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   398篇
  免费   14篇
  国内免费   16篇
测绘学   12篇
大气科学   29篇
地球物理   63篇
地质学   167篇
海洋学   27篇
天文学   3篇
综合类   7篇
自然地理   120篇
  2024年   2篇
  2023年   2篇
  2022年   4篇
  2021年   8篇
  2020年   9篇
  2019年   10篇
  2018年   7篇
  2017年   13篇
  2016年   21篇
  2015年   10篇
  2014年   5篇
  2013年   26篇
  2012年   17篇
  2011年   8篇
  2010年   10篇
  2009年   17篇
  2008年   35篇
  2007年   33篇
  2006年   15篇
  2005年   17篇
  2004年   14篇
  2003年   17篇
  2002年   9篇
  2001年   14篇
  2000年   10篇
  1999年   15篇
  1998年   12篇
  1997年   7篇
  1996年   6篇
  1995年   9篇
  1994年   5篇
  1993年   2篇
  1992年   3篇
  1991年   7篇
  1990年   4篇
  1988年   3篇
  1987年   4篇
  1986年   3篇
  1985年   6篇
  1984年   3篇
  1982年   2篇
  1981年   1篇
  1980年   2篇
  1977年   1篇
排序方式: 共有428条查询结果,搜索用时 15 毫秒
81.
82.
A new dinosaur sauropod from the Golmayo Formation (upper Hauterivian-lower Barremian) in Soria province (Spain) is described as Soriatitan golmayensis gen. et sp. nov. The new material consists of one tooth, three dorsal vertebrae with ribs, a partial sacrum, five caudal centra, two caudal vertebral spines, one chevron, a humerus, an ulna, a radius, two partial ilia, two ischia, a fragment of pubis, and a partial femur. Cladistic analysis identified the material as belonging to Brachiosaruidae within Titanosauriformes. Sauropod material from the Golmayo Formation shares a diagnostic feature with Abydosaurus, Cedarosaurus, Tastavinsaurus and Venenosaurus including anteriorly deflected anterior–middle caudal neural spines and with Cedarosaurus a proximodistally straight lateral margin between the proximal head and the shaft of the humerus. Eight characters are potential autapomorphies in the sauropod from Spain, including the presence of a large rectangular ventral ridge below the preacetabular process of the ilium, the same length of the pubic and ischiadic blades in the ischium, and two lateral ridges in the lateral area of the deltopectoral crest of the humerus. The presence of Early Cretaceous brachiosarids in both, North America and Europe, give support to the hypothesis of a connection between the tectonic plates of these continents at some point during the Early Cretaceous.  相似文献   
83.
This model is based on the concept of transport concentration, defined as the time-averaged concentration in a given location of a lagoon, which determines the long-term net transport of sediments as the sum of a dispersive and an advective flux. Dispersive net flux of sediments is due to the alternate components of the tidal flow, while the advective net flux of sediments is due to the residual (Eulerian) component of the tidal, fluvial and littoral flow and possibly to the asymmetry between flow and ebb tide.  相似文献   
84.
85.
Why is Ortley Beach, New Jersey, known as Superstorm Sandy's ground zero? This article employs qualitative vulnerability analysis to understand why vulnerability of second homes in Ortley Beach resulted in dune failure and slow rebuilding after Sandy. The second-home owners who largely make up the community in Ortley Beach are identified as the key vulnerable group. This group's lack of political representation and financial compensation after Sandy increased house damage and slowed rebuilding. Identifying the level of vulnerability of the majority group in a location is paramount to understanding how the community recovers from a disaster. Such identification can also aid in preparing communities, especially for types of disasters they have not yet encountered.  相似文献   
86.

East-Central Europe is undergoing a rapid political and economic transformation. The unprecedented depth and speed of the economic reforms have produced serious questions about the stability of the region, and its future relations with western Europe and the world economy. This paper surveys and evaluates the size and character of existing debt stocks owed to the West by Hungary, Poland, and Czechoslovakia. The future political and economic stability of East-Central Europe and the European Community depends, to a large extent, on the ability of the Western financial system to respond to the long-term needs of the region.  相似文献   
87.
Abstract

The aim of the article is to determine whether the Walt Disney Company has manufactured a landscape “other” to French culture around its parks in the Eastern Paris Basin. Val d'Europe is contentiously constructed by three main groups, not just one enterprise: the French state, the Walt Disney Company and local and regional governments, as well as by present and future residents, within the constraints of a contract based on French laws. The Company's investment has been a tremendous boost to the French state's project but did not lead to Disneyfication of the Briard landscape of agricultural lands in the Eastern Paris basin. In Val d'Europe the French state did not abdicate its authority in favor of commoditization of Paris as a global metropolis. The French state and French culture were never “weak” and overwhelmed.  相似文献   
88.
This study assesses changes in population distribution and the expansion of urban settlements in Southern Italy between 1871 and 2011. Four demographic phases are identified: (i) spatially balanced, mild population growth (1871–1921); (ii) moderate population increase concentrated in coastal and lowland areas (1921–1951); (iii) rapid and diffused population growth (1951–1981); and (iv) population stability with settlement dispersion (1981–2011). While urban growth in the years preceding the 1980s reinforced the polarization in rich and poor areas along the urban-to-rural gradient, since the early 1990s both urban and rural areas showed population dynamics that consolidated low-density settlements scattered around the largest cities. This path, however, does not reflect the evolution towards a more spatially balanced urban development, as observed in other European regions. Causes and consequences of the persistence of a fragmented urban hierarchy with dense settlements and sprawl concentrated around the main cities are finally discussed.  相似文献   
89.
《Urban geography》2013,34(1):105-128
This article examines sprawl without growth in former East Germany at a number of different metropolitan scales using a dataset from the Bundesamt für Bauwesen und Raumordnung (Federal Office for Building and Regional Planning). Specific political, social, and economic circumstances in eastern Germany following reunification distinguish it not only from other declining regions, but also from some of its post-socialist neighbors that underwent similar urban spatial transformations after the fall of communism. Explanations for this phenomenon include: increasing incomes and latent demand for housing, which remained suppressed under communism; specific policies adopted after reunification that subsidized greenfield development at the metropolitan fringe; a lack of planning at the local, regional, and state levels in the immediate aftermath of reunification; and changing demographic patterns. Although a number of the factors exacerbating sprawl in the post-reunification period have disappeared, overall demographic decline in eastern Germany continues.  相似文献   
90.
A range of intensifying pressures is making the future of European agriculture dynamic and contested. Insights into these pressures are needed to inform debates about the future of the sector. In this study, we use a foresight approach to identify, quantify and map megatrends. Megatrends are long-term driving forces which are observable today and will likely have transformational potential in the future. By mapping these megatrends at the regional scale, we establish a geography of megatrends and detect where they coincide. Four megatrends significant for the future of European agriculture at the regional scale are assessed: Climate change, demographic change, (post-) productivism shifts, and increasingly stringent environmental regulations. The direction and intensity of these megatrends differs between regions, which drives regions into different systemic lock-ins or dynamics. In most regions, megatrends converge to destabilize the current system, forewarning impending systemic changes. While the specific megatrends contributing to this instability differ regionally, this result highlights that many regions are on a dynamic rather than stable trajectory, and the governance challenge is to steer these dynamics towards a desirable future. However, some regions are found to be highly persistent, indicating that megatrends reinforce business as usual, and change needs to be triggered through purposeful governance. In a minority of regions megatrends may drive marginalization as the current system becomes increasingly unviable. We argue that research and policies concerning agricultural sustainability transitions should be cognizant of the regional diversity of European megatrends and the pressures they create.  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