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Complete (1)H and (13)C NMR signal assignments of two lactucin-type sesquiterpene lactone glycosides, derivatives of 11β,13-dihydrolactucin, isolated from roots of Picris conyzoides, were achieved by one- and two-dimensional NMR experiments, allowing the correction of previously published data for cichorioside B and the structure elucidation of its new ester with 3-hydroxy-2-methylpropanoic acid. In addition, seven known sesquiterpene lactones and three phenolic compounds were isolated from the plant material. 相似文献
13.
Zbigniew Kisiel Lech Pszczó?kowski Manfred Winnewisser Eric Herbst 《Journal of Molecular Spectroscopy》2005,233(2):231-243
We report the results of a comprehensive reinvestigation of the rotational spectrum of diethyl ether based on broadband millimetre-wave spectra recently recorded at The Ohio State University and in Warsaw, covering the frequency region 108-366 GHz. The data set for the ground vibrational state of trans-trans diethyl ether has been extended to over 2000 lines and improved spectroscopic constants have been determined. Rotational spectra in the first excited vibrational states of the three lowest vibrational modes of trans-trans-diethyl ether, ν20, ν39, and ν12 have been assigned. The v20 = 1 and v39 = 1 states are near 100 cm−1 in vibrational term value and are coupled by a strong c-axis Coriolis interaction, which gives rise to many spectacular manifestations in the rotational spectrum. All of these effects have been successfully fitted for a dataset comprising over 3000 transitions, leading to precise determination of the energy difference between these states, (ΔE/hc)=10.400222(5) cm−1. A newly developed software package for assignment and analysis of broadband spectra is described and made available. 相似文献
14.
Greggory S. Bennett Richard J. Farris 《Journal of polymer science. Part A, Polymer chemistry》1994,32(1):73-87
It is shown that amine-terminated poly(aryl ether ketone)s based on the reaction of 4,4'-difluorobenzophenone, and a substituted hydroquinone [either methylhydroquinone (MePK), t-butylhydroquinone (tBPK), or phenylhydroquinone (PhPK)] of controlled molecular weight and high amine-termination efficiency can be synthesized by a two-step reaction technique. Attempts to synthesize analogous materials by a one-step method were shown to be unsuccessful. The side groups are shown to have a large influence on the aromatic proton chemical shifts and this effect is characterized. The side groups and molecular weight are also shown to influence the thermal transitions of the respective polymers. The tBPK polymer possessed the highest glass transition temperature, while the MePK polymer was found to be the only semi-crystalline polymer; a unit cell is proposed. The side groups and molecular weight effects are also characterized as a function of thermal stability and mechanical properties. © 1994 John Wiley & Sons, Inc. 相似文献
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Mossety-Leszczak Beata Kisiel Maciej Lechowicz Jaromir B. Buszta Natalia Ostatek Robert Włodarska Magdalena 《Journal of Thermal Analysis and Calorimetry》2019,138(4):2435-2444
Journal of Thermal Analysis and Calorimetry - The curing behaviour of the composition of a liquid-crystalline diepoxy monomer (LCEM) with the central triaromatic mesogenic group was studied using... 相似文献
17.
Dr. Greggory T. Kent Emily Morgan Kaitlin R. Albanese Dr. Anna Kallistova Dr. Alexandra Brumberg Linus Kautzsch Dr. Guang Wu Prof. Pratap Vishnoi Prof. Ram Seshadri Prof. Anthony K. Cheetham 《Angewandte Chemie (International ed. in English)》2023,62(32):e202306000
Halide double perovskites [A2MIMIIIX6] are an important class of materials that have garnered substantial interest as non-toxic alternatives to conventional lead iodide perovskites for optoelectronic applications. While numerous studies have examined chloride and bromide double perovskites, reports of iodide double perovskites are rare, and their definitive structural characterization has not been reported. Predictive models have aided us here in the synthesis and characterization of five iodide double perovskites of general formula Cs2NaLnI6 (Ln=Ce, Nd, Gd, Tb, Dy). The complete crystal structures, structural phase transitions, optical, photoluminescent, and magnetic properties of these compounds are reported. 相似文献
18.
Dr. Iciar Uriarte Dr. Felipe Reviriego Dr. Camilla Calabrese Prof. José Elguero Prof. Zbigniew Kisiel Prof. Ibon Alkorta Dr. Emilio J. Cocinero 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(43):10172-10178
Bond length alternation is a chemical phenomenon in benzene rings fused to other rings, which has been mainly predicted theoretically. Its physical origin is still not clear and has generated discussion. Here, by using a strategy that combines microwave spectroscopy, custom-made synthesis and high-level ab initio calculations, we demonstrate that this phenomenon is clearly observed in the prototype indazole molecule isolated in the gas phase. The 1H-indazole conformer was detected by rotational spectroscopy, and its 17 isotopologues resulting from single and double heavy atom substitution (13C and 15N) were also unambiguously observed. Several experimental structures were determined and, in particular, the most useful semi-experimental equilibrium structure (reSE), allowed determination of the heavy atom bond lengths to milli-Ångstrom precision. The experimentally determined bond length alternation is estimated to correspond to 60:40 contributions from the two resonant forms of 1H-indazole. 相似文献
19.
The strongest vibrational satellites in the rotational spectrum of acrylonitrile have been assigned and frequencies of μa- and μb-type transitions in the frequency range 27–184 GHz are reported for the first two excited states in the lowest frequency in-plane CCN bending vibrational mode and the first excited state in the out-of-plane CCN bending mode. The values of the rotational constants, the quartic and sextic centrifugal distortion constants, and one octic centrifugal distortion constant are determined for each of these states. Less extensive results are also presented for the third quantum of the in-plane bend. The data set for the ground state has been extended by a number of new measurements and the improved ground state constants are used in a discussion of changes in rotational and centrifugal distortion constants with vibrational state where all constants associated with Pzn and P2Pz(n−2) terms in the Hamiltonian are found to reflect the common origin of the two CCN bends. 相似文献
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