem : a European journal of chemical biology》2020,21(1-2):163-170
The hydroxylation of phenols into polyphenols, which are valuable chemicals and pharmaceutical products, is a challenging reaction. The search for green synthetic processes has led to considering microorganisms and pure hydroxylases as catalysts for phenol hydroxylation. Herein, we report the structural and functional characterization of the flavin adenine dinucleotide (FAD)-dependent 4-hydroxyphenylacetate 3-monooxygenase from Escherichia coli, named HpaB. It is shown that this enzyme enjoys a relatively broad substrate specificity, which allows the conversion of a number of non-natural phenolic compounds, such as tyrosol, hydroxymandelic acid, coumaric acid, hydroxybenzoic acid and its methyl ester, and phenol, into the corresponding catechols. The reaction can be performed by using a simple chemical assay based on formate as the electron donor and the organometallic complex [Rh(bpy)Cp*(H2O)]2+ (Cp*: 1,2,3,4,5-pentamethylcyclopentadiene, bpy: 2,2′-bipyridyl) as the catalyst for FAD reduction. The availability of a crystal structure of HpaB in complex with FAD at 1.8 Å resolution opens up the possibility of the rational tuning of the substrate specificity and activity of this interesting class of phenol hydroxylases. 相似文献
84.
Cytotoxicity of CeO2 nanoparticles for Escherichia coli. Physico-chemical insight of the cytotoxicity mechanism 总被引:1,自引:0,他引:1
Thill A Zeyons O Spalla O Chauvat F Rose J Auffan M Flank AM 《Environmental science & technology》2006,40(19):6151-6156
The production of nanoparticles (NPs) is increasing rapidly for applications in electronics, chemistry, and biology. This interest is due to the very small size of NPs which provides them with many interesting properties such as rapid diffusion, high specific surface areas, reactivity in liquid or gas phase, and a size close to biomacromolecules. In turn, these extreme abilities might be a problem when considering a potentially uncontrolled exposure to the environment. For instance, nanoparticles might be highly mobile and rapidly transported in the environment or inside the body through a water or air pathway. Accordingly, the very fast development of these new synthetic nanomaterials raises questions about their impact on the environment and human health. We have studied the impact of a model water dispersion of nanoparticles (7 nm CeO2 oxide) on a Gram-negative bacteria (Escherichia coli). The nanoparticles are positively charged at neutral pH and thus display a strong electrostatic attraction toward bacterial outer membranes. The counting of colony forming units (CFU) after direct contact with CeO2 NPs allows for the defining of the conditions for which the contact is lethal to Escherichia coli. Furthermore, a set of experiments including sorption isotherms, TEM microscopy, and X-ray absorption spectroscopy (XAS) at cerium L3 edge is linked to propose a scenario for the observed toxic contact. 相似文献
85.
A comparative study of three ventilation systems supplying air to a typical Canadian indoor ice rink illustrates the power, energy and operating cost savings which can be achieved by using the relatively warm air from the air cooled condensers of the refrigeration system. The direct use of this warm air for ventilation results in a reduction of energy consumption during the winter amounting to 24.2% of the yearly consumption of the heating system. On the other hand, the use of a heat exchanger to heat the ventilation air results in energy consumption reductions throughout the year. Depending on the size of the heat exchanger these gains can be as high as 60.8% of the heating energy consumption by the existing system. Based on actual prices of electricity and the heat exchanger it is established that the cost savings over the life of the equipment are at least three times higher than the cost of the heat exchanger. 相似文献
86.
87.
Olivier Bouquin Martine Lejeune Jean-Pierre Boilot 《Journal of the American Ceramic Society》1991,74(5):1152-1156
The reaction sequences during calcination of oxide mixtures were studied for the PbMg1/3 Nb2/3 O3 ─PbTiO3 (PMN-PT) system. The effect of reactivity and composition of the starting mixtures was investigated. In the present study, a B-site-deficient, cubic pyrochlore phase in the PbO-Nb2 O5 system was formed at 500°C. The perovskite phase of PMN was formed at 7007deg;C through the diffusion of MgO into the pyrochlore phase. The lattice parameter of the pyrochlore phase decreased as this transformation to perovskite progressed. 相似文献
88.
S. Vranckx K.A. Heufer C. Lee H. Olivier L. Schill W.A. Kopp K. Leonhard C.A. Taatjes R.X. Fernandes 《Combustion and Flame》2011,158(8):1444-1455
Despite considerable interest in butanol as a potential biofuel candidate, its ignition behaviour at elevated pressures still remains largely unexplored. The present study investigates the oxidation of n-butanol in air at pressures near 80 bar. Ignition delays were determined experimentally in the temperature range of 795–1200 K between 61 and 92 bar. The time of ignition was determined by recording pressure and CH-emission time histories throughout the course of the experiments. The results display the first evidence of the influence of negative temperature coefficient (NTC) behaviour which was not observed in earlier ignition studies. The high-pressure measurements show that NTC behaviour is enhanced as pressures are increased. The experimental results were modelled using an improved chemical kinetic mechanism which includes a simplified sub-mechanism for butyl-peroxy formation and isomerisation reactions currently incompletely accounted for in n-butanol kinetic models. The detailed mechanism validated with the high-pressure ignition results for realistic engine in-cylinder conditions can have significant impact on future advanced low-temperature combustion engines. 相似文献
89.
Benoit Charlas Olivier Gillia Pierre Doremus Didier Imbault 《International Journal of Hydrogen Energy》2012
The storage of hydrogen in hydride materials is currently much researched as a mean of energy storage. This reversible storage is achieved by successive hydriding and dehydriding reactions. During these reactions, the material undergoes structural transformations which result in swelling of the hydride powder grains due to the absorption of hydrogen. This phenomenon can generate major mechanical stresses on the cell containing the hydride. The present experimental study examines the cyclic swelling of a granular bed consisting of hydride Ti–Cr–V + Zr–Ni. Two superimposed phenomena are identified: a cyclic rearrangement causing a reduction and then an increase in porosity coupled with gradual densification of the stack. 相似文献
90.
Minh Trung DangGuillaume Wantz Habiba BejboujiMathieu Urien Olivier J. DautelLaurence Vignau Lionel Hirsch 《Solar Energy Materials & Solar Cells》2011,95(12):3408-3418
Polymeric photovoltaic (PV) solar cells have been fabricated using six solvents: chloroform (CHCl3), toluene (T), chlorobenzene (CB), orthodichlorobenzene (ODCB), 1,2,3,4-tetrahydronaphthalene (THN) and 1,2,4-trichlorobenzene (TCB). The active layers were composed of poly(3-hexyl)thiophene (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM). Special care has been taken to keep all experimental parameters constant (thickness of the active layers, donor/acceptor weight ratio, area of active surface and electrodes) in order to avoid artefacts and truly study the effect of solvents. Studies using atomic force microscopy (AFM) and optical absorption (UV-vis) showed the relationship between the photovoltaic performance and the evaporation rate of solvents. The use of solvents with high boiling point results in a higher degree of organization in the structure of P3HT. A direct comparison with devices processed with thermal treatment has also been performed. As often reported thermal annealing increases photo-conversion efficiency of devices created from common solvents, due to better separation of phase between the two materials of the blend. In the case of solvents with high boiling point such as THN and TCB, neither phase separation nor modification of P3HT crystallization induced by thermal annealing has been observed. However thermal treatment appears to enhance performance, ensuing the evaporation of remaining solvent in the active layers. An overview of the effect of solvent on the electrical properties of films containing pure P3HT and P3HT:PCBM blend reported in the literature has been completed for the discussion. 相似文献