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61.
Ab initio calculations have been carried out on low-lying singlet and triplet states of TeO2 at different levels of theory with basis sets of up to the augmented-polarized valence-quintuple-zeta quality. Equilibrium geometrical parameters, harmonic vibrational frequencies, and relative electronic energies of the X1A1, 1B1, 1B2, 1A2, 3A1, 3B1, 3B2, and 3A2 states of TeO2 have been calculated. Potential energy functions (PEFs) of the X1A1 and the (1)1B2 states were computed at the complete-active-space self-consistent-field multireference configuration interaction level, with a basis set of augmented-polarized valence-quadruple-zeta quality. Franck-Condon factors (FCFs) for the electronic transition between the X1A1 and (1)1B2 states of TeO2 were calculated with the above-mentioned ab initio PEFs. The (1)1B2 <-- X1A1 absorption spectrum of TeO2 was simulated employing the computed FCFs, which include Duschinsky rotation and anharmonicity, and compared with the recently published laser-induced fluorescence (LIF) spectrum of Hullah and Brown [J. Mol. Spectrosc. 200, 261 (2000)]. The ab initio results and spectral simulation reported here confirm the upper electronic state involved in the LIF spectrum to be the (1)1B2 state of TeO2 and also confirm the vibrational assignments of Hullah and Brown. However, our simulated spectrum suggests that the reported LIF spectrum from 345 to 406 nm represents only a portion of the full (1)1B2 <-- X1A1 absorption spectrum of TeO2, which extends from ca. 406 to 300 nm. Another dye other than the two used by Hullah and Brown is required to cover the 345-300 nm region of the LIF band. Ab initio calculations show strong configuration mixing of the (1)1B2 electronic surface with higher 1B2 states in a region of large TeO bond length (> or = 2.0 A) and OTeO bond angle (> or = 135.0 degrees). 相似文献
62.
能带是决定固体特性的头等重要的因素。我们用光谱方法对单相YBa2Cu2Ox高T。超导体进行了研究,测量了样品的反射-吸收谱、Raman光谱和荧光光谱.其350和500nm吸收带以及390nm,560nm荧光峰来自晶格中Cu+发光中心,是跃迁过程1A1g(3d10)-1Eg和~3Eg(3d94s1)。其720nm和860nm荧光峰来自Cu2+发光中心,是由于自由离子光谱项2D在八面体晶场、正交晶系晶场中分裂为5个能级之间的跃迁。此外,还有一些光谱可能来自晶格中Cu3+发光中心,其481cm-1和551cm-1声子对说明了312cm-1处声子对与电子系统是强耦合。 相似文献
63.
The “dual constraint” model developed by Mead, Van Dyke et al. is here extended by inclusion of “early-time” contour-length
fluctuations and constraint-release Rouse relaxation, and then evaluated by comparing its predictions with literature data
for over 50 different linear and star polymers. By combining the reptation model of Doi and Edwards with contour-length fluctuations
and constraint release, the model provides a systematic approach to prediction of the rheological properties of polymers.
The parameters are taken from the literature and used consistently for linear polymers, star polymers, and their mixtures
having the same chemical compositions. In most cases, the predictions of the model appears to agree well with data for monodisperse,
bidisperse, and polydisperse linear and star polymers, except at low molecular weights.
Received: 23 December 1999 Accepted: 28 March 2000 相似文献
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Eric M. Peters John D. Van Dyke 《Journal of polymer science. Part A, Polymer chemistry》1992,30(9):1891-1898
Several polymers have been prepared by electropolymerization of mixtures of pyrrole (PY) and 2,2′-bithiophene (BT). Cyclic voltammetry on prepared polymer films shows three anodic oxidation peaks, two of which match the oxidation potentials of homopolymeric PY and BT, and a third which is intermediate. UV/visible spectroscopy displays a unique spectrum for each of the reduced and oxidized forms of these polymers. Nernstian plots from UV/visible data exhibit three well-defined redox couples in polymer films produced at 1.3 V. Overall, the data strongly support the formation of a copolymer, consisting of three distinct oxidizable units. Two of these can be attributed to short blocks of either PY or BT, and a third to random and alternate groupings of PY and BT. The polymers produced are electrically conductive, but the conductivity drops rapidly as BT units are introduced into a homopolymer of PY. © 1992 John Wiley & Sons, Inc. 相似文献
68.
The first band in the vacuum ultraviolet photoelectron spectrum of the silyl radical, corresponding to the process SiH3 (X 1A′1) ← SiH3(X 2A1), has been observed with HeI radiation. Extensive vibrational fine structure associated with the SiH3+ deformation vibration was observed in this band and analysis of the structure gave a value of ω = 820 = 40 cm-1 for the out-of-plane deformation mode in the ion. The vertical and adiabatic ionization energies were measured as 8.74 = 0.01 eV and 8.14 ± 0.01 eV respectively and use of the latter value together with the established heat of formation of the silyl radical allows an improved heat of formation of SiH3-. ΔH2980 (SiH3-) to be derived as 980 ± 7 kJ mol?1. 相似文献
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1-Allyl-2, 3-dimethyl-1, 2-dihydroisoquinoline does not rearrange to 3-allyl-2, 3-dimethyl-3, 4-dihydroisoquinolinium chloride when treated with dilute hydrochloric acid, but the introduction of a C1-Me or a C6-OMe substituent enables a reaction to proceed. A rationalisation is provided for these observations. 相似文献