排序方式: 共有9条查询结果,搜索用时 15 毫秒
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目的:连续多年监测彭州敖平镇川芎药材栽培土壤中重金属镉的含量,分析其对川芎药材中镉含量的影响。方法根据前期研究结果选取敖平镇部分川芎种植地固定采集样品。按照国家标准方法,采取0~20 cm连续根系土柱和川芎药材。采用火焰法对抽样土壤及川芎药材中镉的含量进行检测分析。结果采样区域内土壤中镉含量均符合国家二级土壤环境质量标准;部分土壤中镉的含量呈明显增长趋势。结论川芎种植土壤中镉含量与环境有较高关联,水泥厂粉尘等污染源是土壤中镉含量增加的重要来源。 相似文献
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川芎中有毒重金属元素镉含量超过国家GAP标准,严重影响其出口创汇,也成为制约川芎走向现代化和国际化的瓶颈。介绍了目前对川芎的消化及重金属元素镉的检测方法,并对各方法的利弊进行了分析,从而为准确、高效地检测药材中重金属元素镉的含量提供了有力的参考依据。 相似文献
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In this study, we design periodic grille structures on a single homogenous thin plate to achieve anisotropic acoustic metamaterials that can control flexural waves. The metamaterials can achieve the bending control of flexural waves in a thin plate at will by designing only one dimension in the thickness direction, which makes it easier to use this metamaterial to design transformation acoustic devices. The numerical simulation results show that the metamaterials can accurately control the bending waves over a wide frequency range. The experimental results verify the validity of the theoretical analysis. This research provides a more practical theoretical method of controlling flexural waves in thin-plate structures. 相似文献
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Transformation acoustics are concentrated for the purpose of designing novel acoustic devices to tailor acoustic waves to achieve desirable characteristics. However, these devices require fluid or fluid-like materials with an anisotropic density that generally does not exist in nature. Therefore, we introduce pentamode metamaterials into an alternating multilayer isotropic medium model to build fluid-like metamaterials with an anisotropic density. A 2D acoustic bending based on transformation acoustics is established and investigated to verify our method. This idea provides a method to design broadband and physically realizable acoustic metamaterials with an anisotropic density and is meaningful for the design of acoustic metamaterials. 相似文献
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应用量子主方程理论研究量子点-微腔耦合系统的激射性质.分别探索了不同类型的微腔耦合系统("好的系统"、"中等系统")在外加泵浦场的作用下表现出的激射现象.分析比较了失谐大小及环境纯消相干对这两种微腔耦合系统的内部特性(光场分布、腔内光子数等)产生的影响.数值仿真表明:对于"好的系统",在失谐量不大的情况下,引入适当的纯消相干有利于提高耦合系统的激射性能;对于"中等系统",由于失谐条件下光子在腔内集聚困难,因而很难达到激射,但是通过引入适量的纯消相干可以对腔内光场分布和光子数产生剧烈调制作用.该结果对于研究单量子点激光器,以及探索光与物质相互作用等方面具有指导作用. 相似文献
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