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951.
Alexander J. Turinske Scott A. Nelson Nenad Stojilovic Sulaiman B. Ali Sasa V. Dordevic Edward A. Evans 《Journal of Sol-Gel Science and Technology》2013,65(2):283-286
In the process of fiber production from Zinc acetate and Polyvinylpyrrolidone using the electrospinning method, ZnO forms at temperature as low as 120 °C. The fibers were characterized using scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and ultraviolet–visible (UV–Vis) spectroscopy. Upon heating at 120 °C for 12 h some fibers shrink in diameter down to about 100 nm while others remain in the 400–900 nm range. Within the hybrid fibers, ZnO crystallizes in the wurtzite structure with a bang gap of 3.3 eV. The hybrid fibers exhibit the flexibility of polymer component and optical properties of ZnO phase, and promise to be very useful in various applications. 相似文献
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J.P. Hill C.S. Nelson M. v. Zimmermann Y.-J. Kim D. Gibbs D. Casa B. Keimer Y. Murakami C. Venkataraman T. Gog Y. Tomioka Y. Tokura V. Kiryukhin T.Y. Koo S.-W. Cheong 《Applied Physics A: Materials Science & Processing》2001,73(6):723-730
We review our recent X-ray scattering studies of charge and orbital order in doped manganites, with specific emphasis on the
role of orbital correlations in Pr1-xCaxMnO3. For x=0.25, we find an orbital structure indistinguishable from the undoped structure and long-range orbital order at low
temperatures. For dopings 0.3≤x≤0.5, we find scattering consistent with a charge and orbitally ordered CE-type structure.
While in each case the charge order peaks are resolution limited, the orbital order exhibits only short-range correlations.
We report the doping dependence of the correlation length and discuss the connection between the orbital correlations and
the finite magnetic correlation length observed on the Mn3+ sublattice with neutron-scattering techniques. The physical origin of these domains, which appear to be isotropic, remains
unclear. We find that weak orbital correlations persist well above the phase transition, with a correlation length of 1–2
lattice constants at high temperatures. Significantly, we observe similar correlations at high temperatures in La0.7Ca0.3MnO3, which does not have an orbitally ordered ground state, and we conclude that such correlations are robust to variations in
the relative strength of the electron–phonon coupling.
Received: 22 May 2001 / Accepted: 4 July 2001 / Published online: 5 October 2001 相似文献
955.
Parvej Alam Nelson L. C. Leung Yanhua Cheng Haoke Zhang Junkai Liu Wenjie Wu Ryan T. K. Kwok Jacky W. Y. Lam Herman H. Y. Sung Ian D. Williams Ben Zhong Tang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(14):4584-4588
The development of molecular machines requires new building blocks which are easy to characterize and visualize to realize a complexity comparable to their natural counterparts such as biological enzymes. Furthermore, with the desire to build functional nanobots capable of navigating living organisms, it is necessary that the building blocks show mobility even in the solid state. Herein we report a system which is emissive in the amorphous state but is non‐fluorescent in the crystalline state due to the formation of extensive π‐π interactions. This dual nature could be exploited for easy visualization of its solid‐state molecular rearrangement. The emission of the amorphous film was quenched as the molecules spontaneously formed π‐π interactions even in the solid state. Scratching the non‐emissive film destroyed the interactions and restored the emission of the film. The emission quickly disappeared with an average lifetime of 20 s as the compound reformed the π‐network even at room temperature. 相似文献
956.
Gabriel Cendejas Csar Andrs Flores-Sandoval Nelson Huitrn Rafael Herrera Luis S. Zamudio-Rivera Hiram I. Beltrn Flavio Vzquez 《Journal of Molecular Structure》2008,879(1-3):40-52
In this work, the influence of three different initiators (KOH, KOH dissolved in ethanol and the potassium salt of ethylene glycol) on the propylene oxide polymerization was studied by experimental and theoretical methods. A first series of reactions was carried out to establish the adequate thermal conditions for a minimal monomer transfer during the polymerization. The formation of end insaturations (main consequence of the monomer transfer interference) in the poly(propylene oxide) chains was studied by spectroscopic methods. Furthermore, a second series of poly(propylene oxide)s was prepared by using the mentioned initiators, and characterized by size exclusion chromatography. The initiator efficiency to create active centers in every reactive system was determined from the molecular weight and the conversion data obtained. Experimental results were elucidated by using quantum chemical calculations at density functional theory level, involving thermo-chemistry parameters, and the simulation of the infrared, and 13C nuclear magnetic resonance spectra. This method led to studying the addition of up to ten propylene oxide unit, resulting into important energetic tendencies and regioselectivity, being compared to the physicochemical data of products obtained. These correlations meant further understanding of the reaction course and the type of products obtained, depending on the nature of the initiator. 相似文献
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Michael Souza Adilson Elias Xavier Carlile Lavor Nelson Maculan 《Operations Research Letters》2011,39(6):461-465
This work considers the problem of estimating the relative positions of all atoms of a protein, given a subset of all the pair-wise distances between the atoms. This problem is NP-hard, and the usual formulations are nonsmoothed and nonconvex, having a high number of local minima. Our contribution is an efficient method that combines the hyperbolic smoothing and the penalty techniques that are useful in obtaining differentiability and reducing the number of local minima. 相似文献
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