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排序方式: 共有894条查询结果,搜索用时 15 毫秒
801.
Silvia D'Auria Amir Masoud Pourrahimi Alessia Favero Peter Neuteboom Xiangdong Xu Shuichi Haraguchi Marko Bek Roland Kádár Enrico Dalcanale Roberta Pinalli Christian Müller Jérôme Vachon 《Advanced functional materials》2023,33(36):2301878
Polyethylene based ionomers are demonstrated to feature a thermo-mechanical and dielectric property portfolio that is comparable to cross-linked polyethylene (XLPE), which may enable the design of more sustainable high voltage direct-current (HVDC) power cables, a crucial component of future electricity grids that seamlessly integrate renewable sources of energy. A new type of ionomer is obtained via high-pressure/high-temperature free radical copolymerization of ethylene in the presence of small amounts of ion-pair comonomers comprising amine terminated methacrylates and methacrylic acid. The synthesized ionomers feature a crystallinity, melting temperature, rubber plateau modulus and thermal conductivity like XLPE but remain melt-processable. Moreover, the preparation of the ionomers is free of byproducts, which readily yields a highly insulating material with a low dielectric loss tangent and a low direct-current (DC) electrical conductivity of 1 to 6·10−14 S m−1 at 70 °C and an electric field of 30 kV mm−1. Evidently, the investigated ionomers represent a promising alternative to XLPE-based high voltage insulation, which may permit to ease the production as well as end-of-use recycling of HVDC power cables by combining the advantages of thermoset and thermoplastic materials while avoiding the formation of byproducts. 相似文献
802.
We have investigated the catalytic behavior of Pt encapsulated TiO2 nanotubes for the water gas shift reaction as well as the hydrogenation of CO. Pt–TiO2 nanotube catalysts were prepared by employing fine fiber shaped crystals of [Pt(NH3)4](HCO3)2 complex as a structure determining template material. The turnover frequencies (TOF) of these nanotube catalysts were more than one order of magnitude larger than conventional impregnation Pt/TiO2 catalysts, and the selectivity for methanol in CO–H2 reaction was extraordinary high compared to the impregnation catalysts. The XPS and XRD analyses of the nanotubes revealed characteristic electronic state of reduced TiO2 (Ti3+ in rutile structure) with zerovalent Pt even after the calcination at 773 K. In WGS reaction, electron rich Ti3+ on the nanotube wall may play an important role to activate water molecules for the oxidation of CO. In CO–H2 reaction, similar promotion effect of Ti3+ species may be operating for selective methanol formation by supplying active OH(a). 相似文献
803.
Mineo Mizuno Shijie Zhu Yasuo Nagano Yoshihisa Sakaida Yutaka Kagawa Makoto Watanabe 《Journal of the American Ceramic Society》1996,79(12):3065-3077
Tension-tension cyclic-fatigue tests of a two-dimensional-woven-SiC-fiber-SiC-matrix composite (SiC/SiC) prepared by chemical vapor infiltration (CVI) were conducted in air at room temperature and in argon at 1000°C. The cyclic-fatigue limit (107 cycles) at room temperature was ∼160 MPa, which was ∼80% of the monotonic tensile strength of the composite. However, the fatigue limit at 1000°C was only 75 MPa, which was 30% of the tensile strength of the composite. No difference was observed in cyclic-fatigue life at room temperature and at 1000°C at stresses >180 MPa; however, cyclic-fatigue life decreased at 1000°C at stresses < 180 MPa. The fracture mode changed from fracture in 0° and 90° bundles at high stresses to fracture mainly in 0° bundles at low stresses. Fiber-pullout length at 1000°C was longer than that at room temperature, and, in cyclic fatigue, it was longer than that in monotonic tension. The decrease in the fatigue limit at 1000°C was concluded to be possibly attributed to creep of fibers and the reduction of the sliding resistance of the interface between the matrix and the fibers. 相似文献
804.
Mark Hoffman Yiu-Wing Mai Shuichi Wakayama Masanori Kawahara Teruo Kishi 《Journal of the American Ceramic Society》1995,78(10):2801-2810
It is proposed that reduced transformation zone widths in Mg-PSZ in cyclically versus critically propagated cracks are due to reductions in the crack-tip toughness, consistent with an intrinsic cyclic fatigue mechanism. Cyclic fatigue crack growth in Mg-PSZ was observed in situ in a SEM. Following cyclic fatigue, the samples were critically broken and the fracture surfaces observed. Extensive crack bridging by the precipitate phase was observed near the crack tip, and it is proposed that this crack bridging significantly affects the material's intrinsic toughness. Frictional degradation of the precipitate bridges occurs during cyclic loading and hence reduces the critical crack-tip stress intensity factor for crack propagation. Reductions in the critical crack-tip stress intensity factor also lead to reductions in the transformation zone widths during cyclic loading and hence the level of crack-tip shielding caused by phase transformation. This appears to be the mechanism of cyclic fatigue. A degree of uncracked ligament bridging was also observed and is linked with the frequency of random large precipitates. However, analysis shows that its effect upon crack growth rates under cyclic load is limited. 相似文献
805.
Masanori Yoshida Tomoko Hiura Kazuaki Yamagiwa Akira Ohkawa Shuichi Tezura 《加拿大化工杂志》2008,86(2):160-167
The characteristics of a liquid flow were studied in the impeller region of an unbaffled agitated vessel with an angularly oscillating impeller whose unsteady rotation proceeds while periodically reversing its direction at a set angle. The measurement of the velocity of the liquid flow was performed by particle tracking velocimetry (PTV), abreast of that of the torque of the shaft to which the impeller was attached. When a disk turbine impeller with six flat blades was used with variations in operating conditions, such as the frequency and amplitude of impeller angular oscillation, a series of images obtained during one oscillation cycle were analyzed to characterize the internal and discharge streams inside and outside the impeller rotational region. Energy data were inferred on the basis of the circumferential and radial velocities of an internal flow. Results showed that although the total head provided to the liquid by the impeller blades is almost similar, independent of the amplitude of impeller angular oscillation, namely, the acceleration of its movement, the transformation of energy from the pressure head to the velocity head is more efficient at a larger amplitude. In addition, the discharge flow was characterized in terms of volumetric flow rates calculated from the radial and axial velocities. The operation at a smaller amplitude was shown to transform the flow more successfully from the radial direction to the upward and downward axial directions near the vessel wall. 相似文献
806.
Polyglycidyloxypropyl silsesquioxane, which has an excellent heat resistance, was combined with sheet‐like and spherical titanate as nano‐fillers. The burning property of the composites was related to the shape of the dispersed titanate. A burning test was carried out according to the UL‐94 test method. As a result, though the test specimen burned from one end to the other in the spherical titanate filled composite system, a fire extinguishing property was observed in the sheet‐like titanate filled composite system. The extinguishing time of the latter system classified V‐0 in the specification test. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
807.
The capacity to re-establish a normal rhythm after an excitation while adapting to external or internal stimuli is a process of great complexity. We propose an agent-based framework to model the homeostatic plasticity in neuronal activity incorporating the concept of selforganization. Our model provides the ability for neuroagents to adapt themselves in a series of activities after the excitements of synaptic inputs in a similar way to the nervous system, hence allowing the creation of diversification and a competitive environment. 相似文献
808.
Tomonori Kato Kenji Kawashima Koichi Sawamoto Toshiharu Kagawa 《Precision Engineering》2007,31(3):269-275
Pneumatic vibration isolation systems are widely used in semiconductor production processes. Most of them are controlled with nozzle-flapper type pneumatic servo valves. However, these servo valves require large exhaust air flow rates in order to control pressure precisely.In this paper, the model following control method was applied using a pressure differentiator and a spool type servo valve to actively control a pneumatic isolation table. Experiments were carried out on an air-spring system supporting a heavy granite bed, the displacement of which was modeled with a single degree of freedom.The experimental results gained in this research demonstrate the possibility of realizing a more efficient vibration isolation system than the conventional system using nozzle-flapper type servo valves. More specifically, this investigation showed about a 90% decrease in the steady-state exhaust air flow rate. 相似文献
809.
This study consists of following two sections: (i) interface microstructure observation and (ii) interface degradationevaluation during fatigue. The microstructure of the interfacial reaction layer in SiC(SCS-6) fiberreinforced Ti-15-3 alloy matrix composite has been studied using transmission electron microscopy. 相似文献
810.