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71.
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On the way of the "1990 International Trans-Antarctic Expedition", the first author of this paper, the Chinese member of the expedition, collected 104 snow samples in 25-cm surface snow along a 5986-km route on Antarctic ice sheet from west to east. The geographical distribution of δD across the Antarctica by the longest route is obtained from stable isotope analysis for the first time. After discussing regional differences of physical geographic conditions, maritime-continental influence, altitudes and latitudes at sampling sites, the distribution of δD is considered to have a close relation to latitudes, but the topographic effect is prominent in some particular regions. The mean annual temperature at sampling site and its relationship with δD in surface snow covering Antarctica from west to east are discussed also. The δD-temperature gradient from the south end of Antarctic Peninsula to Vostok obtained in this paper is very close to that in Terre Adelie Land obtained by predecessors. The snow-dri 相似文献
73.
The electrochemical and in-situ surface-enhanced Raman spectroscopy (SERS) techniques were used to investigate the electrooxidation behavior of methanol in acidic, neutral and alkaline media at a Pt-Ru nanoparticle modified glassy carbon (Pt-Ru/GC) electrode. The results showed that methanol could be dissociated spontaneously at the Pt-Ru/GC electrode to produce a strongly adsorbed intermediate, CO. It was found that CO could be oxidized more easily in the alkaline medium than in the acidic and neutral media. The peak potential of methanol oxidation was shifted from 0.663 and 0.708 V in the acidic and neutral media to -0.030 V in the alkaline medium, which is due to that the adsorption strength of CO on the Pt surface in the alkaline medium is weaker than that in the acidic and neutral media. The final product of the methanol oxidation is CO2. However, in the alkaline medium, CO2 produced would form CO3^2- and HCO3^- resulting in the decrease in the alkaline concentration and then in the decrease in the performance of DMFC. Therefore, the performance of the alkaline DMFC is not Stable. 相似文献
74.
正庚烷在超稳Y沸石(USY)负载超强酸催化剂上加氢异构化 总被引:6,自引:0,他引:6
The Pt-bearing SO42-/ZrO2 superacid catalysts supported on ultra stable Y (USY) zeolite were prepared by impregnation and characterized by X-ray diffraction, nitrogen adsorption and Hammett indicators. Their catalytic activities were evaluated in the hydroisomerization of n-heptane with an atmospheric fixed-bed reactor. The catalysts possessed a high surface area, superacidity and well maintained pore structure of USY support. The supported catalysts with a suitable SO42-/ZrO2 loading exhibited a higher catalytic activity and selectivity than the unsupported SO42-/ZrO2 catalyst or the Pt supported on USY catalyst without superacid. At the reaction temperature of 220 ℃, over the catalyst with a Pt loading of 0.8wt% and ZrO2 loading of 10wt%, the conversion of n-heptane could be as high as 35.2% with a selectivity of 87.9% for isomerization products. 相似文献
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76.
Determination of Partial Molar Volumes of EPA and DHA Ethyl Esters in Supercritical Carbon Dioxide 总被引:4,自引:0,他引:4
Mei HUANG Xian Da WANG Ren Tian XIONG Ping Dong WU Qi Long REN* National Laboratory of Secondary Resources Chemical Engineering Zhejiang University Hangzhou 《中国化学快报》2002,13(1)
The use of supercritical fluids (SCFs) as solvents has been attracting widespread interest in the research and commercial applications. The study of partial molar volumes of solutes at infinite dilution in the near-critical region is of considerable fundamental importance, as these data reflects the interactions occurring between the solute and the solvent. Experimental measurements of partial molar volumes may be divided into two categories: direct and indirect methods. The direct methods… 相似文献
77.
3He/4He ratios in samples of sea water obtained at depths from surface to 300 m in the upper layer of the Western Pacific Ocean were measured by a mass spectrometer VG5400. The lateral and vertical distribution of He isotopes in the studied area was discussed in detail on the basis of 3He/4He ratios. Excess and depleted 3He. in relation to δ3He value of surface water in equilibrium with air has been discussed in the area, which may be mainly attributed to the incorporation of the North Pacific Intermediate Water with the Equatorial Upwelling and the exchange of water masses between the South China Sea and the Western Pacific, respectively. The present work in Western Pacific has also indicated that He isotopes may be used as a tracer for mixing processes of water masses and oceanic circulation. 相似文献
78.
薄层色谱法在香兰素合成中的应用 总被引:3,自引:0,他引:3
应用薄层色谱法对愈创木酚、3-甲氧基-4-羟基扁桃酸和香兰素进行了分析,以硅胶GF254作为吸附剂,从几种溶剂系统中选出氯仿:乙酸乙酯:正丙醇:冰乙酸:水=20:1:1:1:2溶液作为展开剂。建立了 香兰素的薄层扫描定量分析方法,测定波长为500nm,参比波长为570nm,线性范围为0.31-6.2μg。 相似文献
79.
常规加热或微波照射下, 含氮杂环1与多聚甲醛反应以良好的产率生成含氮杂环基甲醇3, 反应物物质的量的比、反应温度等对反应产率有影响, 微波条件下的反应时间比常规加热下大大缩短. 化合物3和异氰酸酯4在常规加热或微波照射下生成相应的氨基甲酸含氮杂环甲基酯5a~5m. 反应温度、反应物物质的量的比、反应时间、微波辐射功率等对反应产率都有一定的影响, 与常规加热相比微波条件下的反应时间大大缩短. 化合物5的结构经过IR, 1H NMR, MS, 元素分析测定, 部分化合物经过13C NMR测定. 测定了化合物5的杀虫和除草活性, 结果表明其杀虫活性较低, 除草活性高于杀虫活性, 5a, 5d, 5e和5m对苋菜和黄瓜的防除率高达100%. 相似文献
80.