首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   1938篇
  免费   334篇
  国内免费   145篇
测绘学   21篇
大气科学   49篇
地球物理   771篇
地质学   697篇
海洋学   646篇
综合类   49篇
自然地理   184篇
  2024年   4篇
  2023年   49篇
  2022年   46篇
  2021年   53篇
  2020年   67篇
  2019年   82篇
  2018年   69篇
  2017年   156篇
  2016年   107篇
  2015年   96篇
  2014年   110篇
  2013年   129篇
  2012年   117篇
  2011年   132篇
  2010年   146篇
  2009年   104篇
  2008年   95篇
  2007年   143篇
  2006年   105篇
  2005年   99篇
  2004年   61篇
  2003年   51篇
  2002年   44篇
  2001年   35篇
  2000年   39篇
  1999年   44篇
  1998年   36篇
  1997年   35篇
  1996年   42篇
  1995年   24篇
  1994年   19篇
  1993年   13篇
  1992年   21篇
  1991年   6篇
  1990年   8篇
  1989年   7篇
  1988年   2篇
  1987年   2篇
  1986年   1篇
  1985年   8篇
  1984年   3篇
  1983年   3篇
  1982年   2篇
  1978年   1篇
  1954年   1篇
排序方式: 共有2417条查询结果,搜索用时 15 毫秒
81.
This paper proposes a new methodological approach to silted reservoir management and defence, which combines the reservoir rehabilitation process and the utilization of the recovered water volumes and sediments. This approach, strategic from both the economical and environmental points of view, is here defined as Economic Environmental Defence (EED) of a reservoir. The EED approach is applied to the case study of Guardialfiera reservoir, where the available experimental data allowed the estimation of silta-tion up to date, the analysis of the distribution of sediment particle size along the reservoir bottom and the possibility to propose a feasible utilization of water and sediments resulting from the reservoir rehabilitation.  相似文献   
82.
Suspended matter is an important indicator of water quality in freshwater systems. The flood‐induced turbidity current plays a dominant role in the seasonal dynamic of suspended matter in the Liuxihe Reservoir (23°45′50″N; 113°46′52″E), a large, stratified reservoir at the Tropic of Cancer in southern China. Field measurements show that loading and distribution of suspended matter in the reservoir differ in typical wet, dry and medium years, as a result of different discharge volumes and water level variation patterns. Using historical data and the practical demand for water supply and flood control, we generalized two feasible reservoir operational modes: flood impounding mode (drawing down the reservoir to a low level before flood events to impound inflow during the flooding season) and moderate level change mode (drawing down the reservoir to a moderate level before flood events, then keeping the level within the flood control level during runoff events). To examine the effects of different operational modes and outlet depths on the reservoir's flood‐induced turbidity current, a numerical simulation model was applied in three types of hydrological conditions. The results show that the mode with moderate drawdown and recharge processes can decrease loading of suspended matter in spring and promote turbidity current release during flood events, and upper withdrawal can improve the effects of turbid water release. We suggest that more attention should be focused on water quality management in the reservoir operation stage, severe artificial water level fluctuation being avoided and selective withdrawal becoming an optional management measure. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
83.
Participatory research in environmental and natural resources-related fields is premised on many of the same notions that underlie participatory processes in decision making. This study examines one instance of participatory research to assess the extent to which the documented benefits of participatory decision-making hold up in the context of research. A survey of Chilean shell-fishers engaged in research with marine biologists assesses the relationships between four variables: fishers’ participation in research, fishers’ opinions of biologists, fishers’ trust in biologists, and fishers’ acquisition of knowledge from biologists. Results illuminate the multidimensionality of these variables and suggest that complex interrelationships between them make the benefits of participatory research more nuanced than those reported for participatory decision-making. For instance, participatory research may provide low benefits when participatory research outcomes differ little from those produced solely by scientists. In addition, high-cost scenarios may result when outcomes of participatory research are inferior to those produced solely by scientists. A third downside may result when participation leads participants to increase their deference to scientific knowledge, thereby defeating the corroborative purpose of their participation. A fourth effect may occur when increased trust by in scientists results from participation, decreasing participants’ perceived need to take part in research.  相似文献   
84.
The emergence of export markets for high-value seafood products tends to produce a predictable pattern of serial depletion of resources and social disruption in coastal communities, a phenomenon described as ‘the tragedy of the commodity’. The sea cucumber trade epitomizes these challenges, with cases of rapid growth followed by fishery collapse documented across the Indo-Pacific and the majority of assessed stocks worldwide overexploited. Is this ‘boom-bust’ sequence inevitable? We examine three cases of resistance to the sea cucumber trade from Palau, Pohnpei, and Yap. Despite the overwhelming short-term financial incentives to export, fishers, youth, elected and traditional leaders, and civil society organizations coordinated to ban the trade at its peak, using public protest, court battles, and customary and statutory law. We show that, like the tragedy of the commons, Indigenous peoples and local communities can organize to resist the tragedy of the commodity. They do so by asserting Indigenous values, rights, and institutions, recommonizing the resource and preventing fisheries collapse. These cases challenge the inevitability of the tragedy of the commodity and the narrative of poor fishers as vulnerable and disempowered.  相似文献   
85.
In this paper, we focus on the status and trends of the current Korean fisheries management regime. Specifically, this paper briefly introduces the Korean conventional fisheries management regime (KCFMR) and discusses its problems and limitations. In describing policy evolution, this paper finds reasons why the Korean government has chosen a TAC system, an output control approach, besides input control approaches in force for almost a century. This paper also describes the evolution of the Korean TAC system, which is carrying out a pivotal role in Korean fisheries development, and analyzes problems of the Korean TAC system. Finally, this paper gives a perspective on expanding the Korean TAC system toward Output Control Systems (OCSs) such as Individual Quotas (IQs), Individual Vessel Quotas (IVQs), Individual Transferable Traps (ITTs), Community Quotas (CQs), and Individual Transferable Quotas (ITQs).  相似文献   
86.
1 IntroductionHuman activitieshavebeen stronglyaffecting theworld river sedimentsupply to the oceans since the19thor20thcentury(StanleyandW arne,1993;Fanos,1995;Sm ithandW inkley,1996;Stanley,1996;Yang,Shi,etal.,2004;Yang,Zhao,etal.,2002).Thesedi-m enttra…  相似文献   
87.
88.
89.
90.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号