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951.
Radek Zeipl Jarmila Walachová Martin Pavelka Miroslav Jelínek Václav Studnička Tomáš Kocourek 《Applied Physics A: Materials Science & Processing》2008,93(3):663-667
Room temperature conductivity and the Seebeck coefficient of thin layers prepared by laser ablation from Bi2Te3 target were explored. The power factor was calculated for samples prepared at substrate temperature of 360°C with the density
of the laser beam 5 J cm−2 and at substrate temperature of 410°C with the density of the laser beam 2 J cm−2 during the deposition. Oscillations of the conductivity and the power factor with the layer thickness were observed at room
temperature. The oscillations of conductivity were also verified at the temperature of 77 K. The period of oscillations depends
on the preparation conditions. This behavior has been theoretically explained by the quantum size effect in the layers containing
different phases and in addition, it was demonstrated by the X-ray Diffraction measurement.
The behavior of the power factor of the layers is compared to the behavior of the figure of merit of the layers published
earlier. 相似文献
952.
Miroslav Kocifaj 《Journal of Quantitative Spectroscopy & Radiative Transfer》2009,110(11):879-888
The various aspects of the interaction of electromagnetic radiation with cosmic dust particles are discussed. In particular, attention is paid to discrepancies between optical and physical behavior of realistically shaped particles and volume equivalent homogeneous spheres. The dynamical evolution of morphologically non-identical particles which are driven by gravity, electromagnetic radiation and the Lorentz forces can dramatically differ. Although spherical particles often enable analytical calculations, an orbital evolution of spheres cannot be considered as a representative evolution for real cosmic dust particles. The effect of electromagnetic radiation on the motion of dust grains plays a crucial role here. While irregularly shaped interstellar dust particles may be captured in the Solar System, the spherical particles will not survive due to close encounters with the Sun. Spherical grains can be captured almost only in the evaporation region (in the vicinity of the Sun), where they are destroyed due to high temperatures. The spherical dust particles ejected from comets will monotonously inspiral toward the Sun subject to the Poynting-Robertson effect. However, the non-spherical particles of the same origin may be temporarily stabilized at some heliocentric distances and thus their lifetime may be much longer than that for the Mie spheres. Some dust particles may also be captured in mean-motion resonances with planets (commensurability resonances). While spherical particles are always characterized by the secular decrease of the semi-major axes near mean-motion resonances, this may not be true for non-spherical particles. Resonant captures of arbitrarily shaped dust grains exist for exterior and interior mean-motion resonances with planets. 相似文献
953.
The fluorescence properties of bisheterocyclic compounds that contain purine and the 3-hydroxyquinolin-4(1H)-one skeleton connected with an aliphatic spacer of a different length/structure (3HQP) were examined. It was found that
the introducing of the spacer-purine scaffold led in the comparison to 3HQs themselves to (1) the possibility of the effectual
excitation in the wider range of excitation wavelengths, moreover, some derivatives can be excited at relatively high wavelengths
around 400 nm, (2) the lowering of the quantum yield and (3) the slight longer wavelength shift of the dual emission spectra.
Tested organic solvents did not affect significantly the 3HQP fluorescence properties. The characters of emission spectra
as well as the quantum yields of 3HQPs were notably influenced by the ratio of water and DMSO in their composed mixture applied
as a solvent. With increasing water content in the mixture both I1/I2 and the quantum yield decreased. 相似文献
954.
955.
A simple on-column preconcentration method for capillary electrophoretic determination of eight polyphenolic compounds (carnosic acid, cinnamic acid, caffeic acid and rosmarinic acid, quercetin, apigenin, luteolin and rutin) was devised. The method was applied for the assay of polyphenols in methanolic extract of the medicinal plant Orthosiphon Stamineus Benth. The analysis was carried out in fused silica capillaries (I.D. 50 μm, effective length 50 cm, total length 60 cm) with UV detection at 200 nm. The background electrolyte was 50 mM sodium tetraborate of pH 9.0 (adjusted with phosphoric acid). Large volume sample stacking with polarity switching was used for sensitivity enhancement. With sample injection representing 50% of capillary volume and polarity switching at 1.6 min, an average 90-fold enhancement of absorbance signal of the analytes was achieved. The calibration curves were linear (r = 0.9956–0.9994) in the range 0.2 to 1.8 μg mL?1 of an analyte. The repeatability of migration times and peak areas was characterized by RSD values 0.11–0.57 and 1.63–5.66%, respectively. The proposed method offers favourable limits of detection (9–16 ng mL?1) that compare well with those of LC. 相似文献
956.
The single crystalline Lu3Al5O12 (LuAG) and Y3Al5O12 (YAG) garnet layers doped by Ce3+ ions were grown by the liquid phase epitaxy from the flux. The effect of the flux composition, growth conditions, and substrate polishing on the layer morphology, creation of defects, and on optical and emission properties of layers was studied. The defects typical of the epitaxial growth are discussed. 相似文献
957.
We study the magnetic properties of the erbium based compounds, Na[Er(WO)] and [(Pc)Er{Pc{N(CH)}}], in the framework of an effective spin exchange model involving delocalized electrons occupying molecular orbitals. The calculations successfully reproduce the experimental data available in the literature for the magnetic spectrum, magnetization and molar susceptibility in dc and ac fields. Owing to their similar molecular geometry, the compounds’ magnetic behaviors are interpreted in terms of the same set of active orbitals and thus the same effective spin coupling scheme. For all three complexes, the model predicts a prompt change in the ground state from a Kramer’s doublet at zero fields to a fully polarized quartet one brought about by the action of an external magnetic field without Zeeman splitting. This alteration is attributed to the enhancement of the effect of orbital interactions over the spin exchange as the magnitude of the external magnetic field increases. 相似文献
958.
Non-aqueous capillary electrophoresis was evaluated for the separation of five hydrophobic basic blue dyes for application in forensic dye analysis. The use of a red light emitting diode as a high intensity, low-noise light source provided sensitive detection of the blue dyes while also allowing the evaluation of solvents that absorb strongly in the UV region. Excellent peak shapes and separation selectivity were obtained in methanol, ethanol, acetonitrile and dimethylsulfoxide, however water, tetrahydrofuran, dimethylformamide and acetone were unsuitable as solvents due to poor peak shapes and a lack of sensitivity, most likely due to adsorption onto the capillary wall. Due to the known compatibility of methanol with capillary electrophoresis–mass spectrometry, this solvent was examined further with the relative acidity/basicity of the electrolyte being optimised with an artificial neural network. The optimised method was examined for the separation of ink samples from 6 fibre tip and 2 ball point blue or black pens and showed that a unique migration time for the main dye component in seven of the eight pens could be obtained. 相似文献
959.
We studied Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) content and activity in juvenile tree species ?? broadleaved Fagus sylvatica L. and coniferous Picea abies (L.) Karsten exposed for three growing seasons to ambient (A = 385 ??mol mol?1) and elevated (E = 700 ??mol mol?1) CO2 concentrations. Rubisco content was determined by the SDS-PAGE method, Rubisco activity was assayed spectrophotometrically. The highest content of Rubisco enzyme in F. sylvatica was measured immediately after full leaf development followed by a gradual decrease throughout the growing season. By contrast, Rubisco content in P. abies increased markedly during the growing season. In both tree species, down-regulation of Rubisco content in trees cultivated under elevated CO2 concentration was observed. Rubisco activity was stimulated in F. sylvatica by E treatment but not in P. abies. Because no significant differences were found in Rubisco activation state between A and E, we assume that stimulation of Rubisco activity in E is not a consequence of higher carbamylation but could be caused by the release of inhibitors from active sites of Rubisco under elevated CO2. 相似文献
960.
This paper presents a simulation model of the origin and propagation of speckle field within the Fresnel approximation and verification of the model through a speckle correlation method for determination of in-plane object's translation. There is used a convolution form of the Fresnel–Kirchhoff diffraction integral in the simulation model instead of often used Fast Fourier Transform approach. A possible way of simulation of the light scattering by object's surface and in-plane translation of the illuminated surface is mentioned, whereas two types of illumination (plane wave and Gaussian beam) are used. Finally, results of numerical correlation of generated displaced speckle fields are shown and compared with the results obtained by theoretical relations. 相似文献