全文获取类型
收费全文 | 414篇 |
免费 | 7篇 |
专业分类
化学 | 263篇 |
晶体学 | 8篇 |
力学 | 3篇 |
数学 | 16篇 |
物理学 | 131篇 |
出版年
2021年 | 3篇 |
2020年 | 3篇 |
2019年 | 3篇 |
2017年 | 3篇 |
2016年 | 5篇 |
2015年 | 5篇 |
2014年 | 3篇 |
2013年 | 15篇 |
2012年 | 21篇 |
2011年 | 19篇 |
2010年 | 15篇 |
2009年 | 12篇 |
2008年 | 18篇 |
2007年 | 16篇 |
2006年 | 24篇 |
2005年 | 12篇 |
2004年 | 16篇 |
2003年 | 7篇 |
2002年 | 12篇 |
2001年 | 8篇 |
2000年 | 8篇 |
1999年 | 12篇 |
1998年 | 7篇 |
1997年 | 6篇 |
1995年 | 6篇 |
1994年 | 4篇 |
1989年 | 3篇 |
1988年 | 8篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 15篇 |
1984年 | 4篇 |
1982年 | 8篇 |
1981年 | 5篇 |
1979年 | 3篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1973年 | 5篇 |
1972年 | 4篇 |
1970年 | 8篇 |
1969年 | 3篇 |
1968年 | 3篇 |
1967年 | 6篇 |
1962年 | 4篇 |
1960年 | 5篇 |
1958年 | 3篇 |
1940年 | 2篇 |
1929年 | 2篇 |
1905年 | 2篇 |
1871年 | 2篇 |
排序方式: 共有421条查询结果,搜索用时 15 毫秒
41.
Shahriar KhushrushahiMarkus Zahn 《Journal of magnetism and magnetic materials》2011,323(10):1302-1308
Ferrofluid spin-up flow is studied within a sphere subjected to a uniform rotating magnetic field from two surrounding spherical coils carrying sinusoidally varying currents at right angles and 90° phase difference. Ultrasound velocimetry measurements in a full sphere of ferrofluid shows no measureable flow. There is significant bulk flow in a partially filled sphere (1-14 mm/s) of ferrofluid or a finite height cylinder of ferrofluid with no cover (1-4 mm/s) placed in the spherical coil apparatus. The flow is due to free surface effects and the non-uniform magnetic field associated with the shape demagnetizing effects. Flow is also observed in the fully filled ferrofluid sphere (1-20 mm/s) when the field is made non-uniform by adding a permanent magnet or a DC or AC excited small solenoidal coil. This confirms that a non-uniform magnetic field or a non-uniform distribution of magnetization due to a non-uniform magnetic field are causes of spin-up flow in ferrofluids with no free surface, while tangential magnetic surface stress contributes to flow in the presence of a free surface.Recent work has fitted velocity flow measurements of ferrofluid filled finite height cylinders with no free surface, subjected to uniform rotating magnetic fields, neglecting the container shape effects which cause non-uniform demagnetizing fields, and resulting in much larger non-physical effective values of spin viscosity η′∼10−8−10−12 N s than those obtained from theoretical spin diffusion analysis where η′≤10−18 N s. COMSOL Multiphysics finite element computer simulations of spherical geometry in a uniform rotating magnetic field using non-physically large experimental fit values of spin viscosity η′∼10−8−10−12 N s with a zero spin-velocity boundary condition at the outer wall predicts measureable flow, while simulations setting spin viscosity to zero (η′=0) results in negligible flow, in agreement with the ultrasound velocimetry measurements. COMSOL simulations also confirm that a non-uniform rotating magnetic field or a uniform rotating magnetic field with a non-uniform distribution of magnetization due to an external magnet or a current carrying coil can drive a measureable flow in an infinitely long ferrofluid cylinder with zero spin viscosity (η′=0). 相似文献
42.
Yu.M. Azhniuk A.V. Gomonnai Yu.I. Hutych V.V. Lopushansky I.I. Turok V.O. Yukhymchuk D.R.T. Zahn 《Journal of Crystal Growth》2010,312(10):1709-1716
Variation of the chemical composition of ternary CdS1−xSex nanocrystals grown in borosilicate glass depending on the thermal treatment is studied by resonant Raman spectroscopy. It is shown that only for the nanocrystals with roughly equal content of substitutive S and Se chalcogen atoms (0.4<x<0.6) the nanocrystal composition is independent of the thermal treatment parameters. In other cases an increase of the thermal treatment temperature (625–700 °C) and duration (2–12 h) results in a considerable increase of the predominant chalcogen content in the nanocrystals. 相似文献
43.
D.W. Hough U. Jaenicke‐Roessler G. Zahn A. Belger A. Guembel C.‐G. Oertel W. Skrotzki 《Crystal Research and Technology》2000,35(4):409-417
Y2Pd14B5 is the major phase in as‐cast and annealed multiphase alloys with nominal compositions near YPd5B3C0.3. Its crystal structure determined the first time here by single crystal X‐ray diffraction is body‐centered tetragonal (space group I41/amd). Transmission electron microscopy (TEM) reveals that in as‐cast specimens the tetragonal phase has a modulated structure and is oriented intergrown with a face‐centered cubic phase of similar composition, namely YPd7B2. According to Rietveld analyses of the multiphase system the structure of this phase can be well‐described by space group Fm m. Annealing the sample for 150 hrs at 973 K results in a coarsening and enrichment of the tetragonal phase as well as a disappearance of the modulations allowing a detailed structure analysis by single crystal diffractometry. 相似文献
44.
Meier R Maigut J Kallies B Lehnert N Paulat F Heinemann FW Zahn G Feth MP Krautscheid H van Eldik R 《Chemical communications (Cambridge, England)》2007,(38):3960-3962
The equilibrium between the twist-boat (tb) and half-chair (hc) conformers of the central diamine chelate ring of [Fe(III)(tmdta)]- in solids and aqueous solution has been studied by Raman spectroscopy, supported by calculated Raman spectra using Density Functional Theory. 相似文献
45.
Using ultra-high vacuum scanning tunneling microscopy (UHV-STM), we show that copper-phthalocyanine (CuPc) grows in a well ordered manner on hydrogen passivated vicinal silicon surfaces. CuPc grows one-dimensionally parallel to the monatomic steps on the vicinal silicon surface. Surprisingly, elongated clusters of the CuPc parallel to the step directions are formed even on the middle of the terraces well away from the step edges. The one-dimensional growth mode continues even after the full monolayer coverage on the substrate which results in strongly oriented growth mode of a thin film of CuPc on the vicinal silicon surfaces. 相似文献
46.
Cationic dioxorhenium and dioxotechnetium complexes of the composition [MO(2)(L(1))(4)](+) (L(1) = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene) have been prepared from various starting materials and studied spectroscopically and by X-ray crystallography. The metal-carbon distances range from 2.216(4) to 2.232(4) A indicating mainly sigma-bonding. 相似文献
47.
48.
V. Sivakov G. Andrä C. Himcinschi U. Gösele D.R.T. Zahn S. Christiansen 《Applied Physics A: Materials Science & Processing》2006,85(3):311-315
One-dimensional (1D) silicon (Si) nanostructures were grown by electron-beam evaporation catalyzed by gold nanoparticles on silicon substrates following the vapor–liquid–solid growth mechanism. We report three strikingly different growth morphologies of the 1D Si nanostructures and discuss their formation. The morphology of the silicon nanostructures strongly depends on gold layer thickness, annealing temperature before deposition and growth temperature during the deposition. The formation of nanoscale silicon features such as nanobelts, nanowires and nanowhiskers was observed. The nanoscale silicon features were characterized by transmission and scanning electron microscopy using imaging, diffraction and energy-dispersive X-ray spectroscopy, atomic force microscopy and UV micro-Raman spectroscopy. PACS 68.37.Lp; 68.70.+w; 78.30.-j; 81.15.Jj 相似文献
49.
The combination of valence band photoemission and inverse photoemission spectroscopy is applied to study the densities of occupied and unoccupied states of perylene derivative and phthalocyanine organic layers on inorganic semiconductors. The ionisation energies and electron affinities are determined and it is proposed that the transport gap of the materials can be evaluated from the distance of the HOMO and LUMO edges. The resulting values for the transport gap which are somewhat smaller than other published data are in good agreement with e.g. electrical measurements. The experimental spectra are compared with simulated ones obtained by density functional theory calculations. 相似文献
50.
L. C. Oliveira C. B. Zamboni F. A. Genezini A. M. G. Figueiredo G. S. Zahn 《Journal of Radioanalytical and Nuclear Chemistry》2005,263(3):783-786
Summary In this study we show that the NAA technique can be used to perform clinical analyses of blood and urine, with many advantages towards the conventional methods. From the knowledge of the neutron flux and the induced activity, the concentration ofelements were obtained. In comparison to the conventional techniques, this methodology uses smaller quantities of biological material and allows the simultaneous evaluation of the concentrations of several elements in biological samples at once, something not always possible in the conventional clinical analysis. Another important advantage is that it eliminates the use of standard materials, thus making the analyzing process practical and economic. 相似文献