首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   528篇
  免费   12篇
  国内免费   2篇
电工技术   38篇
综合类   2篇
化学工业   155篇
金属工艺   11篇
机械仪表   8篇
建筑科学   7篇
矿业工程   2篇
能源动力   15篇
轻工业   30篇
石油天然气   1篇
武器工业   1篇
无线电   33篇
一般工业技术   117篇
冶金工业   86篇
原子能技术   15篇
自动化技术   21篇
  2023年   3篇
  2022年   3篇
  2021年   6篇
  2019年   4篇
  2018年   2篇
  2017年   10篇
  2016年   10篇
  2015年   5篇
  2014年   10篇
  2013年   38篇
  2012年   21篇
  2011年   31篇
  2010年   19篇
  2009年   22篇
  2008年   14篇
  2007年   23篇
  2006年   13篇
  2005年   19篇
  2004年   15篇
  2003年   17篇
  2002年   13篇
  2001年   7篇
  2000年   18篇
  1999年   19篇
  1998年   31篇
  1997年   22篇
  1996年   17篇
  1995年   12篇
  1994年   18篇
  1993年   12篇
  1992年   4篇
  1991年   9篇
  1990年   7篇
  1989年   10篇
  1988年   5篇
  1986年   3篇
  1985年   7篇
  1984年   2篇
  1983年   5篇
  1982年   3篇
  1981年   6篇
  1980年   6篇
  1979年   4篇
  1978年   3篇
  1977年   1篇
  1976年   5篇
  1975年   2篇
  1974年   1篇
  1972年   2篇
  1966年   1篇
排序方式: 共有542条查询结果,搜索用时 15 毫秒
41.
Hydrocracking reactions of diphenylmethane and tetralin were carried out over three kinds of zeolites with or without NiW sulfide to discuss the roles of catalytic bifunctionality in two types of hydrocracking reactions. It was found that strong acid sites were not needed for the hydrocracking of diphenylmethane, while the conversion of tetralin required relatively strong acid sites. Ultra-stable Y zeolite with strong acidity exhibited high hydrocracking activity for both reactions. In contrast, mordenite catalysts did not show high activity for either hydrocracking, though isomerization of tetralin and excess hydrocracking to gaseous products proceeded. The superior performances of ultra-stable Y zeolite in the tetralin hydrocracking were suggested to be related to the hydrogen transfer ability. In most cases, the loading of NiW sulfide enhanced catalytic activity. In the diphenylmethane hydrocracking, the role of NiW sulfide was found to supply active hydrogen to the hydrocracking active sites on zeolite and to prevent polymerization of benzyl cations. In the tetralin hydrocracking, the dehydrogenated products from tetralin were re-hydrogenated over NiW sulfide.  相似文献   
42.
Wall-flow channel models and soot deposition models based on micro scale considerations are integrated into global 3D diesel particulate filter simulations. In addition, transient and steady-state simulations are combined to understand at the same time short- and long-time behaviour of the diesel particulate filter (DPF). The functionality of the simulation tool is achieved and correlations with measured data encourage the use of the model as a tool to predict DPF behaviour.  相似文献   
43.
A study was made of a centrifugal pressure nozzle with large orifice diameter (8-10 nun) for producing dry milk in capacity of 2-3 tons per hour to develop some performance data on spray distribution, drop size distribution, and capacity with changing spray drying conditions such as nozzle pressure, orifice diameter and spray angle.

Experimental results were shown as follows.

(1) A centrifugal pressure nozzle of large capacity such as 5,000- 5,500 l/hr at 150 kg/cm2 spray pressure and 110°s ray angle was designed by using the nozzle parameter Si/dedi√di/di.

(2) Atomization characteristics were greatly affected by the ratio of orifice diameter (de) to the length (L) of the nozzle core. The smaller the ratio, around 0.125, the better are the atomizing effects.

(3) The large orifice can be used at least 3,000 hr in the spray drying operation for milk without any wear in the orifice although it is only made of stainless steel.

As a result, a spray dryer of large capacity for dry milk has been operated by a mono nozzle with a large orifice without any trouble for a long time  相似文献   
44.
Build-up substrates have been preferable solutions for small and high performance systems for more than a few decades. Micro-vias need to be smaller to realize ever higher wiring density in build-up substrates, but there has been concern on the reliability. This paper focuses on Cu filled micro-vias of 25 μm in diameter and investigates the strain on micro-vias using a finite element method for varying geometric parameters and material properties. The strain becomes smaller with shrinking micro-vias, and a prediction equation for the strain is developed as a function of the aspect ratio and material properties for both single and stacked micro-vias.  相似文献   
45.
The effect of a magnetic field on the nature of nanocrystallization from a melt-spun Fe73.5Si13.5B9Nb3Cu1 amorphous precursor has been studied with the aim of controlling microstructures and magnetic properties. Annealing for magnetic crystallization was carried out at temperatures between the Curie temperature of the amorphous phase (586 K) and that of the crystalline phase (920 K). It was found that the {110} texture component in crystallized α-Fe(Si) phase increased in importance with increasing magnetic-field strength. An X-ray diffraction analysis based on the Shultz method revealed that the magnetic field caused preferential formation of {110}-oriented nuclei. In addition, the applied field enhanced crystallization kinetics, particularly the nucleation rate. No significant difference in grain growth behavior was observed as a result of applying a magnetic field. We therefore conclude that the development of the {110} texture by magnetic crystallization is predominantly attributable to preferential nucleation, rather than preferential growth, of {110}-oriented nuclei. The saturation magnetization of nanocrystallized specimens, evaluated using a vibrating sample magnetometer (VSM), was increased by the application of a magnetic field up to 4T during nanocrystallization.  相似文献   
46.
47.
Potassium tantalate powders were hydrothermally synthesized at 400 °C using Ta2O5 and KOH as starting materials with various KOH concentrations (0.1–1.0 M) and heating durations (2–48 h). A defect pyrochlore phase of KTa2O5(OH)·nH2O, was obtained at low KOH concentration and short reaction time. The perovskite phase of KTaO3 predominated as the heating duration and the KOH concentration increased. Pure KTaO3 was obtained in 0.5–1.0 M KOH aqueous solutions and reaction times of 8–48 h. Heteroepitaxitial KTaO3 thin films were achieved on the (100) SrTiO3 substrate in 0.5 M KOH solution under supercritical water conditions. Based on the XRD, SEM-EDX and EBSP (Electron BackScatter Pattern) results, epitaxial KTaO3 crystals were grown on the (100) oriented single-crystal SrTiO3 substrate. Synthesis of perovskite KTaO3 crystals in supercritical water employed significantly low KOH concentrations (<0.5 M), which was far less than the very high concentrations (>7 M) required for conventional hydrothermal method.  相似文献   
48.
A coating of barium hexaaluminate (Ba0.75Al11.0O17.25) on an α-SiC substrate and the thermal stability of the formed film were investigated for a high-temperature catalytic application. The film prepared by sol coating consisted of BaAl2Si2O8 and α-Al2O3 phases and always contained many cracks or exfoliations after heating at 1200C. A hexaaluminate porous film was successfully formed by slurry coating without void formation at the interface between the film and the substrate and exfoliation due to the formation of the intermediate layer after heating at 1200°C. The microstructure of the film remained unchanged, even after heating at 1300°C.  相似文献   
49.
Carbon based structures have been widely studied by X-ray absorption (XAS), also called NEXAFS, which is a very useful bulk probing method that allows examining the unoccupied density of states (DOS) and the site selective bonding environment. Two very well known spectral features in the XAS core level spectrum are the σ* and π* bands, and both have been analyzed in several studies for graphitic-like systems. However, among all the carbon materials, the unique one-dimensional electronic properties attributed to single-walled carbon nanotubes (SWCNTs) exhibit features that reveal clearly their electronic structure in the core level XAS spectrum. In this article, we outline the C1s response in XAS, which is related to the DOS of the conduction band in SWCNTs and its fine structure, revealed by experiments performed on metallicity-sorted SWCNT material. The progress in the identification of changes in the site selective conduction band electronic structure with XAS is discussed in detail.  相似文献   
50.
The thermoelectric half-Heusler compounds Ti x NiSn0.998Sb0.002 (x = 1.0 to 1.2) and Ti y Zr0.25Hf0.25NiSn0.998Sb0.002 (y = 0.5 to 0.65) with nonstoichiometric nominal compositions were prepared by spin-casting and subsequent annealing at 1073 K for 24 h. The dimensionless figure of merit ZT at room temperature was maximized at x = 1.1 and y = 0.6 in Ti-rich compounds through an increase in absolute Seebeck coefficients despite a decrease in electrical conductivities. ZT reached 0.07 at x = 1.1 and 0.14 at y = 0.6. In powder x-ray diffraction analysis, minor phases of β-Sn, TiNi, Ti2Sn, and Ti5Sn3 were observed in addition to a major phase of half-Heusler. The quantity of the minor phases was minimized at x = 1.1 and y = 0.55, where the absolute Seebeck coefficients are maximized. In transmission electron microscopic (TEM) analysis of Ti0.55Zr0.25Hf0.25NiSn0.998Sb0.002, crystal grains of the half-Heusler phase, from several hundred nanometers to several micrometers in size, were observed. TEM energy-dispersive spectroscopy measurements indicated that fluctuations of Ti, Zr, and Hf compositions within the Ti-site in the half-Heusler phase may occur. Thermoelectric properties were improved at x = 1.1 and y = 0.6 rather than at the stoichiometric compositions of x = 1.0 and y = 0.5 due to minimization of the precipitate quantities.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号