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111.
112.
Site of protonation of nicotine and nornicotine in the gas phase: pyridine or pyrrolidine nitrogen? 总被引:1,自引:0,他引:1
Graton J Berthelot M Gal JF Girard S Laurence C Lebreton J Le Questel JY Maria PC Naus P 《Journal of the American Chemical Society》2002,124(35):10552-10562
The gas-phase basicities (GBs) of nornicotine, nicotine, and model pyrrolidines have been measured by FT-ICR. These experimental GBs are compared with those calculated (for the two sites of protonation in the case of nicotine and nornicotine) at the B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d,p) level, or those estimated from substituent effects on the GBs of 2-substituted pyrrolidines, 2-substituted N-methylpyrrolidines, and 3-substituted pyridines. It is found that, in contrast to the Nsp(3) protonation in water, in the gas phase nornicotine is protonated on the pyridine nitrogen, because the effects of an intramolecular CH.Nsp(3) hydrogen bond and of the polarizability of the 3-(pyrrolidin-2-yl) substituent add up on the Nsp(2) basicity, while the polarizability effect of the 2-(3-pyridyl) substituent on the Nsp(3) basicity is canceled by its field/inductive electron-withdrawing effect. The same structural effects operate on the Nsp(3) and Nsp(2) basicities of nicotine, but here, the polarizability effect of the methyl group puts the pyrrolidine nitrogen basicity very close to that of pyridine. Consequently, protonated nicotine is a mixture of the Nsp(3) and Nsp(2) protonated forms. 相似文献
113.
Solweig Vitry Audrey Mezzino Catherine Gauthier Jean-Yves Cavaill Frdric Lefebvre lodie Bourgeat-Lami 《Comptes Rendus Chimie》2003,6(11-12):1285-1293
We describe in this work the copolymerization reaction of 3-trimethoxysilyl propyl methacrylate (MPS) with styrene (Styr.) and n-butyl acrylate (BuA) monomers through emulsion polymerization. The so-produced hybrid copolymer (P(BuA-co-MPS)) and terpolymer (P(Styr-co-BuA-co-MPS)) latexes were cast into films that displayed a good optical transparency. The copolymers microstructure in the films was characterized by FTIR, 13C and 29Si solid state NMR spectroscopies, and was found to be highly dependent on parameters such as the monomer feed composition, the suspension pH and the silane addition profile. The films obtained from the hybrid latexes showed improved dynamic mechanical properties indicating that a reinforcing organo-mineral network had formed in the composite materials. The dynamic modulus of the hybrids increased with increasing silane contents while, concurrently, the tan δ peak shifted to higher temperatures, broadened and decreased in intensity. To cite this article: S. Vitry et al., C. R. Chimie 6 (2003). 相似文献
114.
Odobel F Suresh S Blart E Nicolas Y Quintard JP Janvier P Le Questel JY Illien B Rondeau D Richomme P Häupl T Wallin S Hammarström L 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(13):3027-3046
A set of twelve porphyrin dimers has been prepared to give information on how the type of connectivity between a porphyrin core and a bridge can influence the interporphyrin electronic interaction. The new porphyrin systems are substituted directly at the meso position with an oligothiophene chain tethered either with a single C-C sigma bond, a trans ethylenyl group, or a acetylenyl group. The compounds are easily obtained by palladium-catalyzed cross-coupling reactions (Stille, Heck, and Sonogashira) between 5-iodo-10,15,20-(3,5-ditert-butylphenyl)porphyrin and the appropriate oligothiophene derivative. This synthetic approach is straightforward and very effective for preparing oligothiophene-based prophyrin systems. The absorption spectra and the fluorescence properties of the dimers demonstrated the crucial importance of the characteristics of the chemical bond used to connect the bridge to the porphyrin unit. The magnitude of the electronic communication can thus be significantly modulated by altering the type of bond connectivity used to link the chromophore to the bridge. The present work shows that an oligothiophene spacer is a viable class of linker for connecting porphyrins, and that a quaterthiophene appended with ethynyl linkages affords a high electronic interaction over a distance as large as 28 A. A detailed computational study of these dimers has clarified the conditions needed for a conjugated system to behave as a molecular wire. These conditions are full planarity of the molecule and proper energy matching between the frontier orbitals of the bridge and the porphyrin. Intermolecular energy transfer in asymmetrical dyads composed of a zinc porphyrin and a freebase porphyrin has been studied by fluorescence spectroscopy. In all systems, this process is more than 98% efficient, and its rate constant decreases steadily in the order 4ZH > 1ZH > 3ZH approximately 2ZH. Thus, the largest rate (kEnT = 1.2 x 10(11) s-1) was found in the dyad linked with bisethynyl quaterthiophene, which represents the longest bridge within the series. These results clearly demonstrate that strong communication and also efficient photoinduced processes can be promoted over a large distance if the electronic structure of the molecular connector is appropriately chosen. 相似文献
115.
An efficient route to chiral chromene and tetrahydroquinoline ring models 3 and 4 was developed by means of the vanadium epoxidation of chiral homoallylic alcohols 12 and 19 followed by an intramolecular epoxide opening of 3,4-epoxy alcohols 14 and 20. The configuration of all compounds was confirmed using NMR analysis. 相似文献
116.
Salpin JY Mormann M Tortajada J Nguyen MT Kuck D 《European journal of mass spectrometry (Chichester, England)》2003,9(4):361-376
The hitherto unknown gas-phase basicity and proton affinity of 1,3,5-cycloheptatriene (CHT) have been determined by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Several independent techniques were used in order to exclude ambiguities due to proton-induced isomerisation of the conjugate cyclic C(7)H(9)(+) ions, [CHT + H](+). The gas-phase basicity obtained by the thermokinetic method, GB(CHT) = 799 +/- 4 kJ mol(-1), was found to be identical, within the limits of experimental error, with the values measured by the equilibrium method starting with protonated reference bases, and with the values resulting from the measurements of the individual forward and reverse rate constants, when corrections were made for the isomerised fraction of the C(7)H(9)(+) population. The experimentally determined gas-phase basicity leads to the proton affinity of cycloheptatriene, PA(CHT) = 833 +/- 4 kJ mol(-1), and the heat of formation of the cyclo-C(7)H(9)(+) ion, deltaH(f)(0)([CHT + H](+)) = 884 +/- 4 kJ mol(-1). Ab initio calculations are in agreement with these experimental values if the 1,2-dihydrotropylium tautomer, [CHT + H((1))](+), generated by protonation of CHT at C-1, is assumed to be the conjugate acid, resulting in PA(CHT) = 825 +/- 2 kJ mol(-1) and deltaH(f)(0)(300)([CHT + H((1))](+)) = 892 +/- 2 kJ mol(-1). However, the calculations indicate that protonation of cycloheptatriene at C-2 gives rise to transannular C-C bond formation, generating protonated norcaradiene [NCD + H](+), a valence tautomer being 19 kJ mol(-1) more stable than [CHT + H((1))](+). The 1,4-dihydrotropylium ion, [CHT + H((3))](+), generated by protonation of CHT at C-3, is 17 kJ mol(-1) less stable than [CHT + H((1))](+). The bicyclic isomer [NCD + H](+) is separated by relatively high barriers, 70 and 66 kJ mol(-1) from the monocyclic isomers, [CHT + H((1))](+) and [CHT + H((3))](+), respectively. Therefore, the initially formed 1,2-dihydrotropylium ion [CHT + H((1))](+) does not rearrange to the bicyclic isomer [NCD + H](+) under mild protonation conditions. 相似文献
117.
Peter M. Chapple Julien Cartron Ghanem Hamdoun Samia Kahlal Marie Cordier Hassan Oulyadi Jean-Franois Carpentier Jean-Yves Saillard Yann Sarazin 《Chemical science》2021,12(20):7098
The first families of alkaline-earth stannylides [Ae(SnPh3)2·(thf)x] (Ae = Ca, x = 3, 1; Sr, x = 3, 2; Ba, x = 4, 3) and [Ae{Sn(SiMe3)3}2·(thf)x] (Ae = Ca, x = 4, 4; Sr, x = 4, 5; Ba, x = 4, 6), where Ae is a large alkaline earth with direct Ae–Sn bonds, are presented. All complexes have been characterised by high-resolution solution NMR spectroscopy, including 119Sn NMR, and by X-ray diffraction crystallography. The molecular structures of [Ca(SnPh3)2·(thf)4] (1′), [Sr(SnPh3)2·(thf)4] (2′), [Ba(SnPh3)2·(thf)5] (3′), 4, 5 and [Ba{Sn(SiMe3)3}2·(thf)5] (6′), most of which crystallised as higher thf solvates than their parents 1–6, were established by XRD analysis; the experimentally determined Sn–Ae–Sn′ angles lie in the range 158.10(3)–179.33(4)°. In a given series, the 119Sn NMR chemical shifts are slightly deshielded upon descending group 2 from Ca to Ba, while the silyl-substituted stannyls are much more shielded than the phenyl ones (δ119Sn/ppm: 1′, −133.4; 2′, −123.6; 3′, −95.5; 4, −856.8; 5, −848.2; 6′, −792.7). The bonding and electronic properties of these complexes were also analysed by DFT calculations. The combined spectroscopic, crystallographic and computational analysis of these complexes provide some insight into the main features of these unique families of homoleptic complexes. A comprehensive DFT study (Wiberg bond index, QTAIM and energy decomposition analysis) points at a primarily ionic Ae–Sn bonding, with a small covalent contribution, in these series of complexes; the Sn–Ae–Sn′ angle is associated with a flat energy potential surface around its minimum, consistent with the broad range of values determined by experimental and computational methods.The complete series of heterobimetallic alkaline-earth distannyls [Ae{SnR3}2·(thf)x] (Ae = Ca, Sr, Ba) have been prepared for R = Ph and SiMe3, and their bonding and electronic properties have been comprehensively investigated. 相似文献
118.
Jean-Yves Saillard Samia Kahlal Vincent Ferrand Helen Stoeckli-Evans Georg Süss-Fink 《Journal of organometallic chemistry》2001,620(1-2):119-126
Triruthenium clusters containing a methylphenylsulfoximido cap or bridge, Ru3(CO)9(μ2-H)[μ3-NS(O)MePh] (1), Ru3(CO)10(μ2-H)[μ3-NS(O)MePh] (2), Ru3(CO)8(μ3-η2-CPhCHBu)[μ3-NS(O)MePh] (3), Ru3(CO)9(μ3-η2-PhCCCCHPh)[μ2-NS(O)MePh] (4), and Ru3(CO)7(μ2-CO)(μ3-η2-PhCCCCHPh)[μ3-NS(O)MePh] (5) have been examined by EHT and DFT calculations in order to analyze the bonding present in the clusters and to establish the electron counting. They clearly show that a μ3-sulfoximido group is not a 3e− ligand as one may be led to think at first sight, but rather acts as a three-orbital/5e− system, i.e. should be considered as isolobal to an N---R− ligand. Because of some delocalization of its π-type orbitals on the sulfur and oxygen atoms, it is expected to bind slightly less strongly to metal atoms than classical imido ligands. Once in a μ2 coordination mode, the sulfoximido ligand retains a lone pair on its pyramidalized N atom and becomes a two-orbital/3e− ligand. It follows that clusters 1, 2, 4 and 5 are electron-precise, whereas cluster 3 is electron deficient with respect to the 18e− rule but obeys the polyhedral skeletal electron pair electron-counting rules. Consistently, all the calculated clusters exhibit large HOMO–LUMO gaps and no trace of electron deficiency can be found in their electronic structures. 相似文献
119.
Jean-Yves Piquemal Sabine Halut Jean-Marie Brgeault 《Angewandte Chemie (International ed. in English)》1998,37(8):1146-1149
Model compounds for silica surfaces modified with metal complexes are provided by the mononuclear anionic diperoxo species 1 and the dinuclear complex anions 2 (M = Mo, W). They were obtained in fair to nearly quantitative yields by the reactions of Ph3SiOH and [Ph2Si(OH)]2O, respectively, with an aqueous solution of [MO(O2)2(H2O)2]. 相似文献
120.