全文获取类型
收费全文 | 7439篇 |
免费 | 146篇 |
国内免费 | 17篇 |
专业分类
电工技术 | 389篇 |
综合类 | 8篇 |
化学工业 | 1411篇 |
金属工艺 | 250篇 |
机械仪表 | 147篇 |
建筑科学 | 107篇 |
矿业工程 | 6篇 |
能源动力 | 204篇 |
轻工业 | 491篇 |
水利工程 | 23篇 |
石油天然气 | 11篇 |
无线电 | 856篇 |
一般工业技术 | 1243篇 |
冶金工业 | 1786篇 |
原子能技术 | 215篇 |
自动化技术 | 455篇 |
出版年
2023年 | 21篇 |
2022年 | 58篇 |
2021年 | 89篇 |
2020年 | 45篇 |
2019年 | 54篇 |
2018年 | 100篇 |
2017年 | 68篇 |
2016年 | 107篇 |
2015年 | 83篇 |
2014年 | 133篇 |
2013年 | 293篇 |
2012年 | 195篇 |
2011年 | 258篇 |
2010年 | 214篇 |
2009年 | 222篇 |
2008年 | 276篇 |
2007年 | 251篇 |
2006年 | 236篇 |
2005年 | 206篇 |
2004年 | 205篇 |
2003年 | 209篇 |
2002年 | 182篇 |
2001年 | 179篇 |
2000年 | 178篇 |
1999年 | 212篇 |
1998年 | 662篇 |
1997年 | 431篇 |
1996年 | 294篇 |
1995年 | 227篇 |
1994年 | 225篇 |
1993年 | 210篇 |
1992年 | 117篇 |
1991年 | 100篇 |
1990年 | 109篇 |
1989年 | 104篇 |
1988年 | 94篇 |
1987年 | 95篇 |
1986年 | 93篇 |
1985年 | 93篇 |
1984年 | 75篇 |
1983年 | 73篇 |
1982年 | 79篇 |
1981年 | 75篇 |
1980年 | 55篇 |
1979年 | 62篇 |
1978年 | 44篇 |
1977年 | 50篇 |
1976年 | 79篇 |
1975年 | 16篇 |
1974年 | 16篇 |
排序方式: 共有7602条查询结果,搜索用时 15 毫秒
21.
Mohammad Mozammel Hoq Tsuneo Yamane Shoichi Shimizu Tadashi Funada Shiro Ishida 《Journal of the American Oil Chemists' Society》1985,62(6):1016-1021
Continuous hydrolysis of olive oil byCandida cylindracea’s lipase was studied in a microporous hydrophobic membrane bioreactor. Olive oil and buffer solution, fed continuously through two compartments partitioned by membrane, caused reaction at the interface of lipase-adsorbed membrane and buffer solution. Fatty acid was obtained in a single phase without being mixed with components of other phases. At all mean residence times, countercurrent flow mode was superior to cocurrent one. The lipase was adsorbed onto the membrane, and its adsorption was suggested to be partially specific from the experiments with enzymes having various levels of purity. The percent hydrolysis depended hyperbolically on the interfacial enzyme concentration. The hydrolysis seemed to be limited by diffusion of fat or fatty acid through the micropores of the membrane at higher interfacial enzyme concentrations. The lipase was stabilized significantly by glycerol added to the buffer solution. Satisfactory performance of the membrane bioreactor was obtained in a longterm continuous operation which lasted for 24 days by feeding buffer-glycerol (18.0%) solution over the adsorbed lipase. The operational half-life of the adsorbed enzyme was 15 days at 40 C. 相似文献
22.
Microbial sensor for preliminary screening of mutagens utilizing a phage induction test 总被引:1,自引:0,他引:1
For the preliminary screening of mutagens, a novel microbial sensor system was developed utilizing a phage induction test. Escherichia coli lysogenic strain GY5027 and nonlysogenic strain GY5026 were used in this study. The number of living cells was determined by measuring the respiration of cells immobilized onto an oxygen electrode. The injection of a mutagen, such as AF-2 and MNNG, caused the phage induction in the lysogenic strain, resulting in the decreased respiration of only the lysogenic strain immobilized onto the oxygen electrode but not of nonlysogenic strain. The rate of current increase correlated well with the concentration of mutagens. The sensor responses to the antibiotics and bactericides were definitely different from those of mutagens. Therefore, utilization of this microbial sensor system makes possible the estimation of a substrate's mutagenicity. 相似文献
23.
24.
Kitakami O. Ogawa Y. Fujiwara H. Kugiya F. Suzuki M. 《IEEE transactions on magnetics》1989,25(3):2607-2611
A Co-Cr film deposited directly on a substrate has an initial growth layer with low coercivity. However, the existence of a Ti underlayer prevents the formation of such a layer. As a result, Co-Cr film deposited on a Ti underlayer has high perpendicular anisotropy and coercivity even in cases of extremely thin film thickness (200 Å). As for the read-write characteristics of Co-Cr thin-film media, the existence of such an initial growth layer greatly improves the reproduced output level. The cause for this is considered to be that the free charges which appear on the back surface of the perpendicular recording layer are reduced and the demagnetization field acting on the recorded magnetization subsequently decreases due to the existence of the initial growth layer 相似文献
25.
26.
In a bending load test for brittle materials, such as ceramics for spacecraft and aircraft, decreasing the number of test specimens required is a crucial problem. This paper discusses the effectiveness of using the information of both fracture stress and fracture location to decrease the number of specimens required to obtain the same precision as the Weibull estimator. The following results were obtained: It was found that by adding the fracture location information, the precision of the Weibull parameter estimation under the optimal design became 1.5–1.9 times better compared with the case of using only the fracture stresses. This means the number of samples necessary to attain the same precision becomes 1/1.5–1/1.9. Tables and figures which give information on the number of samples necessary to attain the required precision are given. 相似文献
27.
We investigated liquid crystallization of liquid crystalline polyester BB-5 during isothermal annealing by digital high-fidelity microscope and light scattering. A liquid crystalline spherical domain having a radius of micrometers appeared by annealing at around 180 °C. The domain grew dendritically in all directions. Neighboring liquid crystalline regions coalesced and then interconnected. The interconnected structure changed to a co-continuous two-phase structure with increasing ordering of the liquid crystalline phase, and the interface between the liquid crystalline phase and the isotropic phase became smoother over time. Liquid crystallization stopped before volume filling the whole space, and the liquid crystalline phase and isotropic phase coexisted. The liquid crystalline region became narrower with an increase in the temperature of the liquid crystallization. Such structural development is different from the liquid-liquid phase separation via spinodal decomposition, and it may be attributed to the segregation of non-liquid crystallizable low molecular weight molecules from the growth front by fractionation of the molecular weight distribution during the liquid crystallization in terms of the instability of the diffusion-controlled interface. 相似文献
28.
A self-assembled monolayer (SAM) of p-hydroxymethylbenzene HOCH2C6H4 - (HOMB) moiety adsorbed on iron by the formation of a covalent bond between carbon and iron atoms was prepared by electrochemical derivatization of an iron electrode with p-hydroxymethylbenzenediazonium tetrafluoroborate HOCH2C6H4N2BF4. The electrode covered with the HOMB SAM was modified with alkyltriethoxysilanes CnH2n+1Si(OC2H5)3 (CnTES, n = 8 or 18) to prepare a film of one-dimensional polymer. The protective ability of the polymer film was determined by polarization measurement of the covered electrode in an aerated 0.5 M NaCl solution. The ability was enhanced by modification of the HOMB SAM with CnTES markedly. The iron surface coated with the one-dimensional polymer film of the HOMB SAM modified with C8TES was characterized by contact angle measurement and FTIR reflection and X-ray photoelectron spectroscopies. The persistence in the protective ability of the polymer film against iron corrosion in 0.5 M NaCl may be associated with the strong adsorption via the covalent bond, revealed by electron-probe microanalysis. 相似文献
29.
Y. L. Hao R. Yang M. Niinomi D. Kuroda Y. L. Zhou K. Fukunaga A. Suzuki 《Metallurgical and Materials Transactions A》2003,34(4):1007-1012
Alloys for implant devices require improved strength but a reduced Young’s modulus, in order to become mechanically more compatible
with adjacent bone tissues. In this study, a new metastable β-type titanium alloy, Ti-29Nb-13Ta-4.6Zr (wt pct), was subjected to aging treatment to produce different microstructures,
and the resulting mechanical properties, including the Young’s modulus, were measured. The Young’s modulus of this alloy is
found to be sensitive to microstructures generated by various heat treatments. For microstructures varying from (α + β) to (α + β + ω) and (β + ω), the Young’s modulus increases with an accompanying increase in tensile strength and hardness, but decreases in ductility.
The (β + ω) microstructure has a low strength, high modulus, and poor ductility and cannot be used for biomedical applications. For
an (α + β) microstructure, the volume fraction of the phases is shown to be the main factor that determines the mechanical properties. 相似文献
30.
K. Fujii J. Fujimoto H. Hayashii R. Kajikawa Y. Masatani H. Ozaki A. Sugiyama R. Suzaki S. Suzuki T.Y. Tsukamoto T.F. Tsukamoto S. Uno S. Iwata 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1985,236(1):55-63
We constructed and tested a prototype gas sampling electromagnetic calorimeter of the Pb-proportional tube sandwich type. The calorimeter uses conductive plastic tubes and cathode pad readout with a tower structure which resulted in reasonable energy and spatial resolutions for electrons in the momentum range 0.5–4.0 GeV/c; /c). This paper describes the test and the performance studied under various conditions. 相似文献