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Chava Lifshitz 《Trends in analytical chemistry : TRAC》1982,1(13):301-304
The fragmentation patterns of polyatomic ions are the source of the analytical information provided by mass spectrometry. Recent developments in the study of theoretical aspects related to unimolecular dissociations of polyatomic ions have improved our understanding of these processes. 相似文献
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T. Saraidarov R. Reisfeld A. Sashchiuk E. Lifshitz 《Journal of Sol-Gel Science and Technology》2003,26(1-3):533-540
PbS nanocrystals (NCs) ranging between 4–8 nm were incorporated into Zirconium-Silica-Urethane (ZSUR) matrix obtained by the sol-gel method. The sizes of the particles were controlled by temperature treatment and by concentration of PbS in ZSUR matrix. The sizes of PbS NCs were determined by TEM measurements. The quantum size effect could also be extracted from optical absorption and photoluminescence spectra. The new matrix allows incorporation of up to 40% PbS forming a characteristic structure of dendrite by reacting lead acetate with ammonium thiocyanate in sol-gel matrix. The sol precursors of the matrix for Zirconium-Silica-Urethane contained zirconium oxide (ZrO2) matrix solution, tetramethoxysilane (TMOS), 3-glycid oxypropyl trimethoxysilane (GLYMO) and polyethylene urethane silane (PEUS) synthesized separately. The ZrO2 matrix solution was obtained from zirconium n-tetrapropoxide in propanol and acetic acid was used as a chelating agent to stabilize the zirconium oxide precursor. 相似文献
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Kinetic energy releases (KERs) in unimolecular fragmentations of singly and multiply charged ions provide information concerning ion structures, reaction energetics and dynamics. This topic is reviewed covering both early and more recent developments. The subtopics discussed are as follows: (1) introduction and historical background; (2) ion dissociation and kinetic energy release: kinematics; potential energy surfaces; (3) the kinetic energy release distribution (KERD); (4) metastable peak observations: measurements on magnetic sector and time-of-flight instruments; energy selected results by photoelectron photoion coincidence (PEPICO); (5) extracting KERDs from metastable peak shapes; (6) ion structure determination and reaction mechanisms: singly and multiply charged ions; biomolecules and fullerenes; (7) theoretical approaches: phase space theory (PST), orbiting transition state (OTS)/PST, finite heat bath theory (FHBT) and the maximum entropy method; (8) exit channel interactions; (9) general trends: time and energy dependences; (10) thermochemistry: organometallic reactions, proton-bound clusters, fullerenes; and (11) the efficiency of phase space sampling. 相似文献
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Wan Yong Feng Moshe Goldenberg Chava Lifshitz 《Journal of the American Society for Mass Spectrometry》1994,5(8):695-703
Thermal reactions of proton-bound dimers, (CH3CN)2H +, (CH3OCH3)2H +, and (CH3COCH3)2H+, were studied using a selected ion flow tube. Reactions observed include association, switching, and proton transfer. The association channel was observed only for base molecules that had hydrogen bonding protons such as NH3, CH3NH2, (CH3)2NH, and CH3OH. An association-insertion mechaniSoc was proposed in which the central proton of the symmetrically bound dimers is replaced by a protonated base, for example, NH 4 + . These reactions are relatively slow, which demonstrates a central barrier along the potential energy surface. Ether-containing dimers do not demonstrate this insertion reaction, except for diethers, for example, CH3OCH2CH2OCH3, which can form stable bicyclic structures. Dimers such as (HCOOH)2H+, which possess hydrogen bonding protons in the periphery, undergo switching reactions with ammonia and no insertion. 相似文献
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Using mutually modulated cross-gain modulation, Stokes optical frequency changes are converted into modulation phase changes with high sensitivity. In the slow-light transition regime, we demonstrate kilohertz sensitivity to the Stokes optical carrier frequency. The sensitivity is inversely proportional to the modulation frequency of the pump and Stokes beams. 相似文献