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排序方式: 共有103条查询结果,搜索用时 15 毫秒
91.
92.
29Si NMR spectra of polycrystalline Ca6[Si2O7¦(OH)6] and [(CH3)4N] 8Si8O20·69H2O were measured using the cross polarization double-resonance technique. Observed shielding tensors are related to the known Si-O bond systems. The arrangement of the four Si-O bonds in the SiO4 tetrahedra is reflected by the 29Si shielding tensor. The most shielded direction corresponds to the shortest Si-O bond. 相似文献
93.
A.-R. Grimmer D. Müller G. G?zel R. Kniep 《Fresenius' Journal of Analytical Chemistry》1997,357(5):485-488
11B and 31P MAS NMR spectroscopy of three borophosphates was used to monitor their phase composition via the isotropic chemical shifts.
CaBPO5 and BPO4 represent nearly pure samples, SrBPO5 contains β-Sr2P2O7 as well as BPO4 as impurities. The anisotropic chemical shift data provide additional information on the geometry and connectivity of the
BO4 and PO4 building units.
Received: 25 July 1996 / Revised: 19 August 1996 / Accepted: 23 August 1996 相似文献
94.
Zusammenfassung Es wird ein einfaches und selektives Anreicherungsverfahren für polycyclische aromatische Verbindungen angegeben (flüssig-flüssig-Verteilung: Dimethylformamid + Wasser + Cyclohexan; Chromatographie an Sephadex LH 20/Isopropanol; Filtration an Aluminiumoxid/Cyclohexan). Das Gemisch der polycyclischen aromatischen Kohlenwasserstoffe (= PAH) wird gas-chromatographisch an gepackten Hochleistungssäulen getrennt und die FID-Signale mit einem anfangs zugegebenen inneren Standard verglichen. Es wurden 18 Hauptkomponenten quantitativ ausgewertet. Die Variationskoeffizienten einer fünffachen Bestimmung derselben Probe lagen zwischen 1,6 und 11,3%. Die Nachweisgrenze des Verfahrens beträgt bei einer mittleren elektronischen Signalverstärkung in Abhängigkeit von der Retentionszeit 0,5–5 ng (für Benzo(a)pyren 1 ng). Die Charakterisierung der PAH mit 4–7 Ringen erfolgte mit einer GC-MS-Kombination, was für den Routinebetrieb aufgrund der großen Ähnlichkeit der PAH-Profile verschiedener Klärschlammproben nicht erforderlich ist.
Profile-analysis of polycyclic aromatic hydrocarbons in sewage sludge by gas chromatography
Summary A simple and selective method of enrichment of polycylic aromatic compounds is described (liquid-liquid-distribution with DMF + water + Cyclohexane; chromatography on Sephadex LH 20/isopropanol; filtration on aluminium oxide/cyclohexane). The fraction of polycyclic aromatic hydrocarbons (= PAH), separated gas-chromatographically using high performance columns, is evaluated by comparising the FID-signals with those of the internal standard added to the sample. Eightteen main components are evaluated. The variation coefficient of five analyses of the sample is in the range of 1.6–11.3%. The detection limit by moderate amplification depends on retention time of the PAH (0.5–5 ng; for benzo(a)pyrene 1 ng). As the PAH profiles of different samples of sludge are very similar, it is normally not necessary to characterize the PAH by mass spectrometry.相似文献
95.
O. Zaharko A. Cervellino H.-Ch. Mertins H. Grimmer F. Schäfers D. Arvanitis 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(4):441-448
Magnetic circular dichroism (MCD) in X-ray absorption has been measured at the L
2, 3
edges of Fe in ex-situ grown Fe and Fe
0.50
Co
0.48
V
0.02
films by means of the transmission method. A new approach is developed for fitting the observed transmittance, which describes
the resonance lineshapes as (generalized) Fano profiles. Analytical integration of each single resonance allows a more reliable
determination of the orbital and spin magnetic moments based on the MCD sum rules. The results are consistent with an increase
of the Fe spin and orbital magnetic moment in Fe-Co alloys as obtained by other experiments and band structure calculations.
Received 15 August 2000 and Received in final form 11 June 2001 相似文献
96.
97.
Perovskites thin films with the composition La0.6Ca0.4MnO3 doped with 20% Fe, were prepared by pulsed reactive crossed beam laser ablation, where a synchronized reaction gas pulse interacts with the ablation plume. The films were grown on various substrates and the highest colossal magnetoresistance ratio (CMR) was detected by Hall measurements for films grown on LaAlO3 (1 0 0), which was selected as substrate for further investigations.Several growth parameters, such as substrate temperature and target to substrate distance were varied to analyze their influence on the film properties.The structure of the deposited thin films was characterized by X-ray diffraction and atomic force microscope, while Rutherford backscattering (RBS) was used to determine the film stoichiometry. The electrical properties were determined by Hall effect measurements in a magnetic field of 0.51 T.These measurements reveal that the amplitude of the CMR ratio depends strongly on the substrate and that the oxygen content influences the temperature where the transition from semiconductor to metal is observed. 相似文献
98.
99.
F. V. Atkinson R. C. Grimmer W. T. Patula 《Annali di Matematica Pura ed Applicata》1980,126(1):299-317
Summary The number of nonoscillatory solutions of a forced second order linear differential equation is studied under the hypothesis that the homogeneous equation is oscillatory. The main technique involves expressing a general solution of the forced equation in terms of two parameters, given a pair of independent solutions of the homogeneous equation (see (2.4) below). 相似文献
100.
Investigations on Hydrogen Bonded Compounds with High Resolution NMR Spectroscopy in Solids. I. On the Relation between the Chemical Shift of Protons and the Type of OH Groups in Some Crystalline Hydrosilicates By using WHH-4 multiple pulse and combined multiple pulse-magic angle spinning experiments the anisotropies Δσ and the spatial average values σ of the proton chemical shift tensors of OH groups are obtained in the silicates CaNa HSiO4, BaH2SiO4, (CaOH)Ca(HSiO4), [(CaOH)2SiO3]x, (CaOH)2Ca4Si6O17. With the combined method the spectrum of dicalcium silicate hydrate A (CaOH) Ca(HSiO4) unambiguously shows two signals in ratio 1:1 for the acid and basie OH groups. For all investigated compounds the acid OH groups (strongly hydrogen bonded in the solid state) show greater δσ values than the basic (weakly or non hydrogen bonded) OH groups. The σ values for strongly hydrogen bonded OH groups are shifted to lower B0 field in comparison to non hydrogen bonded OH groups. The results agree with theoretical calculations by Ditchfield. The used methods give the possibility to characterize the type of OH groups in solids. Advantages in comparison to IR investigations of this problem are discussed. 相似文献