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981.
Simulation of natural convection under high magnetic field by means of the thermal lattice Boltzmann method 下载免费PDF全文
The thermal lattice Boltzmann method (TLBM), which was proposed by
J. G. M. Eggels and J. A. Somers previously, has been improved in
this paper. The improved method has introduced a new equilibrium
solution for the temperature distribution function on the assumption
that flow is incompressible, and it can correct the effect of
compressibility on the macroscopic temperature computed. Compared to
the previous method, where the half-way bounce back boundary
condition was used for non-slip velocity and temperature, a
non-equilibrium extrapolation scheme has been adopted for both
velocity and temperature boundary conditions in this paper. Its
second-order accuracy coincides with the ensemble accuracy of
lattice Boltzmann method. In order to validate the improved thermal
scheme, the natural convection of air in a square cavity is
simulated by using this method. The results obtained in the
simulation agree very well with the data of other numerical methods
and benchmark data. It is indicated that the improved TLBM is also
successful for the simulations of non-isothermal flows. Moreover,
this thermal scheme can be applied to simulate the natural
convection in a non-uniform high magnetic field. The simulation has
been completed in a square cavity filled with the aqueous solutions
of KCl (11wt%), which is considered as a diamagnetic fluid with
electrically low-conducting, with Grashof number Gr=4.64×
10^4 and Prandtl number Pr=7.0. And three cases, with different
cavity locations in the magnetic field, have been studied. In the
presence of a high magnetic field, the natural convection is quenched
by the body forces exerted on the electrically low-conducting
fluids, such as the magnetization force and the Lorentz force. From the
results obtained, it can be seen that the quenching efficiencies
decrease with the variation of location from left, symmetrical line,
to the right. These phenomena originate from the different
distributions of the magnetic field strengths in the zones of the
symmetrical central line of the magnetic fields. The results are
also compared with those without a magnetic field. Finally, we can
conclude that the improved TLBM will enable effective simulation of the natural
convection under a high magnetic field. 相似文献
982.
Phase-field simulation of the effect of interaction among ordered domains on interdiffusion in Ni--Al--Cr alloys 下载免费PDF全文
The effect of interaction among γ ' ordered domains on the
interdiffusion process in γ +γ ' /γ and γ
+γ ' /γ +γ ' diffusion couples is investigated by
using the phase-field method, in which bulk free energy and mobility
are linked with thermodynamic and kinetic databases. Simulated
results show that the interaction among γ ' ordered domains
has great influence on the microstructure, the interdiffusion
velocity and the volume fraction of γ ' phase on both sides
of the diffusion couples. 相似文献
983.
多体动力学的几何积分方法研究进展 总被引:1,自引:0,他引:1
动力系统的几何积分研究是近20年来工程计算领域非常活跃的方向.多体动力学方程(微分方程, 微分代数方程)是一类典型的动力系统,将其从Lagrange体系向Hamilton系统过渡,目的在于从欧氏几何过渡到辛几何形态, 将对偶变量引入到力学研究中,然后利用辛几何的数学框架对多体系统动力学方程进行数值计算,可以预知多体动力学系统的一些定性信息,并在数值离散时能保持这些定性性质特征,尤其在表示关键的物理意义时需要强调保持这些几何性质.简要介绍多体系统(无约束多刚体系统、完整约束多刚体系统和柔性多体系统)的Hamilton正则方程的建立和几何积分方法的构造,着重介绍了在多体动力学计算中非常有应用前景的高阶辛算法(合成辛算法、分裂合成辛算法和辛精细积分法)、多辛算法,以及广义Hamilton 系统与Lie 群积分方法等计算几何力学方法, 并对Lie群积分的投影方法、流形局部坐标法等方法进行了阐述. 相似文献
984.
一种新型浮升一体化排式飞翼的设计与研究 总被引:2,自引:0,他引:2
设计既有较大的内部容积、又有高气动效率的新型浮升一体化气动布局对此类低速飞行器的发展具有重要的科学研究价值和工程应用前景. 以NACA0030翼型为基础,构造了具有较高体积率(体积/表面积)的排式飞翼气动布局. 对不同排列形式的排式飞翼进行了详细的计算和评估分析,并提出了具有更好操纵性和稳定性的排式后掠飞翼气动布局. 数值模拟结果表明: 通过排式飞翼中后翼对前翼下方气流的阻滞作用,排式直飞翼和排式后掠飞翼的升阻比分别增大40%和 20%, 整个飞行器的气动效率显著提高; 同时, 浮升一体化排式飞翼的弦向尺寸较小,可有效降低材料的表面张力,这为高空飞行器表面柔性材料提供了较宽的选择范围. 相似文献
985.
986.
987.
在考虑面板面内拉伸刚度等非线性因素的基础上,将夹层梁上面板视为弹塑性地基上的梁,由其平衡方程推导准静态压入接触定律. 进而研究了底面固定于刚性平面的夹层梁的低速冲击响应,验证了所推导的准静态压入接触定律在低速冲击下依然足够精确. 最后,用能量守恒模型,离散模型和连续模型分析了两端简支夹层梁的低速冲击响应以及接触持续时间.同时讨论了冲头与夹层梁质量比和初速度对结构响应以及分析模型适用性的影响. 理论分析结果与数值模拟结果比较表明:推导的接触定律是准确有效的. 给定初速度,质量比很小时,只有连续模型有效,而当质量比较大时3种模型均有效;给定质量,初速度较大时只有连续模型比较有效. 连续模型预测的接触持续时间与初速度无关. 相似文献
988.
建立了非微扰外推模式下的几种G3(QCI)方法:G3(QCI/fu1)、G3(QCI/fu2)、G3(QCI/ful)//B3PW91和G3(QCI/fu2)//B3PW91.其中,电子能量用QCISD(T,FC)/G3large直接计算,芯电子相关能分别在MP2/6-31G(d)和MP2/6-31G(d,p)级别上计算,对125个G2-1 test set 的计算结果表明,总体精度与G3和G3 //B3LYP相当;平均绝对偏差分别为4.370、4.389、4.061和4.022kJ mol-1,相应G3和G3//B3LYP分别为4.27和4.05kJ mol-1.文章提出的方法排除了G3中外推办法的不确定因素,且更适用于非平衡几何构型体系能量的定量计算。 相似文献
989.
New glasses in the PbBr2–PbCl2–PbF2–PbO–P2O5 system have been prepared and characterized. The glass-forming regions have been explored and the stability of the glasses against crystallization studied. Results show that the PbBr2–PbCl2–P2O5 ternary system has a broad glass-forming region which extends to 30 mol% P2O5. Most of the glasses in this system show strong stability against crystallization and some have glass transition temperatures as low as 146°C. When 5% PbO or 5% PbF2 is introduced into the PbBr2–PbCl2–P2O5 system, the glass-forming region becomes smaller and the glass transition temperatures increase. However, the introduction of 2.5% PbF2 and 2.5% PbO into the ternary system increases the glass transition temperature and broadens the glass-forming region. The introduction of PbF2 alone improves the glass-forming ability of the system while the introduction of PbO alone lowers the glass-forming ability. 相似文献
990.
《European Journal of Mechanics - B/Fluids》2000,19(2):213-227
Two- and three-dimensional convection flows in a horizontal layer of a low Prandtl number fluid heated from below and rotating about a vertical axis are studied numerically with a Galerkin method. Solutions for subcritical steady finite amplitude convection and convection in the form of standing oscillations are obtained. Parameter regimes that appear to be attainable in laboratory experiments have been emphasized. The stability of subcritical two-dimensional steady convection has been investigated and three-dimensional chaotic states of convection have been found. 相似文献