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61.
Jean-Pierre Croisille Rabia Khanfir Gérard Chanteur 《Journal of scientific computing》1995,10(1):81-92
We introduce a flux-splitting formula for the approximation of the ideal MHD equations in conservative form. The Faraday equation is considered as the average of an abstract kinetic equation, giving a flux-splitting formula. For the other part of the equations, we generalize formally the classical half-Maxwellian flux-splitting of the Euler equations. Numerical results on MHD shock tube problems are displayed. 相似文献
62.
Jean-Pierre Coudreuse 《电信纪事》1995,50(1):98-113
Fifteen years after its first tentative steps in the laboratory, ATM seems to have reached the thankless age of confrontation with the reality of operational networks while others would say the age of potential to fulfil and promises to keep. The following article does not pretend to be an in-depth technical analysis of a particular aspect or development of ATM but rather the thoughts of a witness to a number of past, present and future issues. The objective is much more to stimulate thought on ATM than to provide definitive answers to often difficult questions. 相似文献
63.
Bruno Bazin Josiane Cillard Jean-Pierre Koskas Pierre Cillard 《Journal of the American Oil Chemists' Society》1984,61(7):1212-1215
The autoxidation of arachidonic acid dispersed in aqueous media was evaluated simultaneously with and without different agents,
e.g., α-tocopherol at different concentrations, cysteine, DNA and RNA. The autoxidation rate of arachidonic acid was evaluated
by quantitative gas liquid chromatography (GLC) determination of the unoxidized acid and by spectrophotometric measurement
of conjugated dienes. α-Tocopherol exhibited a prooxidant activity at concentrations of 1.25 × 10−4 M and 1.25 × 10−5 M and a weak antioxidant activity at a concentration of 1.25 × 10−6 M. Cysteine showed antioxidant activity and greatly reduced the prooxidant activity of α-tocopherol. DNA and RNA had no effect
in either case. α-Tocopherol oxidation was followed by high pressure liquid chromatography (HPLC). The prooxidant effect was
accompanied by a rapid oxidation of α-tocopherol, except in the presence of cysteine, which prevented the oxidation of α-tocopherol. 相似文献
64.
Jean-Pierre Coudreuse 《International Journal of Communication Systems》1988,1(4):213-221
The definition of broadband ISDN recently became a major topic of research and predevelopments. Fast packet technologies are widely recognized as the basis for BISDN. Even if international consensus has appeared far more quickly than could have been expected a few years ago, a lot of issues remain open. This paper is a contribution to discussions on some important topics relating to the definition of asynchronous transfer mode. 相似文献
65.
Jean-Pierre Guiraud Radyadour Kh. Zeytounian 《International Journal of Engineering Science》1974,12(4):311-330
An asymptotic theory to the flow in an axial compressor is presented with the aim of devising a coupling process between the so-called meridian through flow and the flow around cascades. The small parameter ? is the inverse of the (supposed ? 1) number of blades per row and/or number of stages. As a matter of fact, the cascade flow is treated as a small perturbation of the through flow and has to be computed, locally, as the two dimensional unsteady flow around an array of couples of cascades alternately fixed and in motion. The array is constructed by developing on a plane the section of the compressor by a circular cylinder, and continuing by periodicity, the couple of cascades, so obtained, at each location. The coupling between through flow and cascade flow is part of the analysis. It occurs by the way that the equations of through flow are obtained through an averaging process, completed on a domain of periodicity of the array of cascades, while the through flow appears, locally, as an unperturbed flow for the linearized problem defining the cascade flow. The tridimensional nature of the complete flow is built in by the coupling itself, as is visualized by the occurence of source terms in each of the two sets of equations describing through flow and cascade flow. This paper is aimed at giving a preliminary answer to the question of how to devise an, as rational as possible, way of inscribing the familiar scheme of cascade flow within the computation of a mean through flow. The main output is that the concept of cascade flow should be revisited and reassessed as one of unsteady flow around an array of cascades. 相似文献
66.
67.
Jean-Pierre Candy Pierre Fouilloux Michel Keddam Hisasi Takenouti 《Electrochimica acta》1981,26(8):1029-1034
Impedances of a gold-powder and a Raney-gold electrode were measured over a wide frequency range, and were found to be very similar to those of cylindrical pore of finite depth. The simulation calculation for sphere-packed electrode impedance was performed. It was observed that even though each sphere-layer shows the impedance related to an occluded pore-shape, the overall impedance is similar to that of a cylindrical pore electrode. When the penetration depth approaches the pore depth, the shape of the pore wall has little influence on the impedance. Thus, impedance measurement techniques can be applied to porous electrodes of more intricate pore-texture, and evaluate the radius, depth and pore number of its equivalent cylindrical pore electrode. These values determined for a Raney-gold electrode are in very good agreement with those determined by other methods. The case of a more realistic fuel cell electrode such as Raney-nickel with a metal-electrolyte-gas system, was also tentatively examined. 相似文献
68.
Genet JP 《Accounts of chemical research》2003,36(12):908-918
This Account covers the design of Ru catalysts and ligands. Two classes of chiral phosphine ligands are prepared: the electron-rich trans-2,4-substituted phosphetanes, readily available from optically pure 1,3-diol cyclic sulfates, and atropoisomeric ligands (SYNPHOS, MeO-NAPhePHOS, bearing heterotopic biaryl moieties, and a chiral water-soluble diguanidinium binaphthyl diphosphine, Digm-BINAP). Applications of these ligands to rhodium- and ruthenium-mediated hydrogenation of ketones and olefins have been reported with high enantioselectivities. The recognition abilities of Ru-SYNPHOS for a wide range of ketones is superior to those observed with BINAP, MeO-NAPhePHOS, and MeO-BIPHEP. Several biologically active compounds have been prepared through dynamic kinetic resolution. This work gives access to a number of highly active catalysts of the type [Ru(biphosphane)(H)(eta(6)-cot)]BF(4). These catalysts have demonstrated their utility in the enantioselective hydrogenation of the tetrasubstituted cyclopentenone "dehydrodione", which leads to the commercially important perfume component Paradisone (Firmenich). 相似文献
69.
Computer-aided method for quantification of cartilage thickness and volume changes using MRI: validation study using a synthetic model 总被引:3,自引:0,他引:3
Kauffmann C Gravel P Godbout B Gravel A Beaudoin G Raynauld JP Martel-Pelletier J Pelletier JP de Guise JA 《IEEE transactions on bio-medical engineering》2003,50(8):978-988
The primary objective of this study was to develop a computer-aided method for the quantification of three-dimensional (3-D) cartilage changes over time in knees with osteoarthritis (OA). We introduced a local coordinate system (LCS) for the femoral and tibial cartilage boundaries that provides a standardized representation of cartilage geometry, thickness, and volume. The LCS can be registered in different data sets from the same patient so that results can be directly compared. Cartilage boundaries are segmented from 3-D magnetic resonance (MR) slices with a semi-automated method and transformed into offset-maps, defined by the LCS. Volumes and thickness are computed from these offset-maps. Further anatomical labeling allows focal volumes to be evaluated in predefined subregions. The accuracy of the automated behavior of the method was assessed, without any human intervention, using realistic, synthetic 3-D MR images of a human knee. The error in thickness evaluation is lower than 0.12 mm for the tibia and femur. Cartilage volumes in anatomical subregions show a coefficient of variation ranging from 0.11% to 0.32%. This method improves noninvasive 3-D analysis of cartilage thickness and volume and is well suited for in vivo follow-up clinical studies of OA knees. 相似文献
70.
Kouamé D Girault JM Remenieras JP Chemla JP Lethiecq M 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2003,50(3):267-278
For pt.I see ibid., vol.50, no.3, p.267-78 (2003). This paper presents an application of continuous wave ultrasound Doppler velocity measurements to two-phase flow in pipes. In many petroleum wells, the multiphase flow is separated into two phases: the first is a liquid phase and the second is a gas phase with small scatterers. The problem of multiphase velocity profile measurements has not been satisfactorily solved by classical approaches due to the multiphase nature of the fluid and the presence of colored noise, which introduces a significant bias in classical frequency estimators. We propose the use of resolution frequency techniques to overcome the classical limitations. Direct estimation of Doppler frequency then obtained using either time frequency maximum frequency or arguments of poles of the parametric model that identifies the Doppler part of the signal is discussed. The tests made with synthetic Doppler signals and two-phase flow have demonstrated the excellent performance of the high resolution techniques based on reassignment and parametric techniques. 相似文献