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排序方式: 共有357条查询结果,搜索用时 234 毫秒
121.
The surface energy change (Δ?s) on ordering in a Ni4Mo alloy has been investigated by atomistic calculation based on a broken bond model coupled with Bragg-Williams approximation. A complete contour map showing orientation dependence of Δ?s on ordering is presented. The features in the contour map of Δ?s are described. 相似文献
122.
We have successfully developed a novel environmentally friendly electrolytic system using recyclable solid-supported bases for in situ generation of a supporting electrolyte from methanol as a solvent. It was found that solid-supported bases are electrochemically inactive at an electrode surface. It was also found that solid-supported bases dissociate methanol into methoxide anions and protons. Therefore, in the presence of solid-supported bases, it was clarified that methanol serves as both a solvent and a supporting electrolyte generated in situ. Anodic methoxylation of various compounds with solid-supported bases was carried out to provide the corresponding methoxylated products in good to excellent yields with a few exceptions. The methoxylated products and the solid-supported bases were easily separated by only filtration, and the desired pure methoxylated products were readily isolated simply by concentration of the filtrates. The separated and recovered solid-supported bases were recyclable for several times. 相似文献
123.
Anzai K Saito K Takeshita K Takahashi S Miyazaki H Shoji H Lee MC Masumizu T Ozawa T 《Magnetic resonance imaging》2003,21(7):765-772
Blood-brain-barrier (BBB)-permeable, 3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine-1-yloxy (MC-PROXYL) and BBB-impermeable carbamoyl-PROXYL were used to assess the ESR imaging technique by comparing with autoradiography. For this purpose, spin probes, 14C-labeled at their five-membered ring, [14C]MC-PROXYL and [14C]carbamoyl-PROXYL, were newly synthesized. These probes were i.p. or i.v. injected into rats and autoradiograms were recorded. The autoradiograms of rat head showed that [14C]MC-PROXYL distributed well in the brain compared to [14C]carbamoyl-PROXYL. In vivo ESR spectra and two-dimensional ESR images of isolated rat brain treated with MC- or carbamoyl-PROXYL also indicated the extensive distribution of MC-PROXYL but not carbamoyl-PROXYL in the rat brain. The three-dimensional ESR images of the head of rats and mice were consistent with the fact that MC-PROXYL but not carbamoyl-PROXYL is incorporated into the brain. The ESR-CT images were better for mice than rats. However, the quality of the ESR-CT images was still not satisfactory. Although the resolution and sensitivity of the ESR-CT images were worse than those of the autoradiographic images, the former technique has unique features and advantages; e.g., functional, noninvasive and three-dimensional detection. 相似文献
124.
Y. Takagaki E. Wiebicke M. Ramsteiner L. Däweritz K.H. Ploog 《Applied Physics A: Materials Science & Processing》2003,76(5):837-840
Micrometer-size crystals are observed to grow spontaneously on chemically etched MnAs surfaces. The wet chemical etching leaves
a nearly exclusive pile of amorphous arsenic on the surface when the MnAs layer is etched incompletely. Using Raman spectroscopy,
we identify that these micro-crystals are the arsenolite crystal of arsenic oxides. The manganese in the MnAs layer is oxidized
by the hydrogen peroxide in the etch solution to MnO2, which then works as the catalyst for the rapid oxidation and crystallization of the amorphous arsenic.
Received: 14 November 2002 / Accepted: 18 November 2002 / Published online: 29 January 2003
RID="*"
ID="*"Corresponding author. Fax: +49-30/20377-515, E-mail: takagaki@pdi-berlin.de 相似文献
125.
Yamada K Kurokawa T Tokuyama H Fukuyama T 《Journal of the American Chemical Society》2003,125(22):6630-6631
The total synthesis of (+)-duocarmycin A and SA through a common indoline intermediate is described. The key reactions include selective lithiation of a 2,6-dibromoiodobenzene derivative and diastereoselective addition to a chiral nitroalkene, copper-mediated aryl amination, and addition of aryllithium to azlactones. 相似文献
126.
Hashimoto A Suenaga K Urita K Shimada T Sugai T Bandow S Shinohara H Iijima S 《Physical review letters》2005,94(4):045504
Atomic correlation between adjacent graphene layers was elucidated for double-wall carbon nanotubes (DWNTs) through a chiral index assignment of two nested nanotubes by high-resolution transmission electron microscopy. Our analysis provides a rather constant diameter difference close to 0.75 nm but no chiral angle correlation between the constituent nanotubes in the concentric DWNTs. The local atomic correlation as a commensurate graphene stacking was repeatedly found in eccentric DWNTs and circumscribed nanotubes, which should lead to elastic deformation and bundling of nanotubes. 相似文献
127.
Studies were made on the polymorphism of p-tert-butylcalix[4]arene derivatives having amino acid groups on the lower rim to stabilize their hydrophilic pseudocavity by circular intramolecular hydrogen bonding. The calixarenes exhibit a polymorphic transformation upon heating in the solid state. This transformation is controlled by the thermal history of solids, accompanying the change on the conformation of the calixarene skeleton and also the change of hydrogen bonding in the hydrophilic pseudocavity. 相似文献
128.
Kuniyuki Kitagawa Toshiki Nanya Shin Tsuge 《Spectrochimica Acta Part B: Atomic Spectroscopy》1981,36(1):9-20
The atomic Faraday effect has been applied to the trace determination of lead in NBS Orchard Leaves, human blood, and volcanic ashes. Suspensions of powder samples and diluted whole blood are directly pipetted into a graphite tube atomizer. Spectroscopic and practical features are discussed of the atomic Faraday effect of lead. The inherent feature of insensitivity to background scattering makes the present technique suitable for practical analysis. The problem associated with loss of transmitted optical energy caused by non-atomic species was overcome by a correction method. Consequently, the present technique enabled us to perform rapid analyses, gave a detection limit of 5 × 10?11 g and fair accuracy, at least satisfactory for practical analysis. Some problems arise from residue build-up in the atomizer. 相似文献
129.
Miyake Y Hosoda A Takagaki M Nomura E Taniguchi H 《Chemical communications (Cambridge, England)》2002,(2):132-133
Ferulic acid derivative assembles with three kinds of non-covalent interactions, i.e., metal coordination, hydrogen bonding and CH-pi interaction: X-ray crystallographic study illustrated the molecular assembly mode. 相似文献
130.
ABSTRACT An attempt was made to prepare a graft copolymer consisting of poly(methyl vinyl ketone) (PMVK) as a backbone chain and polyacrylonitrile, poly(4-vinylpyridine), or polystyrene as a graft chain by UV irradiation of a solution of PMKV in the presence of acrylonitrile, 4-vinylpyridine, or styrene. the influence of reaction conditions on the yield, composition, and viscosity of the resulting graft copolymers was investigated. It was suggested from NMR and gel permeation chromatography that those graft copolymers contained a high molecular weight fraction of narrow distribution and block copolymers as well. the reverse osmosis membranes derived from the oxime and amidoxime of the graft copolymers showed a characteristic performance of exhibiting a maximal difference between rejections against NaCl and CoCl2 at a certain addition ratio of crosslinking agent, which was not observed in the membranes from copolymers by conventional radical copolymerization. the relationship between these phenomena and the branching structure of the graft copolymers was discussed. 相似文献