排序方式: 共有32条查询结果,搜索用时 33 毫秒
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关于流体力学的教学体会刘国强(广州市卫生学校510180)目前,医学物理学在世界上已经发展成为一门独立的边缘科学了,而我们卫生学校,采用的物理学教材,与医学联系很少,面对这种情况,究竟应如何上好医科学生的物理课呢?很值得探讨.医科学校的物理教学,只有... 相似文献
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以硝酸锌和对苯二甲酸为反应物,N,N′-二甲基甲酰胺(DMF)为溶剂,用溶剂热法合成出结构稳定的对苯二甲酸-锌配位化合物(MOF-L)。并采用XRD、TG、低温N2吸附等测试手段对合成的MOF-L进行了表征。结果表明,样品的孔径分布均呈双峰型,孔结构主要由孔径小于1 nm的微孔和少量1.5~2.0 nm的超微孔组成,且小于0.7 nm的极微孔丰富;其表面在极微孔和超微孔范围存在两种吸附位。300 ℃煅烧的样品,Langmuir比表面积和单点总孔容分别为1 243 m2·g-1和0.46 cm3·g-1,在77 K、1.0 bar时的储氢容量为1.3wt%。400 ℃煅烧后,骨架扭曲坍塌,Langmuir比表面积、总孔容及储氢容量分别下降为1 113 m2·g-1、0.43 cm3·g-1和0.8wt%。 相似文献
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The two models of three-level (one upper level and two lower levels, or two upper levels and one lower level) atom embedded in a double-band photonic crystal are adopted. The atomic transitions from the upper levels to the lower levels are assumed to be coupled by the same reservoir which are respectively the isotropic photonic band gap (PBG) modes, the anisotropic PBG modes and the free vacuum modes. The effects of the fine structure of the atomic ground state levels in the model with one upper level and two lower levels, and the quantum interferences in the model with two upper levels and one lower level on the spontaneous emission spectrum of an atom are investigated in detail. Most interestingly, it is shown that new spontaneous emission lines are produced from the fine splitting of atomic ground state levels in the isotropic PBG case. The quantum interferences induce additional narrow spontaneous lines near the transition from the empty upper level to the lower level. 相似文献
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《电磁感应》一课的备课设计刘国强(广州市卫生学校510180)备课是教师进行教学工作的一个重要环节,是提高教学质量,实现教学目的的基础和保证.要上好课,先要备好课.备课主要做到五备:备教材、备学生、备教具、备教法、备习题.下面就《电磁感应现象、楞次定... 相似文献
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建立了亲水作用色谱-串联四极杆质谱测定乳及乳制品中左旋肉碱的分析方法。样品经2%(v/v)乙酸水溶液提取、乙腈沉淀蛋白质净化,以乙酸铵和乙腈为流动相,经Acquity UPLC BEH HILIC色谱柱分离后采用电喷雾质谱多反应监测(MRM)方式扫描,外标法定量。结果表明,左旋肉碱的质量浓度在1~100 μg/L范围内线性关系良好(r2> 0.99),定量限为0.01 mg/kg。标准加入法测定左旋肉碱在高、中、低3个加标水平的回收率为96.0%~103.4%,相对标准偏差(RSD)为1.2%~4.3%。该方法前处理简单、快速,检测结果准确、灵敏,可为各类乳及乳制品中左旋肉碱的含量水平测定、研究和控制提供技术支持。 相似文献
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汉麻杆基活性炭表面织构与储氢性能的研究 总被引:2,自引:0,他引:2
以天然汉麻杆为原料,采用KOH化学活化的方法改变活化时间制备出了高比表面积活性炭,并且对其表面进行硝酸氧化处理,研究活性炭表面化学状态对其吸附性能的影响。采用77 K低温氮气吸附和FTIR对样品进行了表征,并在77 K、100 kPa的条件下测定样品的氢气吸附等温线。结果表明,所有样品具有较高的比表面积(2 435.93~3 240.95 m2·g-1)和总孔容(1.3~1.98 cm3·g-1),且随活化时间的延长而增加,3.5 h达到最大值,之后由于骨架坍塌有所减小。所有样品的孔径分布较为一致呈多峰型分布,主要以小于2 nm的微孔为主,同时含有少量的中孔和大孔。活化3.5 h样品的吸氢量最大,达到3.28wt%。研究发现,吸氢量受比表面积和孔容等参数影响较大,77 K下不仅小于2 nm的微孔对活性炭吸氢行为贡献较大,中孔也有十分重要的影响。样品经硝酸氧化处理后,BET比表面积和总孔容均在一定程度上减小,而氢气吸附量也有所降低。 相似文献
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Conductivity reconstruction algorithms and numerical simulations for magneto–acousto–electrical tomography with piston transducer in scan mode
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Conductivities tomography with the interactions of magnetic field, electrical field, and ultrasound field is presented in this paper. We utilize a beam of ultrasound in scanning mode instead of the traditional ultrasound field generated by point source. Many formulae for the reconstruction of conductivities are derived from the voltage signals detected by two electrodes arranged somewhere on tissue's surface. In a forward problem, the numerical solutions of ultrasound fields generated by the piston transducer are calculated using the angular spectrum method and its Green's function is designed approximately in far fields. In an inverse problems, the magneto-acousto-electrical voltage signals are proved to satisfy the wave equations if the voltage signals are extended to the whole region from the boundary locations of transducers. Thus the time-reversal method is applied to reconstructing the curl of the reciprocal current density. In addition, a least square iteration method of recovering conductivities from reciprocal current densities is discussed. 相似文献