全文获取类型
收费全文 | 274篇 |
免费 | 14篇 |
国内免费 | 31篇 |
专业分类
测绘学 | 14篇 |
大气科学 | 16篇 |
地球物理 | 38篇 |
地质学 | 113篇 |
海洋学 | 26篇 |
天文学 | 61篇 |
综合类 | 7篇 |
自然地理 | 44篇 |
出版年
2023年 | 3篇 |
2022年 | 6篇 |
2021年 | 4篇 |
2020年 | 4篇 |
2019年 | 6篇 |
2018年 | 16篇 |
2017年 | 9篇 |
2016年 | 5篇 |
2015年 | 9篇 |
2014年 | 8篇 |
2013年 | 17篇 |
2012年 | 17篇 |
2011年 | 16篇 |
2010年 | 11篇 |
2009年 | 23篇 |
2008年 | 17篇 |
2007年 | 24篇 |
2006年 | 5篇 |
2005年 | 17篇 |
2004年 | 5篇 |
2003年 | 6篇 |
2002年 | 4篇 |
2001年 | 4篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 8篇 |
1996年 | 3篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1988年 | 2篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 5篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1971年 | 1篇 |
1970年 | 2篇 |
1969年 | 1篇 |
排序方式: 共有319条查询结果,搜索用时 31 毫秒
1.
2.
3.
Surface currents influenced by a wind-driven upwelling event in San Pedro Bay moved total suspended matter (TSM) confined
to the inner shelf on 19 April 1978 seaward, so that by 27 April surface TSM had increased over the outer shelf. Near-bottom
concentrations of TSM also increased across the shelf during this time. This is explained by sediment resuspended by large
surface waves being advected from the inner shelf seaward by the mean flow after this flow had turned from southeasterly to
southerly when upwelling ceased on 26 April. These complex shelf dynamics contribute to the off-shelf transport of mud to
the slope and deep basins. 相似文献
4.
Theoretical and laboratory results indicate that bottom velocities within shoaling internal gravity waves intensify upslope approximately inversely proportional to the water depth. The elevated velocities (and bottom stresses) caused by shoaling and, possibly, breaking internal waves might explain the generation and maintenance of near-bottom nepheloid zones and attached turbid plumes that have been observed over certain continental shelves and slopes. This process is proposed as an explanation of zones of relatively low transmissibility that emanate from the upper continental slope near Newport submarine canyon off southern California. 相似文献
5.
Pilar Drake Alberto M. Arias Francisco Baldó José A. Cuesta Antonio Rodríguez Alfonso Silva-Garcia Ignacio Sobrino Diego García-González Carlos Fernández-Delgado 《Estuaries and Coasts》2002,25(3):451-468
The aquatic macrofauna of the Guadalquivir estuary were sampled (1 mm mesh persiana net) at 5 sampling sites located along the entire (except the tidal freshwater region) estuarine gradient of salinity (outer 50 km). A total of 134 fish and macroinvertebrate species was collected but only 62 were considered common or regularly present in the estuary. Univariate measures of the community structure showed statistically significant differences among sampling sites: species richness, abundance, and biomass decreased in the upstream direction, being positively correlated with the salinity. Temporal differences of these three variables were also statistically significant. While a clear seasonal pattern (minimum densities in winter and maximum in spring-summer) was observed for abundance and biomass, no such pattern existed for the number of species. Mysids was the most dominant group throughout the estuary (96% to 99% of abundance; 49% to 85% of biomass), although fish biomass was also important at the outer estuary (36% to 38%). Multivariate analyses indicated highly significant spatial variation in the macrofaunal communities observed along the salinity gradient. These analyses suggest that the underlying structure was a continuum with more or less overlapping distributions of the species dependent on their ability to tolerate different physicochemical conditions. There were also significant temporal (intermonthly + interannual) variation of the estuarine community; the relative multivariate dispersion indicated that monthly variation was more considerable (relative multivariate dispersion >1) at the outer part of the estuary during the wet year (last 20 km) and was higher in the inner stations during the dry year (32 to 50 km from the river mouth). Since a clear negative exponential relationship was observed between the freshwater input (from a dam located 110 km upstream) and water salinity at all sampling stations, it is concluded that the human freshwater management is probably affecting the studied estuarine communities. While the higher seasonal (long-term) stability of the salinity gradient, due to the human control of the freshwater input, may facilitate the recruitment of marine species juveniles during the meteorologically unstable early-spring, the additional (short-term) salinity fluctuations during the warm period may negatively affect species that complete their lifecycle within the estuary. 相似文献
6.
7.
8.
9.
10.
通过内蒙古地区近46 a降水和潜在蒸散量以及湿润度在气温突变前后的倾向率和差值变化分析,得出该区域主要植被类型干湿环境演变的时空变化特征。研究结果表明:降水在气温突变前“东增西减”,突变后呈相反的变化趋势。46 a降水倾向率增加区域主要集中在呼伦贝尔市东部和乌兰察布市以西大部地区;潜在蒸散量在气温突变前呈减少趋势,突变后有增加趋势,突变后潜在蒸散量明显小于突变前。内蒙古46 a潜在蒸散量倾向率大部地区偏小,偏大区域仅存在于中东部偏北地区,气温突变后全区大部地区存在明显的“蒸发悖论”;大兴安岭西麓和乌兰察布市以西地区突变后湿润度增加明显,暖湿的气候环境有利于当地植被建设和生态恢复,内蒙古东南部、呼伦贝尔草原和锡林郭勒盟草原区有暖干化趋势,上述草原区存在潜在退化风险。 相似文献