全文获取类型
收费全文 | 945篇 |
免费 | 195篇 |
国内免费 | 82篇 |
专业分类
测绘学 | 66篇 |
大气科学 | 16篇 |
地球物理 | 255篇 |
地质学 | 208篇 |
海洋学 | 291篇 |
天文学 | 5篇 |
综合类 | 59篇 |
自然地理 | 322篇 |
出版年
2024年 | 8篇 |
2023年 | 26篇 |
2022年 | 78篇 |
2021年 | 100篇 |
2020年 | 71篇 |
2019年 | 46篇 |
2018年 | 44篇 |
2017年 | 55篇 |
2016年 | 46篇 |
2015年 | 39篇 |
2014年 | 55篇 |
2013年 | 52篇 |
2012年 | 52篇 |
2011年 | 62篇 |
2010年 | 57篇 |
2009年 | 51篇 |
2008年 | 56篇 |
2007年 | 50篇 |
2006年 | 65篇 |
2005年 | 43篇 |
2004年 | 28篇 |
2003年 | 26篇 |
2002年 | 15篇 |
2001年 | 13篇 |
2000年 | 16篇 |
1999年 | 16篇 |
1998年 | 3篇 |
1997年 | 11篇 |
1996年 | 6篇 |
1995年 | 6篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1992年 | 9篇 |
1991年 | 1篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有1222条查询结果,搜索用时 468 毫秒
41.
42.
矿山地质环境问题治理是一项复杂的长期系统工程,本文以某矿区为例,简要阐述了矿山地质环境存在问题,有针对性地提出治理措施。经济建设同时,坚持生态优先、绿色发展道路,切实把绿色发展理念贯穿于矿山资源开发、利用、保护的全过程,全力推进矿山地质环境治理和生态修复工程。 相似文献
43.
44.
富营养化会导致浅水湖泊发生稳态转换,生态系统服务严重受损。磷是驱动湖泊发生稳态转换的重要环境因子,探究湖水磷浓度的变化规律是湖泊管理的关键。通过磷动力学模型,从影响湖水磷浓度的主要参数入手,探讨了每种参数变化对磷浓度的具体影响。结合前人研究结果,详细讨论了不同类型气候变化和人类活动对湖泊稳态转换时间、滞后时长、修复速率等的影响。研究认为,气候变化所导致的温度升高、光强减弱、风浪增强等和人类活动所导致的生物扰动、水位波动增强等因素变化虽不会改变湖泊稳态转换突变时间,但会推迟湖泊修复时间,造成突变阈值减小,滞后时间延长,稳态增大。在湖泊保护中要重点考虑主要外力驱动对湖泊稳态转换过程影响的区别,避免有害突变的发生。 相似文献
45.
矿山开采生产的生态保护与修复工作,涉及自然资源、生态环境、水利、林草等多部门,结合矿政管理工作实际,梳理了矿山生态保护修复资金类型,总结剖析了目前不同部门分头管理存在的问题,在此基础上,提出应整合各部门矿山生态保护修复方案及资金,形成管理合力,把生态保护修复工作贯穿到从地质勘查、矿山建设、开采、闭坑、管护的全过程,边开采边治理,整体保护,综合整治,系统修复。 相似文献
46.
为研究矿山开采及修复过程中如何开展生物多样性管理,本文借鉴IUCN(世界自然保护联盟)发布的《矿山生物多样性管理系列指南》成果,将相关理论和方法应用到广东大宝山矿生态修复实践中。文章在介绍IUCN的“综合生物多样性管理体系”方法主要内容的基础上,将其作为大宝山矿实施生态修复依据,阐述了该管理体系在矿山生态修复工程中的应用,并结合广东大宝山矿的实际情况,提出了大宝山矿生物多样性管理的保护与修复框架,包括全周期的生物多样性管理手段,重点阐述大宝山矿生物多样性调查与监测、评价、保护与受损控制及恢复的技术方案,最后分析了对中国矿山生物多样性保护和修复的启示,IUCN矿山生物多样性管理系列指南对于指导我国矿山生态修复具有重要作用。 相似文献
47.
48.
Being a key ecological security barrier and production base for grassland animal husbandry in China,the balance between grassland forage supply and livestock-carrying pressure in North China directly affects grassland degradation and restoration,thereby impacting grassland ecosystem services.This paper analyzes the spatiotemporal variation in grassland vegetation coverage,forage supply,and the balance between grassland forage supply and livestock-carrying pressure from 2000 to 2015 in North China.We then discuss the spatial pattern of grassland ecological conservation under the impacts of grassland degradation and restoration,and livestock-carrying pressure.Over the last 16 years,the total grassland area in North China decreased by about 16,000 km2,with vegetation coverage degraded by 6.7% of the grasslands but significantly restored by another 5.4% of grasslands.The provisioning of forage by natural grassland mainly increased over time,with an annual growth rate of approximately 0.3 kg/ha,but livestock-carrying pressure also increased continuously.The livestock-carrying pressure index without any supplementary feeding reached as high as 3.8.Apart from the potential livestock-carrying capacity in northeastern Inner Mongolia and the central Tibetan Plateau,most regions in North China are currently overloaded.Considering the actual supplementary feeding during the cold season,the livestock-carrying pressure index is about 3.1,with the livestock-carrying pressure mitigated in central and eastern Inner Mongolia.Assuming full supplementary feeding in the cold season,livestock-carrying pressure index will fall to 1.9,with the livestock-carrying pressure alleviated significantly in Inner Mongolia and on the Tibetan Plateau.Finally,we propose different conservation and development strategies to balance grassland ecological conservation and animal husbandry production in different regions of protected areas,pastoral areas,farming-pastoral ecotone,and farming areas,according to the grassland ecological protection patterns. 相似文献
49.
A. Vela V. Pasqualini V. Leoni A. Djelouli H. Langar G. Pergent C. Pergent-Martini L. Ferrat M. Ridha H. Djabou 《Estuarine, Coastal and Shelf Science》2008,79(4):591-598
Mapping marine biocenoses is an efficient method for providing useful data for the management and conservation of Mediterranean lagoons. Fused images from two satellites, SPOT 5 and IKONOS, were tested as management tools for identifying specific ecosystems in the El Bibane lagoon, situated in southern Tunisia near the Libyan border. The objectives of this study were to provide a precise map of the entire El Bibane lagoon using fused images from SPOT 5 and to compare fused images from SPOT 5 and IKONOS over a test-area. After applying a supervised classification, pixels are automatically classified in four classes: low seagrass cover, high seagrass cover, superficial mobile sediments and deep mobile sediments. The maps of the lagoon revealed and confirmed an extremely wide distribution of seagrass meadows within the lagoon (essentially Cymodocea nodosa; 19 546 ha) and a large area of mobile sediments more or less parallel to the shore (3 697 ha). A direct comparison of overall accuracy between SPOT 5 over the entire area, SPOT 5 over the test-area and IKONOS over the test-area revealed that these tools provided accurate mapping of the lagoon environment (83.25%, 85.91% and 73.41% accuracy, respectively). The SPOT 5 images provided greater overall accuracy than the IKONOS image, but did not take into account the heterogeneous spatial structure of the seagrasses and sediments present in the lagoon environment. Although IKONOS imagery provided lower overall accuracy than SPOT 5, it proved a very useful tool for the mapping of heterogeneous structures as it enabled the patchiness of formations to be better taken into account. The use of SPOT 5 and IKONOS fused images appears to be very promising for completing the mapping of lagoons in other regions and countries of the Mediterranean Sea. 相似文献
50.
Losses of pelagic diatom production resulting from silica limitation have not only been blamed for toxic algal blooms, but for the reduction in ability of coastal food webs to support higher trophic levels. Recent research has shown the importance of advective seepage water fluxes of dissolved silica (DSi) from freshwater marshes to pelagic waters during moments of riverine Si-limitation. In this study, we investigated the potential impact of recently installed new tidal areas along the Schelde estuary, located in former polder areas and characterized by so-called controlled reduced tidal regimes (CRT). Nine mass-balance studies were conducted in a newly constructed CRT in the freshwater Schelde estuary. During complete tidal cycles both DSi and amorphous silica (ASi) concentrations were monitored at the entrance culverts and in different habitats in the marsh. A swift DSi-delivery capacity was observed despite the shifted spatiotemporal frame of exchange processes compared to reference marshes. As silica-accumulating vegetation is not yet present, and difference with reference marshes’ deliveries is surprisingly small, we indicate diatomaceous debris and phytoliths to be the main silica source. Although further research is necessary on the driving forces of the different processes involved, restoration of former agricultural areas under CRT-regime provide the potential to buffer silica in the estuary. 相似文献