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31.
32.
Ramachandran PV Rudd MT Burghardt TE Ram Reddy MV 《The Journal of organic chemistry》2003,68(24):9310-9316
A modified hydroalumination protocol for the preparation of [alpha-(ethoxycarbonyl)vinyl]diisobutylaluminum and its beta-methyl or -phenyl analogues was developed. These vinylaluminum reagents react with aldehydes and ketones to provide the corresponding functionalized allyl alcohols in good to excellent yields. Perfluoroalkyl and -aryl carbonyl compounds, alpha-keto esters, alpha-acyl cyanides, and alpha-acetylenic ketones provide the corresponding alpha-hydroxyalkenes in high yields. The allyl alcohol product ratios from the vinylalumination of unsymmetrical alpha-diketones with [alpha-(ethoxycarbonyl)vinyl]diisobutylaluminum and its beta-methyl or -phenyl analogues depend on the steric and electronic environments of the ketones as well as the reagents. The products from the vinylalumination of alpha-bromoaldehydes and -ketones were cyclized with K2CO3 or KF under nonaqueous conditions to provide functionalized vinylepoxides in high yields. Vinylaluminations of keto-protected pyruvaldehyde provided the products, which were converted to alpha-alkylidene-beta-hydroxy-gamma-lactones. 相似文献
33.
MA Freitas SR Dillon RC Dougherty AG Marshall 《Rapid communications in mass spectrometry : RCM》1999,13(15):1622-1625
The self-chemical ionization of diethylzinc is examined by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry and semiempirical molecular orbital calculations. Electron impact of diethylzinc neutral produces the radical cation, C(4)H(15)Zn(+) (m/z x 122), which reacts further with the neutral (C(2)H(5))(2)Zn to give the following product ions: Zn(+) (m/z x 64), C(2)H(5)Zn(+) (m/z x 93), C(4)H(9)Zn(+) (m/z x 121), C(4)H(11)Zn(2)(+) (m/z x 187), and C(6)H(15)Zn(2)(+) (m/z x 215). To determine the structure and pathways for production of these ions, monoisotopic (12)C(4)H(15)(64)Zn(+), (64)Zn(+) and (12)C(2)H(5)(64)Zn(+) were individually isolated and reacted with the neutral background. We also performed semiempirical molecular orbital calculations (ZINDO/1). The molecular orbital calculations and experimental data are consistent in predicting that the ethyl group on the diethylzinc cation carries the positive charge. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
34.
Gromov EV Burghardt I Köppel H Cederbaum LS 《The journal of physical chemistry. A》2005,109(20):4623-4631
The low-lying excited singlet states of trans-p-coumaric acid (CA) and trans-p-coumaric thio acid (CTA) are investigated in view of characterizing the chromophore of the photoactive yellow protein (PYP), with particular regard to the impact of sulfur on the chromophore's electronic structure. The comparative ab initio study, performed with the highly accurate EOM-CCSD method, shows that the electronic state ordering upon vertical excitation and following in-plane geometry relaxation indeed depends in a very sensitive fashion on the presence of either sulfur or oxygen. The study identifies three relevant excited singlet states, two of which are of pi-pi type while the third state is of n-pi character. The study highlights the role of the latter n-pi state which is shown to be the lowest-lying excited state of CTA at all in-plane geometries under consideration, whereas this is not the case for CA. 相似文献
35.
F. J. Burghardt 《International Journal of Theoretical Physics》1980,19(11):843-866
In this paper we investigate a modal calculus of quantum metalogic which is complete and sound with respect to a dialogic semantics. This calculus calledM
eff(Q
eff) has three parts: one covering the formal metalogic, one reflecting the calculus of the object language, and one which is a link between object language and metalanguage. This third part is invariant with respect to a variation of the object language 相似文献
36.
Dysprosium atoms were isotope selectively excited by cw dye laser light. They were ionized by charge transfer collisions with Cs+ ions. The process was found to discriminate well between ground state and excited state atoms. The cross section ration for the two competing processes was determined to be about 103. 相似文献
37.
R. Burghardt 《Annalen der Physik》1990,502(5):383-390
Group Action and Differential Geometry The interdependence of group theory and differentialgeometry is worked out in respect to a fully covariant formulation of higher dimensional field theories. 相似文献
38.
Charles A. Burghardt 《Fresenius' Journal of Analytical Chemistry》1891,30(1):226-227
Ohne Zusammenfassung 相似文献
39.
R. Burghardt 《Annalen der Physik》1987,499(5):340-344
Covariant Principle of Variation in the Theory of Gravitation Gravitation theory treated in H.-J. Treder's version of Lorentz space is supplemented by a coordinate invariant variation principle. 相似文献
40.
The quantum-dynamical mechanism of photoinduced subpicosecond exciton dissociation and the concomitant formation of a charge-separated state at a semiconducting polymer heterojunction is elucidated. The analysis is based upon a two-state vibronic coupling Hamiltonian including an explicit 24-mode representation of a phonon bath comprising high-frequency (C==C stretch) and low-frequency (torsional) modes. The initial relaxation behavior is characterized by coherent oscillations, along with the decay through an extended nonadiabatic coupling region. This region is located in the vicinity of a conical intersection hypersurface. A central ingredient of the analysis is a novel effective mode representation, which highlights the role of the low-frequency modes in the nonadiabatic dynamics. Quantum dynamical simulations were carried out using the multiconfiguration time-dependent Hartree method. 相似文献