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排序方式: 共有925条查询结果,搜索用时 9 毫秒
911.
Hajime Kobori Atsushi Sekiya Nobuhiro Yasuda Keiichi Noguchi Tomohiro Suzuki Jae-Hoon Choi Hirofumi Hirai Hirokazu Kawagishi 《Tetrahedron letters》2013
Three novel compounds were isolated from the culture broth of Armillaria sp. Their structures were elucidated mainly by spectroscopic data analyses. All the compounds regulated hypocotyl and root growth of lettuce. 相似文献
912.
一种中孔硫酸化的、只含Br?nsted酸位的氧化锆-氧化硅催化剂可将甘油转化为丙烯醛,其产率和选择性分别为81%和82%.即使在低温(523 K)下,产物时空收率可高达9.0 mmol h–1 gcat–1.本催化剂的活性和选择性高于典型的硫酸化的ZrO2催化剂.氧化硅稀释了锆物种而使得催化剂酸性更温和,较大的孔径使得传质更快,因此催化剂性能提高. 相似文献
913.
Ho RM Li MC Lin SC Wang HF Lee YD Hasegawa H Thomas EL 《Journal of the American Chemical Society》2012,134(26):10974-10986
Here, we report the mechanisms of chiral transfer at various length scales in the self-assembly of enantiomeric chiral block copolymers (BCPs*). We show the evolution of homochirality from molecular chirality into phase chirality in the self-assembly of the BCPs*. The chirality of the molecule in the BCP* is identified from circular dichroism (CD) spectra, while the handedness of the helical conformation in the BCP* is determined from a split-type Cotton effect in vibrational circular dichroism spectra. Microphase separation of the BCP* is exploited to form a helical (H*) phase, and the handedness of helical nanostructure in the BCP* is directly visualized from transmission electron microscopy tomography. As examined by CD and fluorescence experiments, significant induced CD signals and a bathochromic shift of fluorescence emission for the achiral perylene moiety as a chemical junction of the BCPs* can be found while the concentration of the BCPs* in toluene solution is higher than the critical micelle concentration, suggesting a twisting and shifting mechanism initiating from the microphase-separated interface of the BCPs* leading to formation of the H* phase from self-assembly. 相似文献
914.
Hirokazu Oka 《Semigroup Forum》1996,53(1):25-43
In this paper we study mild and classical solutions of the second order linear Volterra integrodifferential equation $$(VE^f )\left\{ {\begin{array}{*{20}c} {u''(t) = Au(t) + {\text{ }}\int_0^t {B(t - s)u(s)ds + f(t){\text{ }}for{\text{ }}t \in [0,T]} } \\ {u(0) = x{\text{ }}and{\text{ }}u'(0) = y,} \\ \end{array} } \right.$$ whereA is a closed linear operator whose domainD(A) is not necessarily dense in a Banach spaceX, and {B(t)|t≥0} is a family of bounded linear operators from the Banach space,D(A) endowed with the graph norm intoX. We also give two examples to illustrate the abstract results. 相似文献
915.
Hirokazu Shimooka Ken-Ichi Yamada Seiji Takahashi Makoto Kuwabara 《Journal of Sol-Gel Science and Technology》1998,13(1-3):873-876
Transparent, partially-crystallized nanostructured barium titanate (BaTiO3) monolithic xerogels (dried at 90°C) have been successfully synthesized via hydrolysis of Ba, Ti alkoxide precursor solutions in a concentration range of 1.0 mol/l with addition of water with a molar ratio of H2O/Ba 6.3. Transparent monolithic xerogels obtained from a precursor solution of 1.0 mol/l remained transparent even after firing at 500°C in oxygen, although the degree of their transparency was considerably decreased. Firing at temperatures above 500°C yielded translucent ceramics of BaTiO3, and ultimately, firing above 600°C resulted in normal opaque ceramic bodies. Those obtained from a more concentrated precursor solution of 1.2 mol/l were, on the other hand, still transparent after firing at 600°C in oxygen, and turned opaque at 700°C. The results demonstrate that the materials retained their transparency even after pyrolysis of organic compounds involving exothermic oxidation at temperatures in the range of 200 to 400°C. The densification behavior of transparent BaTiO3 monolithic xerogels obtained was found to be excellent; for example, those derived from a 1.0 mol/l precursor solution could be sintered to form monolithic BaTiO3 ceramics with a relative sintered density of about 94% and an average grain size of 1 m by firing at 1100°C for 2 h in oxygen. 相似文献
916.
A Yanagida T Kanda T Shoji M OhnishiKameyama T Nagata 《Journal of chromatography. A》1999,855(1):181-190
Oligomeric constituents of apple procyanidins were fractionated by size-exclusion chromatography using a TSKgel Toyopearl HW-40F column. The best separation was obtained using a mobile phase of acetone-8 M urea (6:4; adjusted to pH 2) at a flow-rate of 1.0 ml/min. In this chromatographic system, the use of 8 M urea in the mobile phase resulted in a molecular sieve effect without any surface affinity interaction between the gel beads and the procyanidin molecules. Each fraction obtained was examined by reversed-phase high-performance liquid chromatography and time-of-flight mass spectrometry. The order of elution of the procyanidins from the column was coincident with their degree of polymerization. 相似文献
917.
Micropatterns of the electrically conjugating cardiomyocytes were prepared on a single cell level by microcontact printing (microCP), and the localized chemical stimulations were applied to the cellular pattern using multiple laminar flows. The locally delivered 1-octanol inactivated part of the myocyte patterns, while the other areas retained the activity showing spontaneous and synchronous pulsatility. Since both the cells and flows were well defined as micropatterns and each integrated on a chip, the obtained results simply demonstrate the cellular responses in a single-cell network. 相似文献
918.
Hirokazu Hayashi Hiromichi Hagiya Seong-Yun Kim Yasuji Morita Mitsuo Akabori Kazuo Minato 《Journal of Radioanalytical and Nuclear Chemistry》2013,296(3):1275-1286
Curium was separated and recovered as an oxalate from a Cm–Pu mixed oxide which had been a 244Cm oxide sample prepared more than 40 years ago and the ratio of 244Cm to 240Pu was estimated to 0.2:0.8. Radiochemical analyses of the solution prepared by dissolving the Cm–Pu mixed oxide in nitric acid revealed that the oxide contained about 1 at% of 243Am impurity. To obtain high purity curium solution, plutonium and americium were removed from the solution by an anion exchange method and by chromatographic separation using tertiary pyridine resin embedded in silica beads with nitric acid/methanol mixed solution, respectively. Curium oxalate, a precursor compound of curium oxide, was prepared from the purified curium solution. 11.9 mg of Cm oxalate having some amounts of impurities, which are 243Am (5.4 at%) and 240Pu (0.3 at%) was obtained without Am removal procedure. Meanwhile, 12.0 mg of Cm oxalate (99.8 at% over actinides) was obtained with the procedure including Am removals. Both of the obtained Cm oxalate sample were supplied for the syntheses and measurements of the thermochemical properties of curium compounds. 相似文献
919.
Goto A Zushi H Hirai N Wakada T Tsujii Y Fukuda T 《Journal of the American Chemical Society》2007,129(43):13347-13354
A novel class of living radical polymerizations with germanium, tin, and phosphorus catalysts were developed. The polymerizations are based on a new reversible activation mechanism, Reversible chain Transfer (RT) catalysis. Low-polydispersity (M(w)/M(n) approximately 1.1-1.3) polystyrene, poly(methyl methacrylate), poly(glycidyl methacrylate), and poly(2-hydroxyethyl methacrylate) with predicted molecular weight were obtained with fairly high conversion in a fairly short time. The pseudo-first-order activation rate constant kact for the styrene/GeI4 (catalyst) system was large enough, even with a small amount of GeI4, explaining why the system provides low-polydispersity polymers from an early stage of polymerization. The retardation in the polymerization rate observed for the styrene/GeI4 system was kinetically proven to be mainly due to the cross-termination between the propagating radical with GeI3*. Attractive features of the germanium, tin, and phosphorus catalysts include their high reactivity hence small amounts (1-10 mM) being required under relatively mild conditions (at 60-100 degrees C), high solubility in organic media without ligands, insensitivity to air hence sample preparation being allowed in the air, and minor color and smell. The germanium and phosphorus catalysts may also be attractive for their low toxicity. The phosphorus catalysts may also be attractive for their low cost. 相似文献
920.
Takahiro Ohishi Hirokazu Nanba Masashi Izumida Kohei Mori Makoto Ueda Kenji Inoue 《Tetrahedron letters》2007,48(19):3437-3440
A scalable and cost-effective synthesis of d- and l-α-methylcysteine is described. A key step is d-selective cyclization of N-carbamoyl S-tert-butyl-d,l-α-methylcysteine catalyzed by hydantoinase. d-5-tert-Butylthiomethyl-5-methylhydantoin and N-carbamoyl S-tert-butyl-l-α-methylcysteine were obtained with excellent yield and optical purity, and these compounds were easily separated by filtration. After hydrolysis and cleavage of the tert-butyl group, d- and l-α-methylcysteine hydrochloride were obtained. 相似文献