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101.
The ionization and appearance potentials for the molecular and [M ? Me]+ ions of several stereoisomeric methyl-1,3-oxathianes were measured. The differences between the ionisation and/or appearance potentials are shown to correlate well with the conformational energy differences in question.  相似文献   
102.
Hydrolysis and speciation of aluminium sulfate octadecahydrate Al2(SO4)3·18H2OAl2(SO4)3·18H2O was studied by electrospray time of flight mass spectrometry (ESI TOF MS). Several novel polymeric species were determined. Highly charged polymers, characterized by other methods, such as the Keggin cation [Al13O4(OH)24(H2O)12]7+ and the octameric aluminium hydroxide cluster [Al8(OH)14(H2O)18](SO4)5 16H2O, were found using ESI-MS as the anions [Al13O4(OH)25(SO4)4]2− and [Al8O(OH)14(SO4)5(H2O)4]2−. All the main species identified contained sulfate or hydrogen sulfate. The compositions of the determined ions mimicked those of several stable mineral forms.  相似文献   
103.
The kinetics of the radical reactions of CH3 with HCl or DCl and CD3 with HCl or DCl have been investigated in a temperature controlled tubular reactor coupled to a photoionization mass spectrometer. The CH3 (or CD3) radical, R, was produced homogeneously in the reactor by a pulsed 193 nm exciplex laser photolysis of CH3COCH3 (or CD3COCD3). The decay of CH3/CD3 was monitored as a function of HCl/DCl concentration under pseudo-first-order conditions to determine the rate constants as a function of temperature, typically from 188 to 500 K. The rate constants of the CH3 and CD3 reactions with HCl had strong non-Arrhenius behavior at low temperatures. The rate constants were fitted to a modified Arrhenius expression k = QA exp (−Ea/RT) (error limits stated are 1σ + Students t values, units in cm3 molecule−1 s−1): k(CH3 + HCl) = [1.004 + 85.64 exp (−0.02438 × T/K)] × (3.3 ± 1.3) × 10−13 exp [−(4.8 ± 0.6) kJ mol−1/RT] and k(CD3 + HCl) = [1.002 + 73.31 exp (−0.02505 × T/K)] × (2.7 ± 1.2) × 10−13 exp [−(3.5 ± 0.5) kJ mol−1/RT]. The radical reactions with DCl were studied separately over a wide ranges of temperatures and in these temperature ranges the rate constants determined were fitted to a conventional Arrhenius expression k = A exp (−Ea/RT) (error limits stated are 1σ + Students t values, units in cm3 molecule−1 s−1): k(CH3 + DCl) = (2.4 ± 1.6) × 10−13 exp [−(7.8 ± 1.4) kJ mol−1/RT] and k(CD3 + DCl) = (1.2 ± 0.4) × 10−13 exp [−(5.2 ± 0.2) kJ mol−1/RT] cm3 molecule−1 s−1.  相似文献   
104.
5-(Diphenylphosphanyl)-10,15,20-triarylporphyrins (meso-phosphanylporphyrins) underwent complexations with palladium(II) and platinum(II) salts to afford phosphapalladacycle- and phosphaplatinacycle-fused coplanar porphyrin dimers, respectively, via regioselective peripheral β-C-H activation of the meso-phosphanylporphyrin ligands. The optical and electrochemical properties of these metal-linked porphyrin dimers as well as their porphyrin monomer/dimer references were investigated by means of steady-state UV-vis absorption/fluorescence spectroscopy, cyclic and differential pulse voltammetry, time-resolved spectroscopy (fluorescence and transient absorption lifetimes and spectra), and magnetic circular dichroism spectroscopy. All the observed data clearly show that the palladium(II) and platinum(II) linkers play crucial roles in the electronic communication between two porphyrin chromophores at the one-electron oxidized state and in the singlet-triplet intersystem-crossing process at the excited state. It has also been revealed that the C-Pt-C linkage makes more significant impacts on these fundamental properties than the C-Pd-C linkage. Furthermore, density functional theory calculations on the metal-linked porphyrin dimers have suggested that the antibonding dπ-pπ orbital interaction between the peripherally attached metal and adjacent pyrrolic β-carbon atoms destabilizes the highest occupied molecular orbitals of the porphyrin π-systems and accounts for the observed unique absorption properties. On the basis of these experimental and theoretical results, it can be concluded that the linear carbon-metal-carbon linkages weakly but definitely perturb the optical, photophysical, and electrochemical properties of the phosphametallacycle-linked coplanar porphyrin dimers.  相似文献   
105.
The excited-state proton transfer and subsequent intramolecular ion pair formation of a cupreidine-derived Cinchona organocatalyst () were studied in THF-water mixtures using picosecond time-resolved fluorescence together with global analysis. Full spectral and kinetic characterization of all the fluorescent species allowed us to monitor the 3-step process for the ion pair dissociation. In the first step, proton transfer occurs through a water "wire" from the 6-hydroxyquinoline unit (excited-state acid) to the covalently bonded basic quinuclidine moiety, resulting in a hydrogen bonded ion pair. This was confirmed by the observed kinetic isotope effect in the presence of heavy water. In the second step, the formed ions are further solvated by a few solvent molecules, producing the solvent separated ion pair. Finally, a fully solvated ion pair is formed. The 5-exponential global model derived from the reaction scheme describes the experimental data very well.  相似文献   
106.
The details of the mechanism of persistent luminescence were probed by investigating the trap level structure of Sr2MgSi2O7:Eu2+,R3+ materials (R: Y, La-Lu, excluding Pm and Eu) with thermoluminescence (TL) measurements and Density Functional Theory (DFT) calculations. The TL results indicated that the shallowest traps for each Sr2MgSi2O7:Eu2+,R3+ material above room temperature were always ca. 0.7 eV corresponding to a strong TL maximum at ca. 90 °C. This main trap energy was only slightly modified by the different co-dopants, which, in contrast, had a significant effect on the depths of the deeper traps. The combined results of the trap level energies obtained from the experimental data and DFT calculations suggest that the main trap responsible for the persistent luminescence of the Sr2MgSi2O7:Eu2+,R3+ materials is created by charge compensation lattice defects, identified tentatively as oxygen vacancies, induced by the R3+ co-dopants.  相似文献   
107.
Chromium trioxide forms an adduct with zwitterionic quinolinic acid. The structure of the product was found to be (quinolinium-3-carboxylato-O)trioxidochromium(VI), determined by single-crystal X-ray diffraction methods. To evaluate the bonding properties of the compound, its structure was optimized at the B3LYP/6-311G* level of theory. The electronic characteristics were investigated by topological methods applied to the total charge density in various model compounds including the title compound, title compound with a HF molecule presenting a hydrogen bonding and anionic moiety. Calculated aromaticity indices indicate that the quinolinic rings tend to conserve their degree of aromaticity against hydrogen bonding. However, when there is hydrogen bonding involving an N-H bond or when the quinolinium zwitterion is deprotonated, there are clear changes in the interaction between chromium trioxide and the quinolinic moiety.   相似文献   
108.
The existence of the different R2+/R3+/RIV (R: rare earth) ions as well as the modifications in the structural environment around the dopant and co-dopants in CaAl2O4:Eu2+,R3+ persistent luminescence materials was studied by LIII edge X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) measurements at Hamburger Synchrotronstrahlungslabor (HASYLAB) at Deutsches Elektronen-Synchrotron (DESY) (Hamburg, Germany). The measurements were carried out at 10 and 296 K for selected rare earth (co-)dopants (Eu2+; Ce3+, Nd3+, Sm3+, and Yb3+).  相似文献   
109.
Z-configured 1,4-diene or β, γ-unsaturated carbonyl systems are readily available by the Wittig reaction. Isomerization required for access into the E-series can easily be accomplished by irradiation using an ordinary tungsten lamp and diphenyl disulphide sensitizer. There is very little formatation of conjugated isomers (less than 1%).  相似文献   
110.
Fractional Brownian surfaces have frequently been used to model various physical processes and to generate artificial landscapes. We study a closely related process, called two-dimensional fractional Gaussian noise. We devise a method for generating realizations of this process using an approximate conditioning approach, motivated by results from the corresponding one-dimensional process applied in teletraffic modeling.  相似文献   
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