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71.
Dr. Simona Rizzo Prof. Tiziana Benincori Dr. Valentina Bonometti Dr. Roberto Cirilli Prof. Patrizia R. Mussini Prof. Marco Pierini Dr. Tullio Pilati Prof. Francesco Sannicolò 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(1):182-194
A series of tris‐aryl phosphanes, structurally designed to exist as residual enantiomers or diastereoisomers, bearing substituents differing in size and electronic properties on the aryl rings, were synthesized and characterized. Their electronic properties were evaluated on the basis of their electrochemical oxidation potential determined by voltammetry. The configurational stability of residual phosphanes, evaluated by dynamic HPLC on a chiral stationary phase or/and by dynamic 1H and 31P NMR spectroscopy, was found to be rather modest (barriers of about 18–20 kcal mol?1), much lower than that shown by the corresponding phosphane oxides (barriers of about 25–29 kcal mol?1). For the first time, the residual antipodes of a tris‐aryl phosphane were isolated in enantiopure state and the absolute configuration assigned to them by single‐crystal anomalous X‐ray diffraction analysis. In this case, the racemization barrier could be calculated also by CD signal decay kinetics. A detailed computational investigation was carried out to clarify the helix reversal mechanism. Calculations indicated that the low configurational stability of tris‐aryl phosphanes can be attributed to an unexpectedly easy phosphorus pyramidal inversion which, depending upon the substituents present on the blades, can occur even on the most stable of the four conformers constituting a single residual stereoisomer. 相似文献
72.
There have been synthesized Pt(II) stereoisomeric complexes with hydroxy-α-amino acid serine (SerH = NH2CH(CH2OH)COOH is α-amino-β-hydroxypropionic acid): trans-[Pt(S-SerH)2Cl2], trans-[Pt(R-SerH)(S-SerH)Cl2] with monodentately (through NH2 group ) bound SerH and cis-, trans-[Pt(R-Ser)(S-Ser)], trans-[Pt(S-Ser)2] with bidentately bound (through groups NH2 and COO) ligands (R, S is the absolute configuration of asymmetric carbon atom). The successive phases in the synthesis of Pt(II) stereoisomeric complexes with serine were studied by 195Pt NMR spectroscopy. To identificate the compounds synthesized the method of elemental analysis, IR and NMR (195Pt, 13C, 1H) spectroscopy were used. For trans-[Pt(R-Ser)(S-Ser)] the X-ray diffraction data were obtained. 相似文献
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Ali Ramazani Sadegh Salmanpour Issa Amini 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3):699-704
Protonation of the highly reactive 1:1 intermediates, produced in the reaction between triphenylphosphine and alkyl acetylenecarboxylates by 2-naphthalenethiol, leads to vinyltriphenylphosphonium salts, which undergo an addition–elimination reaction to produce the corresponding S-vinyl thioethers. The NMR spectra indicated that the compounds contained two stereoisomers for each S-vinyl thioether; their ratio was determined on the basis of 1 H NMR spectra. The reaction is fairly stereoselective. 相似文献