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71.
We present a model of a new paramagnetic defect center which results from the interaction of atomic hydrogen with the MgO(1 0 0) surface. DFT calculations have been performed using periodic supercells and embedded cluster models where long-range polarization effects are included explicitly. The H atom promotes the creation of an oxygen vacancy (F center) by formation of the FS+(OH−) defect where an hydroxyl group is adsorbed near an electron trapped in an oxygen vacancy. This new center has some characteristics similar to those of the classical FS+ centers but a smaller formation energy; furthermore, being globally neutral, it can be treated also with supercell methods. 相似文献
72.
J. Friedl F. E. Wagner J. A. Sawicki D. C. Harris J. A. Mandarino Ph. Marion 《Hyperfine Interactions》1992,70(1-4):945-948
A survey of the197Au Mössbauer spectra of naturally occurring gold species is given. Gold minerals have been studied as natural specimens or as synthetic analogues. Gold impurities have been identified in pyrites and arsenopyrites. An example of the use of121Sb, and57Fe Mössbauer spectroscopy in characterizing gold-bearing ore minerals is given. 相似文献
73.
74.
Sublette Kerry L. Plato Amy Woolsey Marion Yates R. G. Camp Carl Bair Tom 《Applied biochemistry and biotechnology》1996,57(1):1013-1019
Applied Biochemistry and Biotechnology - Preliminary experiments have shown thatT. denitrificans strain F can be immobilized in DuPont BIO-SEP beads and used to treat refinery spent sulfidic... 相似文献
75.
Kiyohisa Fujimori Gregory T. Trainor Marion J. Costigan 《Journal of polymer science. Part A, Polymer chemistry》1984,22(10):2479-2487
A 1:1 hydrogen-bonded complex was formed between acrylic acid (AA) or methacrylic acid (MA) and the pyridine group of poly(4-vinylpyridine) (P4VP) in dilute solutions. A shift of infrared absorption of the hydrogen-bonded acid O? H to a lower energy direction and an upfield shift of acid proton in the NMR were observed when the monomers were added with pyridine. The equilibrium constants of the 1:1 complexation with P4VP measured by using a semipermeable membrane were 0.58 and 0.26 for AA and MA, respectively, at 25°C in methanol. The bromometrically measured initial rate of radical polymerization showed only a slight enhancement in the presence of P4VP, the rate being maximum at the 4VP unit:monomer mole ratio of 0.25 and 0.5 for AA and MA, respectively, in dilute methanol solution at 60°C. 相似文献
76.
Camden JP Bechtel HA Ankeny Brown DJ Martin MR Zare RN Hu W Lendvay G Troya D Schatz GC 《Journal of the American Chemical Society》2005,127(34):11898-11899
A comparison between theory and experiment for the benchmark H + CD4 --> HD + CD3 abstraction reaction yields a reinterpretation of the reaction mechanism and highlights the unexpected contribution of a stripping mechanism. Whereas the best analytic surface fails to reproduce experiment, a first-principles direct-dynamics (on the fly) treatment is in good agreement, showing that the H + CD4 reaction exhibits extreme sensitivity to modest differences in the potential energy surface. We find that bent H-D-C transition state geometries play an important role in the dynamics. A simple model that relates the scattering angle impact parameter and cone of acceptance accounts well for the overall reaction dynamics. 相似文献
77.
78.
79.
The chemical state of gold in gold ores, mattes and roaster products has been studied by197Au Mössbauer spectroscopy. Gold minerals were studied in order to provide reference data for the ore spectra.57Fe Mössbauer spectroscopy was used to monitor the iron compounds always present in gold ores and to follow their transformations caused by smelting and roasting. 相似文献
80.
Catherine E. Housecroft Ronald Snaith Karen Moss Robert E. Mulvey Marion E. ONeill Kenneth Wade 《Polyhedron》1985,4(11):1875-1881
Cluster bond enthalpies, EL(BB), and orders, n?(BB), for the structurally characterised closo anions, BnHn2? (n = 6 and 8–12), have been estimated using the logarithmic length—enthalpy and enthalpy—order relationships EL(BB) (kJ mol?1) = 1.766 × 1011 [L(BB)]?4.0 and EL(BB) (kJ mol?1) = 318.8[n?(BB)]0.697, respectively. In a parallel study, the molecular-orbital bond index CNDO-based calculation method has been used to give BB and BH bond indices, I(BB) and I(BH), from which bond index based bond enthalpies, EI, have been calculated using the relationships EI(BB) = 297.9 I(BB) and EI(BH) = 374.8I(BH) (enthalpies in kJ mol?1; lengths in pm). From these, total skeletal bond enthalpies Σ E(BB), and total bond enthalpies, Σ E(BB) + Σ E(BH), have been calculated. Although calculated values of EL and Σ EL generally exceed those of EI and Σ EI by some 8% and calculated values of I generally exceed those of n? by a greater amount, the trends in these parameters for the series of BnHn2? anions are very similar, showing the greater efficiency with which the n + 1 skeletal electron pairs are used as n increases. However, the two approaches differ in that, whereas the Σ EI values suggest that the anions are all of comparable stability, the ΣEL values clearly show B6H62?, B10H102? and B12H122? to be more stable than B8H82?, B9H92? and B11H112?. The interatomic distances in B7H72? and in the unknown B5 H52? are estimated and used to assess their relative stabilities. The EL values suggest that B7 H72? is of comparable stability to B8H82? etc., but show B5H52? as relatively unstable. The EI values suggest that both of these anions should be relatively stable members of the series of closo anions. 相似文献