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201.
Polyetherols containing a thermally stable pyrimidine ring were obtained upon the reaction of hydroxymethyl derivatives of barbituric acid with an excess of ethylene or propylene oxide. The reaction was monitored by 1H‐NMR and IR spectroscopy for the systems with variable starting molar ratios of reagents. We found that formaldehyde rearranged from N‐hydroxymethyl and oxymethylene bridges into the end of the polyetherol chain during the reaction. Simultaneously, the O‐hydroxymethyl groups underwent blocking by oxirane. The structures of the polyetherols was deduced on the basis of the course of the reaction and the analytical data. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 相似文献
202.
Periodic mesoporous silica was modified with metal organic reagents via direct surface substitution reactions, thus introducing functional groups into the channels of the structure. Using materials functionalised with basic aromatic molecules as catalysts, the efficient Michael addition of diethyl malonate to trans-β-nitrostyrene was achieved. The catalysts anchored to the silica surface show high activity in the catalytic process even at low concentrations and low temperatures. The catalysts also prove to be stable during many recycling procedures. In combination with the remarkably reduced cost for the synthesis of these solid bases, the new hybrid systems are promising candidates for a new generation of catalysts. 相似文献
203.
针对旧房的抗震加固一直是结构设计人员面临的一大课题,通过对旧住宅加层的阐述,分析了旧房加层的常见做法,并提出了一些抗震加固构造措施,以保证加层后新旧结构协调工作,提高房屋的抗震能力. 相似文献
204.
R.G. Baligidad U. Prakash A. Radha Krishna 《Materials Science and Engineering: A》1997,230(1-2):188-193
Addition of carbon in the range of 0,14–0.5 wt.% to the Fe3Al-based intermetallic Fe-16wt.%Al (Fe-28at.%Al) alloy results in the formation of a thermally stable dispersion of Fe,AIC carbide phase. The volume fraction of these precipitates increases with increase in carbon content. Processing of these alloys through a combination of air induction melting and electroslag remelting leads to enhanced elevated temperature mechanical properties compared to those reported for the low (< 0.01 wt.%) carbon alloys with similar Al contents. Enhancement of up to 30% in elevated temperature yield strength was observed at the test temperatures (600, 700 and 800°C) used. The improvement in mechanical properties may be attributed to the presence of strengthening Fe3AlC phase as well as the interstitial carbon present in the alloy matrix. The addition of carbon also leads to improved room temperature mechanical properties in contrast with other alloying additions (such as Mo, Ti and Si) used for enhancing elevated temperature properties of Fe3Al-based intermetallic alloys. It is suggested that carbon may be an important alloying addition to these alloys. 相似文献
205.
This account highlighted the recent advances of our research on the synthesis of enantiopure 2-amino-2′-hydroxy-1,1′-binaphthyl (NOBIN) and its derivatives as well as their applications in asymmetric catalysis, including diethyl zinc addition to aldehydes, allylic addition to aldehydes, allylic substitutions, and hetero-Diels–Alder reactions. 相似文献
206.
连铸保护渣的绝热保温性能 总被引:7,自引:1,他引:6
提出了描述连铸保护渣绝热保温性能的综合评价指数JRBW,其物理意义可理解为单位时间内单位长度上渣层中的温差变化。随着配碳量的增加,JRBW逐渐增大,连铸保护渣的绝热保温性能逐渐好转,连铸保护渣的渣粒形状对其绝热保温性能影响显。 相似文献
207.
Influence of yttrium as a minority alloying element on the corrosion behavior in Fe-based bulk metallic glasses 总被引:1,自引:0,他引:1
The role of yttrium in corrosion behavior in an HCl solution was studied systematically by comparing bulk FeCrMoCB metallic glasses with and without yttrium. The corrosion resistance was very sensitive to minor yttrium addition. The material exhibits a detrimental effect on corrosion resistance at 0.5 at.% yttrium addition while a beneficial effect at more yttrium additions. Such effects are argued to be associated with variations of the semiconductor properties of passive film (i.e. defects concentration and band structure of passive film), induced by minority yttrium alloying element doping. It was shown that there exhibits a bi-layer structure of passive film on Fe-based metallic glasses. The outer layer with high valence cations is responsible for the dissolution behavior of the passive film, whereas the inner layer with doped oxides connects with the semiconductor properties. This result presents us an important hint that the corrosion resistance of metallic glasses can be improved by elaborately tailoring the defect structure of passive film via proper additions of minor alloying elements. 相似文献
208.
Summation and numerousness judgments by 2 chimpanzees (Pan troglodytes) were investigated when 2 quantities of M&Ms were presented sequentially, and the quantities were never viewed in their totality. Each M&M was visible only before placement in 1 of 2 cups. In Experiment 1, sets of 1 to 9 M&Ms were presented. In Experiment 2, the quantities in each cup were presented as 2 smaller sets (e.g., ?+?2 vs. 4?+?1). In Experiment 3, the quantities were presented as 3 smaller sets (e.g., 2?+?2?+?3 vs. 3?+?4?+?1). In Experiment 4, an M&M was removed from 1 set before the chimpanzees' selection. In Experiments 1 and 2, the chimpanzees selected the larger quantity on significantly more trials than would be predicted by chance. In Experiments 3 and 4, 1 chimpanzee performed at a level significantly better than chance. Therefore, chimpanzees mentally represent quantity and successfully combine and compare nonvisible, sequentially presented sets of items. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
209.
针对武钢四烧的现有水质,结合工作实践,从清洗预膜、药剂选择和投加、控制微生物等方面,讨论了四烧循环冷却水的水质稳定处理。 相似文献
210.
在经编产品设计、分析过程中,确定正确的垫纱运动是至关重要的环节,同时对产品生产也有决定性影响。介绍了趋零计量法在经编产品组织结构分析中的应用,指出这对于快速有效地设计、分析出正确的垫纱运动图,以提高经编产品设计、分析效率,进而提高生产效率是一种有效的途径。 相似文献