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排序方式: 共有199条查询结果,搜索用时 515 毫秒
191.
本文讨论了用原子吸收和电感耦合等离子体发射光谱法(ICP-AES)测定经高压釜溶解的营养性埃及植物,如胡芦巴、甘草和莲座丛,并讨论了该法用于被消解植物样品中多元素日常分析的优点。这些样品具有较宽的元素含量范围,准确地测定这些营养性样品的主量和微量元素特别是有毒元素,对埃及人民的健康非常重要。ICP-AES法同时也用于被视为尼罗河净化剂的水生风信子的分析。分析结果表明,该植物能够有效地吸收有毒元素。被研究的植物经高压釜溶解,其溶液经原子吸收和ICP-AES法测定。作者对分析结果进行了对比,并阐明了二者之间的关系。 相似文献
192.
A new one-vessel reaction has been developed for the synthesis of substituted aminocyanopyridines 2 and cyanopyridin-2-ones 3. Compounds 2a-c and 3a-c were readily obtained by heating molar amounts of 5-nitro-benzothiophene-2-carboxaldehyde 1 , the appropriate acetyl derivative and the active methylene compound (malononitrile or ethyl cyanoacetate) in presence of ammonium acetate. The new method had the advantage of being quick, economic and of general application. A possible mechanism for the reaction, has been suggested. 相似文献
193.
E. M. E. Zayed 《International Journal of Theoretical Physics》2000,39(1):189-205
We study the influence of a finite container on an ideal gas. The trace of theheat kernel (t) =
= 1exp(–t), where {}
= 1are the eigenvalues of the negative Laplacian – 2 = – 3
= 1(/x
)2 in the (x
1, x
2, x
3)-space,is studied for a general bounded domain with a smooth bounding surface S, where afinite number of Dirichlet, Neumann, and Robin boundary conditions on thepiecewise smooth parts S
i
(i = 1, ..., n) of S are considered such that S =U
i = 1
S
i
. Some geometrical properties of (the volume, the surface area, the meancurvature, and the Gaussian curvature) are determined. Furthermore,thermodynamic quantities, particularly the energy, for an ideal gas enclosed inthe general bounded domain with Dirichlet, Neumann, and Robin conditionsare examined with the help of the asymptotic expansions of (t) for short timet. We show that these thermodynamic quantities depend on some geometricproperties of . 相似文献
194.
A series of new α-hydroxyphosphonate (5–14) have been synthesized in high yields by reaction of β-chloro-α,β-unsaturated aldehydes (1–4) and trialkyl phosphite in the presence of chlorotrimethylsilane at room temperature under solvent-free conditions. In addition, compounds (5–14) were reacted with acetic anhydride in DBU to give the new α-acetoxyphosphonate derivatives (15–23). All these phosphonates (5–23) were obtained as mixtures of two (E and Z) isomers and fully characterized by multinuclear (1H, 13C, and 31P) NMR, IR spectroscopy and HRMS. 相似文献
195.
We have performed firstly studies of the photoinduced second order susceptibilities in the Au nanoparticles (NP) A, B and C under simultaneous influence of the bicolor 1064 nm and bicolor laser treatment (1064 nm 10 ns pulsed laser with pulse power densities 532 nm 10 ns laser treatment and the cw 300 mW 532 nm SHG coherent laser beams. We have studied three types of samples possessing irregular and different dense parameters of the Au NP deposited on the ITO substrate. We have found that the maximal bicolor (1064 nm and 532 nm) stimulated optical second harmonic generation for the 10 ns pulse duration was observed for the samples possessing irregular Au NP deposited on the ITO. We have performed studies of the photoinduced second order susceptibilities in the Au NP under simultaneous influence of the bicolor 1064 nm and bicolor laser treatment (1064 nm 10 ns pulsed laser with pulse power densities 532 nm 10 ns laser treatment and the cw 300 mW 532 nm SHG coherent laser beams). We have found that during the 15-20 min of the cw treatment there occur the principal changes in the absorption maxima. These maxima indicate on the occurrence of the additional absorption nearby the 308 nm and 310 nm and 345 nm spectral bands. The later are caused by the occurrence of the trapping levels in the border between the ITO substrate and the Au nanoparticles. 相似文献
196.
The \(\phi ^{6}\)-model expansion method combined with the conformable time-fractional derivative is applied in this paper for finding many new exact solutions including Jacobi elliptic function solutions, solitary wave solutions, trigonometric function solutions and other solutions to the nonlinear conformable time-fractional Schrödinger equation with fourth-order dispersion and parabolic law nonlinearity. This method presents a wider applicability for handling the nonlinear partial differential equations. Comparing our results with the well-known results are given. 相似文献
197.
The reaction between Br2 and paracetamol(p-AAP) leads to the formation of a coloured product, which can be used for spectrophotometric determination of the p-AAP content in its pure form and in different pharmaceutical preparations with p-AAP. The stoichiometric composition of the reaction was found to be n(p-AAP)∶n(bromine)=1∶3. The effects of pH and time on the spectra of p-AAP-bromine redox reaction product were studied. The interference of different additives on the measured spectra of the obtained product was also studied. The results obtained by the present method were compared with those obtained by the standard method. The F- and t- test values were calculated for both of the applied procedures and they met a confidence level of 99%. The proposed procedure actually needs no separation of these drugs from their sources before analysis and was unaffected by interference of other phenolic compounds. The proposed method is simpler and faster than the repoeted ones. 相似文献
198.
E. M. E. Zayed 《计算数学(英文版)》1989,7(3):301-312
The spectral function $\hatμ(t)=\sum\limits_{j=1}^\infty e^{-itλ^{\frac{1}{2}}_j}$ where $\{λ_j\}^\infty_{j=1}$ are the eigenvalues of the three-dimensional Laplacian is studied for a variety of domains, where $- \infty<t<\infty$ and $i=\sqrt{-1}$. The dependence of $\hat{\mu}(t)$ on the connectivity of a domain and the impedance boundary condition (Robbin conditions) are analyzed. Particular attention is given to the spherical shell together with Robbin boundary conditions on its surface. 相似文献
199.