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51.
The behavior of protonated binary solvents injected into deuterated binary mobile phases in capillary LC is studied with NMR. Specifically, the solvent elution is followed on-flow with a capillary LC coupled to a 900 nL volume microcoil NMR probe. A range of identical composition 5% protonated (and 95% deuterated) solvents is injected into composition-matched deuterated mobile phases of CD(3)CN/D(2)O and CD(3)OD/D(2)O. The protonated components separate for all solvent combinations except at 80% CD(3)CN/20% D(2)O and similar to 72% CD(3)OD/28% D(2)O where only a single retention time is observed. The more hydrophilic protonated component, HOD, elutes first with higher percentages of hydrophilic solvent, D(2)O, in the mobile phase whereas retention is reversed with the higher percentage of the more hydrophobic solvent (CD(3)CN and CD(3)OD) in the mobile phase. The hydrophilic/hydrophobic nature of the chromatographic system as a function of mobile phase composition is characterized by following the retention times of protonated solvents. 相似文献
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Hebbinghaus G Rzaca-Urban T Senff C Lieder RM Gast W Krämer-Flecken A Schnare H Urban W de Angelis G Kleinheinz P Starzecki W Styczen J von Brentano P Dewald A Eberth J Lieberz W Mylaeus T v d Werth A Wolters H Zell KO Heppner S Hübel H Murzel M Grawe H Kluge H 《Physical review letters》1987,59(18):2024-2027
54.
Since in recent time several authors have questioned the traditional opinion on electromagnetic boundary conditions and the derivation of Fresnel's equations, this problem is reexamined from a strictly phenomenological point of view. Two kinds of surface-singularities are considered: those which are necessary to fullfill the boundary conditions and those which stem from a special surface-susceptibility. The discussion is confined to the case where there is no spatial dispersion. 相似文献
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Vasily N. Tsarev Dr. Dennis Wolters Dipl.‐Chem. Hans‐Joachim Gais Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(9):2904-2915
The Pd0 complex 1 that bears the Trost ligand 2 undergoes a facile redox reaction with 1,4‐biscarbonates 5 b – d and rac‐ 22 under formation of the diamidato–PdII complex 7 and the corresponding 1,3‐cycloalkadienes 8 b – d . The redox deactivation of complex 1 was the dominating pathway in the reaction of 5 b – d with HCO3? at room temperature. However, at 0 °C the six‐membered biscarbonate 5 b , catalytic amounts of complex 1 , and HCO3? mainly reacted in an allylic alkylation, which led to a highly selective desymmetrization of the substrate and gave alcohol 6 b with ≥99 % ee in 66 % yield. An increase of the catalyst loading in the reaction of 5 b with 1 and HCO3? afforded the bicyclic carbonate 12 b (96 % ee, 92 %). Formation of carbonate 12 b involves two consecutive inter‐ and intramolecular substitution reactions of the π‐allyl–PdII complexes 16 b and 18 b , respectively, with O‐nucleophiles and presumably proceeds through the hydrogen carbonate 17 b as key intermediate. The intermediate formation of 17 b is also indicated by the conversion of alcohol rac‐ 6 b to carbonate 12 b upon treatment with HCO3? and 1 . The Pd0‐catalyzed desymmetrization of 5 b with formation of 12 b and its hydrolysis allow an efficient enantioselective synthesis of diol 13 b . The reaction of the seven‐membered biscarbonate 5 c with ent‐ 1 and HCO3? afforded carbonate ent‐ 12 c (99 % ee, 39 %). The Pd0 complex 1 is stable in solution and suffers no intramolecular redox reaction with formation of complex 7 and dihydrogen as recently claimed for the similar Pd0 complex 9 . Instead, complex 1 is rapidly oxidized by dioxygen to give the stable PdII complex 7 . Thus, formation of the PdII complex 10 from 9 was most likely due to an oxidation by dioxygen. Oxidative workup (air) of the reaction mixture stemming from the desymmetrization of 5 c catalyzed by 1 gave the PdII complex 7 in high yield besides carbonate 12 c . 相似文献
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Munshi G Mustafa Sudhir Raniwala T Awes B Rai RS Bhalerao JG Contreras RV Gavai SK Ghosh P Jaikumar GC Mishra AP Mishra H Mishra B Mohanty J Nayak J-Y Ollitrault SC Phatak L Ramello R Ray PK Sahu AM Srivastava DK Srivastava VK Tiwari 《Pramana》2006,67(5):961-981
This is the report of Heavy Ion Physics and Quark-Gluon Plasma at WHEPP-09 which was part of Working Group-4. Discussion and
work on some aspects of quark-gluon plasma believed to have created in heavy-ion collisions and in early Universe are reported. 相似文献
60.
Our purpose is to understand the mechanism through which pH affects the competition between base-induced elimination and substitution. To this end, we have quantum chemically investigated the competition between elimination and substitution pathways in H2O+C2H5OH2+ and OH−+C2H5OH, that is, two related model systems that represent, in a generic manner, the same reaction under acidic and basic conditions, respectively. We find that substitution is favored in the acidic case while elimination prevails under basic conditions. Activation-strain analyses of the reaction profiles reveal that the switch in preferred reactivity from substitution to elimination, if one goes from acidic to basic catalysis, is related to (1) the higher basicity of the deprotonated base, and (2) the change in character of the substrates LUMO from Cβ−H bonding in C2H5OH2+ to Cβ−H antibonding in C2H5OH. 相似文献