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141.
The identification of radical species is possible by the electron spin resonance technique. However, the antioxidants in complex matrices such as biological and food samples are difficult to determine. Hence, we developed novel screening systems for antioxidants, which are mainly eliminating superoxide anion radical (O(2)(-)) and hydrogen peroxide (H(2)O(2)), by HPLC with luminol-based chemiluminescence (CL) detection. When the sample contains antioxidants, inhibited peaks corresponding to each antioxidant are observed on the chromatogram. The antioxidant activities of catechins and flavones were determined with flow injection analysis by the proposed indirect CL. The scavenging activity for H(2)O(2) and O(2)(-) were different from each catechin and flavone. Furthermore, the potential was dependent upon the number and the position of OH functional group in the structure. Some applications such as the screening of antioxidants in tea products were also investigated. In spite of many peaks appeared on the chromatogram at UV detection, only the peaks corresponding to the compounds having elimination effect to O(2)(-) and/or H(2)O(2) were detected as inhibited peaks. Consequently, the proposed HPLC-CL seems to provide new screening systems for antioxidants possessing inhibition activity of O(2)(-) and H(2)O(2). 相似文献
142.
Yuichiro Tada Masakatsu Ueno Noriaki Tsuchihashi Kiyoshi Shimizu 《Journal of solution chemistry》1994,23(9):973-987
The limiting molar conductances ° of potassium deuteroxide KOD in D2O and potassium hydroxide KOH in H2O were determined at 5 and 45°C as a function of pressure to clarify the difference in the temperature, pressure and isotope effects on the proton jump between an OD– (OH–) and a D3O+ (H3O+) ion. The excess conductances of the OD– ion in D2O and the OH– ion in H2O,
E
0
(OD-) and
E
0
(OH-), increase with increasing temperature and pressure as in the case of the excess deuteron and proton conductances,
E
0
(D+) and
E
0
(H+). However, the temperature effect on the excess conductance is larger for the OD–(OH–) ion than for the D3O+ (H3O+) ion but the pressure effect is much smaller for the OD– (OH–) ion than for the D3O+ (H3O+) ion. These findings are correlated with larger activation energies and less negative activation volumes found for the OD– (OH–) ion than for the D3O+ (H3O+) ion. Concerning the isotope effect, the value of
E
0
(OH-)/
E
0
(OD-) deviates considerably from
at each temperature and pressure in contrast with that of
E
0
(H+)/
E
0
(D+), although both of them decrease with increasing temperature and pressure. These results are discussed mainly in terms of the difference in repulsive force between the OD– (OH–) or the D3O+ (H3O+) ion and the adjacent water molecule, the difference in strength of hydrogen bonds in D2O and H2O, and their variations with temperature, pressure, and isotope. 相似文献
143.
144.
Hiroaki Tada Tetsuji Ishida Ayako Takao Seishiro Ito Sudip Mukhopadhyay Tomoki Akita Koji Tanaka Hisayoshi Kobayashi 《Chemphyschem》2005,6(8):1537-1543
TiO2 particles loaded with silver nanoparticles with a mean diameter of 1.5 nm exhibit a high photocatalytic activity (84 % conversion after 1 h irradiation) for the reduction of nitrobenzene to aniline with 100 % selectivity in the presence of CH3OH (concentration=100 mM). High-resolution transmission electron microscopic studies of Pt-photodeposited Ag/TiO2 demonstrate that the Ag nanoparticles act as reduction sites in the photocatalytic reaction. Both spectroscopic measurements and density functional theory (DFT) calculations reveal that nitrobenzene is selectively adsorbed onto the Ag surfaces of Ag/TiO2 via partial electron transfer from Ag to nitrobenzene, whereas the interaction between aniline and Ag/TiO2 is weak. The kinetic analysis indicates that the recombination between the electrons flowing into the Ag nanoparticle and the holes left in the TiO2 valence band is significantly suppressed, particularly in the presence of CH3OH. The high activity and selectivity in the present Ag/TiO2-photocatalyzed reduction are rationalized in terms of the charge separation efficiency, the selective adsorption of the reactants on the catalyst surfaces, and the restriction of the product readsorption. 相似文献
145.
A water-soluble phospholipid polymer having an active ester group in the side chain, poly[2-methacryloyloxyethyl phosphorylcholine (MPC)-co-n-butyl methacrylate (BMA)-co-p-nitrophenyloxycarbonyl polyethyleneglycol methacrylate (MEONP)(PMBN), was used for the immobilization of an enzyme on a plastic microchip. The MPC polymers with BMA units were adsorbed onto the poly(methyl methacrylate)(PMMA) microchip, and the active ester group in the MEONP unit reacted with the amino groups of the proteolytic enzyme, trypsin. Trypsin was immobilized on the sample reservoir, and catalyzed the hydrolysis of the fluorescently labeled ArgOEt to Arg. The consequent separation of product from the substrate, and their detection, were integrated on the microchip and this meant that all procedures from the enzymatic activity to product detection were completed in less than three minutes. 相似文献
146.
147.
148.
Synthesis of 8-hydroxypurine nucleosides 总被引:4,自引:0,他引:4
149.
Miyoko Kamigauchi Kinuko Iwasa Narao Takao Toshimasa Ishida Masatoshi Inoue 《Helvetica chimica acta》1987,70(6):1482-1486
The crystal structure of corycavine, a protopine-type alkaloid, has been determined by X-ray analysis. A conformational feature observed is the existence of a strong electrostade interaction between the N- and C-atom at a distance of 2.618 Å. Such an interaction stabilizes the 10-membered ring conformation of the structure. Analyses of NMR spectra indicate that corycavine has the same conformation in solution as in the crystal state. 相似文献
150.
Illudin S (lampterol) 总被引:1,自引:0,他引:1