全文获取类型
收费全文 | 37109篇 |
免费 | 293篇 |
国内免费 | 212篇 |
专业分类
测绘学 | 721篇 |
大气科学 | 1705篇 |
地球物理 | 7046篇 |
地质学 | 14627篇 |
海洋学 | 3529篇 |
天文学 | 8792篇 |
综合类 | 98篇 |
自然地理 | 1096篇 |
出版年
2022年 | 487篇 |
2021年 | 705篇 |
2020年 | 754篇 |
2019年 | 826篇 |
2018年 | 1696篇 |
2017年 | 1544篇 |
2016年 | 1637篇 |
2015年 | 614篇 |
2014年 | 1414篇 |
2013年 | 2035篇 |
2012年 | 1619篇 |
2011年 | 1898篇 |
2010年 | 1790篇 |
2009年 | 1986篇 |
2008年 | 1766篇 |
2007年 | 1978篇 |
2006年 | 1737篇 |
2005年 | 898篇 |
2004年 | 815篇 |
2003年 | 808篇 |
2002年 | 741篇 |
2001年 | 764篇 |
2000年 | 630篇 |
1999年 | 416篇 |
1998年 | 436篇 |
1997年 | 474篇 |
1996年 | 336篇 |
1995年 | 357篇 |
1994年 | 335篇 |
1993年 | 281篇 |
1992年 | 284篇 |
1991年 | 290篇 |
1990年 | 337篇 |
1989年 | 272篇 |
1988年 | 258篇 |
1987年 | 260篇 |
1986年 | 191篇 |
1985年 | 301篇 |
1984年 | 302篇 |
1983年 | 295篇 |
1982年 | 274篇 |
1981年 | 248篇 |
1980年 | 265篇 |
1979年 | 203篇 |
1978年 | 242篇 |
1977年 | 204篇 |
1976年 | 177篇 |
1975年 | 184篇 |
1974年 | 171篇 |
1973年 | 206篇 |
排序方式: 共有10000条查询结果,搜索用时 562 毫秒
761.
762.
763.
764.
J. C. Kurtz N. D. Detenbeck V. D. Engle K. Ho L. M. Smith S. J. Jordan D. Campbell 《Estuaries and Coasts》2006,29(1):107-123
Coastal ecosystems are ecologically and commercially valuable, productive habitats that are experiencing escalating compromises
of their structural and functional integrity. The Clean Water Act (USC 1972) requires identification of impaired water bodies
and determination of the causes of impairment. Classification simplifies these determinations, because estuaries within a
class are more likely to respond similarly to particular stressors. We reviewed existing classification systems for their
applicability to grouping coastal marine and Great Lakes water bodies based on their responses to aquatic stressors, including
nutrients, toxic substances, suspended sediments, habitat alteration, and combinations of stressors. Classification research
historically addressed terrestrial and freshwater habitats rather than coastal habitats. Few efforts focused on stressor response,
although many well-researched classification frameworks provide information pertinent to stressor response. Early coastal
classifications relied on physical and hydrological properties, including geomorphology, general circulation patterns, and
salinity. More recent classifications sort ecosystems into a few broad types and may integrate physical and biological factors.
Among current efforts are those designed for conservation of sensitive habitats based on ecological processes that support
patterns of biological diversity. Physical factors, including freshwater inflow, residence time, and flushing rates, affect
sensitivity to stressors. Biological factors, such as primary production, grazing rates, and mineral cycling, also need to
be considered in classification. We evaluate each existing classification system with respect to objectives, defining factors,
extent of spatial and temporal applicability, existing sources of data, and relevance to aquatic stressors. We also consider
classification methods in a generic sense and discuss their strengths and weaknesses for our purposes. Although few existing
classifications are based on responses to stressors, may well-researched paradigms provide important information for improving
our capabilities for classification, as an investigative and predictive management tool. 相似文献
765.
766.
767.
768.
769.
Analyzing the tables and probability maps posted by Yan Y. Kagan and David D. Jackson in April 2002–September 2004 at http://scec.ess.ucla.edu/~ykagan/predictions_index.html and the catalog of earthquakes for the same period, the conclusion is drawn that the underlying method could be used for prediction of aftershocks, while it does not outscore random guessing when main shocks are considered. 相似文献