全文获取类型
收费全文 | 3116篇 |
免费 | 540篇 |
国内免费 | 607篇 |
专业分类
测绘学 | 96篇 |
大气科学 | 208篇 |
地球物理 | 647篇 |
地质学 | 789篇 |
海洋学 | 2049篇 |
天文学 | 58篇 |
综合类 | 215篇 |
自然地理 | 201篇 |
出版年
2024年 | 11篇 |
2023年 | 33篇 |
2022年 | 82篇 |
2021年 | 116篇 |
2020年 | 103篇 |
2019年 | 152篇 |
2018年 | 99篇 |
2017年 | 130篇 |
2016年 | 118篇 |
2015年 | 124篇 |
2014年 | 171篇 |
2013年 | 186篇 |
2012年 | 179篇 |
2011年 | 164篇 |
2010年 | 166篇 |
2009年 | 198篇 |
2008年 | 199篇 |
2007年 | 219篇 |
2006年 | 171篇 |
2005年 | 158篇 |
2004年 | 177篇 |
2003年 | 150篇 |
2002年 | 144篇 |
2001年 | 114篇 |
2000年 | 100篇 |
1999年 | 108篇 |
1998年 | 88篇 |
1997年 | 89篇 |
1996年 | 70篇 |
1995年 | 62篇 |
1994年 | 71篇 |
1993年 | 62篇 |
1992年 | 51篇 |
1991年 | 43篇 |
1990年 | 23篇 |
1989年 | 27篇 |
1988年 | 17篇 |
1987年 | 12篇 |
1986年 | 8篇 |
1985年 | 17篇 |
1984年 | 9篇 |
1983年 | 14篇 |
1982年 | 13篇 |
1981年 | 10篇 |
1980年 | 2篇 |
1979年 | 3篇 |
排序方式: 共有4263条查询结果,搜索用时 203 毫秒
31.
Modeling bed-load transport of coarse sediments in the Great Bay Estuary, New Hampshire 总被引:1,自引:0,他引:1
A. Bilgili M. R. Swift D. R. Lynch J. T. C. Ip 《Estuarine, Coastal and Shelf Science》2003,58(4):937-950
Current, sea level and bed-load transport are investigated in the Lower Piscataqua River section of the Great Bay Estuary, New Hampshire, USA—a well-mixed and geometrically complex system with low freshwater input, having main channel tidal currents ranging between 0.5 and 2 m s−1. Current and sea level forced by the M2M4M6 tides at the estuarine mouth are simulated by a vertically averaged, non-linear, time-stepping finite element model. The hydrodynamic model uses a fixed boundary computational domain and accounts for flooding–drying of tidal flats by making use of a groundwater component. Inertia terms are neglected in comparison with pressure gradient and bottom friction terms, which is consistent with the observed principal dynamic balance for this section of the system. The accuracy of hydrodynamic predictions in the study area is demonstrated by comparison with four tidal elevation stations and two cross-section averaged current measurements. Simulated current is then used to model bed-load transport in the vicinity of a rapidly growing shoal located in the main channel of the lower system. Consisting of coarse sand and gravel, the shoal must be dredged every five to eight years. Two approaches are taken—an Eulerian parametric method in which nodal bed-load flux vectors are averaged over the tidal cycle and a Lagrangian particle tracking approach in which a finite number of sediment particles are released and tracked. Both methods yield pathways and accumulations in agreement with the observed shoal formation and the long-term rate of sediment accumulation in the shoal area. 相似文献
32.
Li Yucheng Wang Fenglong Professor Dalian University of Technology Dalian Senior Engineer Dalian University of Technology Dalian 《中国海洋工程》1993,(1)
- The wave-current forces on vertical piles in side-by-side arrangement induced by irregular waves with opposing current are investigated experimentally in this paper. The characteristics in both time and frequency domain of in-line, lift and resultant forces are analyzed. The grouping effect coefficients of inline, lift and resultant forces on piles related to KC number and relative spacing parameters are given. These results are compared with those in the case of irregular waves combined with following currents. It is found that the results in these two cases are quite different. The range of KC number tested is 10- 60, the range of Reynolds number is (0.55-3.43) ×104. 相似文献
33.
Zhang Furan Zhao Jun Zhang Xueqin Assistant Researcher Tianjin Research Institute of Water Transport Engineering Tianjin Assistant Engineer Tianjin Research Institute of Water Transport Engineering Tianjin 《中国海洋工程》1993,(2)
In respect of an offshore berthing pillar, the test study result of current force acting on mooring ships is described in this paper. Empirical and semi-empirical relationships of current force coefficient are given according to the angle between the flow direction and the ship's longitudinal axis, which are coincident with the result of theoretical analysis. 相似文献
34.
A Computational Model for Velocity Separation in Shallow Sea 总被引:1,自引:0,他引:1
Based on the hydrodynamical feature and the theoretical velocity profiles of tidal flow and vvind-induced flow in shal-low sea, a computational model is established for the first time, which can separate observed velocity into tidal velocity and wind-induced velocity by use of the least square method. With the model, not only the surface velocities of tidal flow and vvind-induced flow are obtained, but also the bed roughness height is determined and the wind velocity above the wa-ter surface is estimated. For verification of the model, the observed velocity in the Yellow River Estuary and the laborato-ry test is separated, then it is applied to the Yangtze River Estuary. All the results are satisfactory. The research results show that the model is simple in method, feasible in process and reasonable in result. The model is a valid approach to analysis and computation of field dala, and can be applied to separate the observed velocity in shallow sea; at the same time, reasonable boundary conditions of th 相似文献
35.
36.
37.
本文对北部湾三维潮波进行了数值研究,并将所得结果与现有观测资料作了比较。通过比较发现两者相当一致。文中还绘制了M_2和K_1分潮的同潮图,并对其作了讨论。可以断定,北部湾的日潮优势是由日潮共振所引起的。M_2和K_1分潮流的水平分布表明,强流区位于它们各自的蜕化无潮点附近。还讨论了分潮流的铅直结构,可以看出这种结构十分接近实际分潮流场的特征。 相似文献
38.
对含多资料的分潮波模型的超定问题进行探讨,建立一种有限差分—最小二乘方法,该方法使得岸边资料直接进入了计算方程,并保证岸界法向流速为零条件。通过对渤海的四大分潮的试算,证实本方法可行。 相似文献
39.
40.
Li Dashan Shen Ying Ren Rushu Chen Yao
Senior Engineer River Harbour Department Nanjing Hydraulic Research Institute Nanjing Engineer River Harbour Department Nanjing Hydraulic Research Institute Nanjing Associate Professor Hohai University Nanjing Master Hohai University Nanjing 《中国海洋工程》1997,(1)
In this paper,the characteristics of density current under the action of waves are describedwith the help of flume experiment and theoretical analysis.The study shows that turbid water under the ac-tion of the waves can present three types of motion,i.e.significant stratification,fragile stratification andstrong mixing.The motion of turbid water presents significant stratification when(H/D)/△ρ/ρ~(1/2)≤4.5,generally this state is known as density current.The formulas of motionvelocity,thickness,and discharge of density current moving on horizontal bottom are derived by use of ba-sic equations such as momemtum equation,equation of energy conservation and continuity equation offluid.The time-average velocity and the thickness of density current under the action of waves have a rela-tionship with such parameters as relative density(△ρ/ρ),wave height(H),and water depth(D).Whenthese parameters are determined,the time-average thickness and motion velocity of density current are al-so determined.The relat 相似文献