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排序方式: 共有66条查询结果,搜索用时 15 毫秒
51.
Renato Pucci Marcello Baldo Antonio Grassi Pasquale Tomasello 《International journal of quantum chemistry》1980,18(1):11-18
The many-body perturbation theory is reformulated within the dielectric function method presented in the preceding paper [12]. The self-energy effects are explicitly considered. These corrections turn out to be important and are calculated to the same level of approximation as the corresponding local-field terms. The method is at the moment applicable to π-electron systems within the zero differential overlap approximation. Explicit calculations of the excitation energies for the benzene molecule, using different parametrizations, are presented. Comparison is made with the results obtained in the random phase approximation (RPA ) and other schemes. 相似文献
52.
R. Pucci M. Baldo A. Martin-Rodero G. Piccitto P. Tomasello 《International journal of quantum chemistry》1984,26(5):783-791
In the framework of the SCF -RPA scheme and ppp approximation we studied the excitation spectrum of pyrene, coronene, ovalene, and hexabenzocoronene. The triplet stability matrix of the corresponding Hartree–Fock solution was also studied for each molecule. At variance with the case of long linear polyacenes [M. Baldo, G. Piccitto, R. Pucci, and P. Tomasello, Phys. Lett. 95A , 201 (1983)], all these molecules do not display Hartree–Fock triplet instability. Furthermore, the theoretical analysis indicates that the electronic structure of the molecular series can be characterized by a dimensionality intermediate between one and two, with a smooth transition between the two limits. The transition is essentially determined by the molecular shape. The analysis is supported by the fairly good agreement of the theoretical spectra with the available experimental data. 相似文献
53.
A review is presented on the formation and occurrence in the atmosphere of nitrated polycyclic aromatic hydrocarbons. Some analytical methodologies (covering various matrices) are also considered. 相似文献
54.
Structure-based design of alkyl sugar-1-phosphates provides an efficient nucleotidylyltransferase-catalyzed synthesis of a series of new lipophilic sugar nucleotides possessing long or branched alkyl chains, thereby demonstrating the utility of nucleotidylyltransferases to catalyze the synthesis of sugar nucleotides with potential applications in lipopolysaccharide and lipoglycopeptide biosynthesis. 相似文献
55.
Alice Dal Fovo Mariaelena Fedi Gaia Federico Lucia Liccioli Serena Barone Raffaella Fontana 《Molecules (Basel, Switzerland)》2021,26(17)
Fayum mummy portraits, painted around 2000 years ago, represent a fascinating fusion of Egyptian and Graeco-Roman funerary and artistic traditions. Examination of these artworks may provide insight into the Roman Empire’s trade and economic and social structure during one of its most crucial yet still hazy times of transition. The lack of proper archaeological documentation of the numerous excavated portraits currently prevents their chronological dating, be it absolute or relative. So far, their production period has been defined essentially on the basis of the relevant differences in their pictorial style. Our study introduces the use of Accelerator Mass Spectrometry (AMS) to assess the age of a fragment of an encaustic painting belonging to the corpus of the Fayum portraits. The unexpected age resulting from 14C analysis suggests the need to reconsider previous assumptions regarding the period of production of the Fayum corpus. Furthermore, our multi-analytical, non-invasive approach yields further details regarding the fragment’s pictorial technique and constituting materials, based on spectral and morphological analysis and cross-sectional examination. 相似文献
56.
We study the slow dynamics of hydration water upon cooling in two different biological aqueous solutions, one containing a molecule of lysozyme and another with trehalose molecules. In particular we test if the glassy behaviour of these solutions fulfils the predictions of the popular Mode Coupling Theory of glassy dynamics. In particular we test the Time Temperature Superposition Principle and the matching of the exponents of the theory. Our results confirm that this theory is able to describe the dynamical behaviour of supercooled water also in non ideal cases as the ones under investigation in the region of mild supercooling. 相似文献
57.
58.
Giuliana Righi Emanuela Mandic’ Ilaria Tirotta Gaia Clara Mercedes Naponiello Carla Sappino Cristina Marucci 《Natural product research》2016,30(14):1655-1660
A stereocontrolled, facile and high-yield approach for producing (+)-altroDNJ, has been developed starting from the inexpensive commercial cis 2-butene-1,4-diol. Sharpless epoxidation and a subsequent dihydroxylation were used for the introduction of all stereocentres; finally, the ring closure under basic conditions afforded the piperidine heterocycle. 相似文献
59.
Maura Pellei Simone Alidori Giancarlo Gioia Lobbia Gaia Emanuela Gioia Lobbia 《Journal of organometallic chemistry》2008,693(6):996-1004
The new sodium bis(1-methyl-1H-imidazol-2-ylthio)acetate, Na[(S-tim)2CHCO2], has been prepared in ethanol solution using 2-mercapto-1-methylimidazole, dibromoacetic acid and NaOH. New di- and tri-organotin(IV) derivatives have been synthesized from reaction between SnRnCl4−n (R = Ph, Cy and nBu, n = 2-3) acceptors and Na[(S-tim)2CHCO2]. Complexes of the type {[κ1O-(S-tim)2CHCO2]SnR3} and related decarboxylated species {[κ2N,N-(S-tim)2CH2]SnR2Cl2} have been obtained and characterized by elemental analyses, FT-IR, ESIMS and multinuclear (1H, 13C and 119Sn) NMR spectral data. The adduct {κ1O-[(S-tim)2CHCO2]Sn(H2O)(C4H9)3} was characterized by single crystal X-ray studies. The dichloromethane reaction solution of {κ1O-[(S-tim)2CHCO2]Sn(C6H5)3} was re-crystallized and the decarboxylated species {[(S-tim)2CH2]SnCl(H2O)(C6H5)3} was obtained as a crystalline solid and characterized by X-ray crystallography. 相似文献
60.
Francesca Leonelli Barbara Caschera Lavinia Silvestri Alessandro Prastaro Gaia Corso Francesca Ceccacci Angela La Bella Luisa Maria Migneco Rinaldo Marini Bettolo 《Helvetica chimica acta》2008,91(4):598-607
An expeditious preparation of the 6‐exo‐hydroxybicyclo[2.2.2]octan‐2‐one ethylene dithioacetal 2b , a key intermediate in the synthesis of (+)‐13‐stemarene ( 4 ) and (+)‐18‐deoxystemarin ( 5 ) is described. Compound 2b was obtained as the major product by equilibrating the endo rich mixture of 6‐hydroxybicyclo[2.2.2]octan‐2‐one ethylene dithioacetals 2 with TsOH in benzene at reflux, easily available from the corresponding hydroxy ketones 9 . The model experiments which preceeded the above transformation, not previously described in the literature, are also presented. 相似文献