全文获取类型
收费全文 | 6412篇 |
免费 | 1732篇 |
国内免费 | 1558篇 |
专业分类
测绘学 | 96篇 |
大气科学 | 1011篇 |
地球物理 | 3118篇 |
地质学 | 1804篇 |
海洋学 | 2852篇 |
天文学 | 79篇 |
综合类 | 324篇 |
自然地理 | 418篇 |
出版年
2024年 | 28篇 |
2023年 | 87篇 |
2022年 | 163篇 |
2021年 | 221篇 |
2020年 | 253篇 |
2019年 | 375篇 |
2018年 | 267篇 |
2017年 | 259篇 |
2016年 | 259篇 |
2015年 | 338篇 |
2014年 | 351篇 |
2013年 | 362篇 |
2012年 | 403篇 |
2011年 | 420篇 |
2010年 | 323篇 |
2009年 | 421篇 |
2008年 | 389篇 |
2007年 | 535篇 |
2006年 | 440篇 |
2005年 | 398篇 |
2004年 | 408篇 |
2003年 | 347篇 |
2002年 | 316篇 |
2001年 | 264篇 |
2000年 | 266篇 |
1999年 | 247篇 |
1998年 | 250篇 |
1997年 | 198篇 |
1996年 | 210篇 |
1995年 | 200篇 |
1994年 | 167篇 |
1993年 | 139篇 |
1992年 | 105篇 |
1991年 | 92篇 |
1990年 | 46篇 |
1989年 | 44篇 |
1988年 | 38篇 |
1987年 | 21篇 |
1986年 | 11篇 |
1985年 | 9篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 1篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1954年 | 11篇 |
排序方式: 共有9702条查询结果,搜索用时 312 毫秒
131.
132.
徐肇廷 《中国海洋大学学报(自然科学版)》1989,(3)
本文从流体力学基本方程组出发,在非地转条件下导得了分层海洋的内孤立波方程—Kbv和mKdv方程,证实了在非地转条件下,一类海洋非线性波动是可以严格满足内孤立波方程的。在地转条件下采用f平面近似导出了KdV方程的演化形式一有源KdV方程,地转的影响含于源项中。由初步的分析得出,f对KdV方程的影响是微弱的。由已得的KdV和mKdV方程的解可知,内孤立波与线性波有着本质差别。 相似文献
133.
A finite-difference scheme and a modified marker-and-cell (MAC) algorithm have been developed to investigate the interactions of fully nonlinear waves with two- or three-dimensional structures of arbitrary shape. The Navier–Stokes (NS) and continuity equations are solved in the computational domain and the boundary values are updated at each time step by the finite-difference time-marching scheme in the framework of a rectangular coordinate system. The fully nonlinear kinematic free-surface condition is implemented by the marker-density function (MDF) technique developed for two fluid layers.To demonstrate the capability and accuracy of the present method, the numerical simulation of backstep flows with free-surface, and the numerical tests of the MDF technique with limit functions are conducted. The 3D program was then applied to nonlinear wave interactions with conical gravity platforms of circular and octagonal cross-sections. The numerical prediction of maximum wave run-up on arctic structures is compared with the prediction of the Shore Protection Manual (SPM) method and those of linear and second-order diffraction analyses based on potential theory and boundary element method (BEM). Through this comparison, the effects of non-linearity and viscosity on wave loading and run-up are discussed. 相似文献
134.
Based on the ray theory and Longuet-Higgins’s linear model of sea waves, the joint distribution of wave envelope and apparent wave number vector is established. From the joint distribution, we define a new concept, namely the outer wave number spectrum, to describe the outer characteristics of ocean waves. The analytical form of the outer wave number spectrum, the probability distributions of the apparent wave number vector and its components are then derived. The outer wave number spectrum is compared with the inner wave number spectrum for the average status of wind-wave development corresponding to a peakness factor P = 3. Discussions on the similarity and difference between the outer wave number spectrum and inner one are also presented in the paper. 相似文献
135.
To the first order in a Stokes expansion, the pressure force exerted by a sea state on a large horizontal cylinder represents a stationary random Gaussian process. A relationship is obtained between the spectrum of this process and the wave spectrum. As a consequence, the basic statistical properties of the height and period of the individual waves of the force-process are also obtained. It is proven that these statistical properties agree very well with the data from a small scale field experiment. 相似文献
136.
波浪作用下海床动力反应的数值分析 总被引:2,自引:3,他引:2
近海和离岸建筑物的基通常处于连续不断的小风浪作用之下,可将其变形视为弹性。基于二维广义Biot理论,提出了线性或非线性波浪作用下饱和弹性海床动力应应的时域有限元数值解法。静力平衡条件和Biot方程组成的边值方程可视为其特例,在比较算例中,数值计算得到的孔压和有效应力幅值沿海床深度的分布与解析解十分吻合。土骨架和孔隙流体的加速度对海床动力反应的影响很小。具体算例表明,线性波沿缓坡海床传播时,土层中超静孔压和有效应力幅值随之增大,有可能发生滑动坡坏。所提出的数值解法能够灵活地处理非线性波浪荷载,海底复杂地质条件和波浪沿缓坡传播等复杂情况。 相似文献
137.
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
138.
太平洋波高分布及变化规律研究 总被引:4,自引:0,他引:4
使用 Topex/ Poseidon卫星高度计 1 992年 1 0月~ 1 998年 1 2月连续 75个月 ,2 30个重复周期的有效波高资料对南北太平洋的有效波高进行了统计 ,分析了太平洋有效波高的多年平均、多年各月平均和多年各季平均的空间分布特征和时间变化规律。结果表明 ,太平洋波高分布具有明显季节变化的规律 ,与太平洋的风速分布特征具有良好的对应关系 相似文献
139.
-The hydrodynamic forces on a smooth inclined circular cylinder exposed to oscillating flow were experimentally investigated at Reynolds number (Re) in the range 40000-200000 and Keulegan-Capenter number (KC) in the interval from 5-40. In the test, Re number and KC number were varied systematically. The inertia force coefficient (Cu) and the drag force coefficient (CD) in Morison equation were determined from the measured loads and the water particle kinematics. In this analysis a modified form of Morison equation was used since it uses the normal velocity and acceleration. Thus, the applicability of the Cross Flow Principle was assumed. This principle, simply stated, is as follows: the force acting in the direction normal to the axis of a cylinder placed at some oblique angle with the direction of flow is expressed in terms of the normal component of flow only, and the axial component is disregarded. Both the total in-line force coefficient (CF) and transverse force (lift) coefficient (Cf) were analyzed 相似文献
140.
The stochastic properties of the drag force maxima on a circular cylinder subjected to nonlinear random waves are investigated. Unseparated laminar high Reynolds number flow is considered. A simplified approach based on second order Stokes waves is presented, including the sum-frequency effect only. It is demonstrated how a drag force formula valid for regular linear waves can be used to find the cumulative distribution function of individual drag force maxima for nonlinear irregular waves. Here the [Wang, 1968] drag force coefficient is used. 相似文献