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   333篇
  免费   30篇
  国内免费   27篇
测绘学   25篇
大气科学   44篇
地球物理   57篇
地质学   78篇
海洋学   83篇
综合类   19篇
自然地理   84篇
  2024年   2篇
  2023年   7篇
  2022年   10篇
  2021年   15篇
  2020年   19篇
  2019年   15篇
  2018年   9篇
  2017年   30篇
  2016年   27篇
  2015年   24篇
  2014年   26篇
  2013年   31篇
  2012年   10篇
  2011年   15篇
  2010年   21篇
  2009年   11篇
  2008年   14篇
  2007年   15篇
  2006年   19篇
  2005年   15篇
  2004年   8篇
  2003年   7篇
  2002年   5篇
  2001年   7篇
  2000年   5篇
  1999年   6篇
  1998年   1篇
  1997年   4篇
  1996年   3篇
  1995年   3篇
  1991年   2篇
  1990年   1篇
  1989年   2篇
  1987年   1篇
排序方式: 共有390条查询结果,搜索用时 15 毫秒
81.
黑河中下游荒漠区植物多样性分布对土壤水分变化的响应   总被引:9,自引:0,他引:9  
基于对黑河流域中下游荒漠区植被和土壤生境的调查分析,以土壤水分在各调查样地中的差异来反映研究区的生态水文特征,采用种的丰富度和多度来代表荒漠植物多样性研究了荒漠植物,包括隐花植物多样性分布对土壤水分变化的响应。土壤水分变化不仅直接影响着荒漠植物的多样性,而通过影响其它生境因子又间接地影响着多样性的维持。因此,如何维持中下游相对稳定的土壤水分来源是该区荒漠植物多样性保育今后所要面临的挑战。  相似文献   
82.
The effects of circular economy on biodiversity are poorly understood. This study provides observations on approaches for assessing circular economy and illustrates, with a Finnish case study, the potential of circular economy to mitigate pressures on biodiversity. The case study focuses on the construction and real estate sectors, as well as the forest industry. The findings imply that circular economy actions that reduce the extraction of virgin raw materials and relieve land use pressures are effective. Improving material efficiency, increasing the cascading use of wood, and optimizing the use and reuse of materials and products, as well as extending the lifetime of buildings and optimizing space use, have good potential for mitigating pressures on biodiversity in Finland. However, as forest utilization has a major impact on Finnish biodiversity, certain actions that possibly increase the use of forest resources (e.g., replacing fossil-based, concrete, or steel materials with wood-based solutions) may impair biodiversity if biodiversity-enhancing forest management practices are not utilized. Assessing the biodiversity impacts of circular economy is challenging, and the need for further research and the development of indicators and assessment methods is clear.  相似文献   
83.
The use of wild species is extensive in both high- and low-income countries. At least 50,000 wild species are used by billions of people around the world for food, energy, medicine, material, education or recreation, contributing significantly to efforts to achieve the United Nations Sustainable Development Goals. However, overexploitation remains a major threat to many wild species. Ensuring and enhancing the sustainability of use of wild species is thus essential for human well-being and biodiversity conservation. Globally, the use of wild species is increasing due to growing human demand and efficiency, but its sustainability varies and depends on the social-ecological contexts in which the use occurs. Multiple environmental and social (including economic) drivers affect the sustainability of use of wild species, posing major current and future challenges. In particular, climate change has already increased the vulnerability of many uses and is expected to increase it further in the coming decades, while global and illegal trades are, in many cases, key drivers of unsustainability. There is no single “silver bullet” policy to address these and other major challenges in the sustainable use of wild species. Rather, effective policies need to integrate inclusive actions at multiple scales that adopt right-based approaches, pay attention to equitable distribution of access and costs and benefits, employ participatory processes, strengthen monitoring programs, build robust customary or government institutions and support context-specific policies, as well as adaptive management.  相似文献   
84.
气候变化与生物多样性丧失是当前全球面临的两大热点和难点环境问题,二者协同推进的必要性和重要性也在全球范围内形成广泛共识。文中在总结我国“双碳”目标下应对气候变化与保护生物多样性协同的现状与挑战的基础上,对近年来各国应对气候变化和保护生物多样性协同方面的政策实践进行了系统梳理与总结,各主要国家近年来在战略规划、生态空间、绿色金融、科技创新等方面进行了大量实践探索以推动二者协同,在这些实践推动下,全球已逐渐将“碳中和”和“生物多样性”融入生态环境治理新格局、将基于自然的解决方案(NbS)作为二者协同领域最有效的新路径、将绿色金融和科技创新作为推动二者协同发展的新动力。鉴于此,我国在二者协同推进中亟需将生物多样性保护纳入双碳“1+N”政策体系,注重将基于自然的解决方案融入城镇化、乡村振兴等重大国家发展战略,鼓励引导绿色金融、数字科技支持二者协同的重点领域,提高公众认知和社会参与,以推进二者协同并助力我国成为全球生态治理的重要参与者、贡献者和引领者。  相似文献   
85.
针对超市经营者进行选址优化和空间配置问题,该文以南京市主城区内苏果超市为例,利用平面核密度方法,对城市内零售超市的空间结构与分布模式进行分析,系统地研究不同类型超市的空间分布特征并进行热点区域的探测。研究表明,热点区域的探测结果符合商业网点分布的一般规律,南京主城区内不同类型苏果超市的空间分布表现出较大的空间区域分异:购物广场的热点分布于中心城区外围的次一级中心,社区店和标准超市的热点分布于居住区,便利店的热点大多分布于人口密集区域。  相似文献   
86.
This article examines the relationship between place attachment and resistance during participatory planning of the Sengwe Tshipise Wilderness Corridor, located in southeast Zimbabwe, a region that falls within the Great Limpopo Transfrontier Conservation Area. Field research was conducted from July to December 2013 using 69 semistructured interviews, seven focus-group discussions, and analysis of secondary data. By following the dominant narratives articulated by villagers affected by this Corridor, we illustrate the multiple ways in which place attachment becomes part of everyday politics of resistance. Results show that a strong place-based identity is at the center of narratives deployed by villagers displaced by war, conservation, and veterinary fencing restrictions. Through deploying this place-based identity, communities collectively influenced both the spatial extent of the corridor and institutional governance arrangements. This article contributes to debates on the role of community agency in the implementation of transfrontier conservation areas.  相似文献   
87.
我国西部冬季扰动源涡与东部夏季雨带分布   总被引:4,自引:8,他引:4  
柳艳香  汤懋苍 《高原气象》2001,20(1):109-112
我国西部 (85°10 5°E)冬季“扰动源涡”的位置对夏季东部雨带的配置具有支配作用。当西部“源涡”位于 35°N以北时 ,东部雨带多出现在黄河流域及其以北 (Ⅰ类雨型 ) ;源涡位于 32°35°N之间时 ,夏季雨带多出现在淮河流域 (Ⅱ类雨型 ) ;当源涡位于 32°N以南时 ,雨带多出现在长江流域或江南 (Ⅲ类雨型 )。藏东南热点区冬季的中强地热脉冲对我国夏季江淮和川黔的大水具有很强的指示作用  相似文献   
88.
The taxonomic status of previously misplaced species of an ant-like stone beetle from Spanish amber (Albian) is clarified. Specimens of Kachinus magnificus (originally placed as incertae sedis within Scydmaenitae) were re-examined and their characters were found different from those of the type species of Kachinus from Myanmar amber. Consequently, Archeutheia gen. nov. is proposed to accommodate the Spanish species, resulting in Archeutheia magnifica comb. nov. Moreover, in a comprehensive phylogenetic analysis Archeutheia was placed as a sister group to extant Eutheia, within the tribe Eutheiini of Cephenniitae. A specimen of an undetermined genus from Myanmar amber clearly belonging in Cephenniini is also recorded. Both taxa represent the first definite Cretaceous Cephenniitae, a supertribe whose recent members are distributed on all continents but are especially diverse in the Oriental and East Palaearctic regions. This finding demonstrates a diversification of two presently most species-rich tribes of Cephenniitae already in Early Cretaceous. Archeutheia is strikingly similar to the extant species of Eutheia and Veraphis, showing male dimorphic characters (modified protrochanters) and antennal cavities characteristic of Palaearctic Eutheiini. This fact suggests a long morphological stability in the supertribe. A previously proposed hypothesis of an early presence of the Cephenniitae in the Northern Hemisphere is for the first time supported by the fossil record, and the palaeolocalities (western Europe and Southeast Asia) demonstrate a wide distribution of Cephenniitae in the Cretaceous and an early split of its ancestral lineage.  相似文献   
89.
New cold‐water coral (CWC) sites were recorded along the Apulian margin (Central Mediterranean). The species composition and depth distribution of CWCs were updated. A distribution of the CWC sites coincident with the course of the dense‐water masses that flow between the Southern Adriatic and Northern Ionian was confirmed. The faunal assemblages of five of these CWC sites were investigated and compared using experimental longlines during the spring–summer and autumn–winter seasons, between 2010 and 2014. Differences in ecological variables amongst the sites in each season were evaluated by means of a set of univariate and multivariate methods (analysis of variance, permutational multivariate analysis of variance, non‐metric multidimensional scaling). Although some differences were detected in relation to the different depths examined during spring–summer, the CWC sites showed similar features in terms of species richness and diversity as well as in the abundance of the same fish species (Galeus melastomus, Conger conger, Helicolenus dactylopterus, Merluccius merluccius, Phycis blennoides and Pagellus bogaraveo) most probably because of the distribution of adult specimens in structurally complex and heterogeneous habitats, which act as a potential ‘refuge network’ with respect to commercial fishing. The presence of maturing and mature individuals as well as post‐reproductive females indicates that these CWC sites also act as spawning areas, representing a potential ‘renewal network’ for the fish populations. The term ‘network’ used here refers to several similar subsystems (CWC sites) that play the same ecological role in a wider system (Apulian margin). These CWC communities need coherent conservation measures and management strategies according to the Ecosystem Approach to Fisheries.  相似文献   
90.
Many physical and sociological processes are represented as discrete events in time and space. These spatio-temporal point processes are often sparse, meaning that they cannot be aggregated and treated with conventional regression models. Models based on the point process framework may be employed instead for prediction purposes. Evaluating the predictive performance of these models poses a unique challenge, as the same sparseness prevents the use of popular measures such as the root mean squared error. Statistical likelihood is a valid alternative, but this does not measure absolute performance and is therefore difficult for practitioners and researchers to interpret. Motivated by this limitation, we develop a practical toolkit of evaluation metrics for spatio-temporal point process predictions. The metrics are based around the concept of hotspots, which represent areas of high point density. In addition to measuring predictive accuracy, our evaluation toolkit considers broader aspects of predictive performance, including a characterisation of the spatial and temporal distributions of predicted hotspots and a comparison of the complementarity of different prediction methods. We demonstrate the application of our evaluation metrics using a case study of crime prediction, comparing four varied prediction methods using crime data from two different locations and multiple crime types. The results highlight a previously unseen interplay between predictive accuracy and spatio-temporal dispersion of predicted hotspots. The new evaluation framework may be applied to compare multiple prediction methods in a variety of scenarios, yielding valuable new insight into the predictive performance of point process-based prediction.  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