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   1049篇
  免费   74篇
  国内免费   105篇
测绘学   104篇
大气科学   34篇
地球物理   44篇
地质学   371篇
海洋学   465篇
天文学   12篇
综合类   71篇
自然地理   127篇
  2024年   1篇
  2023年   9篇
  2022年   26篇
  2021年   29篇
  2020年   37篇
  2019年   30篇
  2018年   21篇
  2017年   74篇
  2016年   56篇
  2015年   47篇
  2014年   73篇
  2013年   50篇
  2012年   71篇
  2011年   58篇
  2010年   85篇
  2009年   61篇
  2008年   61篇
  2007年   60篇
  2006年   54篇
  2005年   20篇
  2004年   40篇
  2003年   27篇
  2002年   23篇
  2001年   15篇
  2000年   17篇
  1999年   17篇
  1998年   24篇
  1997年   19篇
  1996年   20篇
  1995年   12篇
  1994年   14篇
  1993年   10篇
  1992年   8篇
  1991年   6篇
  1990年   6篇
  1989年   10篇
  1988年   2篇
  1987年   1篇
  1985年   9篇
  1984年   5篇
  1983年   4篇
  1982年   13篇
  1981年   1篇
  1980年   1篇
  1977年   1篇
排序方式: 共有1228条查询结果,搜索用时 15 毫秒
441.
The present study analysed the major features of two important acts and an ordinance in Bangladesh that govern coastal and marine fishery exploitation and conservation. The problems with the implementation of these regulations were identified, and the level of compliance among fishers and reasons for their noncompliance were assessed. Based on two case studies on coastal and marine ecosystems, the findings revealed that the level of noncompliance is highly prevalent, particularly in hilsa sanctuaries in the Meghna River estuary. The study identified coastal poverty, the inadequate and improper distribution of incentives, insufficient logistic support, limited alternative occupations, political interference and a lack of awareness regarding fishery regulations as the major limitations in the implementation. The drawbacks of proper implementation and the noncompliance of fishery regulations lead to fishery degradation, directly affect the sustainability of the coastal and marine ecosystem of Bangladesh and may be barriers to achieving Goal 14 of the Sustainable Development Goals (SDGs). Establishing a co-management mechanism for sanctuary management, creating economic opportunities outside of fishery sectors, declaring more protected areas in the coastal and marine ecosystem, enhancing logistic support to the enforcing agencies and building awareness are critical to improving the compliance level among fishers. Finally, the study submits that understanding the fishers’ reasons for compliance and noncompliance of the regulations is important for devising fishery policies through the consultation and engagement of stakeholders at all levels.  相似文献   
442.
Fisheries policy and management processes for federal waters off western Alaska currently lack consistent and considered integration of traditional knowledge (TK), TK holders, social science of TK, and subsistence information. The incorporation of these into fisheries work can lead to more informed, equitable and effective policy and management practices. This paper includes information and recommendations derived from previous work by the authors as well as from two community workshops with indigenous TK holders and fisheries experts. Discussions of TK and related concepts, TK research in the Bering Strait and Yukon River regions, and Alaska federal fisheries management-related institutions and processes as pertains to TK are presented. Substantive recommendations are provided for improving processes, increasing tribal representation, capacity building, effective communication, outreach and relationship-building, the incorporation of indigenous concerns and values, and regarding the development of a Fisheries Ecosystem Plan for the Bering Sea.  相似文献   
443.
This paper analyzes the impact of reducing fisheries subsidies in a general equilibrium model for a fishery with heterogeneous vessels. It considers the impact of the stock effect, which determines the participation of vessels in a likely increased stock abundance. In equilibrium, the productivity of the fleet is endogenous as it depends on the stock of fish along the equilibrium path. The model concludes that any impact of a subsidy drop will depend on the stock effect. If that effect is large, fishing firms will benefit from the stock recovery and the elimination of the subsidy will increase future returns on investment. The model is particularised to industrial shrimp fisheries in Mexico. It is shown that the complete elimination of a subsidy increases biomass, capitalisation, marginal productivity, and consumption and reduces inequality when the effect of the induced increase in the stock is considered. However, if that effect is not considered, capital and consumption decrease, and inequality and hence, the social costs of a subsidy drop, increase.  相似文献   
444.
This paper undertakes a critical assessment of the present state of fisheries insurance in India. Various factors that contribute to the poor performance of fisheries insurance in the country were identified and ranked based on the responses of fishermen and fish farmers in major maritime states. In the light of the findings, measures such as leveraging the potential of technological interventions, developing innovative institutional mechanisms, bridging the trust deficit amongst the stakeholders and bringing about attitudinal changes through awareness drives are suggested as way forward towards harnessing the potential of insurance as a safety net tool in fisheries sector of India.  相似文献   
445.
A number of fisheries development projects are undertaken every year in recognition of the important role fisheries play in many coastal communities. The objectives vary, but typically go beyond a limited focus on fisheries management and the ecosystem. This makes it difficult to evaluate the contribution of a project, particularly in data poor environments such as most developing countries. This paper used the recently developed Fisheries Performance Indicators (FPIs) to evaluate the impact of a World Bank development project in a Liberian coastal community. FPIs are designed to capture economic and social performance of a fisheries system in addition to the management and environmental impacts. The results show improvements in most ecological dimensions, and also in many social and economic dimensions targeted by the project. Hence, the project intervention appears to be positive. However, some indicators, particularly in relation to general governance in Liberia, showed a negative development which was not caused by the project.  相似文献   
446.
Small-scale fisheries have been estimated to contribute up to 30% of the global landed value, which is caught by approximately 22 million fishers, some of which can be attributed to developed countries. Socio-economic analysis of small-scale fisheries often focuses on developing countries and fails to recognize the presence and contribution of small-scale fisheries in the developed world. Fisheries in British Columbia are diverse and often regarded as being industrialized and large-scale when analyzed in a global context. This study aims to demonstrate that features of small-scale fisheries are present within British Columbia's fleets. A list of re-occurring features of small-scale fisheries is curated from the literature to capture physical, economic and social features of small-scale fisheries. These commonly identified features of small-scale fisheries are applied to Aboriginal Food, Social and Ceremonial fisheries and all commercial fisheries in British Columbia are analyzed to determine the presence or absence of each small-scale fishery feature. The results of this research create a gradient of fisheries from smallest to largest scale. This approach determines that Aboriginal Food, Social and Ceremonial fisheries are the most small-scale, while the sablefish fishery is the largest scale. The qualitative nature of this framework creates an opportunity for any group of fisheries in the world to be compared.  相似文献   
447.
文章以上海市、浙江省和山东省113户渔业生产者的问卷调研数据为基础,通过运用Logistic回归模型分析渔业生产者参与实施捕捞限额制度意愿的影响因素。研究表明,年龄、受教育水平、渔船总功率、年均捕捞量、捕捞收入与家庭总收入比例、举报奖励额与超额价值比例以及年监管次数均对渔业生产者参与实施捕捞限额制度的意愿产生显著影响。基于实证研究结果,提出应加大渔业培训力度,切实控制渔船功率,暂不设立举报机制以及结合目前的投入控制制度推行循序渐进、逐步严格的监管机制等建议,以提高渔业生产者参与实施捕捞限额制度的意愿,为制定有效的渔业资源管理制度提供参考依据,推进渔业现代化改革。  相似文献   
448.
以城市土地、建筑、房屋和人口(法人)四个领域数据为研究对象,探讨面向"地-楼-房-人"一体化集成框架组成以及一体化化数据模型、城市空间编码中心、多维数据自动融合、非空间信息自动寻址、数据协同更新等关键技术,并在工程项目中验证了本研究的可行性和有效性。  相似文献   
449.
地球化学元素空间定量组合求异模型及其应用   总被引:1,自引:0,他引:1  
由于成矿过程的多期性与多源性,成矿区地球化学元素在空间上表现出共生组合特征。为刻画组合特征的类型与特点,提出一种地球化学元素空间定量组合求异方法,构建了因子泛克里格模型、多元序列典型趋势面模型及特征分析组合模型。将上述3种空间定量组合求异模型应用于云南哀牢山墨江地区1∶20万化探数据进行处理分析,目的在于从多元角度刻画元素异常,提高矿异常预测精度。计算结果表明:该区存在4种异常类型,反映了不同地质条件下元素共生组合及其在成岩成矿过程中的内在组配机制和空间关系。由此得出结论:在成矿预测过程中应按不同的定量组合异常类型及其相应地质背景进行预测。  相似文献   
450.
以县域为研究单元,在综合考虑各县域人均GDP和GDP总量变化的基础上,运用ESDA空间相关分析方法,分析了新疆玛纳斯河流域绿洲县域经济差异的时空变化趋势及不同的县域经济发展类型。结果表明,绿洲内各县域经济发展不均衡,并呈现出3种类型,即主导型县域、附属型县域和潜力型县域;绿洲经济呈现出显著的地带性差异,经济发展水平较高的几个县域都处在绿洲东部天山北坡经济带中,而经济发展水平较低的几个县域大多处于西北部沙漠边缘;从总体分布格局来看,8个研究年份中,Global Moran’s I 估计值呈下降的趋势,并且在符号上发生了质的变化,表明区域内县域的自相关性在不断下降,其发展的有序性逐渐减弱,无序性逐渐增强;从局部分布格局来看,绿洲内各县域经济虽然有了一定的发展,但总体发展水平不均,县域之间的经济差异有了一定的扩大,主要表现为属于LL和HH类型的县域在逐步减少,属于LH和HL类型的县域在逐步增加。  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