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   923篇
  免费   156篇
  国内免费   109篇
化学   287篇
晶体学   8篇
力学   94篇
综合类   9篇
数学   222篇
物理学   568篇
  2024年   14篇
  2023年   17篇
  2022年   21篇
  2021年   22篇
  2020年   29篇
  2019年   39篇
  2018年   21篇
  2017年   39篇
  2016年   38篇
  2015年   29篇
  2014年   44篇
  2013年   68篇
  2012年   51篇
  2011年   49篇
  2010年   46篇
  2009年   73篇
  2008年   58篇
  2007年   55篇
  2006年   51篇
  2005年   30篇
  2004年   36篇
  2003年   39篇
  2002年   37篇
  2001年   47篇
  2000年   30篇
  1999年   33篇
  1998年   38篇
  1997年   15篇
  1996年   21篇
  1995年   9篇
  1994年   11篇
  1993年   8篇
  1992年   8篇
  1991年   11篇
  1990年   4篇
  1989年   3篇
  1988年   6篇
  1987年   6篇
  1986年   5篇
  1985年   5篇
  1984年   4篇
  1983年   3篇
  1982年   5篇
  1981年   1篇
  1980年   1篇
  1979年   3篇
  1978年   2篇
  1977年   1篇
  1973年   1篇
  1963年   1篇
排序方式: 共有1188条查询结果,搜索用时 15 毫秒
1.
Manganites of the LA1−x Ca x MnO3 family show a variety of new and poorly understood electronic, magnetic and structural effects. Here we outline a new approach recently proposed by us, where we argue that due to strong Jahn-Teller (JT) coupling with phonons the twofold degeneratee g states at the Mn sites dynamically reorganize themselves into localised, JT polaronsl with exponentially small inter-site hopping, and band-like, nonpolaronic statesb, leading to anew 2-band model for manganites which includes strong Coulomb and Hund’s couplings. We also discuss some results from a dynamical mean-field theory treatment of the model which explains quantitatively a wide variety of experimental results, including insulator-metal transitions and CMR, in terms of the influence of physical conditions on the relative energies and occupation of thel andb states. We argue that this microscopic coexistence of the two types of electronic states, and their relative occupation and spatial correlation is the key to manganite physics. Dedicated to Professor C N R Rao on his 70th birthday  相似文献   
2.
The spherical-model limitn of then-vector model in a random field, with either a statistically independent distribution or with long-range correlated random fields, is studied to demonstrate the correctness of the replica method in which then and replica limits limits are interchanged, provided the replica and thermodynamic limits are taken in the right order, in the case of long-range correlated random fields. A scaling form for the two-point correlation function relevant to the first-order phase transition below the lower critical dimensionality of the random system is also obtained.  相似文献   
3.
Using the numerical renormalization group method, the dependences on temperature of the magnetic susceptibility χ(T) and specific heat C(T) are obtained for the single-impurity Anderson model with inclusion of d-f the Coulomb interaction. It is shown that the exciton effects caused by this effect (charge fluctuations) can significantly change the behaviour of C(T) in comparison with the standard Anderson model at moderately low temperatures, whereas the behaviour of χ(T) remains nearly universal. The ground-state and temperature-dependent renormalizations of the effective hybridization parameter and f-level position caused by the d-f interaction are calculated, and satisfactory agreement with the Hartree-Fock approximation is derived.  相似文献   
4.
The propagation of an external transverse magnetic signal acting locally on a 1d chain of spins generates a disturbance which runs through the system. This quantum effect can be interpreted as a classical travelling wave which contains a superposition of a large set of frequencies depending on the size of the chain. Its local amplitude fixes the size of the z-component of the spins at any location in the chain. The average and maximum value of the group velocity are determined and compared with the transmission velocity fixed by the Lieb-Robinson upper bound inequality.  相似文献   
5.
曹辉  赵清 《物理学报》2010,59(4):2187-2192
研究了在不同的相互作用和隧穿耦合强度比值情况下双势阱中冷原子的隧穿现象.两格点Bose-Hubbard模型不能完全解释实验.为此,对此模型做了高阶修正.取双势阱的基态和第一激发态作基矢,写出哈密顿量的表示,解释了用两格点Bose-Hubbard模型分析实验时参数不能定量符合的原因.另外,通过计算两阱中原子纠缠度的变化,结合三态上原子布居数分布,直观描述了整个隧穿过程.  相似文献   
6.
A ferromagnetic ground state was identified for the compounds CeCuGe (TC=10 K), CeCuSi (TC=15 K) [F. Yang, et al., J. Appl. Phys. 69 (1991) 4705] and CeAuGe (TC=10 K) [R. Pottgen, J. Magn. Magn. Mater. 152 (1996) 196]. The observed saturation magnetic moment values at low temperatures for all three compounds are considerably less than the theoretically expected value gJJ=2.14μB for the free Ce3+ ion involving the entire six-fold J=5/2 multiplet, and thus provide a first indication of partial lifting of the f-electron level degeneracy in these compounds. Specific heat data yield crystal electric field (CEF) excitation energies (ΔSch) equivalent to 140 K for CeCuGe, 110 K for CeCuSi and 280 K for CeAuGe. To confirm the presence of CEF excitations directly, we have carried out inelastic neutron scattering (INS) measurements on all three compounds, using the HET spectrometer at ISIS Facility. Here, we present a detailed analysis of the INS spectra of CeCuSi on the basis of a CEF model and the detailed analysis of the INS of the other two compounds will be reported elsewhere.  相似文献   
7.
8.
CuGeO3 exhibits a Spin-Peierls (SP) transition, at T SP = 14.3 K, which is announced above 19 K by an important regime of one-dimensional (1D) pretransitional lattice fluctuations which can be detected until about 40 K using X-ray diffuse scattering investigations. A quantitative analysis of this scattering shows that in this 1D direction the correlation length follows the “universal” behaviour expected for the thermal fluctuations of a real order parameter which characterizes the lattice dimerization. This allows to define a 1D mean-field temperature, T SP MF , of about 60 K and invalidates any mean field scenario for the SP transition of CuGeO3. As T SP MF is as high as 4 T SP we propose that the 3D-SP order is achieved by the interchain coupling between 1D solitons which form below about 16-20 K. CuGeO3 being in the non-adiabatic regime, it is also suggested that the observed pretransitional fluctuations of CuGeO3 originate from the X-ray scattering on a very broad damped critical response of lower frequency than the “critical” phonon modes. From the quantitative analysis of the 1D fluctuations we also estimate the microscopic parameters of the SP chain. These parameters allow to locate CuGeO3 close to the quantum critical boundary separating the gapped SP ground state to the ungapped anti-ferromagnetic ground state. The vicinity of a quantum critical point emphasizes the role of the quantum and non-adiabatic fluctuations and the importance of the interchain coupling in the physics of CuGeO3. Finally we compare these findings with those obtained for the organic SP systems (BCPTTF)2PF6, (TMTTF)2PF6 and MEM(TCNQ)2. From a similar analysis of the pretransitional lattice fluctuations it is found that (BCPTTF)2PF6 and (TMTTF)2PF6 are located on the SP gapped classical-quantum boundary and are in the adiabatic regime where the fluctuations lead to the formation of a pseudo-gap in the spin degrees of freedom. Differently, we place MEM(TCNQ)2 inside the SP quantum phase around the crossover line between the adiabatic and non-adiabatic regimes. Received 13 September 2000 and Received in final form 6 February 2001  相似文献   
9.
We present the Fermi surface properties in strongly correlated electron systems of rare earth and uranium compounds via de Haas–van Alphen experiments. The conduction electrons with large cyclotron effective masses over 100m0 (m0: rest mass of an electron) are detected in CeRu2Si2, CeCoIn5 and UPt3. These electrons move slowly in the crystal. The topology of the Fermi surface and the cyclotron mass are compared to those of energy band calculations.  相似文献   
10.
Specific heat versus temperature curves for various pressures, or magnetic fields (or some other external control parameter) have been seen to cross at a point or in a very small range of temperatures in many correlated fermion systems. We show that this behavior is related to the possibility of existence of a quantum critical point. Vicinity to a quantum critical point in these systems leads to a crossover from quantum to classical fluctuation regime at some temperature . The temperature at which the curves cross turns out to be near this crossover temperature. We have discussed the case of the normal phase of liquid Helium three and the heavy fermion systems CeAl3 and UBe13 in detail within the spin fluctuation theory, a theory which inherently contains a low energy scale which can be identified with . When the crossover scale is a homogeneous function of these control parameters there is always crossing at a point. We also mention other theories exhibiting a low energy scale near a quantum critical point and discuss this phenomenon in those theories. Received 25 June 1999  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