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31.
Amido Ligands for the Synthesis of Polynuclear Lanthanoid Complexes By 1 : 1 reaction of LnBr3 with NaNHPh in THF the Rare-Earth Complexes [Ln2Br4(μ2-NHPh)2(thf)5] (Ln = Sm ( 1 ), Ln = Gd ( 2 )) with two bridging anilido ligands are obtained. In the system LnBr3/NaNHPh/(Me2SiO)3 the tetranuclear compounds [Ln4(μ4-O)(NHPh)3(OSiMe2NPh)6Na5(thf)7] · THF (Ln = Gd ( 3 ), Ln = Yb ( 4 )) can be built up. They have a central μ4-oxygene atom in the Ln4-tetrahedron. It has an oxa-dimethylsilyl-N-phenylamido ligand over all edges and an anilido ligand on three vertexes. By this reaction small amount of [Na4(thf)6Yb2(OSiMe2NPhSiMe2O)2(OSiMe2NPh)2(NHPh)2] ( 5 ) with a O- and N-bridged Yb–Na polyhedron and N-phenyl-bis(dimethylsilanolato)-ligands coordinating μ2-η2 with its oxygen atoms are obtained. Reaction of Lanthanideshalides with LiNHtBu leads to dimeric complexes. The formation of bridging oxasilylamido ligands is also observed. The compound [Li2Ln(OSiMe2NtBu)2(HNtBu)(thf)]2 (Ln=Sm ( 6 ), Gd ( 7 ) and Yb ( 8 )) contains now an O- and N-bridged Ln–Li polyhedron. (Crystal Data of 1–8 see ‘‘Inhaltsverzeichnis”︁”︁). 相似文献
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P. G. Thirolf D. Habs A. Henig D. Jung D. Kiefer C. Lang J. Schreiber C. Maia G. Schaller R. Schützhold T. Tajima 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,55(2):379-389
The ultra-high fields of high-power short-pulse lasers are expected to contribute to understanding fundamental properties of the quantum vacuum and quantum theory in very strong fields. For example, the neutral QED vacuum breaks down at the Schwinger field strength of 1.3×1018 V/m, where a virtual e+e- pair gains its rest mass energy over a Compton wavelength and materializes as a real pair. At such an ultra-high field strength, an electron experiences an acceleration of aS=2×1028g and hence fundamental phenomena such as the long predicted Unruh effect start to play a role. The Unruh effect implies that the accelerated electron experiences the vacuum as a thermal bath with the Unruh temperature. In its accelerated frame the electron scatters photons off the thermal bath, corresponding to the emission of an entangled pair of photons in the laboratory frame. While it remains an experimental challenge to reach the critical Schwinger field strength within the immediate future even in view of the enormous thrust in high-power laser developments in recent years, the near-future laser technology may allow to probe the signatures of the Unruh effect mentioned above. Using a laser-accelerated electron beam (γ~300) and a counter-propagating laser beam acting as optical undulator should allow to create entangled Unruh photon pairs (i.e., signatures of the Unruh effect) with energies of the order of several hundred keV. An even substantially improved experimental scenario can be realized by using a brilliant 20 keV photon beam as X-ray undulator together with a low-energy (γ≈2) electron beam. In this case the separation of the Unruh photon pairs from background originating from linearly accelerated electrons (classical Larmor radiation) is significantly improved. Detection of the Unruh photons may be envisaged by Compton polarimetry in a 2D-segmented position-sensitive germanium detector. 相似文献
35.
Kriegel I Jiang C Rodríguez-Fernández J Schaller RD Talapin DV da Como E Feldmann J 《Journal of the American Chemical Society》2012,134(3):1583-1590
The optical properties of stoichiometric copper chalcogenide nanocrystals (NCs) are characterized by strong interband transitions in the blue part of the spectral range and a weaker absorption onset up to ~1000 nm, with negligible absorption in the near-infrared (NIR). Oxygen exposure leads to a gradual transformation of stoichiometric copper chalcogenide NCs (namely, Cu(2-x)S and Cu(2-x)Se, x = 0) into their nonstoichiometric counterparts (Cu(2-x)S and Cu(2-x)Se, x > 0), entailing the appearance and evolution of an intense localized surface plasmon (LSP) band in the NIR. We also show that well-defined copper telluride NCs (Cu(2-x)Te, x > 0) display a NIR LSP, in analogy to nonstoichiometric copper sulfide and selenide NCs. The LSP band in copper chalcogenide NCs can be tuned by actively controlling their degree of copper deficiency via oxidation and reduction experiments. We show that this controlled LSP tuning affects the excitonic transitions in the NCs, resulting in photoluminescence (PL) quenching upon oxidation and PL recovery upon subsequent reduction. Time-resolved PL spectroscopy reveals a decrease in exciton lifetime correlated to the PL quenching upon LSP evolution. Finally, we report on the dynamics of LSPs in nonstoichiometric copper chalcogenide NCs. Through pump-probe experiments, we determined the time constants for carrier-phonon scattering involved in LSP cooling. Our results demonstrate that copper chalcogenide NCs offer the unique property of holding excitons and highly tunable LSPs on demand, and hence they are envisaged as a unique platform for the evaluation of exciton/LSP interactions. 相似文献
36.
A Mukherjee M Dasgupta DJ Hinde CR Morton AC Berriman RD Butt JO Newton H Timmers 《Pramana》2001,57(1):195-198
Fusion cross-sections for the 7Li + 12C reaction have been measured at energies above the Coulomb barrier by the direct detection of evaporation residues. The heavy
evaporation residues with energies below 3 MeV could not be separated out from the α-particles in the spectrum and hence their
contribution was estimated using statistical model calculations. The present work indicates that suppression of fusion cross-sections
due to the breakup of 7Li may not be significant for 7Li + 12C reaction at energies around the barrier. 相似文献
37.
G. M. Marshall A. Adamczak J. M. Bailey J. L. Beveridge G. A. Beer J. H. Brewer V. M. Bystritsky M. P. Faifman B. M. Forster M. C. Fujiwara T. M. Huber R. Jacot-Guillarmod P. Kammel K. R. Kendall N. P. Kherani S. K. Kim P. E. Knowles A. R. Kunselman M. Maier V. E. Markushin V. S. Melezhik G. R. Mason F. Mulhauser A. Olin C. Petitjean T. A. Porcelli L. A. Schaller V. A. Stolupin J. Zmeskal 《Hyperfine Interactions》2001,138(1-4):203-211
Since the discovery that muonic deuterium at energies near a few eV could travel distances of the order of 1 mm in condensed
hydrogen, and in particular that muonic tritium and muonic deuterium could emerge from the surface of a solid hydrogen layer,
the advantages of solid targets have enabled the study of several processes important in muon catalyzed fusion. A review of
the results is presented, emphasizing the strengths and limitations of the use of solid hydrogen layer targets.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
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Ohne Zusammenfassung
Optimization of gas-chromatographic element analysis via di(trifluoroethyl)dithiocarbamates相似文献
40.
H. Schaller und R. Neeb 《Fresenius' Journal of Analytical Chemistry》1986,323(5):469-472
Zusammenfassung Die Reaktion des Cr(VI) mit Dialkyldithiocarbamaten in saurer wäßriger Lösung wurde untersucht. Als Nebenprodukte konnten, außer im Falle des fluorierten Chelates, sauerstoffhaltige Cr(III)-Chelate nachgewiesen werden.Zur capillar-gas-chromatographischen Bestimmung des Cr(VI) erwies sich das Di(trifluorethyl)dithiocarbamat, mit Einschränkung auch das Diethyldithiocarbamat, als geeignet. Mit Hilfe des Di(trifluorethyl)dithiocarbamats ist die Bestimmung des Cr(VI) im unteren ppb-Bereich möglich.
Teil III: Fresenius Z Anal Chem 315:422
Die Untersuchungen wurden in dankenswerter Weise durch Mittel der Deutschen Forschungsgemeinschaft und des Verbands der Chemischen Industrie — Fonds der Chemie —, sowie durch das leihweise Überlassen einer Capillarsäule durch die Firma Macherey & Nagel unterstützt. 相似文献
Dialkyldithiocarbamates as reagents for the gas-chromatographic determination of metalsIV. Reaction of Cr(VI) with dialkyldithiocarbamates in aqueous solution — Application for the capillary-gas-chromatographic determination of chromium
Summary The reaction of Cr(VI) with dialkyldithiocarbamates in acid aqueous solution is investigated. Oxygen-containing Cr(III) chelates were found to be formed as byproducts, except in the case of the fluorinated chelate.For the capillary-gas-chromatographic determination of Cr(VI) di(trifluoroethyl)dithiocarbamate was suitable, with restriction also diethyldithiocarbamate. The determination of Cr(VI) was possible at the lower ppb-level with di(trifluoroethyl) dithiocarbamate.
Teil III: Fresenius Z Anal Chem 315:422
Die Untersuchungen wurden in dankenswerter Weise durch Mittel der Deutschen Forschungsgemeinschaft und des Verbands der Chemischen Industrie — Fonds der Chemie —, sowie durch das leihweise Überlassen einer Capillarsäule durch die Firma Macherey & Nagel unterstützt. 相似文献