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21.
Robert van Leeuwen Oleg Gritsenko Evert Jan Baerends 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1995,33(4):229-238
In this work we analyze the exchange-correlation potentialv xc within the Kohn-Sham approach to density functional theory for the case of atomic systems. The exchange-correlation potential is written as the sum of two potentials. One of these potentialsv xc,scr is the long-range. Coulombic potential of the coupling constant integrated exchange-correlation hole which represents the screening of the two-particle interactions due to exchange-correlation effects. The other potentialv xc,scr resp contains the functional derivative with respect to the electron density of the coupling constant integrated pair-correlation function representing the sensitivity of this exchange-correlation screening to density variations. As explicit expression of the exchange-part of this functional derivative is derived using an approximation for the Greens function of the Kohn-Sham system and is shown to display a distinct atomic shell structure. The corresponding potentialv xc,scr resp has a clear step structure and is constant within the atomic shells and changes rapidly at the atomic shell boundaries. Numerical examples are presented for the Be and Kr atoms using the Optimized Potential Model (OPM). 相似文献
22.
Bjrn Fritzell Britta Hammarberg Helge Schiratzki Stig Haglund Evert Knutsson Anders Mrtensson 《Journal of voice》1993,7(2)
From a total of 43 adductor spasmodic patients over a 10-year period, 11 underwent resection of a portion of the recurrent laryngeal nerve on one side. The initial results were excellent but a varying degree of recurrence took place in 8 patients. In 4, a reoperation was done. At the final follow-up, 2–8 years after the primary operation, 4 patients were no longer suffering from spasmodic dysphonia, another 5 were better off than before surgery, and 1 remained unchanged. Only 1 was worse off. Electromyographic findings indicated that the recurrence of symptoms was due to regeneration of the nerve fibers. 相似文献
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25.
Evert J. Elzinga Yuanzhi Tang Jason McDonald Stephanie DeSisto Richard J. Reeder 《Journal of colloid and interface science》2009,340(2):153-159
The interaction of selenate, selenite, and chromate with the hydrated surface of γ-Al2O3 was studied using a combination of macroscopic pH edge data, electrophoretic mobility measurements, and X-ray absorption spectroscopic analyses. The pH edge data show generally increased oxyanion adsorption with decreasing pH, and indicate ionic strength-(in)dependent adsorption of chromate and selenate across the pH range 4–9, and ionic strength-(in)dependent adsorption of selenite in this pH range. The adsorption of chromate peaks at pH 5.0, whereas for selenate and selenite no pH adsorption maxima are observed. Electrophoretic mobility measurements show that all three oxyanions decrease the zeta potential of γ-Al2O3 upon adsorption; however, only selenite decreased the pHPZC of the γ-Al2O3 sorbent. EXAFS data indicate that selenite ions are coordinated in a bridging bidentate fashion to surface AlO6 octahedra, whereas no second-neighbor Al scattering was observed for adsorbed selenate ions. Combined, the results presented here show that pH is a major factor in determining the extent of adsorption of selenate, selenite, and chromate on hydrated γ-Al2O3. The results point to substantial differences between these anions as to the mode of adsorption at the hydrated γ-Al2O3 surface, with selenate adsorbing as nonprotonated outer-sphere complexes, chromate forming a mixture of monoprotonated and nonprotonated outer-sphere adsorption complexes, and selenite coordinating as inner-sphere surface complexes in bridging configuration. 相似文献
26.
Martin J. Lofthouse Evert Ditzel Andrew J. Poole David J. Cole-Hamilton 《Journal of Cluster Science》2006,17(1):27-45
Reaction of CO with hydrogen in the presence of [Ru3(CO)12], KI and N-methylpyrrolidone produces small amounts of methanol under mild conditions. Using D2 the methanol is CD3OD confirming that it is a product of CO hydrogenation. In the presence of added H2O, CH
x
D1-y
OH/D (y=0–3) are produced. Carrying out the same reaction in the presence of MeI water and RhCl3·xH2O (x=3–4) produces ethanoic acid in a slow reaction which continues for at least 64 h. The effects of different reaction parameters
are discussed and labelling using 13CH3I shows that some of the ethanoic acid originates from sources other than MeI whilst labelling with D2, CD3I, and/or D2O suggest that some originates from CO and H2. Electrospray mass spectrometry and high pressure infra-red spectroscopic studies show that the main species present in catalytic
solutions are [HRu3(CO)11]−, [HRu4(CO)13]− and [Ru(CO)3I3]− for methanol carbonylation, [Ru(CO)3I3]− and [RhI2(CO)2]− for ethanoic acid production. A reaction carried out in the absence of [Ru3(CO)12] gave similar results to a reaction in which it was added, suggesting that the entire process may be catalysed by rhodium
complexes alone.
Electronic Supplementary Material Supplementary material for this article is available at and is accessible for authorized users.
相似文献
David J. Cole-HamiltonEmail: |
27.
We study systematically the vibrational circular dichroism (VCD) spectra of the conformers of a simple chiral molecule, with one chiral carbon and an "achiral" alkyl substituent of varying length. The vibrational modes can be divided into a group involving the chiral center and its direct neighbors and the modes of the achiral substituent. Conformational changes that consist of rotations around the bond from the next-nearest neighbor to the following carbon, and bond rotations further in the chain, do not affect the modes around the chiral center. However, conformational changes within the chiral fragment have dramatic effects, often reversing the sign of the rotational strength. The equivalence of the effect of enantiomeric change of the atomic configuration and conformational change on the VCD sign (rotational strength) is studied. It is explained as an effect of atomic characteristics, such as the nuclear amplitudes in some vibrational modes as well as the atomic polar and axial tensors, being to a high degree determined by the local topology of the atomic configuration. They reflect the local physics of the electron motions that generate the chemical bonds rather than the overall shape of the molecule. 相似文献
28.
Neugebauer J Baerends EJ Efremov EV Ariese F Gooijer C 《The journal of physical chemistry. A》2005,109(10):2100-2106
The results of time-dependent density functional theory (TDDFT) calculations of resonance Raman intensities are combined with experimental deep-ultraviolet resonance Raman measurements at a single wavelength, i.e., 244 nm, in order to test the possibility to distinguish several very similar compounds. Pyrene and three of its substituted derivatives, in which a single hydrogen atom has been replaced by a halogen atom, are compared. The fixed 244 nm excitation wavelength overlapped with the same electronic transition of the four pyrenes. Ground-state calculations using the BP86 exchange-correlation functional were used to predict the Raman frequencies, whereas excited-state calculations have been carried out employing the "statistical averaging of (model) orbital potentials" (SAOP) potential within a linear-response TDDFT framework in combination with the short-time approximation of resonance Raman intensities. In view of the simplistic theoretical approach, we find a surprisingly good agreement between the simulated and measured resonance Raman spectra of pyrene and its substituted analogues in terms of frequencies and intensities, which shows that the calculations can be used reliably to interpret the experimental spectra. With this combined information, it is possible to find criteria to distinguish the compounds under investigation, although many features of their vibrational spectra are similar. 相似文献
29.
Wang F Ziegler T van Lenthe E van Gisbergen S Baerends EJ 《The Journal of chemical physics》2005,122(20):204103
In the present work, we propose a relativistic time-dependent density-functional theory (TDDFT) based on the two-component zeroth-order regular approximation and a noncollinear exchange-correlation (XC) functional. This two-component TDDFT formalism has the correct nonrelativistic limit and affords the correct threefold degeneracy of triplet excitations. The relativistic TDDFT formalism is implemented into the AMSTERDAM DENSITY FUNCTIONAL program package for closed-shell systems with full use of double-group symmetry to reduce the computational effort and facilitate the assignments. The performance of the formalism is tested on some closed-shell atoms, ions, and a few diatomic molecules containing heavy elements. The results show that the fine structure of the excited states for most atoms and ions studied here can be accurately accounted for with a proper XC potential. For the excitation energies of the molecules studied here, the present formalism shows promise and the error encountered is comparable to that of nonrelativistic TDDFT calculations on light elements. 相似文献
30.
We report a Car-Parrinello molecular dynamics study of the liquid-liquid phase transition in phosphorus. We employed a gradient corrected density functional (B-LYP) to describe the electronic structure and performed simulations at constant pressure. Upon increasing pressure we observed, along the 1500 K isotherm, a structural transition converting the molecular P4 liquid into an atomic liquid with a network structure. Our calculations suggest this transition to be first order with a discontinuous density increase accompanied by an insulator into metal transition. The transition pressure is significantly higher than obtained by employing the less accurate local density functional (LDA) [Morishita, Phys. Rev. Lett. 87, 105701 (2001)], which matches the experimental value for the pressure. We argue why the LDA result should be considered fortuitous. The change of the calculated structure factor upon the transition shows the same trend as experimentally observed. Analysis of the structural changes during the phase transition revealed that a chain of linked and opened up ("butterfly") P4 molecules may serve as a seed triggering the transition from the molecular to the network phase. 相似文献