全文获取类型
收费全文 | 13673篇 |
免费 | 986篇 |
国内免费 | 205篇 |
专业分类
电工技术 | 68篇 |
综合类 | 624篇 |
化学工业 | 10176篇 |
金属工艺 | 102篇 |
机械仪表 | 35篇 |
建筑科学 | 100篇 |
矿业工程 | 26篇 |
能源动力 | 64篇 |
轻工业 | 545篇 |
水利工程 | 7篇 |
石油天然气 | 906篇 |
武器工业 | 25篇 |
无线电 | 195篇 |
一般工业技术 | 1729篇 |
冶金工业 | 62篇 |
原子能技术 | 108篇 |
自动化技术 | 92篇 |
出版年
2024年 | 44篇 |
2023年 | 123篇 |
2022年 | 127篇 |
2021年 | 226篇 |
2020年 | 236篇 |
2019年 | 256篇 |
2018年 | 223篇 |
2017年 | 303篇 |
2016年 | 348篇 |
2015年 | 397篇 |
2014年 | 635篇 |
2013年 | 630篇 |
2012年 | 886篇 |
2011年 | 922篇 |
2010年 | 713篇 |
2009年 | 832篇 |
2008年 | 762篇 |
2007年 | 921篇 |
2006年 | 994篇 |
2005年 | 831篇 |
2004年 | 724篇 |
2003年 | 652篇 |
2002年 | 503篇 |
2001年 | 454篇 |
2000年 | 363篇 |
1999年 | 364篇 |
1998年 | 260篇 |
1997年 | 229篇 |
1996年 | 137篇 |
1995年 | 132篇 |
1994年 | 122篇 |
1993年 | 134篇 |
1992年 | 97篇 |
1991年 | 68篇 |
1990年 | 36篇 |
1989年 | 42篇 |
1988年 | 21篇 |
1987年 | 12篇 |
1986年 | 10篇 |
1985年 | 21篇 |
1984年 | 24篇 |
1983年 | 19篇 |
1982年 | 23篇 |
1980年 | 1篇 |
1951年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
72.
Summary: A semi‐batch process using nitroxide mediated polymerization, was explored for the design of low molecular weight solvent‐borne coatings, typical of those used in the automotive industry. While living radical polymerization (LRP) offers many advantages in the control of polymer chain microstructure that may confer important physical and chemical property benefits to coatings, adapting LRP to a semi‐batch process poses significant challenges in the design and operation of the process. Using styrene monomer, various two‐component initiating systems (free radical initiator, 4‐hydroxy‐TEMPO) were studied to understand the effects of different initiators on the course of polymerization. In addition, an alkoxyamine was synthesized and used as the initiating source. The initiators Luperox 7M75 and Luperox 231 give higher polymerization rates and reasonable control over polymerization, while benzoyl peroxide (BPO), Vazo 67, and the alkoxyamine are less effective. The number of polymer chains in the final product is always less than the theoretical value, reflecting poor initiation efficiency, probably resulting from undesirable termination reactions that become important due to the nature of the semi‐batch process. Adding camphorsulfonic acid (CSA) or charging initiator concurrently with monomer during semi‐batch feed, can increase the polymerization rate while maintaining the living character of the polymerization. The copolymerization of styrene and butyl acrylate is also shown to exhibit living character.
73.
Experimental data on the monomer conversion, xm, and the weight average molecular weight, Mw, have been generated under several isothermal and non-isothermal conditions for the polymerization of methyl methacrylate in a rheometer-reactor assembly. The non-isothermal results, in particular, can be used to provide more stringent tests of kinetic models than isothermal data alone. A simple empirical model has been used to describe this system that accounts for the gel (Trommsdorff) and glass effects. The model involves only xm and the temperature, and is quite general. The model parameters are tuned using only three sets of isothermal data. Good agreement is found between the experimental results and model predictions for a whole variety of experimental conditions, including non-isothermal operation and with intermediate addition of initiator. Because of its generality, this model is quite suitable for use for on-line optimizing control as well as for describing industrial reactors. 相似文献
74.
介绍了环保型反应性乳化剂ADEKA?REASOAP?SR-10、ER-30的结构和特性,重点分析了反应性乳化剂在水性木器乳液聚合中的应用及其对聚合物性能的影响。实验证明,应用反应性乳化剂所得的聚合物性能要远远优于非反应性乳化剂所得聚合物性能,而且应用了非离子反应性乳化剂所得的聚合物性能要优于单独使用阴离子反应性乳化剂所得聚合物性能。最后预测了环保型反应性乳化剂的良好应用前景。 相似文献
75.
介绍了纳米碳酸钙原位聚合聚氯乙烯的结构和性能,同时对该树脂进行了有关的应用试验,并对其发展前景作了科学展望。 相似文献
76.
77.
The solid‐state polymerization (SSP) reaction kinetics of poly(ethylene terephthalate) were investigated in connection with the initial precursor intrinsic viscosity (IV; molecular weight). Evaluations were performed with otherwise equivalent precursors melt‐polymerized to IVs of 0.50, 0.56, and 0.64 dL/g. The changes in the molecular weight and other properties were monitored as functions of the reaction times at solid‐state temperatures of 160–230°C. Precursors with higher initial molecular weights exhibited higher rates of SSP than those with lower initial values, as discussed in connection with the levels of crystallinity and the carboxyl and hydroxyl end‐group composition. Activation energies decreased at temperatures above 200°C, and this indicated a change in the SSP reaction mechanism. At temperatures of 200–230°C, similar activation energies were required for the polymerization of all three precursors. Lower temperature polymerizations, from 160 to 200°C, required higher activation energies for all precursors, with the 0.50‐IV material requirement almost twice as high as that calculated for the higher IV precursors. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 197–212, 2003 相似文献
78.
I. Hama T. Okamoto E. Hidai K. Yamada 《Journal of the American Oil Chemists' Society》1997,74(1):19-24
For the purpose of estimating the reaction mechanism of the direct ethoxylation of a fatty ester in the presence of an Al-Mg
composite oxide catalyst, a labeled fatty methyl ester C11H23CO18OCH3 containing 18O isotope was synthesized and directly ethoxylated. The product was evaluated by gas chromatography-mass spectrometry (GC-MS).
The GC-MS spectra showed that the 18O isotope label was present only in the methoxy group at the molecular end of the ethoxylated fatty methyl ester. This supports
the reaction mechanism of coordination anionic polymerization where the bond between the acyl and methoxy groups of the fatty
methyl ester molecule was broken, caused by the bifunctional effect of the acid-base active sites; an intermediate chemisorption
species was formed; and then ethylene oxide was addition-polymerized sequentially, in parallel. 相似文献
79.
80.
Two different methods of producing bi‐ and trimodal latices of a mixture of methyl methacrylate, butyl acrylate, and small amounts of acrylic acid were tested. It is shown that a combination of concentrating blends of seed particles by semibatch reaction, followed by a nucleation of small particles plus a second semibatch phase allowed us to obtain stable latices with solids contents over 65% and viscosities of below 2500 mPa s?1 with little coagulum formation. The key parameter in determining latex stability, coagulum formation, and viscosity appears to be the the particle size distribution, and especially its modification attributed to secondary nucleation. Because it is not possible to eliminate water‐soluble monomers from the polymerization recipe, secondary (homogeneous) nucleation must be minimized by careful addition of the free‐radical initiator and choice of monomer feed flow rates. The nucleation of the third population in the trimodal latices is best accomplished with a mixed surfactant system because renucleation by anionic surfactant alone leads to detrimental changes in the particle size distribution (PSD) resulting from excessive flocculation of particles. In addition, it was found that the viscosity of the final products was not sensitive to small changes in the ionic strength of the latex, although neutralization to a pH of 6 effectively doubles the final latex viscosity. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1916–1934, 2002; DOI 10.1002/app.10513 相似文献