全文获取类型
收费全文 | 3051篇 |
免费 | 56篇 |
国内免费 | 10篇 |
专业分类
电工技术 | 122篇 |
综合类 | 4篇 |
化学工业 | 688篇 |
金属工艺 | 160篇 |
机械仪表 | 56篇 |
建筑科学 | 46篇 |
能源动力 | 122篇 |
轻工业 | 150篇 |
水利工程 | 2篇 |
石油天然气 | 3篇 |
无线电 | 241篇 |
一般工业技术 | 498篇 |
冶金工业 | 686篇 |
原子能技术 | 92篇 |
自动化技术 | 247篇 |
出版年
2023年 | 6篇 |
2022年 | 31篇 |
2021年 | 40篇 |
2020年 | 27篇 |
2019年 | 25篇 |
2018年 | 40篇 |
2017年 | 35篇 |
2016年 | 66篇 |
2015年 | 25篇 |
2014年 | 55篇 |
2013年 | 119篇 |
2012年 | 106篇 |
2011年 | 135篇 |
2010年 | 112篇 |
2009年 | 114篇 |
2008年 | 125篇 |
2007年 | 112篇 |
2006年 | 113篇 |
2005年 | 89篇 |
2004年 | 90篇 |
2003年 | 98篇 |
2002年 | 81篇 |
2001年 | 65篇 |
2000年 | 49篇 |
1999年 | 66篇 |
1998年 | 292篇 |
1997年 | 153篇 |
1996年 | 102篇 |
1995年 | 70篇 |
1994年 | 76篇 |
1993年 | 80篇 |
1992年 | 56篇 |
1991年 | 37篇 |
1990年 | 29篇 |
1989年 | 33篇 |
1988年 | 27篇 |
1987年 | 28篇 |
1986年 | 21篇 |
1985年 | 32篇 |
1984年 | 23篇 |
1983年 | 22篇 |
1982年 | 33篇 |
1981年 | 27篇 |
1980年 | 21篇 |
1979年 | 20篇 |
1978年 | 13篇 |
1977年 | 19篇 |
1976年 | 30篇 |
1975年 | 9篇 |
1973年 | 7篇 |
排序方式: 共有3117条查询结果,搜索用时 31 毫秒
61.
A distributed multiple server system is designed and implemented with Web-DB based services for distance learning as well as emergency communication. The system has employed multiple servers located in a distributed campus network environment. Each server of the system has multi-core processors. With so-called “server virtualization” technology, some programs are executed in parallel (on the virtual servers) so that such a system can efficiently perform several functions. For example, two or more application services can be performed simultaneously as “cloud services” on the whole system. The system can provide distance learning scheme for educational tool, at the same time it can also support Web-based surveillance facilities for emergency contact. With qualitative and quantitative approach, trial evaluation of system has been performed in some classrooms of distributed campus. And users can obtain some good results from the above evaluation. 相似文献
62.
Imoto Taiji; Ueda Tadashi; Tamura Tomohiro; Isakari Yoshimasa; Abe Yoshito; Inoue Makoto; Miki Takeyoshi; Kawano Keiichi; Yamada Hidenori 《Protein engineering, design & selection : PEDS》1994,7(6):743-748
Mutations around His15 which lie far away from the active site,stimulated glycol chitin activity of lysozyme at physiologicaltemperature. Del-Argl4Hisl5 lysozyme, a mutant lysozyme whoseArgl4 and Hisl5 were deleted together, and has the highest activityamong these mutant lysozymes, had a similar binding abilityto a trimer of N-acetyl-glucosamine, a substrate analogue, relativeto native lysozyme. This suggests that the increased activitywas due to an increased kcat in the catalysis reaction. TheH-D exchange rate of the N-1 proton in the Trp63 which is locatedin the active site cleft, was enhanced in the Del-Argl4Hisl5lysozyme, while 2-D proton NMR analysis revealed no conformationalchange around Trp63. We conclude that some sort of fluctuationat the active site might be required for the manifestation ofactivity. This theory is supported by the finding that the Del-Argl4Hisl5lysozyme showed a shift in temperature dependency of activityto lower temperatures compared with that of native lysozyme. 相似文献
63.
ihiro Kasuga † ‡ Tatsuya Inoue† Kenji Tsuji† Yoshio Ota† § Yoshihiro Abe † 《Journal of the American Ceramic Society》1995,78(1):245-247
High-strength calcium metaphosphate fibers for biomedical applications are extracted from crystallized products of calcium ultraphosphate glasses by aqueous leaching. In the present work, new types of porous ceramics with a skeleton composed of the crystalline fibers are prepared by heating the fibrous products extracted. The fibers in the ceramic are interlinked to each other by glassy phases formed during the heating. This porous material has a large porosity of >60%. The surface of the skeleton can be successfully converted into new calcium phosphate phases such as apatite by heating the porous material treated with a molten salt mixture of CaCl2 -Ca(NO3 )2 . 相似文献
64.
The rate of evaporation of monodisperse water droplets was first evaluated by solving numerically the modified Maxwell equation, assuming the cellular model for a droplet clouds. The results are discussed in comparison with those for a single isolated droplet, which can be obtained analytically. The critical conditions for the droplet cloud to be stable are then evaluated as a function of droplet number concentration, droplet size and initial conditions of the surrounding air. Secondly, the equilibrated system, where a water droplet cloud is steadily mixed with unsaturated air, was analysed on the basis of enthalpy and material balance of the system to evaluate the total volume change of the droplets. Some of these analyses were verified by experiment, using an ultramicroscopic technique which is useful for droplet size analysis. 相似文献
65.
Xinwen Zhu Tetsuo Uchikoshi Tohru S. Suzuki Yoshio Sakka 《Journal of the American Ceramic Society》2007,90(3):797-804
The roles of polyethylenimine (PEI) in the hydrolysis and dispersion properties of aqueous Si3 N4 suspensions were studied in terms of the hydrolysis, adsorption, electrokinetic, and rheological measurements. It was found that the pH change of the suspensions in the acidic environment could be minimized in the presence of ≥0.5 dwb% PEI. The ammonia and oxygen measurements suggest that this phenomenon is primarily attributed to the buffer mechanism generated by the ionized PEI, instead of the protection mechanism. The constant pH enables the suspensions to retain a better stability with time at acidic pH. The adsorption of PEI on Si3 N4 is a high-affinity type at highly basic pH, but is a low-affinity type at acidic pH. As the PEI amount increases, the adsorption shifts the isoelectric point (IEP) of Si3 N4 from pH 5.9 to pH ∼11 until complete coverage is attained. The stability of Si3 N4 suspensions is found to depend strongly on the saturated adsorption of PEI, which is as a function of the pH and PEI amount. Once the saturated adsorption limit is reached, the excess free PEI molecules become more detrimental to the stability with increased solid loading. The stabilization mechanisms of Si3 N4 suspensions by PEI were discussed in detail. 相似文献
66.
Yoshiyuki Abe Kazuyuki Kakegawa Yoshinori Sasaki 《Journal of the American Ceramic Society》1992,75(1):234-236
A complex perovskite of Sr(Cu x Zn1- x )1/2 W1/2 O3 (SCZW) is synthesized by a new combination of wet and dry processess. Mixed oxides containing Cu2+ and Zn2+ (CZ) are prepared by the wet process (coprecipitate method). SCZW is obtained by the dry process (mixed-oxide method) from a mixture of CZ, SrCO3 , and WO3 . SCZW has practically no compositional, unlike solid solutions prepared by the conventional dry method. The wet–dry process method is useful because the wet process is applied to only B-site cations having the same valence. 相似文献
67.
Zhe-Feng Zhang Zheng Ming Sun Hitoshi Hashimoto Toshihiko Abe 《Journal of the American Ceramic Society》2003,86(3):431-436
Ti/Si/2TiC powders were prepared using a mixture method (M) and a mechanical alloying (MA) method to fabricate Ti3 SiC2 at 1200°–1400°C using a pulse discharge sintering (PDS) technique. The results showed that the Ti3 SiC2 samples with <5 wt% TiC could be rapidly synthesized from the M powders; however, the TiC content was always >18 wt% in the MA samples. Further sintering of the M powder showed that the purity of Ti3 SiC2 could be improved to >97 wt% at 1250°–1300°C, which is ∼200°–300°C lower than that of sintered Ti/Si/C and Ti/SiC/C powders using the hot isostatic pressing (HIPing) technique. The microstructure of Ti3 SiC2 also could be controlled using three types of powders, i.e., fine, coarse, or duplex-grained, within the sintering temperature range. In comparison with Ti/Si/C and Ti/SiC/C mixture powders, it has been suggested that high-purity Ti3 SiC2 could be rapidly synthesized by sintering the Ti/Si/TiC powder mixture at relatively lower temperature using the PDS technique. 相似文献
68.
Films of alicyclic polyamic acid and polyimide containing cyclobutane ring in dianhydride moiety and aromatic ring with p- or m-linkages in diamine moiety were characterized by infrared (IR) spectroscopy, dynamic viscoelasticity, differential-scanning calorimetry (DSC), density, and wide-angle X-ray diffraction analyses. Partially and fully imidized polyimides were obtained by varying the imidization temperature, e.g., 150°C, 250°C, and 350°C. It was found from the results of IR spectra, dynamic viscoelasticity, and DSC measurements that the imidization of alicyclic polyamic acid was reduced at about 150°C and needed a higher imidization temperature than aromatic polyamic acid. Alicyclic polyimide with m-linkage in the diamine moiety had a higher density and a much more ordered structure than with p-linkage. © 1994 John Wiley & Sons, Inc. 相似文献
69.
Z. F. Zhang Z. M. Sun H. Hashimoto T. Abe 《Journal of the European Ceramic Society》2002,22(16):2957-2961
To synthesize Ti3SiC2 samples, pulse discharge sintering (PDS) technique was utilized to sinter elemental powders of Ti/Si/C with stoichiometric and off-stoichiometric ratios in a temperature range of 1200–1500 °C. The results showed that high purity Ti3SiC2 could not be obtained from the Ti/Si/C powder with molar ratio of 3:1:2, and Ti3SiC2 preferred to form at relatively low sintering temperature for a short time. When 5Ti/2Si/3C and 3Ti/1.5Si/2C powders were sintered for 15 min, the TiC content was respectively decreased to 6.4 and 10 wt.% at 1250–1300 °C. The corresponding relative density of the samples sintered from 5Ti/2Si/3C powder was calculated to be as high as 99% at the temperature above 1300 °C. It is suggested that low-temperature rapid synthesis of Ti3SiC2 would be possible through the PDS technique, provided that the composition of the starting powders should be adjusted to be off-stoichiometric ratio from 3:1:2. 相似文献
70.
Katsuhiro Inomata Daisuke NakanishiAi Banno Eiji NakanishiYosuke Abe Ryuta KuriharaKentaro Fujimoto Takuhei Nose 《Polymer》2003,44(18):5303-5310
Association behavior and physical gelation mechanism of ABA triblock copolymer dissolved in B-selective solvent have been studied systematically from dilute to moderately concentrated solutions. Static and dynamic light scattering and nuclear magnetic resonance measurements for dilute solutions of poly(methyl methacrylate)-block-poly(tert-butyl acrylate)-block-poly(methyl methacrylate) (PMMA-PtBuA-PMMA) in 1-butanol (PtBuA selective solvent) indicated that PMMA-PtBuA-PMMA chains are molecularly dissolved above 50 °C. With decreasing temperature, the triblock copolymers form associated micelles consisting PMMA associated core and PtBuA shell. Linear dynamic viscoelastic measurements for solutions with moderate concentration (3.9-12.0 wt%) revealed that the system was viscous sol state at 60 °C. Drastic increase of shear storage modulus (G′) occurred with decreasing temperature, and at 25 °C, G′ showed rubbery plateau with weak frequency dependency, means the formation of elastic physical gel. The consistency between the temperature for micelle formation and that at the increase in G′ indicates that the physical gelation is owing to the network formation as the result of the association of PMMA chains and the bridging PtBuA chains connecting the PMMA cores. Master curves for the dynamic moduli were derived by time-temperature superposition along the frequency axis. Just above sol-gel transition concentration (Cgel), the master curves suggest the existence of fairy amount of aggregate that is not incorporated in the macroscopic network. With the increase in polymer concentration, the master curves become to reveal Maxwell-type viscoelasticity with narrow relaxation time distribution, suggesting the formation of transient network with easily generation and destruction of crosslinks. Concentration dependency of the plateau modulus is stronger than the theoretically expected, means the macroscopic transient network grows with polymer concentration by increasing the fraction of elastically effective bridging PtBuA chain above Cgel. 相似文献