全文获取类型
收费全文 | 4375篇 |
免费 | 149篇 |
国内免费 | 10篇 |
专业分类
电工技术 | 67篇 |
综合类 | 29篇 |
化学工业 | 1338篇 |
金属工艺 | 105篇 |
机械仪表 | 85篇 |
建筑科学 | 265篇 |
矿业工程 | 8篇 |
能源动力 | 73篇 |
轻工业 | 348篇 |
水利工程 | 25篇 |
石油天然气 | 1篇 |
无线电 | 257篇 |
一般工业技术 | 808篇 |
冶金工业 | 585篇 |
原子能技术 | 39篇 |
自动化技术 | 501篇 |
出版年
2022年 | 48篇 |
2021年 | 56篇 |
2020年 | 46篇 |
2019年 | 57篇 |
2018年 | 65篇 |
2017年 | 55篇 |
2016年 | 94篇 |
2015年 | 82篇 |
2014年 | 112篇 |
2013年 | 207篇 |
2012年 | 170篇 |
2011年 | 254篇 |
2010年 | 185篇 |
2009年 | 164篇 |
2008年 | 195篇 |
2007年 | 185篇 |
2006年 | 132篇 |
2005年 | 157篇 |
2004年 | 132篇 |
2003年 | 103篇 |
2002年 | 85篇 |
2001年 | 83篇 |
2000年 | 85篇 |
1999年 | 88篇 |
1998年 | 107篇 |
1997年 | 87篇 |
1996年 | 72篇 |
1995年 | 76篇 |
1994年 | 70篇 |
1993年 | 74篇 |
1992年 | 70篇 |
1991年 | 49篇 |
1990年 | 74篇 |
1989年 | 47篇 |
1988年 | 46篇 |
1987年 | 54篇 |
1986年 | 42篇 |
1985年 | 61篇 |
1984年 | 54篇 |
1983年 | 47篇 |
1982年 | 51篇 |
1981年 | 43篇 |
1979年 | 43篇 |
1978年 | 44篇 |
1977年 | 65篇 |
1976年 | 44篇 |
1975年 | 42篇 |
1974年 | 56篇 |
1972年 | 41篇 |
1970年 | 40篇 |
排序方式: 共有4534条查询结果,搜索用时 31 毫秒
41.
42.
This paper reports on experimental results of aqueous heterophase polymerizations with monomers of quite different solubility in water ranging from the water-soluble 2-hydroxyethyl methacrylate to lauryl methacrylate with solubility in water of only about 10−4 mM. A calorimetric study revealed the strong influence of both the hydrophilicity of the monomer and the stirrer speed on the rate of polymerization in the absence of surfactants. In order to obtain maximum latex yield and high efficiency (which is a measure considering colloidal properties, polymerization recipe, and polymerization parameters) the initiator-surfactant combination must be properly chosen in dependence on the hydrophilicity of the monomer. Results are presented for sodium alkyl sulfates or disodium-N-stearoyl-l-glutamate as surfactant and potassium peroxodisulfate, or poly(ethylene glycol)-azo- compounds, or 2,2′-azobis(N-2′-methylpropanoyl-2-amino-alkyl-1)-sulfonates as initiators. 相似文献
43.
44.
The secondary diamine 1,3,5,7-tetrahydro[1,2c:4,5c'] benzodipyrrole (3) and 1,2,4,5-tetrabromomethylbenzene (1) form a polymeric ionene with spirane structure through a repetitive alkylation reaction. The structure of the product could be proven by13C-NMR spectroscopy by comparison with suitable reference compounds. Solutions in aqueous methanol exhibit a typical polyelectrolyte effect. Variation of the counterions produces sufficient solubility in organic solvents. From the crystal structure of a similar model compound one can conclude that the synthesized polymer has a rod-like shape. 相似文献
45.
Aqueous heterophase polymerization of styrene—a study by means of multi-angle laser light scattering
An online multi-angle laser light scattering study of ab initio surfactant-free styrene emulsion polymerization reveals unexpected results regarding the development of the dispersity during the whole reaction starting from mixing styrene and water at reaction temperature. The experimentally observed change in the dispersity, which is an indirect measure of the average characteristic size of the colloidal objects, allows the identification of three characteristic intervals. During interval A the equilibration of styrene in water is characterized by the formation of styrene domains, which increase in number and size until an equilibrium state is reached. This means that there is virtually no homogeneous/molecular styrene in water solution but rather nanodroplets of about 200 nm in diameter (assuming spherical shape) are formed. During interval B, after initiation of the polymerization and particle formation, the dispersity increases again as the average size decreases and the number of scattering objects increases. The polymer particles suck up the monomer from the monomer nanodroplets, which leads to the disappearance of the nanodroplets and to a decrease in the average size. During interval C the average size increases again due to the predominantly growth of the polystyrene particles. 相似文献
46.
The removal of soluble components from an ovine hepatic microsomal preparation decreased the ω-hydroxylation of dodecanoic
and hexadecanoic acids. The results suggest that one or more soluble components play a role in the microsomal ω-hydroxylation
of fatty acids. The possible roles in the reaction of catalase (known to stimulate the microsomal desaturations of fatty acids
and alkylglycerols) and superoxide dismutase were investigated. The addition of these enzymes to the complete (but not the
washed) microsomal preparation stimulated both the initial ω-hydroxylation reaction and the subsequent dehydrogenation reactions
of the ω-oxidation pathway. The similarity of the effects of catalase and superoxide dismutase and stimulation of two different
steps of the ω-oxidation pathway suggest that these agents are acting indirectly by removing active oxygen species rather
than directly on the enzymes of microsomal fatty acid ω-hydroxylation. 相似文献
47.
The heterogeneous bulk polymerization of acrylonitrile initiated by AIBN has been studied by means of an improved dilatometric technique and a new method of analysis, where the initial reaction rate (vw)0 results from the intercept of a straight line in a \documentclass{article}\pagestyle{empty}\begin{document}$ \frac {\ln \left( 1 \hbox{---} {\rm U} \right)} {{\rm e}^{{- 0,5} {\rm k}_{\rm s}{\rm t} \hbox{---} 1}}$\end{document} versus t plot. It has been found that the initial reaction rate is proportional to the square root of the initial catalyst concentration S0. The ratio of the rate coefficients of propagation and termination\documentclass{article}\pagestyle{empty}\begin{document}$\frac { {\rm k}_{\rm a} } { {\rm k}_{ {\rm w}^{2} } } $\end{document} could be calculated from the slope of a straight line passing through the origin in a plot of (vw)0 versus \documentclass{article}\pagestyle{empty}\begin{document}$\sqrt { {\rm S}_{0} }$\end{document} and yielded a value of 280 mol 1?1. 相似文献
48.
Various commercial supported palladium hydrogenation catalysts were studied by XPS and treated at ambient pressure with hydrogen and air. Unused catalysts exhibit a significant fraction of divalent Pd (oxide) which is reduced by hydrogen treatment at room temperature. Exposure to air in systems with carbonate, alumina, silica or active carbon as support causes the formation of a solid solution of oxygen in Pd characterized by a Pd 3d chemical shift of ca. + 0.4 eV. The absolute binding energy of Pd depends strongly on the matrix, indicating a significant contribution of extra-atomic screening, which prevents a direct comparison of reference samples and supported catalysts. Using the oxidation of CO to CO2 at 300 K as in situ chemical probe it was confirmed that Pd supported on carbonate, silica and alumina exists in the same metallic state which could be activated for the test reaction irrespective of the variation in XPS binding energies. 相似文献
49.
50.
Summary Novel organic nanoparticles functionalized with nucleophilic polypropyleneoxide (PPO) chains on their surfaces for supporting metallocene catalysts in heterogeneous olefin polymerization are presented. The nanoparticles (60–100 nm) were obtained by miniemulsion polymerization of styrene, divinylbenzene and PPO functionalized styrene. It is demonstrated that Me2Si(2MeBenzlnd)2ZrCl2/MAO supported on these nanoparticles is suitable for the homopolymerization of ethylene, resulting in excellent product morphologies and high activities. lt is shown that by varying the MAO/Zr ratios and Zr concentrations the activities and productivities of the catalysts as well as the qualities of the polyethylene products can be tuned. These new supported catalysts are also suitable for the copolymerization of ethylene with several comonomers (1-hexene, 1-octene, 1-decene or norbornene). As the obtained product properties like crystallinity, melting temperature or bulk density match the results of silica supported systems, these organic nanoparticles can be considered as alternative carriers in comparison to the established inorganic ones. 相似文献