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31.
151Eu and 121Sb Mössbauer spectroscopy of EuSbSe3 and EuBiSe3 were measured at different temperatures. The presence of divalent europium and trivalent antimony were confirmed. The largely negative values of the isomer shift in 151Eu spectrum show highly ionic bonding within these two compounds. Both of them show magnetic hyperfine field splitting at 4.2 K, which indicates a change in the orientation of the EFG principal axis with respect to the magnetic hyperfine field direction. EuSbSe3 has slightly smaller electron density at the antimony nuclei, compared to Sb2Se3. 相似文献
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The valence levels of phridine adsorbed on Ph(111) at room temperature are investigated by angle-resolved UV photoemission using Hel and Hell resonance radiation. The spectra are interpreted in terms of a reduction of the surface molecule symmetry from C2v to C8. We suggest that pyridine is adsorbed with its aromatic ring plane tilted wit respect to the surface interaction with the substrate taking place through both N lone-pair and π electrons. 相似文献
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Florian Pielnhofer Jan Rothballer Philipp Peter Wenjie Yan Falko M. Schappacher Rainer Pöttgen Richard Weihrich 《无机化学与普通化学杂志》2014,640(2):286-294
In the shandite type solid solution InxSn2–xCo3S2 the transition from half metal ferromagnetic Sn2Co3S2 to the new thermoelectric InSnCo3S2 is related to A = In, Sn on different crystallographic sites. Effects and origin of crystal and electronic structure changes induced by A = In are now investigated within the solid solution 0 ≤ x ≤ 2 including In2Co3S2. Effects are studied from X‐ray data, 119Sn Mößbauer spectroscopy, and ab initio calculations. Their origin is explored by DFT modeling on site preference of In and Sn in a supercell, electric field gradients (EFG), spin polarization, band structures, and direct space analyses (ELF, AIM). Indium is found to cause the crystal structure distortion on one A site, the electronic structure distortion to the other, as a consequence of inverted anisotropic bonding. 相似文献
37.
A General Strategy for the Catalytic,Highly Enantio‐ and Diastereoselective Synthesis of Indolizidine‐Based Alkaloids
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Falko Abels Chris Lindemann Prof. Dr. Christoph Schneider 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(7):1964-1979
Sixteen indolizidine‐based alkaloids (IBAs) that were isolated as poison constituents of the skin of frogs were synthesized in a highly flexible and stereoselective manner. As a key step, a three‐component, organocatalytic, highly enantio‐ and diastereoselective vinylogous Mukaiyama–Mannich reaction was employed furnishing optically highly enriched butyrolactams as central intermediates on a multigram scale. The attached six‐membered ring was constructed through cyclization of the pendant enoate moiety onto the pyrrolidine ring. The absolute configuration of the bridgehead chiral center and the adjacent 8‐position was established in the initial vinylogous Mannich reaction, whereas the 3‐ and 5‐substituents were introduced through organometallic addition at a late stage of the synthesis with full stereochemical control from the substrate. With this strategy, simple as well as even more complex alkaloids were accessible in good overall yields as single stereoisomers. These syntheses also served to establish the absolute and relative configuration of those IBAs that had never been synthesized before. 相似文献
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A study has been made of the temperature dependence of deformation of CaA, CaX, and LaX zeolites when krypton or xenon is adsorbed, and also the deformation of activated carbon when dimethyl ether is adsorbed. It has been shown that the volume compressibility and the standard chemical potential of the adsorbate in a vacancy solution, within the interval of temperatures and pressures that were investigated, can be considered as linear functions of temperature. In this case, knowledge of the temperature dependence of sorptive deformation offers a means for calculating sorptive deformation curves for other temperatures.Institute of Physical Chemistry, Russian Academy of Sciences, 117915 Moscow. Institute of Petrochemical Synthesis, Russian Academy of Sciences. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 23–28, January, 1992. 相似文献
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Falko Schlottig Joachim Schreckenbach Klaus Witke Günter Marx 《Mikrochimica acta》1997,125(1-4):161-163
The composition and structure of the thin conversion films at pre- and breakdown state are investigated. The breakdown leads to a modified structure and composition. Raman spectra of modified films show the formation of glassy carbon with a defined size of crystallites. A typical morphology characterized by a strong structured surface indicates this breakdown state. Electron diffraction patterns of the pre-breakdown state show the presence of titanium nitride, titanium carbide and titanium oxide.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday 相似文献
40.
The adsorption of H2O on Al(111) has been studied by ESDIAD (electron stimulated desorption ion angular distributions), LEED (low energy electron diffraction), AES (Auger electron spectroscopy) and thermal desorption in the temperature range 80–700 K. At 80 K, H2O is adsorbed predominantly in molecular form, and the ESDIAD patterns indicate that bonding occurs through the O atom, with the molecular axis tilted away from the surface normal. Some of the H2O adsorbed at 80 K on clean Al(111) can be desorbed in molecular form, but a considerable fraction dissociates upon heating into OHads and hydrogen, which leaves the surface as H2. Following adsorption of H2O onto oxygen-precovered Al(111), additional OHads is formed upon heating (perhaps via a hydrogen abstraction reaction), and H2 desorbs at temperatures considerably higher than that seen for H2O on clean Al(111). The general behavior of H2O adsorption on clean and oxygen-precovered Al(111) (θO ? monolayer) is rather similar at low temperature, but much higher reactivity for dissociative adsorption of H2O to form OH adsis noted on the oxygen-dosed surface around room temperature. 相似文献