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41.
Multiconfigurational second order perturbation theory, with extended atomic basis sets and inclusion of scalar relativistic effects, was employed to investigate the low-lying (1)Sigma(+) electronic states of RhB. The [20.0] (1)Sigma(+) state is represented by a single configuration, mid R:[ellipsis (horizontal)]10sigma(2)11sigma(1)5pi(4)2delta(4)12sigma(1), derived from a single excitation (11sigma-->12sigma) from the ground state, which defines its electronic nature. A new excited state, coined as [9.0] (1)Delta (R(0)=1.786A, DeltaG(12)=792 cm(-1)), located 9221 cm(-1) above the X(1)Sigma(+) state, and described by the |...10sigma(2)11sigma(2)5pi(4)2delta(3)12sigma(1)> electronic configuration, was also identified. 相似文献
42.
Lucena JR Ventura E do Monte SA Araújo RC Ramos MN Fausto R 《The Journal of chemical physics》2007,127(16):164320
Extended complete active space self-consistent field (CASSCF), multireference configuration interaction with singles and doubles (MR-CISD), and multireference average quadratic coupled cluster (MR-AQCC) calculations have been performed on the ground (S(0)) and first excited (nsigma(*),S(1)) states of the CF(3)Cl molecule. Full geometry optimizations have been carried out for S(0) as well as "relaxed" potential energy calculations for both states, along the C-Cl bond distance. Vertical excitation energies (DeltaE(vertical)), dissociation energies (DeltaE(diss)), dissociation enthalpies (DeltaH(diss)), and the oscillator strength (f) have also been computed. Basis set effects, basis set superposition error (BSSE), and spin-orbit and size-extensivity corrections have also been considered. The general agreement between theoretical and available experimental results is very good. The best results for the equilibrium geometrical parameters of S(0) (at MR-AQCCaug-cc-pVTZ+d level) are 1.762 and 1.323 A, for the C-Cl and C-F bond distances, respectively, while the corresponding experimental values are 1.751 and 1.328 A. The [angle](ClCF) and [angle](FCF) bond angles are in excellent agreement with the corresponding experimental values (110.3 degrees and 108.6 degrees ). The best calculated values for DeltaE(vertical), DeltaH(diss), and f are 7.63 eV [at the MR-AQCCaug-cc-pV(T+d)Z level], 3.59 eV[MR-AQCCaug-cc-pV(T+d)Z level+spin-orbit and BSSE corrections], and 2.74x10(-3) (MR-CISD/cc-pVTZ), in comparison with the corresponding experimental values of 7.7+/-0.1 eV, 3.68 eV, and 3.12 x 10(-3)+/-2.50 x 10(-4). The results concerning the potential energy curves for S(0) and S(1) show a tendency toward the nonoccurrence of crossing between these two states (in the intermediate region along the C-Cl coordinate), as the basis set size increases. Such tendency is accompanied by a decreasing well depth for the S(1) state. Dynamic electronic correlation (especially at the MR-AQCC level) is also an important factor toward an absence of crossing along the C-Cl coordinate. Further investigations of a possible crossing using gradient driven techniques (at CASSCF and MR-CISD levels) seem to confirm its absence. 相似文献
43.
44.
Danillo Valverde Adalberto V. S. de Araújo Antonio Carlos Borin 《Molecules (Basel, Switzerland)》2021,26(17)
The photophysical relaxation mechanisms of 1-cyclohexyluracil, in vacuum and water, were investigated by employing the Multi-State CASPT2 (MS-CASPT2, Multi-State Complete Active-Space Second-Order Perturbation Theory) quantum chemical method and Dunning’s cc-pVDZ basis sets. In both environments, our results suggest that the primary photophysical event is the population of the bright state. Afterwards, two likely deactivation pathways can take place, which is sustained by linear interpolation in internal coordinates defined via Z-Matrix scans connecting the most important characteristic points. The first one (Route 1) is the same relaxation mechanism observed for uracil, its canonical analogue, i.e., internal conversion to the ground state through an ethylenic-like conical intersection. The other route (Route 2) is the direct population transfer from the bright state to the triplet state via an intersystem crossing process involving the (/) singlet-triplet crossing point. As the spin-orbit coupling is not too large in either environment, we propose that most of the electronic population initially on the state returns to the ground following the same ultrafast deactivation mechanism observed in uracil (Route 1), while a smaller percentage goes to the triplet manifold. The presence of a minimum on the potential energy hypersurface in water can help to understand why experimentally it is noticed suppression of the triplet states population in polar protic solvent. 相似文献
45.
Tara A. McCampbell Blaine A. Kinkel Susie M. Miller Monte L. Helm 《Journal of chemical crystallography》2006,36(4):271-275
The crystal structures of M(P{Si(CH3)3}3)(CO)5, M = Cr (1), Mo (2), and W (3), have been determined. Crystal data for 1, trigonal crystal system, space group = P31, a, b = 9.2118(6) ?, c = 22.416(3) ?, V = 1647.3(2) ?3, Z = 3; for 2, trigonal crystal system, space group = P32, a, b = 9.3394(3) ?, c = 22.7375(12) ?, V = 1717.56(12) ?3, Z = 3; trigonal crystal system, space group = P32, a, b = 9.3147(5) ?, c = 22.6955(16) ?, V = 1705.33(18) ?3, Z = 3. All three structures show distorted octahedral coordination environments around the metal center and exhibit especially long M–P bond distances, illustrating the unique steric and electronic properties of this bulky phosphine ligand. The 31P{1H} NMR spectra of the compounds are also reported. 相似文献
46.
47.
Santos AK Machado LL Bizerra AM Monte FJ Santiago GM Braz-Filho R Lemos TL 《Natural product communications》2012,7(6):729-730
A new indole alkaloid of the pyridocarbazole type, named 6N-hydroxy-olivacine, and two known compounds, 2N-oxide-olivacine and olivacine, were isolated from roots of Peschiera affinis. The structures of the compounds were determined by spectroscopic {IR and extensive NMR (COSY, HMQC, HMBCand NOESY)} and EIMS analysis. 相似文献
48.
Manuel J.S. Monte Sónia P. Pinto Ana I.M.C. Lobo Ferreira Luísa M.P.F. Amaral Vera L.S. Freitas Maria D.M.C. Ribeiro da Silva 《The Journal of chemical thermodynamics》2012,45(1):53-58
This work reports new experimental thermodynamic results on fluorene. Vapor pressures of both crystalline and liquid phases were measured using a pressure gauge (capacitance diaphragm manometer) and Knudsen effusion methods over a wide temperature range (292.20 to 412.16) K yielding accurate determination of enthalpy and entropy of sublimation and of vaporization. The enthalpy of sublimation was also determined using Calvet microcalorimetry. The enthalpy of fusion was derived from vapor pressure results and from d.s.c. experiments. Static bomb calorimetry was used to determine the enthalpy of combustion of fluorene from which the standard enthalpy of formation in the crystalline phase was calculated. The enthalpy of formation in the gaseous phase was calculated combining the result derived for the crystalline phase with the enthalpy of sublimation. 相似文献
49.
Ulf Ryde Mats H. M. Olsson Björn O. Roos Antonio Carlos Borin 《Theoretical chemistry accounts》2001,105(6):452-462
The accuracy of theoretical calculations on models of the blue copper proteins is investigated using density functional theory
(DFT) Becke's three-parameter hybrid method with the Lee–Yang–Parr correlation functional (B3LYP) and medium-sized basis sets.
Increasing the basis set to triple-zeta quality with f-type functions on all heavy atoms and enlarging the model [up to Cu(imidazole-CH3)2(SC2H5) (CH3SC2H5)0/+] has only a limited influence on geometries and relative energies. Comparative calculations with more accurate wave-function–based
methods (second-order M?ller–Plesset perturbation theory, complete-active-space second-order perturbation theory, coupled-cluster
method, including single and double replacement amplitudes and in addition triple replacement perturbatively) and a variety
of basis sets on smaller models indicate that the DFT/B3LYP approach gives reliable results with only a small basis set dependence,
whereas the former methods strongly depend on the size of the basis sets. The effect of performing the geometry optimizations
in a continuum solvent is quite small, except for the flexible Cu-SMet bond. The results of this study confirm the earlier results that neither the oxidized nor the reduced copper site in the
blue proteins is strained to any significant degree (in energy terms) by the protein surrounding.
Received: 7 July 2000 / Accepted: 17 November 2000 / Published online: 21 March 2001 相似文献
50.
It is shown that the Einstein and Yang-Mills equations arise from the conditions for the space-time to be a submanifold of
a pseudo-Euclidean space with dimension greater than 5. Some possible applications to cosmology, spin-2 fields, and geometrodynamics
are discussed. 相似文献