全文获取类型
收费全文 | 2475篇 |
免费 | 725篇 |
国内免费 | 1633篇 |
专业分类
测绘学 | 43篇 |
大气科学 | 2781篇 |
地球物理 | 822篇 |
地质学 | 650篇 |
海洋学 | 96篇 |
天文学 | 3篇 |
综合类 | 101篇 |
自然地理 | 337篇 |
出版年
2024年 | 34篇 |
2023年 | 101篇 |
2022年 | 125篇 |
2021年 | 169篇 |
2020年 | 164篇 |
2019年 | 193篇 |
2018年 | 181篇 |
2017年 | 200篇 |
2016年 | 162篇 |
2015年 | 200篇 |
2014年 | 208篇 |
2013年 | 386篇 |
2012年 | 235篇 |
2011年 | 212篇 |
2010年 | 164篇 |
2009年 | 197篇 |
2008年 | 189篇 |
2007年 | 263篇 |
2006年 | 253篇 |
2005年 | 212篇 |
2004年 | 152篇 |
2003年 | 135篇 |
2002年 | 106篇 |
2001年 | 84篇 |
2000年 | 81篇 |
1999年 | 65篇 |
1998年 | 68篇 |
1997年 | 65篇 |
1996年 | 47篇 |
1995年 | 42篇 |
1994年 | 40篇 |
1993年 | 28篇 |
1992年 | 14篇 |
1991年 | 16篇 |
1990年 | 9篇 |
1989年 | 6篇 |
1988年 | 12篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有4833条查询结果,搜索用时 15 毫秒
251.
The spatial organization of decadal and bidecadal components (fluctuations) of annual rainfall is identified in this research for two regions: (1) southern South America, and (2) southern North America (conterminous USA, southeastern Canada and northern and central Mexico). Findings indicate that these decadal and bidecadal components have highly coherent wave-like spatial organization. Two types of organization of decadal and bidecadal components of annual rainfall were identified: a train of propagating fluctuations and quasi-standing fluctuations. For decadal components, such patterns alternate in time. A widespread change in the spatial organization of decadal component of annual rainfall took place simultaneously in both continents in 1932. The bidecadal component is organized as standing fluctuations in southern North America and as travelling fluctuations in southern South America, The spatial pattern of decadal fluctuations of annual rainfall has 12- and 13-year cycles, and the spatial pattern of bidecadal fluctuations has predominantly 21- and 22-year cycles. 相似文献
252.
G Nageswara Rao 《Journal of Earth System Science》2001,110(1):87-94
It is well known that heavy rainfall occurs in the southwestern sector of the monsoon depressions due to strong convergence
in that sector. By examining the rainfall distribution associated with the monsoon disturbances (lows and depressions) in
one of the central Indian river basins, ‘Godavari’, the author found that when the disturbance-centre is away from the basin,
heavy rainfall may also occur in the basin area close to the confluence line and cause severe floods in the river. The confluence
line is the zone of convergence between the northeasterlies to the west of the disturbance centre and the monsoon westerlies.
This study further reveals the importance of the position and movement of the confluence line with respect to the basin, on
which the intensity and the raising period of the resulting flood depend. 相似文献
254.
干旱、半干旱区域降水趋势可预报期限的初步研究 总被引:1,自引:0,他引:1
应用中国西北和美洲大陆中部干旱、半干旱区域7个长记录站的月降水量记录,分析了降水趋势的可预报期限问题。结果表明:月降水量标准化系数序列的可预报尺度为3个月左右。将该序列进行差分运算后,误差倍增时间会显著加长。 相似文献
255.
256.
1995年3月19日,新疆和硕县那音克乡发生Ms5.0级地震。震前,乌鲁木齐地区地下水中溶解气体Ar、CH4、CO2、H2S等和库尔勒地区的断层气Rn相继出现明显的异常。异常具有短期临震性质,主要表现为短期趋势升高,临震突跳。 相似文献
257.
258.
A synoptic climatology is developed for Virginia using 21 years of late spring and summer surface and upper air observations. The climatology is produced by applying a combination of principal components analysis and cluster analysis such that each day is classified into one of a distinct number of synoptic situations. Days on which at least one severe storm occurred in Virginia are merged with the synoptic climatology. A majority of severe storms are associated with one synoptic situation distinguished by moderate instability and a high moisture content. 相似文献
259.
亚热带马尾松人工林的降雨截留作用 总被引:8,自引:0,他引:8
本文通过分别实测降雨过程中林外降雨、林内降雨及树干截流的变化,分析了不同降雨量、降雨持续时间、前期降雨等因素的影响,讨论了马尾松人工林地内雨量分布的变化特点,并提出了计算模式。统计分析结果表明,林内雨和树干流只有当降雨分别到达1.6mm和4.32mm的情况下才出现,其总量分别占林外降雨的75%和4.3%,并以面源和点源的形式输入流域。此外,还阐述了降雨过程中林地内营养元素的输入及循环过程的特点。 相似文献
260.
P. I. A. Kinnell 《地球表面变化过程与地形》2006,31(3):355-367
Rain‐impacted flows dominate sheet and interrill erosion and are important in eroding soil rich in nutrients and other chemicals which may have deleterious effects on water quality. Erosion in rain‐impacted flow is associated with raindrop detachment followed by transport either by the combination of flow velocity and raindrop impact (raindrop‐induced flow transport, RIFT) or the inherent capacity of the flow to transport detached material. Coarse particles tend to be transported by RIFT, while fine particles tend to be transported without any assistance from raindrop impact. Because the transport process associated with coarse particles is not 100 per cent efficient, it generates a layer of loose particles on the soil surface and this layer protects the underlying soil from detachment. Simulations were performed by modelling the uplift and downstream movement of both fine and coarse particles detached from the soil surface by individual raindrop impacts starting with a surface where no loose material was present. The simulations produced a flush of fine material followed by a decline in the discharge of fine material as the amount of loose material built up on the bed. The decline in the discharge of fine material was accompanied by an increase in the discharge of coarse material. The relative amounts of coarse and fine material discharged in the flow varied with flow velocity and cohesion in the surface of the soil matrix. The results indicate that the discharge of various sized sediments is highly dependent on local soil, rain and flow conditions and that extrapolating the results from one situation to another may not be appropriate. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献