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排序方式: 共有632条查询结果,搜索用时 12 毫秒
131.
F. Cavani E. Etienne M. Favaro A. Galli F. Trifirò G. Hecquet 《Catalysis Letters》1995,32(1-2):215-226
The oxidation of isobutane to methacrolein and methacrylic acid was carried out over potassium/ammonium salts of 12-molybdophosphoric acid (Keggin-type heteropoly compounds), with overall selectivity to the desired products higher than 50%. The addition of iron to the catalyst composition led to a substantial enhancement of the catalytic activity, with an increase in the yield to the desired products, even though the selectivity decreased. The catalysts all have a secondary cubic structure, and are stable in the reaction environment. No trace of structural decomposition was found in spent catalysts. It was found that the addition of iron led to a substantial increase in the catalyst acidity and it is proposed that the Lewis acidity might play a role in the activation of the paraffin. 相似文献
132.
Tom Mélange Mike NachtegaelStefan Schulte Etienne E. Kerre 《Image and vision computing》2011,29(6):407-419
In this paper a new fuzzy filter for the removal of random impulse noise in digital grayscale image sequences is presented. The filter consists of different noise detection and filtering steps, in which the fuzzy set theory is used. This noise detection is based both on spatial and on temporal information and has the aim to prevent the filtering of noise free image pixels. The filtering of the detected noisy pixels is finally performed in a motion compensated way. Experimental results show that our method outperforms other state-of-the-art filters in terms of the peak-signal-to-noise ratio as well as visual quality. 相似文献
133.
Barnard E 《Neural computation》2011,23(7):1899-1909
We discuss the no-free-lunch NFL theorem for supervised learning as a logical paradox--that is, as a counterintuitive result that is correctly proven from apparently incontestable assumptions. We show that the uniform prior that is used in the proof of the theorem has a number of unpalatable consequences besides the NFL theorem, and propose a simple definition of determination (by a learning set of given size) that casts additional suspicion on the utility of this assumption for the prior. Whereas others have suggested that the assumptions of the NFL theorem are not practically realistic, we show these assumptions to be at odds with supervised learning in principle. This analysis suggests a route toward the establishment of a more realistic prior probability for use in the extended Bayesian framework. 相似文献
134.
Sandrine Ventre Etienne Derat Muriel Amatore Corinne Aubert Marc Petit 《Advanced Synthesis \u0026amp; Catalysis》2013,355(13):2584-2590
A simple hydrido‐cobalt complex efficiently catalyses the highly regio‐ and stereoselective dimerisation of various terminal arylacetylenes under mild conditions. The corresponding (E)‐1,4‐enynes are obtained as sole isomers with good to excellent yields. DFT calculations revealed that the reaction proceeds via a C H activation/hydrocobaltation pathway.
135.
Etienne Savary Sylvain MarinelFranck Gascoin Yoshiaki KinemuchiJulien Pansiot Richard Retoux 《Journal of Alloys and Compounds》2011,509(21):6163-6169
Non-ohmic properties of doped zinc oxide are widely used in varistors applications. It is well established that final properties of the component are strongly correlated with reactivity of the added phases during sintering process and with final microstructure. In this paper, the specific effects of the hybrid single-mode microwave sintering process on the microstructure and electrical properties of a ZnO-based composition are investigated. Nano-sized ZnO-based powder with a proper amount of Bi2O3, Sb2O3, CoO and MnO is synthesized by a liquid route and is sintered within a short time (less than 10 min) in a conventional (CV) or by an hybrid single-mode microwave (MW) furnaces. Distinct differences can be seen in the density, reaction kinetics and dopant diffusivity: higher kinetics of MW leads to denser pellet, faster reaction among dopants and faster diffusion of cobalt and manganese into ZnO grains although grain sizes are almost identical between CV and MW. These differences in terms of chemistry and microstructure lead to sharp contrasts in electrical properties. 相似文献
136.
Alexandre Badev Sylvain Marinel Romain Heuguet Etienne Savary Dinesh Agrawal 《Acta Materialia》2013,61(20):7849-7858
A study of the densification behavior and grain growth mechanisms of ZnO-based varistors composed of 98 mol.% ZnO–2 mol.% (Bi2O3, Sb2O3, Co3O4, MnO2) has been carried out. The pressed samples were sintered in microwave electric (E) and magnetic (H) fields using a single-mode cavity of 2.45 GHz. The effect of the sintering temperature (900–1200 °C), holding time (5–120 min) and sintering mode (E, H) on the microstructure and electrical properties of the sintered varistor samples were investigated. The grain growth kinetics was studied using the simplified phenomenological equation Gn = kte(?Q/RT). The grain growth exponent (n) and apparent activation energy (Q) values were estimated for both electric and magnetic heating modes and were found to be n = 3.06–3.27, Q = 206–214 kJ mol?1, respectively. The lower value of n estimated in the E field was attributed to a volume diffusion mechanism, whereas the higher n value in the H field sintering was correlated mainly to a combined effect of volume and surface diffusion processes. Samples sintered in the H and E fields showed high final densities. Moreover, the ones sintered in the H field presented slightly higher density values and bigger grains for all sintering temperatures than E field heated ones. The optimal sintering conditions were achieved at 1100 °C for a 5 min soaking time for both H and E field processed samples, where respectively densities of 99.2 ± 0.5% theoretical density (TD) and 98.3 ± 0.5% TD along with grain size values of G = 7.2 ± 0.36 μm and G = 6.6 ± 0.33 μm were obtained. Regarding the electrical properties, breakdown voltage values as high as 500–570 V mm?1 were obtained, together with high non-linear coefficients α = 29–39 and low leakage currents (Jl ≈ 5 × 10?3 mA cm?2), respectively, for E and H field sintered varistor samples. Moreover, samples sintered in an H field systematically exhibited higher breakdown voltage values compared to the ones sintered in the E field. This was attributed to an improved coupling between the H field and the present dopants within the ZnO matrix, this latter being mostly semiconductive, thus leading to an enhanced reactivity and improved properties of the electrostatic barrier. 相似文献
137.
138.
Etienne George Don Elthon James K. Meen 《Journal of the American Ceramic Society》1995,78(12):3309-3315
Phase equilibria in the CuO-rich (≥33% CuO) portion of the SrO–CaO–CuO system have been determined at 950°C in 1 atm of pure oxygen and at 10 kbar (1 bar = 105 Pa). Three solid-solution series occur under these conditions. There is a complete solid solution between the Ca2 CuO3 and Sr2 CuO3 endmembers at both 1 atm and 10 kbar, as has been previously noted in experiments conducted in air. Another solid-solution series extends continuously between SrCuO2 and (Sr0.38 Ca0.62 )CuO2 in 1 atm of oxygen, but is limited to between SrCuO2 and (Sr0.64 Ca0.36 )CuO2 at 10 kbar. At 10 kbar, more Ca-rich phases in this solid-solution series are not stable, but (Sr0.3 Ca0.7 )CuO2 and (Sr0.1–0.16 Ca0.9–0.84 )CuO2 are stable at 1 atm. The third solid-solution series ranges between Srl4 Cu24 O38 and (Sr0.41 CaO.59 )14 -Cu24 O38 in 1 atm of oxygen; the Ca-rich limit of this solid solution changes only slightly to (Sr0.39 Ca0.61 )14 Cu24 O38 at 10 kbar. 相似文献
139.
The moist agglomeration process by high-shear mixing/granulation, i.e. the wet massing, screening and subsequent drying is a wide spread but critical unit operation. Since for decades formulators are looking for the correct “end-point” of this important process, i.e. when do you need to stop massing or stop with the addition of granulating liquid? What is the correct amount of granulating liquid? A similar situation exists in case of the moist agglomeration in fluidized bed equipment. In the latter case the simultaneous drying of the still moist granules have to be taken into account. Recently a science-based virtual equipment simulator could be developed mimicking the granule size evolution in a fluidized bed granulator during the addition of granulating liquid. For the simultaneous drying the Mollier chart is used. With this virtual equipment simulator it is possible to simulate “crash situations”, i.e. by overwetting or by an incorrect use of the parameter setting. However the determination of the “end-point” depends only on the operator, who desires a certain granule size distribution and a well-defined final moisture content of the batch. Thus the existence of a process intrinsic “end-point” has to be questioned. The same situation can be reported in case of high-shear mixing/granulation based on many years of research. In fact nobody could clearly show the existence of an intrinsic “end-point”. However during the continuous addition of a granulating low viscous liquid a sudden increase in power consumption can be measured, which levels off. Such a measurement depends on the formulation and leads to an “early signal” not to the “end-point”. This signal can be used for a tight control of the granulation process and leads to a low batch to batch variability in the final granule size distribution. The latter is the goal of the PAT (Process Analytical Technology) Initiative emphasizing “Quality by Design”. 相似文献
140.
Fabrice Patisson Etienne Lebas François Hanrot Denis Ablitzer Jean-Leon Houzelot 《Metallurgical and Materials Transactions B》2000,31(2):381-390
A mathematical model is presented which describes the pyrolysis of a single grain of coal and is designed to be incorporated
into an overall model simulating the rotary kiln coal pyrolysis process. The grain model takes into account the principal
physical phenomena occurring during the conversion of coal to coke, namely, heat transfer toward and within the grain, drying
of the coal, and the evolution of volatile species. Particular care has been taken in the determination of the thermophysical
and kinetic parameters necessary for the model. Thus, the drying kinetics for Lorraine coal were measured by thermogravimetry.
The kinetics of pyrolysis were determined by both thermogravimetry and gasphase chromatography, in order to separately monitor
the evolution of the nine gaseous species considered. The true specific heat and the thermal conductivity of the solid were
also measured as a function of temperature. The numerical model, based on the finite-volume method, calculates the temperature,
composition, and mass flow rates for the different gases evolved at each point in the grain at any instant of time. The model
was, finally, validated by comparing the calculated and measured values of the overall conversion of the pyrolysis reaction
and the temperature at the center of the grain. 相似文献