全文获取类型
收费全文 | 648篇 |
免费 | 82篇 |
国内免费 | 58篇 |
专业分类
化学 | 42篇 |
力学 | 1篇 |
综合类 | 7篇 |
数学 | 343篇 |
物理学 | 395篇 |
出版年
2024年 | 2篇 |
2023年 | 11篇 |
2022年 | 10篇 |
2021年 | 16篇 |
2020年 | 19篇 |
2019年 | 21篇 |
2018年 | 19篇 |
2017年 | 13篇 |
2016年 | 20篇 |
2015年 | 19篇 |
2014年 | 26篇 |
2013年 | 52篇 |
2012年 | 41篇 |
2011年 | 40篇 |
2010年 | 46篇 |
2009年 | 42篇 |
2008年 | 52篇 |
2007年 | 47篇 |
2006年 | 41篇 |
2005年 | 40篇 |
2004年 | 30篇 |
2003年 | 27篇 |
2002年 | 24篇 |
2001年 | 13篇 |
2000年 | 14篇 |
1999年 | 20篇 |
1998年 | 15篇 |
1997年 | 11篇 |
1996年 | 8篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 7篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1969年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有788条查询结果,搜索用时 15 毫秒
101.
Walter Schempp 《Acta Appl Math》1997,48(2):185-234
Due to its unequalled advantages, the magnetic resonance imaging (MRI) modality has truly revolutionized the diagnosis and evaluation of pathology. Because many morphological anatomic details that may not be visualized by other high tech imaging methods can now be readily shown by diagnostic MRI, it has already become the standard modality by which all other clinical imaging techniques are measured. The unique quantum physical basis of the MRI modality combined with the imaging capabilities of current computer technology has made this imaging modality a target of interdisciplinary interest for clinicians, physicists, biologists, engineers, and mathematicians. Due to the fact that MRI scanners perform corticomorphic processing, this modality is by far more complex than all the other high tech clinical imaging techniques. The purpose of this paper is to outline a phase coherent wavelet approach to Fourier transform MRI. It is based on distributional harmonic analysis on the Heisenberg nilpotent Lie group G and the associated symplectically invariant symbol calculus of pseudodifferential operators. The contour and contrast resolution of MRI scans which is controlled by symplectic filter bank processing gives the noninvasive MRI modality superiority over X-ray computed tomography (CT) in soft tissue differentiation. 相似文献
102.
Heide Narnhofer 《Journal of statistical physics》1982,29(4):761-771
Under intuitively reasonable assumptions it is shown that in two dimensions different phases cannot exist locally. In three dimensions we discuss the possibility of local coexistence of districts with different magnetization for the Heisenberg ferromagnet and show that an interaction that breaks rotational invariance is necessary for this phenomenon. 相似文献
103.
By means of the Monte Carlo sampling technique the equilibrium thermodynamics of fluids and magnets can be calculated numerically. We show that the questions of convergence and accuracy of this method can be understood in terms of the dynamics of the appropriate stochastic model. Also, we discuss to what extent various choices of transition probabilities lead to different dynamic properties of the system. As examples of applications, we consider Ising and Heisenberg spin systems. The numerical results about the dynamic correlation functions are compared to simple approximations taken from the theory of the kinetic Ising model. 相似文献
104.
105.
通过分析系统的杂质位与其余部分间的纠缠N1-A以及单个正常位与其余部分间的纠缠NL-A研究了匀强磁场作用下含杂质Heisenberg XX链的纠缠特性.研究表明三量子位时纠缠存在的临界温度依赖于杂质参数J1和匀强磁场B.研究发现,当量子位L为奇数时,纠缠N1-A随量子位的增加而增大,而L为偶数时则相反,并且量子位L为偶数时的纠缠大于量子位L为奇数时的纠缠;对NL-A,量子位L为奇数时,纠缠随杂质参数J1的变化与L=3类似,而L为偶数时纠缠随杂质参数|J1|的增加而增加. 相似文献
106.
通过分析系统的杂质位与其余部分间的纠缠N1-A以及单个正常位与其余部分间的纠缠NL-A研究了匀强磁场作用下含杂质Heisenberg XX链的纠缠特性.研究表明三量子位时纠缠存在的临界温度依赖于杂质参数J1和匀强磁场B.研究发现,当量子位L为奇数时,纠缠N1-A随量子位的增加而增大,而L为偶数时则相反,并且量子位L为偶数时的纠缠大于量子位L为奇数时的纠缠;对NL-A, 量子位L为奇数时,纠缠随杂质参数J1的变化与L=3类似,而L为偶数时纠缠随杂质参数|J1|的增加而增加. 相似文献
107.
Stephen G. Low 《Foundations of Physics》2006,36(7):1036-1069
The frame associated with a classical point particle is generally noninertial. The point particle may have a nonzero velocity and force with respect to an absolute inertial rest frame. In time–position–energy–momentum-space {t, q, p, e}, the group of transformations between these frames leaves invariant the symplectic metric and the classical line element ds2 = d t2. Special relativity transforms between inertial frames for which the rate of change of momentum is negligible and eliminates the absolute rest frame by making velocities relative but still requires the absolute inertial frame. The Lorentz group leaves invariant the symplectic metric and the line elements and . General relativity for particles under only the influence of gravity avoids the issue of noninertial frames as all particles follow geodesics and hence have locally inertial frames. For other forces, the question of the absolute inertial frame remains.) Born conjectured that the line element should be generalized to the pseudo-orthogonal metric . The group leaving this metrics and the symplectic metric invariant is the pseudo-unitary group of transformations between noninertial frames. We show that these transformations also eliminate the need for an absolute inertial frame by making forces relative and bounded by b and so embodies a relativity that is shape reciprocal in the sense of Born. The inhomogeneous version of this group is naturally the semidirect product of the pseudo-unitary group with the nonabelian Heisenberg group. This is the quaplectic group. 相似文献
108.
The effects of spin-spin interaction on thermed entanglement of a two-qubit Heisenberg XYZ model with different inhomogeneous magnetic fields are investigated. It is shown that the entanglement is dependent on the spin-spin interaction and the inhomogeneous magnetic fields. The larger the Ji (i-axis spin-spin interaction), the higher critical value the Bi (i-axis uniform magnetic field) has. Moreover, in the weak-field regime, the larger Ji corresponds to more entanglement, while in the strong-field regime, different Ji correspond to the same entanglement. In addition, it is found that with the increase of Ji, the concurrence can approach the maximum value more rapidly for the smaller Bi, and can reach a larger value for the smaller bi (i-axis nonuniform magnetic field). So we can get more entanglement by increasing the spin-spin interaction Ji, or by decreasing the uniform magnetic field Bi and the nonuniform magnetic field hi. 相似文献
109.
The magnetic behaviors of ferromagnetic single-walled nanotubes are systematically investigated by use of the many-body Green's function method of quantum statistical theory. The spontaneous magnetization, absolute value of ferromagnetic energy, area of hysteresis loop and coercivity increase with diameter of the tubes and spin quantum number, and decrease with temperature. Curie temperature increases with diameter and spin quantum number. As the diameter of the tube tends to infinity, all the numerical results approach to those of a two-dimensional monolayer. The dependences of initial susceptibility on temperature and diameter below and above Curie point are contrary. The calculated results are compared with experimental results where possible, and are qualitatively in agreement with the latter. The Curie temperature is determined by the tube diameter and independent of rolling helicities. 相似文献
110.
I.V. Vernyhora R. Patte H. Zapolsky 《Journal of magnetism and magnetic materials》2010,322(17):2465-51
The NixFe1−x alloys close to the stoichiometric Ni3Fe composition are modeled by means of Monte Carlo simulations. To describe the atomic and magnetic configurations, the Ising and Heisenberg models with nearest-neighbor interactions have been used, respectively. The pairwise interactions have been fitted to the experimentally measured Curie and Kurnakov temperatures, the Fe-Fe magnetic exchange interaction has been considered antiferromagnetic. The mutual influence of the magnetic and chemical ordering is evidenced and a good agreement with the phase diagram is obtained. Our numerical results show that the magnetic order is able to increase the Kurnakov temperature and, reciprocally, the chemical order is responsible for a rise in the Curie temperature. Also, the influence of the applied magnetic field on the chemical order is investigated and an increase of the Kurnakov temperature with the external field is observed. 相似文献