全文获取类型
收费全文 | 772篇 |
免费 | 15篇 |
国内免费 | 135篇 |
专业分类
化学 | 554篇 |
晶体学 | 1篇 |
力学 | 38篇 |
数学 | 1篇 |
物理学 | 328篇 |
出版年
2023年 | 29篇 |
2022年 | 13篇 |
2021年 | 18篇 |
2020年 | 19篇 |
2019年 | 21篇 |
2018年 | 14篇 |
2017年 | 27篇 |
2016年 | 27篇 |
2015年 | 30篇 |
2014年 | 37篇 |
2013年 | 47篇 |
2012年 | 57篇 |
2011年 | 84篇 |
2010年 | 63篇 |
2009年 | 111篇 |
2008年 | 81篇 |
2007年 | 83篇 |
2006年 | 51篇 |
2005年 | 29篇 |
2004年 | 21篇 |
2003年 | 21篇 |
2002年 | 10篇 |
2001年 | 9篇 |
2000年 | 6篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1990年 | 1篇 |
排序方式: 共有922条查询结果,搜索用时 337 毫秒
821.
S. Laureti D. Peddis L. Del Bianco A.M. Testa G. Varvaro E. Agostinelli C. Binns S. Baker M. Qureshi D. Fiorani 《Journal of magnetism and magnetic materials》2012
We have studied the Exchange Bias (EB) effect in nanocomposite films consisting of Fe nanoparticles (mean size ∼1.9 nm) embedded in an antiferromagnetic Mn matrix. They were produced by co-deposition through a gas aggregation cluster source and molecular beam epitaxy and have different Fe volume filling fractions (2.2% and 24.8%). The exchange field, higher in the sample with higher Fe concentration (at T=5 K, Hex∼460 Oe for 24.8% and ∼310 Oe for 2.2% ), in both the samples decreases with increasing T, finally disappearing at T∼40 K. The EB properties have been studied in conjunction with results on the thermal dependence of the magnetic coercivity, zero-field-cooled and field-cooled magnetization and thermoremanence. The different Fe content strongly affects the magnetothermal properties, featuring superparamagnetic relaxation in the diluted sample and a reentrant ferromagnet-type transition in the concentrated one. Hence, the EB properties of the two samples have been discussed in consideration of such peculiarities of the magnetic behavior and highlighting the role of the Mn matrix. 相似文献
822.
S.S. Kalyan Kamal P.K. Sahoo L. Durai P. Ghosal M. Manivel Raja S. Ram 《Journal of magnetism and magnetic materials》2012
Small crystallites of a metastable phase Co0.5Pt0.5 are precipitated by heating a rheological liquid precursor of cobalt–hydrazine complex and platinum chloride H2PtCl6·xH2O in polymer molecules of poly(vinylpyrrolidone) (PVP) in ethylene glycol. The hydrazine co-reduces nascent atoms from the Co2+ and Pt4+ that recombine and grow as Co0.5Pt0.5. The PVP molecules cap a growing Co0.5Pt0.5 as it achieves a critical size so that it stops growing further in given conditions. X-ray diffraction pattern of a recovered powder reveals a crystalline Co0.5Pt0.5 phase (average crystallite size D∼8 nm) of a well-known Fm3m-fcc crystal structure with the lattice parameter a=0.3916 nm (density ρ=14.09 g/cm3). A more ordered L10 phase (ρ=15.91 g/cm3) transforms (D≥25 nm) upon annealing the powder at temperature lesser than 700 °C (in vacuum). At room temperature, the virgin crystallites bear only a small saturation magnetization Ms=5.54 emu/g (D=8 nm) of a soft magnet and it hardly grows on bigger sizes (D≤31 nm) in a canted ferromagnetic structure. A rectangular hysteresis loop is markedly expanded on an optimally annealed L10 phase at 800 °C for 60 min, showing a surface modified coercivity Hc=7.781 kOe with remnant ratio Mr/Ms=0.5564, and Ms=39.75 emu/g. Crystallites self-assembled in an acicular shape tailor large Hc from ideal single domains and high magnetocrystalline anisotropy of a hard magnet L10 phase. 相似文献
823.
The effect of a quasi-homogeneous external magnetic field on a created and decaying space nanoparticle structure and its distribution in a sample of a magnetic fluid was studied. This space structure was created as a grating by applying an interference field of two crossed Ar laser beams. The magnetic field was formed using two electromagnets and was applied in three main directions of the created nanoparticle grating. The magnetic field oriented parallel to the strips of the grating or perpendicular to the grating plain does not significantly change the shape of it. The magnetic field oriented in the perpendicular direction to the grating plain causes redistribution of the nanoparticles and as a consequence a perpendicular nanoparticle “quasi-grating” arises. 相似文献
824.
Gaoxue Wang Chunhui DongChangjun Jiang Guozhi ChaiDesheng Xue 《Journal of magnetism and magnetic materials》2012
Co92Zr8(50 nm)/Ag(x) soft magnetic films have been prepared on Si (111) substrates by oblique sputtering at 45°. Nanoparticle size of Co92Zr8 soft magnetic films can be tuned by thickening Ag buffer layer from 9 nm to 96 nm. The static and dynamic magnetic properties show great dependence on Ag buffer layer thickness. The coercivity and effective damping parameter of Co92Zr8 films increase with thickening Ag buffer layer. The intrinsic and extrinsic parts of damping were extracted from the effective damping parameter. For x=96 nm film, the extrinsic damping parameter is 0.028, which is significantly larger than 0.004 for x=9 nm film. The origin of the enhancement of extrinsic damping can be explained by increased inhomogeneity of anisotropy. Therefore, it is an effective method to tailor magnetic damping parameter of thin magnetic films, which is desirable for high frequency application. 相似文献
825.
Jing Liqiang Wang Baiqi Li Shudan Cai Weimin 《Journal of solid state chemistry》2004,177(11):4221-4227
In this paper, ZnO nanoparticle photocatalysts were modified by depositing Pd on their surfaces with a photoreduction method. We mainly investigated the modification mechanisms as well as the effects on the photocatalytic activity of ZnO nanoparticles of deposited Pd by means of XPS and SPS (Surface Photovoltage Spectroscopy), and the effects of Pd content on SPS responses were also discussed from the point of the electronic energy level. The results showed that the content of crystal lattice oxygen on the surface of ZnO nanoparticle decreased after an appropriate amount of Pd was deposited, while that of adsorbed oxygen increased, indicating that Pd was mainly deposited on the crystal lattice oxygen. At the same time, the intensity of SPS responses of ZnO nanoparticles remarkably decreased. In addition, the activity of ZnO nanoparticles could be greatly improved by depositing an appropriate amount of Pd in the gas phase photocatalytic oxidation of n-C7H16. Thus, it could be concluded that the increase in surface content of adsorbed oxygen could facilitate the photocatalytic reaction, and there were close relationships between the SPS response and photocatalytic activity, i.e. the weaker the SPS response, the higher the photocatalytic activity, of Pd-deposited ZnO nanoparticles. 相似文献
826.
采用胶体化学法制备了稳定的SnO2纳米粒子(nanoparticleNP)水溶胶,用膜天平和原位布儒斯特角显微镜(BAM)考察了经典成膜材料花生酸(AA)在此水溶胶气-液界面的成膜性,并用LB膜技术在不同基底上制得了单层和多层AA-Sno2NP复合LB膜,通过TEM、小角X-ray、IR和UV-VIS光谱,进一步考察了该有序组装体的结构和周期性,以及组装作中Sno2纳米粒子的形貌、粒度分布和表面聚集状态.结果表明,用这种方法能够制得粒度分布均匀、农致密的Sno2纳米粒子复合LB膜,并且多层复合膜具有良好的周期性. 相似文献
827.
Gerko Oskam 《Journal of Sol-Gel Science and Technology》2006,37(3):161-164
The synthesis of metal oxide nanoparticles is described in terms of precursor formation, nucleation, growth, and aging processes.
The main parameters governing these processes are the solution properties, including the solvent viscosity, dielectric constant
and the presence of adsorbing anions, the solubility of the metal oxide, and the metal oxide surface energy. 相似文献
828.
Star-shaped poly(ethylene glycol) (PEG)-poly(?-caprolactone) (?-PCL) block copolymers were synthesized via a ring-opening polymerization. Nanoparticles prepared by the precipitation/solvent evaporation technique exhibit a core-shell structure. The hydrolytic degradation of 3-arm PEG-PCL copolymeric nanoparticles was studied by dynamic light scattering (DLS), nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC). It was found that copolymers with shorter PCL block length degraded faster. The sizes of nanoparticles fluctuated during the initial degradation period, and then increased slightly before finally dropping off. The degradation mainly occurred at CL-CL linkages firstly then at the EO-CL linkages. The CL/EO molar ratios and the molecular weights of copolymers decreased as degradation time and a zero-order degradation behavior was observed. 相似文献
829.
XU Wei-Xing* 《物理化学学报》2007,(2)
Nano-materials have been extensively studied in the past[1]. The quantum effect makes the properties of nano-materials dif- ferent from that of bulk materials. A few of publications regard- ing the catalysis, electronic structure, and optics of the nanome… 相似文献
830.
Mechanochemical-hydrothermal synthesis of calcium phosphate powders with coupled magnesium and carbonate substitution 总被引:1,自引:0,他引:1
Wojciech L. Suchanek Kullaiah Byrappa Pavel Shuk Richard E. Riman Victor F. Janas 《Journal of solid state chemistry》2004,177(3):793-799
Magnesium- and carbonate-substituted calcium phosphate powders (Mg-, CO3-CaP) with various crystallinity levels were prepared at room temperature via a heterogeneous reaction between MgCO3/Ca(OH)2 powders and an (NH4)2HPO4 solution using the mechanochemical-hydrothermal route. X-ray diffraction, infrared spectroscopy, and thermogravimetric analysis were performed. It was determined that the powders containing both Mg2+ and CO32− ions were incorporated uniformly into an amorphous calcium phosphate phase while in contrast, the as-prepared powder free of these dopants was crystalline phase-pure, stoichiometric hydroxyapatite. Dynamic light scattering revealed that the average particle size of the room temperature Mg-, CO3-CaP powders was in the range of 482 nm-700 nm with a specific surface area between 53 and 91 m2/g. Scanning electron microscopy confirmed that the Mg-, CO3-CaP powders consisted of agglomerates of equiaxed, ≈20-35 nm crystals. 相似文献