全文获取类型
收费全文 | 6113篇 |
免费 | 218篇 |
专业分类
公路运输 | 2122篇 |
综合类 | 1595篇 |
水路运输 | 1319篇 |
铁路运输 | 1218篇 |
综合运输 | 77篇 |
出版年
2024年 | 45篇 |
2023年 | 196篇 |
2022年 | 198篇 |
2021年 | 216篇 |
2020年 | 201篇 |
2019年 | 186篇 |
2018年 | 75篇 |
2017年 | 116篇 |
2016年 | 126篇 |
2015年 | 191篇 |
2014年 | 256篇 |
2013年 | 259篇 |
2012年 | 318篇 |
2011年 | 348篇 |
2010年 | 327篇 |
2009年 | 338篇 |
2008年 | 350篇 |
2007年 | 319篇 |
2006年 | 289篇 |
2005年 | 263篇 |
2004年 | 249篇 |
2003年 | 244篇 |
2002年 | 185篇 |
2001年 | 189篇 |
2000年 | 135篇 |
1999年 | 95篇 |
1998年 | 89篇 |
1997年 | 78篇 |
1996年 | 95篇 |
1995年 | 57篇 |
1994年 | 60篇 |
1993年 | 63篇 |
1992年 | 48篇 |
1991年 | 50篇 |
1990年 | 38篇 |
1989年 | 34篇 |
1965年 | 5篇 |
排序方式: 共有6331条查询结果,搜索用时 125 毫秒
981.
982.
983.
Green-Naghdi (G-N) theory is a fully nonlinear theory for water waves. Some researchers call it a fully nonlinear Boussinesq model. Different degrees of complexity of G-N theory are distinguished by “levels” where the higher the level, the more complicated and presumably more accurate the theory is. In the research presented here a comparison was made between two different levels of G-N theory, specifically level II and level III G-N restricted theories. A linear analytical solution for level III G-N restricted theory was given. Waves on a planar beach and shoaling waves were both simulated with these two G-N theories. It was shown for the first time that level III G-N restricted theory can also be used to predict fluid velocity in shallow water. A level III G-N restricted theory is recommended instead of a level II G-N restricted theory when simulating fully nonlinear shallow water waves. 相似文献
984.
Sandwich plate systems (SPS) are advanced materials that have begun to receive extensive attention in naval architecture and
ocean engineering. At present, according to the rules of classification societies, a mixture of shell and solid elements are
required to simulate an SPS. Based on the principle of stiffness decomposition, a new numerical simulation method for shell
elements was proposed. In accordance with the principle of stiffness decomposition, the total stiffness can be decomposed
into the bending stiffness and shear stiffness. Displacement and stress response related to bending stiffness was calculated
with the laminated shell element. Displacement and stress response due to shear was calculated by use of a computational code
write by FORTRAN language. Then the total displacement and stress response for the SPS was obtained by adding together these
two parts of total displacement and stress. Finally, a rectangular SPS plate and a double-bottom structure were used for a
simulation. The results show that the deflection simulated by the elements proposed in the paper is larger than the same simulated
by solid elements and the analytical solution according to Hoff theory and approximate to the same simulated by the mixture
of shell-solid elements, and the stress simulated by the elements proposed in the paper is approximate to the other simulating
methods. So compared with calculations based on a mixture of shell and solid elements, the numerical simulation method given
in the paper is more efficient and easier to do. 相似文献
985.
986.
987.
988.
989.
990.
软黏土在我国沿海地区广泛存在,且物理力学特性复杂.通过现场取样进行室内试验,研究土体的各种力学特性,并选取合适的参数进行数值计算,模拟模型试验中土体的固结变形及其演化规律,解释试验中的一些特殊现象,得到一些重要结论.在固结变形中,超软淤泥的特殊力学特性使得土体越渗越密,越密越难渗,表现出与其他土体不同的固结特性,因此,必须考虑土体渗透系数随土体孔隙比变化和土体非线性的力学特征等规律. 相似文献