全文获取类型
收费全文 | 259篇 |
免费 | 16篇 |
国内免费 | 7篇 |
专业分类
测绘学 | 4篇 |
大气科学 | 28篇 |
地球物理 | 52篇 |
地质学 | 94篇 |
海洋学 | 16篇 |
天文学 | 52篇 |
自然地理 | 36篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 3篇 |
2020年 | 8篇 |
2019年 | 7篇 |
2018年 | 17篇 |
2017年 | 12篇 |
2016年 | 10篇 |
2015年 | 4篇 |
2014年 | 8篇 |
2013年 | 12篇 |
2012年 | 5篇 |
2011年 | 14篇 |
2010年 | 18篇 |
2009年 | 14篇 |
2008年 | 8篇 |
2007年 | 10篇 |
2006年 | 6篇 |
2005年 | 6篇 |
2004年 | 7篇 |
2003年 | 14篇 |
2002年 | 11篇 |
2001年 | 10篇 |
2000年 | 8篇 |
1999年 | 8篇 |
1998年 | 2篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 3篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1989年 | 3篇 |
1986年 | 2篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 3篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1966年 | 2篇 |
排序方式: 共有282条查询结果,搜索用时 15 毫秒
281.
We analyzed interannual variability in a long-term record of chlorophyll concentration and phytoplankton species composition
in the Rhode River, Maryland (USA). Over the approximately 30-year record, there was no long-term monotonic trend in phytoplankton
chlorophyll concentration, though temporary directional trends related to precipitation patterns sometimes persisted for a
decade before reversing. From counts on preserved samples, we estimated the dominance by different pigment-bearing groups
and size classes. Diatoms, dinoflagellates, and cryptophytes comprised about 80–97% of the annual averaged class-specific
biovolume. Cryptophytes dominated the first 2 years in the data set but displayed a long-term decline, after which diatoms
dominated in all but four consecutive years in which there were large dinoflagellate blooms. There was a long-term increase
in cells with equivalent spherical diameters from 4 to 10 μm, accompanied by declines in the proportion of cells in the 2-
to 4- and 10- to 20-μm size classes. The main cause of these changes in size classes was a long-term increase in Chroomonas sp. and Apedinella radians and long-term decline in Microcystis sp. and an unidentified cryptophyte, respectively. These taxa were cosmopolitan in their seasonal and spatial distributions,
and hence the long-term changes in taxa did not conform well with conceptual models based on succession of “life-forms.” The
segregation of diatoms and dinoflagellates expected on the basis of “life-forms” applied to seasonal and spatial patterns.
Characterizing the phytoplankton community in terms of diversity, size, and class-specific biovolume gave results that were
consistent with one another and added insight to the broad-scale changes in chlorophyll concentration. Subtle changes in the
size distribution of cryptophytes were not apparent from biovolume measures and would not have been apparent without microscopy.
Though causes of such shifts may be difficult to identify, identifying the causes and predicting potential consequences cannot
even be attempted without awareness of the phenomena. 相似文献
282.