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41.
Carlos R. Vera Carlos L. Pieck Kiyoyuki Shimizu Jos M. Parera 《Applied Catalysis A: General》2002,230(1-2):137-151
An assessment of the influence of the crystal structure, surface hydroxylation state and previous oxidation/reduction pretreatments on the activity of sulfate-zirconia catalysts for isomerization of n-butane was performed using crystalline and amorphous zirconia supports. Different sulfation methods were used for the preparation of bulk and supported SO42−-ZrO2 with monoclinic, tetragonal and tetragonal+monoclinic structures. Activity was important only for the samples that contained tetragonal crystals. The catalysts prepared from pure monoclinic zirconia showed negligible activity. SO42−-ZrO2 catalysts prepared by sulfation of crystalline zirconia displayed sites with lower acidity and cracking activity than those sulfated in the amorphous state. Prereduction of the zirconia samples with H2 was found to greatly increase the catalytic activity, and a maximum rate was found at a reduction temperature of 550–600 °C, coinciding with a TPR peak supposedly associated with the removal of lattice oxygen and the creation of lattice defects. A weaker dependence of catalytic activity on the density or type of surface OH groups on zirconia (before sulfation) was found in this work.
A model of active site generation was constructed in order to stress the dependence on the crystal structure and crystal defects. Current and previous results suggest that tetragonal structure in active SO42−-ZrO2 is a consequence of the stabilization of anionic vacancies in zirconia. Anionic vacancies are in turn supposed to be related to the catalytic activity for n-butane isomerization through the stabilization of electrons from ionized intermediates. 相似文献
42.
Tetsuya Tanigami Nobuyuki Maruyama Koji Yamazaki Yoko Ichikawa Hiroyuki Nagai Kaori Shimizu 《应用聚合物科学杂志》2002,86(7):1807-1815
An almost fully saponified atactic poly(vinyl alcohol) and an atactic poly(vinyl alcohol‐block‐vinyl acetate) of which degree of saponification is 89 mol % were blended by a solution casting method. The phase structure of the blend film was analyzed by optical microscopy, 13C‐NMR, and differential scanning calorimetry. The most remarkable structure of the blend was composed of cylindrical domains penetrating the film. The swelling behavior of the blend films was also investigated in the dimethylsulfoxide and water mixed solvents to find differences in solubility and diffusion behavior between the matrix and the domain. The cylindrical domains could be selectively dissolved away in water and the film became porous. We tried to change the size of the cylindrical domain with various film preparation conditions. This aimed to turn the film into the useful filter membrane. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1807–1815, 2002 相似文献
43.
Amorphous anodic titania, stabilised by incorporation of silicon species, is shown to grow to high voltages on sputter-deposited, single-phase Ti-Si alloys during anodizing at a constant current density in ammonium pentaborate electrolyte. The films comprise two main layers, with silicon species confined to the inner layers. An amorphous-to-crystalline transition occurs at ∼60 V on the Ti-6 at.% Si alloy, while the transition is suppressed to voltages above 140 V on alloys with 12 and 26 at.% silicon. The crystalline oxide, nucleated at a depth of ∼40% of the film thickness, is associated with the presence of a precursor of crystalline oxide in the pre-existing air-formed oxide. The modified structure of the air-formed oxide due to increased incorporation of silicon species suppresses the amorphous-to-crystalline transition until the onset of dielectric breakdown. The transport numbers of cations and anions during growth of the anodic oxides are independent of the concentration of silicon species in the inner layer, despite the marked change in the field strength. 相似文献
44.
45.
Takashi Hayakawa Hideo Orita Masao Shimizu Katsuomi Takehira Arnfinn G. Andersen Kiyoshi Nomura Yusuke Ujihira 《Catalysis Letters》1992,16(4):359-371
The catalytic activity of LaCoO3–-based mixed oxides for the oxidative coupling of methane has been tested by TPR and cyclic reaction. Characterization has been done by XRD, TGA and Mössbauer spectrometry. It is likely that the perovskite-crystal structure containing hypervalent metal ions has an important role and that unique structural oxygen species in the perovskite contribute to the partial oxidation of methane. 相似文献
46.
Sakayu Shimizu Kengo Akimoto Yoshifumi Shinmen Hiroshi Kawashima Michihiro Sugano Hideaki Yamada 《Lipids》1991,26(7):512-516
Incubation with sesame oil increases the mycelial dihomo-γ-linolenic acid content of an arachidonic acid-producing fungus,Mortierella alpina, but decreases its arachidonic acid content [Shimizu, S., K. Akimoto, H. Kawashima, Y. Shinmen and H. Yamada (1989)J. Am. Oil Chem. Soc. 66, 237–241]. The factor causing these effects was isolated and identified to be (+)-sesamin. The results obtained in experiments
with both a cell-free extract of the fungus and with rat liver microsomes demonstrated that (+)-sesamin specifically inhibits
Δ5 desaturase at low concentrations, but does not inhibit Δ6, Δ9 and Δ12 desaturases. Kinetic analysis showed that (+)-sesamin
is a noncompetitive inhibitor (Ki for rat liver Δ5 desaturase, 155 μM). (+)-Sesamolin, (+)-sesaminol and (+)-episesamin, also inhibited only Δ5 desaturases
of the fungus and liver. These results demonstrate that (+)-sesamin and related lignan compounds present in sesame seeds or
its oil are specific inhibitors of Δ5 desaturase in polyunsaturated fatty acid biosynthesis in both microorganisms and animals.
On leave from Suntory Ltd. 相似文献
47.
Akio Takemura Yoshinori Shimizu Bunichiro Tomita Hiroshi Mizumachi 《The Journal of Adhesion》1992,37(1):161-172
Dynamic mechanical properties and adhesive strengths of power feed copolymer and random copolymer synthesized using styrene or methyl methacrylate and n-butyl acrylate were investigated. Although the two systems were synthesized from the same raw materials, power feed copolymer had a very broad transition compared with random copolymer. This fact was explained by the fact that the system synthesized through power feed method was an alloy of copolymers which are a continuous series from monomer A rich copolymers to monomer B rich copolymers. The dynamic mechanical behavior of film cast from solution was almost the same as that of emulsion film, which indicated more extensive application of power feed copolymer. In the P(nBA/St) system, power feed copolymer maintained its adhesive strengths over a wide temperature range compared with random copolymer. The absolute value, however, was not so high. This was due to the low cohesive strengths of the films. 相似文献
48.
Efficient usage of highly dispersed Pt on carbon nanotubes for electrode catalysts of polymer electrolyte fuel cells 总被引:2,自引:0,他引:2
T. Matsumoto T. Komatsu H. Nakano K. Arai Y. Nagashima E. Yoo T. Yamazaki M. Kijima H. Shimizu Y. Takasawa J. Nakamura 《Catalysis Today》2004,90(3-4):277-281
A Pt-deposited carbon nanotube (CNT) shows higher performance than a commercial Pt-deposited carbon black (CB) with reducing 60% Pt load per electrode area in polymer electrolyte fuel cells (PEFCs) below 500 mA/cm2. K2PtCl4 and H2PtCl6·6(H2O) are used for the Pt deposition onto multi-walled CNTs (MWCNTs), which are produced by the catalytic decomposition of hydrocarbons. The electric power densities produced using the Pt/CNT electrodes are greater than that of the Pt/CB by a factor of two to four on the basis of the Pt load per power. CNTs are thus found to be a good support of Pt particles for PEFC electrodes. TEM images show 2–4-nm Pt nanoparticles dispersed on the CNT surfaces. These high performances are considered to be due to the efficient formation of the triple-phase boundaries of gas–electrode–electrolyte. The mechanisms of Pt deposition are discussed for these Pt-deposited CNTs. 相似文献
49.
Shimizu Sakayu Akimoto Kengo Kawashima Hiroshi Shinmen Yoshifumi Yamada Hideaki 《Journal of the American Oil Chemists' Society》1989,66(2):237-241
The mycelial dihomo-γ-linolenic acid content of an arachidonic acid-producing fungus,Mortierella alpina 1S-4, was found to increase, with an accompanying marked decrease in its arachidonic acid content, on cultivation with sesame
oil. The resultant mycelia were found to be a rich source of dihomo-γ-linolenic acid. This unique phenomenon was suggested
to be due to specific repression of the conversion of dihomo-γ-linolenic acid to arachidonic acid by the oil. After fractionation
of the oil with acetone into oil and non-oil fractions, it was found that the effective factor(s) was present in the non-oil
fraction. In a study on optimization of the culture conditions for the production of dihomo-γ-linolenic acid byM. alpina 1S-4, a medium containing glucose, yeast extract and the non-oil fraction was found to be suitable for the production. Under
the optimal conditions in a 50-1 fermentor, the fungus produced 107 mg of dihomo-γ-linolenic acid/g dry mycelia (2.17 g/l
of culture broth). This value accounted for 23.1% of the total fatty acids in the lipids extracted from the mycelia. The mycelia
were also rich in arachidonic acid (53.5 mg/g dry mycelia, 11.2%). Other major fatty acids in the lipids were palmitic acid
(24.1%), stearic acid (7.0), oleic acid (20.1), linoleic acid (6.6) and γ-linolenic acid (4.1).
On leave from Suntory Ltd. 相似文献
50.
Three-dimensional simulation using fixed coarse-grid thermal-fluid scheme and conduction heat transfer scheme in distinct element method 总被引:1,自引:0,他引:1
Yoshiyuki Shimizu 《Powder Technology》2006,165(3):140-152
Three-dimensional simulation using particle-thermal-fluid coupling scheme with a mixed Lagrangian-Eulerian approach is presented and the scheme is described by extending author's previous research [Y. Shimizu, 2004. “Fluid Coupling in PFC2D and PFC3D”, numerical modeling in micromechanics via particle methods—2004, Proceeding of 2nd International PFC Conference, Balkema, 2004, pp. 281-287]. The scheme solves the continuity, Navier-Stokes (N-S) and thermal energy equations numerically in Eulerian Cartesian coordinates, then derives pressure, velocity vectors and temperature for each fixed cell by considering particle existence. On the other hand, driving forces and thermal energy from fluid are applied to the particles as external body forces and a source term in the force-displacement law and the heat transfer calculations, respectively. This paper describes the thermal scheme for both fluid and particles. Results of two- and three-dimensional simulations involving forced convective heat transfer by fluid and conduction heat transfer within particles are presented. 相似文献