首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   279篇
  免费   20篇
  国内免费   1篇
化学   5篇
晶体学   14篇
物理学   281篇
  2022年   1篇
  2019年   1篇
  2013年   1篇
  2012年   2篇
  2011年   3篇
  2010年   9篇
  2009年   60篇
  2008年   60篇
  2007年   51篇
  2006年   41篇
  2005年   11篇
  2004年   4篇
  2003年   17篇
  2002年   13篇
  2001年   7篇
  2000年   3篇
  1999年   3篇
  1998年   3篇
  1996年   1篇
  1995年   1篇
  1993年   2篇
  1989年   2篇
  1988年   1篇
  1985年   1篇
  1981年   1篇
  1977年   1篇
排序方式: 共有300条查询结果,搜索用时 31 毫秒
211.
The electric field gradient resulting from Ta substitutional defect in normal monoclinic phase is studied using all-electron ab initio NFP-LMTO method. Hyperfine parameters in Pbca and Pnma phases have also been calculated to determine the usefulness of quadrupolar interactions in the investigation of phase diagrams under hydrostatic pressure. Predictions for hyperfine parameters in high temperature P42nmc and Fm3m phases were also developed. Given the donor behavior of Ta in HfO2, two charge states, 0 and +1, have been studied for each phase. Although HFI do not vary significantly with charge, it was determined that for a Ta+1 in P21/c phase hyperfine parameters is consistent with experimental results. Quadrupolar interactions for transitions to denser phases show important variations with respect to that of the normal phase: asymmetry parameter for Pbca and the electric field gradient for Pnma both increase substantially. At high temperature phases, drastic decrease in both EFG and asymmetry parameter in P42nmc is observed, while they almost vanish in Fm3m.  相似文献   
212.
The ground state donor binding energy is estimated using the simple first order perturbation method for a GaAs-Al x Ga1−x As spherical quantum dot. The calculated energy is computed as a function of Al-concentration. Donor binding energy is found to be quite sensitive to Al-concentration (x), specifically for smallx. Furthermore, the binding energy is found to be highest for the smallest and the center-doped dot indicating the strongest confinement in those cases.  相似文献   
213.
Cold collisions between electrostatically trapped linear polar molecules are theoretically investigated. It is consequently shown that the inelestic collision cross-section is determined by S-wave scattering alone, while the contribution of D-wave scattering to the elastic collision cross-section becomes significant when the electric field strength is high. It is also shown that as the temperature decreases, it becomes difficult to obtain the evaporative cooling effect without collision loss. Received 12 September 2002 / Received in final form 21 November 2002 Published online 29 April 2003 RID="a" ID="a"e-mail: kajita@crl.go.jp  相似文献   
214.
The influence of the surface roughness of polypropylene on the contact angle hysteresis is investigated by means of ethylene glycol drops in order to estimate the true Young’s equilibrium contact angle. A new relationship between the contact angle hysteresis and Wenzel’s contact angle is derived. In addition, the determination of Wenzel’s roughness factor by means of scanning force microscopy opens an alternative way to obtaining Young’s equilibrium contact angle without any surface manipulation. The experimental results presented verify this new approach. Received: 2 September 2002 / Accepted: 2 September 2002 / Published online: 5 March 2003 RID="*" ID="*"Corresponding author. Fax: +49-3328/352-452, E-mail: helmut.kamusewitz@gkss.de  相似文献   
215.
Layers of dihydroxy silicon phthalocyanine tetrasulfonic acid and oligo-μ-oxo silicon phthalocyanine tetrasulfonic acid were prepared by solution-casting methods. The purity of the material was checked by X-ray photoemission spectroscopy. The orientation of the molecules in respect to the substrate plane was investigated by angle-dependent near-edge X-ray absorption fine-structure spectroscopy. The morphology was characterized by atomic force microscopy. Most samples exhibited a significant orientation that was accompanied by crystalline structures; others had no orientation at all with a dominant amorphous morphology. This behavior indicates that several preparation parameters affect the crystallinity and the orientation of the phthalocyanines. Received: 16 January 2002 / Accepted: 11 February 2002 / Published online: 3 May 2002 RID="*" ID="*"Corresponding author. Fax: +1-919/515-7331, E-mail: harald_ade@ncsu.edu RID="**" ID="**"Present address: Southern Illinois University, Physics, Mailcode 4401, Carbondale, IL 62901, USA  相似文献   
216.
Using the fluid model for the nonlinear response of ions, we have studied the nonlinear scattering of an electromagnetic ion cyclotron wave off the ion acoustic wave in a plasma. The low frequency nonlinearity arises through the parallel ponderomotive force on ions and the high frequency nonlinearity arises through the nonlinear current density of ions. For a typical nonisothermal plasma (T e/T i∼10) the threshold for this instability in a uniform plasma is ∼1mW/cm2. At power densities ≳102 W/cm2, the growth rate for backscatter turns out to be ∼104s−1.  相似文献   
217.
The electronic structures and absorption spectra for the perfect PbWO4 (PWO) crystal and the crystal containing lead vacancy have been calculated using density functional theory code CASTEP with the lattice structure optimized. The calculated absorption spectra of the PWO crystal containing exhibit seven absorption bands peaking at 1.72 eV (720 nm), 2.16 eV (570 nm), 2.81 eV (440 nm), 3.01 eV (410 nm), 3.36 eV (365 nm), 3.70 eV (335 nm) and 4.0 eV (310 nm), which are very close to the experimental values. It predicts that the 330, 360, 420, 500-750 nm absorption bands are related to the existence of in the PWO crystal.  相似文献   
218.
Extremely low density InAs quantum dots (QDs) are grown by molecular beam droplet epitaxy. The gallium deposition amount is optimized to saturate exactly the excess arsenic atoms present on the GaAs substrate surface during growth, and low density InAs/GaAs QDs (4× 10^6 cm^-2) are formed by depositing 0.65 monolayers (MLs) of indium. This is much less than the critical deposition thickness (1.7 ML), which is necessary to form InAs/GaAs QDs with the conventional Stranski-Krastanov growth mode. The narrow photoluminescence linewidth of about 24 meV is insensitive to cryostat temperatures from IO K to 250K. All measurements indicate that there is no wetting layer connecting the QDs.  相似文献   
219.
We propose a novel scheme to trap cold polar molecules on the surface of an insulating substrate (i.e. a chip) by using an inhomogeneous electrostatic field, which is generated by the combination of a circular charged wire (a ring electrode) and a grounded metal plate. The spatial distributions of the electrostatic field from the above charged wire layout and its Stark potentials for CO molecules are calculated. Our study shows that when the voltage applied to the wire is U = 15 kV, a ring radius is R = 5 mm, the thickness of the insulating substrate is b = 5 mm, and a wire radius is r = 1mm, the maximum efficient trapping potential (i.e., as equivalent temperature) for CO molecules is greater than 141.7mK, which is high enough to trap cold polar molecules with a temperature of 50 mK in the low-field-seeking states.  相似文献   
220.
One-dimensional metal lines of silver nanoparticles with a nano-sized width were generated onto silicon surface by using a nano-level lithography technique, field induced oxidation (FIO) by AFM, on self-assembled monolayer-modified Si wafers. This FIO technique provided SiO2 lines a width of less than 100 nm. Short-time immersion of partially anodized silicon surface which is covered by a cationic silanol surfactant ((CH3O)3SiCH2CH2CH2N(CH3)3+Cl)-monolayer into quaternary ammonium (HSCH2CH2N(CH3)3+Br)-covered silver nanoparticles readily and reproducibly gave nano-metal lines of silver onto silicon wafers. Hydrophilicity of the whole wafer surface was indispensable for homogeneously wetting the anodized SiO2 area with a nanodimensional width.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号