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大叶白麻叶化学成分的研究 总被引:1,自引:0,他引:1
从大叶白麻[poacynumhendersonii(Hookf)woodson]叶中分得2个木脂素类化舍物,经理化常数测定和光谱分析,分别鉴定为(-)-丁香脂素[(-)-Syringaresino1]和( )-松脂素-4-O-β-D-葡萄糖甙[( )-Pinoresionol-4-0-β-D-glucopyranoside]. 相似文献
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卫星导航设备时延精密标定方法与测试技术研究 总被引:1,自引:0,他引:1
分析和研究了卫星导航设备时延标定的方法,并针对卫星导航设备时延的特点,提出卫星导航设备时延应用统计量和稳定性来表征,并提出了基于射频采样和软件无线电的精密设备时延测量方法(RFSR),能够准确地分析设备时延和设备时延的稳定性,通过仿真分析验证了方法正确性;通过建立试验验证系统,对可编程延迟线、电缆等设备的模拟测量,验证了该方法的正确性和优越性. 相似文献
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Carbon nanotubes can act as electron sources with very rigid structures, making them particularly interesting for use as point electron sources in high-resolution electron-beam instruments. Promising results have been reported with respect to some important requirements for such applications: a stable emitted current and a long lifetime. Two parameters of an electron source affect the resolution of these instruments: the energy spread of the emitted electrons and a parameter called the reduced brightness, which depends on the angular current density and the virtual source size. Several authors have measured a low energy spread associated with electron emission. Here we measure the reduced brightness, and find a value that is more than a factor of ten larger than provided by state-of-the-art electron sources in electron microscopes. In addition, we show that an individual multi-walled carbon nanotube emits most current into a single narrow beam. On the basis of these results, we expect that carbon nanotube electron sources will lead to a significant improvement in the performance of high-resolution electron-beam instruments. 相似文献
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