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We report the production of carbon nanotubes by high dose of electron irradiation. The irradiation was performed with a 2 MeV Van de Graaff accelerator, while the irradiation conditions were the following: voltage 1.3 MeV, current 5 µA, dose rate 25 kGy/min, and total dosage 1000 kGy. The samples were analyzed in a high-resolution transmission electron microscope. The main features observed on the samples, were huge nanotubes of several nanometer long and few nanometer wide, which are capped at one end. It is good to point out, that at this level of irradiation, we were not able to find either onion-like or particle structures throughout the material, as it is usual in similar hexagonal structures. This behavior could be attributed to the level of irradiation used to create the nanotubes under investigation. 相似文献
4.
I. Litvinchev S. Rangel M. Mata J. Saucedo 《Journal of Computer and Systems Sciences International》2009,48(3):363-369
Classical and modified Lagrangian bounds for the optimal value of optimization problems with a double decomposable structure are studied. For the class of many-to-many assignment problems, this property of constraints is used to design a subgradient algorithm for solving the modified dual problem. Numerical results are presented to compare the quality of classical and modified bounds, as well as the properties of the corresponding Lagrangian solutions. 相似文献
5.
Thomaz Cabral Rangel Cláudio César Weber Backes Alexandre Fassini Michels Daniel Eduardo Weibel 《Advanced Engineering Materials》2023,25(12):2201592
The field of superamphiphobic surface fabrication has evolved rapidly in the last decade; however, research on important issues such as sustainability and green chemistry procedures is still scarce. Herein, a simple method of microwave irradiation (MW) to minimize energy consumption during the preparation of superamphiphobic aluminum (Al) surfaces is reported. Al substrates are first etched in diluted HCl solutions to generate a microstructure and then irradiated in a commercial microwave unit for several time intervals, temperatures, and pressures. The surfaces are then coated with different compounds, and the wettability is tested with high and very-low surface tension liquids. Optical profilometry and scanning electron microscopy images show that the density of hierarchical micro-nanostructures increases with MW time, temperature, and pressure. At 170 °C and 7.9 bar, the surfaces present a high density of structures and re-entrant topographies. The obtained coatings display excellent repellence to liquids with surface tensions as low as 27.5 mN m−1. X-ray photoelectron spectroscopy data show the importance of efficient surface functionalization for the production of superamphiphobicity in Al substrates. The results show that MW irradiation of Al substrates can be a green and efficient method for fabricating superamphiphobic surfaces. 相似文献
6.
L. O. Tavares W. S. Vianna G. S. Bobrovnitchii A. L. D. Skury J. J. A. Rangel 《Journal of Superhard Materials》2012,34(4):225-233
A new system to control a 630-ton and a 2500-ton presses has been developed. By using this system it has been made possible to define new parameters related to pressure and temperature and the influence of certain factors on them. Furthermore, the new system has been shown to indicate that other parameters, such as height of the gasket formed (h c ), electrical resistance of the reaction cell, and the frequency of activation of the pump or multiplier, can serve as important indicators of the improvement of superhard material production technologies, implementing the Computational Intelligence (CI). 相似文献
7.
Fátima C. Teixeira Ana I. de Sá António P.S. Teixeira V.M. Ortiz-Martínez A. Ortiz I. Ortiz C.M. Rangel 《International Journal of Hydrogen Energy》2021,46(33):17562-17571
Proton exchange membranes remain a crucial material and a key challenge to fuel cell science and technology. In this work, new Nafion membranes are prepared by a casting method using aryl- or azaheteroaromatic bisphosphonate compounds as dopants. The incorporation of the dopant, considered at 1 wt% loading after previous selection, produces enhanced proton conductivity properties in the new membranes, at different temperature and relative humidity conditions, in comparison with values obtained with commercial Nafion. Water uptake and ionic exchange capacity (IEC) are also assessed due to their associated impact on transport properties, resulting in superior values than Nafion when tested in the same experimental conditions. These improvements by doped membranes prompted the evaluation of their potential application in fuel cells, at different temperatures. The new membranes, in membrane-electrode assemblies (MEAs), show an increased fuel cell maximum power output with temperature until 60 °C or 70 °C, followed by a decrease above these temperatures, a Nafion-like behaviour when measured in the same conditions. The membrane doped with [1,4-phenylenebis(hydroxymethanetriyl)]tetrakis(phosphonic acid) (BP2) presents better results than Nafion N-115 membrane at all studied temperatures, with a maximum power output performance of ~383 mW cm?2 at 70 °C. Open circuit potentials of the fuel cell were always higher than values obtained for Nafion MEAs in all studied conditions, indicating the possibility of advantageous restrain to gas crossover in the new doped membranes. 相似文献
8.
A two-dimensional, non-isothermal and dynamic model was developed to describe a sodium borohydride/hydrogen reactor for stationary use. All relevant transport phenomena were treated in detail and the kinetic model developed previously by the authors was introduced into the algorithm. In this paper the reactive solution was modelled as a two phase flow; with this approach the impact of the hydrogen production on the solution stirring could be observed and quantified. 相似文献
9.
C. O. Soares M. D. Carvalho M. E. Melo Jorge A. Gomes R. A. Silva C. M. Rangel M. I. da Silva Pereira 《Journal of Applied Electrochemistry》2012,42(5):325-332
LaNiO3 coatings on nickel-foam supports were prepared by brush painting. The electrochemical properties were investigated by cyclic
voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Comparative studies were performed with LaNiO3-pelleted electrodes. The roughness factors were determined by CV and found to be 5,208 ± 350 and 4,037 ± 250 for the pelleted
and coated electrodes, respectively. EIS measurements confirm the results obtained by CV. Values lower than 0.3 were calculated
for the morphology factors for both electrodes, indicating low electrochemical porosity. The experimental method used in this
work to synthesise the oxide coupled with the use of Ni foam as support has proved to be very effective in producing oxide
electrodes with surface areas higher than those referred to in relevant literature. 相似文献
10.
Synthesis of Bi2S3 nanorods supported on ZrO2 semiconductor as an efficient photocatalyst for hydrogen production under UV and visible light 下载免费PDF全文