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71.
The rate of reaction of the compacted powders of CuO-η-Al2O3 and ZnO-η-Al2O3 systems was measured in air at 800 to 900° C and the effect of the mixing procedure (dry and wet mixing) and compaction pressure
(0 to 8.3×108 Pa) of reactant oxides on the fraction of reaction completed (α) was investigated. In the reaction of the CuO-η-Al2O3 system, the α-values obtained for the sample prepared by wet mixing in ethanol were higher than those for the sample prepared
by dry mixing in air and were not influenced by the compaction pressure, whereas in the case of dry mixing they varied with
the compaction pressure and had a maximum value at 2.1×108 Pa. On the other hand, in the reaction of the ZnO-η-Al2O3 system the α-values for the sample obtained by wet mixing were lower than the values obtained by dry mixing, in contrast
to the results in CuO-η-Al2O3 system, and the α-values for the samples prepared by both dry and wet mixing were not influenced by the compaction pressure.
The effect of mixing procedure and compaction pressure of reactant powders on the α-values was found to be explained on the
basis of the aggregate size of CuO and ZnO dispersed in the matrix of η-Al2O3 fine powder. 相似文献
72.
Takayuki Mizuno Kazutoshi Nagayama Tadashi Ashikaga Tadao Kobayashi 《Electrical Engineering in Japan》1996,117(5):110-123
Permanent magnet type synchronous machines have been widely used for industrial applications. It is commonly known that they are operated at high efficiency since no excitation input is required. However, it is difficult to control the air-gap magnetic flux, because the magnetic flux is determined by the property of the permanent magnet and approximately kept constant. On the other hand, synchronous machines with the field winding make it easy to control the air-gap magnetic flux. But the copper loss of the field winding becomes large at the rated load. In order to realize the magnetic flux control easily and improve the performance of the conventional synchronous machine, we propose a hybrid excitation type synchronous machine (HSY) with the permanent magnets and the field winding. Advantages of HSY are (1) it has no brushes (maintenance free), (2) required excitation input is small (high efficiency), (3) it is easy to get a sufficient magnetic flux control, and others. Therefore, HSY has a great possibility of use for various applications. In this paper, basic principles and characteristics of HSY are mainly discussed and made clear. 相似文献
73.
Juro Watanabe Tadao Iwadate Yasuhiko Tanaka Takeo Yokobori Kotoji Ando 《Engineering Fracture Mechanics》1987,28(5-6):589-600
In order to study the origin of the scatter in the fracture toughness in the transition region and to specify the lower bound of the scatter, approximately 100 pieces 0.5T-CT NiCrMoV steel specimens were tested in the transition region, and their fracture surfaces were investigated. Major portion of the scatter was caused by the scatter in the length of preceding dimple crack which was generated at the fatigue precrack before conversion to final cleavage fracture. A method to predict the lower bound of the scatter in the small-specimen fracture toughness was proposed. It employs Weibull plot of new parameter J1 which represents the scatter in the cleavage strength of material. The cleavage fracture origin may be associated with micro-stress-concentration in the microstructure which may not be caused by the micromechanism in terms of grain size unit. 相似文献
74.
Minoru Ito Motoaki Iwasaki Kenichi Taniguchi Tadao Kasami 《Theoretical computer science》1984,34(3):315-335
In relational databases, a query can be formulated in terms of a relational algebra expression using projection, selection, restriction, cross product and union. In this paper, we consider a problem, called the membership problem, of determining whether a given dependency d is valid in a given relational expression E over a given database scheme R that is, whether every instance of the view scheme defined by E satisfies d (assuming that the underlying constraints in R are always satisfied).Consider the case where each relation scheme in R is associated with functional dependencies (FDs) as constraints, and d is an FD. Then the complement of the membership problem is NP-complete. However, if E contains no union, then the membership problem can be solved in polynomial time. Furthermore, if E contains neither a union nor a projection, then we can construct in polynomial time a cover for valid FDs in E, that is, a set of FDs which implies every valid FD in E.Consider the case where each relation scheme in R is associated with multivalued dependencies (MVDs) as well as FDs, and d is an FD or an MVD. Even if E consists of selections and cross products only, the membership problem is NP-hard. However, if E contains no union, and each relation scheme name in R occurs in E at most once, then the membership problem can be solved in polynomial time. As a corollary of this result, it can be determined in polynomial time whether a given FD or MVD is valid in , where R1,…,Rs are relation schemes with FDs and MVDs, and is the natural join of Ri and Rj. 相似文献
75.
1Mbit D-RAM. the most advanced VLSI device, is realized by a high performance stepper with the conventional optical techniques. However, as the optical lithography has an inherent limit of resolution, new technologies are being developed rapidly for the development of new generation VLSI devices (4M-16Mbit D-RAM) using shorter wavelength photons of i-line. Electron beam (EB) lithography is already in practical mask making products, but the resolution limit is about 0.5 μm because of proximity effects. In order to make higher resolution and higher precision masks, high voltage EB technique is being developed to minimize the proximity effect, and fabricated 0.25 μm line and space by a single scan at 50kV. X-ray technology 1; becoming practical after a long laboratory-level study, using high performance X-ray resists (CPMS: chlorinated polymetylstylene). Focused Ion Beam (FIB) technology has been anticipated for its capability of submicron lithography due to a reduced proximity effect. High speed submicron Si MOSFET and GaAs MESFET with 0.25 μm gate have been fabricated using FIB technology. Activities of submicron lithography technology in Japan (optical stepper, EB, X-ray, and FIB) are described. 相似文献
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77.
这项工程的初衷是修复基地上的一座17世纪的帕拉蒂奥式的别墅。使其重获新生。这个研究中心将接待来自世界各地的年轻学生,展示建筑设计、摄影艺术、绘画艺术、图像媒介和纺织品等实用艺术的成就。 相似文献
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