全文获取类型
收费全文 | 10071篇 |
免费 | 682篇 |
国内免费 | 854篇 |
专业分类
化学 | 2760篇 |
晶体学 | 51篇 |
力学 | 903篇 |
综合类 | 83篇 |
数学 | 3080篇 |
物理学 | 4730篇 |
出版年
2024年 | 9篇 |
2023年 | 115篇 |
2022年 | 110篇 |
2021年 | 134篇 |
2020年 | 216篇 |
2019年 | 173篇 |
2018年 | 192篇 |
2017年 | 292篇 |
2016年 | 341篇 |
2015年 | 287篇 |
2014年 | 518篇 |
2013年 | 897篇 |
2012年 | 530篇 |
2011年 | 734篇 |
2010年 | 537篇 |
2009年 | 651篇 |
2008年 | 662篇 |
2007年 | 684篇 |
2006年 | 587篇 |
2005年 | 469篇 |
2004年 | 429篇 |
2003年 | 402篇 |
2002年 | 364篇 |
2001年 | 331篇 |
2000年 | 313篇 |
1999年 | 257篇 |
1998年 | 234篇 |
1997年 | 173篇 |
1996年 | 158篇 |
1995年 | 161篇 |
1994年 | 90篇 |
1993年 | 89篇 |
1992年 | 92篇 |
1991年 | 63篇 |
1990年 | 42篇 |
1989年 | 39篇 |
1988年 | 36篇 |
1987年 | 32篇 |
1986年 | 22篇 |
1985年 | 29篇 |
1984年 | 21篇 |
1983年 | 11篇 |
1982年 | 11篇 |
1981年 | 8篇 |
1980年 | 13篇 |
1979年 | 14篇 |
1978年 | 6篇 |
1976年 | 7篇 |
1973年 | 7篇 |
1971年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
921.
二维Fredholm积分方程Nystrom方法的渐近展开及其外推 总被引:1,自引:0,他引:1
本文讨论了求解二维第二类Fredholm积分方程的Nystrom方法,得到了数值解的逐项渐近展开,从而可进行Richardson外推,提高数值解的精度。 相似文献
922.
圆柱面绕任意轴回转形成的包络面分析 总被引:1,自引:1,他引:0
在分析及计算椭圆上距离任意已知点最远或最近的点基础上,分析了最远点及最近点在圆柱面绕任意轴回转形成包络面过程中的作用,从而由最远点及最近点的计算公式导出了多种形式的包络面方程,并由此找出了包络面受各种因素影响的规律. 相似文献
923.
924.
Highly oriented (100) thin films of LaVO3 and La1−xSrxVO3 have been fabricated by pulsed laser deposition in a reducing atmosphere. The films show a transition from insulating to metallic behaviour in the composition region of x, 0.175<x<0.200. In the single crystals of the antiferromagnetic insulating phase, a first-order structural phase transition is observed few degrees below the magnetic transition, which manifests itself as a kink in the temperature dependence of resistivity. In the highly oriented thin films of LaVO3 and La1−xSrxVO3 fabricated on lattice matched substrates in this study, the structural phase transformation in the insulating phase has been suppressed. The electrical conduction is found to take place via hopping through localized states at low temperatures. The metallic compositions show a non-linear (T1.5) behaviour in the temperature dependence of resistivity. V (2p) core level spectra of these films show a gradual change in the relative intensities of V3+ and V4+ ions as the value of x increases. 相似文献
925.
926.
从理论和实验上对二极管激光阵列在Talbot外腔中的锁相进行了研究。在同相模和异相模近场分布的基础上,利用1维情况下的菲涅耳衍射公式计算了其远场分布。根据同相模和异相模在Talbot腔中的分布特性,采用1/2 Talbot腔并将外腔镜倾斜一个角度a的方法既能选择同相模,又能使模式的功率损耗最小。二极管激光阵列芯片采用CD金刚石材料,“三明治”结构对其进行封装,明显地减小了阵列的“smile”效应。在实验中实现了二极管激光阵列同相模的锁相输出,远场单瓣模的半高全宽为0.11 mm。 相似文献
927.
S BugaV Blank Å FranssonN Serebryanaya B Sundqvist 《Journal of Physics and Chemistry of Solids》2002,63(2):331-343
C60 and C70 fullerenes polymerized under pressures between 9.5 and 13 GPa and temperatures between 670 and 1850 K were investigated by differential scanning calorimetry (DSC) in the range 240-640 K. Endothermal heat effects were observed with a peak maximum just below 540 K, a temperature characteristic for breakdown of (2+2) intermolecular links in dimers, 1D and 2D polymers. Exothermal effects, starting from 380 K, were observed for the first time in polymeric fullerenes. These effects are attributed to relaxation processes and to breakdown of other types of intermolecular bonds such as common four-sided rings and (3+3) interlinks. 相似文献
928.
This research study deals with the numerical solutions of linear and nonlinear time-fractional subdiffusion equations of distributed order. The main aim of our approach is based on the hybrid of block-pulse functions and shifted Legendre polynomials. We produce a novel and exact operational vector for the fractional Riemann–Liouville integral and use it via the Gauss–Legendre quadrature formula and collocation method. Consequently, we reduce the proposed equations to systems of equations. The convergence and error bounds for the new method are investigated. Six problems are tested to confirm the accuracy of the proposed approach. Comparisons between the obtained numerical results and other existing methods are provided. Numerical experiments illustrate the reliability, applicability, and efficiency of the proposed method. 相似文献
929.
A low order nonconforming mixed finite element method (FEM) is established for the fully coupled non-stationary incompressible magnetohydrodynamics (MHD) problem in a bounded domain in 3D. The lowest order finite elements on tetrahedra or hexahedra are chosen to approximate the pressure, the velocity field and the magnetic field, in which the hydrodynamic unknowns are approximated by inf-sup stable finite element pairs and the magnetic field by $H^1(\Omega)$-conforming finite elements, respectively. The existence and uniqueness of the approximate solutions are shown. Optimal order error estimates of $L^2(H^1)$-norm for the velocity field, $L^2(L^2)$-norm for the pressure and the broken $L^2(H^1)$-norm for the magnetic field are derived. 相似文献
930.
Jiajie Li Shengfeng Zhu Xiaoqin Shen 《Numerical Methods for Partial Differential Equations》2023,39(2):1604-1634
For shape optimization of fluid flows governed by the Navier–Stokes equation, we investigate effectiveness of shape gradient algorithms by analyzing convergence and accuracy of mixed finite element approximations to both the distributed and boundary types of shape gradients. We present convergence analysis with a priori error estimates for the two approximate shape gradients. The theoretical analysis shows that the distributed formulation has superconvergence property. Numerical results with comparisons are presented to verify theory and show that the shape gradient algorithm based on the distributed formulation is highly effective and robust for shape optimization. 相似文献