全文获取类型
收费全文 | 28017篇 |
免费 | 2540篇 |
国内免费 | 1854篇 |
专业分类
化学 | 4846篇 |
晶体学 | 136篇 |
力学 | 3124篇 |
综合类 | 230篇 |
数学 | 17000篇 |
物理学 | 7075篇 |
出版年
2024年 | 60篇 |
2023年 | 342篇 |
2022年 | 328篇 |
2021年 | 443篇 |
2020年 | 733篇 |
2019年 | 758篇 |
2018年 | 694篇 |
2017年 | 802篇 |
2016年 | 923篇 |
2015年 | 811篇 |
2014年 | 1279篇 |
2013年 | 2840篇 |
2012年 | 1249篇 |
2011年 | 1766篇 |
2010年 | 1402篇 |
2009年 | 1791篇 |
2008年 | 1752篇 |
2007年 | 1760篇 |
2006年 | 1600篇 |
2005年 | 1279篇 |
2004年 | 1115篇 |
2003年 | 1056篇 |
2002年 | 1025篇 |
2001年 | 830篇 |
2000年 | 832篇 |
1999年 | 727篇 |
1998年 | 623篇 |
1997年 | 594篇 |
1996年 | 455篇 |
1995年 | 307篇 |
1994年 | 298篇 |
1993年 | 212篇 |
1992年 | 167篇 |
1991年 | 159篇 |
1990年 | 132篇 |
1989年 | 133篇 |
1988年 | 122篇 |
1987年 | 101篇 |
1986年 | 67篇 |
1985年 | 105篇 |
1984年 | 135篇 |
1983年 | 72篇 |
1982年 | 89篇 |
1981年 | 84篇 |
1980年 | 82篇 |
1979年 | 78篇 |
1978年 | 66篇 |
1977年 | 38篇 |
1976年 | 33篇 |
1973年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
CV Tomy D Pal SS Banerjee S Ramakrishnan AK Grover S Bhattacharya MJ Higgins G Balakrishnan McK Paul 《Pramana》2002,58(5-6):925-935
The weakly pinned single crystals of the hexagonal 2H-NbSe2 compound have emerged as prototypes for determining and characterizing the phase boundaries of the possible order-disorder
transformations in the vortex matter. We present here a status report based on the ac and dc magnetization measurements of
the peak effect phenomenon in three crystals of 2H-NbSe2, in which the critical current densities vary over two orders of magnitude. We sketch the generic vortex phase diagram of
a weakly pinned superconductor, which also utilizes theoretical proposals. We also establish the connection between the metastability
effects and pinning. 相似文献
982.
对流占优扩散方程的一种特征差分算法 总被引:3,自引:0,他引:3
A new kind of characteristic-difference scheme for convection-diffusion equations is constructed by characteristic method and bilinear interpolation method. The convergence of the scheme is proved. The advantages of this scheme are to obtain the solutions of the convection diffusion equations with variable coefficient expediently and to reduce the numerical oscillations of the convectiondominanted diffusion equations effectively. 相似文献
983.
一个各向异性插值定理及其在二阶问题混合元中的应用 总被引:3,自引:1,他引:3
At first this paper presents an interpolate theorem with anisotropic property, which can be applied to estimate the interpolate error based on different directions. Then a discrete mixed form for the second order elliptic problem is constructed.The gradient vector is approximated by non-full piesewise double quadratic polynomials, the function u by piecewise constants only. The advantage is that this scheme is still convergent without regularity assumption of subdivision to domain Ω. 相似文献
984.
Richard L. Liboff 《International Journal of Theoretical Physics》2002,41(10):1957-1970
Three problems related to the spherical quantum billiard in
are considered. In the first, a compact form of the hyperspherical equations leads to their complex contracted representation. Employing these contracted equations, a proof is given of Courant's nodal-symmetry intersection theorem for diagonal eigenstates of spherical-like quantum billiards in
. The second topic addresses the first-excited-state theorem for the spherical quantum billiard in
. Wavefunctions for this system are given by the product form, (
)Z
q+()Y
(n)
, where is dimensionless displacement,
is angular-momentum number, qis an integer function of dimension, Z() is either a spherical Bessel function (nodd) or a Bessel function of the first kind (neven) and represents (n– 1) independent angular components. Generalized spherical harmonics are written
. It is found that the first excited state (i.e., the second eigenstate of the Laplacian) for the spherical quantum billiard in
is n-fold degenerate and a first excited state for this quantum billiard exists which contains a nodal bisecting hypersurface of mirror symmetry. These findings establish the first-excited-state theorem for the spherical quantum billiard in
. In a third study, an expression is derived for the dimension of the th irreducible representation (irrep) of the rotation group O(n) in
by enumerating independent degenerate product eigenstates of the Laplacian. 相似文献
985.
This paper analyzes the high bit-rate optical pulse trasmission in single mode optical fiber with chromatic dispersion, polarization mode dispersion (small random birefringence) and nonlinearity. Numerical method employed can precisely describe their interactive effect on transmission performance. Different dispersion maps and the related performance are analysed. Various simulation results and discussion are given. The results show that chromatic dispersion compensation should be carefully designed. Appropriate dispersion management can also alleviate the effect of polarization mode dispersion. 相似文献
986.
We consider the problem of determining the dielectric permittivity for a nonconducting and nonmagnetic medium. As information we take the traces of the tangential components of the electromagnetic field on the lateral surface of a cylindrical domain. These traces correspond to a solution to some direct problem for the Maxwell system. The impulse source of the current flux lies outside the domain in which the coefficient is sought. The main result of the article is a stability estimate for a solution to the inverse problem in question. 相似文献
987.
The rotating flow in the presence of a magnetic field is a problem belonging to hydromagnetics and deserves to be more widely studied than it has been to date. In the non‐linear regime the literature is scarce. We develop the governing equations for the unsteady hydromagnetic rotating flow of a fourth‐order fluid past a porous plate. The steady flow is governed by a boundary value problem in which the order of differential equations is more than the number of available boundary conditions. It is shown that by augmenting the boundary conditions based on asymptotic structures at infinity it is possible to obtain numerical solutions of the nonlinear hydromagnetic equations. Effects of uniform suction or blowing past the porous plate, exerted magnetic field and rotation on the flow phenomena, especially on the boundary layer structure near the plate, are numerically analysed and discussed. The flow behaviours of the Newtonian fluid and second‐, third‐ and fourth‐order non‐Newtonian fluids are compared for the special flow problem, respectively. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
988.
Toshihiro Kobayashi 《Mathematical Methods in the Applied Sciences》2004,27(18):2171-2184
In this paper low‐gain adaptive stabilization of undamped semilinear second‐order hyperbolic systems is considered in the case where the input and output operators are collocated. The linearized systems have an infinite number of poles and zeros on the imaginary axis. The adaptive stabilizer is constructed by a low‐gain adaptive velocity feedback. The closed‐loop system is governed by a non‐linear evolution equation. First, the well‐posedness of the closed‐loop system is shown. Next, an energy‐like function and a multiplier function are introduced and the exponential stability of the closed‐loop system is analysed. Some examples are given to illustrate the theory. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
989.
该文证明了平面上满足一定条件的零级代数体函数至少存在一条强Borel方向,并且它还是通常的关于型函数的Borel方向. 相似文献
990.
助于符号计算软件Maple,通过一种构造非线性偏微分方程更一般形式行波解的直接方 法,即改进的广义射影Ricccati方程方法,求解(2 1)维色散长波方程,得到该方程的新的 更一般形式的行波解,包括扭状孤波解,钟状解,孤子解和周期解.并对部分新形式孤波解画 图示意. 相似文献