全文获取类型
收费全文 | 11126篇 |
免费 | 1525篇 |
国内免费 | 1316篇 |
专业分类
测绘学 | 1828篇 |
大气科学 | 797篇 |
地球物理 | 1222篇 |
地质学 | 4803篇 |
海洋学 | 1440篇 |
天文学 | 23篇 |
综合类 | 1128篇 |
自然地理 | 2726篇 |
出版年
2024年 | 27篇 |
2023年 | 94篇 |
2022年 | 254篇 |
2021年 | 363篇 |
2020年 | 378篇 |
2019年 | 374篇 |
2018年 | 288篇 |
2017年 | 505篇 |
2016年 | 408篇 |
2015年 | 493篇 |
2014年 | 673篇 |
2013年 | 778篇 |
2012年 | 628篇 |
2011年 | 713篇 |
2010年 | 652篇 |
2009年 | 684篇 |
2008年 | 686篇 |
2007年 | 701篇 |
2006年 | 753篇 |
2005年 | 608篇 |
2004年 | 529篇 |
2003年 | 489篇 |
2002年 | 515篇 |
2001年 | 448篇 |
2000年 | 374篇 |
1999年 | 352篇 |
1998年 | 246篇 |
1997年 | 206篇 |
1996年 | 134篇 |
1995年 | 135篇 |
1994年 | 106篇 |
1993年 | 87篇 |
1992年 | 64篇 |
1991年 | 45篇 |
1990年 | 32篇 |
1989年 | 29篇 |
1988年 | 31篇 |
1987年 | 20篇 |
1986年 | 17篇 |
1985年 | 13篇 |
1984年 | 12篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1971年 | 2篇 |
1954年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 437 毫秒
71.
72.
Catch-quota balancing in multispecies individual fishing quotas 总被引:2,自引:1,他引:2
Individual fishery quotas (IFQs) are an increasingly prevalent form of fishery management around the world, with more than 170 species currently managed with IFQs. Yet, because of the difficulties in matching quota holdings with catches, many argue that IFQs are not appropriate for multispecies fisheries. Using on-the-ground-experience with multispecies IFQ fisheries in Iceland, New Zealand, Australia, and Canada, we assess the design and use of catch-quota balancing mechanisms. Our methodology includes a mix of interviews with fishery managers, industry representatives, and brokers, literature review, and data analysis. We find that a combination of incentives and limits on use rates for the mechanisms provide sufficient flexibility to the quota owner without the fishery manager incurring excessive levels of overexploitation risk. Contrary to some opinions, these programs are evidence that it is possible to implement IFQ programs for multispecies fisheries and that they can be profitable and sustainable. 相似文献
73.
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
74.
75.
76.
77.
78.
79.
80.
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