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   7200篇
  免费   739篇
  国内免费   532篇
测绘学   1343篇
大气科学   484篇
地球物理   1179篇
地质学   2074篇
海洋学   1632篇
天文学   22篇
综合类   568篇
自然地理   1169篇
  2024年   16篇
  2023年   44篇
  2022年   140篇
  2021年   199篇
  2020年   225篇
  2019年   235篇
  2018年   192篇
  2017年   343篇
  2016年   284篇
  2015年   316篇
  2014年   403篇
  2013年   497篇
  2012年   406篇
  2011年   488篇
  2010年   420篇
  2009年   451篇
  2008年   487篇
  2007年   515篇
  2006年   448篇
  2005年   384篇
  2004年   316篇
  2003年   250篇
  2002年   260篇
  2001年   207篇
  2000年   161篇
  1999年   171篇
  1998年   111篇
  1997年   114篇
  1996年   54篇
  1995年   77篇
  1994年   48篇
  1993年   42篇
  1992年   31篇
  1991年   22篇
  1990年   26篇
  1989年   18篇
  1988年   17篇
  1987年   11篇
  1986年   4篇
  1985年   9篇
  1984年   12篇
  1983年   8篇
  1982年   5篇
  1981年   1篇
  1980年   1篇
  1979年   1篇
  1971年   1篇
排序方式: 共有8471条查询结果,搜索用时 31 毫秒
101.
We propose a framework for enabling a systematic evaluation of a fisheries resource management system, which we define as a feed-back mechanism coupled to a fishery. The resource management system includes four basic functions: diagnostics, intervention, goal setting, and decision making. This model allows for the development of an evaluation framework for fisheries resource management by facilitating a typology of failures. We suggest that the potential for systemic and interdisciplinary learning will be significantly enhanced through the process of developing such a framework.  相似文献   
102.
This paper explores the application of the US Sea Grant model of applied research, extension, and education to two case studies in Latin America: Coastal Ecuador and the Gulf of Fonseca. The analysis is based on a series of meetings and roundtables with in-country partners and leaders of the US Sea Grant program. We conclude that the Sea Grant model provides an institutional structure that Latin America lacks and the model's features would improve governance of marine and coastal resources through more effective linkages between coastal communities, universities, and policy/decision makers at local, national, and international levels.  相似文献   
103.
104.
105.
INTRODUCTIONTheDenglouCape ,inthesouthwestoftheLeizhouPeninsula ,isatthenorthmarginoftropicalzone .SeveralresearchesandcartographiesoftheregionalgeomorphologyandQuater narygeology ,whichwerecarriedoutinthepast,allincludethisarea (MGL ,SCSIO ,CAS ,1 978;GPCSGRCZT…  相似文献   
106.
顾燕  张鹰 《海洋技术学报》2004,23(2):103-106
海岸带是影响人类活动的重要地带,海岸带专题地图能够详细表示出海岸带的特性。随着海洋经济的发展,海岸图的需求日益增加。从地图的数学要素出发,提出目前海岸图绘制存在的问题,并从地图学、海洋学、遥感地学的角度,对地图投影的选择、坐标系转换、比例尺对海岸图编绘的影响及控制点的确定等问题进行了综合分析。  相似文献   
107.
Five different coastal area morphodynamic models have been set up to run on the same offshore breakwater layout and an intercomparison carried out on the hydrodynamic and morphodynamic output produced by each scheme. In addition, the predicted morphodynamics was checked against available laboratory and field data.It is concluded that the models are capable of producing realistic estimates for the dominant morphodynamic features associated with offshore breakwaters. Coupling of the wave, current and sediment transport components of each scheme is shown to yield bathymetry which attains a state of equilibrium, unlike models which are based on the initial transport field only.  相似文献   
108.
A phase-resolving wave transformation module is combined with an intra-wave sediment transport module to calculate the on-/offshore sediment transport rates. The wave module is based on the Boussinesq equations extended into the surf zone. The vertical variation of the mean undertow and the intra-wave sediment concentrations are calculated. The net sediment transport rates are calculated, and the equation for conservation of sediment is solved to predict the beach profile evolution. The results of the present paper showed that the undertow contribution to the sediment transport rates is not dominating in all parts of the surf zone, even for eroding beaches, suggesting that other contributions should not be neglected. The present model also showed that for the same offshore wave energy the time series of the oscillatory motion is important and that the effect of wave groups cannot be disregarded.  相似文献   
109.
110.
Participatory fisheries management has been increasingly proposed as a useful management approach to address fisheries problems. However, the criteria regarding its applicability and measures of success still seem unclear. This study reviews the main concepts and theory behind two participatory resource-management approaches and compares them to the reality of fisheries management in Costa Rica. The analysis shows that while the implementation of a participatory approach in fisheries management should be encouraged, it is essential to keep in mind the possible limitations these approaches have. Furthermore, it seems important to improve institutional coordination and develop social, legal and economic policies that will allow the state, together with coastal communities, to contribute in an effective way to fisheries management.  相似文献   
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