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排序方式: 共有368条查询结果,搜索用时 15 毫秒
131.
Lomlim L Einsiedel J Heinemann FW Meyer K Gmeiner P 《The Journal of organic chemistry》2008,73(9):3608-3611
A practical and efficient synthesis of spirobarbiturates of type III is reported when NH acidity of the imide function of the hydrophilic linker element allowed the introduction of different substituents. Structural characterization, which was based on both X-ray crystallography and spectroscopic investigations, indicated type II beta-turn formation. Introduction of the molecular scaffold into solid phase peptide synthesis gave rise to spirocyclic neuropeptide analogs. 相似文献
132.
Anton I. Kudelin Konstantinos Papathanasiou Vera Isaeva Juergen Caro Tapio Salmi Leonid M. Kustov 《Molecules (Basel, Switzerland)》2021,26(2)
The coordination polymer CPO-27-Mg was rapidly synthesized under microwave irradiation. This material exhibits a sufficiently high drug loading towards aspirin (~8% wt.) and paracetamol (~14% wt.). The binding of these two molecules with the inner surface of the metal-organic framework was studied employing the Gaussian and Plane Wave approach of the Density Functional Theory. The structure of CPO-27-Mg persists after the adsorption of aspirin or paracetamol and their desorption energies, being quite high, decrease under solvent conditions. 相似文献
133.
We present a low-cost miniaturized fluorescence detection system for lab-on-a-chip applications with a sensitivity in the low nanomolar range; a built-in lock-in amplifier enables measurements under ambient light. 相似文献
134.
Kickuth R Laufer U Pannek J Adamietz IA Liermann D Adams S 《Magnetic resonance imaging》2002,20(9):691-694
Fluid-fluid levels have been reported as an extremely infrequent and non-specific condition in many benign and malignant bone lesions. We present the first reported MRI findings of bone marrow metastasis with fluid-fluid levels from small cell neuroendocrine carcinoma of the urinary bladder to the lumbar spine. Radiologists should be aware of the MRI appearance of these extraordinary lesions in order to provide a complete differential diagnosis and to guide clinicians in adequate treatment. 相似文献
135.
I Matanović JL Belof B Space K Sillar J Sauer J Eckert Z Bačić 《The Journal of chemical physics》2012,137(1):014701
We report rigorous quantum five-dimensional (5D) calculations of the coupled translation-rotation (T-R) eigenstates of a H(2) molecule adsorbed in metal organic framework-5 (MOF-5), a prototypical nanoporous material, which was treated as rigid. The anisotropic interactions between H(2) and MOF-5 were represented by the analytical 5D intermolecular potential energy surface (PES) used previously in the simulations of the thermodynamics of hydrogen sorption in this system [Belof et al., J. Phys. Chem. C 113, 9316 (2009)]. The global and local minima on this 5D PES correspond to all of the known binding sites of H(2) in MOF-5, three of which, α-, β-, and γ-sites are located on the inorganic cluster node of the framework, while two of them, the δ- and ε-sites, are on the phenylene link. In addition, 2D rotational PESs were calculated ab initio for each of these binding sites, keeping the center of mass of H(2) fixed at the respective equilibrium geometries; purely rotational energy levels of H(2) on these 2D PESs were computed by means of quantum 2D calculations. On the 5D PES, the three adjacent γ-sites lie just 1.1 meV above the minimum-energy α-site, and are separated from it by a very low barrier. These features allow extensive wave function delocalization of even the lowest translationally excited T-R eigenstates over the α- and γ-sites, presenting significant challenges for both the quantum bound-state calculations and the analysis of the results. Detailed comparison is made with the available experimental data. 相似文献
136.
基于FAIMS谱图峰位置的离子迁移率非线性函数解析 总被引:1,自引:0,他引:1
离子迁移率的非线性函数反映了物质本身的微观碰撞特性,是FAIMS技术实现离子分离检测的基础。现有的离子迁移率非线性函数求解方法多是近似求解,存在较大误差。该工作提出了一种基于半正弦分离电压和FAIMS谱图峰位置下的严格求解方法,推导出严格的二阶、四阶系数求解方程。利用自制的高场不对称波形离子迁移谱仪分别对乙醇、间二甲苯和正丁醇三种典型的醇和苯类物质进行检测,获取了三种物质的FAIMS谱图,通过谱图峰位置获得了不同分离电压值下的补偿电压,利用最小二乘法求出三种离子非线性函数二阶、四阶系数。拟合后的均方误差表明FAIMS非线性函数严格求解的方法,明显优于现有的求解方法。有助于提高FAIMS检测分辨率,进而有助于建立更加准确的FAIMS图谱,实现FAIMS对检测物质的精准识别。 相似文献
137.
Abstract BaF2/YSZ (yttria stabilized zirconia) bicrystals are investigated by means of impedance spectroscopy. The spectra show two semicircles
in the complex impedance plane, and both arcs exhibit very similar temperature dependences. The high frequency semicircle
can be attributed to the ideal (quasi one-dimensional) bulk resistance of BaF2, and the low frequency arc is caused by an additional resistance in BaF2 due to the current constriction taking place close to the contact spots at the imperfect bicrystal interface. This interpretation
is supported by finite element calculations revealing that bicrystals with imperfect contacts indeed exhibit an additional
semicircle in the complex impedance plane even without any ion transfer resistance between the two crystals. The low frequency
arc of the BaF2/YSZ bicrystal drastically increases upon bias voltage, but relaxes to its original value after removing the bias. This phenomenon
can be associated with a strong decrease of the vacancy concentration in YSZ (close to the interfacial contact spots), which
is caused by F− ions being pumped into YSZ and acting as a counter dopant to Y3+.
Graphical Abstract
相似文献
138.
The supraglottal flow exhibits many complex phenomena such as recirculation, jet instabilities, jet attachment to one vocal fold wall, jet flapping, and transition to turbulence. The acoustical relevance of these flow structures to low-frequency voice production was evaluated by disturbing the supraglottal flow field using a cylinder and observing the consequence on the resulting sound pressure field. Despite a significantly altered supraglottal flow field due to the presence of the cylinder, only small changes in sound pressure amplitude and spectral shape were observed. The implications of the results on our understanding of phonation physics and modeling of phonation are discussed. 相似文献
139.
Qi Xia Miroslaw Batentschuk Andres Osvet Albrecht Winnacker Juergen Schneider 《Radiation measurements》2010,45(3-6):350-352
A series of red-emitting light converters Ca1?xSrxS:Eu2+, with tunable composition-dependent emission maxima were synthesized and characterized concerning their photoluminescent (PL) properties. X-ray diffraction patterns, photoluminescence spectra, luminosities and quantum yields were compared for phosphors with strontium concentrations varying from 0 to 100%. The maxima wavelength of emission shifts from 663 down to 619 nm, originating from the dependence of Eu2+ 5d state energy on the surrounding crystal field. Upon increasing the temperature from 20 to 420 K, a broadening of emission spectra along with thermal quenching of emission intensity and quantum yield occurs. Satisfying PL properties and their thermal stability demonstrate that the phosphors could be used as light converters in light emitting diodes (LEDs). 相似文献
140.
Christine Thomas Ute Hestermann Juergen Kopitz Konstanze Plaschke Peter Oster Martin Driessen Christoph Mundt Matthias Weisbrod 《BMC neuroscience》2008,9(1):1-10