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本文介绍一种采用阻抗自调控限流电路的CO2激光器电源,它可使CO2激光器的输出激光功率从零到满功率大范围连续可调,能得到小纹波甚至无纹波的激光束. 相似文献
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基于股票换手率的市场时机与外部融资方式选择研究——来自中国A股上市公司的经验证据 总被引:1,自引:0,他引:1
市场时机资本结构理论认为企业在股票价格高估时发行股权融资,低估时选择回购股票或发行债务融资,当前资本结构是企业过去融资发行市场时机的累积结果.目前的实证研究主要基于市值账面比(M/B)指标作为市场时机代理变量,然而这一指标引起学者们很大争议,研究结论缺乏可靠性.本文根据我国资本市场实际特征选择股票换手率作为市场时机代理变量,实证检验了市场时机与外部融资方式选择的关系,以及对资本结构动态变动的综合影响.研究结论显示,换手率在企业权益融资中具有重要作用,换手率较高时企业选择发行更多的股权融资.并对资本结构变动具有显著的负向影响.这表明我国上市公司确实存在着融资选择的市场时机效应. 相似文献
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Heteroepitaxial LaAlO3 films were grown on a SrTiO3/Si (100) substrate by laser molecular beam epitaxy under different oxygen pressures, and their properties such as crystallinity and electrical characteristics were experimentally investigated using the various measurement methods. The results show that most properties depend mainly on the deposition oxygen pressure. The crystallinity and the C-V and I-V characteristics can be greatly improved with the increasing oxygen deposition pressure. Moreover, after annealed at 1050~C in N2 ambient, the C-V and I-V characteristics of LAO films deposited at the lower oxygen pressure are also improved due to the decrease of oxygen vacancies in LAO films. 相似文献
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本文介绍半波倍压和全波整流复合及全波倍压和全波整流复合两种新型的直流电源电路.该电路具有全波整流电路和倍压电路的共同特性,用它不仅可装成适合气体放电特性等特殊要求的电源,而且用此两种电路对维修某些电器设备与仪器也是简便实用的. 相似文献
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We report on the photovoltaic properties of Lao.7Sro.3MnO3//ZnO heterojunction fabricated by pulsed laser deposition methods. Nanosecond photovoltaic pulses are observed in this junction in the wavelength range from ultraviolet-visible to infrared. A qualitative explanation is presented, based on an analysis of the photovoltaic signals of p-n heterojunction. 相似文献
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