全文获取类型
收费全文 | 17188篇 |
免费 | 1395篇 |
国内免费 | 1088篇 |
专业分类
测绘学 | 4400篇 |
大气科学 | 1106篇 |
地球物理 | 1809篇 |
地质学 | 3119篇 |
海洋学 | 1870篇 |
天文学 | 40篇 |
综合类 | 1561篇 |
自然地理 | 5766篇 |
出版年
2024年 | 43篇 |
2023年 | 115篇 |
2022年 | 589篇 |
2021年 | 702篇 |
2020年 | 708篇 |
2019年 | 680篇 |
2018年 | 592篇 |
2017年 | 911篇 |
2016年 | 810篇 |
2015年 | 867篇 |
2014年 | 942篇 |
2013年 | 1326篇 |
2012年 | 1109篇 |
2011年 | 1111篇 |
2010年 | 815篇 |
2009年 | 868篇 |
2008年 | 924篇 |
2007年 | 1036篇 |
2006年 | 980篇 |
2005年 | 806篇 |
2004年 | 740篇 |
2003年 | 566篇 |
2002年 | 523篇 |
2001年 | 383篇 |
2000年 | 304篇 |
1999年 | 268篇 |
1998年 | 183篇 |
1997年 | 159篇 |
1996年 | 103篇 |
1995年 | 91篇 |
1994年 | 83篇 |
1993年 | 59篇 |
1992年 | 60篇 |
1991年 | 32篇 |
1990年 | 35篇 |
1989年 | 23篇 |
1988年 | 25篇 |
1987年 | 18篇 |
1986年 | 13篇 |
1985年 | 27篇 |
1984年 | 18篇 |
1983年 | 9篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1971年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
Emma L. Jackson Martin J. Attrill Malcolm B. Jones 《Estuarine, Coastal and Shelf Science》2006,68(3-4):421
Recent research and management plans for seagrass habitats have called for landscape level approaches. The present study examines the spatial utilisation of subtidal seagrass beds by fish and decapods around the coast of Jersey (49°N 02° W). A hierarchical scale of landscape configuration and the plant characteristics of eight seagrass beds were measured and the contributions of these variables as predictors of the properties of the fish and decapod assemblages were evaluated using multiple linear regression models. The results indicated that total diversity had a negative relationship with transect heterogeneity and total species number had a weak negative association with increasing fragmentation. Both total diversity and total species number showed a positive relationship with depth. In fact, in all models of species number and densities, values were higher in deeper seagrass beds. Total decapod density increased with aggregation of seagrass patches within a landscape. In addition to landscape configuration, smaller-scale structural changes in both canopy height and epiphyte load appeared to influence densities of decapod crustaceans. At night, fewer patterns could be explained by the independent variables in the model. 相似文献
102.
103.
104.
105.
106.
107.
ABSTRACT Environmental sustainability and the long-term wellbeing of Māori (the indigenous people of New Zealand) are interdependent and degradation of landscapes risks the progressive degradation of Māori wellbeing. The present study developed an analysis framework based on Ki Uta Ki Tai (holistic-mountains to the sea- management philosophy advocated by Ngāi Tahu) for exploring relationships between landcover and Māori values to enable predictions of cultural values through space and time. We used this framework to predict how two Māori values (Overall Health and Cultural Land Use) have been altered as a result of landcover change between 2001–2012 in three Canterbury catchments. The area of native vegetation declined while exotic pasture increased between 2001–2012, and there were corresponding declines in both cultural health scores. These results suggest that the change in landcover has reduced the ability of the landscape to support Māori values. This framework for assessing changes in Māori values with respect to changing environmental conditions may identify opportunities for Māori to better engage in land use management decisions. 相似文献
108.
探讨了windows编程环境下,编绘软件的网络实现方法。通过对WinSock编程方法的讨论,表明了编绘软件电子图板实现网络化编辑的可行性。 相似文献
109.
110.
Viability theory for an ecosystem approach to fisheries 总被引:1,自引:1,他引:1