全文获取类型
收费全文 | 2380篇 |
免费 | 647篇 |
国内免费 | 537篇 |
专业分类
测绘学 | 82篇 |
大气科学 | 1059篇 |
地球物理 | 981篇 |
地质学 | 757篇 |
海洋学 | 420篇 |
天文学 | 105篇 |
综合类 | 60篇 |
自然地理 | 100篇 |
出版年
2024年 | 3篇 |
2023年 | 11篇 |
2022年 | 27篇 |
2021年 | 48篇 |
2020年 | 60篇 |
2019年 | 103篇 |
2018年 | 79篇 |
2017年 | 110篇 |
2016年 | 85篇 |
2015年 | 98篇 |
2014年 | 150篇 |
2013年 | 136篇 |
2012年 | 110篇 |
2011年 | 150篇 |
2010年 | 138篇 |
2009年 | 229篇 |
2008年 | 250篇 |
2007年 | 220篇 |
2006年 | 182篇 |
2005年 | 153篇 |
2004年 | 141篇 |
2003年 | 102篇 |
2002年 | 115篇 |
2001年 | 94篇 |
2000年 | 81篇 |
1999年 | 93篇 |
1998年 | 99篇 |
1997年 | 97篇 |
1996年 | 84篇 |
1995年 | 57篇 |
1994年 | 76篇 |
1993年 | 63篇 |
1992年 | 35篇 |
1991年 | 27篇 |
1990年 | 15篇 |
1989年 | 18篇 |
1988年 | 11篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有3564条查询结果,搜索用时 31 毫秒
951.
Three-dimensional numerical modelling of wind-driven circulation in a homogeneous lake 总被引:1,自引:0,他引:1
A three-dimensional numerical model has been developed to study wind-induced circulation patterns in a shallow homogeneous lake with a complex bathymetry. The governing equations are the unsteady Reynolds-Averaged Navier–Stokes equations in which the non-hydrostatic pressure distribution has been included. The model was tested against analytical solutions and laboratory data for wind-induced currents and then applied to Esthwaite Water, a small lake in Cumbria, UK. The model was used to study the main model parameters and to generate typical circulation patterns for a variety of conditions in the lake. Simulations showed that a non-hydrostatic pressure distribution did not have any noticeable influence on the overall circulation pattern in the lake. However, comparisons with field data at some measurement stations in the near-shore region with sharply varying bottom topography showed that the hydrodynamic pressure component had some influence on the vertical velocity profile. 相似文献
952.
Groundwater flow and solute transport through fractured rock is highly responsive to the hydraulic anisotropy and heterogeneity that are specific to every major fracture. A major fracture is modeled as the combination of some primal master fractures and several splay fractures that branch out from primal master fractures: step structures (or jog parts). Step structures are commonly observed along a major fracture on various scales. Master fractures were formed and developed by shear movement while some splay fractures were formed by extension normal to their wall. This difference in fracturing process may lead to a permeability difference between master fractures and splay fractures which seems to be one of the major factors controlling flow and solute transport through the fracture networks due to its hydraulic anisotropic and heterogeneous features. This study is composed of two major components: (1) identification and characterization of a step structure from borehole data; (2) evaluation of effect of some idealized step structures on breakthrough curve by numerical simulations. The fracture data of four 1000-m boreholes were used to make clear fracture patterns in the Tono area of Japan. Some major fractures were identified using stereographic projection technique. On the basis of these results, several idealized models of a major fracture having a step was constructed for the numerical study. The obtained results from numerical simulations clearly imply that geometry of step structure plays an important role in flow and transport through the fracture networks. 相似文献
953.
954.
Variable-density groundwater flow and solute transport in porous media containing nonuniform discrete fractures 总被引:1,自引:0,他引:1
Variations in fluid density can greatly affect fluid flow and solute transport in the subsurface. Heterogeneities such as fractures play a major role for the migration of variable-density fluids. Earlier modeling studies of density effects in fractured media were restricted to orthogonal fracture networks, consisting of only vertical and horizontal fractures. The present study addresses the phenomenon of 3D variable-density flow and transport in fractured porous media, where fractures of an arbitrary incline can occur. A general formulation of the body force vector is derived, which accounts for variable-density flow and transport in fractures of any orientation. Simulation results are presented that show the verification of the new model formulation, for the porous matrix and for inclined fractures. Simulations of variable-density flow and solute transport are then conducted for a single fracture, embedded in a porous matrix. The simulations show that density-driven flow in the fracture causes convective flow within the porous matrix and that the high-permeability fracture acts as a barrier for convection. Other simulations were run to investigate the influence of fracture incline on plume migration. Finally, tabular data of the tracer breakthrough curve in the inclined fracture is given to facilitate the verification of other codes. 相似文献
955.
Influence of a low-viscosity layer between rigid inclusion and viscous matrix on inclusion rotation and matrix flow: A numerical study 总被引:1,自引:0,他引:1
We have used 2-D finite element modelling to investigate the influence of a permanent low-viscosity layer between matrix and inclusion on matrix flow and inclusion rotation under viscous simple shear flow. Rigid inclusions of different shape (circle, square, ellipse, lozenge, rectangle and skewed rectangles) and aspect ratio (R) were used. The calculated matrix flow pattern is neither bow tie nor eye-shaped. It is a new flow pattern that we call cat eyes-shaped, which is characterized by: (i) straight streamlines that slightly bend inwards at the inclusion's crests; (ii) elongate eye-shaped streamlines on each side of the inclusion; (iii) stagnation points in the centre of the eyes; (iv) absence of closed streamlines surrounding the inclusion; (v) changes in flow configuration with inclusion orientation; the lines of flow reversal bend and tilt, closed streamline circuits may disappear, and streamlines may bend outwards at the inclusion's crests.Concerning inclusion rotation, the numerical results show that: (i) a low-viscosity layer (LVL) makes inclusions with R = 1 rotate synthetically, but the rotation rate depends upon shape (circle or square) and orientation. Therefore, shape matters in the slipping mode. (ii) All studied shapes with R > 1 rotate antithetically when starting with the greatest principal axis (e1) parallel to the shear direction ( = 0°); (iii) rotation is limited because there is a stable equilibrium orientation (se) for all studied shapes with R > 1. (iii) There is also an unstable equilibrium orientation (ue), and both se and ue depend upon inclusion's R and shape.The present numerical results closely agree with previous results of analogue experiments with a permanent low viscosity interface. Only minor deviations related with small shape differences were detected. 相似文献
956.
刘羽 《物探化探计算技术》2006,28(4):342-345
Occam反演以其稳定收敛和不依赖初始模型的特性,在大地电磁数据处理中得到了广泛应用。但拉格朗日乘子的求取,导致了大量的正演计算,使反演速度较低。在讨论拉格朗日乘子计算方法的基础上,提出用基于机群的并行计算来解决这一问题,并采用主-从编程模式,实现了拉格朗日乘子扫描和一维搜索的并行计算。将扫描任务编组分派到不同的节点完成,减少了通信量,也较好地实现了负载均衡。算例表明,并行计算可以比较显著地提高处理速度。 相似文献
957.
苏北一次强降雹过程的数值模拟研究 总被引:6,自引:3,他引:6
应用中科院大气所研制的三维弹性冰雹云模式,对2003年7月19日发生在苏北地区的一次冰雹云过程进行了数值模拟研究,再结合天气形势、雷达回波和天气实况资料分析了这次冰雹云发生发展的过程及其微物理结构的变化,发现该模式能较好地模拟该例冰雹云*过程,碰并增长是云中各种水物质主要的形成和增长方式,雹的增长主要来源于霰的自动转化。 相似文献
958.
959.
本文将背风波三层模式的理论应用于典型的背风波个例,判断了其解所属的类型,计算了这些个例的波长;指出当有多个波解存在时,最长波长所对应的波解是实际解;本文还用ARPS模式对这些个例作了数值模拟,模拟结果与解析解则有较好的一致性。 相似文献
960.
On July 20, 2003, following a short duration of heavy rainfall, a debris-flow disaster occurred in the Minamata–Hougawachi area, Kumamoto Prefecture, Japan. This disaster was triggered by a landslide. In order to assess the landslide and debris-flow hazard potential of this mountainous region, the study of historic landslides is critical. The objective of the study is to couple 3D slope-stability analysis models and 2D numerical simulation of debris flow within a geographical information systems in order to identity the potential landslide-hazard area. Based on field observations, the failure mechanism of the past landslide is analyzed and the mechanical parameters for 3D slope-stability analysis are calculated from the historic landslide. Then, to locate potential new landslides, the studied area is divided into slope units. Based on 3D slope-stability analysis models and on Monte Carlo simulation, the spots of potential landslides are identified. Finally, we propose a depth-averaged 2D numerical model, in which the debris and water mixture is assumed to be a uniform continuous, incompressible, unsteady Newtonian fluid. The method accurately models the historic debris flow. According to the 2D numerical simulation, the results of the debris-flow model, including the potentially inundated areas, are analyzed, and potentially affected houses, river and road are mapped. 相似文献