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排序方式: 共有128条查询结果,搜索用时 593 毫秒
91.
施国勇 《宁波大学学报(理工版)》1994,(2)
本文用Lie群理论中无穷小变换的延拓方法(Prolongationofinfinitesimaltransformations)推导动力学系统的守恒定律与场的守恒定律。这一方法统一、简洁,避免了应用中推导的繁琐,且便于推广。 相似文献
92.
93.
Wen G Yan J Zhou Y Zhang D Mao L Zhu D 《Chemical communications (Cambridge, England)》2006,(28):3016-3018
The electrode potential of a photochromic spiropyran-modified Au electrode could be reversibly modulated by UV/visible light irradiation in the presence of Zn2+, and a new molecular switch and an "AND" logic gate based on this electronic transduction of the optical signals were established. 相似文献
94.
Guoyong Song Xingwei Li Prof. Dr. Zhongcheng Song Jing Zhao Prof. Dr. Hongjie Zhang Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(22):5535-5544
Phosphine‐assisted C? H activation of the methyl group of 2‐methylimidazolium compounds led to a series of iridium, rhodium, and palladium complexes of 2‐methyleneimidazolines. Experimental results confirmed that the product of methyl C? H activation is the kinetic product, whereas the aryl C? H activation product is the thermodynamic product (see scheme).
95.
We propose a simple dual-wavelength Er-doped fiber laser configuration based on a dual-wavelength fiber Bragg grating written on the splice joint between two different fibers for wavelength-selective filter in the Sagnac loop interferometer. The wavelength separation between the adjacent lasing wavelengths is 1.12 nm and the side-mode suppression ratio (SMSR) is over 55 dB. The output power variation is less than 0.8 dB over a two-minute period. Moreover, the lasing wavelength can be effectively tuned using the thermal heating method. 相似文献
96.
从理论上设计并从实验上实现了一种简单易行的环形谐振腔结构,它仅由两个耦合器连接成一个环形谐振腔,可以使得逆时针运行光的增益高于顺时针运行光的增益,其比值取决于两个耦合器耦合比的选取。将此作为掺铒光纤激光器的谐振腔,由于两个相反方向具有不同的损耗,因而可以实现在不需要隔离器的情况下也能保证激光的单向运行,从而简化了器件结构,消除隔离器的插入损耗,降低了成本。在实验的过程中使用两个3dB耦合器,结果表明,在阈值及其以上抽运功率下,两个相反方向的输出功率差始终大于17dBm,基本实现了激光的单向运行。 相似文献
97.
Guoyong Luo Zhijian Huang Shitian Zhuo Chengli Mou Jian Wu Zhichao Jin Yonggui Robin Chi 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(48):17349-17353
Disclosed herein is a new catalytic approach for an efficient access to cyclic β‐amino acids widely found in bioactive small molecules and peptidic foldamers. Our method involves addition of the remote γ‐carbon atoms of α,β‐unsaturated imines to enals by iminium organic catalysis. This highly chemo‐ and stereo‐selective reaction affords cyclic β‐amino aldehydes that can be converted to amino acids bearing quaternary stereocenters with exceptional optical purities. Our study demonstrates the unique power of organic catalytic remote carbon reactions in rapid synthesis of functional molecules. 相似文献
98.
Shuquan Wu Changyi Liu Guoyong Luo Zhichao Jin Pengcheng Zheng Yonggui Robin Chi 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(51):18581-18584
An N‐heterocyclic carbene (NHC)‐catalyzed reaction between α‐bromoenals and 2‐aminoaldehydes has been developed. Key steps include chemoselective reaction of the NHC catalyst with one of the aldehyde substrates (the bromoenal) to eventually generate an α,β‐unsaturated acylazolium intermediate. Addition of the nitrogen atom of aminoaldehyde to the unsaturated azolium ester intermediate followed by intramolecular aldol reaction, β‐lactone formation, and decarboxylation leads to chiral dihydroquinolines with high optical purity. The dihydroquinoline products, which are quickly prepared by using this method, can be readily transformed into a diverse set of functional molecules such as pyridines and chiral piperidines. 相似文献
99.
室温下稳定的多波长掺铒光纤激光器的研究 总被引:10,自引:4,他引:6
通过在线形谐振腔中引入一段缠绕在压电陶瓷上的单模光纤作为正弦相位调制器,使得激射波长的损耗不固定,抑制由于掺铒光纤的均匀展宽效应引起的模式竞争,从而避免了在室温下不稳定的单波长激射,实现了多波长掺铒光纤激光器的稳定输出。为了获得平坦的多波长输出,在谐振腔里使用了一个损耗峰位于1530nm处的长周期光纤光栅,以获得较为平坦的增益谱。通过两个3dB耦合器制成的反射型梳状滤波器的滤波作用,实验中观察到稳定的多波长激射,相邻波长间隔约为0.45nm。中心9个波长的输出功率平坦度为10dB,边模抑制比大于25dB。 相似文献
100.
JIN Guoyong YANG Tiejun LIU Zhigang JI Zhenlin LIWanyou 《声学学报:英文版》2007,26(2):138-157
The structural-acoustic coupling characteristics, mechanisms, effect of structural-acoustic coupling on natural mode and natural frequencies of the system are analyzed theoretically and numerically. Formulae for the natural frequencies of the coupled system are derived. Some new conclusions are obtained. Analytical results demonstrate that the strongly coupled system indicates obvious closed-loop feedback characteristics, whereas the weakly coupled system indicates obvious feedforward characteristics, and it is because of the presence of the feedback loop that the natural characteristics and natural frequencies are changed. Cluster coupling characteristic between the structural and acoustic modes for the regular cavity and panel system is found, which determines the coupling interaction between the flexible panel and cavity. Any mode in one mode cluster only interferes the modes and the modal natural frequencies in the same cluster independently. The modal cluster coupling changes not only the natural frequencies of the system but also the modal order and structural mode shape. 相似文献