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排序方式: 共有150条查询结果,搜索用时 15 毫秒
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Arefeh Dadras M. Reza Naimi‐Jamal Firouz Matloubi Moghaddam Seyed Ebrahim Ayati 《应用有机金属化学》2018,32(2)
Aryl halides and especially inactive aryl chlorides were coupled to benzenoid aromatic rings in a Suzuki–Miyaura coupling reaction in the absence of organic solvents and toxic phosphine ligands. The reaction was catalysed by a recoverable magnetic nanocatalyst, Pd@Fe3O4, in aqueous media. This method is green, and the catalyst is easily removed from the reaction media using an external magnetic field and can be re‐used at least 10 times without any considerable loss in its activity. The catalyst was characterized using scanning and transmission electron microscopies, thermogravimetric analysis, inductively coupled plasma spectroscopy, Fourier transform infrared spectroscopy, CHN analysis, X‐ray diffraction and vibrating sample magnetometry. 相似文献
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Synthesis of some novel 1,2,4‐triazoles, 1,3,4‐oxadiazoles and 1,3,4‐thiadiazoles bearing a (R) 5‐(1‐(4‐(5‐chloro‐3‐fluoropyridin‐2‐yloxy)phenoxy)ethyl) unit, as a moiety of commercial herbicide, using their thiosemicarbazides in an alkaline, iodine and acidic media is reported, respectively. The structure of the synthesized compounds was characterized by IR, 1H, 13C NMR spectroscopic data, and elemental analyses. The herbicidal activities of synthesized compounds were evaluated against Echinochloa cruss‐galli, Avena fatua, and Sorgum halepense weeds. Compounds 7 and 12a showed potential herbicidal activity against gramineous weeds. Our results may provide some guidance for synthesis development of some novel oxa or thiadiazole and triazole‐based herbicidal lead structures. 相似文献
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The behaviour of a dislocation pileup with a finite-strength source is investigated in the presence of various stress gradients within a continuum model where a free-dislocation region exists around the source. Expressions for dislocation density and stress field within the pileup are derived for the situation where there are first and second spatial gradients in applied stress. For a pileup configuration under an applied stress, yielding occurs when the force acting on the leading dislocations at the pileup tips reaches the obstacle strength, and at the same time, it is required that the source be at the threshold stress for dislocation production. A numerical methodology is presented to solve the underlying equations that represent the yielding conditions. The yield stress calculated for a pileup configuration is found to depend on stress gradients, obstacle spacing and source/obstacle strengths. It increases with increasing the first stress gradient, yet dependent on the second stress gradient. Furthermore, while the dependency of yield stress on the obstacle spacing intensifies with increasing the first stress gradient, it diminishes with an increase of second stress gradient. Therefore, the second stress gradient, as a newly introduced parameter, can provide a new physical insight into the size-dependent plasticity phenomena at small length scales. 相似文献
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Zeinab Abdeveiszadeh Siamak Noorizadeh 《International journal of quantum chemistry》2020,120(11):e26185
DFT calculations are performed to investigate the structure, stability, and nature of chemical bonding of some neutral noble gas insertion compounds containing a Xe-Xe bond; including HXeXeR, FXeXeR as well as RXeXeR (R = CN, NC, CCH, and BS). Geometry optimization of the considered molecules anticipate the existence of just four stable compounds (HXeXeCN, HXeXeNC, FXeXeCN, and FXeXeCCH); and rest of the molecules dissociate during the structural optimization. The results of NBO and AIM calculations show that a H(F)XeXeR molecule has a covalent H(F)-Xe bond in the H(F)XeXe+ fragment, which is bonded to R− mainly through columbic interaction. Thermodynamic study indicates that all of the considered unimolecular dissociation channels for decomposition of H(F)XeXeR molecules to neutral fragments are both exothermic and exorergic; but dissociation to ionic species (H(F)XeXe+ and R−) is endothermic. Also kinetic study of the most probable dissociation reaction shows that FXeXeR molecules are metastable with respect to the global minimum F-R + 2Xe. Therefore, FXeXeCN molecule is more kinetically protected against the decomposition reaction than the other molecules and its experimental detection is more likely. 相似文献
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Siamak Shahabi 《Physics letters. A》1979,72(3):212-214
Hartree-Fock calculations for the photoelectron angular distribution assymmetry parameters β (1,3P) for the processes Al 3s23p(2P) + ω → Al+ 3s3p(1,3P) + e? are carried out neglecting interchannel interactions. While the β's are found to differ from 2, as predicted for open-shell atom s-subshells by Starace, Rast and Manson, the deviations are found to be rather small in Al due to the absence of Cooper minima in the corresponding photoionization cross sections above threshold. 相似文献
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Reza Moazzemi Abdollah Mohammadi Siamak S. Gousheh 《The European Physical Journal C - Particles and Fields》2008,56(4):585-590
We discuss the effects of non-trivial boundary conditions or backgrounds, including non-perturbative ones, on the renormalization
program for systems in two dimensions. We present an alternative renormalization procedure in which these non-perturbative
conditions can be taken into account in a self-contained and, we believe, self-consistent manner. These conditions have profound
effects on the properties of the system, in particular all of its n-point functions. To be concrete, we investigate these effects in the λ
φ
4 model in two dimensions and show that the mass counterterms turn out to be proportional to the Green’s functions which have
a non-trivial position dependence in these cases. We then compute the difference between the mass counterterms in the presence
and absence of these conditions. We find that in the case of non-trivial boundary conditions this difference is minimum between
the boundaries and infinite on them. The minimum approaches zero when the boundaries go to infinity. In the case of non-trivial
backgrounds, we consider the kink background and show that the difference is again small and localized around the kink. 相似文献