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991.
In the classical
Peierls--Nabarro (P-N) theory of dislocation,
there is a long-standing contradiction that the stable configuration
of dislocation has maximum energy rather than minimum energy. In
this paper, the dislocation energy is calculated rigorously in the
context of the full lattice theory. It is found that besides the
misfit energy considered in the classical P-N theory, there is an
extra elastic strain energy that is also associated with the
discreteness of lattice. The contradiction can be automatically
removed provided that the elastic strain energy associated with the
discreteness is taken into account. This elastic strain energy is
very important because its magnitude is larger than the misfit
energy, its sign is opposite to the misfit energy. Since the elastic
strain energy and misfit energy associated with discreteness cancel
each other, and the width of dislocation becomes wide in the lattice
theory, the Peierls energy, which measures the height of the
effective potential barrier, becomes much smaller than that given in
the classical P-N theory. The results calculated here agree with
experimental data. Furthermore, based on the results obtained, a
useful formula of the Peierls stress is proposed to fully include
the discreteness effects. 相似文献
992.
Simulating high Reynolds number flow in two-dimensional lid-driven cavity by multi-relaxation-time lattice Boltzmann method 总被引:3,自引:0,他引:3
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By coupling the non-equilibrium extrapolation scheme for boundary condition with the
multi-relaxation-time lattice Boltzmann method, this paper finds that the stability
of the multi-relaxation-time model can be improved greatly, especially on
simulating high Reynolds number (Re) flow. As a discovery, the super-stability
analysed by Lallemand and Luo is verified and the complex structure of the cavity
flow is also exhibited in our numerical simulation when Re is high enough. To the
best knowledge of the authors, the maximum of Re which has been investigated by
direct numerical simulation is only around 50,000 in the literature; however,
this paper can readily extend the maximum to 1000,000 with the above combination. 相似文献
993.
WANG Shi-En YANG Dao-Sheng 《理论物理通讯》2006,46(2):233-238
We obtain the multisolitary solutions of the extended Bose-Hubbard model which describes dipolar Bose- Einstein condensates in optical lattices under time-dependent magnetic fields, and indicate that the nonlinearity is due to both on-site short-range interactions and also (long-range) dipole-dipole interactions which can act between neighboring sites. The discrete breathers as nonlinear excitations are always oscillatory in time and can also be spatially localized, while the oscillatory frequencies are determined by an external field. We show that these excitations will be observable and discuss how the parameters can be tuned in future experiments. 相似文献
994.
格子Boltzmann方法中的曲边界处理 总被引:4,自引:2,他引:2
研究了格子Boltzmann方法中实现曲边界条件的3种格式,对它们的精度和稳定性进行了分析和比较.通过二维Poiseuille流和等边三角域上空腔流的模拟,讨论了这3种格式的数值精度和稳定性. 相似文献
995.
单组分多相系统驱替过程的格子Boltzmann模拟 总被引:1,自引:1,他引:0
结合格子Boltzmann方法中的Shan-Chen单组分多相模型,引入流体相间的内聚力和流体与
固体壁面间的黏附力,对二维孔隙网格中非浸润气相驱替完全浸润液相的过程进行模拟,流
体相间的交界面自然形成,整个驱替过程属于毛细指进. 随着毛细数的增加,黏性力的主导
作用增强,使得气相入侵的孔隙尺度减小,因此驱替形态随毛细数的不同有很大差别. 在微
重力的作用下,整个驱替过程受毛细力、重力和黏性力的共同作用,重力起到了稳定交界面
避免窜流的作用. 相似文献
996.
This paper studies the cascading failure on random networks and
scale-free networks by introducing the tolerance parameter of edge
based on the coupled map lattices methods. The whole work focuses on
investigating some indices including the number of failed edges,
dynamic edge tolerance capacity and the perturbation of edge. In
general, it assumes that the perturbation is attributed to the
normal distribution in adopted simulations. By investigating the
effectiveness of edge tolerance in scale-free and random networks,
it finds that the larger tolerance parameter λ can more
efficiently delay the cascading failure process for scale-free
networks than random networks. These results indicate that the
cascading failure process can be effectively controlled by
increasing the tolerance parameter λ. Moreover, the
simulations also show that, larger variance of perturbation can
easily trigger the cascading failures than the smaller one. This
study may be useful for evaluating efficiency of whole traffic
systems, and for alleviating cascading failure in such systems. 相似文献
997.
We use the Monte Carlo method to study an antiferromagnetical Ising spin
system on a centred honeycomb lattice, which is composed of two kinds
of 1/2 spin particles A and B. There exist two different bond
energies JA-A and JA-B in this lattice. Our
study is focused on how the ratio of JA-B to JA-A influences the critical behaviour of this system by analysing the physical quantities, such as the energy, the order parameter,
the specific heat, susceptibility, {etc} each as a function of temperature for a given ratio of JA-B to JA-A. Using these results together with the finite-size scaling method,
we obtain a phase diagram for the ratio JA-B / JA-A. This work is helpful for studying the phase transition
problem of crystals composed of compounds. 相似文献
998.
Lattice Boltzmann simulation of fluid flows in two-dimensional channel with complex geometries
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Boundary conditions (BCs) play an essential role in lattice
Boltzmann (LB) simulations. This paper investigates several most
commonly applied BCs by evaluating the relative L2-norm errors
of the LB simulations for two-dimensional (2-D) Poiseuille flow. It
is found that the relative L2-norm error resulting from FHML's
BC is smaller than that from other BCs as a whole. Then, based on
the FHML's BC, it formulates an LB model for simulating fluid flows
in 2-D channel with complex geometries. Afterwards, the flows
between two inclined plates, in a pulmonary blood vessel and in a
blood vessel with local expansion region, are simulated. The
numerical results are in good agreement with the analytical
predictions and clearly show that the model is effective. It is
expected that the model can be extended to simulate some real
biologic flows, such as blood flows in arteries, vessels with
stenosises, aneurysms and bifurcations, etc. 相似文献
999.
In this paper we study the existence and stability of two-dimensional discrete gap
breathers in a two-dimensional diatomic face-centered square lattice
consisting of alternating light and heavy atoms, with on-site
potential and coupling potential. This study is focused on
two-dimensional breathers with their frequency in the gap that
separates the acoustic and optical bands of the phonon spectrum. We
demonstrate the possibility of the existence of two-dimensional gap
breathers by using a numerical method. Six types of two-dimensional
gap breathers are obtained, i.e., symmetric, mirror-symmetric and
asymmetric, whether the center of the breather is on a light or a
heavy atom. The difference between one-dimensional discrete gap
breathers and two-dimensional discrete gap breathers is also
discussed. We use Aubry's theory to analyze the stability of
discrete gap breathers in the two-dimensional diatomic face-centered
square lattice. 相似文献
1000.
Effects of periodic optical lattice potential on dark solitons in a Bose Einstein condensate
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This paper investigates the dynamics of dark solitons in a
Bose--Einstein condensate with a magnetic trap and an optical
lattice (OL) trap, and analyses the effects of the periodic OL
potential on the dynamics by applying the variational approach based
on the renormalized integrals of motion. The results show that the
dark soliton becomes only a standing-wave and free propagation
of the dark soliton is not possible when the periodic length of the
OL potential is approximately equal to the effective width of the
dark soliton. When the periodic length is very small or very large,
the effects of the OL potential on the dark soliton will be sharply
reduced. Finally, the numerical results confirm these theoretical
findings. 相似文献