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111.
112.
Gregor W Grabner G Adelwöhrer C Rosenau T Gille L 《The Journal of organic chemistry》2005,70(9):3472-3483
[structure: see text] Chromanol-type compounds act as antioxidants in biological systems by reduction of oxygen-centered radicals. Their efficiency is determined by the reaction rate constants for the primary antioxidative reaction as well as for disproportionation and recycling reactions of the antioxidant-derived radicals. We studied the reaction kinetics of three novel chromanols: cis- and trans-oxachromanol and the dimeric twin-chromanol, as well as ubichromanol and ubichromenol, in comparison to alpha-tocopherol and pentamethylchromanol. The antioxidant-derived radicals were identified by optical and electron spin resonance spectroscopy (ESR). The kinetics of the primary antioxidative reaction and the disproportionation of the chromanoxyl radicals were assessed by stopped-flow photometry in different organic solvents to simulate the different polarities associated with biomembranes. Furthermore, the reduction of the chromanoxyl radicals by ubiquinol and ascorbate was measured after laser-induced one-electron chromanol oxidation in ethanol and in a micellar system, respectively. The rate constants showed that twin-chromanol had better radical scavenging properties than alpha-tocopherol and a significantly slower disproportionation rate of its corresponding chromanoxyl radical. In addition, the radical derived from twin-chromanol is reduced by ubiquinol and ascorbate at a faster rate than the tocopheroxyl radical. Finally, twin-chromanol can deliver twice as many reducing equivalents, which makes this compound a promising new candidate as artificial antioxidant in biological systems. 相似文献
113.
M. R. Blake J. L. Garnett I. K. Gregor S. B. Wild 《Journal of mass spectrometry : JMS》1978,13(1):20-24
The negative ion mass spectra of a series of monomeric and dimeric η5-cyclopentadienyl transition metal carbonyls have been examined. The base peak in the case of the monomeric compounds (η5-C5H5)V(CO)4, (η5-C5H5)Mn(CO)3 and (η5-CH3C5H4)Mn(CO)3 arises from a reductive decarbonylation of the parent molecule—the resulting radical anion [M–CO]? is formally isoelectronic with the molecular cations [M]? observed in the positive ion mass spectra of these compounds and subsequently undergoes successive decarbonylations to the ‘aromatic’ cyclopentadienyl anions. For the compound (η5-C5H5)Co(CO)2, however, a molecular anion was observed as the base peak which has been formulated as [(η3-C5H5)Co(CO)2]? in the light of considerations based on the rare gas rule. As expected, the dimeric molecules [(η5-C5H5)M(CO)3]2 (where M = Cr or Mo) and [(η5-C5H5)Fe(CO)2]2 (and its methyl analogue) undergo reductive cleavage of their metal-metal bonds to give the anions [(η5-C5H5)M(CO)3]? and [(η5-C5H5)Fe(CO)2]? as the base peaks in their negative ion mass spectra. The dimeric nickel compound [(η5-C5H5)Ni(CO)]2, however, reductively decarbonylates to the [M-CO]? radical anion as its predominant fragmentation in the gas phase. Very low abundances of [(η5-C5H5)Fe(CO)2] and [(η5-CH3C5H4)Fe(CO)2] were also observed. 相似文献
114.
The quantitative analysis of a low vapor pressure unstable solid mixture of amino acids is possible by putting the solid mixture in a crucible which is then placed directly into the ionization chamber of a mass spectrometer. Relative sensitivities for the various acids in a mixture can be established by the proper use of a particular amino acid as an internal-calibrating standard. The success of the method depends upon: (1) the reproducibility of the mass spectra of the pure components, (2) the ideal vapor pressure behavior of the solid mixture, (3) the preparation of an intimate solid mixture by rapid freezing of the water solution of the acids with subsequent vacuum sublimation of the ice and ball-milling the dried mixture. 相似文献
115.
116.
Hill NJ Reeske G Moore JA Cowley AH 《Dalton transactions (Cambridge, England : 2003)》2006,(40):4838-4844
The new Ar-BIAN complexes [(mes-BIAN)InCl(3)(THF)] (1), [(mes-BIAN)(2)Tl][PF(6)] (2), [(dipp-BIAN)SnCl(4)] (3), [(dipp-BIAN)SbCl(3)] (4), [(dipp-BIAN)BiCl(3)] (5) and [(mes-BIAN)BiCl(3)] (6) have been prepared by treatment of the neutral mes- and dipp-substituted BIAN ligands with the p-block reagents InCl(3), TlPF(6), SnCl(4), SbCl(3), and BiCl(3). The molecular structures of complexes 1-6 have been determined by single-crystal X-ray diffraction methods. However, only the atom connectivity was established for 5. 相似文献
117.
Reduction of AsCl3 with SnCl2, followed by treatment of the "AsCl" with a 1,4-diimine results in electron transfer and formation of an arsenic(III) salt, while treatment of this arsenic(I) reagent or AsI3 with an alpha,alpha'-diiminopyridine ligand forms an arsenic(I) salt. 相似文献
118.
119.
We provide a characterization in terms of Fatou closedness for weakly closed monotone convex sets in the space of \({\mathcal P}\)-quasisure bounded random variables, where \({\mathcal P}\) is a (possibly non-dominated) class of probability measures. Applications of our results lie within robust versions the Fundamental Theorem of Asset Pricing or dual representation of convex risk measures. 相似文献
120.
Floreano L Cossaro A Cvetko D Bavdek G Morgante A 《The journal of physical chemistry. B》2006,110(10):4908-4913
We studied the growth of pentacene (C22H14) on the Au(110) surface by means of He atom scattering and Synchrotron X-ray photoemission. We found that two-dimensional commensurate growth only occurs in the monolayer range for a substrate temperature, T(s), higher than approximately 370 K. Larger amounts of deposited molecules forms three-dimensional uncorrelated clusters on the wetting layer. The desorption of second layer molecules occurs at T(s) > or = 420 K. The highest coverage ordered phase displays a (6 x 8) symmetry and corresponds to the saturation coverage at T(s) = 420 K. The (3 x 6) symmetry phase, recently reported for a multilayer planar film [Ph. Guaino, et al. Appl. Phys. Lett. 2004, 85, 2777], is only found at a coverage slightly lower than the (6 x 8) one. The (3 x 6) phase corresponds to the saturation coverage of the first layer at T(s) = 470 K. 相似文献