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81.
Lawrence F. Shampine Lorraine S. Baca 《Journal of Computational and Applied Mathematics》1984,11(2):197-207
When solving ordinary differential equations numerically, the local error is estimated at each step. In the classical situation of ‘small’ step sizes, it is clear what is required of the error estimators. Stiff problems are solved with ‘large’ step sizes. The quality of error estimators is studied in this situatuion, and it is shown how to modify unsatisfactory estimators so as to improve them greatly. Several formulas from the literature are treated as examples. 相似文献
82.
Rosie J. Somerville Andryj M. Borys Marina Perez-Jimenez Ainara Nova David Balcells Lorraine A. Malaspina Simon Grabowsky Ernesto Carmona Eva Hevia Jesús Campos 《Chemical science》2022,13(18):5268
More than four decades ago, a complex identified as the planar homoleptic lithium nickelate “Li3NiPh3(solv)3” was reported by Taube and co-workers. This and subsequent reports involving this complex have lain dormant since; however, the absence of an X-ray diffraction structure leaves questions as to the nature of the Ni–PhLi bonding and the coordination geometry at Ni. By systematically evaluating the reactivity of Ni(COD)2 with PhLi under different conditions, we have found that this classical molecule is instead a unique octanuclear complex, [{Li3(solv)2Ph3Ni}2(μ-η2:η2-C6H4)] (5). This is supported by X-ray crystallography and solution-state NMR studies. A theoretical bonding analysis from NBO, QTAIM, and ELI perspectives reveals extreme back-bonding to the bridging C6H4 ligand resulting in dimetallabicyclobutane character, the lack of a Ni–Ni bond, and pronounced σ-bonding between the phenyl carbanions and nickel, including a weak σC–Li → sNi interaction with the C–Li bond acting as a σ-donor. Employing PhNa led to the isolation of [Na2(solv)3Ph2NiCOD]2 (7) and [Na2(solv)3Ph2(NaC8H11)Ni(COD)]2 (8), which lack the benzyne-derived ligand. These findings provide new insights into the synthesis, structure, bonding and reactivity of heterobimetallic nickelates, whose prevalence in organonickel chemistry and catalysis is likely greater than previously believed.We disclose the actual octanuclear nature of the major compound from reacting Ni(COD)2 and PhLi, assigned for more than four decades as ‘Li3NiPh3(solv)3’. We provide a thorough bonding analysis and discuss its potential implications in catalysis. 相似文献
83.
Lorraine E. Combettes Philip Clausen‐Thue Dr. Michael A. King Dr. Barbara Odell Dr. Amber L. Thompson Prof. Véronique Gouverneur Dr. Tim D. W. Claridge 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(41):13133-13141
A series of 3‐fluoropyrrolidines have been studied to investigate the influence of the stereoelectronic fluorine gauche effect on ring conformations in the solid state by single‐crystal X‐ray analysis and in solution phase by NMR spectroscopy. As part of these studies 1D 19F–1H heteronuclear NOE (HOESY) experiments have been optimised for applications to small molecules and are described in detail. These have been employed to estimate 19F–1H internuclear distances and were combined with vicinal 3J(F,H) and 3J(H,H) scalar coupling constants to analyse the ring conformations. Where possible the derived solution‐phase structural data have been compared with those of the crystalline state. The results demonstrate the influence of the gauche effect in stabilising Cγ‐exo conformations of the fluorinated pyrrolidines. It was further shown that when steric interactions were also present, this conformational bias was diminished and the contribution of the alternative Cγ‐endo conformation was seen to increase in solution at lower sample temperatures. 相似文献
84.
85.
Price KK McCormick AV Francis LF 《Langmuir : the ACS journal of surfaces and colloids》2012,28(28):10329-10333
Nonuniformities, such as heavy edges or "coffee rings", frequently develop as particulate coatings dry. One idea for avoiding these nonuniformities is to engineer the substrate edges. In this work, monodisperse latex coatings were deposited on substrates with photoresist walls around their edges. Cryogenic scanning electron microscopy (cryoSEM) results show particle accumulation near the walls and at the free surface. The contact line, pinned at the wall, generates lateral transport of water and particles, leading to a nonuniform coating thickness. Still, coatings on substrates with walls were shown to have a higher degree of thickness uniformity after drying than those without walls. 相似文献
86.
Vicinal JHH couplings were investigated for a series of substituted dihydronaphthalenes allowing the conformation of the non-aromatic ring to be evaluated. It was found that the substitution of bromine for hydrogen increases the total puckering amplitude of the non-aromatic ring. Different formulations of the Karplus equation were investigated and the influence on the observed results are discussed. 相似文献
87.
The 60 MHz 1H NMR spectra of 3-ethyl-3-phenylpyrrolidine-2,5-dione, 1, were studied in CDCl3 at 28° using the achiral lanthanide shift reagent (LSR) tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato)europium(III), Eu(FOD)3 2, for spectral simplification, and the chiral LSR, tris[3-heptafluoropropylhydroxymethylene)-(+)-camphorato]-europium(III), Eu(HFC)3 3, to induce enantiomeric shift differences (δδδ) for several nuclei. A non-racemic sample of 1 was treated with 3 to determine the sense of magnetic nonequivalence of selected nuclei. Significant δδδ is seen for the signals of the methyl and aryl ortho protons. Modest δδδ can also be seen for the NH signal and for one of the H-4 protons, although LSR-induced broadening for the two latter signals is severe. The (-) enantiomer appeared to exhibit an upfield sense of magnetic nonequivalence (3:1 molar ratio ca. 0.15—0.35) for the methyl signal but a downfield sense for Hortho (3:1 ratio ca. 0.6). 相似文献
88.
89.
Marian Olaru Daniel Duvinage Yannik Naß Lorraine A. Malaspina Stefan Mebs Jens Beckmann 《Angewandte Chemie (International ed. in English)》2020,59(34):14414-14417
Transient phosphenium and arsenium ions, generated by fluoride abstraction from bis(m‐terphenyl)fluoropnictogens, underwent intramolecular electrophilic attack prior to methyl group migration and gave rise to isolable 9‐phospha‐ and 9‐arsena‐fluorenium ions. 相似文献
90.
Alice MesnageGuy Deniau Lorraine TessierVincent Mévellec Serge Palacin 《Applied Surface Science》2011,257(17):7805-7812
In this work we present two techniques that provide localized functionalization of the surface of materials. Both lead to localized grafted thin organic films (10-200 nm). The localization is brought by a chemical lift-off process, which relies on patterned weakly bonded films as sacrificial layers, combined with electrochemical (SEEP) or chemical (GraftFast©) processes which provides the final robust pattern on the surface. Both grafting processes, which were recently described, take advantage of the redox activation of diazonium salts associated with vinylic monomers in aqueous solution, and lead to similar grafted polymer films. Thanks to the high difference in adhesion between the grafted polymer and the patterned sacrificial layer (either an ink or weakly bound self-assembled monolayers), the latter may be easily removed, which unveils uncovered areas of the substrate. 相似文献