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Some transition metal complexes of β-dicarbonyl compounds react with electrophiles at α-C. These reactions, carried out under
neutral conditions, offer a broader scope than their conventional counterparts, and are generally performed in the presence
of stoichiometric or catalytic amounts of strong bases. Mechanistic observations using different reaction conditions are also
relevant from a synthetic point of view.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 418–427, March, 1997. 相似文献
23.
Comelles J Moreno-Mañas M Pérez E Roglans A Sebastián RM Vallribera A 《The Journal of organic chemistry》2004,69(20):6834-6842
Cu(SbF6)2-AdamBox and copper(II) bis-(5-tert-butylsalicylaldehydate) catalyze the Michael addition in neutral media. Mechanistic studies, based on UV-vis, IR, and electrospray ionization mass spectrometry (ESI-MS), suggest that copper enolates of the beta-dicarbonyl formed in situ are the active nucleophilic species. 相似文献
24.
Marcial Moreno-Mañas Roser Pleixats Adelina Vallribera 《Journal of organometallic chemistry》2004,689(23):3669-3684
15-Membered macrocycles (E,E,E)-1,6,11-tris(arenesulfonyl)-1,6,11-triazacyclopentadeca-3,8,13-trienes (1) are prepared from arenesulfonamides and trans-1,4-dibromo-2-butene. Macrocycles 1 coordinate palladium(0), platinum(0), and silver(I). The palladium complexes are useful and reutilizable catalysts or precatalysts in Suzuki cross-couplings, butadiene telomerizations, hydroarylation of alkynes, and in the Heck reaction. Structurally related macrocycles are also available by similar synthetic procedures. 相似文献
25.
We will consider global problems in the ringK[X
1, …,X
n] on the polynomials with coefficients in a subfieldK ofC.
LetP=(P
1, …,P
n):K
n
→K
n be a polynomial map such that (P
1,…,P
n) is a quasi-regular sequence generating a proper ideal, the main thing we do is to use the algebraic residues theory (as
described in [5]) as a computational tool to give some result to test when a map (P
1, …,P
n) is a proper map by computing a finite number of residue symbols. 相似文献
26.
Liu Ming Granados Albert Reyes-Mesa David Arosemena-Angulo E. Leonardo Calvo-Torras María Ángeles Pleixats Roser Vallribera Adelina 《Cellulose (London, England)》2022,29(16):8889-8905
Cellulose - The preparation of antifungal-functionalized silica nanoparticles by covalent attachment of several silylated derivatives based on the topical antifungal agent Micozanole is described.... 相似文献
27.
Cross-training of nursing staff has been used in hospitals to reduce labor cost, provide scheduling flexibility, and meet patient demand effectively. However, cross-trained nurses may not be as productive as regular nurses in carrying out their tasks because of a new work environment and unfamiliar protocols in the new unit. This leads to the research question: What is the impact of productivity on optimal staffing decisions (both regular and cross-trained) in a two-unit and multi-unit system. We investigate the effect of mean demand, cross-training cost, contract nurse cost, and productivity, on a two-unit, full-flexibility configuration and a three-unit, partial flexibility and chaining (minimal complete chain) configurations under centralized and decentralized decision making. Under centralized decision making, the optimal staffing and cross-training levels are determined simultaneously, while under decentralized decision making, the optimal staffing levels are determined without any knowledge of future cross-training programs. We use two-stage stochastic programming to derive closed form equations and determine the optimal number of cross-trained nurses for two units facing stochastic demand following general, continuous distributions. We find that there exists a productivity level (threshold) beyond which the optimal number of cross-trained nurses declines, as fewer cross-trained nurses are sufficient to obtain the benefit of staffing flexibility. When we account for productivity variations, chaining configuration provides on average 1.20% cost savings over partial flexibility configuration, while centralized decision making averages 1.13% cost savings over decentralized decision making. 相似文献
28.
Smirnova A Proskurnin MA Bendrysheva SN Nedosekin DA Hibara A Kitamori T 《Electrophoresis》2008,29(13):2741-2753
In this paper, we compared the methods of photothermal spectroscopy used in different spatial scales, namely thermal-lens spectrometry (TLS) and thermal-lens microscopy (TLM) to enhance the performance parameters in analytical procedures. All of the experimental results were confirmed by theoretical calculation. It was proven that the design for both TLM and TLS, despite a different scale for the effect, is governed by the same signal-generating and probing conditions (probe beam diameter at the sample should be equal to the diameter of the blooming thermal lens), and almost does not depend on the nature of the solvent. Theoretical and experimental instrumental error curves for thermal lensing were coincident. TLM obeys the same law of instrumental error as TLS and shows better repeatability for the same levels of thermal-lens signals or absorbances. TLS is more advantageous for studying low concentrations in bulk, while TLM shows much lower absolute LODs due to better repeatability for low amounts. The behavior of the thermal-lens signal with different flow rates was studied and optimum conditions, with the minimum contribution to total error, were found. These conditions are reproducible, are in agreement with the existing theory of the thermal response in thermal lensing, and do not significantly affect the design of the optimum scheme for setups. TLM showed low LODs in solvent extraction (down to 10(-8) M) and electrokinetic separation (10(-7) M), which were shown to be governed by discussed instrumental regularities, instead of by microchemistry. 相似文献
29.
De novo sequencing of tryptic peptides by post source decay (PSD) or collision induced dissociation (CID) analysis using MALDI TOF-TOF instruments is due to the easy interpretation facilitated by the introduction of N-terminal sulfonated derivatives. Recently, a stable and cheap reagent, 4-sulfophenyl isothiocyanate (SPITC), has been successfully used for N-terminal derivatization. Previously described methods have always used desalting and concentration by reverse-phase chromatography prior to mass spectrometric analysis. Here we present an on-target sample preparation method based on AnchorChip target technology. The method was optimized for reduction of by-products and sensitivity with SPITC-derivatized tryptic BSA peptides, and successfully applied to protein identification from silver-stained two-dimensional electrophoretic gels of fish liver extracts. The method is simple and sensitive and allowed protein identification based on de novo sequencing and BLAST search from species with limited sequence information. 相似文献
30.
Maria Crişan Ana Brăileanu D. Crişan Mălina Răileanu N. Drăgan Diana Mardare V. Teodorescu Adelina Ianculescu Ruxandra Bîrjega M. Dumitru 《Journal of Thermal Analysis and Calorimetry》2008,92(1):7-13
Among the great number of sol-gel materials prepared, TiO2 holds one of the most important places due to its photocatalytic properties, both in the case of powders and coatings. Impurity
doping is one of the typical approaches to extend the spectral response of a wide band gap semiconductor to visible light.
This work has studied some un-doped and Pd-doped sol-gel TiO2 nanopowders, presenting various surface morphologies and structures. The obtained powders have been embedded in vitreous
TiO2 matrices and the corresponding coatings have been prepared by dipping procedure, on glass substrates. The relationship between
the synthesis conditions and the properties of titania nanosized materials, such as thermal stability, phase composition,
crystallinity, morphology and size of particles, and the influence of dopant was investigated.
The influence of Pd on TiO2 crystallization both for supported and unsupported materials was studied (lattice parameters, crystallite sizes, internal
strains). The hydrophilic properties of the films were also connected with their structure, composition and surface morphology.
The methods used for the characterization of the materials have been: simultaneous thermogravimetry and differential thermal
analysis, powder X-ray diffraction, electron microscopy (TEM, SAED) and AFM. 相似文献