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排序方式: 共有1236条查询结果,搜索用时 343 毫秒
1.
目的建立超高效液相色谱-串联质谱法同时测定糕点中6种常用合成甜味剂的分析方法。方法选用超纯水作为提取溶剂,涡旋和超声提取后,低温离心,取部分上清液加入正己烷除脂,Waters Atlantis■T3色谱柱、甲醇-5 mmol/L甲酸铵(含0.1%甲酸)作为流动相、亲水亲脂平衡型固相萃取柱HLB(hydrophile-lipophile balance)净化。结果6种甜味剂在质量浓度为10~200 ng/mL的曲线范围内呈良好线性关系,相关系数r均大于0.999,平均加标回收率在85.0%-98.2%之间,相对平均偏差(relative standard deviation,RSD)为1.3%~6.7%。结论该方法具有前处理简单、灵敏度高、检测速度快等优点,适合糖精钠、甜蜜素、三氯蔗糖、阿斯巴甜、阿力甜、纽甜的检测,但不适用于安赛蜜的检测。 相似文献
2.
《Journal of the European Ceramic Society》2020,40(12):3824-3828
Reactive hot pressing was utilized to synthesize and densify four ZrB2 ceramics with impurity contents low enough to avoid obscuring the effects of dopants on thermal properties. Nominally pure ZrB2 had a thermal conductivity of 141 ± 3 W/m K at 25 °C. Additions of 3 at% of Ti, Y, or Hf decreased the thermal conductivity by 20 %, 30 %, and 40 %, respectively. The thermal conductivity of (Zr,Hf)B2 was similar to ZrB2 synthesized from commercial powders containing the natural abundance of Hf as an impurity. This is the first study to demonstrate that Ti and Y additions decrease the thermal conductivity of ZrB2 ceramics and report intrinsic values for thermal conductivity and electrical resistivity of ZrB2 containing transition metal additions. Previous studies were unable to detect these effects because the natural abundance of Hf present masked the effects of these additions. 相似文献
3.
在第一部分综合讨论的基础上对甘三酯立体专一分析方法作了初步探讨。以液体油(菜油)及固体脂(猪脂)为基质,系统地研究了这一分析方法,取得了经验并补充了一些具体验证方法。分析液体油的结果与文献数据相一致,分析猪脂的结果欠佳,还存在一些问题需待进一步研究。 相似文献
4.
C R Chakravorty 《Bulletin of Materials Science》1994,17(6):733-745
Magnesium-lithium alloys are among the lowest density metallic materials. Addition of lithium, with a relative density of
0·53, in magnesium reduces the density of the alloy significantly. Furthermore, addition of nearly 11 wt.% lithium converts
hexagonal close packed structure of pure magnesium to a body centered cubic lattice, markedly improving formability of the
alloy. The development of these alloys, however, had been hampered due to the high reactivity of lithium and magnesium in
the molten state and also, due to poor creep resistance and instability of mechanical properties at room temperature. In an
attempt to indigenize these ultra light alloys for possible applications in Indian satellite programme, detailed research
work was initiated in DMRL. The difficulties associated with producing sound cast ingots have been overcome by controlling
melting and casting parameters of these alloys. Extensive work has been done on structure-property correlation of alloys with
varying lithium content and minor alloying additions. Based on these work, advanced magnesium-lithium alloys have been developed
with improved tensile properties, room temperature stability and creep resistance. Wrought products (plates/sheets) of magnesium-lithium
alloy have been supplied to ISAC, Bangalore and are being used in their INSAT-2 programme. This paper describes the systematic
studies carried out in the laboratory to indigenize these ultra light alloys. 相似文献
5.
超宽带无线通信技术概述 总被引:3,自引:0,他引:3
主要介绍了超宽带(UWB)无线通信技术的起源、概念及其基本工作原理,包括信号产生、系统构成、天线、接收机、调制方式等,阐述了UWB中的关键技术及性能特点,对UWB的局限性作了简要的介绍。 相似文献
6.
宽带被动导引头天线系统性能分析 总被引:2,自引:1,他引:1
详细讨论了宽带被动导引头中的关键部件-超宽频带天线的性能,并在此基础上分析了三种具备大视角特性的被动测角方法。由于宽带天线没有确定的相位中心,因此不能采用通常的振幅和差式单脉冲法进行宽频带测角。本文提出的波束运算网络可用于一个宽带螺旋天线同时得到两个交叉波束的振幅-振幅式单脉冲系统中。此外,对比幅相干测向法中的测角模糊问题也进行了研究。 相似文献
7.
8.
Pseudomonas fluorescens UQM2490, resistant to 250 μg rifampicin/ml, was derived from P. fluorescens JC1, a proteolytic psychrotroph isolated from raw milk. Growth of UQM2490 was followed in raw and ultra heat-treated milk, by viable counting on rifampicin-containing agar medium. The growth curves obtained demonstrate slower growth in raw milk than in treated milk and the variation in growth with change in inoculum level. Generation times in ultra heat-treated milk ranged from 9.5 to 14.1 h compared with 9.6 to 33 h in raw milk. 相似文献
9.
混凝土抗硫酸盐侵蚀试验的一种新方法 总被引:4,自引:0,他引:4
提出了一个测定混凝土抗硫酸盐侵蚀能力的新方法。采用这种方法对超高强混凝土的抗化学腐蚀性能进行了试验,并和普通混凝土进行了对比。发现用一般硅酸盐水泥配制的超高强混凝土虽然在抵抗化学侵蚀能力方面比普通混凝土有所提高,但由于化学组成上的原因,它对高浓度的(NH4)2SO4等化学介质也难以抵抗。 相似文献
10.
Beatriz A. Rodas-Junco Graciela E. Racagni-Di-Palma Michel Canul-Chan Javier Usorach S. M. Teresa Hernndez-Sotomayor 《International journal of molecular sciences》2021,22(5)
Plants are subject to different types of stress, which consequently affect their growth and development. They have developed mechanisms for recognizing and processing an extracellular signal. Second messengers are transient molecules that modulate the physiological responses in plant cells under stress conditions. In this sense, it has been shown in various plant models that membrane lipids are substrates for the generation of second lipid messengers such as phosphoinositide, phosphatidic acid, sphingolipids, and lysophospholipids. In recent years, research on lipid second messengers has been moving toward using genetic and molecular approaches to reveal the molecular setting in which these molecules act in response to osmotic stress. In this sense, these studies have established that second messengers can transiently recruit target proteins to the membrane and, therefore, affect protein conformation, activity, and gene expression. This review summarizes recent advances in responses related to the link between lipid second messengers and osmotic stress in plant cells. 相似文献