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71.
Voszka I Szabó Z Csík G Maillard P Gróf P 《Journal of photochemistry and photobiology. B, Biology》2005,79(2):83-88
The effect of the symmetry and polarity of the porphyrin molecules on their membrane localization and interaction with membrane lipids were investigated by electron paramagnetic resonance (EPR). For this purpose, two glycoconjugated tetraphenyl porphyrin derivatives were selected, respectively, symmetrically and asymmetrically substituted. Small unilamellar liposomes composed of dipalmitoylphosphatidylcholine (DPPC) and spin labeled stearic acids were prepared. The spin probe was located at the 5th or 7th or 12th or 16th position of the hydrocarbon chain in order to monitor various regions of the lipid bilayer. EPR spectra of porphyrin-free and porphyrin-bound liposomes were recorded at various temperatures below and above the phase transition temperature of DPPC. The effect on membrane fluidity proved to be stronger with the asymmetrical porphyrin derivative than with the symmetrical one. The rigidity increased when the spin label was near lipid head groups. The difference observed between control and porphyrin-treated samples when measured below the main lipid transition temperature disappeared at higher temperature. When the spin label was near the end of the hydrophobic tails, the symmetrical porphyrin derivative caused increase in fluidity, while the asymmetrical one slightly decreased it. To explain this phenomenon we propose that the asymmetrical derivative exerts a stronger ordering effect caused by its fluorophenyl group located at the level of the lipid heads, which is attenuated to the hydrophobic tails. The perturbing effect of the symmetric derivative could not lead to similar extent of ordering at the head groups and looses the hydrocarbon chains deeper in the membrane. 相似文献
72.
András Fási Péter Zsák István Pálinkó Klára Hernádi 《Reaction Kinetics and Catalysis Letters》2006,87(2):349-357
Summary Bimetallic (Fe-Co) catalyst samples prepared from different precursors over various supports were tested in carbon nanotube
(CNT) production. In order to quicken the evaluation of the performance of the catalysts a combinatorial arrangement was used.</o:p> 相似文献
73.
Rebeka Nádasdi István Szilágyi Gergely Kovács Sándor Dóbé Tibor Bérces Ferenc Márta 《Reaction Kinetics and Catalysis Letters》2006,89(1):193-199
Summary The fast flow technique with OH resonance fluorescence detection has been applied at T = 298 ± 2 K to study the kinetics of the overall reaction: H + CH3C(O)Cl → products (1) A rate constant value of k1 = (1.02 ± 0.12) x 1010 cm3 mol-1 s-1 has been determined which is the first direct kinetic parameter reported for reaction (1) in the literature (the error given
refers to 2σ accuracy). 相似文献
74.
For the 9-dimensional bicovariant differential calculi on the quantum group O(O
q(3)) several kinds of exterior algebras are examined. The corresponding dimensions, bicovariant subbimodules and eigenvalues of the antisymmetrizer are given. Exactly one of the exterior algebras studied by the authors has a unique left invariant form with maximal degree. 相似文献
75.
Hallberg F Weise CF Yushmanov PV Pettersson ET Stilbs P Furó I 《Journal of the American Chemical Society》2008,130(24):7550-7551
Electrophoretic mobilities obtained on a molecularly selective manner by electrophoretic NMR can be used to provide a quantitative characterization of the composition and stoichiometry of molecular complexes. This is demonstrated in complexes formed by uncharged cyclodextrins which attain an electrophoretic mobility upon inclusion of charged surfactants. 相似文献
76.
Dávid Ádám Zoltán Mincsovics Emil Pápai Katalin Ludányi Krisztina Antal István Klebovich Imre 《平面色谱法杂志一现代薄层色谱法》2008,21(2):119-123
JPC – Journal of Planar Chromatography – Modern TLC - A new, simplified open-vessel microwave extraction (OVME) method has been used to prepare aqueous extracts of Sennae folium and... 相似文献
77.
Mihály Molnár László Palcsu István Futó Éva Svingor Zoltán Major Mihály Veres Péter Ormai István Barnabás 《Journal of Radioanalytical and Nuclear Chemistry》2010,286(3):745-750
To obtain reliable estimates of the quantities and rates of the gas production in L/ILW a series of measurements was carried
in the last 7 years in Hungary. The typical gas production rates were 0.05–0.2 STP litre gas/day for CO2 and CH4 generation, and less for H2. No explosive gas mixture was indicated in the L/ILW drums during the investigated storage period. Compositions of headspace
gases in closed L/ILW vaults were in agreement with gas generation processes observed in L/ILW drums. The stable carbon isotope
measurements show that the main source of the CO2 gas is the degradation of organic matter and indicates microbial degradation processes as the main sources of CH4. Typical tritium activity concentrations were <10 Bq/l gas in the drums and <1,000 Bq/l gas in the vaults. Typical 14C activity values of the headspace gases were <2.0 Bq/l gas in the drums and <1,000 Bq/l gas in the vaults. 相似文献
78.
Lajos Kovács Pál Herczegh Gyula Batta István Farkas 《Journal of carbohydrate chemistry》2013,32(5):585-599
ABSTRACT The reactivity of the title compounds has been studied toward different nucleophiles and electrophiles. Unlike other ketene dithioacetals, compounds 3-5 did not add nucleophiles to the double bond. Instead, in the presence of Lewis acids they underwent substitution reaction at position 3. If the nucleophile was not strong enough, formation of 6 and 7 were observed. With 2,3,4,6-tetra-O-acetyl-1-thio-β-D-glucopyranose (18), a 3:1 mixture of 11 and 12 was formed from 4. These observations may be interpreted in terms of easy formation of the allylic carbocation I which gives diastereomers with nucleophiles. However, this allylic ether-like behaviour was ruled out by the fact that compounds 9 and 10 did not undergo [2,3] sigmatropic rearrangement with lithium diisopropylamide. With N-bromosuccinimide compound 3 gave the 2-bromo derivative 8. Compounds 3 and 8 resisted common mercury salt assisted demercaptalization procedures. 相似文献
79.
We have measured the variation of atmospheric pressure and of 222Rn activity concentration in the air of a wine cellar with an AlphaGAURD type ionization chamber radon monitor. We have found
that the 222Rn activity concentration varies inversely with pressure. To explain this behavior we have done model calculations. We have
compared the results of model calculations with the results of experimental measurements, and we have found that the model
is capable to reproduce some part of the variation of 222Rn activity concentration. 相似文献
80.
István Hargittai 《Structural chemistry》2010,21(1):1-7
Linus Pauling, arguably the greatest chemist of the twentieth century, never publicly admitted that there was a race for the
determination of the structure of the most important biopolymers. But according to his competitors there was a race, in fact,
there were two, and Pauling won one and lost the other. He had a tremendous amount of ideas, many of them worthless, but a
few were spectacular. Not only did he make seminal discoveries, he was also a master of announcing them in a most dramatic
way. Eventually, Pauling shifted toward politics and controversial issues, but his science ensured him his place among the
greats. Here, we follow Pauling’s route to the discovery of the alpha-helix; the defeat of the star-studded British team in
the same quest; and a seemingly unrelated story about the fate of the theory of resonance that assured Pauling’s victory yet
at the same time it was excommunicated in the Soviet Union. 相似文献