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The use of an in situ generated Ni(0) catalyst associated with 2,2'-bipyridine or N,N'-bis(2,6-diisopropylphenyl)dihydroimidazol-2-ylidene (SIPr) as a ligand and NaO-t-Bu as the base for the intramolecular coupling of aryl chlorides with amines is described. The procedure has been applied to the formation of five-, six-, and seven-membered rings. [reaction: see text] 相似文献
3.
The compounds P2O3F4 and K2P2O5F2 have been studied by vibrational spectroscopy. From the shifts of the symmetric vibration of the terminal PO bonds it appears that the molecular structure contracts as the number of PO (bridged) and/or PF bonds increases. The changes occur at the expense of PO terminal bonds. In these tetrahedral phosphorus (V) compounds the PO (bridged) and PF bonding have a similar role, and the same phenomenon occurs in sulfur VI oxide fluoride compounds. 相似文献
4.
Phosphorescence has been simultaneously observed from both a 3π, π* and a 3n,π* level of 5-methylbicyclo-[4.3.01,5non-1-en-3-one. The emission from the higher energy 3n,π* state, which is in thermal equilibrium with the 3π,π* state, is quenched by lowering the temperature and also quenched by increasing the solvent polarity so as to raise the energy of the 3n,π* state relative to the 3π,π* state. 相似文献
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Ab initio HF/6-31G and DFT B3LYP/6-31G (d,p) calculations for the cleavage of Menger’s aliphatic amide 3 (a peptidase model) under physiological conditions, indicate that the rate limiting step in the cleavage process is a proton transfer from one of the carboxyl groups onto the amidic carbonyl oxygen. The acceleration in rates is mainly due to proximity orientation, and the effect of pseudoallylic strain relief on the rates is negligible. Moreover, the calculations reveal that the mode and the mechanism of the amide cleavage are largely dependent on the pH of the reaction. These results explain the findings that peptidase enzymes are reactive around neutral pH while their activities vanish under basic medium. 相似文献
7.
Numerical modeling of multiphase flow generally requires a special procedure at the solid wall in order to be consistent with Young's law for static contact angles. The standard approach in the lattice Boltzmann method, which consists of imposing fictive densities at the solid lattice sites, is shown to be deficient for this task. Indeed, fictive mass transfer along the boundary could happen and potentially spoil the numerical results. In particular, when the contact angle is less than 90 degrees, the deficiencies of the standard model are major. Various videos that demonstrate this behavior are provided (Supporting Information). A new approach is proposed and consists of directly imposing the contact angle at the boundaries in much the same way as Dirichlet boundary conditions are generally imposed. The proposed method is able to retrieve analytical solutions for static contact angles in the case of straight and curved boundaries even when variable density and viscosity ratios between the phases are considered. Although the proposed wetting boundary condition is shown to significantly improve the numerical results for one particular class of lattice Boltzmann model, it is believed that other lattice Boltzmann multiphase schemes could also benefit from the underlying ideas of the proposed method. The proposed algorithm is two‐dimensional, and the D2Q9 lattice is used. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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Measurements of18O self-diffusion in hematite (Fe2O3) natural single crystals have been carried out as a function of temperature at constant partial pressure aO 2=6.5·10?2 in the temperature range 890 to 1227 °C. The aO 2 dependence of the oxygen self-diffusion coefficient at fixed temperature T=1150 °C has also been deduced in the aO 2 range 4.5·10?4 - 6.5·10?1. The concentration profiles were established by secondary-ion mass spectrometry; several profiles exhibit curvatures or long tails; volume diffusion coefficients were computed from the first part of the profiles using a solution taking into account the evaporation and the exchange at the surface. The results are well described by $$D_O \left( {{{cm^2 } \mathord{\left/ {\vphantom {{cm^2 } s}} \right. \kern-\nulldelimiterspace} s}} \right) = 2.7 \cdot 10^8 a_{O_2 }^{ - 0.26} \exp \left( { - \frac{{542\left( {{{kJ} \mathord{\left/ {\vphantom {{kJ} {mol}}} \right. \kern-\nulldelimiterspace} {mol}}} \right)}}{{RT}}} \right)$$ From fitting a grain boundary diffusion solution to the profile tails, the oxygen self-diffusion coefficient in sub-boundaries has been deduced. They are well described by $$D''_O \left( {{{cm^2 } \mathord{\left/ {\vphantom {{cm^2 } s}} \right. \kern-\nulldelimiterspace} s}} \right) = 3.2 \cdot 10^{25} a_{O_2 }^{ - 0.4} \exp \left( { - \frac{{911\left( {{{kJ} \mathord{\left/ {\vphantom {{kJ} {mol}}} \right. \kern-\nulldelimiterspace} {mol}}} \right)}}{{RT}}} \right)$$ Experiments performed introducing simultaneously18O and57Fe provided comparative values of the self-diffusion coefficients in volume: iron is slower than oxygen in this system showing that the concentrations of atomic point defects in the iron sublattice are lower than the concentrations of atomic point defects in the oxygen sublattice. The iron self-diffusion values obtained at T>940 °C can be described by $$D_{Fe} \left( {{{cm^2 } \mathord{\left/ {\vphantom {{cm^2 } s}} \right. \kern-\nulldelimiterspace} s}} \right) = 9.2 \cdot 10^{10} a_{O_2 }^{ - 0.56} \exp \left( { - \frac{{578\left( {{{kJ} \mathord{\left/ {\vphantom {{kJ} {mol}}} \right. \kern-\nulldelimiterspace} {mol}}} \right)}}{{RT}}} \right)$$ The exponent - 1/4 observed for the oxygen activity dependence of the oxygen self-diffusion in the bulk has been interpreted considering that singly charged oxygen vacancies V O ? are involved in the oxygen diffusion mechanism. Oxygen activity dependence of iron self-diffusion is not known accurately but the best agreement with the point defect population model is obtained considering that iron self-diffusion occurs both via neutral interstitals Fe x i and charged ones. 相似文献
9.
The new compounds IO2PO2F2 and IO3PO2F2 have been prepared by the reaction of iodic and periodic acids on F2OPOPOF2. Raman spectra show a dimeric structure for IO3+ ion but a monomeric structure for IO2+ ion. 相似文献
10.
[reaction: see text] Reductive cleavage of the carbon-sulfur bond present in S-alkyl-thionocarbonates (xanthates) was achieved by high-yielding, tin-free radical reactions based on phosphorus reagents. The combination hypophosphorous acid/triethylamine/AIBN led to fast, efficient, and smooth formation of the alkane. Reduction with diethyl phosphite was sufficiently slow to permit sequential intermolecular addition of a 2-oxoalkyl xanthate onto an olefin followed by cleavage of the newly formed carbon-sulfur bond. 相似文献