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41.
In this paper we will be concerned with questions of existence and multiplicity of radial nonnegative solutions of the quasilinear elliptic equation We will use variational methods in order to prove the existence of multiple solutions in case f is a sign-changing nonlinearity. 相似文献
42.
The basic relationships required to analyse permeability data of fluorite-based solid electrolytes are rewritten in order
to account for an overpotential term related to slow surface exchange. Results of a gadolinia doped ceria solid electrolyte
suggest that surface exchange might limit the permeability especially at low Po2 and temperature. However, the analysis of the data with different relationships leads to somewhat different estimates of
the electron and hole conductivity and overpotential values.
Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998 相似文献
43.
Cadmium determination in biological samples by direct solid sampling flame atomic absorption spectrometry 总被引:1,自引:0,他引:1
rico Marlon de Moraes Flores Jos Neri Gottfried Paniz Ayrton Figueiredo Martins Valderi L. Dressler Edson Irineu Müller Adilson Ben da Costa 《Spectrochimica Acta Part B: Atomic Spectroscopy》2002,57(12):2187-2193
A direct solid sampling flame atomic absorption spectrometric procedure for trace determination of cadmium in biological samples has been developed. Test samples (0.05–2.00 mg) were ground and weighed into small polyethylene vials, which were connected to the device for solid sample introduction into a conventional air/acetylene flame. Test samples were carried as a dry aerosol to a quartz cell, placed between the burner and the optical path, which had a perpendicular entrance and a slit in the upper part. The atomic vapor generated in the flame produced a transient signal that was totally integrated within 1 s. The effect of operating conditions and the extent of grinding on the analytical signal were evaluated. Background signals were always low and a characteristic mass of 0.29 ng Cd was obtained. Calibration was performed using different masses of solid certified reference materials. Results obtained for certified and in-house reference materials were typically within the 95% confidence interval of the certified and/or reference value, and the precision, expressed as relative standard deviation, was between 3.8 and 6.7%. The proposed system is simple and it might be adapted to conventional atomic absorption spectrometers allowing the determination of Cd in more than 80 test samples per hour, excluding weighing. 相似文献
44.
We report measurements of non-linear charge transport in epitaxial (La1−x
Pr
x
)0.7Ca0.3MnO3 thin films fabricated on (100) oriented SrTiO3 single crystals by pulsed laser deposition. The end members of this series, namely Pr0.7Ca0.3MnO3 and La0.7Ca0.3MnO3 are canonical charge-ordered (CO) and ferromagnetic manganites, respectively. The onset of the CO state in Pr0.7Ca0.3MnO3 is manifested by a pronounced insulating behavior below ∼ 200 K. The CO state remains stable even when a large (∼ 2×105 V/cm) electric field is applied across the thin film samples. However, on substitution of Pr with La, a crossover from the
highly resistive CO state to a state of metallic character is observed at relatively low electric fields. The current-voltage
characteristics of the samples at low temperatures show hysteretic and history dependent effects. The electric field driven
charge transport in the system is modelled on the basis of an inhomogeneous medium consisting of ferromagnetic metallic clusters
dispersed in a CO background. 相似文献
45.
It has been shown by Trudinger and Moser that for normalized functions u of the Sobolev space ??1, N (Ω), where Ω is a bounded domain in ?N, one has ∫Ω exp(αN|u|N/(N ? 1))dx ≤ CN, where αN is an explicit constant depending only on N, and CN is a constant depending only on N and Ω. Carleson and Chang proved that there exists a corresponding extremal function in the case that Ω is the unit ball in ?N. In this paper we give a new proof, a generalization, and a new interpretation of this result. In particular, we give an explicit sequence that is maximizing for the above integral among all normalized “concentrating sequences.” As an application, the existence of a nontrivial solution for a related elliptic equation with “Trudinger‐Moser” growth is proved. © 2002 John Wiley & Sons, Inc. 相似文献
46.
47.
Zusammenfassung Zur Berechnung des Impulstransports in einer abwärts gerichteten, turbulenten Zweiphasenströmung, bestehend aus einer Gasphase und einem Flüssigkeitsfilm (Kern/Film-Strömung) mit welliger Phasengrenzfläche, wird ein Mehrfluidmodell eingeführt. Das Strömungsfeld wird in einen Grundfilm-, einen Wellen- und einen Kernbereich eingeteilt.Die Phasenverteilung im Strömungsfeld wird durch die unvollständige Gamma-Funktion dargestellt, die Reibung zwischen den Phasen durch einen Reibungsbeiwert, welcher von einem dimensionslosen Druckgradienten abhängig ist.Durch Lösung des Gleichungssystems ergibt sich der Druckabfall der Kern/Film-Strömung als Funktion der Reynolds-Zahl des Films und des Kerns. Der berechnete Druckabfall stimmt mit dem aus empirischen Korrelationen gut überein.
A multifluid-model for turbulent gas- and liquid-film flow
A multifluid-model is introduced for the momentum transport of a downwards directed turbulent two-phase-flow consisting of a gaseous core and a liquid film (core-film-flow) with wavy interface. The flow field is subdivided into a basic film region, a wavy region and the gaseous core.The phase distribution is represented by the incomplete Gamma-function, and the friction between the phases is given by a friction factor depending on a dimensionsless pressure gradient.From the solution of the governing equations the pressure drop of the core-film-flow is obtained as a function of the liquid- and the core-Reynolds-number. The calculated pressure drop is in good agreement with that obtained from empirical correlations.相似文献
48.
Ferric phosphates resulting from the thermal breakdown of natural Fe3(PO4)2.8H2O are studied by X-ray powder diffraction and Mössbauer spectroscopy. Total iron oxidation and water release give rise to an amorphous material. During heating, a transitional cristobalite-type ferric orthophosphate recrystallizes prior to the stable berlinite-type. The main additional final product is a poorly characterized “Fe3PO7” phase with iron in octahedral coordination. 相似文献
49.
L. C. Oliveira C. B. Zamboni F. A. Genezini A. M. G. Figueiredo G. S. Zahn 《Journal of Radioanalytical and Nuclear Chemistry》2005,263(3):783-786
Summary In this study we show that the NAA technique can be used to perform clinical analyses of blood and urine, with many advantages towards the conventional methods. From the knowledge of the neutron flux and the induced activity, the concentration ofelements were obtained. In comparison to the conventional techniques, this methodology uses smaller quantities of biological material and allows the simultaneous evaluation of the concentrations of several elements in biological samples at once, something not always possible in the conventional clinical analysis. Another important advantage is that it eliminates the use of standard materials, thus making the analyzing process practical and economic. 相似文献
50.
Adelaide Figueiredo 《Computational Statistics》2017,32(4):1213-1240
The problem of testing the null hypothesis of a common direction across several populations defined on the hypersphere arises frequently when we deal with directional data. We may consider the Analysis of Variance (ANOVA) for testing such hypotheses. However, for the Watson distribution, a commonly used distribution for modeling axial data, the ANOVA test is only valid for large concentrations. So we suggest to use alternative tests, such as bootstrap and permutation tests in ANOVA. Then, we investigate the performance of these tests for data from Watson populations defined on the hypersphere. 相似文献