全文获取类型
收费全文 | 1424篇 |
免费 | 144篇 |
国内免费 | 111篇 |
专业分类
化学 | 513篇 |
晶体学 | 69篇 |
力学 | 62篇 |
综合类 | 12篇 |
数学 | 67篇 |
物理学 | 956篇 |
出版年
2024年 | 2篇 |
2023年 | 26篇 |
2022年 | 31篇 |
2021年 | 31篇 |
2020年 | 24篇 |
2019年 | 33篇 |
2018年 | 37篇 |
2017年 | 65篇 |
2016年 | 68篇 |
2015年 | 66篇 |
2014年 | 65篇 |
2013年 | 139篇 |
2012年 | 69篇 |
2011年 | 106篇 |
2010年 | 77篇 |
2009年 | 88篇 |
2008年 | 97篇 |
2007年 | 95篇 |
2006年 | 90篇 |
2005年 | 59篇 |
2004年 | 48篇 |
2003年 | 46篇 |
2002年 | 54篇 |
2001年 | 35篇 |
2000年 | 33篇 |
1999年 | 27篇 |
1998年 | 35篇 |
1997年 | 8篇 |
1996年 | 10篇 |
1995年 | 13篇 |
1994年 | 11篇 |
1993年 | 9篇 |
1992年 | 7篇 |
1991年 | 6篇 |
1990年 | 7篇 |
1989年 | 5篇 |
1988年 | 9篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 3篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1974年 | 2篇 |
1973年 | 5篇 |
1948年 | 1篇 |
排序方式: 共有1679条查询结果,搜索用时 15 毫秒
101.
3D FDTD Implementation for Scattering of Electric Anisotropic Dispersive Medium Using Recursive Convolution Method 总被引:1,自引:0,他引:1
Lixia Yang 《International Journal of Infrared and Millimeter Waves》2007,28(7):557-565
The finite-difference time-domain method based on recursive convoltion method (RC-FDTD) for the electric anisotropic dispersive
medium is discussed in detail. To exemplify the availability of the three-dimensional RC-FDTD algorithm, the backscattering
Radar-Cross-Section(RCS) of a non-magnetized plasma sphere is computed, and the numerical results are the same as the one
of the Shift Operater-FDTD method, and show that the RC-FDTD method is correct and efficient. In addition, the co-polarized
and cross-polarized backscattering time-domain of a magnetized plasma sphere are obtained by the RC-FDTD algorithm. The results
show that when the external magnetic field is implemented, the cross-polarized component appear, evidently. 相似文献
102.
The aim of this paper is to point out the influence of dielectric barrier discharge treatment on tribocharging of granular insulating materials. Particles of Polyvinyl Chloride (PVC) and Polypropylene (PP) were subjected to an AC dielectric barrier discharge (DBD) plasma treatment in ambient airprior to tribocharging in a vibratory device. The charge to mass ratio was measured for treated and untreated materials. Electrostatic separation of a mixture of granular materials (PVC and PP) to measure the effectiveness of DBD treatment was evaluated by processing treated and untreated PVC/PP granular mixtures in a free-fall electrostatic separator. The obtained results clearly indicate that DBD has the capability to influence surface charging proprieties of polymer granular materials. In case of short treatment time, typically less than 3 s, a marked increase in the charge to mass ratios was observed for both PVC (about 35%) and PP (roughly 45%). In the same way, the quantity of DBD-treated materials, recovered after electrostatic separation, was increased by about 104% and 30% for PVC and PP, respectively, as compared to untreated case. The DBD treatment time is a key factor to increase the tribo electric effect. 相似文献
103.
D.P.A. Hardwick S.L. Naylor S. Bujkiewicz T.M. Fromhold D. Fowler A. Patan L. Eaves A.A. Krokhin P.B. Wilkinson M. Henini F.W. Sheard 《Physica E: Low-dimensional Systems and Nanostructures》2006,32(1-2):285
We study the effects of inter-miniband electron tunneling and electric field domains on the current–voltage and conductance–voltage curves of biased semiconductor superlattices under the action of a magnetic field that is tilted relative to the plane of the layers. For this geometry, electrons in the superlattice minibands exhibit a unique type of stochastic semiclassical motion. At certain critical values of the electric field within the superlattice layers, the stochastic trajectories change abruptly from fully localized to completely unbounded, and map out an intricate web-like mesh of conduction channels in phase space. Delocalization of the electron paths produces a series of strong resonant peaks in the electron drift velocity versus electric field curves. We use these drift velocity characteristics to make self-consistent drift-diffusion calculations of the current–voltage and differential conductance–voltage curves of the superlattices, which reveal strong resonant features originating from the sudden delocalization of the stochastic single-electron paths. We show that this delocalization has a pronounced effect on the distribution of space charge and electric field domains within the superlattices. Inter-miniband tunneling greatly reduces the amount of space-charge buildup, thus enhancing the domain structure and both the strength and number of the current resonances. 相似文献
104.
Boltzmann-transport equation is analytically solved for two-component magnetoplasma using Chapman-Enskog analysis to include
collisional diffusion transport having anisotropies in both streaming velocity and temperature components. The modified collisional
integrals are analytically solved with flux integrals and perturbed kinetic equation to arrive at drift diffusion velocity
and resulting transport coefficients which are markedly affected by both streaming and temperature anisotropy. The early isotropic
results are recovered in the limit V
0 = 0 and T
‖ = T
⊥ which reduce to eqs (11.30) and (11.31) of [1] and eqs (2.7) and (2.13) of [2]. The electrical resistivity (η⊥) diminishes sharply in fusion temperature limit kT
⊥ = 1 keV. The shape of the curves for both electrical resistivity and thermal conductivity is rectangular hyperbolic. However,
for low thermal ratio (T
‖/T
⊥ < 1), the curves are raised up and for high thermal ratio (T
‖/T
⊥ > 1), they are lowered down the isotropic case (T
‖/T
⊥ > 1), showing comparatively diminished magnitudes of the quantities.
相似文献
105.
In this work we study the binding energy of the ground state for a hydrogenic donor impurity in laterally coupled GaAs/Ga1−xAlxAs quantum well wires, considering the simultaneous effects of hydrostatic pressure and applied electric field. We have used a variational method and the effective mass and parabolic band approximations. The low dimensional structure consists of two quantum well wires with rectangular transverse section coupled by a central Ga1−xAlxAs barrier. Our results are reported for several sizes of the structure and we have taken into account variations of the impurity position along the growth direction of the heterostructure. 相似文献
106.
M.J. KarimiG. Rezaei 《Physica B: Condensed Matter》2011,406(23):4423-4428
In this work, influences of external electric and magnetic fields on the optical rectification coefficient, the linear and the third-order nonlinear optical absorption coefficients as well as refractive index changes of finite semi-parabolic quantum dots are investigated. In this regard, energy eigenvalues and eigenfunctions of the system are calculated numerically, and optical properties are obtained using the compact density matrix approach. The results show that external electric and magnetic fields have a great influence on these optical quantities. 相似文献
107.
108.
La1-x/2Pr1-x/2SrxCuOy(LPSCO)多晶样品采用传统的固相反应法制备.X射线衍射表明:LPSCO具有典型的空穴搀杂的T-214相的结构.磁化率测量显示:Sr搀杂在0.05≤x≤0.30范围内具有超导转变;Tc随x的增大呈抛物线形式变化,且在x=0.18时达到最大值28K.电阻的测量显示:随搀杂量的增大,系统呈现从绝缘到半导体,最后到金属的导电行为的变化;在欠掺杂区,正常态电阻温度关系符合ρ(T)=ρ0 αT-ClnT;而在过掺杂区,对数项消失.本文从替代所引起的晶体结构和载流子特性变化解释了Sr掺杂样品的电输运行为和超导特性. 相似文献
109.
Non-equilibrium molecular dynamics (NEMD) simulations have been performed for static electric fields for a range of positively charged spherical rutile-titania nanoparticles with radii of 1.5 to 2.9 nm for two different salt concentrations in water, in order to simulate electrophoresis directly. Using the observed limiting drag velocities, Helmholtz-Smoluchowski (HS) theory was used to estimate their ζ potentials. These estimates were compared to values from numerical solution of the non-linear Poisson-Boltzmann (PB) equation for representative configurations of the nanoparticles, in addition to idealised analytic and Debye-Hückel (DH) solutions about spherical particles of the same geometry and charge state, for the given salt concentrations. It was found that reasonable agreement was obtained between the various approaches, with the NEMD-HS results some 15%-15% smaller than the numerical PB results for more highly charged nanoparticles. 相似文献
110.
The beam quality factors (or M2 parameter) of coherent and incoherent superposition of the several lower-order LP modes emerging from a step-index fiber have been calculated by using the second-order moment method. The results indicate that, for an individual LP mode, the M2 parameter takes its maximum value when the normalized frequency V of the step-index fiber approaches the cut-off frequency, and it gradually becomes constant as V increases. In the case of incoherent superposition, the larger the fraction intensity carried by the higher-order mode, the larger the beam quality factor M2. Under certain circumstances, the value of the M2 parameter of the mixed mode that comprises several LP-modes contents may become even smaller and closer to the ideal Gaussian beam than that of the fundamental mode in a step-index fiber. However, in the case of the coherent superposition, the value of the M2 parameter of the mixed mode may be greater than that of the higher-order constituent mode. The results reported here could be helpful for the application of the high-power fiber laser systems. 相似文献