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   569篇
  免费   46篇
  国内免费   76篇
测绘学   8篇
大气科学   3篇
地球物理   44篇
地质学   13篇
海洋学   509篇
综合类   86篇
自然地理   28篇
  2024年   3篇
  2023年   5篇
  2022年   15篇
  2021年   17篇
  2020年   16篇
  2019年   18篇
  2018年   19篇
  2017年   26篇
  2016年   21篇
  2015年   22篇
  2014年   27篇
  2013年   40篇
  2012年   15篇
  2011年   21篇
  2010年   20篇
  2009年   27篇
  2008年   18篇
  2007年   51篇
  2006年   36篇
  2005年   38篇
  2004年   30篇
  2003年   27篇
  2002年   25篇
  2001年   25篇
  2000年   23篇
  1999年   23篇
  1998年   15篇
  1997年   11篇
  1996年   11篇
  1995年   18篇
  1994年   8篇
  1993年   5篇
  1992年   8篇
  1991年   1篇
  1990年   3篇
  1988年   1篇
  1986年   1篇
  1984年   1篇
排序方式: 共有691条查询结果,搜索用时 390 毫秒
531.
In Europe, 88% of fish stocks are being fished beyond Maximum Sustainable Yield and 30% of stocks are outside of biological limits. The blue whiting fishery is also following a consistent trend of a declining, and the EU recently adopted a 93% quota decrease for this species. Despite the abundant literature related to genetic aspects of population structure of aquatic resources, few studies have specifically addressed the link between fisheries management and population genetics. Given potential differences in the behavior of different subpopulations, population genetics has great relevance in the correct interpretation of the evolution of stocks. Ignoring the congruence of spatial scales between the population structure of fish species and management units can result in reduced productivity and local reduction of populations.  相似文献   
532.
Since the 1960s Taiwan has been a significant player in the global distant water tuna fisheries (DWTF). However, Taiwan's lack of political recognition has led some fisheries businesses to employ less conventional methods including Flags of Convenience (FOCs) in harvesting tuna resources. Meanwhile, Taiwan has been experiencing the painful cost of readjusted DWTF policies. This paper compares the readjusted policies in accordance with international management instruments and tuna compliance requirements (Compliance Agreement and UNFSA) and domestic laws are already undergoing adjustments to take these into account. This again demonstrates Taiwan's unique position in the international community: despite it not being a member of the United Nations, Taiwan spares no effort to ensure the sustainability of marine resources, and does its utmost to fulfill the responsibilities and duties of a Flag State.  相似文献   
533.
洱海渔业资源与渔业发展模式   总被引:2,自引:0,他引:2  
费骥慧  唐涛  邵晓阳 《湿地科学》2011,9(3):277-283
洱海是云南省主要的水产基地之一.于2009年8月和11月,对洱海进行了鱼类资源调查,渔获物中有鱼类23种,隶属于6目9科,其中,子陵栉(鱼叚)虎鱼(Ctenogobius giurinus)、波氏栉(鱼叚)虎鱼(Ctenogobius cliffordpopei)、麦穗鱼(Pseudorasbora parva)等小型...  相似文献   
534.
研究海洋渔业产业结构优化对碳排放的影响,对于促进海洋渔业高质量发展具有重要的现实意义。文章基于2008—2017年我国沿海9省(自治区)的面板数据,运用数据包络方法计算海洋渔业碳排放效率,并采用空间计量模型,探讨海洋渔业产业结构优化对碳排放效率的影响。研究结果表明:我国海洋渔业碳排放效率的地区差异显著,除河北和广西外,其他地区均具有较高的海洋渔业碳排放效率;从空间特征看,海洋渔业产业结构优化水平具有显著的空间集聚性,海洋渔业碳排放效率也存在一定的空间依赖性,碳排放效率的"高-高"集聚特征较为明显;从回归结果看,海洋渔业产业结构优化和海洋渔业经济水平对海洋渔业碳排放效率具有显著的正向影响,这种影响不仅作用于本地区,而且辐射和扩散到邻近地区;渔民收入、渔业科研投入和渔业对外开放水平对海洋渔业碳排放效率存在一定的负面影响。  相似文献   
535.
渔业产量和资源生物量数值模型及相关因子的初步研究   总被引:2,自引:0,他引:2  
对于渔业的中长期预报计算,是渔业种群补充的关键问题。本文在单位补充量产量和单位补充量生物量模型中加入了亲体一补充模型即密度相关过程,并引入了白色噪音以模拟环境变化。结果表明:本研究(1)可以明确地给出渔业种群崩溃的可能性,估计出达到崩溃时的捕捞死亡率;(2)可以估计最大持续产量的绝对值;(3)引入的白色噪音可以模拟环境变化对产量与捕捞死亡率和产量与亲体生物量关系曲线的影响。虽然亲体补充关系仍多是个假设,补充与亲体之间存在的补偿机制需要进一步的研究。  相似文献   
536.
中国明对虾摄食后的特殊动力作用   总被引:4,自引:0,他引:4  
采用耗氧量推算和能量收支推算方法,计算了中国明对虾的呼吸能量消耗,并计算了中国明对虾摄食配合饵料后的表观特殊动力作用(SDA).体重范围为1.814~18.552g的中国明对虾摄食配合饵料后,24h内摄食1g 干饵料、1g蛋白质、1kJ能量所产生的SDA分别为7.492kJ、16.454kJ和0.383kJ,而体重范围为2.998~19.012g的中国明对虾在28d内利用能量收支方程计算的相应结果为8.570~11.153kJ、20.131~26.197kJ和0.446~0.580kJ.平均体重为1.53g的中国明对虾摄食鱼肉(FF)、虾肉(SF)、蛤肉(CF)、沙蚕(PW)、配合饲料(FD)和混合饲料(MD)后所产生的表观SDA占摄食能的比例分别为0.660,0.679,0.656,0.523,0.592,0.641,对不同饵料的SDA比例与转化效率的相关分析表明:饵料的转化效率与SDA比例负相关,即SDA比例越高的饵料分配到生长的能量比例越少.另外还对能量收支方法在SDA研究中的应用进行了探讨.  相似文献   
537.
The diverse clam shrimp Nestoria-Keratestheria fauna is widely distributed in the Dabeigou Formation in northern Hebei and eastern Inner Mongolia of China. Its important component genus Magumbonia from the Dabeigou Formation in the Luanping Basin, northern Hebei, China, is revised on the basis of a scanning electron microscope (SEM) examination of the type species M. jingshangensis Wang, 1984, which revealed morphological features not recognized previously. These include coarse reticulation on the umbo and prominent growth lines ornamented with densely spaced, small tubercles and fine lirae.  相似文献   
538.
To date, none of the fisheries in the U.S. Pacific Islands Region is managed under a catch share program. In light of the NOAA policy to encourage the use of catch shares as a fishery management tool, the Western Pacific Fishery Management Council (WPFMC) listed six commercial fisheries, including the Hawaii pelagic longline fishery, the largest in the region, as potential candidates for catch share programs. This study examines the baseline economic characteristics and the main challenges facing the Hawaii pelagic longline fishery and evaluates the impact of these on the desirability and feasibility of a catch share program for this particular fishery.  相似文献   
539.
The initial factors that cause a decline in the survival of in situ settled corals remain poorly understood. In this study, we demonstrated through field experiments that the design of artificial grid plates may influence the initial survival of Acropora corals, with narrower grids being the most effective. In fact, grid plates with a 2.5-cm mesh presented the highest recorded survival rate (14%) at 6 months after settlement (representing approximately 50 corals per 0.25 m2 of plate). This is the first study where such high survival rates, matching those of cultures under aquarium conditions, were obtained in the field without using additional protective measures, such as guard nets against fish grazing after seeding. Therefore, our results provide a foundation for establishing new and effective coral restoration techniques for larval seeding, in parallel to clarifying the details of the early life stages of reef-building corals.  相似文献   
540.
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