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排序方式: 共有146条查询结果,搜索用时 578 毫秒
1.
Chemical constituents of Taraxacum formosanum 总被引:1,自引:0,他引:1
Three new compounds, taraxacine-A (1), taraxacine-B (2) and taraxafolin (3) together with twenty-five known compounds, which include two beta-carboline alkaloids, two indole alkaloids, two chlorophylls, two flavonoids, one coumarin, two triterpenoids, one monoterpenoid, one ionone, four steroids and eight benzenoids, were isolated and characterized from the fresh aerial parts of Taraxacum formosanum. Structures of new compounds were determined by spectral analysis. 相似文献
2.
Seven new compounds, sodium aristolochate-VII (1), aristolactam-CIV (2), madolin-I (3), -J (4), -K (5), -L (6) and -M (7) together with 71 known compounds were isolated and characterized from the fresh root and stem of Aristolochia heterophylla Hemsl. Their structures were determined by spectral methods. Compound 8 was revised as aromadendrane-4beta, 10beta-diol by spectral data and single-crystal X-ray analysis. 相似文献
3.
The Raman spectra of powdered biphenyl, p-terphenyl, and p-quaterphenyl are compared with each other and also with the Raman spectrum of benzene. Most Raman lines in polyphenyls can be considered as derived from normal vibrations in benzene. The intense lines are thus assigned and the correlations between them are established. 相似文献
4.
5.
The ZnO nanorod arrays are grown on the sol–gel-derived seed layer through aqueous chemical growth, and then assembled as gas sensors for detecting carbon monoxide (CO). It is found that the structural and photoluminescent properties of the ZnO nanorod arrays are different as they are grown on seed layers annealed at different temperature (300–700 °C), which is ascribed to distinct growth kinetics of nanorods on the annealed seed layer. Moreover, the correlation between the exposed surface area and the defect density of those ZnO nanorod arrays points out the intrinsic (interior) defects can dominate the green emission instead of surface defects in the present study. Furthermore, the quantities of chemisorbed oxygen on ZnO nanorod arrays can be estimated through XPS analysis. Consequently, the influence of intrinsic defects and chemisorbed oxygen on the electrical properties and gas sensitivities of ZnO nanorod arrays has been clearly elucidated. It is demonstrated that the more adsorbed oxygen and an appropriate amount of intrinsic defects is advantageous to obtain superior CO gas sensitivity for ZnO nanorod arrays. 相似文献
6.
Santosh RajputChao-wei Leu Kasey WoodDavid StC Black Naresh Kumar 《Tetrahedron letters》2011,52(52):7095-7098
The activated dimethoxypyrrolo[3,2,1-ij]quinolin-6-one ring system was synthesized via two approaches, starting from an indole and quinolin-4-one, respectively. Subsequent demethylation led to both monohydroxy- and dihydroxypyrrolo[3,2,1-ij]quinolin-6-ones. 相似文献
7.
The bifunctional activities of α-amylase and pullulanase are found in the cloned recombinant amylopullulanase. It was encoded
in a 2.9-kb DNA fragment that was amplified using polymerase chain reaction from the chromosomal DNA of Thermoanaerobacter ethanolicus 39E. An estimated 109-kDa recombinant protein was obtained from the cloned gene under the prokaryotic expression system.
The optimum pH of the recombinant amylopullulanase was 6.0. The most stable pH for the α-amylase and pullulanase activity
was 5.5 and 5.0, respectively. The optimum temperature for the α-amylase activity was 90°C, while its most stable temperature
was 80°C. Regarding pullulanase activity, the optimum temperature and its most stable temperature were found to be 80 and
75°C, respectively. Pullulan was found to be the best substrate for the enzyme. The enzyme was activated and stabilized by
the presence of Ca2+, whereas EDTA, N-bromosuccinimide, and α-cyclodextrin inhibited its bifunctional activities. A malto-2–4-oligosac-charide was the major product
obtained from the enzymatic reaction on soluble starch, amylose, amylopectin, and glycogen. A single maltotriose product was
found in the pullulan hydrolysis reaction using this recombinant amylopullulanase. Kinetic analysis of the enzyme indicated
that the K
m
values of α-amylase and pullulanase were 1.38 and 3.79 mg/mL, respectively, while the V
max values were 39 and 98 μmol/(min · mg of protein), respectively. 相似文献
8.
Four new compounds, three phenanthrene derivatives, aristolochic acid-III methyl ester (1), cepharanone C (2), and sodium 7-hydroxyl-8-methoxyaristolate (3), and the benzoate derivative, sodium 3,4-dimethoxybenzoate (4), together with 53 known compounds were isolated and characterized from the fresh root and stem of Aristolochia cucurbitifolia. Their structures were elucidated by spectral analyses and chemical transformations. The cytotoxicity and antiplatelet activity of the isolated compounds are also discussed. 相似文献
9.
This paper provides an effective uniform rate of metastability (in the sense of Tao) on the strong convergence of Halpern iterations of nonexpansive mappings in CAT(0) spaces. The extraction of this rate from an ineffective proof due to Saejung is an instance of the general proof mining program which uses tools from mathematical logic to uncover hidden computational content from proofs. This methodology is applied here for the first time to a proof that uses Banach limits and hence makes a substantial reference to the axiom of choice. 相似文献
10.
This paper presents the derivation of the precise relation between the displacement of a light spot on an object's surface and the displacement of its image on the detector in an optical triangulation device, along with applications of the design of triangulation devices. Based on this relation, improved designs of optical triangulation devices, including devices of adjustable configurations, are proposed and discussed. 相似文献