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81.
82.
The G0W0, evGW0, evGW, and scGW0 approximations to many-body perturbation theory combined with the Bethe-Salpeter approach (BSE) are applied to calculate electronic and optical properties of the open-shell spinel ferrite ZnFe2O4. The effect of the various degrees of self-consistency is assessed by comparison to recent experimental results. Furthermore, the influence of the method for obtaining the ground-state wavefunction is studied, including the GGA functional PBE with and without an intermediate step using the COHSEX approximation, as well as PBE+U, where we try to minimize the influence of the Hubbard potential U. Best agreement for the optical band gap and the first maxima of the excitation spectrum is obtained with the evGW method based on a PBE+U wavefunction. This method is chosen and converged carefully to yield quantitative results for the optical spectra of four different magnetic structures and cation distributions of ZnFe2O4. With the results we provide a possible explanation for inconsistency in experimental results. 相似文献
83.
84.
Summary Quenching of luminescence of 1-amino-5, 6, 7, 8-tetrahydronaphthalene (ATHN) in nonpolar and polar solvents at 300 K and 77
K by the chloroalkanes carbon tetrachloride (CCl4), methyl chloroform (CH3CCl3), chloroform (CHCl3) and methylene chloride (CH2Cl2) is reported. Different photophysical parameters at 77 K of unperturbed and perturbed fluorescer ATHN in ternary solutions
are determined. The bimolecular dynamic fluorescence quenching rate constant (K
q) increases with the electron affinity (EA) of the quenchers and a linear correlation exists between lnK
q and EA. The quenching depends on polarity of solvents. The quenching is ascribed to contact CT exciplex formed between chloroalkanes
and excited singlet ATHN.
Riassunto Si riporta lo spegnimento di luminescenza dell' l-amino-5, 6, 7, 8-tetraidronaftalene (ATHN) in solventi non polari e polari a 300 K e 77 K mediante i cloroalcani tetracloruro di metilene (CH2Cl2). Si determinano diversi parametri fotofisici a 77 K di ATHN fluorescente perturbato e non perturbato in soluzioni ternarie. La constante (K q) del valore di smorzamento di fluorescenza dinamico bimolecolare aumenta con l'affinità elettronica (EA) degli spegnitori ed esiste una correlazione lineare tra lnK q ed EA. Lo spegnimento dipende dalla polarità dei solventi. Lo spegnimento è attribuito all'exciplex CT di contatto formato tra cloroalcani e ATHN a singoletti eccitati.相似文献
85.
Photodesorption and photofragmentation of disilane adsorbed on a hydrogen terminated Si(100) surface
The photochemical mechanisms leading to the desorption and fragmentation of Si2H6 adsorbed on a hydrogen terminated Si(100) surface have been explored by recording the time-of-flight distributions of products escaping from the surface and by using electron energy loss spectroscopy to probe possible electronic excitations. Photodesorption of intact Si2H6 involves hot electrons that lose energy and move to the conduction band edge before initiating desorption. When the wavelength of the incident light is 193 nm, Si2H6 fragments give mostly Si, SiH2, H2 and SiH4, but this pathway is quenched at longer wavelengths. This is consistent with direct excitation, but we also show that a negative ion resonance is accessible to substrate electrons that have been excited by 193 nm light. 相似文献
86.
A self-assembled monolayer of ferrocene-capped alkanethiols is produced in two stable oxidation states of Fe (Fe2+ and Fe3+). These oxidation states are detected with sub-monolayer sensitivity by the fine structure of the Fe2p absorption edge. The native Fe2+ ferrocene layer is converted chemically to Fe3+, and the Fe3+ layer can be transformed back to Fe2+ or possibly Fe0 by irradiation with soft X-rays. The results have implications on switching mechanisms in molecular electronics. 相似文献
87.
Photoredox-catalyzed radical reactions have attracted intense interest from synthetic chemists over the past several years. The photoredox-catalyzed C(sp2)–N coupling reactions, including Ullmann type C–N coupling (C–X/N–H type coupling), redox neutral C–N coupling (C–H/N–X type coupling) and oxidative C–N coupling (C–H/N–H type coupling), have been summarized in this digest. 相似文献
88.
The dynamics of S(3P2,1,0; 1D2; 1S0) production from the 193 nm photodissociation of CH3SH has been examined by 2+1 resonance-enhanced-multiphoton-ionization (REMPI) techniques. Using the rate equation scheme, we have rationalized the intensities of S(3P2,1,0; 1D2; 1S0) observed according to the sequential two-photon dissociative pathways, (A): CH3SH + hv (193 nm) → CH3S + hv (193 nm) → S and (B): CH3SH + hv (193 nm) → HS + hv (193 nm) → S, as the major mechanisms for S production. We have satisfactorily fitted the photodissociation laser power dependencies for S(3P) and S(1D) produced from CH3SH by invoking photodissociation cross sections and branching ratios S(3P)/S(1D) for CH3S and HS similar to those determined previously in the 193 nm photodissociation of CH3SCH3 and H2S. This observation supports that the 193 nm photodissociation of CH3S and HS prepared from CH3SH yield predominantly S(lD) and S(3P), similar to the cases for CH3S prepared from CH3SCH3 and for HS prepared from H2S, respectively. A small amount of S(1S0) observed from the 193 nm photodissociation of CH3SH is attributed to pathway (B). 相似文献
89.
Irradiation of 5,5-dimethyl-6-oxocyclohex- l-ene- l-carbonitrile ( 1 ) in the presence of 2,3-dimethylbut-2-ene afforded 3,3,4,4,7,7-hexamethyl-3,4,4a,5,6,7-hexahydroindeno[1,7-c,d]-],2-oxazole (3) in nearly quantitative yield. In contrast, 4,4-dimethyl-5-oxo-cyclopent-l-ene-l-carbonitrile ( 2 ) under the same conditions reacted not to a tricyclic isoxazole but to a 2:1 mixture of 3,3,6,6,7,7-hexamethyl-2-oxo-bicyclo[3.2.0]heptane-l-carbonitrile ( 4 ) and trans-3,3-dimethyl-2-oxo-5-(2,3-dimethylbut-3-en-2-yl)cyclopentane-l-carbonitrile ( 5 ), respectively. 相似文献
90.
Ole Buchardt 《Angewandte Chemie (International ed. in English)》1974,13(3):179-185
The reactions induced by circularly polarized light are reviewed and a general discussion of the induction of optical activity by circularly polarized light is presented. It is concluded that three different mechanisms, or their combinations, can cause asymmetric induction. In each case the optical yield is dependent on the optical anisotropy factor g, the ratio between the circular dichroism (Δ?) and the extinction coefficient (?). The results are discussed in terms of the presumed mechanisms, and particular attention is paid to the asymmetric synthesis of helicenes. It is concluded that this kind of photochemistry may have analytical importance. 相似文献