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81.
Kowalewski J Egorov A Kruk D Laaksonen A Nikkhou Aski S Parigi G Westlund PO 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2008,195(1):103-111
Aqueous solutions of simple nickel(II) salts are a classical test case for theories of the paramagnetic relaxation enhancement (PRE) and its dependence on the magnetic field (nuclear magnetic relaxation dispersion, NMRD), going back to late fifties. We present here new experimental data, extending the NMRD range up to 21T (900 MHz). In addition to salt solutions in (acidified) water, we have also measured on solutions containing glycerol. The aqueous solution data do not show any significant changes compared to the earlier experiments. The interpretation, based on the general ("slow-motion") theory is also similar to the earlier work from our laboratory. The NMRD-data in mixed solvents are qualitatively different, indicating that the glycerol not only changes the solution viscosity, but may also enter the first coordination sphere of the metal ion, resulting in lower symmetry complexes, characterized by non-vanishing averaged zero-field splitting. This hypothesis is corroborated by molecular dynamics simulations. A strategy appropriate for interpreting the NMRD-data for the chemically complicated systems of this type is proposed. 相似文献
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84.
Photon energy upconversion in porphyrins: one-photon hot-band absorption versus two-photon absorption 总被引:2,自引:0,他引:2
M. Drobizhev A. Karotki M. Kruk A. Krivokapic H. L. Anderson A. Rebane 《Chemical physics letters》2003,370(5-6):690-699
We study the porphyrin S1→S0 fluorescence and the photosensitized singlet oxygen 1Δg→3Σg phosphorescence, both originating from absorption of photons with energy less than the porphyrin S0→S1 transition energy. By measuring the excitation intensity dependence of fluorescence at lowered sample temperatures, we are able to discriminate between two parallel processes of one-photon hot-band absorption (HBA) and simultaneous two-photon absorption (TPA). When the HBA and TPA contributions are comparable in magnitude, we use this new method to determine absolute TPA cross-section. We also demonstrate for the first time a singlet oxygen photosensitization via HBA in porphyrin. 相似文献
85.
Photocycloadition of ethylvinylether and cyclopentene to 3,5-dimethylanisole yields derivatives of 1-methoxy-2, 4-dimethyltricyclo [3.3.0.02,8]oct-3-ene in which the substituents at positions 6 and/or 7 are endo. Structural proofs are based on 250 MHz 1H and 62.9 MHz 13C NMR spectra. 相似文献
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Bonner BE Buchanan JA Carey DC Clement JM Coleman RN Corcoran MD Cossairt JD Derevshchikov AA Grosnick DP Hill DA Imai K Lehar F de Lesquen A Lopiano D Luehring FC Kruk JW Kuroda K Maki T Makino S Masaike A Matulenko YA Meshchanin AP Michalowicz A Miettinen HE Miller DH Miyake K Mohammadzadeh AH Mutchler GS Nagamine T Nessi-Tedaldi F Nessi M Nurushev SB Nguyen C Ohashi Y Pauletta G Penzo A Phillips GC Read AL Roberts JB van Rossum L Salvato G Schiavon P Shima T Solovyanov VL Spinka HM 《Physical review letters》1988,61(17):1918-1921
88.
Belorizky E Fries PH Helm L Kowalewski J Kruk D Sharp RR Westlund PO 《The Journal of chemical physics》2008,128(5):052315
The enhancement of the spin-lattice relaxation rate for nuclear spins in a ligand bound to a paramagnetic metal ion [known as the paramagnetic relaxation enhancement (PRE)] arises primarily through the dipole-dipole (DD) interaction between the nuclear spins and the electron spins. In solution, the DD interaction is modulated mostly by reorientation of the nuclear spin-electron spin axis and by electron spin relaxation. Calculations of the PRE are in general complicated, mainly because the electron spin interacts so strongly with the other degrees of freedom that its relaxation cannot be described by second-order perturbation theory or the Redfield theory. Three approaches to resolve this problem exist in the literature: The so-called slow-motion theory, originating from Swedish groups [Benetis et al., Mol. Phys. 48, 329 (1983); Kowalewski et al., Adv. Inorg. Chem. 57, (2005); Larsson et al., J. Chem. Phys. 101, 1116 (1994); T. Nilsson et al., J. Magn. Reson. 154, 269 (2002)] and two different methods based on simulations of the dynamics of electron spin in time domain, developed in Grenoble [Fries and Belorizky, J. Chem. Phys. 126, 204503 (2007); Rast et al., ibid. 115, 7554 (2001)] and Ann Arbor [Abernathy and Sharp, J. Chem. Phys. 106, 9032 (1997); Schaefle and Sharp, ibid. 121, 5387 (2004); Schaefle and Sharp, J. Magn. Reson. 176, 160 (2005)], respectively. In this paper, we report a numerical comparison of the three methods for a large variety of parameter sets, meant to correspond to large and small complexes of gadolinium(III) and of nickel(II). It is found that the agreement between the Swedish and the Grenoble approaches is very good for practically all parameter sets, while the predictions of the Ann Arbor model are similar in a number of the calculations but deviate significantly in others, reflecting in part differences in the treatment of electron spin relaxation. The origins of the discrepancies are discussed briefly. 相似文献
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Prof. Danuta Kruk Dr. Pawel Rochowski Dr. Elzbieta Masiewicz Dr. Slawomir Wilczynski Milosz Wojciechowski Dr. Lionel M. Broche Prof. David J. Lurie 《Chemphyschem》2019,20(21):2816-2822
1H spin−lattice nuclear magnetic resonance relaxation experiments were performed for five kinds of dermal fillers based on hyaluronic acid. The relaxation data were collected over a broad frequency range between 4 kHz and 40 MHz, at body temperature. Thanks to the frequency range encompassing four orders of magnitude, the dynamics of water confined in the polymeric matrix was revealed. It is demonstrated that translation diffusion of the confined water molecules exhibits a two-dimensional character and the diffusion process is slower than diffusion in bulk water by 3–4 orders of magnitude. As far as rotational dynamics of the confined water is concerned, it is shown that in all cases there is a water pool characterized by a rotational correlation time of about 4×10−9 s. In some of the dermal fillers a fraction of the confined water (about 10 %) forms a pool that exhibits considerably slower (by an order of magnitude) rotational dynamics. In addition, the water binding capacity of the dermal fillers was quantitatively compared. 相似文献