全文获取类型
收费全文 | 8501篇 |
免费 | 1497篇 |
国内免费 | 2387篇 |
专业分类
测绘学 | 518篇 |
大气科学 | 354篇 |
地球物理 | 2602篇 |
地质学 | 6851篇 |
海洋学 | 1003篇 |
天文学 | 98篇 |
综合类 | 393篇 |
自然地理 | 566篇 |
出版年
2024年 | 42篇 |
2023年 | 121篇 |
2022年 | 253篇 |
2021年 | 295篇 |
2020年 | 422篇 |
2019年 | 461篇 |
2018年 | 423篇 |
2017年 | 529篇 |
2016年 | 465篇 |
2015年 | 514篇 |
2014年 | 712篇 |
2013年 | 794篇 |
2012年 | 681篇 |
2011年 | 499篇 |
2010年 | 405篇 |
2009年 | 499篇 |
2008年 | 485篇 |
2007年 | 572篇 |
2006年 | 580篇 |
2005年 | 448篇 |
2004年 | 438篇 |
2003年 | 387篇 |
2002年 | 321篇 |
2001年 | 295篇 |
2000年 | 290篇 |
1999年 | 245篇 |
1998年 | 202篇 |
1997年 | 195篇 |
1996年 | 149篇 |
1995年 | 134篇 |
1994年 | 129篇 |
1993年 | 93篇 |
1992年 | 84篇 |
1991年 | 49篇 |
1990年 | 44篇 |
1989年 | 33篇 |
1988年 | 39篇 |
1987年 | 25篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1980年 | 1篇 |
1979年 | 6篇 |
1977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
71.
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
72.
The North Yellow Sea Basin ( NYSB ), which was developed on the basement of North China (Huabei) continental block, is a typical continental Mesozoic Cenozoic sedimentary basin in the sea area. Its Mesozoic basin is a residual basin, below which there is probably a larger Paleozoic sedimentary basin. The North Yellow Sea Basin comprises four sags and three uplifts. Of them, the eastern sag is a Mesozoic Cenozoic sedimentary sag in NYSB and has the biggest sediment thickness; the current Korean drilling wells are concentrated in the eastern sag. This sag is comparatively rich in oil and gas resources and thus has a relatively good petroleum prospect in the sea. The central sag has also accommodated thick Mesozoic-Cenozoic sediments. The latest research results show that there are three series of hydrocarbon source rocks in the North Yellow Sea Basin, namely, black shales of the Paleogene, Jurassic and Cretaceous. The principal hydrocarbon source rocks in NYSB are the Mesozoic black shale. According to the drilling data of Korea, the black shales of the Paleogene, Jurassic and Cretaceous have all come up to the standards of good and mature source rocks. The NYSB owns an intact system of oil generation, reservoir and capping rocks that can help hydrocarbon to form in the basin and thus it has the great potential of oil and gas. The vertical distribution of the hydrocarbon resources is mainly considered to be in the Cretaceous and then in the Jurassic. 相似文献
73.
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
74.
AbstractWith the large-scale development and utilization of ocean resources and space, it is inevitable to encounter existing submarine facilities in pile driving areas, which necessitates a safety assessment. In this article, by referring to a wharf renovation project as a reference, the surrounding soil response and buried pipe deformation during pile driving in a near-shore submarine environment are investigated by three-dimensional (3D) numerical models that consider the pore water effect. Numerical studies are carried out in two different series: one is a case of a single pile focusing on the effect of the minimum plane distance of the pile–pipe, and the other is a case of double piles focusing on the effect of the pile spacing. 相似文献
75.
76.
Combining indicator trends to assess ongoing changes in exploited fish communities: diagnostic of communities off the coasts of France 总被引:1,自引:1,他引:1
77.
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
78.
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
79.
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
80.
This paper presents a potential based boundary element method for solving a nonlinear free surface flow problem for a ship moving with a uniform speed in finite depth of water. The free surface boundary condition is linearized by the systematic method of perturbation in terms of a small parameter up to third order. The surfaces are discretized into flat quadrilateral elements and the influence coefficients are calculated by Morino's analytical formula. Dawson's upstream finite difference operator is used in order to satisfy the radiation condition. The second order solution gives better result than the first or third order solution. So the present method with the second order solution can be adopted as a powerful tool for the hydrodynamic analysis of the thin ship in finite depth of water. 相似文献