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排序方式: 共有2217条查询结果,搜索用时 156 毫秒
1.
Edmond P. Saliklis David P. Billington Anneliza W. Carmalt 《Canadian Metallurgical Quarterly》2007,13(2):72-77
This paper presents new aspects of Anton Tedesko’s design for an important thin shell concrete roof. The study of this roof results from the examination of original engineering drawings and calculations which we present with the goal of promoting a greater understanding of the structural design of a major figure in the tradition of 20th century building. 相似文献
2.
新型重整催化剂的研究——Pt/L中沸石酸碱性的作用 总被引:2,自引:0,他引:2
Pt/KL、Pt/BaKL及Pt/HL上的铂与沸石的酸碱位发生相互作用,导致催化剂上存在不同电子状态和粒度分布的铂位,从而产生有着完全不同催化作用、不同抗硫性能的两类催化剂,即以碱性沸石为载体的“单功能”催化剂和以酸性沸石为载体的“双功能”催化剂。在Pt/KL、Pt/BaKL催化剂上,存在着对硫敏感的具有环化脱氢功能和对硫不敏感的仅具有脱氢功能的两类铂活性位。 相似文献
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The architects and builders in the past lacked our knowledge concerning fluid dynamics, but they exhibited a deep rooted ability to observe and reflect - thus, different cultures have developed by trial and error. The authors have produced a stimulating analysis which couples the science of fluid dynamics and a sensitive understanding of past cultures. The paper is recommended reading. 相似文献
6.
The interactions of VOHPO4· 0.5H2O and (VO)2P2O7 with the ammoxidation feed and the single components such as ammonia, oxygen, water and component mixtures were studied in detail using XRD and temperature-programmed reaction spectroscopy. The aim of this work was to improve the knowledge of the formation of the active phases or active sites of the catalysts from their precursors under the condition of the ammoxidation reaction. Similar catalytic properties of various applied VPO materials were discussed in terms of the presence of similar structure elements (domains of adjacent edge-sharing VO6 octahedra-units and P-O-NH4 groups). 相似文献
7.
河南洛阳龙门道上,有一孔古朴的石拱桥,上建小亭,为隋唐天津桥故址残迹。天津桥经历了的历代的兴衰,见证了从隋炀帝大业元年到新中国成立后的历史和发展。 相似文献
8.
福禄宫位于湖南长沙市城西区,始建于清代光绪年间。解放后,福禄宫因未及时修理维护,朽损情况严重,1983年底被拆毁。通过对残留木制装修构件拼凑,推算出该建筑的蝼蜂窠部分测绘图。福禄宫蝼蜂窠类似于北方斗栱中的平身科,是一种装饰性构件。福禄宫的昂嘴采用翼龙飞凤交错排列的形式,部分昂嘴端部另加雕饰花板。蝼蜂窠采用层层叠置出踩的形式,其表面只施以桐油或光油等透明涂料,未施其它色漆及彩绘。 相似文献
9.
L. Savary J. Saussey G. Costentin M. M. Bettahar M. Gubelmann-Bonneau J. C. Lavalley 《Catalysis Today》1996,32(1-4):57-61
A VPO/TiO2 catalyst tested in the oxydehydrogenation reaction (ODH) of propane between 300 and 400°C shows satisfactory performances (up to 80% of propene selectivity at 2% of propane conversion at 300°C or 56% of propene selectivity at 9% of propane conversion at 400°C). Addition of water or pyridine in the feed gas tends to decrease the propane conversion and enhances the propene selectivity. It is shown that water increases the number of Brönsted surface acid sites by dissociative adsorption which, in turn, enhances propene selectivity at the expense of the COx selectivity. These results are in good agreement with spectroscopic IR observations performed under catalytic conditions showing that the Lewis acid sites are linked to COxformation, whereas it seems that Brönsted sites would rather be linked to propene formation. 相似文献
10.
Nucleation and crystallization of polypropylene by mineral fillers: relationship to impact strength 总被引:3,自引:0,他引:3
P.M. McGenity J.J. Hooper C.D. Paynter A.M. Riley C. Nutbeem N.J. Elton J.M. Adams 《Polymer》1992,33(24):5215-5224
The mechanical properties of mineral-filled polypropylene (PP) are determined not only by the size, shape and modulus of the filler particles, but also by microstructure. For example, poor impact strength is correlated with a high capacity for nucleation of crystallization. In the present study, optical microscopy has been used to measure the growth rate of spherulites in PP. In tandem with this, isothermal d.s.c. measurements have been made of the crystallization of the PP filled with talc, calcium carbonate and stearate-coated carbonate at different loading levels. Computer simulation of spherulite growth has been used to derive the number of nucleating sites per unit volume of polymer and, using surface area measurements, the number of sites per unit area of mineral surface was obtained. Values for talc were, as expected, considerably higher than those for carbonate (and especially coated carbonate) fillers. The presence of filler affects not only the nucleation and kinetics of the crystallization process but also the crystallinity and orientation indices and the proportion of β-phase crystallites present. The connection between these factors and impact strength is discussed. It is concluded that impact properties are determined by inter alia crack pinning and blocking by filler particles, stress concentrations at the edges of the filler particles, and the nucleating ability of the filler. 相似文献