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This paper mainly introduces the role of isotopes in exploring the origin of life and related principles. In addition, by reviewing the discovery history of isotopes and summarizing the contributions of major scientists, we hope to show the general process of science developments to the public. 相似文献
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Optical windows with external surfaces shaped to satisfy operational environment needs are known as special windows. A novel special window, a sphere-cone-polynomial (SCP) window, is proposed. The formulas of this window shape are given. An SCP MgF2 window with a fineness ratio of 1.33 is designed as an example. The field-of-regard (FOR) angle is ±75°. From the window system simulation results obtained with the calculated fluid dynamics (CFD) and optical design software, we find that compared to the conventional window forms, the SCP shape can not only introduce relatively less drag in the airflow, but also have the minimal effect on imaging. So the SCP window optical system can achieve a high image quality across a super wide FOR without adding extra aberration correctors. The tolerance analysis results show that the optical performance can be maintained with a reasonable fabricating tolerance to manufacturing errors. 相似文献
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本文综述了稀土金属离子与一系列氨基多羧酸配体(如nta(=氨基三乙酸),edta(=乙二胺四乙酸),cydta(=反式-1,2-环己二胺四乙酸),dtpa(=二乙三胺五乙酸)和ttha(=三乙四胺六乙酸)等)形成配合物的分子结构和晶体结构,发现了这些配合物的配位规律和结构变化,说明了稀土金属离子象其它过渡金属离子一样,与氨基多羧酸配体形成配合物的配位数和配位结构取决于稀土金属离子的离子半径,电子结构和配体形状以及配电离子等。 相似文献
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The crystal and molecular structures of K3[TbIII(nta)2(H2O)](5.5H2O (nta = nitrilotriacetic acid) and K3[YbIII(nta)2](5H2O complexes have been determined by single-crystal Xray structural analyses. Because TbIII and YbIII have different ionic radii and electronic configura- tions, they take nine- and eight-coordinate structures with two nta ligands, respectively. The crystal of K3[TbIII(nta)2(H2O)](5.5H2O belongs to orthorhombic, space group Pccn with a = 1.6374(7), b = 1.9913(8), c = 1.5068(6) nm, V = 4.913(3) nm3, Z = 8, Mr = 769.54, Dc = 2.081 g/cm3, μ= 3.476 mm-1 and F(000) = 3048. The final R and wR are 0.0432 and 0.0916 for 4961 observed reflections (I > 2.0(σI)), and 0.0814 and 0.1042 for all 21921 reflections, respectively. The [TbIII(nta)2(H2O)]3- complex anion has a nine-coordinate pseudo-monocapped square anti-prismatic structure, in which two N and six O coordinated atoms are from two nta ligands and the left ninth O atom from one water molecule. The crystal of K3[YbIII(nta)2]·5H2O is of monoclinic, space group P21/c with a = 1.5579(5), b = 0.9981(3), c = 1.5956(5) nm, β = 109.776(5), V = 2.3348(13) nm3, Z = 4, Mr = 756.62, Dc = 2.153 g/cm3, μ= 4.624 mm-1 and F(000) = 1484. The final R and wR are 0.0253 and 0.0657 for 4123 observed reflections (I > 2.0(σI)), and 0.0320 and 0.0731 for all 9414 reflections, respectively. The [YbIII(nta)2]3- complex anion has an eight-coordination structure with a distorted square antiprismatic prism, in which each nta acts as a tetradentate ligand with one N atom from the amino group and three O atoms from the carboxylic groups. 相似文献
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近红外光谱法直接检测甜叶菊叶片甜菊糖苷模型建立 总被引:1,自引:0,他引:1
使用近红外光谱技术直接扫描甜叶菊干叶片,建立了甜菊苷(stevioside,ST)和莱鲍迪苷A(rebaudioside A,RA)的检测模型。对甜菊苷含量在0.27%~1.40%,莱鲍迪苷A含量在0.61%~3.98%范围内的不同品种的甜叶菊干叶片进行了近红外光谱扫描,共扫描了105份。采用偏最小二乘法建立甜菊糖苷的检测模型,比较了减去一条直线、多元散射校正、一阶导数和二阶导数等不同的光谱预处理方法对模型的影响。结果显示减去一条直线的数据预处理方法为ST的最优建模方法。ST校正集相关系数为0.986,校正均方根误差为0.341,预测均方根误差为1.00,相对分析误差为2.8;RA采用无光谱预处理建模,RA的建模结果相关系数为0.967,校正均方根误差为1.50,预测均方根误差为1.98,相对分析误差为4.17。说明近红外光谱技术检测甜叶菊干叶片中ST和RA的含量具有一定的可行性。同时与甜叶菊粉末ST模型结果相关系数为0.986,校正均方根误差为0.32,预测均方根误差为0.601,相对分析误差为2.86和RA模型结果相关系数为0.968,校正均方根误差为1.50,预测均方根误差为1.48,相对分析误差为4.2相比差异不明显。但减少了叶片粉末检测过程中的烘干、研磨的步骤,节省了时间,降低了工作量。 相似文献
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