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101.
102.
以脉冲微型反应技术研究了脱铝八面沸石对异丙苯的催化裂化行为,并与反应条件下表面酸性进行了关联。样品裂化活性随骨架Si/Al比增加呈山峰形变化,Si/Al=5.38时最大;反应条件下酸中心数随脱铝深度增加却单调降低。动力学数据表明,样品裂化反应速度常数与强质子酸中心数随骨架Si/Al比增加具有平行的山峰形变化规律,Si/Al比为8.87附近的样品最高。 相似文献
103.
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105.
自行研制了电子碰撞离子化的飞行时间型质量分析器(TOFMS),用于物质的化学分析。用研制的TOFMS测量了Ar离子化的飞行时间谱和离子的部分电离截面积比与碰撞电子能量的依赖关系,将它与Stepshan等人的实验结果进行了比较。 相似文献
106.
107.
Summary The members of the power divergence family of statistics
all have an asymptotically equivalent χ2 distribution (Cressie and Read [1]). An asymptotic expansion for the distribution function is derived which shows that the
speed of convergence to this asymptotic limit is dependent on λ. Known results for Pearson'sX
2 statistic and the log-likelihood ratio statistic then appear as special cases in a continuum rather than as separate (unrelated)
expansions. 相似文献
108.
Sánchez-Machado DI López-Cervantes J López-Hernández J Paseiro-Losada P Simal-Lozano J 《Biomedical chromatography : BMC》2004,18(2):90-97
A high-performance liquid chromatographic (HPLC) method is described for determination of the ratio of beta-d-mannuronic acid to alpha-l-guluronic acid (M/G ratio) in dietary fibre of edible seaweeds. Total dietary fibre (TDF) content was determined gravimetrically. The TDF fraction was hydrolysed with 12 m and 1 m H(2)SO(4), then neutralized with AG 4 x 4 resin. The uronic acids were separated in a Tracer Extrasil SAX 5 micro m column (25 cm x 4 mm) at 35 degrees C, with 2 mm KH(2)PO(4) containing 5% methanol as mobile phase at a fl ow rate of 1.5 mL/min. The detection wavelength was UV 210 nm. The chromatographic identifications of beta-d-mannuronic acid and alpha-l-guluronic acid were confirmed by liquid chromatography-mass spectrometry (LC-MS). The method precision was 1.4% for beta-d-mannuronic acid and 3.5% for alpha-l-guluronic acid. The method was used to determine M/G ratio in canned seaweeds (Saccorhiza polyschides and Himanthalia elongata) and in dried seaweeds (H. elongata, Laminaria ochroleuca, Undaria pinnatifida, Palmaria sp. and Porphyra sp.). 相似文献
109.
O. Nilsson 《Journal of separation science》1979,2(12):720-722
Kaiser's “abt” concept rests on the experimental establishment of a linear relation between band width at half height, b0.5, and capacity ratio, k, according to His column specification quantity, hreal, is dependent on the square of the slope a, obtained from a linear regression analysis based on this relation. It is shown in the present paper that an improvement of the experimental conditions leading to a lower extra-column contribution to band broadening, b, introduces a tendency towards a negative curvature in the plot at low k values. The mean slope increases, and an uncritical linear regression would yield an hreal-value which is higher than before and which would be in the opposite direction to the requirements of a reliable column specification. Generally the linear regression analysis has to be moved to higher k regions in cases of curvature, especially as it is also shown that hreal is an estimation of the traditional HETP value, H∞, that would be obtained when k approaches infinity. This theoretically expected relation is a strong motivation for the use of hreal as a column specification, since the b0.5-value associated with H∞ is expected to be practically independent of b. 相似文献
110.
Bruno Ameduri Bernard Boutevin Fouad Malek 《Journal of polymer science. Part A, Polymer chemistry》1994,32(16):3161-3169
The synthesis of maleimides that have pyrazolic or bipyrazolic pendant groups is described. Their homopolymerization and their copolymerization with 2-chloroethyl vinyl ether (CEVE) is reported. The homopolymerizations of such maleimides were performed under various conditions and led to low molecular-weight polymers. However, alternating copolymers were obtained from CEVE as comonomers whatever the monomers feed compositions. A similar behavior was also observed for maleimides that do not exhibit any spacer, whereas for bulky vinyl ethers, random copolymers were produced. A comparison of the thermal behavior between these copolymers (glass transition temperatures, Tg, and decomposition temperatures) and other copolymers having different spacers between the nitrogenated cycles and the chain are related. Thus, an important decrease of Tg, was observed when C3H6CO2CH2 groups were used as the spacer instead of methylene groups. Moreover, the thermal weakness of these copolymers may come from the substituents of the vinyl ether and is discussed. © 1994 John Wiley & Sons, Inc. 相似文献