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71.
A new quark interaction is derived, by means of a Tamm-Dancoff reduction, from an effective field theory constituent quark
model. In contrast to the standard Coulombic potential, the obtained interaction is nonlocal and energy dependent. Furthermore,
it becomes positive and rises up to a maximum value when the interquark distance increases, partially resembling some aspects
of the phenomenological Cornell potential. 相似文献
72.
Néstor?Armesto Leticia?Cunqueiro Carlos?A.?Salgado 《The European Physical Journal C - Particles and Fields》2009,61(4):775-778
We present a Monte Carlo implementation of medium-induced gluon radiation in the final-state branching process. Medium effects are introduced through an additive term in the splitting functions. We have implemented such modification within PYTHIA. We show the medium effects on the hump-backed plateau, and the transverse-momentum and angular distributions with respect to the parent parton. As expected, with increasing medium densities there is an increase (decrease) of partons with small (large) momentum fraction, and angular broadening is observed. The effects on the transverse-momentum distributions are more involved, with an enhancement of low- and intermediate-p T partons and a decrease at large p T, which is related to energy conservation, and to the lack of momentum exchange with the medium in our approach. 相似文献
73.
Manuela Leticia Kim 《Talanta》2009,79(3):940-930
In this work, a non-chromatographic procedure for the on-line determination of ultratraces of V(V) and V(IV) is presented. The method involves a solid phase extraction-flow injection system coupled to electrothermal atomic absorption spectrometry (SPE-FI-ETAAS). The system holds two microcolumns (MC) set in parallel and filled with lab-made mesoporous silica functionalized with 3-aminopropyltriethoxy silane (APS) and mesoporous silica MCM-41, respectively. The pre-concentration of V(V) is performed by sorption onto the first MC (C1) filled with APS at pH 3, whilst that of V(IV) is performed by sorption onto the second column (C2) filled with mesoporous silica MCM-41 at pH 5. Aqueous samples containing both analytes are loaded and, after pre-concentration (pre-concentration factor PCF = 10, sorption flow rate = 1 mL min−1, sorption time = 10 min), they are eluted in separate vessels with hydroxylammonium chloride (HC) 0.1 mol L−1 in HCl 0.5 mol L−1 (elution volume = 1 mL, elution flow rate = 0.5 mL min−1). Afterwards, both analytes are determined through ETAAS with graphite furnace. Under optimized conditions, the main analytical figures of merit for V(V) and V(IV) are, respectively: detection limits (3 s): 0.5 and 0.6 μg L−1, linear range: 2-100 μg L−1 (both analytes), sensitivity: 0.015 and 0.013 μg−1 L and sample throughput: 6 h−1 (both analytes). Recoveries of both species were assayed in different water samples. Validation was performed through certified reference materials for ultratraces of total vanadium in river water. 相似文献
74.
The influence of α-substitution in the structure, bonding and thermochemical properties of trifluoromethyl-pyridinol derivatives and their protonated counterparts has been studied by means of density functional theory. The geometries of the neutral and protonated species were optimized at the B3-LYP/6-311G(d,p) level of theory. Final energies were obtained through single point B3-LYP/6-311+G(3df,2p) calculations.The relative orientation of the different substituents within the heterocycle ring favours the formation of unexpected intramolecular hydrogen bonds (IHB), which have been characterized by means of the Atoms in Molecules theory of Bader. Although weak, these IHB are of great importance for understanding the gas phase structure and the thermodynamical properties of these compounds. Surprisingly, most of the substituted investigated pyridinols present proton affinities below or close to that calculated for the unsubstituted pyridine molecule. Only pyridinols bearing strong σ or π donor activating groups show proton affinities greater than that of pyridine. 相似文献
75.
Anharmonic vibrational frequencies, equilibrium bond lengths, rotational constants, and vibrational absorption spectra have been calculated for the triatomic anions, FHF(-) and OHF(-), and the heavier isotopomers FDF(-) and ODF(-). The triatomic anions are assumed to maintain a collinear configuration throughout all calculations, so only the symmetric (nu(1)) and asymmetric (nu(3)) stretching modes are considered. The two-dimensional permanent dipole surfaces and potential energy surfaces are then constructed along bond coordinates, using high-level ab initio methods. Fundamental and combination bands are obtained from the vibrational eigenfunctions, resulting in anharmonic frequencies, which can be compared with the available theoretical and experimental data. The agreement is very good, especially for the pure symmetric modes, while the asymmetric ones show larger discrepancies, presumably due to the neglected coupling between stretching and bending modes. Strong inverse anharmonicity is found in the level spacing of the asymmetric modes, for both FHF(-) and OHF(-) anions. The calculated mixed modes (nnu(1)+mnu(3), n, m=0-3) also agree reasonably with the few available experimental data, supporting our model. Based on the vibrational eigenfunctions, isotope effects are also rationalized. Infrared absorption spectra are calculated from the dipole autocorrelation function for FHF(-) and FDF(-), and for OHF(-) and ODF(-). Peak locations and relative intensities are assigned in terms of the fundamental and mixed transitions. 相似文献
76.
Jiménez-González L García-Muñoz S Alvarez-Corral M Muñoz-Dorado M Rodríguez-García I 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(34):8762-8769
2,3-Dihydrobenzofurans can be diastereoselectively prepared by condensation of aromatic aldehydes with 2,3-dihydrobenzoxasilepines under the catalysis of Ag(I) complexes, and in the presence of a source of fluoride ion. The application of this strategy by using chiral catalysts leads to a new enantioselective total synthesis of natural cis-pterocarpans and their trans isomers. Through this method, the first enantioselective total synthesis of the antifungal agent (-)-pterocarpin was achieved. In addition, a new entry into the heteroaromatic system of 2,5-dihydrobenzoxepine is also presented. 相似文献
77.
The electronic spectroscopy of CH3Mn(CO)5 has been investigated by means of ab initio multiconfigurational MS-CASPT2/CASSCF calculations. The absorption spectrum is characterized by a series of Metal-Centered (MC) excited states in the UV energy domain (below 290 nm) that could be responsible for the observed photoreactivity starting at 308 nm. The upper part of the spectrum is overcrowded between 264 and 206 nm and dominated by a high density of Metal-to-Ligand-Charge-Transfer (MLCT) states corresponding mainly to 3d(Mn) --> pi*(CO) excitations. A non-negligible contribution of Metal-to-sigma-Bond-Charge-Transfer (MSBCT) states corresponding to 3d(Mn) --> sigma*(Mn-CH3) excitations is also present in the theoretical spectrum of CH3Mn(CO)5. However, in contrast to other transition metal hydrides and methyl substituted (HMn(CO)5, HCo(CO)4, and CH3Co(CO)4) these MSBCT transitions do not participate to the lowest bands of the spectrum as main contributions. The photochemistry of CH3Mn(CO)5, namely the loss of a CO ligand vs. the metal-methyl bond homolysis, is investigated by means of MS-CASPT2 states correlation diagrams. This study illustrates the complexity of the photodissociation mechanism of this class of molecules, which involves a large number of nearly degenerate electronic states with several channels for fragmentation. 相似文献
78.
79.
Kinzel D González-Vázquez J González L 《Physical chemistry chemical physics : PCCP》2012,14(18):6241-6249
Non-adiabatic molecular dynamics simulations have been performed in the fluoro-olefin (4-methylcyclohexylidene) fluoromethane (4MCF) using multiconfigurational CASSCF (complete active space self-consistent field) on-the-fly calculations. As an olefin containing a C[double bond, length as m-dash]C double bond, 4MCF is expected to undergo cis-trans isomerization after light irradiation. However, ab initio molecular dynamics shows that a preferential dissociation of atomic hydrogen is taking place after population transfer to the bright ππ* state. This state is strongly mixed with πσ* states allowing dissociation in the electronic excited state before deactivation to the ground state occurs. A minor amount of trajectories experiences F-dissociation, followed by pyramidalization at the sp(2) carbons and CHF dissociation. In contrast, the amount of trajectories undergoing torsion around the double bond, and therefore cis-trans isomerization, is marginal. The H-abstraction reaction is ultrafast, taking place in less than 60 fs. 相似文献
80.
Benjamin Schulze Dr. Daniel Escudero Christian Friebe Dr. Ronald Siebert Dr. Helmar Görls Stephan Sinn Martin Thomas Sebastian Mai Prof. Dr. Jürgen Popp Prof. Dr. Benjamin Dietzek Prof. Dr. Leticia González Prof. Dr. Ulrich S. Schubert 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(13):4010-4025
A systematic series of heteroleptic bis(tridentate)ruthenium(II) complexes of click‐derived 1,3‐bis(1,2,3‐triazol‐4‐yl)benzene N^C^N‐coordinating ligands was synthesized, analyzed by single crystal X‐ray diffraction, investigated photophysically and electrochemically, and studied by computational methods. The presented comprehensive characterization allows a more detailed understanding of the radiationless deactivation mechanisms. Furthermore, we provide a fully optimized synthesis and systematic variations towards redox‐matched, broadly and intensely absorbing, cyclometalated ruthenium(II) complexes. Most of them show a weak room‐temperature emission and a prolonged excited‐state lifetime. They display a broad absorption up to 700 nm and high molar extinction coefficients up to 20 000 M ?1 cm?1 of the metal‐to‐ligand charge transfer bands, resulting in a black color. Thus, the complexes reveal great potential for dye‐sensitized solar‐cell applications. 相似文献