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排序方式: 共有423条查询结果,搜索用时 62 毫秒
1.
Several 5-substituted derivatives of 7-ethoxycarbonyl-6,8-dimethyl-1(2H)- phthalazinone were prepared by means of nitration, reductive amination, and diazonium decomposition. The substituents introduced included NO2, NH2, F, Cl, CN. Among the derivatives, the fluorine compound was obtained only in poor yield because intramolecular cyclization occurred predominantly. 相似文献
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Toshiaki Asakai Ryota Minegishi Norie Inaba Yutaka Ishimura Mariko Murayama Tatsuhiko Tanaka 《Analytical sciences》2006,22(3):461-463
The drying conditions for primary standards of volumetric analysis have a significant effect on the titration results due to changes in the purity, stability and homogeneity. Amidosulfuric acid, a strong acid used as a reference material for volumetric analysis in Japan, was dried in a vacuum desiccator or heated at different temperatures, and then measured by Karl-Fischer titration, thermogravimetry/mass spectroscopy (TG-MS), ion chromatography and coulometric titration. The optimum drying conditions were at 50 degrees C for 24 h with crushing. 相似文献
4.
Kullback-Leibler divergence and the Neyman-Pearson lemma are two fundamental concepts in statistics. Both are about likelihood ratios: Kullback-Leibler divergence is the expected log-likelihood ratio, and the Neyman-Pearson lemma is about error rates of likelihood ratio tests. Exploring this connection gives another statistical interpretation of the Kullback-Leibler divergence in terms of the loss of power of the likelihood ratio test when the wrong distribution is used for one of the hypotheses. In this interpretation, the standard non-negativity property of the Kullback-Leibler divergence is essentially a restatement of the optimal property of likelihood ratios established by the Neyman-Pearson lemma. The asymmetry of Kullback-Leibler divergence is overviewed in information geometry. 相似文献
5.
Shizuko Eguchi Mitsuru Nakayama Shûichi Hayashi 《Journal of mass spectrometry : JMS》1976,11(6):574-581
The doubly charged ion mass spectra of anhydropisatin, 4-methoxyanhydropisatin, 3, 8, 9-trimethoxypterocarpen and 3, 4, 8, 9-tetramethoxypterocarpen were determined, and the fragmentation was explained by assuming that the paired electrons were partially localized in the fragmentations and by comparing the spectra with that of 3-(CD3)-anhydropisatin. Conventional mass spectra of these compounds were very simple, but the doubly charged ion spectra were sufficiently characteristic for the reliable identification. 相似文献
6.
Okada T Komatsu K Kawamoto T Yamanaka T Kagi H 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(10):2423-2427
In situ Raman spectroscopic measurements of water in the region of OH vibration were conducted up to 0.4 GPa at 23 and 52 degrees C. The frequencies of the decomposed OH stretching bands initially decreased with increasing pressure, reached a minimum at 0.15 GPa and increased up to 0.3 GPa and then decreased, which corresponds to the variations of the strength of hydrogen bonding. This variation was observed at 23 degrees C, but not at 52 degrees C, which suggests a change in pressure dependence on the hydrogen bond interaction between these two temperatures. Based on the equilibration model between hydrogen-bonded and nonhydrogen-bonded molecules, the present experimental results indicate that the pressure variation of the viscosity depends on the ratio of hydrogen-bonded molecules, rather than the strength of hydrogen bonding between molecules. 相似文献
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Labeling experiments using several deuterated lipids were pursued to study the biosynthesis of macrocyclic isoprenoidal lipids of thermophilic methanogenic archaea, Methanothermobacter thermautotrophicus. The isopropylidene terminal of geranylgeranyl group of monomeric precursor appeared to be important for the CC bond formation at the hydrophobic end in the macrocyclic lipids. A mechanism involving a radical trigger at the allylic methyl group is proposed for this CC bond formation. 相似文献
10.
Changes in the structure of water deduced from the pressure dependence of the Raman OH frequency 总被引:3,自引:0,他引:3
We report on the Raman spectra of water under high temperature and pressure conditions and show a discontinuity in the pressure dependence of the OH stretching frequency. As pressure increases, the strength of hydrogen bonding increases rapidly in the pressure ranges up to 0.4+/-0.1 GPa at 25 degrees C, 1.0+/-0.1 GPa at 100 degrees C, and 1.3+/-0.1 GPa at 300 degrees C and slowly above these pressures. This finding clearly demonstrates the existence of discontinuities in the pressure response of the hydrogen bonds of water, which suggests a possible structural change under these conditions. 相似文献