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221.
Four new cyclopropyl-triterpenes, 27-nor-3beta-hydroxy-25-oxocycloartane (1), (22E)-25,26,27-trinor-3beta-hydroxycycloart-22-en-24-al (2), 3beta-acetoxy-15alpha-hydroxy-13,27-cyclours-11-ene (3), 3beta-acetoxy-12alpha-formyloxy-13,27-cycloursan-11alpha-ol (4), together with (23E)-27-nor-3beta-hydroxycycloart-23-en-25-one (5) were isolated from the aerial roots of Ficus microcarpa. Compounds 3 and 4 are rare 13,27-cycloursane-type triterpenes. Their structures were elucidated by spectroscopic and chemical methods. 相似文献
222.
The paper deals with results of thermal analysis of low-alloyed chromium-molybdenum steel. The methods of analysis were dilatometry,
differential thermal analysis (DTA) and differential scanning calorimetry (DSC). The Ac1 and Ac3 temperatures of the steel samples measured by dilatometry and DTA during the heating period were in good agreement. Generated
by cooling a martensitic structure first became apparent at 503 K. Tempering of the as-quenched samples showed the presence
of the second tempering stage in the region between 473 and 573 K. At that stage heat capacity decreased from 0.48 to 0.32
J g-1 K-1, as a result of conversion of transition carbide due to heat consumption. After normalization of the as-quenched samples
the heat capacity values were restored to between 0.42 and 0.47 J g-1 K-1 in the temperature range from 373 to 673 K.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
223.
[reaction: see text] Copper(I)-mediated C-N bond formation has been employed to prepare both N-acyl vinylogous carbamic acids and ureas. The novel N-acyl vinylogous carbamic acid antibiotic, CJ-15,801, was synthesized using this methodology. 相似文献
224.
225.
Qiong Yu Lai Ji Zheng LuXiao Bo Su Xiao Yang Ji 《Journal of solid state chemistry》2002,165(2):312-316
Spinel compound LiNi1−xMnxVO4 (0≤x≤0.4) had been prepared by using the moist chemical method. X-ray diffraction spectra showed that the lattice constant increased with x in the LiNi1−xMnxVO4, XPS spectra indicating that Li1s had a chemical shift towards lesser binding energy, and manganese in LiNi1−xMnxVO4 existing as the mixed valence of Mn2+ and Mn3+. The electrochemical charge and discharge testing at a current density of 0.1 mA/cm2 between the potentials of 4.0 and 3.0 V vs Li/Li+ in 1 mol/dm3 LiPF6/EC+DEC (1:1 by volume) at 25°C showed that LiNi1−xMnxVO4 cell has a better rechargeability, but a lower cell voltage of 4.0 V vs Li/Li+ than that without the doping sample, and the capacity and the cycle efficiency of the Li/LiNi1−xMnxVO4 cells increased with x in the LiNi1−xMnxVO4. 相似文献
226.
A novel approach has been found and the first total synthesis of (±)-Salvirecognine was accomplished by using it. In which intramolecular cyclization and Friedel-Crafts alkylation took place simultaneously to afford key intermediates for synthesis of aromatic tricyclic diterpenoids OMe PPA O O O OMe 1 2 Scheme 1 As shown in Scheme 1 intramolecular cyclization and Friedel-Crafts alkylation took place simultaneously when compound 1 was treated by PPA at 125 ℃. In which the i-pr… 相似文献
227.
介绍了锗在光纤通信中的作用,分析了世界光纤市场的变化及其对锗的市场结构的影响,预测近期国内锗的市场结构不会有大的变化。 相似文献
228.
229.
The McLafferty-type rearrangements, which are the most facile fragmentation for the styryl- and the alkyl propenyl sulfoxides, have been proven to involve at least a β-hydrogen by deuterium labelling studies. γ-Hydrogen also rearranges, yet a cyclopropane instead of an alkene is eliminated. Furthermore, alkyl propenyl sulfoxides undergo hydrogen migration only to the surfinyl oxygen. 相似文献
230.
Kim MS Seo KS Khang G Lee HB 《Langmuir : the ACS journal of surfaces and colloids》2005,21(9):4066-4070
A gradient polyethylene (PE) surface was created through corona treatment, in which the corona power increased along the 5 cm length of the PE. The gradient surface was treated with polyethyleneimine and then biotin. Fluorescein-conjugated streptavidin (SAV) caged within 5-carboxymethoxy-2-nitrobenzyl (CMNB) adsorbed onto the biotinylated gradient PE surface following molecular recognition principles. Photoirradiation decomposed the CMNB cage and allowed the fluorescein-conjugated SAV to fluoresce, the intensity of which increased gradually along the PE surface. 相似文献