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81.
R. U. Beisembaev Yu. N. Vavilov M. I. Vil’danova N. G. Vil’danov V. V. Zhukov A. V. Kruglov R. A. Nam V. P. Pavlyuchenko V. A. Ryabov A. V. Stepanov Zh. S. Takibaev V. I. Yakovlev 《Bulletin of the Russian Academy of Sciences: Physics》2011,75(3):354-356
Extensive air showers (EASes) at zenith angles of 70–80 degrees with Vavilov-Cherenkov radiation having two and three maxima were registered at the Tian Shan Mountain Station of the Lebedev Physical Institute. In each such event, the subsequent maxima came with a time delay of 100 or more nanoseconds. Extensive air showers at a zenith angle of 70° with charged particles and Vavilov-Cherenkov radiation were also registered. 相似文献
82.
83.
Eva Vrublová Jitka Ulrichová Vilím Šimánek Miroslav Fojta Jan Vacek 《Electroanalysis》2010,22(24):2879-2883
This paper describes oxidation of the isoquinoline alkaloid, protopine (PR) at a pyrolytic graphite electrode (PGE) using cyclic and square‐wave voltammetry. In the alkaline range (pH 7.5–10.5) of a Britton–Robinson (B–R) buffer, a PR oxidation can be observed as a well‐developed voltammetric peak around +0.9 V (vs. Ag|AgCl|3 M KCl). With increasing pH of the B–R buffer, the PR peak is shifted to less positive potentials. The acquired voltammetric data suggest that PR strongly adsorbs onto the surface of the pyrolytic graphite where it is subjected to irreversible electrochemical oxidation in its uncharged free (tricyclic) base form. The results are discussed in connection with the electrochemical oxidation of other isoquinoline alkaloids and the potential applications of these data. 相似文献
84.
Vilà-Nadal L Mitchell SG Long DL Rodríguez-Fortea A López X Poblet JM Cronin L 《Dalton transactions (Cambridge, England : 2003)》2012,41(8):2264-2271
We present a combined theoretical and mass spectrometry study of the rotational isomerism of the non-classical Wells-Dawson anions. The structure is larger than the Keggin anion and six geometric isomers are predicted (α, β, γ, α*, β*, γ*) on the basis of structural arguments. This work explores the geometrical differences between the isomers and evaluates the stability of these unusual clusters based upon the inclusion of the different heteroatoms. We connect the theoretical results with experimental studies by exploring the fragmentation of the parent clusters by electrospray-ionisation mass spectrometry (ESI-MS). Both approaches show a general stability trend that can be postulated as follows: γ* > β* > α* > α ? β > γ where the isomers γ*, β* and α are the only anions of this type known to have been synthesised. 相似文献
85.
Primary alkylamines attach spontaneously from acetonitrile (ACN) solutions onto glassy carbon and metallic surfaces (Au, Pt, Cu, and Fe). The surface concentration of the organic layer measured from the integration of cyclic voltammograms appears close to or lower than that of a compact monolayer. The rate of the attachment depends on the concentration of the primary amino compound; it reaches a maximum after 3 h of immersion for the most concentrated solutions (20 mM). The modified surfaces have been characterized by cyclic voltammetry (CV), energy dispersive X-ray spectrometry (EDX), X-ray photoelectron spectroscopy (XPS), and infrared spectroscopy (ATR). The possible reaction mechanisms are discussed. 相似文献
86.
Rimola A Rodríguez-Santiago L Sodupe M 《The journal of physical chemistry. B》2006,110(47):24189-24199
The coordination properties of the four natural aromatic amino acids (AA(arom) = Phe, Tyr, Trp, and His) to Cu+ and Cu2+ have been exhaustively studied by means of ab initio calculations. For Cu+-Phe, Cu+-Tyr and Cu+-Trp, the two charge solvated tridentate N/O/ring and bidentate N/ring structures, with the metal cation interacting with the pi system of the ring, were found to be the lowest ones, relative DeltaG(298K) energies being less than 0.5 kcal/mol. The Cu+-His ground-state structure has the metal cation interacting with the NH2 group and the imidazole N. For these low-lying structures vibrational features are also discussed. Unlike Cu+ complexes, the ground-state structure of Cu2+-Phe, Cu2+-Tyr, and Cu2+-Trp does not present cation-pi interactions due to the oxidation of the aromatic ring induced by the metal cation. The ground-state structure of Cu2+-His does not present oxidation of the amino acid, the coordination to Cu2+ being tridentate with the oxygen of the carbonyl group, the nitrogen of the amine, and the N of the imidazole. Other less stable isomers, however, show oxidation of His, particularly of the imidazole ring, which can induce spontaneous proton-transfer reactions from the NH of the imidazole to the NH2 of the backbone. Finally, the computed binding energies for Cu+-AA(arom) and Cu2+-AA(arom) systems have been computed, the order found for the single charged systems being Cu+-His > Cu+-Trp > Cu+-Tyr > Cu+-Phe, in very good agreement with the experimental data. 相似文献
87.
V. A. Shabashov S. V. Borisov A. E. Zamatovskii A. V. Litvinov V. V. Sagaradze N. F. Vil’danova 《Bulletin of the Russian Academy of Sciences: Physics》2010,74(3):363-367
A nanostructuring procedure similar to that proposed previously for iron alloys with carbides, nitrides (γ′-Fe4N, TiN), and oxides, was implemented for X22 fcc alloy and X18H8 austenitic stainless steel. The procedure is based on the
deformation-induced dissolution of disperse CrN nitride particles in the alloy matrices and the formation of supersaturated
solid solutions of nitrogen, followed by the precipitation of secondary nanonitrides inhibiting the grain growth in the matrix
during heating. 相似文献
88.
Gianvito Vilé Dr. Sara Colussi Dr. Frank Krumeich Prof. Alessandro Trovarelli Prof. Javier Pérez‐Ramírez 《Angewandte Chemie (International ed. in English)》2014,53(45):12069-12072
The determination of structure–performance relationships of ceria in heterogeneous reactions is enabled by the control of the crystal shape and morphology. Whereas the (100) surface, predominantly exposed in nanocubes, is optimal for CO oxidation, the (111) surface, prevalent in conventional polyhedral CeO2 particles, dominates in C2H2 hydrogenation. This result is attributed to the different oxygen vacancy chemistry on these facets. In contrast to oxidations, hydrogenations on CeO2 are favored over low‐vacancy surfaces owing to the key role of oxygen on the stabilization of reactive intermediates. The catalytic behavior after ageing at high temperature confirms the inverse face sensitivity of the two reaction families. 相似文献
89.
90.
Vilà-Nadal L Mitchell SG Rodríguez-Fortea A Miras HN Cronin L Poblet JM 《Physical chemistry chemical physics : PCCP》2011,13(45):20136-20145
A complimentary combination of Density Functional Theory (DFT) methodology and Electrospray Ionization-Mass Spectrometry (ESI-MS) has been utilized to increase our limited understanding of the first nucleation steps in the formation of the [XM(12)O(40)](n-) Keggin polyoxometalates (POMs) (where addenda metal atom M = W or Mo, and the heteroatom X = P or As). We postulate that the first key steps of nucleation into discrete, high nuclearity heteropolyanions proceed via the formation of isodinuclear species (e.g. [M(2)O(7)](2-)), which undergo successive steps of protonation and water condensation to form a heterotrinuclear fragment, which acts as a template for the constituent parts required for subsequent aggregation and formation of the plenary Keggin heteropolyanion. The stability of calculated structures of the numerous postulated intermediates has been analysed and discussed in detail, and these results complemented using experimental mass spectrometry, using an assembly (reaction solution analysis) and disassembly (fragmentation of single crystals) approach. Overall, no significant differences between the Keggin POMs were found when changing the addenda metal atom (W or Mo) or the heteroatom (P or As); although small differences among the lowest-energy structures were detected. 相似文献