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81.
82.
Abdallah Aissa Michel Gruselle René Thouvenot Rainer Traksmaa 《Journal of solid state chemistry》2007,180(8):2273-2278
The reaction between phenyl phosphonic dichloride (C6H5P(O)Cl2) and synthetic calcium hydroxy- and fluorapatite has been investigated. The presence of mono- or polymeric (C6H5PO) fragment bound to hydroxyapatite was evidenced by IR, and solid-state 31P NMR spectroscopy. X-ray powder analysis has shown that the apatitic structure remains unchanged during the reaction. In contrast, no reaction was found using fluorapatite. According to the results found for these two different apatites a mechanism was proposed for the formation of covalent P-O-P bonds as the result of a reaction between the C6H5P(O)Cl2 organic reagent and (HPO4)− and/or OH− ions of the hydroxyapatite. 相似文献
83.
Azotobacter vinelandii, a nitrogen-fixing soil bacterium, secretes in iron deficiency azotobactin delta, a highly fluorescent pyoverdin-like chromopeptidic hexadentate siderophore. The chromophore, derived from 2,3-diamino-6,7 dihydroxyquinoline, is bound to a peptide chain of 10 amino acids: (L)-Asp-(D)-Ser-(L)-Hse-Gly-(D)-beta-threo-HOAsp-(L)-Ser-(D)-Cit-(L)-Hse-(L)-Hse lactone-(D)-N(delta)-Acetyl, N(delta)-HOOrn. Azotobactin delta has three different iron(III) binding sites which are one hydroxamate group at the C-terminal end of the peptidic chain (N(delta)-Acetyl, N(delta)-HOOrn), one alpha-hydroxycarboxylic function in the middle of the chain (beta-threo-hydroxyaspartic acid), and one catechol group on the chromophore. The coordination properties of its iron(III) and iron(II) complexes were measured by spectrophotometry, potentiometry, and voltammetry after the determination of the acid-base functions of the uncomplexed free siderophore. Strongly negatively charged ferric species were observed at neutral p[H]'s corresponding to a predominant absolute configuration Lambda of the ferric complex in solution as deduced from CD measurements. The presence of an alpha-hydroxycarboxylic chelating group does not decrease the stability of the iron(III) complex when compared to the main trishydroxamate siderophores or to pyoverdins. The value of the redox potential of ferric azotobactin is highly consistent with a reductive step by physiological reductants for the iron release. Formation and dissociation kinetics of the azotobactin delta ferric complex point out that both ends of this long siderophore chain get coordinated to Fe(III) before the middle. The most striking result provided by fluorescence measurements is the lasting quenching of the fluorophore in the course of the protonation of the ferric azotobactin delta complex. Despite the release of the hydroxyacid and of the catechol, the fluorescence remains indeed quenched, when iron(III) is bound only to the hydroxamic acid, suggesting a folded conformation at this stage, around the metal ion, in contrast to the unfolded species observed for other siderophores such as ferrioxamine or pyoverdin PaA. 相似文献
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85.
The DELPHI Collaboration J. Abdallah et al. 《The European Physical Journal C - Particles and Fields》2003,26(4):505-525
In some supersymmetric models, the gluino () is predicted to be light and stable. In that case, it would hadronize to form R-hadrons. In these models, the missing energy
signature of the lightest supersymmetric particle is no longer valid, even if R-parity is conserved. Therefore, such a gluino
is not constrained by hadron collider results, which looked for the decay . Data collected by the DELPHI detector in 1994 at 91.2 GeV have been analysed to search for events. No deviation from Standard Model predictions is observed and a gluino mass between 2 and 18 GeV/c2 is excluded at the 95% confidence level in these models. Then, R-hadrons produced in the squark decays were searched for
in the data collected by DELPHI at the centre-of-mass energies of 189 to 208 GeV, corresponding to an overall integrated luminosity
of 609 Pb-1. The observed number of events is in agreement with the Standard Model predictions. Limits at 95% confidence level are derived
on the squark masses from the excluded regions in the plane ()
GeV/c2, and GeV/c2 for purely left squarks.
GeV/c2, and GeV/c2 independent of the mixing angle.
Received: 6 November 2002 / Published online: 15 January 2003 相似文献
86.
S. A. Pikuz T. A. Shelkovenko V. M. Ramanova J. Abdallah Jr. G. Csanak R. E. H. Clark A. Ya. Faenov I. Yu. Skobelev D. A. Hammer 《Journal of Experimental and Theoretical Physics》1997,85(3):484-491
The first experimental studies of an electron beam generated in an X pinch on the XP machine (Cornell University, USA) and the BIN machine (P. N. Lebedev Physical Institute, Russian Academy
of Sciences) are reported. It is shown that it is possible in an X pinch to isolate the effect of a plasma-generated electron beam on the multiply charged ion radiation. The intensities of
the satellite lines corresponding to Li-, Be-, B-, and C-like ions are calculated for the Al spectrum on the basis of a collisional-radiative
model with a non-Maxwellian electron distribution in the plasma. The effect of an electron beam on the multiply charged light
ion radiation in an X-pinch plasma is demonstrated. Comparing our calculations with the experimental spectra, we conclude that the present model
can be used to estimate the electron beam intensity.
Zh. éksp. Teor. Fiz. 112, 894–909 (September 1997) 相似文献
87.
88.
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In the atomic absorption spectrometric determination of chromium(III), the interfering effects of different complexing agents can be completely eliminated by addition of excess of cyanide, boric acid or sulphosalicyclic acid. The effect of some complexing agents on the production of chromium atoms is discussed, and the mechanism of cyanide interaction is investigated in detail. 相似文献
90.