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   1464篇
  免费   234篇
  国内免费   99篇
化学   446篇
晶体学   15篇
力学   230篇
综合类   13篇
数学   184篇
物理学   909篇
  2023年   10篇
  2022年   21篇
  2021年   28篇
  2020年   28篇
  2019年   27篇
  2018年   31篇
  2017年   51篇
  2016年   35篇
  2015年   41篇
  2014年   62篇
  2013年   116篇
  2012年   62篇
  2011年   107篇
  2010年   93篇
  2009年   101篇
  2008年   97篇
  2007年   101篇
  2006年   96篇
  2005年   66篇
  2004年   81篇
  2003年   84篇
  2002年   66篇
  2001年   47篇
  2000年   49篇
  1999年   53篇
  1998年   39篇
  1997年   36篇
  1996年   23篇
  1995年   28篇
  1994年   17篇
  1993年   16篇
  1992年   16篇
  1991年   8篇
  1990年   7篇
  1989年   14篇
  1988年   5篇
  1987年   3篇
  1986年   6篇
  1985年   5篇
  1984年   3篇
  1983年   1篇
  1982年   3篇
  1981年   5篇
  1980年   1篇
  1977年   1篇
  1976年   4篇
  1974年   1篇
  1971年   1篇
  1959年   1篇
排序方式: 共有1797条查询结果,搜索用时 171 毫秒
91.
Two-center nuclear attraction integrals over Slater type orbitals with integer and noninteger principal quantum numbers in nonlined up coordinate systems have been calculated by means of formulas in our previous work (T. Özdoan and M. Orbay, Int. J. Quant. Chem. 87 (2002) 15). The computer results for integer case are in best agreement with the prior literature. On the other hand, the results for noninteger case are not compared with the literature due to the scarcity of the literature, but also compared with the limit of integer case and good agreements are obtained. The proposed algorithm for the calculation of two-center nuclear attraction integrals over Slater type orbitals with noninteger principal quantum numbers in nonlined-up coordinate systems permits to avoid the interpolation procedure used to overcome the difficulty introduced by the presence of noninteger principal quantum numbers. Finally, numerical aspects of the presented formulae are analyzed under wide range of quantum numbers, orbital exponents and internuclear distances.  相似文献   
92.
93.
Let (X t ,P x ) be a rotation invariant (RI) Feller process on R d {0}, d2. We study certain type of strong Markov extensions of (X t ,P x ) to R d . It turns out that that the unique (RI) extension always exists and is of that type. We give a kind of quasi-ergodicy condition (E) under which the (RI) extension is the only extension of that type. A class of processes fulfilling (E) is also characterized.  相似文献   
94.
The recent development at the Paul Scherrer Institute of a beam of low energy muons allows depth dependent muon spin rotation and relaxation investigations in thin samples, multilayers and near surface regions (low energy SR, LE-SR). After a brief overview of the LE-SR method, some representative experiments performed with this technique will be presented. The first direct determination of the field profile just below the surface of a high-temperature superconductor in the Meissner phase illustrates the power and sensitivity of low energy muons as near-surface probe and is an example of general application to depth profiling of magnetic fields. The evolution of the flux line lattice distribution across the surface of a YBa2Cu3O7 film in the vortex phase has been investigated by implanting muons on both sides of a normal-superconducting boundary. A determination of the relaxation time and energy barrier to thermal activation in iron nanoclusters, embedded in a silver thin film matrix (500nm), demonstrates the use of slow muons to measure the properties of samples that cannot be made thick enough for the use of conventional SR. Other experiments investigated the magnetic properties of thin Cr(001) layers at thicknesses above and below the collapse of the spin density wave.  相似文献   
95.
Circularly rotating axisymmetric perfect fluid space-times are investigated to second order in the small angular velocity. The conditions of various special Petrov types are solved in a comoving tetrad formalism. A number of theorems are stated on the possible Petrov types of various fluid models. It is shown that Petrov type II solutions must reduce to the de Sitter spacetime in the static limit. Two space-times with a physically satisfactory energy-momentum tensor are investigated in detail. For the rotating incompressible fluid, it is proven that the Petrov type cannot be D. The equation of the rotation function can be solved for the Tolman type IV fluid in terms of quadratures. It is also shown that the rotating version of the Tolman IV space-time cannot be Petrov type D.  相似文献   
96.
The dynamics of the side chain of the radical anions of ubiquinones Q-1 (2,3-dimethoxy-5-methyl-6-[3-methyl-2-butenyl]-1,4-benzoquinone), Q-2, Q-6, and Q-10 have been investigated using electron nuclear double-resonance (ENDOR) spectroscopy. When radicals are produced in the liquid phase, secondary radicals are also formed. The EPR spectra of these additional radicals overlap with the radical of interest. ENDOR spectroscopy was found to be capable for studying the dynamical properties of such conditions. The temperature dependence of the isotropic hyperfine coupling constants of the beta- and gamma-protons of the side chain was measured. The activation energy of the rotation and other dynamical properties of the side chain were calculated assuming that rotation can be modeled by the classical two-jump model. The rotation energy barrier for Q-1 was also determined by the hybrid Hartree-Fock/density functional method UB3LYP with the 6-31G(d) basis set. Calculated results were in good agreement with the experimental results. Despite the numerous parameters affecting the ENDOR linewidth ENDOR spectroscopy was shown to be a potential method for studying the dynamical properties of the mixtures of the radicals. Prominent forbidden transitions appear in the ENDOR spectra when alkali ions are present in the sample. From these transitions measured ENDOR-induced EPR spectra showed an additional doublet and phase transition in electron Zeeman frequency.  相似文献   
97.
98.
使用Gaussian03程序包中的“对称性匹配簇-组态相互作用”方法、在0.13—2.0nm的核间距范围内利用6-311 G(d,p)基组对7Li2(23Πu)分子的势能曲线进行了计算,同时使用最小二乘法将计算结果拟合成了解析势能函数.利用拟合出的解析势能函数并结合Rydberg-Klein-Rees方法,计算了该态的谐振频率,进而计算了该态的其他光谱常数,分别为Te=3.6701eV,De=1.0764eV,Re=0.3000nm,ωe=285.69cm-1,ωeχe=1.8351cm-1,αe=0.00942cm-1和Be=0.5340cm-1,其中光谱常数Te,De,Re和ωe的值与文献值相符很好.以得到的解析势能函数为基础,通过求解双原子分子核运动的径向Schr dinger方程,发现J=0时7Li2(23Πu)分子存在67个振动态,求出了相应于每一振动态的振动能级、振动经典转折点及转动惯量.  相似文献   
99.
This paper describes a method for measuring the three-dimensional (3D) refractive-index distribution in a single cell. The method can be used to observe the distribution of cell components without fluorescence staining. The two-dimensional optical path length distributions from multiple directions are obtained by non-contact rotation of the cell. These optical path lengths are converted into the line integrals of the refractive index, and the 3D refractive-index distribution is reconstructed by means of computed tomography. The refractive-index distribution in a breast cancer cell can be measured using a phase-shifting Mach—Zehnder interferometer in conjunction with proximal two-beam optical tweezers.  相似文献   
100.
Collision of swift ions with atoms was considered in this paper. The projectile and target atoms were modeled as assemblies of quantum oscillators and it was assumed that both, target and projectile could be excited or ionized, without charge exchange. The model presented here is an extension of the one given by Sigmund and Haagerup [Phys. Rev. A 34, 892 (1986)]. The number of electrons bound to the projectile, as a function of the projectile velocity, was used from Cabrera-Trujillo et al. [Phys. Rev. A 55, 2864 (1997)]. Contributions to energy loss from excitation of the projectile and targets were separately considered. It has been found that projectile excitation contributes up to 20% to the total energy loss in the lower energy region. Comparisons with other authors, including SRIM 2003, are also given and good agreement was found.  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