全文获取类型
收费全文 | 1055篇 |
免费 | 89篇 |
国内免费 | 87篇 |
专业分类
测绘学 | 54篇 |
大气科学 | 91篇 |
地球物理 | 133篇 |
地质学 | 239篇 |
海洋学 | 203篇 |
天文学 | 1篇 |
综合类 | 59篇 |
自然地理 | 451篇 |
出版年
2024年 | 1篇 |
2023年 | 14篇 |
2022年 | 26篇 |
2021年 | 42篇 |
2020年 | 45篇 |
2019年 | 33篇 |
2018年 | 30篇 |
2017年 | 70篇 |
2016年 | 53篇 |
2015年 | 39篇 |
2014年 | 66篇 |
2013年 | 91篇 |
2012年 | 38篇 |
2011年 | 57篇 |
2010年 | 53篇 |
2009年 | 36篇 |
2008年 | 66篇 |
2007年 | 62篇 |
2006年 | 54篇 |
2005年 | 40篇 |
2004年 | 39篇 |
2003年 | 43篇 |
2002年 | 34篇 |
2001年 | 29篇 |
2000年 | 32篇 |
1999年 | 24篇 |
1998年 | 21篇 |
1997年 | 19篇 |
1996年 | 11篇 |
1995年 | 18篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 2篇 |
排序方式: 共有1231条查询结果,搜索用时 15 毫秒
71.
Hoffmann TC 《Marine pollution bulletin》2002,44(11):1281-1293
This research focuses on coral reef health in the South Pacific region, an area of high global coral diversity. Coral reef health surrounding four island case studies in the Cook Islands and Fiji have been assessed in areas that have not been previously surveyed. This study compares four islands with barrier and fringing reefs that have different levels of economic development, population pressure, land-use practices, and marine management practices. This interdisciplinary research methodology includes both ecological and social data collection to further understanding of human environment interactions. In comparing the reefs with different socio-economic factors, this research shows that reefs with traditional systems of resources management are healthier, population pressure is not the main factor causing the demise of the reefs and agro-industry is the main industry causing the degradation of the reef in these four South Pacific Islands. In addition, researchers need to use a whole reef perspective to examine coral reef health. 相似文献
72.
73.
The use of riparian vegetated filter strips to reduce river sediment loads: an overestimated control measure? 总被引:1,自引:0,他引:1
The spatially distributed soil erosion and sediment delivery model WATEM/SEDEM was used to simulate the impact of riparian vegetated filter strips (RVFSs) on river sediment delivery at different spatial scales. For a field plot with a straight slope, sediment reduction by the RVFSs is comparable to results obtained through experimental set‐ups elsewhere (i.e. >70%). However, at the scale of an entire catchment, sediment reduction is much less (i.e. ±20%) due to (1) overland flow convergence, which reduces the sediment trapping efficiency of an RVFS, and (2) because part of the sediment bypasses the RVFSs through ditches, sewers and road surfaces. These results suggest that, at the catchment scale, RVFSs should be accompanied with other conservation techniques that are more appropriate for reducing river sediment loads, and that also reduce on‐site soil erosion. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
74.
75.
1 Introduction The mean meridional circulation plays an important role in the transportation and balance of heat, momen- tum, vortex and vapor between different latitudes. According to the data analysis, there are three circula- tions from the equator to the polar area: the Hadley circulation, a heat-driven circulation which rises around the equator and sinks at a certain latitude; the subpolar circulation, another heat-driven circulation around the polar area; and the Ferrel circulation, an i… 相似文献
76.
Conservation and community in the new South Africa: A case study of the Mahushe Shongwe Game Reserve 总被引:1,自引:0,他引:1
Brian H. King 《Geoforum》2007,38(1):207-219
The idealization of natural landscapes and peoples during colonialism, coupled with the popularity of sustainable development in the postcolonial era, has contributed to the expansion of conservation planning throughout the African continent. Concerns surrounding the promotion of national and international conservation agendas at the expense of local livelihood needs have generated interest in community conservation projects that attempt to include local participation and knowledge in natural resource management. The early excitement associated with community conservation has waned in light of recent assessments that it has been unsuccessful in meeting its ecological and social goals. This parallels other research that suggests communities are understood in generic or homogenous ways that influence how these initiatives are understood. Using a case study of the Mahushe Shongwe Game Reserve, this paper evaluates how rural households access environmental and economic resources to produce livelihoods, and how these access patterns impact their views of the project. It is argued that there are significant livelihood variations within the community that shape the ways households engage with, and benefit from, conservation planning. Rather than strictly viewing Mahushe Shongwe as a constraint to environmental resource access or site for limited employment, community members identify a number of benefits from its existence including education and development opportunities. Additionally, transformations in governance systems in the region impact community views of the project since younger residents are less likely to engage with the Matsamo Tribal Authority, which participates in managing the reserve. The consequence is that conservation has various impacts and meanings within a specific community that remain tied to the livelihood and governance systems being renegotiated in the post-apartheid era. 相似文献
77.
Analysis of the impact of conservation measures on stream flow regime in catchments of the Loess Plateau,China 总被引:3,自引:0,他引:3
Catchments in the Loess Plateau have been under the influence of human activities for centuries. In the last four decades, soil conservation measures have accelerated and intensified. These measures were designed to reduce soil erosion, improve agricultural productivity, and enhance environmental quality. It is important to evaluate the effects of these measures on hydrology in order to develop sustainable catchment management plans in the region. This study evaluated changes in stream flow data for four selected catchments in the Loess Plateau following large‐scale soil conservation measures. The non‐parametric Mann–Kendall test was used to identify trends in annual stream flow and the results showed significant downward trends in three of the four catchments. The Pettitt test indicated that a change point occurred in 1978 in these three catchments. Annual precipitation in all the catchments showed no significant trend during the period of record. Comparison of daily flow duration curves for two 20‐year periods (1957–1978) and (1979–2003) showed significant changes in stream flow regime. Reduction in most percentile flows varied between 20 and 45%, and the reduction in low flows was greatest. Overall, the reductions in daily flow were increasing with time, with significant changes occurring in the 1990s. However, it is not clear whether these catchments have seen the full effects of the soil conservation measures, so the results of this study might underestimate the final impact of soil conservation on stream flow regime. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
78.
刘红玉 《中国地理科学(英文版)》1998,8(3):281-288
Wetland,withveryhighbiologicalproductivity,tremendousresourcepotentialandenvironmentfunction,isaspecialecosystemintheearthan... 相似文献
79.
秦岭珍稀濒危植物资源的利用价值与保护 总被引:1,自引:0,他引:1
秦岭分布着国家保护的珍稀濒危植物42种,其中属国家一级保护1种,二级保护15种,三级保护26种.这些珍稀濒危植物在医药、木材、花卉、化工等方面具有较高的开发利用价值 相似文献
80.
Conflicts arise increasingly in Tanzania which involve claims in land located in conservation areas. These conflicts arise,
in many cases, between members of the local communities and the state authorities in charge of the conservation areas. They
concern customary land rights both of pastoral and of agricultural communities, a topic which also touches upon their identities.
The article investigates the legal dimension of these disputes by discussing the law governing conservation areas in the wider
context of land tenure legislation. Within this context, the legal framework of conservation areas is discussed from both
historical and contemporary perspectives. Nature conservation must respect the needs of the local population affected. It
is therefore argued that concepts of community-based conservation should be developed further to work towards the goal of
integrating nature conservation and the sustainable use of natural resources.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献