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排序方式: 共有930条查询结果,搜索用时 16 毫秒
921.
Summary A method is described for the extraction of clebuterol from bovine retina samples by diphasic dialysis using gas chromatography—mass
spectrometry (GC-MS) as the procedure of determination. Following chemical digestion of retinal tissue in alkaline medium
at 80°C, clenbuterol is extracted by diphasic dialysis using diethyl ether as solvent at 37°C, for 4 h at 150 rpm. Diethyl
ether is evaporated to dryness and clenbuterol determined by GC-MS after butylboronic acid (BBA) derivatization. A detection
limit of 2.5 ng g−1, repeatability of 9.0% and reproducibility of 22.9%, with recoveries always >86% (n=5), are achieved as validation criteria. 相似文献
922.
采用圆二色谱方法对钕和镧离子与转移核糖核酸间的相互作用进行了研究,结果显示在1.5~6 μmol/L Nd3+或La3+离子存在下,tRNA分子CD谱260 nm(+)峰蓝移2~3 nm, 260 nm(+)峰值分别增加6%和20%左右;210 nm(-)峰在不同摩尔比Nd3+/tRNA作用下,谱峰蓝移或红移,峰值增加或降低50%左右。结果说明结合在tRNA分子上的Nd3+或La3+可能引起tRNA分子构象的变化。Eu3+对大肠杆菌LeuRS或tRNALeu-LeuRS复合物的CD谱具有一定的影响。 相似文献
923.
924.
Using sesquiterpene lactone rule, the absolute configurations of seven sesquiterpene α-methylene-γ-lactones were confirmed. Compounds 1, 2, 3, 4 and 6, 7 are cis-fused γ-lactones, and compound 5 is trans-fused γ-lactone. 相似文献
925.
宓陈静 《浙江大学学报(理学版)》2006,33(1):14-18,31
设{Yi;-∞<I<∞}是同分布的ρ*混合随机变量序列,{ai;-∞<I<∞}是绝对可加的实数序列,{Xnk;1≤k≤n,n≥1}是行内随机变量为ρ*混合的随机变量组列,令Cnk=EXnkI{|Xnk|≤n1/p}.在适当的条件下建立了{n∑k=1∞∑I=-∞ai+kYi/nα;n≥1}和{n∑k=1(Xnk-Cnk)/n1/p;n≥1)}的完全收敛性. 相似文献
926.
Two new alkali metal germanophosphates,namely,Na3[Ge(OH)(PO4)2]·2 H2 O and Li2Na[GeO(HPO4)(PO4)],have been prepared by solvothermal method,and their crystal structures were determined by single-crystal X-ray diffraction.The title two compounds crystalize in the same orthorhombic space group Pbcm(No.57)and feature similar chain-like structure which is built from zig-zag GeO6 octahedral thread loop branched by PO4 tetrahedra.For Na3[Ge(OH)(PO4)2]·2 H2O,a=10.1650(9),b=13.1975(12),c=6.9751(7)?,V=935.73(15)?3,Z=4,R=0.0356 and wR=0.1109;and for Li2Na[GeO(HPO4)(PO4)],a=6.9855(5),b=14.5809(18),c=6.6620(5)?,V=678.56(11)?3,Z=4,R=0.0286,and w R=0.0762.The partial substitution of Na ions by Li ions not only significantly influences the total structural features and the water molecule contents,but also impacts on their thermal stabilities.Li2Na[GeO(HPO4)(PO4)]is thermally stable up to 400℃,whereas only 150℃ for Na3[Ge(OH)(PO4)2]·2 H2 O. 相似文献
927.
Victor Hugo Souto Bezerra Samuel Leite Cardoso Yris Fonseca-Bazzo Dmaris Silveira Prola Oliveira Magalhes Paula Monteiro Souza 《Molecules (Basel, Switzerland)》2021,26(22)
The purpose of this systematic review was to identify the available literature of production, purification, and characterization of proteases by endophytic fungi. There are few complete studies that entirely exhibit the production, characterization, and purification of proteases from endophytic fungi. This study followed the PRISMA, and the search was conducted on five databases: PubMed, PMC, Science Direct, Scopus Articles, and Web of Science up until 18 May 2021, with no time or language restrictions. The methodology of the selected studies was evaluated using GRADE. Protease production, optimization, purification, and characterization were the main evaluated outcomes. Of the 5540 initially gathered studies, 15 met the inclusion criteria after a two-step selection process. Only two studies optimized the protease production using statistical design and two reported enzyme purification and characterization. The genus Penicillium and Aspergillus were the most cited among the eleven different genera of endophytic fungi evaluated in the selected articles. Six studies proved the ability of some endophytic fungi to produce fibrinolytic proteases, demonstrating that endophytic fungi can be exploited for the further production of agents used in thrombolytic therapy. However, further characterization and physicochemical studies are required to evaluate the real potential of endophytic fungi as sources of industrial enzymes. 相似文献
928.
This paper addresses the resolution of non-linear problems arising from an implicit time discretization in CFD problems. We study the convergence of the Newton–GMRES algorithm with a Jacobian approximated by a finite difference scheme and with restarting in GMRES. In our numerical experiments we observe, as predicted by the theory, the impact of the matrix-free approximations. A second-order scheme clearly improves the convergence in the Newton process. 相似文献
929.
930.
Raul Quijada Jairton Dupont Dione Corrêa Silveira Mrcia S. Lacerda Miranda Rosngela B. Scipioni 《Macromolecular rapid communications》1995,16(5):357-362
This work reports a comparative study of the catalytic behaviour for a series of metallocenes derived from Ti, Zr, Hf and Nb, which after activation with methylaluminoxane can polymerize ethylene. Results show that the Zr metallocene with a (CH3)2Si Bridge presents the highest activity, and the metallocenes based on Hf and Nb do not show any significant activity under the tested conditions. 相似文献