全文获取类型
收费全文 | 10399篇 |
免费 | 2131篇 |
国内免费 | 2978篇 |
专业分类
测绘学 | 1350篇 |
大气科学 | 1712篇 |
地球物理 | 2344篇 |
地质学 | 5616篇 |
海洋学 | 1944篇 |
天文学 | 403篇 |
综合类 | 910篇 |
自然地理 | 1229篇 |
出版年
2024年 | 53篇 |
2023年 | 165篇 |
2022年 | 507篇 |
2021年 | 580篇 |
2020年 | 481篇 |
2019年 | 561篇 |
2018年 | 544篇 |
2017年 | 563篇 |
2016年 | 604篇 |
2015年 | 625篇 |
2014年 | 624篇 |
2013年 | 769篇 |
2012年 | 817篇 |
2011年 | 833篇 |
2010年 | 833篇 |
2009年 | 783篇 |
2008年 | 830篇 |
2007年 | 687篇 |
2006年 | 622篇 |
2005年 | 562篇 |
2004年 | 424篇 |
2003年 | 382篇 |
2002年 | 414篇 |
2001年 | 386篇 |
2000年 | 353篇 |
1999年 | 275篇 |
1998年 | 199篇 |
1997年 | 176篇 |
1996年 | 142篇 |
1995年 | 125篇 |
1994年 | 103篇 |
1993年 | 93篇 |
1992年 | 91篇 |
1991年 | 61篇 |
1990年 | 44篇 |
1989年 | 42篇 |
1988年 | 40篇 |
1987年 | 18篇 |
1986年 | 23篇 |
1985年 | 15篇 |
1984年 | 11篇 |
1983年 | 4篇 |
1981年 | 7篇 |
1980年 | 3篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1974年 | 2篇 |
1958年 | 3篇 |
1957年 | 6篇 |
1954年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Qiu Dahong 《中国海洋工程》1992,(2)
Based on the 1st order cnoidal wave theory, the nonlinear wave diffraction around a circular cylinder in shallow water is studied in this paper. The equation of the wave surface around the cylinder is formulated and by using this formula the wave surface elevation on the cylinder surface can be obtained. In this paper, the formula for calculating the cnoidal wave force on a circular cylinder is also derived. For the wave conditions which are often encountered in practical engineering designs, the ratios of the nonlinear wave forces to the linear wave forces are calculated, and the results are plotted in this paper for design purposes. In order to verify the theoretical results, model tests are conducted. After comparing the test results with the theoretical ones, it is concluded that, in shallow water, for the case of T g / d~(1/2) > 8-10 and H / d > 0.3, the cnoidal wave theory should be used to calculate the wave action on a cylindrical pier. 相似文献
52.
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
53.
54.
55.
Qiu Xinfang 《海洋学报(英文版)》1991,10(2):271-280
By using the expressions for the maximum absorption per wavelength (αλ),and the relaxation frequency fr of the boric acid relaxation derived previously by the author and employing the related oceanographic literatures, the effects of pressure, temperature, pH and salinity on (αλ)r and ∫r of the boric acid relaxation in sea water have been estimated. Results show that ( αλ), not only increases with pH but also increases approximately linearly with pressure and temperature, and is nearly proportional to the 1. 35 power of salinity. However, pressure, pH and salinity have negligible effect on ∫r; therefore, ∫r, can be approximately expressed as a function of temperature only. Comparisons of the predicted with the measured ( αλ)r and ∫r in different ocean areas are given. 相似文献
56.
57.
大沽河是胶州湾最大的入海河流,每年都会给胶州湾带来大量泥沙。本文利用三维的ECOMSED水动力-泥沙数值模型对洪水期的大沽河进行了数值模拟,得到了洪水存在期间以及洪水结束后胶州湾的余流分布、大沽河河道上中下游各层盐度、泥沙浓度随时间变化的趋势以及入海冲淡水和泥沙对胶州湾的影响。 相似文献
58.
A vertical two-dimensional turbulence numerical model for the interaction of waves and currents is developed in the paper based on the nonlinear two-equation k-ε model with the VOF method.The one-dimensional equivalent advection velocity and equivalent mixing coefficient are defined and the solving process is introduced:The pollutant concentration field,generated by an instant source in waves and currents,is calculated with the model,and then the equivalent advection velocity and equivalent mixing coefficient are obtained by calculating the time derivative of the mean and variance of pollutant concentration probability distribution.The effects of wave period and wave height on the equivalent mixing coefficient for waves and wave-currents are also investigated. 相似文献
59.
60.