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851.
852.
We present a detailed study of the work function of pristine and doped single-walled carbon nanotubes (SWCNTs) using a novel screened exchange hybrid density functional. We find that SWCNTs with diameters larger than 0.9 nm tend asymptotically and smoothly to the graphene limit of 4.6 eV. On the other hand, the work function of narrow tubes exhibits a strong dependence on their diameter and chiral angle. Boron or nitrogen doping, with concentrations from 1% to 2%, not only changes the electronic behavior by introducing new states around the Fermi level, but also produces a significant change of the work function that can vary between 3.9 (N doping) and 5.2 eV (B doping). 相似文献
853.
Fabrizio Bardelli Germana Barone Vincenza Crupi Francesca Longo Giacomo Maisano Domenico Majolino Paolo Mazzoleni Valentina Venuti 《Journal of synchrotron radiation》2012,19(5):782-788
The present work reports a detailed investigation on the speciation of iron in the pigments of decorated pottery fragments of cultural heritage relevance. The fragments come from the Gioiosa Guardia archaeological site in the area of the `Strait of Messina' (Sicily, Southern Italy), and date back to VI–V century BC. The purpose of this study is to characterize the main pigmenting agents responsible for the dark‐red coloration of the specimens using non‐destructive analytical techniques such as synchrotron radiation X‐ray absorption spectroscopy (SR‐XAS), a well established technique for cultural heritage and environmental subjects. Absorption spectra were collected at the Fe K‐edge on the Italian beamline for absorption and diffraction (BM8‐GILDA) at the European Synchrotron Radiation Facility in Grenoble (France). In order to determine the speciation of Fe in the samples, principal component analysis and least‐squares fitting procedures were applied to the near‐edge part of the absorption spectra (XANES). Details on the local structure around the Fe sites were obtained by analyzing the extended part of the spectra (EXAFS). Furthermore, an accurate determination of the average Fe oxidation state was carried out through analysis of the pre‐edge peaks of the absorption spectra. Samples resulted composed of an admixture of Fe2O3 (hematite or maghemite) and magnetite (Fe3O4), occurring in different relative abundance in the dark‐ and light‐colored areas of the specimens. The results obtained are complementary to information previously obtained by means of instrumental neutron activation analysis, Fourier transform infrared absorbance and time‐of‐flight neutron diffraction. 相似文献
854.
Sébastien Neukirch Joël Frelat Alain Goriely Corrado Maurini 《Journal of sound and vibration》2012,331(3):704-720
The small-amplitude in-plane vibrations of an elastic rod clamped at both extremities are studied. The rod is modeled as an extensible, shearable, planar Kirchhoff elastic rod under large displacements and rotations, and the vibration frequencies are computed both analytically and numerically as a function of the loading. Of particular interest is the variation of mode frequencies as the load is increased through the buckling threshold. While for some modes there are no qualitative changes in the mode frequencies, other frequencies experience rapid variations after the buckling threshold, the thinner the rod, the more abrupt the variations. Eventually, a mismatch for half of the frequencies at buckling arises between the zero thickness limit of the extensible model and the inextensible model. 相似文献
855.
Shape measurement by a multi-view methodology based on the remote tracking of a 3D optical scanner 总被引:4,自引:0,他引:4
Sandro Barone Alessandro Paoli Armando Viviano Razionale 《Optics and Lasers in Engineering》2012,50(3):380-390
Full field optical techniques can be reliably used for 3D measurements of complex shapes by multi-view processes, which require the computation of transformation parameters relating different views into a common reference system. Although, several multi-view approaches have been proposed, the alignment process is still the crucial step of a shape reconstruction.In this paper, a methodology to automatically align 3D views has been developed by integrating a stereo vision system and a full field optical scanner. In particular, the stereo vision system is used to remotely track the optical scanner within a working volume. The tracking system uses stereo images to detect the 3D coordinates of retro-reflective infrared markers rigidly connected to the scanner. Stereo correspondences are established by a robust methodology based on combining the epipolar geometry with an image spatial transformation constraint.The proposed methodology has been validated by experimental tests regarding both the evaluation of the measurement accuracy and the 3D reconstruction of an industrial shape. 相似文献
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857.
The LaX3, GdX3, LuX3, and ThX4 systems (X = F, Cl, Br, and I) have been chosen as test cases to analyze the performances of a computational protocol, resting on a recently proposed density functional method, the so‐called PBE0 model. Relativistic effects were taken into account by means of two different sets of quasi‐relativistic effective core potentials. All static data were found to be in very good agreement with those provided by post‐HF methods. Because experimental geometries have been determined at high temperature (1000–1800 K), the effect of nuclear motions have been considered through a variational numerical procedure. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 1153–1166, 2000 相似文献
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860.
Laura Gagliardi Chris‐Kriton Skylaris Andrew Willetts John M. Dyke Vincenzo Barone 《ChemInform》2000,31(38):no-no
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option. 相似文献