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391.
Reaction between 3,4,5-triamino-1,2,6-thiadiazine 1,1-dioxides and aldehydes, in acetic acid or DMF, under anhydrous conditions, leads to a mixture of imidazo[4,5-c]- and pyrazino[2,3-c]-1,2,6-thiadiazine derivatives. The ratio of both compounds depends on the nature of the aldehydes used. The same reaction, in the absence of solvent, affords, only pyrazinothiadiazine derivatives. The uv, 1H- and 13C-nmr data of the new compounds are reported. 相似文献
392.
Relative values of the total reaction cross section σR for the crossed molecular beam reaction K + C2H5I → KI + C2H5 have been measured over the translational energy (ET) range 0 17–0.55 eV. It is found that σR decreases monotonically with ET over this range, any maximum in σR(ET) is presumed to lie below 0.17 eV. 相似文献
393.
A collision model for the kinetic energy dependence of the reaction cross section has been obtained by considering total angular momentum limitation at the entrance (reactants) or exit (products) reactive channel in the atom—diatom scheme. The model provides a satisfactory representation of the main “translational cross section features” (i.e., Arrhenius like behaviour near threshold, maximum, post-maximum decline and minimum) found in the reaction cross section by molecular beam experiments. Maximum and minimum explanations, including some predictions as well as a comparison with previous theoretical treatments are reported. Also an approximate method to obtain dissociation energies of the product diatom from the cross-section data is presented with relative success. 相似文献
394.
395.
We report experimental and numerical results showing how certain N-dimensional dynamical systems are able to exhibit complex time evolutions based on the nonlinear combination of N-1 oscillation modes. The experiments have been done with a family of thermo-optical systems of effective dynamical dimension varying from 1 to 6. The corresponding mathematical model is an N-dimensional vector field based on a scalar-valued nonlinear function of a single variable that is a linear combination of all the dynamic variables. We show how the complex evolutions appear associated with the occurrence of successive Hopf bifurcations in a saddle-node pair of fixed points up to exhaust their instability capabilities in N dimensions. For this reason the observed phenomenon is denoted as the full instability behavior of the dynamical system. The process through which the attractor responsible for the observed time evolution is formed may be rather complex and difficult to characterize. Nevertheless, the well-organized structure of the time signals suggests some generic mechanism of nonlinear mode mixing that we associate with the cluster of invariant sets emerging from the pair of fixed points and with the influence of the neighboring saddle sets on the flow nearby the attractor. The generation of invariant tori is likely during the full instability development and the global process may be considered as a generalized Landau scenario for the emergence of irregular and complex behavior through the nonlinear superposition of oscillatory motions. (c) 2000 American Institute of Physics. 相似文献
396.
B. P. Sobolev I. A. Sviridov V. I. Fadeeva S. N. Sulyanov N. I. Sorokin Z. I. Zhmurova P. Herrero A. Landa-Canovas R. M. Rojas 《Crystallography Reports》2005,50(3):478-485
The nonstoichiometric Ca1−x
LaxF2+x
phase (x ≥ 0.1) is obtained by mechanochemical synthesis from CaF2 and LaF3 single crystals. This phase is the first representative of fluorite fluorides obtained by mechanochemical synthesis in the
MFm-RFn systems (m < n ≤ 4). The average grain size ranges within 10–30 nm. The temperature dependence of ionic conductivity of the mechanochemically
synthesized phase pressurized at 600 MPa (at its high-temperature portion at temperatures exceeding 200–250°C) coincides with
the conductivity of the single crystals of the same composition (Ca0.8La0.2F2.2). The activation energy of ionic conductivity (0.95 eV) corresponds to migration of interstitial fluoride ions in the crystal
bulk. Mechanochemical synthesis of a multicomponent fluoride material with nanometer grains opens a new chapter in the chemistry
of inorganic fluorides. A decrease of the sintering temperature of the powders with nanometer grains is very important for
preparing dense fluoride ceramics of complicated compositions and other polycrystalline forms of fluoride materials.
__________
Translated from Kristallografiya, Vol. 50, No. 3, 2005, pp. 524–531.
Original Russian Text Copyright ? 2005 by Sobolev, Sviridov, Fadeeva, Sul’yanov, Sorokin, Zhmurova, Herrero, Landa-Canovas,
Rojas. 相似文献
397.
Herrero E Chen QS Hernández J Sun SG Feliu JM 《Physical chemistry chemical physics : PCCP》2011,13(37):16762-16771
The oxidation of adsorbed CO on Pt single crystal electrodes has been studied in alkaline media. The surfaces used in this study were the Pt(111) electrode and vicinal stepped and kinked surfaces with (111) terraces. The kinked surfaces have either (110) steps broken by (100) kinks or (100) steps broken by (110) kinks and different kink densities. The voltammetric profiles for the CO stripping on those electrodes show peaks corresponding to the oxidation of CO on the (111) terraces, on the (100) steps/kinks and on the (110) steps/kinks at very distinctive potentials. Additionally, the stripping voltammograms always present a prewave. The analysis of the results with the different stepped and kinked surfaces indicates that the presence of the prewave is not associated with defects or kinks in the electrode surface. Also, the clear separation of the CO stripping process in different peak contributions indicates that the mobility of CO on the surface is very low. Using partial CO stripping experiments and studies at different pH, it has been proposed that the low mobility is a consequence of the negative absolute potential at which the adlayers are formed in alkaline media. Also, the surface diffusion coefficient for CO in these media has been estimated from the dependence of the stripping charge of the peaks with the scan rate of the voltammetry. 相似文献
398.
Del Colle V Souza-Garcia J Tremiliosi-Filho G Herrero E Feliu JM 《Physical chemistry chemical physics : PCCP》2011,13(26):12163-12172
Ethanol oxidation on platinum stepped surfaces vicinal to the (111) pole modified by tin has been studied to determine the role of this adatom in the oxidation mechanism. Tin has been slowly deposited so that the initial stages of the deposition take place on the step, and deposition on the terrace only occurs when the step has been completely decorated. Voltammetric and chronoamperometric experiments demonstrate that tin on the step catalyzes the oxidation. The maximum enhancement is found when the step is completely decorated by tin. FTIR experiments using normal and isotopically labeled ethanol have been used to elucidate the effect of the tin adatoms in the mechanism. The obtained results indicate that the role of tin is double: (i) when the surface has sites capable of breaking the C-C bond of the molecule, that is, when the step sites are not completely covered by tin, it promotes the oxidation of CO formed from the molecular fragments to CO(2) through a bifunctional mechanism and (ii) it catalyzes the oxidation of ethanol to acetic acid. 相似文献
399.
400.
Roxanne Bercy Dr. Jean-Noël Rebilly Dr. Christian Herrero Dr. Régis Guillot Hélène Maisonneuve Prof. Frédéric Banse 《欧洲无机化学杂志》2023,26(34):e202300236
Three new amine/pyridine FeII complexes bearing pentadentate ligand with one, two or three electron enriched 4-methoxy-3,5-dimethylpyridine were used as catalysts for the oxidation of small organic molecules by hydrogen peroxide. The distribution of products formed suggests that these ligands are not enough electron donating to promote the O−O heterolytic cleavage of the oxidant in order to generate selective FeV(O) species. Using acetic acid in the reaction mixtures results in a significant increase of the efficiency of these catalytic systems. Our investigations show that the use of AcOH leads to the protonation/dissociation of a pyridyl moiety and the formation of (N4)FeII(OAc)(OH) species. These complexes readily react with excess hydrogen peroxide to yield (N4)FeIII(OAc)(OOH) intermediates. These latter intermediates are proposed to evolve into (N4)FeIV(OAc)(O), which are more efficient than the usual (N4)FeIV(O) and (N5)FeIV(O). 相似文献