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排序方式: 共有193条查询结果,搜索用时 156 毫秒
51.
Xi Z Zhang WX Song Z Zheng W Kong F Takahashi T 《The Journal of organic chemistry》2005,70(22):8785-8789
[reaction: see text] Vinyl allenes were prepared in high yields by the Wittig-Horner reaction of 1-lithio-1,3-dienyl phosphine oxides with aldehydes. 1-Lithio-1,3-dienyl phosphine oxides were generated in situ from lithiation of 1-iodo-1,3-dienyl phosphine oxides, which were obtained by iodination of alpha-phosphinozirconacyclopentadienes. As a whole, a vinyl allene is synthesized from two different alkynes and one aldehyde. 相似文献
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53.
We report the synthesis of nanostructured copper compound films on a copper surface under mild conditions. A series of low-dimensional structures including Cu(OH)(2) fibers and scrolls, CuO sheets and whiskers, and Cu(2)(OH)(2)CO(3) rods have been successfully grown on the copper surfaces at ambient temperature and pressure. Most of the structures are phase-pure single crystallites. The films were formed by the direct oxidation of copper in aqueous solutions of NaOH with an oxidant (NH(4))(2)S(2)O(8). The evolution of the ultrafine structures as a function of the reaction conditions has been revealed, from fibers of Cu(OH)(2) to scrolls of Cu(OH)(2) to sheets or whiskers of CuO. By replacing NaOH with NaHCO(3) in the synthesis, square/rectangular rod arrays of Cu(2)(OH)(2)CO(3) were obtained. The controlled reactions allow the large-scale, template-free, cost-effective synthesis of copper compound films with ordered, uniform, stable, ultrafine structures. 相似文献
54.
The hydrozirconation reaction of 1-alkynyl sulfoxides or sulfones with Cp2Zr(H)Cl in THF at room temperature predominantly gave Z-beta-zirconated vinyl sulfoxides or sulfones with excellent regioselectivity. Compared with 1-alkynyl sulfoxides, the hydrozirconation reaction of 1-alkynyl sulfones exhibits great synthetic potential, leading to the efficient preparation of Z-beta-halovinyl sulfones, Z-beta-sulfonyl alpha,beta-unsaturated ketones, and Z-beta-alkynyl vinyl sulfones. Although the reaction mechanisms are still not clear, the neighboring group participation of the sulfinyl or sulfonyl group may be playing an important role in this unique hydrozirconation reaction. 相似文献
55.
Γ-环和广义Γ-环的强幂零性 总被引:1,自引:1,他引:0
In this paper, we study the strongly nilpotency of Γ-rings and generalized Γ-rings.(Ⅰ) With what conditions is a strongly nil subring of Γ-rings strongly nilpotent?(Ⅱ) With what conditions is a nil subring of Γ-rings strongly nilpotent?For(Ⅰ), the condition is one of the following conditions:(1) ascending chain condition on the- strongly nilpotent subrings.(2) Noether's condition.(3) Goldie's condition.(4) ascending chain condition on right annihilators and on left annihilators. For(Ⅱ), the conditions is (2) or (3). In order that the above results may contain the corresponding results of associative rings, a new concept, generalized Γ-ring is introduced, so that any associative ring is naturally explained as a generalized Γ-ring. It is proved that the above results are valid in generalized Γ-rings. Thence the well-known results of associative rings are special cases in generalized Γ-rings. 相似文献
56.
57.
本文提出了有限条塑性系数增量初应力法,用于分析钢压杆的弹塑性稳定极限承载力,该法采用分级加载,用有限条法建立结构的增量平衡方程;在塑性范围,引入截面的塑性系数对弹性刚度进行折减得到结构的弹性刚度矩阵;用修正的Newto-Raphson方法迭代求解,数值结果表明,本法效率较高,与钢压杆试验结果吻合良好,可以考虑残余应力和载荷偏心的影响,可望实现大型超静定结构的极限载力分析。 相似文献
58.
An improved solid-state reaction route has been employed to synthesize Mg2+-doped LiFePO4/C nanocomposite cathode by calcining the precursor obtained via evaporating the mixture of ascorbic acid, LiCH3COO·2H2O, Mg(CH3COO)2·4H2O, and amorphous FePO4 nanoparticles in anhydrous ethanol under continuous stirring. Ascorbic acid used here acted as both reducing agent and carbon source. The amorphous FePO4 was pre-prepared via a simple and fast oxidic precipitation method. Electrochemical tests showed that the final product exhibited good rate and cycling performance, with discharge capacities of 145.2 mAh g?1 at 0.2 C, 129.8 mAh g?1 at 1 C, 107.6mAh g?1 at 5 C, and 81.4 mAh g?1 at 20 C, respectively. The Mg2+-doped LiFePO4/C showed enhanced charge–discharge performance compared with undoped LiFePO4/C, especially at high rates. The enhanced electrochemical performance of the composite could be attributed to a combination result of the fine particle size with narrow particle size distribution, homogeneous carbon coating on the surface of the particles, and magnesium ion doping. 相似文献
59.
Hierarchical Fe5(PO4)4(OH)3·2H2O microflower was synthesized by a hydrothermal reaction with self-prepared β-FeOOH nanorod as raw material. The microflowers were self-assemblies of symmetric building blocks with deep grooves. The possible morphology evolution process was proposed. The microflowers morphology was retained when they were lithiated to prepare LiFePO4/C composites through a carbothermal reduction method with citric acid as both reducing agent and carbonaceous coating conductor source. As cathode materials for lithium ion batteries, the as-obtained LiFePO4/C composites deliver a high discharge capacity of 156 mAh g?1 at 0.1 C rate and exhibit excellent cycling stability, which may be ascribed to the homogeneous coated carbon and the unique microflower structure with grooves. 相似文献
60.
Dandan Li Rui Xue Zhixiong Li Mingcang Chen Weixin Jiang Chenggang Huang 《Chromatographia》2014,77(11-12):853-858
Timosaponin BIII, as one of the steroid saponins isolated from Anemarrhena asphodeloides Bge., was proved to have many pharmacological activities in recent years and became a natural active compound with good development prospect. In the present study, a simple and rapid method using high-performance liquid chromatography/quadrupole-time-of-flight mass spectrometry was developed for the determination of the structures of timosaponin BIII and its metabolites in rats after administrating intragastrically at 300 mg kg?1. By comparing their changes in molecular masses (ΔM), retention times and spectral patterns with those of the parent compound, nine metabolites were detected and identified in urine, and eight in plasma as well as four in brain. It is also indicated that the deglycosylation and oxidation reactions were the main metabolic pathways in the biotransformation of timosaponin BIII in vivo and the structures of the nine metabolites were identified and proposed to be timosaponin BII(M1), the hydroxylated metabolite of TBII(M2), the hydroxylated metabolites of TBIII(M3 and M4), deglycosylation and monooxygenation product of TBIII(M5), the deglycosylation product of TBII(M6), timosaponin AIII(M8), the isomers of timosaponin AIII(M7 and M9). 相似文献