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排序方式: 共有3413条查询结果,搜索用时 10 毫秒
61.
62.
Thepyrimidinesasaclassareknowntopossessextraordinarybiologicalpropertiesthataregenerallydistinguishedqualitativelybytheirapplicationsinpesticide,herbicide,bactericide,andmedicineinter-mediates犤1犦.Asurveyoftheseapplicationsandanum-beroftherelatedvariationsthataredevelopedrecent-ly,suchastheextraordinaryeffectiveherbicideofsulfonylsulfourea,revealsthebroadbiologicalimpor-tancejustbecauseofthewideoccurrenceofpyrimi-dinesringsystemsinthesemolecules犤2犦.Ithasbeenshownthatthemedicineintermediates… 相似文献
63.
64.
Thermochemical Investigations of the Systems Ti/Ni and Ti/Co By treatment of solid Ni or Co with a H2/TiCl4-gas mixture at sufficient high temperature (T ≥ 900°C) the intermetallic phases TiNi3 and TiCo3, resp., are formed. The conversion grade depends on the H2/TiCl4-ratio. From the experimentally determined conversion grades and the known thermodynamic data of all other species existing in equilibrium the free enthalpies and the heats of formation of TiN3 and TiCo3 have been calculated (TiNi3: ΔH(298) = ?133.3 ± 6 kJ/mol; TiCo3: ΔH(298) = ?104.7 ± 6 kJ/mol). 相似文献
65.
66.
用质谱技术对钾、钙同位素体系特征参数测定的初探 总被引:1,自引:0,他引:1
报道了用FinniganMAT 2 62质谱技术和同位素稀释法测定了光谱纯CaO和国际二级标准Tahiti(CaCO3)的同位素40 Ca 42 Ca比值以及后者的40 Ca含量 ,RSD分别为 0 .0 2 %和 0 .1 %。对国家钾标样的测定表明 :39K、40 K和41 K同位素丰度分别为 0 .93 2 60± 0 .0 0 1 2、0 0 0 0 1 1 2 0± 0 .0 0 0 0 1 2 9和 0 .0 672 86± 0 .0 0 0 1 2 5。其中39K含量为 0 .1 2 1 72± 0 .0 0 0 2 9,与标准值在误差范围内一致。实验测定结果为在我国开展40 K 40 Ca同位素体系的定年和环境的示踪研究打下了基础 相似文献
67.
Jarl Forstén 《Accreditation and quality assurance》1998,3(6):256-257
Confidence in laboratory operations is discussed based on the ongoing revision of the ISO/IEC Guide 25. Confidence is a subjective
attribute, which also depends on whose interest is considered. New and better-defined quality systems and technical elements
will be included, and these are beneficial to the transparency of laboratory operations, as well as to the accreditation process.
The ultimate aim is, of course, to satisfy customers. The testing laboratories' industrial customers are, however, generally
unfamiliar with the ISO/IEC Guide 25 and accreditation. The main reason for improved confidence in testing and calibration
laboratories is foreseen to come from closer interaction between laboratories and their customers. 相似文献
68.
Carmen Luna Concepción Lloreda Juan F. Almagro Bello Jaime Botella Maria J. Orts Ana Gozalbo 《Mikrochimica acta》2004,145(1-4):121-127
Non-metallic inclusions in steel are formed due to interactions between liquid steel and its environment in the melting shop (refractories and slags). Particles not trapped in the slag remain in the cast steel, impairing steel properties in service. Inclusion composition varies and certified standards covering the whole compositional range are unavailable.The present study describes the preparation of a set of homogeneous, glassy and crystalline standards with a wide compositional range for use in analysing non-metallic steel inclusions. For this, materials were designed based on knowledge of the compositional range of interest in the Al2O3–SiO2–CaO–MgO–CaF2 system, which is the matrix of the most frequent steel inclusions. The composition and microstructural homogeneity of the reference materials was verified. 相似文献
69.
Delatour T 《Analytical and bioanalytical chemistry》2004,380(3):515-523
Liquid chromatography–tandem mass spectrometry (LC-MS/MS) is a versatile coupling system which combines both selectivity and sensitivity and certainty. Hence, it is generally considered as the most reliable technique to quantify chemical compounds in complex matrices. In the present paper, we evaluate the performance of LC-MS/MS methods for the quantification of 3-nitrotyrosine in human urine in order to point out its dependence on the design of the quantification method, and emphasize the role of matrix effects in the performance. We compare external and internal calibrations, isotope dilution and isotopomer-based exact matching. The role of both sample preparation and multiple transitions monitoring is particularly addressed. 相似文献
70.
Yu H. G. Yu Dong J. X. Qin C. Q. Liu Y. Qu S. S. 《Journal of Thermal Analysis and Calorimetry》2004,75(3):807-813
The energy of combustion of crystalline 3,4,5-trimethoxybenzoic acid in oxygen at T=298.15 K was determined to be -4795.9±1.3 kJ mol-1 using combustion calorimetry. The derived standard molar enthalpies of formation of 3,4,5-trimethoxybenzoic acid in crystalline
and gaseous states at T=298.15 K, ΔfHm
Θ (cr) and ΔfHm
Θ (g), were -852.9±1.9 and -721.7±2.0 kJ mol-1, respectively. The reliability of the results obtained was commented upon and compared with literature values.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献