全文获取类型
收费全文 | 4334篇 |
免费 | 58篇 |
国内免费 | 11篇 |
专业分类
电工技术 | 32篇 |
综合类 | 10篇 |
化学工业 | 373篇 |
金属工艺 | 37篇 |
机械仪表 | 62篇 |
建筑科学 | 64篇 |
矿业工程 | 4篇 |
能源动力 | 40篇 |
轻工业 | 327篇 |
水利工程 | 11篇 |
石油天然气 | 8篇 |
武器工业 | 1篇 |
无线电 | 233篇 |
一般工业技术 | 404篇 |
冶金工业 | 2490篇 |
原子能技术 | 25篇 |
自动化技术 | 282篇 |
出版年
2021年 | 13篇 |
2019年 | 12篇 |
2018年 | 22篇 |
2017年 | 28篇 |
2016年 | 28篇 |
2015年 | 27篇 |
2014年 | 32篇 |
2013年 | 95篇 |
2012年 | 58篇 |
2011年 | 104篇 |
2010年 | 67篇 |
2009年 | 66篇 |
2008年 | 96篇 |
2007年 | 88篇 |
2006年 | 65篇 |
2005年 | 102篇 |
2004年 | 68篇 |
2003年 | 63篇 |
2002年 | 63篇 |
2001年 | 60篇 |
2000年 | 50篇 |
1999年 | 114篇 |
1998年 | 707篇 |
1997年 | 438篇 |
1996年 | 310篇 |
1995年 | 169篇 |
1994年 | 171篇 |
1993年 | 150篇 |
1992年 | 49篇 |
1991年 | 57篇 |
1990年 | 49篇 |
1989年 | 72篇 |
1988年 | 63篇 |
1987年 | 56篇 |
1986年 | 39篇 |
1985年 | 78篇 |
1984年 | 38篇 |
1983年 | 25篇 |
1982年 | 29篇 |
1981年 | 35篇 |
1980年 | 37篇 |
1979年 | 36篇 |
1978年 | 40篇 |
1977年 | 69篇 |
1976年 | 151篇 |
1975年 | 30篇 |
1974年 | 25篇 |
1973年 | 24篇 |
1972年 | 22篇 |
1971年 | 18篇 |
排序方式: 共有4403条查询结果,搜索用时 0 毫秒
61.
The triplet-triplet spectra of three commercial anthraquinone vat dyes (C.I. 67300, C.I. 59100 and C.I. 60515) were studied in solution at room temperature using laser photolysis. The triplet states of these dyes react with oxygen, and the rate constants for the quenching process were measured, together with the rates of energy transfer from the triplet state to anthracene. These observations are considered in relation to the photoreactivity of these dyes. 相似文献
62.
A parametric investigation of NH4OH catalyzed solvent delignification of poplar was conducted to define pretreatment conditions which would yield an optimal separation of the biomass components and an enzymatic susceptible solid carbohydrate phase. Delignification parameters of interest included concentration of NH4OH, time and temperature of the reaction, and type of solvent. The addition of 0.82 M NH4OH to the delignification liquor increased lignin removal and decreased carbohydrate degradation, but increasing NH4OH concentration had no additional effect. At lower reaction temperatures, the extent of delignification increased with reaction time; at higher temperatures, a “relignification” of the pretreated wood was observed. The delignification and hemicellulose solubilization were modelled and rate constants reported. No major difference between three potential pulping solvents—ethanol, butanol, phenol—was observed. The enzymatic susceptibility of pretreated wood samples was approximately 6-fold greater than that of the untreated poplar. UV absorbance was used to qualitatively characterize the soiubilized lignins. 相似文献
63.
Intuition tells us that any decrease in the catalytically active surface area should result in an equivalent decrease in the reaction yield and efficiency. Our findings counter this by showing that the active surface and hence the catalyst loading can be reduced drastically in the diffusion-limited heterogeneous reaction systems, while the conversion rate remains essentially unchanged by using fractals for spatial distribution of the catalyst load. The results of this study provide an unusual circumstance for optimal design of chemically active surfaces and can be used to drastically reduce cost of heterogeneous chemical and biological reactors, sensors, and electrodes of fuel cells. The proposed approach can be exploited to its fullest extent in chemical microsystems by utilizing the latest advances in our abilities to manipulate matter on the micro/nano scale. 相似文献
64.
Min Chan Kim David M. Phillips Myung S. Jhon Xiaoding 《Chemical Engineering Communications》2004,191(1):1-16
The surface diffusion characteristics of nonpolar perfluoropolyether (PFPE) Z on carbon surfaces are investigated in two regimes, submonolayer and multilayer, for nano-thin films. For the submonolayer regime, the two-dimensional, cubic van der Waals equation of state is applied to determine the dependence of the surface diffusion coefficient on the film thickness, as experimental surface diffusion coefficients increase with increasing film thickness. For the multilayer regime, a conventional fluid mechanics analysis with position dependent viscosity and a van der Waals disjoining pressure gradient is applied to investigate the surface diffusion characteristics. The present theoretical analysis qualitatively agrees with the experimental results. 相似文献
65.
Lisa N. Yee Casimir C. Akoh Robert S. Phillips 《Journal of the American Oil Chemists' Society》1997,74(3):255-260
Pseudomonas sp. lipase PS was immobilized by adsorption and tested for its ability to catalyze the synthesis of citronellyl butyrate
and geranyl caproate by transesterification in n-hexane. The reaction parameters investigated were: enzyme load, effect of substrate concentration, added water, temperature,
time course, organic solvent, pH memory, and enzyme reuse. Yields as high as 96 and 99% were obtained for citronellyl butyrate
and geranyl caproate, respectively, with 300 units (approx. 15% w/w of reactants) of lipase PS. Increasing amounts of terpene
alcohol inhibited lipase activity, while excess acyl donor (triacylglycerol) concentration enhanced ester production. Optimal
yields were obtained at temperatures from 30–50°C after 24-h incubation time. Yields of 90 and 99% were obtained for citronellyl
and geranyl esters, respectively, with 2% added water. Solvents with log P values ≥ 2.5 showed the highest conversion yields. pH 7 and 6–8 seemed to be ideal for citronellyl butyrate and geraniol
caproate, respectively. The lipase remained active after reusing 12 times. 相似文献
66.
Reactive dyes exhibit a higher level of initial exhaustion, in the presence of small concentrations of electrolyte, on never-dried lyocell than on never-dried viscose and modal. This difference is particularly noticeable in the case of high substantivity bis-monochloro- s -triazinyl reactive dyes, which exhibit the same differentiated performance on the corresponding dried fibres. Low salt quantities (comparable to those used for applying direct dyes to cellulosic substrates) can therefore be used for applying high substantivity dyes and effect chemicals by an exhaustion process to both never-dried and dried lyocell substrates. 相似文献
67.
Norman S. Allen Kenneth O. Fatinikun A.Keith Davies Barry J. Parsons Glyn O. Phillips 《Dyes and Pigments》1981,2(3):219-229
The photofading of two anthraquinone dyes has been studied in aqueous solution using ultraviolet-visible absorption spectroscopy and flash photolysis. The influence of alcohol concentration, pH, atmosphere, photosensitisers and stabilisers have been examined and these lead to some important conclusions on the mechanism of dye fading. Essentially, the results indicate the photoexcited triplet state of the dye undergoes a process of either electron or hydrogen-atom abstraction depending on the nature of the environment. Other factors such as aggregation and singlet oxygen also appear to play an important role in solution photofading. The relevance of these results to photofading in a polymeric phase is discussed. 相似文献
68.
2,4-Dichloro-6-(β-sulphatoethylsulphonyl)anilino- s -triazine is used as a cross-linking agent to improve the wet abrasion resistance of Lyocell fibres. The agent, which exhibits poor water solubility, is sold as an aqueous dispersion. During application to Lyocell in the presence of alkali, the agent enters a solution phase before reacting with the fibres. High pressure liquid chromatography analysis and solution studies support the view that the two electrophilic species taking part in the cross-linking reaction are vinylsulphone plus one of the chlorine atoms of the dichlorotriazine residue and that preliminary hydrolysis of one of the chlorine atoms is not the cause of the observed solubility changes. 相似文献
69.
This study reports the effects of up to 4 at.%rhenium addition on the cyclicoxidation behavior of-NiAl + -Cr alloys having a basecomposition (in at.%) Ni-40Al-17Cr. Tests were conductedin still air at 1100°C for up to 250 1-hr cycles.The ternary alloy (without rhenium addition) exhibitedpoor cyclic-oxidation resistance, undergoing extensivescale spallation and internal oxidation. Additions of rhenium considerably improved the oxidationbehavior, reducing the extent of both scale spallationand internal oxidation. These beneficial effectsincreased with increasing rhenium content. Rhenium additions improved cyclic-oxidation resistanceby both decreasing the solubility of chromium in the phase and causing the interdendritic -Crprecipitates in the alloy microstructure to become more spheroidized and disconnected. Theseeffects aided in preventing both interdendritic attackand the dissolution of the -Cr precipitates fromthe subsurface region of the alloy. The maintenance of -Cr precipitates at the alloy-scaleinterface decreased the extent of scale spallation byproviding a lower coefficient of thermal-expansion (CTE)mismatch between the alloy and theAl2O3-rich scale. 相似文献
70.
为应用d-电子合金设计理论(或新相分计算法(New PHACOMP))设计发展新型抗热腐蚀单晶高温合金,首先对高Cr抗热腐蚀IN738LC系列合金Ni—16Cr—9.5Al—4.0Ti-8.0Co—0.55Nb—0.06Zr—0.05B—0.47C-Ta—W—Mo(at-%)的相稳定性进行了综合评价得出抑制σ相析出的稳定性临界条件为Mdt<0.991或Mdγ<0.93同时证明这两个临界电子参数具有等价性,可以用Mdt代替Mdγ简化合金设计过程.这一结果可适用于其它高Cr系列抗热腐蚀镍基合金的d-电子合金设计 相似文献