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1.
Behavior of cellulose in NaOH/Urea aqueous solution characterized by light scattering and viscometry
Cellulose was dissolved in 6 wt % NaOH/4 wt % urea aqueous solution, which was proven by a 13C NMR spectrum to be a direct solvent of cellulose rather than a derivative aqueous solution system. Dilute solution behavior of cellulose in a NaOH/urea aqueous solution system was examined by laser light scattering and viscometry. The Mark–Houwink equation for cellulose in 6 wt % NaOH/4 wt % urea aqueous solution at 25 °C was [η] = 2.45 × 10?2 weight‐average molecular weight (Mw)0.815 (mL g?1) in the Mw region from 3.2 × 104 to 12.9 × 104. The persistence length (q), molar mass per unit contour length (ML), and characteristic ratio (C∞) of cellulose in the dilute solution were 6.0 nm, 350 nm?1, and 20.9, respectively, which agreed with the Yamakawa–Fujii theory of the wormlike chain. The results indicated that the cellulose molecules exist as semiflexible chains in the aqueous solution and were more extended than in cadoxen. This work provided a novel, simple, and nonpollution solvent system that can be used to investigate the dilute solution properties and molecular weight of cellulose. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 347–353, 2004 相似文献
2.
Thermodynamics and dynamics of metallic glass formers: their correlation for the investigation on potential energy landscape 总被引:3,自引:0,他引:3
Great progress has been made in basic features of the potential energy landscape (PEL) theoretically. The present work, however, attempts to cast new light on it from experimental aspects. By a survey of experimental data related to thermodynamics or dynamics of metallic glass-forming liquids, it is found that the increased rate of excitation of vibrational entropy at glass transition tends to increase the rate of generation of configurational part. Although for the type of metallic materials a generally positive relationship exists between the density of the energy minima at glass transition and the liquid fragility strength, just as expected, our main attention is paid to the phenomenon of the scattering of the slopes. Analysis shows that the phenomenon results from the different average height of energy barriers between minima near glass transition. Investigation on the PdNiP metallic system indicates that the mismatch entropy is a dominant factor in the barrier height: a large value of it results in low energy barriers. Our previous work on the AlNiCe system gives the support to this finding. 相似文献
3.
采用固相反应法成功制备出一批Y123与Y211的摩尔比为1∶0.47的混合物,并在此混合物的基础上掺入CeO2,掺入的比例x分别为0.5wt%、1.0wt%、2.0wt%、3.0wt%、4.0wt%。采用了X-射线衍射仪对样品的晶格结构进行了分析,测量结果表明:x=1.0wt%时掺杂效果最好,同时也充分说明Y123的晶格结构与其超导电性之间存在着一种内在的必然关联。并通过对其测试临界转变温度以及转变宽度,测量结果也充分验证了上述结论。 相似文献
4.
Ba0.70Sr0.30TiO3 (BST) thin films doped by Co (BSTC) are fabricated by sol-gel method on a Pt/Ti/SiO2/Si substrate. A strong correlation is observed among the microstructure, dielectric, ferroelectric, ferromagnetic properties and Co concentration. The dielectric constant of BST thin films can be tailored from 343 to 119 by manipulating the Co concentration. The dielectric loss of BSTC thin films are still kept below 0.020 and the tunability is above 30% at a dc-applied electric field of 500 kV/cm. With increasing Co doping up to 10 mol%, the coexistence of ferromagnetism and ferroelectrics is found. Suitable dielectric constant, low-dielectric loss, and high tunability of this kind of thin films can be useful for potential tunable applications. 相似文献
5.
The surface and interfacial properties of polymers are important for their applications. In one of our previous articles, we discussed the relationship between the dispersive surface tension component and the density and molecular weight of solvents and polymers to seek a simple and easy method to estimate the rationality of surface tension results of polymers. We found that for 30 organic solvents and 12 polymers, there was a good relationship between the dispersive surface tension and the experiential parameter 1/ρ2 M 0.2 w . In this article, the existence of the squared density term is simply deduced from the general molecular interaction energy equation and is proved with four pairs of polymer/monomer; these are polystyrene/styrene, polyisoprene/isoprene, polymethyl methacrylate/methyl methacrylate, and polyvinyl acetate/vinyl acetate. 相似文献
6.
Duy Duc Nguyen Lina Nakhimovsky Jens Spanget-Larsen 《Journal of Molecular Spectroscopy》2010,264(1):19-25
A comparative study of the electronic transitions of fluorene and its hetero-analogues dibenzofuran, carbazole, and dibenzothiophene was performed in a wide energy range. Gas phase, crystal phase, and linear dichroism electronic transmittance spectra were measured with synchrotron radiation. Electronic transitions to excited singlet states were predicted with time-dependent density functional theory, TD-B3LYP/6-31+G(d,p). Based on the experimental and theoretical results, symmetry assignments of electronic transitions in the vacuum and near-UV region are suggested. The correspondence between excited states in these molecules, similarities, and differences between their electronic spectra are discussed. 相似文献
7.
8.
Lina Zhang Heqing Yang Junhu Ma Li Li Xuewen Wang Lihui Zhang Sha Tian Xinyue Wang 《Applied Physics A: Materials Science & Processing》2010,100(4):1061-1067
ZnO nanorods with a cone and different aspect ratios and short-and-fat ZnO microrods were synthesized via a hydrothermal reaction
of Zn with Zn(CH3COO)2 and H2O. The control over these ZnO nanocrystals with a wurtzite structure and different shapes was achieved by adjusting only the
reaction temperature and time. A possible kinetic mechanism was proposed to account for the growth of these ZnO nanocrystals
with different shapes. Photocatalytic activities of ZnO nanocrystals with distinctive shapes in the degradation of methyl
orange were investigated. The results indicate that the photocatalytic ability of the ZnO nanorods with a cone and different
aspect ratios is stronger than that of the short-and-fat microrods. 相似文献
9.
10.
By expanding the Debye theory into the tight focusing of partially coherent field, the intensity and spatial correlation properties of partially coherent radially polarized vortex beams are studied. Expressions are derived for the intensity distribution and the spectral degree of coherence in the focal region. It is found that the intensity and the transverse and longitudinal coherence degrees in the focal region change with the variation of the topological charge and coherence length of the vortex beam. In addition, the degree of coherence is shown to exhibit phase singularities. 相似文献