全文获取类型
收费全文 | 730篇 |
免费 | 55篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 78篇 |
综合类 | 14篇 |
化学工业 | 161篇 |
金属工艺 | 22篇 |
机械仪表 | 20篇 |
建筑科学 | 34篇 |
矿业工程 | 5篇 |
能源动力 | 17篇 |
轻工业 | 80篇 |
水利工程 | 15篇 |
石油天然气 | 12篇 |
武器工业 | 1篇 |
无线电 | 52篇 |
一般工业技术 | 108篇 |
冶金工业 | 58篇 |
原子能技术 | 5篇 |
自动化技术 | 106篇 |
出版年
2023年 | 3篇 |
2022年 | 15篇 |
2021年 | 16篇 |
2020年 | 12篇 |
2019年 | 13篇 |
2018年 | 24篇 |
2017年 | 22篇 |
2016年 | 28篇 |
2015年 | 12篇 |
2014年 | 28篇 |
2013年 | 30篇 |
2012年 | 78篇 |
2011年 | 77篇 |
2010年 | 28篇 |
2009年 | 36篇 |
2008年 | 20篇 |
2007年 | 25篇 |
2006年 | 14篇 |
2005年 | 30篇 |
2004年 | 18篇 |
2003年 | 24篇 |
2002年 | 36篇 |
2001年 | 36篇 |
2000年 | 9篇 |
1999年 | 8篇 |
1998年 | 20篇 |
1997年 | 20篇 |
1996年 | 15篇 |
1995年 | 12篇 |
1994年 | 3篇 |
1993年 | 7篇 |
1992年 | 6篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 12篇 |
1984年 | 2篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1972年 | 8篇 |
1970年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有788条查询结果,搜索用时 15 毫秒
111.
The thermic-kinetic behaviour of hydrogen tungsten bronze, HxWO3, was investigated by differential scanning calorimetry and X-ray analysis. It is shown that the thermal decomposition of bronze into hydrogen and WO3, is exothermic. Further, it is shown that the hexagonal WO3 system is exothermally transformed (irreversibly) to the monoclinic WO3 system. Activation energies, frequency factors and rate constants of the corresponding processes are determined. It is shown that the hexagonal WO3 system adsorbs hydrogen at approximately 480 K, and desorbs at room temperature in air or an argon-nitrogen atmosphere. It is also shown that HxWO3 is unstable and that it decomposes with time, forming brown WO3 which gives no yellow modification during the WO3 phase transformation. The newly formed modification adsorbs hydrogen without changing colour. 相似文献
112.
The performance of a trickle bed reactor is investigated by the moment technique. Residence time distributions of SO2 tracer in both gas (Helium) and liquid (distilled water) effluents are used to predict zero reduced and first absolute moments and these values are compared with the derived theoretical expressions. Correlations are suggested for gas-liquid mass transfer coefficient, liquid hold up, and extent of axial mixing in liquid phase.True adsorption equilibrium constant of the system is estimated as 0.378 from liquid full bed experiments and contacting efficiency of the trickle bed reactor is found as 0.987.Effect of axial dispersion is not significant on gas-liquid mass transfer coefficient since absorption factor is small, but is found to be quite important on the true estimation of adsorption factor. 相似文献
113.
114.
115.
运用自行研制的试验装置对水下不同结构参数的自激吸气脉冲射流喷嘴的吸气性能进行试验,研究了喷嘴的上下喷嘴直径、腔径和腔长等不同的组合配比对喷嘴吸气量的影响,以及喷嘴吸气量对喷嘴冲击性能的影响。结果表明:喷嘴吸气是提高水下自激脉冲射流冲击性能的有效途径,喷嘴的相对冲击力随着喷嘴吸气量的增加而提高;在较优的喷嘴结构参数配比范围内,喷嘴的吸气比率最大;最佳吸气比率的喷嘴面积比、相对腔长和相对腔径配比范围分别为3.5~4.0、8~9、11~12.5。 相似文献
116.
The single-pellet moment techniques previously developed for the evaluation of effective diffusion coefficient and effective thermal conductivity of a porous solid are combined and a procedure is proposed for the simultaneous evaluation of these constants from a single set of pulse response experiments. It is shown that both temperature and concentration response curves can be measured from a single pulse of oxygen injected into hydrogen carrier gas flowing past a catalyst pellet. It is shown that the zeroth moment of the concentration response peaks are sufficient for finding the effective diffusivity while both zeroth and first order moments are required for thermal conductivity. Experiments conducted at 110°C with a boehmite pellet of porosity 0.57 gave a thermal conductivity value of 3.6 x 10-4 cal/cm °K s and an effective diffusivity (for H2O) of 0.054 cm2/s. The adsorption equilibrium constant of H2O was determined as ρpK = 24.5 from the first moment data. If sorption resistance to diffusion through the pellet is included in the diffusion coefficient, an apparent value of 0.0011 cm2/s would be obtained for Deff. This result indicates the importance of separation of diffusion and sorption parameters in the analysis. 相似文献
117.
Tests on mineral oil lubricated deep groove ball bearings show that there is an optimum lubricant viscosity to ensure maximum rolling contact fatigue life. The results are explained by lubricant film thickness measurements and the application of E.H.L. theory. The optimum lubricant viscosity increases with increase of load and decreases with reduction of speed. 相似文献
118.
Teresa Montero Esperanza Moll Maria A Martín-Cabrejas Francisco J Lpez-Andru 《Journal of the science of food and agriculture》1998,77(2):230-234
Gibberellic acid (GA3) treatments (30 and 60 μg litre−1) were applied to young plants (Fragaria ananassa cv Chandler). Fruits were harvested at various developmental stages (14, 21, 28 and 35 days from fruit set). Weight and size, phenolic compounds (total polyphenols and anthocyanins) and enzyme activities, phenylalanine ammonia-lyase (PAL) and tyrosine ammonia-lyase (TAL) were determined. Our aim was to obtain detailed information about PAL and TAL activities related to the strawberry colour during development and ripening processes and to determine the effects of exogenous treatments of GA3 on PAL and TAL activities. Exogenous treatments of GA3 improve weight, size and colour of strawberry fruits, and affect PAL and TAL activities. We found that the anthocyanin content and PAL activity are enhanced by the exogenous treatment of GA3 in the range of 30 μg litre−1. However, with the higher GA3 treatment, only the anthocyanin content is affected in that way. These findings suggest that gibberellic acid effect on PAL, TAL and ultimately anthocyanin enhancement is dosage related and saturation of the response occurs at 30 μg litre−1. © 1998 SCI. 相似文献
119.
Feroz A. Mir Shakeel u Rehman K. Asokan S. H. Khan G. M. Bhat 《Journal of Materials Science: Materials in Electronics》2014,25(3):1258-1263
The current–voltage (I–V) and optical characteristics of 4-hydroxy coumarin Schottky diode were investigated. The conventional methods related with device were used to extract the various diode parameters. From dielectric study low dielectric constant and loss was observed. From its optical study, an indirect allowed transition is shown by this compound. The optical band gap (E g ) was found to be around 3.78 eV. The observed properties shown by this molecule give a bright opportunity to explore its application for different organic devices. 相似文献
120.
通过PL 谱和Raman谱对MOCVD生长Si基Al N的深陷阱中心进行了研究,发现三个深能级Et1 ,Et2 ,Et3,分别在Ev 上2 .6 1,3.10 ,2 .11e V.Et1 是由氧杂质和氮空位(或Al间隙原子)能级峰位靠近重合共同引起的,Et2 、Et3都是由于衬底Si原子扩散到Al N引起的.在Si浓度较低时,Si主要以取代Al原子的方式存在,产生深陷阱中心Et2 .Si浓度高于某个临界浓度时,部分Si原子以取代N原子位置的方式存在,形成深陷阱中心Et3.实验还表明,即使经高温长时间退火,Al N中Et1 和Et2 两个深陷阱中心也是稳定的 相似文献