全文获取类型
收费全文 | 20864篇 |
免费 | 4307篇 |
国内免费 | 1554篇 |
专业分类
化学 | 4355篇 |
晶体学 | 671篇 |
力学 | 1224篇 |
综合类 | 231篇 |
数学 | 5524篇 |
物理学 | 14720篇 |
出版年
2024年 | 45篇 |
2023年 | 180篇 |
2022年 | 347篇 |
2021年 | 413篇 |
2020年 | 512篇 |
2019年 | 465篇 |
2018年 | 489篇 |
2017年 | 685篇 |
2016年 | 786篇 |
2015年 | 682篇 |
2014年 | 1163篇 |
2013年 | 1865篇 |
2012年 | 1306篇 |
2011年 | 1388篇 |
2010年 | 1067篇 |
2009年 | 1259篇 |
2008年 | 1496篇 |
2007年 | 1393篇 |
2006年 | 1293篇 |
2005年 | 1195篇 |
2004年 | 1026篇 |
2003年 | 942篇 |
2002年 | 920篇 |
2001年 | 837篇 |
2000年 | 787篇 |
1999年 | 681篇 |
1998年 | 588篇 |
1997年 | 545篇 |
1996年 | 417篇 |
1995年 | 375篇 |
1994年 | 309篇 |
1993年 | 229篇 |
1992年 | 192篇 |
1991年 | 152篇 |
1990年 | 101篇 |
1989年 | 96篇 |
1988年 | 86篇 |
1987年 | 66篇 |
1986年 | 45篇 |
1985年 | 59篇 |
1984年 | 53篇 |
1983年 | 26篇 |
1982年 | 37篇 |
1981年 | 23篇 |
1980年 | 20篇 |
1979年 | 24篇 |
1978年 | 16篇 |
1977年 | 8篇 |
1976年 | 9篇 |
1973年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
41.
GU Bai-Ping REN Zhong-Zhou 《理论物理通讯》2005,44(2):337-342
The Dirac optical potential for p-^14 Be elastic scattering is evaluated by the relativistic impulse approximation. Each of the real part and the imaginary part of the potential shows a pronounced “long tail” for the proton elastic scattering from halo nucleus ^14Be compared with the potentials for proton scattering from its adjacent nuclei ^12C and ^16O, which do not have halo structures.This kind of “long tail” phenomenon suggests another signature for halo nuclei. 相似文献
42.
差分吸收光谱法测量大气痕量气体浓度误差分析及改善方法 总被引:8,自引:2,他引:6
差分吸收光谱技术(DOAS)中采用线性最小二乘拟合方法,用痕量气体标准差分吸收截面对测量得到的差分吸收光谱进行拟合,得出大气中痕量气体的浓度.计算结果的准确性不仅取决于光谱的测量精度,而且受标准差分吸收截面以及仪器函数和温度等诸多因素的影响.详细地分析了计算误差的产生原因,提出了用高浓度样品池得到标准吸收截面的方法,针对光谱固有结构,以及温度对标准吸收截面的影响,改进了浓度反演算法.大量的实验表明,综合运用上述方法,即便对低浓度的样气,相对测量误差也能降低到10%以下. 相似文献
43.
Within the framework of a piecewise homogeneous body model, with the use of three-dimensional geometrically nonlinear exact equations of elasticity theory, a method for determining the stress—strain state in unidirectional fibrous composites with locally curved fibers is developed for the case where the interaction between the fibers is neglected. All the investigations are carried out for an infinite elastic body containing a single locally curved fiber. Numerical results illustrating the effect of geometrical nonlinearity on the distribution of the self-balanced normal and shear stresses acting on the interface and arising as a result of local curving of the fiber are presented.__________Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 41, No. 4, pp. 433–448, July–August, 2005. 相似文献
44.
We discuss the problem of transmitting polarized pulses along optical fibers with variable dispersion. The dissipation and mean dispersion are assumed to be zero, which allows using the model of the vector nonlinear Schrödinger equation. We consider an optical fiber consisting of arms of equal length, which is assumed to be large. We propose an asymptotic recursive procedure for calculating the amplitude and the phase of an optical pulse propagating along the optical cable with variable dispersion. 相似文献
45.
We establish a relation between stable distributions in probability theory and the fractional integral. Moreover, it turns out that the parameter of the stable distribution coincides with the exponent of the fractional integral. It follows from an analysis of the obtained results that equations with the fractional time derivative describe the evolution of some physical system whose time degree of freedom becomes stochastic, i.e., presents a sum of random time intervals subject to a stable probability distribution. We discuss relations between the fractal Cantor set (Cantor strips) and the fractional integral. We show that the possibility to use this relation as an approximation of the fractional integral is rather limited. 相似文献
46.
47.
B.I. Sturman A.S. Gorkunova K.H. Ringhofer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(2):291-297
We investigate analytically and numerically the influence of the type of the photorefractive nonlinear response on the periodic
states (attractors) which occur during feedback controlled 2W-coupling and correspond to almost 100% diffraction efficiency
of the dynamic index grating. In addition to the case of the local response typical, for example, for LiNbO3 crystals we consider the cases of nonlocal (diffusive) response (BaTiO3, SBN) and resonant response (DC-biased BSO, BTO, and BGO crystals). It is shown that the conditions for the transition to
the periodic states and their apparent characteristics are strongly different for the two limiting cases above.
Received 16 July 2002 / Received in final form 29 October 2002 Published online 4 March 2003 相似文献
48.
We study nonlinear dynamics of optical pulse propagation in the spectral region inside the polariton gap. It is shown that the Kerr nonlinearity can lead to formation of solitary waves in this region of frequencies. 相似文献
49.
50.
李永祥 《数学物理学报(A辑)》2003,23(2):245-252
该文讨论四阶常微分方程边值问题u^(4)(t)=f(t,u,u″), t∈[0,1],u(0)=u(1)=u″(0)=u″(1)=0解的存在性, 其中f(t,u,v):[0,1]×R×R→R为Carathéodory函数. 在不限制f关于u,v的增长阶, 不假定f关于u,v的单调性的一般情形下, 用上下解方法获得了解的存在性结果,并讨论了单调迭代求解的有效性. 相似文献