全文获取类型
收费全文 | 469175篇 |
免费 | 4254篇 |
国内免费 | 1083篇 |
专业分类
电工技术 | 8363篇 |
综合类 | 274篇 |
化学工业 | 70874篇 |
金属工艺 | 22909篇 |
机械仪表 | 16193篇 |
建筑科学 | 9756篇 |
矿业工程 | 4288篇 |
能源动力 | 10368篇 |
轻工业 | 29237篇 |
水利工程 | 5865篇 |
石油天然气 | 14751篇 |
武器工业 | 40篇 |
无线电 | 51089篇 |
一般工业技术 | 104393篇 |
冶金工业 | 77046篇 |
原子能技术 | 14597篇 |
自动化技术 | 34469篇 |
出版年
2021年 | 4523篇 |
2019年 | 4272篇 |
2018年 | 7906篇 |
2017年 | 8204篇 |
2016年 | 8616篇 |
2015年 | 4883篇 |
2014年 | 8559篇 |
2013年 | 20065篇 |
2012年 | 12544篇 |
2011年 | 16291篇 |
2010年 | 13204篇 |
2009年 | 14893篇 |
2008年 | 15440篇 |
2007年 | 15061篇 |
2006年 | 12836篇 |
2005年 | 11294篇 |
2004年 | 11022篇 |
2003年 | 11089篇 |
2002年 | 10487篇 |
2001年 | 10785篇 |
2000年 | 10233篇 |
1999年 | 10080篇 |
1998年 | 22899篇 |
1997年 | 16575篇 |
1996年 | 12711篇 |
1995年 | 9794篇 |
1994年 | 8897篇 |
1993年 | 8990篇 |
1992年 | 6932篇 |
1991年 | 6878篇 |
1990年 | 6852篇 |
1989年 | 6533篇 |
1988年 | 6354篇 |
1987年 | 5841篇 |
1986年 | 5697篇 |
1985年 | 6103篇 |
1984年 | 5760篇 |
1983年 | 5537篇 |
1982年 | 5213篇 |
1981年 | 5193篇 |
1980年 | 5139篇 |
1979年 | 5119篇 |
1978年 | 5137篇 |
1977年 | 5635篇 |
1976年 | 7027篇 |
1975年 | 4591篇 |
1974年 | 4637篇 |
1973年 | 4640篇 |
1972年 | 4079篇 |
1971年 | 3625篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
G. I. Glazov A. M. Garaiev R. V. Timerkhanov 《Chemistry and Technology of Fuels and Oils》2003,39(1-2):26-53
A series of small–capacity units has recently been constructed in regions of oil field development and crude oil and gas condensate production to satisfy the requirements for such petroleum products as naphtha, diesel fuel, kerosene, and boiler fuel and to reduce costs for delivery of these products. There are almost no data in the technical literature, particularly in periodicals, on the construction and operation of small–capacity units. We attempt to generalize the experience of Orgeneftekhimzavody Trust in this area. We hope that this experience will be useful to specialists in the development and management of small–capacity plants. 相似文献
22.
Hogari K. Tetsutani S. Jian Zhou Yamamoto F. Sato K. 《Lightwave Technology, Journal of》2003,21(2):540-545
Many cables containing 1.3-/spl mu/m zero-dispersion single-mode (SM) optical fibers are installed in trunk and access networks. Recently, there have been a number of studies on wavelength-division-multiplexing (WDM) systems designed to increase transmission capacity and flexibility. If we can construct WDM systems using SM optical-fiber cable networks designed to transmit using wavelengths in the 1.3-/spl mu/m window (O-band), this will prove very effective in reducing construction costs. It is therefore important to examine the wavelength dependence of the transmission characteristics of SM optical-fiber cables and networks that have already been installed and in which several optical fibers are joined. In this paper, we describe the measured optical characteristics of SM optical-fiber cables and installed optical-fiber cable networks at various wavelengths. The optical characteristics were stable in the 1.46 to 1.625-/spl mu/m wavelength range and we confirmed that the installed SM optical-fiber cable networks could be used for WDM system applications. 相似文献
23.
Kee S. Moon M. Levy Yong K. Hong H. Bakhru S. Bakhru 《Ferroelectrics Letters Section》2003,30(3):47-57
Advances in the fabrication of solid-solution single crystal relaxor ferroelectrics have made it possible to produce highly efficient piezoelectric crystals, and have attracted renewed interest in the use of these crystals for a new generation of piezoelectric transducers, actuators and sensors. Of particular interest is their incorporation into micro-electromechanical systems (MEMS). In this paper we report on the laser-induced wet chemical etching of lead zinc niobate-lead titanate (PZN-PT) in hydrochloric acid (HCl). Argon-ion laser radiation at power levels up to 4 W is focused to a spot diameter of about 15μm and results in the chemical etching of grooves at patterning speeds up to 5μm/sec. Crystal ion slicing, an ion-implant-based film separation technique, is used in combination with laser etching to form 5 to 10μm-thick patterned and freestanding films for incorporation into micro-electromechanical devices. 相似文献
24.
A. V. Butko A. A. Klimov S. A. Nikitov Yu. A. Filimonov 《Journal of Communications Technology and Electronics》2006,51(8):944-947
The magneto-optical Kerr effect for red (628 nm) and green (532 nm) light is used to study magnetization processes in 2D magnonic crystals obtained by etching pits with the diameter D ≈ 32 μm to a depth of t ≤ 2 μm in a 16.1-μm-thick film of yttrium iron garnet (YIG). Hysteresis loops obtained in the case of the inplane crystal magnetization at 628 nm are characterized by lower saturation fields H s and higher remanent magnetizations than those obtained at 532 nm, a result that is attributed to different absorption coefficients of the YIG film at these wavelengths. This difference between the magnetization curves reflects the fact that the magnonic-crystal surface probed with the green light makes a greater contribution to the magneto-optical Kerr effect. Therefore, the green light is more sensitive to the demagnetizing fields, which govern magnetization processes in the magnonic crystals. 相似文献
25.
A VQ-based blind image restoration algorithm 总被引:5,自引:0,他引:5
Learning-based algorithms for image restoration and blind image restoration are proposed. Such algorithms deviate from the traditional approaches in this area, by utilizing priors that are learned from similar images. Original images and their degraded versions by the known degradation operator (restoration problem) are utilized for designing the VQ codebooks. The codevectors are designed using the blurred images. For each such vector, the high frequency information obtained from the original images is also available. During restoration, the high frequency information of a given degraded image is estimated from its low frequency information based on the codebooks. For the blind restoration problem, a number of codebooks are designed corresponding to various versions of the blurring function. Given a noisy and blurred image, one of the codebooks is chosen based on a similarity measure, therefore providing the identification of the blur. To make the restoration process computationally efficient, the principal component analysis (PCA) and VQ-nearest neighbor approaches are utilized. Simulation results are presented to demonstrate the effectiveness of the proposed algorithms. 相似文献
26.
27.
S. V. Doronin 《Chemical and Petroleum Engineering》2006,42(7-8):461-464
Current features are considered in the calculation of carrying capacities for constructions in engineering plant (EP). Methods
and algorithms are described for EP calculations with comprehensive incorporation of the effects from technological and working
defects on the behavior of structures under standard and emergency conditions.
__________
Translated from Khimicheskoe i Neftegazovoe Mashinostroenie, No. 8, pp. 38–40, August, 2006. 相似文献
28.
V. N. Pavlechko 《Journal of Engineering Physics and Thermophysics》2004,77(1):115-120
Relations for determining a motive force in a complex model of mass transfer as applied to concurrent, countercurrent, and cross motion of the vapor and liquid phases have been introduced. These forces have been compared for different forms of organization of the flow, and their comparison with similar quantities from the known Murphree and Hausen models is presented. 相似文献
29.
The hydrocarbon-group composition and distribution of naphthenoaromatic hydrocarbons of West Siberian oils were studied by the technique of mass spectrometry. Naphthenoaromatic hydrocarbons of the general formula CnH2n?z , where z is 8, 10, 12, 14, 16, or 18, containing from one to six saturated cycles are present in oils in significant concentrations. Naphthenomonoarenes with one saturated cycle dominate in all oils. An increase in the amount of compounds containing 3–6 saturated cycles in their molecule with the occurrence depth was noted. Naphthenobiarenes of the general formula CnH2n?z , where z is 14, 16, 18, 20, 22, or 24 containing from one to six saturated cycles are present in oils in concentrations from 20.0 to 54.0 wt % of the biaromatic fraction. Most oils are characterized by the prevalence of structures with one and two saturated cycles in their molecule. The dependence of the number of cycles in naphthenobiarenes on the nature of original organic matter (OM) was not traced. The lack of correlation between the number of cycles and the OM type is presumably due to the fact that, for the most part, fused polycyclic naphthenobiarenes reflect the degree of catagenetic alteration of organic matter. 相似文献
30.
The selector activated sludge (SAS) systems are known to prevent excessive growth of filamentous microorganisms responsible for bulking sludge, but these systems were hardly ever modelled. This study aimed to develop a model capable of predicting rapid substrate removal in the SAS systems. For this purpose, the Activated Sludge Model No. 3 (ASM3) was extended with three processes (adsorption, direct growth on the adsorbed substrate under aerobic or anoxic conditions). The modified ASM3 was tested against the results of batch experiments with the biomass originating from two full-scale SAS systems in Germany. The endogenous biomass was mixed with various readily biodegradable substrates (acetate, peptone, glucose and wastewater) and the utilisation of substrate (expresses as COD) and oxygen uptake rates (OURs) were measured during the experiments. In general, model predictions fitted to the experimental data, but a considerable number of kinetic (5) and stoichiometric (2) parameters needed to be adjusted during model calibration. The simulation results revealed that storage was generally a dominating process compared to direct growth in terms of the adsorbed substrate utilisation. The contribution of storage ranged from 65-71% (Plant A) and 69-92% (Plant B). 相似文献