全文获取类型
收费全文 | 774篇 |
免费 | 14篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 18篇 |
化学工业 | 155篇 |
金属工艺 | 8篇 |
机械仪表 | 10篇 |
建筑科学 | 27篇 |
矿业工程 | 1篇 |
能源动力 | 60篇 |
轻工业 | 33篇 |
水利工程 | 3篇 |
无线电 | 83篇 |
一般工业技术 | 194篇 |
冶金工业 | 119篇 |
自动化技术 | 78篇 |
出版年
2023年 | 6篇 |
2022年 | 4篇 |
2021年 | 13篇 |
2020年 | 11篇 |
2019年 | 15篇 |
2018年 | 17篇 |
2017年 | 9篇 |
2016年 | 11篇 |
2015年 | 10篇 |
2014年 | 14篇 |
2013年 | 49篇 |
2012年 | 22篇 |
2011年 | 22篇 |
2010年 | 16篇 |
2009年 | 19篇 |
2008年 | 26篇 |
2007年 | 27篇 |
2006年 | 18篇 |
2005年 | 15篇 |
2004年 | 8篇 |
2003年 | 13篇 |
2002年 | 15篇 |
2001年 | 13篇 |
2000年 | 11篇 |
1999年 | 20篇 |
1998年 | 35篇 |
1997年 | 33篇 |
1996年 | 25篇 |
1995年 | 17篇 |
1994年 | 12篇 |
1993年 | 17篇 |
1992年 | 14篇 |
1991年 | 14篇 |
1990年 | 11篇 |
1989年 | 12篇 |
1988年 | 5篇 |
1987年 | 18篇 |
1986年 | 20篇 |
1985年 | 14篇 |
1984年 | 16篇 |
1983年 | 15篇 |
1982年 | 16篇 |
1981年 | 19篇 |
1980年 | 10篇 |
1979年 | 13篇 |
1978年 | 8篇 |
1977年 | 8篇 |
1976年 | 10篇 |
1974年 | 7篇 |
1972年 | 5篇 |
排序方式: 共有789条查询结果,搜索用时 15 毫秒
41.
This paper describes the fabrication, experimentation and simulation stages of converting a 165 l domestic electric refrigerator to a solar powered one. A conventional domestic refrigerator was chosen for this purpose and was redesigned by adding battery bank, inverter and transformer, and powered by solar photovoltaic (SPV) panels. Various performance tests were carried out to study the performance of the system. The coefficient of performance (COP) was observed to decrease with time from morning to afternoon and a maximum COP of 2.102 was observed at 7 AM. Simulations regarding economic feasibility of the system for the climatic conditions of Jaipur city (India) were also carried out using RETScreen 4. It was observed that the system can only be economically viable with carbon trading option taken into account, and an initial subsidy or a reduction in the component costs – mainly SPV panels and battery bank. 相似文献
42.
Mathur S. Story B.H. Rodriguez J.J. 《IEEE transactions on audio, speech, and language processing》2006,14(5):1754-1762
Digital waveguide models are commonly used for simulating vocal-tract acoustics based on physiological data. In particular, waveguide models with half-sample delays are known to be well suited for speech production research. This paper presents enhancements to such a model, aimed at improved accuracy in mapping physiological vocal-tract data (shape and length of the airway) to waveguide parameters. The enhancements allow the length of the vocal tract to be continuously varied, thus enabling more realistic synthesis. This is achieved by smoothly varying the individual segment lengths of a piecewise-cylindrical representation of the airway, without altering the system sampling frequency. Fractional-delay filters are used for spatial interpolation of the digital waveguide model. The algorithms are validated by modeling the protrusion of lips, lowering of larynx and lengthening of intermediate segments for a static vowel shape. 相似文献
43.
44.
Extended tuning range in sampled grating DBR lasers 总被引:1,自引:0,他引:1
Jayaraman V. Mathur A. Coldren L.A. Dapkus P.D. 《Photonics Technology Letters, IEEE》1993,5(5):489-491
The authors demonstrate, for the first time, successful implementation of a distributed Bragg reflector laser with two sampled grating mirrors, which they previously predicted should give tuning range in excess of 50 nm. This device uses a uniform grating pitch throughout the structure, and relies on the same fabrication technology as a standard DBR laser. Initial results show 57 nm of mathematical tuning at 1.475 μm with side-mode suppression ratio (SMSR)>30 dB over much of the tuning range. The observed change in operating wavelength versus mirror currents along with below threshold spectra agree with theoretical expectations 相似文献
45.
MEASUREMENT OF PARTICLE VELOCITY IN PNEUMATIC TRANSPORT OF COAL USING CROSS-CORRELATION TECHNIQUE 总被引:1,自引:0,他引:1
Particle velocity has been determined experimentally in a solid-gas flow using the cross-correlation technique. Signals from two flow-monitoring devices, one based on the measurement of the dielectric constant of coal/air and the other based on the rate of static charge transfer technique, have been utilized to determine the cross-correlation function and hence the time delays between the signals. Other pertinent fluid dynamic parameters have been evaluated using experimentally determined particle velocities. 相似文献
46.
Flow measurement in pneumatic transport of pulverized coal 总被引:3,自引:0,他引:3
47.
A new technique for the modification of PAN fibers has evolved, in which the starting precursor material is impregnated with an aliphatic carboxylic acid, as well as KMnO4. The bimodification of PAN, attempted by us for the first time, is aimed at achieving dual advantages in plasticization effect, as well as in a catalytic effect in a single treatment. The unmodified, unimodified, and bimodified precursors have been characterized for their mechanical, thermal, and physical behavior during various stages of processing to carbon fibers. These results are discussed in detail. The study further shows an 18% improvement in the mechanical properties of carbon fibers, prepared from bimodified precursor, as compared to that of unmodified precursor. One of the reasons for such improvement is the lowering in diameter of PAN fibers and in the resulting carbon fibers. © 1993 John Wiley & Sons, Inc. 相似文献
48.
Measurements of the Hall coefficient and the d.c. conductivity were made on polycrystalline films prepared from mercury-rich HgTe. It was found that, in addition to grain boundary potential barrier scattering, the contribution of ionized impurity scattering is also quite significant. The effect of excess mercury in HgTe is to increase the mobility and to reduce compensating effects. 相似文献
49.
In the n.m.r. spectrum of a styrene (Sty)-methyl methacrylate (MMA) copolymer prepared in presence of zinc chloride at 60°C the phenyl protons of the styrene unit appeared as one peak at 3τ, the methoxy protons of methyl methacrylate unit appeared as three peaks at 6.4–6.8τ, 7.1–7.3τ and 7.5τ. The position of these peaks indicated an alternate copolymer. This was further confirmed by estimation of copolymer composition from n.m.r. spectrum and element analysis. The value of ‘σ’ which is the probability of alternating MMA and Sty units having same configuration was also determined and found to be 0.865 ±0.006. It was found that the value of ‘σ’ was a direct function of concentration of zinc chloride. 相似文献
50.
Study of the activities of hyaluronidase, lactate dehydrogenase isoenzyme-X and the dehydrogenases of sorbitol, alpha-glycerophosphate, glucose-6-phosphate, malate, glyceraldehyde-3-phosphate and isocitrate in the testes of mice of different ages showed that the changes were correlated with the stages of spermatogenic cell differentiation. The first 4 enzymes had activities which were low in newborn mice and high in adults; this pattern was reversed for the other enzymes. 相似文献