全文获取类型
收费全文 | 5506篇 |
免费 | 533篇 |
国内免费 | 309篇 |
专业分类
测绘学 | 1049篇 |
大气科学 | 297篇 |
地球物理 | 803篇 |
地质学 | 1404篇 |
海洋学 | 1414篇 |
天文学 | 12篇 |
综合类 | 485篇 |
自然地理 | 884篇 |
出版年
2024年 | 12篇 |
2023年 | 20篇 |
2022年 | 77篇 |
2021年 | 131篇 |
2020年 | 160篇 |
2019年 | 163篇 |
2018年 | 136篇 |
2017年 | 290篇 |
2016年 | 206篇 |
2015年 | 252篇 |
2014年 | 317篇 |
2013年 | 403篇 |
2012年 | 316篇 |
2011年 | 352篇 |
2010年 | 331篇 |
2009年 | 318篇 |
2008年 | 370篇 |
2007年 | 366篇 |
2006年 | 353篇 |
2005年 | 289篇 |
2004年 | 249篇 |
2003年 | 178篇 |
2002年 | 196篇 |
2001年 | 157篇 |
2000年 | 123篇 |
1999年 | 138篇 |
1998年 | 79篇 |
1997年 | 79篇 |
1996年 | 48篇 |
1995年 | 48篇 |
1994年 | 36篇 |
1993年 | 31篇 |
1992年 | 18篇 |
1991年 | 13篇 |
1990年 | 15篇 |
1989年 | 11篇 |
1988年 | 16篇 |
1987年 | 10篇 |
1986年 | 5篇 |
1985年 | 12篇 |
1984年 | 12篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 1篇 |
1971年 | 1篇 |
排序方式: 共有6348条查询结果,搜索用时 156 毫秒
41.
42.
Managing marine fisheries using output controls in the form of individual transferable quotas (ITQs) can be an attractive alternative to more traditional input controls. There are now a number of examples of where ITQ-managed fisheries have been able to reduce the impact of the major management problems in global fisheries, namely, gross over-capitalisation and effort. However, ITQs are not the perfect management tool and one of the lesser known consequences of ITQ-managed fisheries where ITQs consist of a harvest right is the implicit relationship between ITQ property rights and rights of access to the fishing grounds. This implicit spatial right to the grounds can provide obstacles in the way of allocating water-space within fishing grounds for alternative uses such as marine-protected areas, large-scale aquaculture, and wind farms. These lesser-known consequences of ITQ-managed fisheries are discussed here. 相似文献
43.
An inherent tension exists between legal approaches to nature conservation and fisheries management in the European Union, as the former remains the remit of Member States while the latter is under the exclusive legislative jurisdiction of the European Community (EC). This tension is of particular importance when addressing the conservation of habitats or species that are under threat from fishing activities. This article examines recent developments in offshore marine conservation in the North-East Atlantic in light of the legislative developments and political frameworks that are currently evolving. By analysing the emergency closure of the Darwin Mounds area of cold-water corals and the UK pair-trawl ban, it becomes evident that the precautionary principle is a key factor in the tension between fisheries management and marine nature conservation, and is not always taken into account. 相似文献
44.
本文阐述了东亚海区海岸带综合管理实践如何从地方性的示范发展到区域性的合作管理框架,如何实现海洋和海岸带资源的可持续利用.文中着重突出了厦门市政府在维持环境保护和经济发展的平衡,启动和实施海岸带综合管理,以及与沿海国在国际合作方面的经验,总结了厦门实施海岸带综合管理的主要经验,包括多部门间综合协调机制、海岸带综合管理法律框架、科技支撑体系的建立,海洋功能区划、环境剖面和战略环境管理计划的制定,以及实现海上联合执法等等.同时阐述了东亚海域环境管理区域合作计划(PEMSEA)与澳大利亚合作伙伴之间的关系在推动沿海城市的国际合作中将起到的作用. 相似文献
45.
46.
47.
A bottom longline fishery operated in the EEZ of New Caledonia from 1988 to 1991. Fishing focused on five seamounts with summits at depths ranging from 500 to 750 m. The target species was alfonsino, Beryx splendens. As the soundings available from marine charts were not detailed enough, the fishing masters had to make their own charts in order to set the gear in the right location. A series of 11 scientific cruises devoted to a research program on alfonsino was launched in late 1991. During the first scientific cruises, several days were spent mapping the seabed to improve the existing knowledge of the topography of three seamounts by coupling the EDO echosounder depth measurements to the GPS positions. As this procedure is slow, it is applicable to limited areas or, if a wider grid is used, to large zones to locate major structures such as ridges and seamounts. The emergence of the multibeam echosounder has greatly improved seabed mapping performance. This tool seems to fit the requirement of exploratory deep-bottom fishing particularly well, as it covers large areas while providing details of the bottom. The EM 12 was used to obtain bathymetry and imagery of the SE portion of the EEZ of New Caledonia, covering an approximate area of 70,000 km2 in two weeks. For depths ranging from 500 to 4,500 m, the results were impressive. They confirmed the known major features and provided greater topographical detail, revealing fine unknown structures. They also provided information on the type of substratum, information which might influence the fishing strategy. Finally, they made it possible to obtain an accurate estimate of the exploitable area which in turn led to new stock estimates. 相似文献
48.
Being a littoral state, Malaysian maritime sectors provide the basis for the growth and development of marine-related activities. As the country enters the new millennium along with the ‘2020 Vision’ which serves as the basic template against which the economic performance of these sectors should be judged, it poses a new challenge for Malaysia in developing these sectors. This paper attempts to address three basic issues: Firstly, is there any national ocean policy in place? Secondly, are the maritime sectors adequately organized to play an important role in achieving the objectives? Thirdly, what are the opportunities available in developing the ocean?It can be seen that existing policies to develop comprehensive ocean governance have not received the full attention they deserve. Organizational structures governing the ocean for implementing national policies are well in place but in a fragmented and uncoordinated fashion. As a result, sectoral and intersectoral management problems were created such as multiple-use conflicts, overlapping of jurisdiction and duplication of efforts. Environmental problems have also not been properly addressed. A few sectors have been identified as offering opportunities to further develop the Malaysian maritime areas. Among these are marine education and human resources development, marine tourism and the seafood industry. 相似文献
49.
50.