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排序方式: 共有322条查询结果,搜索用时 15 毫秒
1.
This paper presents a simple chaotic circuit consisting of two capacitors, one linear two-port VCCS and one time-state-controlled
impulsive switch. The impulsive switch causes rich chaotic and periodic behavior. The circuit dynamics can be simplified into
a one-dimensional return map that is piecewise linear and piecewise monotone. Using the return map, we clarify parameter conditions
for existence of chaotic and periodic attractors and coexistence state of attractors. 相似文献
2.
Three protocols for shotgun process are put forth in which simultaneous multi-fold reactions occur exclusively to each other. The first one involves simple combination of selective and non-selective reactions. Even if the simple protocol fails to give rise to the high selectivity, satisfactory outcome can be achieved by kinetic control or adjustment of functional groups. 相似文献
3.
On treatment of the 2-allyl-3-aminocyclohexenones with mercury(II) acetate, either sequence, dehydrogenation—oxymercuration or dehydrogenation—aminomercuration, occurred depending on the nature of the amino group in the substrate to yield the dihydrobenzofurans or indoles, respectively. 相似文献
4.
[reaction: see text] Base-promoted cyclocondensation of C-chloro oximes with cyclic 1,3-diketones affords functionalized isoxazoles in good yield and under convenient reaction conditions. This process enables the synthesis of highly substituted products with notable functional group tolerance. The products obtained are directly converted to a variety of polyketide-derived polycyclic structures including xanthenes, anthracenes, and benzophenones. 相似文献
5.
We report enantioselective synthesis of phyllanthurinolactone (1), a leaf-closing substance of Phyllanthus urinaria L., and its analogs with sugars other than d-glucose. Structure-activity relationship study using them revealed that the structure of the sugar moiety did not affect their bioactivity at all. This result is very important for the development of molecular probes based on the structure of 1. 相似文献
6.
Katsuhiko?Kamio Yoshifumi?Kusumoto Masashi?Sakai Katumitu?HayakawaEmail author 《Colloid and polymer science》2003,281(7):608-613
The conformation of the sodium salt of poly(l-glutamic acid) (P(Glu)) in solutions of the cationic bipolar amphiphile 1, 20-isosanediylbis(alkylammonium chloride) (C 20(RA) 2) with different alkyl head groups as a function of amphiphile concentration was investigated using circular dichroism (CD). RA included methylammonium (MA), ethylammonium (EA), propylammonium (PA), butylammonium (BA), and pentylammonium (PeA) cationic groups. The CD spectrum of each C 20(RA) 2 had a double minima corresponding to the a-helix of P(Glu), which was replaced by CD spectra with a single minimum at wavelengths larger than 222 nm as concentration increased. These changes in the CD spectrum were ascribed to the conformational change from random coil to a-helix and to aggregates of helices. In C 20(EA) 2 solutions, a step-like change in the CD intensity was observed at 222 nm as a function of the ratio of C 20(RA) 2 to P(Glu). At the step, the CD spectrum of the complete a-helix was observed. At 10–35 °C, an a-helix was induced in P(Glu) in the order: C 20(EA) 2>C 20(MA) 2>C 20(PA) 2>C 20(BA) 2>C 20(PeA) 2. This order was ascribed to the best fit of ethylammonium to the P(Glu) side chain. 相似文献
7.
Fujita M Nakao Y Matsunaga S Seiki M Itoh Y Yamashita J Van Soest RW Fusetani N 《Journal of the American Chemical Society》2003,125(51):15700-15701
A novel MMP inhibitor, ageladine A (1) with antiangiogenic activity was isolated from a marine sponge Agelas nakamurai. Structure 1 was determined by a combination of spectroscopic and chemical methods to be an unprecedented structure of 4-(4,5-dibromo-1H-pyrrol-2-yl)]-1H-imidazo[4,5-c]pyridin-2-amine. 相似文献
8.
Bis(pyridine)iodonium tetrafluoroborate (IPy2BF4) was successfully used as a diiodination reagent for carbazole and its derivatives to give 3,6-diiodocarbazoles in excellent yield. Subsequent rhodium-catalyzed disilylation of 3,6-diiodocarbazoles with triethoxysilane gave the corresponding 3,6-bis(triethoxysilyl)carbazoles, which are precursors for sol-gel polymerization, in good yield. 相似文献
9.
Masao Matsuoka Tsuyoshi Matsuda June Tamaki Yoshifumi Yamamoto Chiaki Iwakura 《Research on Chemical Intermediates》2006,32(5):389-402
Laves-phase hydrogen storage alloy has a high potential for use as negative electrode material as alternative for the misch-metal-based
material. In order to improve the energy density and the rate capability of negative electrode, chemical and mechanical modification
of Lavesphase alloy with different stoichiometric ratios was carried out. Discharge capacity and high-rate dischargeabilty
was evaluated by electrochemical methods and the characterization of Laves-phase alloy was made by X-ray diffraction, SEM
observation and PCT measurement. The best result in discharge capacity could be obtained for stoichiometric Laves-phase alloy
with a composition of Zr0.9Ti0.1Ni1.1Co0.1Mn0.5V0.2Cr0.1 by boiling in 10 M KOH solution. On the other hand, the high-rate dischargeability was increased remarkably by introducing
mechanical grinding before alkali treatment. The cause for improved performance was discussed on the basis of thermodynamic
stability of metal hydride and changes in crystal structure and surface morphology influencing on diffusion coefficient and
diffusion path length of hydrogen. 相似文献
10.
Anna Miyazaki Yoshifumi Tachibana Eibai Lee Gyongyi Bokonyi Yuko Tsuda Yoshio Okada 《Tetrahedron letters》2004,45(33):6323-6327
It was reported that the somatostatin analog TT-232, d-Phe-c(Cys-Tyr-d-Trp-Lys-Cys)-Thr-NH2, exhibited a highly potent antitumor activity in vitro and in vivo. Using pyrazinone analogs and aliphatic amino acids instead of the disulfide bond, we prepared novel type somatostatin analogs including the sequence essential for antitumor activities, Tyr-d-Trp-Lys. These analogs exhibited antiproliferative effect on A431 tumor cells. 相似文献