全文获取类型
收费全文 | 6908篇 |
免费 | 1775篇 |
国内免费 | 1758篇 |
专业分类
测绘学 | 86篇 |
大气科学 | 1218篇 |
地球物理 | 3388篇 |
地质学 | 1913篇 |
海洋学 | 3002篇 |
天文学 | 80篇 |
综合类 | 335篇 |
自然地理 | 419篇 |
出版年
2024年 | 50篇 |
2023年 | 141篇 |
2022年 | 206篇 |
2021年 | 262篇 |
2020年 | 303篇 |
2019年 | 408篇 |
2018年 | 295篇 |
2017年 | 285篇 |
2016年 | 295篇 |
2015年 | 355篇 |
2014年 | 382篇 |
2013年 | 387篇 |
2012年 | 432篇 |
2011年 | 427篇 |
2010年 | 344篇 |
2009年 | 428篇 |
2008年 | 405篇 |
2007年 | 546篇 |
2006年 | 458篇 |
2005年 | 402篇 |
2004年 | 410篇 |
2003年 | 352篇 |
2002年 | 333篇 |
2001年 | 277篇 |
2000年 | 279篇 |
1999年 | 251篇 |
1998年 | 265篇 |
1997年 | 217篇 |
1996年 | 221篇 |
1995年 | 214篇 |
1994年 | 187篇 |
1993年 | 157篇 |
1992年 | 120篇 |
1991年 | 107篇 |
1990年 | 62篇 |
1989年 | 53篇 |
1988年 | 45篇 |
1987年 | 28篇 |
1986年 | 12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 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
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
22.
Abstract. Four sites were sampled in kelp (Macrocysiis pyrifera) forests occupying rocky bottom habitats along a wave exposure gradient in central California. Consistent betwecn-site differences were found in the three major structural elements - the surface canopy, the undcrstory assemblage, and the ground cover/turf assemblage - of kelp forest communities. Macrocysiis pyrifera was found at all four sites. Nereucyslis tuelkeana only at the most exposed site. The understory kelps Laminaria setchellii and Pterygopltora californica were also characteristic of exposed sites. Articulated coralline algae were more abundant at exposed sites than protected, while fleshy red algae showed the opposite pattern. All four study sites were located along 8.5 km of coastline, and thus were assumed to have available to them the same species pool for colonization. The substrate composition was the same and the amount of unconsolidated substrate was similar at all four sites. We suggest that exposure to wave-generated water motion, through its influence on the surface canopy and therefore on the amount of light reaching the bottom, is responsible for these between-site differences. 相似文献
23.
Two commonly used methods of simulating random time series, given a target power spectrum, are discussed. Wave group statistics, such as the mean length of runs of high waves, produced by the different simulation schemes are compared. The target spectra used are obtained from ocean measurements, and cover a wide range of ocean conditions. For a sufficiently large number of spectral components, no significant differences are found in the wave group statistics produced by the two simulation techniques. 相似文献
24.
25.
26.
27.
28.
29.
The effect of asymmetry and irregularity of the inputted seismic waves on the earthquake-induced differential settlement of the buildings on natural subsoil is investigated in terms of the earthquake damage phenomena, theoretical analyses, dynamic triaxial tests and shaking table tests. A conclusion can be drawn from the investigation results that, the asymmetrical and irregular character of the inputted seismic waves themselves may have a significant contribution to the differential settlement of subsoil and buildings in some cases, and this is a necessary factor to be considered in reasonable evaluation for the differential settlement and other problems relating to the soil deformation due to earthquakes. 相似文献
30.