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Ohne ZusammenfassungMit 5 Abbildungen. 相似文献
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Arnim Spitzer 《Fresenius' Journal of Analytical Chemistry》1916,55(5-6):271
Ohne Zusammenfassung 相似文献
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A combined flash photolysis and pulse radiolysis experiment was carried out to produce triplet pyrene (P) molecules in micelles of cetyltrimethylammonium bromide and Br2? in the surrounding aqueous medium. The reaction 3Pmic + Br → P + 2 Br? was followed by optical absorption measurements in the 10?8?10?4–sec range. This reaction possesses a “fast” and a “slow” component with respective rate constants of 2.3 × 106 sec?1 and 1 × 109M?1 · sec?1. The fast component is related to the probability of a Br2? radical meeting a triplet pyrene containing micelle on the first encounter (only 16% of the micelles contained a triplet molecule). Reactions involving more than one Br2? radical–micelle encounter are ascribed to the slow component. The presence of two components reflects the fact that the residence time of a Br2? radical in the vicinity of a cationic micelle is substantially longer than the diffusion time of the radical between micelles. Thus the conditions met in micellar chemistry differ dramatically from those in ordinary solution kinetics where the encounter time is generally much shorter than the time between encounters. Some considerations on the energetics of this electron transfer reaction are also presented. 相似文献
5.
Aqueous solutions of Nal containing CCl4 and MgCl2 at various concentrations were irradiated under air with 1 MHz ultrasound and the yield of I3− was determined. The yield was not affected by MgCl2 at concentrations up to 0.1 M. This contrasts with the finding of Lepoint and co-workers, who reported a sharp minimum in the yield at a MgCl2 concentration of 2.5 × 10−3M, the yield decreased to 60% at 1 M MgCl2, the reason being the lower solubility of CCl4 at high MgCl2 concentrations. In the absence of CCl4, another dependence on the MgCl2 concentration was observed: the yield was not affected up to 1 M, and at higher MgCl2 concentrations the yield rapidly decreased owing to the increased viscosity of the solution. On the basis of these observations, there is no strong reason to postulate an electrical mechanism for the initiation of chemical reactions in the cavitation bubbles. 相似文献
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A. Henglein G. Schrader und R. Mühlmann 《Fresenius' Journal of Analytical Chemistry》1954,141(4):276-281
Ohne Zusammenfassung 相似文献
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Ohne Zusammenfassung 相似文献
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We present a parallel implementation of second-order M?ller-Plesset perturbation theory with the resolution-of-the-identity approximation (RI-MP2). The implementation is based on a recent improved sequential implementation of RI-MP2 within the Turbomole program package and employs the message passing interface (MPI) standard for communication between distributed memory nodes. The parallel implementation extends the applicability of canonical MP2 to considerably larger systems. Examples are presented for full geometry optimizations with up to 60 atoms and 3300 basis functions and MP2 energy calculations with more than 200 atoms and 7000 basis functions. 相似文献
10.
A generalization of the spin-component scaling and scaled opposite-spin modifications of second-order M?ller-Plesset perturbation theory to the approximate coupled-cluster singles-and-doubles model CC2 (termed SCS-CC2 and SOS-CC2) is discussed and a preliminary implementation of ground and excited state energies and analytic gradients is reported. The computational results for bond distances, harmonic frequencies, adiabatic and 0-0 excitation energies are compared with experimental results to benchmark their performance. It is found that both variants of the spin-scaling increase the robustness of CC2 against strong correlation effects and lead for this method even to somewhat larger improvements than those observed for second-order M?ller-Plesset perturbation theory. The spin-component scaling also enhances systematically the accuracy of CC2 for 0-0 excitation energies for pi --> pi* and n --> pi* transitions, if geometries are determined at the same level. 相似文献