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991.
The chiral binaphthol-derived titanium perchlorate (or triflate) is shown to serve efficiently as an asymmetric catalyst for the ene cyclization of type {3,4exo,exo} and {2,4exo′,exo} involving -alkoxy aldehyde as an internal enophile to afford the 6- and 7- membered cyclic ethers in high enantiomeric purity. 相似文献
992.
Hajime Takayama 《Zeitschrift für Physik A Hadrons and Nuclei》1973,263(4):329-340
Making use of the theory for the phonon damping in an impure metal developed recently by Eisenriegler, we study the interaction between electrons and long wave-length longitudinal phonons, and its effects on electronic properties at low temperatures. On account of the inelastic scattering of electrons by impurity ions, a minimum in the electrical resistivity is found when plottedvs temperature, although its value is extremely small. 相似文献
993.
994.
Kitaoka Y Kasazumi K Morikawa A Yokoyama T Sugita T Mizuuchi K Yamamoto K Takayama T Takigawa S Yuri M 《Optics letters》2003,28(11):914-916
We have demonstrated wavelength stabilization in an 821-nm AlGaAs three-section tunable distributed Bragg reflector (DBR) semiconductor laser diode (LD) that consists of active, phase-controlled, and DBR regions. We injected two separate, complementary currents into the active and the phase-controlled regions in the DBR-LD to suppress wavelength shift. This modulation method was applied to the LD fundamental wave in a second-harmonic-generation (SHG) laser, and the oscillating wavelength was maintained within the phase-matching acceptance range of the SHG device during modulation. A peak blue-violet light power of 62 mW was obtained for the ideal modulation waveform. 相似文献
995.
We apply the ab initio spin density functional theory to study magnetism in all-carbon nanostructures. We find that particular systems, which are related to schwarzite and contain no undercoordinated carbon atoms, carry a net magnetic moment in the ground state. We postulate that, in this and other nonalternant aromatic systems with negative Gaussian curvature, unpaired spins can be introduced by sterically protected carbon radicals. 相似文献
996.
Eiji?YamadaEmail author Takashi?Kusaka Kensaku?Miyamoto Satoshi?Tanaka Shin?Morita Shouichi?Tanaka Yongping?Cao Satoshi?Mori Hiromichi?Norimatsu Susumu?Itoh 《Optical Review》2003,10(5):436-439
The purpose of this study was to investigate the relationships of rate of deoxygenation determined using near-infrared spectroscopy (NIRS) during isometric contraction exercise (Ratedeoxy) with maximal muscle strength, muscle thickness and muscle oxidative capacity of knee extensors in eight well-trained male athletes. The subjects performed sustained isometric extension at 30% and 50% of the maximal voluntary contraction (MVC) load for 10s and 30 repetitive maximal isokinetic knee extensions. Ratedeoxy in the final 5s of 30% MVC was negatively correlated with maximal muscle strength, muscle thickness of knee extensors and the half-time of deoxygenation recovery (T1/2) determined by NIRS after 30 repetitive maximal isokinetic contractions, defined as muscle oxidative capacity. The results suggest that Ratedeoxy during submaximai isometric contraction reflects muscle aerobic capacity. 相似文献
997.
998.
[reaction: see text] Efficient and practical synthesis of a variety of 1-iodo-4-trimethylsilylbut-1-en-3-yne derivatives with trans- and cis-olefinic configuration, and their repeated use as building blocks for the synthesis of trans- and cis-oligoenynes, respectively, are described. 相似文献
999.
Keisuke Kurita Masahiro Yamakawa Keiji Iida Eiji Susa Yoshiyuki Koyama 《Journal of polymer science. Part A, Polymer chemistry》1989,27(13):4297-4303
A procedure for synthesizing an open-chain polyimide has been developed. O-Substituted hydroxylamines were found to behave as difunctional nucleophiles in acylation under appropriate conditions, and thus the reaction of equimolar amounts of benzyloxyamine and terephthaloyl chloride gave rise to the corresponding novel type of polyimide, an open-chain polyimide. The results of polymerization under various conditions indicated the reaction to proceed efficiently in N, N-dimethylacetamide in the presence of an acid acceptor system composed of double the molar quantity of triethylamine and the molar quantity of pyridine to give the polyimide with a high molecular weight. In contrast to the conventional polyimides having cyclic imide structures, the resulting open-chain polyimide exhibited remarkable solubility in common organic solvents and a low glass transition temperature. 相似文献
1000.