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   1792篇
  免费   102篇
  国内免费   68篇
测绘学   57篇
大气科学   165篇
地球物理   57篇
地质学   363篇
海洋学   278篇
天文学   3篇
综合类   156篇
自然地理   883篇
  2024年   3篇
  2023年   25篇
  2022年   52篇
  2021年   71篇
  2020年   50篇
  2019年   43篇
  2018年   54篇
  2017年   109篇
  2016年   83篇
  2015年   83篇
  2014年   91篇
  2013年   97篇
  2012年   61篇
  2011年   98篇
  2010年   68篇
  2009年   79篇
  2008年   81篇
  2007年   93篇
  2006年   96篇
  2005年   74篇
  2004年   52篇
  2003年   57篇
  2002年   62篇
  2001年   83篇
  2000年   72篇
  1999年   58篇
  1998年   50篇
  1997年   22篇
  1996年   12篇
  1995年   13篇
  1994年   18篇
  1993年   10篇
  1992年   5篇
  1991年   5篇
  1990年   4篇
  1989年   6篇
  1988年   6篇
  1987年   4篇
  1986年   1篇
  1985年   3篇
  1984年   4篇
  1983年   2篇
  1982年   1篇
  1981年   1篇
排序方式: 共有1962条查询结果,搜索用时 46 毫秒
141.
本文通过对1992—2013年全国夜间灯光数据的校正和处理,获得全国及流域夜间灯光数据影像,进行经济空间聚合分析,以及与相关因子进行对比分析。研究结果表明:经济空间聚合高的区域分布在黄河河道附近,从黄河上游到下游,热力强度逐渐增强,并且以省会城市为核心区向外扩散,即呈现为在旧聚合点聚合度加剧的情况下,聚合区域有向周边分散的趋势;夜间灯光数据的变化趋势与GDP的变化趋势具有一定的相似性,并且与城镇化率、人口数量、第三产比例、人均公园绿地面积、流域发展指数(BDI)具有一定的相关性;流域9省(自治区)的夜间灯光数据整体变化趋势与全国灯光数据的变化趋势基本一致,呈稳定上升的趋势,但整体值均低于全国的夜间灯光数据,并且差距有所扩大,黄河流域高质量发展迫在眉睫。  相似文献   
142.
Natural resource management and conservation programs that promote building capacity and social learning among participants often lead to the formation of learning networks: a type of social network where learning is both a goal and potential outcome of the network. Through forming relationships and sharing information, participants in a learning network build social capital that can help a network achieve social and environmental goals. In this study, we explored social capital in a learning network that emerged through a large-scale marine governance effort, the Coral Triangle Initiative on Coral Reefs, Fisheries, and Food Security. Through a mixture of social network analysis and key informant interviews, we examined the major patterns of information exchange among individuals who had participated in regional learning exchanges; evaluated whether the network's structure resulted in information sharing; and considered implications for strengthening network sustainability, capacity building, and learning. We found that the Regional Exchange network fostered information sharing among participants across national and organizational boundaries. While the network had individuals who were more central to information sharing, the network structure was generally decentralized, indicating potential resilience to changes in leadership and membership. Participants stressed the importance of the knowledge and connections they had acquired through the learning network; however, they expressed doubts regarding its sustainability and stressed the need for a strong coordinating entity. Our findings suggest that conservation learning networks have the ability to bridge cultural divides and promote social learning; however, a strong network coordinator and continuing efforts to support information sharing and learning are crucial to the network's strength and sustainability. The tangible learning and capacity development outcomes cultivated through Regional Exchange network underscore the value of and need to invest in conservation networks that support peer-to-peer learning.  相似文献   
143.
Human–environment interactions are studied by several groups of scholars who have elaborated different approaches to describe, analyze, and explain these interactions, and eventually propose paths for management. The SETER project (Socio-Ecological Theories and Empirical Research) analyzed and compared how “flag-holders” of distinct school of thought in human–environment scholarship approached a number of empirical problems of environmental management. This paper presents the findings from this experiment by concentrating on how representatives of four schools of thought approached one of these case studies: the plant health crisis in greenhouse tomato production in south of France. Our analysis suggests that these approaches share a common conceptual vocabulary composed of four explanatory elements of change (Power, Incentives, System and Adaptation-PISA). We argue that what distinguishes these schools from one another is the syntax—the “rules” by which researchers in each of the sub-disciplines tend to organize the components of this shared conceptual vocabulary. In other words, the schools under scrutiny are differentiated not so much by what they speak of, but rather in what order, or hierarchy, do they tend to rank the importance and/or the sequence of each of these concepts in human–environment explanations. The results of our experiment support the view that communication and cooperation across the diverse human–environment traditions is possible and productive. At the same time, however, we argue that it is the distinctiveness of the claims yielded by these different schools of thought that augment our collective understanding of complex socio-ecological problems. Attempts to integrate these perspectives in one unitary approach would undermine the intellectual wealth necessary to meet the challenges of the Anthropocene.  相似文献   
144.
Successful adaptation to environmental change and variability is closely connected with social groups’ ability to act collectively, but many social-ecological challenges exceed local adaptive capacity which necessitate assistance from governmental institutions. Few studies have investigated how local collective action can be used to enrol external support for adaptation. This paper reduces this research gap by analysing a locally driven adaptation process in response to coastal erosion in Monkey River Village, Belize. Drawing on literature on adaptation and political ecology, we examine the different strategies the local residents have used over time to influence government authorities to support them in curbing the coastal erosion. Our findings show that the local mobilisation generated government support for a temporary sea defence and that collective strategies emerge as a response to threats to a place specific way of life. Our case illustrates that it was essential that the villagers could ally with journalists, researchers and local NGOs to make their claims for protection heard by the government. The paper contributes to adaptation research by arguing that local collective action, seen as contestation over rights to protection from environmental change, can be a means for places and communities not prioritised by formal policies to enrol external support for adaptation. Our study supports and adds to the perspective that attention to formal arrangements such as adaptation policy alone has limited explanatory power to understand collective responses to change.  相似文献   
145.
The estuary of the Danshuei River, a hypoxic subtropical estuary, receives a high rate of untreated sewage effluent. The Ecopath with Ecosim software system was used to construct a mass-balanced trophic model for the estuary, and network analysis was used to characterize the structure and matter flow in the food web. The estuary model was comprised of 16 compartments, and the trophic levels varied from 1.0 for primary producers and detritus to 3.0 for carnivorous and piscivorous fishes. The large organic nutrient loading from the upper reaches has resulted in detritivory being more important than herbivory in the food web. The food-chain length of the estuary was relatively short when compared with other tropical/subtropical coastal systems. The shortness of food-chain length in the estuary could be attributed to the low biomass of the top predators. Consequently, the trophic efficiencies declined sharply for higher trophic levels due to low fractions of flows to the top predators and then high fractions to detritus. The low biomass of the top predators in the estuary was likely subject to over-exploitation and/or hypoxic water. Summation of individual rate measurements for primary production and respiration yielded an estimate of −1791 g WW m−2 year−1, or −95 g C m−2 year−1, suggesting a heterotrophic ecosystem, which implies that more organic matter was consumed than was produced in the estuary.  相似文献   
146.
Andrew Boulton 《Geoforum》2010,41(2):329-336
This paper is set against the backdrop of an increasingly pervasive discursive coupling of peace with development, and of extremism with underdevelopment. An evolving knowledge economy discourse casts education as both a key determinant of economic development, and as a crucial tool in the battle for “hearts and minds” in a global war against terrorism and extremism. Education for development, and education as anti-extremism are the twin goals of the Filipino CD for Peace - a contribution to the UN-backed International Power Users of ICT (Information Communication Technology) Symposium. In this paper, I examine the ways in which this youth Symposium feeds into and mobilizes powerful logics around the links between education and development/counterterrorism. My argument is that education for development, and one of its articulations, the CD for Peace, are undergirded by and reproduce neoliberal development logics in several overlapping respects. I illustrate the ways in which the language of connection and collaboration reproduces a distinct rationality related both to the transformative potential of (private investment in) ICT and to the production of particular kinds of subjectivities: youth as connected, informed, economically valuable global citizens beyond the reach of extremists. The Power Users project works to (re)construct teenagers as “gurus”; conflict (and poverty, and terrorism) becomes solvable through education and ICT. I show how knowledge economy discourse powerfully constructs youth as learning subjects who come to imagine their own roles and identities in specifically neoliberal ways: not only as learners, but also as advocates for this nexus of technology, education, development and peace.  相似文献   
147.
Al James  Bhaskar Vira 《Geoforum》2010,41(3):364-376
This paper explores the lived experiences and aspirational social constructions of call centre work and employment in India’s high profile IT Enabled Services-Business Process Outsourcing (ITES-BPO) industry; the ways in which they differ from those previously documented amongst call centre workers in the Global North (specifically the UK); and the consequences of that geographical reconfiguration of offshored call centre work for the replicability in India of workplace collective bargaining strategies successfully developed in some UK call centres. These issues are analysed using new empirical evidence from a regional survey of 511 non-unionised ITES-BPO workers and 42 in-depth interviews in India’s National Capital Region. Based on this analysis, the paper then discusses the operation, outcomes and ongoing challenges faced by the newly formed ‘Union for ITES Professionals’ (UNITES Pro) in developing an alternative occupational organising model better suited to the particular needs, motivations and preferences of India’s young, mobile, call centre workers. The empirical analysis presented in the paper is located, therefore, within wider debates on the role of geographical context in shaping possibilities for organising white-collar service workers at different ends of global service chains in the new economy.  相似文献   
148.
随着海洋环境问题的日益凸显,协调海洋经济发展与海洋生态保护已成为学术界的研究热点。本文使用C2NLS方法对2003—2016年中国沿海11省区市海洋生态效率进行测度,使用SDE方法对海洋生态效率的时空演进特征进行分析,最后对影响海洋生态效率的因素进行实证探索。结果表明:①海洋生态效率整体呈上升趋势,但地区差距并未显著缩小,海洋生态效率的地区分布出现极化趋势。②海洋生态效率重心表现出西南向移动特征,东北—西南向的空间格局更加明显。③环境规制、海洋科技和对外开放可以有效提高海洋生态效率水平;产业结构效应不显著,可能是由于高污染行业同时具有高产出与高排放的特征导致;区位因素效应不显著;海洋生态效率与地区发展水平之间没有明显的二次型关系,与中国海洋经济整体发展仍处于“倒U”型曲线的上升通道情况相符,部分印证了“环境的库兹涅茨”曲线理论。  相似文献   
149.
养殖过程的循环水交换量能够显著影响皱纹盘鲍(Haliotis discus hannai)的生理状态, 进而影响其养殖存活率和生长率, 然而不同循环水量对于皱纹盘鲍的生理状态影响的分子机制尚不明确。本实验以皱纹盘鲍(Haliotis discus hannai)为研究对象, 将鲍分别置于循环水交换频率为1次/d、2次/d、4次/d的条件下(编号为C0、T2和T4组)暂养3 d, 然后利用Illumina Hiseq 2500技术测定不同处理组鲍鱼的肌肉组织中转录组表达情况。结果表明, 单次换水组(C0)和多次换水组(T2和T4)间差异表达的基因个数较多, 分别为4 095和3 617个, 而T2与T4组之间的差异表达基因个数则较少, 仅为232个。对差异表达基因进行GO和KEGG功能分析显示, 单次换水组(C0)和多次换水组(T2和T4)间差异表达的基因主要集中在能量代谢和免疫反应相关通路或基因, 随机选取10个差异基因进行荧光定量PCR验证, 定量PCR结果与转录谱结果一致, 证实了转录组测序结果的可靠性。本研究说明了更高的水交换量下, 鲍的代谢和免疫相关通路被激活, 可能有助于鲍鱼维持较好的生理和免疫状态, 从而表现出更好的生长、存活等表型。  相似文献   
150.
为充分发挥粤港澳大湾区港口的竞争优势,促进港口经济的协调发展,文章基于粤港澳大湾区主要港口的实际情况,构建供应链博弈模型并进行数值仿真,研究相关因素对深圳港和香港港绩效的影响。研究结果表明:随着商品价格和库存成本的提高,货物从深圳港向香港港转移,但转移幅度逐渐趋缓;深圳港在中低端商品的货源收集方面具有明显的竞争优势,而香港港对高端商品的吸引力更强;货运结构逐渐向中高端商品过渡对于提高港口收益具有促进作用,其中深圳港应通过降低商品库存成本而降低经营风险;深中通道和港珠澳大桥通车有效缩短腹地运输时间,对于绝大部分商品价格和库存成本组合都将提高粤港澳大湾区港口的总收益。  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