全文获取类型
收费全文 | 8744篇 |
免费 | 1822篇 |
国内免费 | 3212篇 |
专业分类
测绘学 | 268篇 |
大气科学 | 254篇 |
地球物理 | 1684篇 |
地质学 | 9587篇 |
海洋学 | 971篇 |
天文学 | 42篇 |
综合类 | 471篇 |
自然地理 | 501篇 |
出版年
2024年 | 34篇 |
2023年 | 143篇 |
2022年 | 317篇 |
2021年 | 324篇 |
2020年 | 339篇 |
2019年 | 442篇 |
2018年 | 343篇 |
2017年 | 350篇 |
2016年 | 380篇 |
2015年 | 460篇 |
2014年 | 573篇 |
2013年 | 527篇 |
2012年 | 546篇 |
2011年 | 609篇 |
2010年 | 494篇 |
2009年 | 592篇 |
2008年 | 594篇 |
2007年 | 660篇 |
2006年 | 706篇 |
2005年 | 532篇 |
2004年 | 536篇 |
2003年 | 479篇 |
2002年 | 412篇 |
2001年 | 480篇 |
2000年 | 397篇 |
1999年 | 394篇 |
1998年 | 317篇 |
1997年 | 299篇 |
1996年 | 251篇 |
1995年 | 228篇 |
1994年 | 246篇 |
1993年 | 170篇 |
1992年 | 147篇 |
1991年 | 92篇 |
1990年 | 80篇 |
1989年 | 71篇 |
1988年 | 57篇 |
1987年 | 56篇 |
1986年 | 23篇 |
1985年 | 21篇 |
1984年 | 16篇 |
1983年 | 11篇 |
1982年 | 7篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1954年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
This paper describes the simulation of the flow of a viscous incompressible Newtonian liquid with a free surface. The Navier–Stokes equations are formulated using a streamline upwind Petrov–Galerkin scheme, and solved on a Q-tree-based finite element mesh that adapts to the moving free surface of the liquid. Special attention is given to fitting the mesh correctly to the free surface and solid wall boundaries. Fully non-linear free surface boundary conditions are implemented. Test cases include sloshing free surface motions in a rectangular tank and progressive waves over submerged cylinders. 相似文献
92.
立足样品测试数据,利用空间分析、空间插值、地质统计以及景观生态学方法,深入分析了深圳大鹏湾表层沉积物碎屑矿物的空间分布特征,并使用球状模型对相应半变异函数进行理论建模。结果表明,碎屑矿物分布的Hurst分维数为0.28~0.97,空间几何分维数为1.03~1.72;Moran Ⅰ型空间自相关系数-0.15~0.53。在此基础上,以等值线分布所包围范围作为划分尺度,以Shannon-Wiener信息指数作为度量,得到的矿物分布所反映出的信息量或者富集程度指数为0.88~1.85。 相似文献
93.
重矿物组合、含量变化和特征矿物的分布及变化规律是沿海泥沙来源和运移趋势判断的重要手段之一。通过对廉州湾南部海域海底表层沉积物的重矿物分析 ,发现该区重矿物分布以北海地角为界 ,其百分含量和特征矿物南北有别 ,可能分别代表不同的物质来源区。其中廉州湾北部南流江流域来沙是该区主要物源 ,运移趋势为自 NE向 SW;地角西南岸段、岭南侧海岸侵蚀及银滩来沙也为该区提供了部分物源 ,运移趋势为绕过冠头岭沿海岸向 N方向运移。由于缺乏北海陆域陆相地层重矿物含量等相关资料 ,暂未做物质来源区的具体判断 相似文献
94.
A numerical model to compute wave field is developed. It is based on the Berkhoff diffraction-refraction equation, in which an energy dissipation term is added, to take into account the breaking and the bottom friction phenomena. The energy dissipation function, by breaking and by bottom friction, is introduced in the Berkhoff equation to obtain a new equation of propagation.The resolution is done with the hybrid finite element method, where lagrangians elements are used. 相似文献
95.
96.
Various offshore structures, especially large structures such as Tension Leg Platforms (TLP), are usually supported by concrete piles as the foundation elements. The stress distribution within such a large structure is a dominant factor in the design procedure of an offshore pile. To provide a more accurate and effective design for offshore foundation systems under axial and lateral wave loads, a finite element model is employed herein to determine the stresses and displacements in a concrete pile under similar loading conditions. A parametric study is also performed to examine the effects of the stress distribution due to the changing loading conditions. 相似文献
97.
98.
利用Minolta CM-2002光谱光度计对南黄海陆架136个短柱样品20~25cm段的沉积物进行了颜色反射率数据测量,通过化学元素、粒度、磁化率等来确定影响沉积物颜色反射率变化的成分和因素,介绍了反射率光谱的一阶导数和因子分析的方法。分析结果表明,南黄海陆架沉积物颜色反射率受控于沉积物中的铁氧化物、有机质以及粘土矿物和钙质生物碎屑含量。主因子F1指示氧化环境,并与陆源物质相关,F2指示弱氧化环境,F3指示弱还原环境,主因子的波长范围分别是405~445 nm和495~595 nm,605~695 nm,445~485 nm。 相似文献
99.
A time-domain method is applied to simulate nonlinear wave diffraction around a surface piercing 3-D arbitrary body. The method involves the application of Taylor series expansions and the use of perturbation procedure to establish the corresponding boundary value problems with respect to a time-independent fluid domain. A boundary element method based on B-spline expansion is used to calculate the wave field at each time step, and the free surface boundary condition is satisfied to the second order of wave steepness by a numerical integration in time. An artificial damping layer is adopted on the free surface for the removal of wave reflection from the outer boundary. As an illustration, the method is used to compute the second-order wave forces and run-up on a surface-piercing circular cylinder. The present method is found to be accurate, computationally efficient, and numerically stable. 相似文献
100.
A model for solving the two-dimensional enhanced Boussinesq equations is presented. The model equations are discretised in space using an unstructured finite element technique. The standard Galerkin method with mixed interpolation is applied. The time discretisation is performed using an explicit three-step Taylor–Galerkin method. The model is extended to the surf and swash zone by inclusion of wave breaking and a moving boundary at the shoreline. Breaking is treated by an existing surface roller model, but a new procedure for the detection of the roller thickness is devised. The model is verified using four test cases and the results are compared with experimental data and results from an existing finite difference Boussinesq model. 相似文献