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   213篇
  免费   19篇
  国内免费   3篇
测绘学   2篇
大气科学   34篇
地球物理   50篇
地质学   94篇
海洋学   31篇
天文学   6篇
综合类   2篇
自然地理   16篇
  2024年   1篇
  2023年   1篇
  2022年   1篇
  2021年   5篇
  2020年   10篇
  2019年   6篇
  2018年   10篇
  2017年   14篇
  2016年   9篇
  2015年   9篇
  2014年   9篇
  2013年   13篇
  2012年   16篇
  2011年   13篇
  2010年   17篇
  2009年   9篇
  2008年   17篇
  2007年   6篇
  2006年   10篇
  2005年   6篇
  2004年   10篇
  2003年   5篇
  2002年   7篇
  2001年   1篇
  2000年   1篇
  1998年   1篇
  1997年   1篇
  1996年   1篇
  1995年   1篇
  1994年   1篇
  1993年   4篇
  1992年   1篇
  1991年   1篇
  1990年   1篇
  1987年   1篇
  1984年   4篇
  1983年   1篇
  1982年   1篇
  1980年   3篇
  1975年   3篇
  1973年   1篇
  1969年   1篇
  1967年   1篇
  1921年   1篇
排序方式: 共有235条查询结果,搜索用时 15 毫秒
201.
202.
Research on coralline algal responses to ocean acidification and other environmental stressors has increased in recent years as coralline algae is thought to stand a higher chance of being affected by acidification stress than other macroalgae. To provide context and enhance the existing eco‐physiological framework for climate change studies, it is important to understand the effects of non‐extreme stressors experienced regularly by inter‐tidal coralline algae. In this study, we tested the potentially interacting effects of diurnal and tidal treatments on calcification in the geniculate coralline algae Corallina frondescens and Corallina vancouveriensis using 13C‐labeled bicarbonate. Both species deposited more calcium carbonate during the day than at night, and also when submerged (high tide) compared with when emerged (low tide) in their apical and mature segments (intergenicula). These results indicate that inter‐tidal coralline algae do in fact pay a cost for living inter‐tidally at the edge of an adaptive zone.  相似文献   
203.
204.
We examined 14 subaerially deposited speleothems retrieved from submerged caves in the northeastern Yucatán Peninsula (Mexico). These speleothems grew during the Middle to Late Quaternary and were dated by 230Th-U techniques to provide upper depth limits for past sea levels. We report the first relative sea-level limits for Marine Isotope Stages (MIS) 11 and 6, and present new evidence for sea-level oscillations during MIS 5 and early MIS 1. For the latter periods, the origin of growth interruptions is evaluated by combining petrographic methods with trace element analyses. The MIS 5c sea-level highstand probably occurred between 103.94 ± 0.58 ka and 96.82 ± 0.42 ka and must have exceeded -10.8 m (relative to present-day local sea level). The minimum average rate of sea-level fall over a 9.4 ka-long period during the MIS 5e/5d transition is calculated from stalagmite and published coral data at 1.74 ± 0.37 m/ka. For the early Holocene, previous discrepancies with respect to a potential multimetre oscillation of local sea level were found to be challenging to reconcile with the existing speleothem data from the area.  相似文献   
205.
This paper records the findings from c. 80 prehistoric sites that have been discovered in the alluvial deposits of the rivers Creuse, Cher, and Loir, tributaries of the middle Loire River, over the period since 1981. These deposits comprise river terrace aggradations formed during successive glacial–interglacial cycles which have recorded climate and environment during Quaternary time. The systematic dating of these river deposits by Electron Spin Resonance (ESR) applied to optically bleached sedimentary quartz has resulted in the establishment of a chronological framework for the evolution of these rivers during Lower and Middle Pleistocene (between 1.7 Ma and 130 ka). Evidence for Early Palaeolithic (Mode 1) industries with an in situ context (workshops, soils) in the highest aggradations indicates that Hominins were present in the study area, near the geographical centre of France (47°N), around 1.1 Ma. Examination of the sites indicates that Human occupations were located along valley bottom sites during temperate episodes. Subsequently, after a gap of several hundred thousand years industries with handaxes appear in the Middle Loire Basin in the interval between 700 and 600 ka, and then continuously from 400 ka. These two phases of settlement produced industrial assemblages with clear differences in their responses to the supplies of raw materials and in the modes of making flakes.  相似文献   
206.
This reply is in response to Burgess et al.’s Commentary on our original article, “The REDD Menace: Resurgent protectionism in Tanzania's mangrove forests.” Their commentary, we argue, shifts the focus from WWF's past conservation work and environmental narratives in the Rufiji Delta North, the subject of our article, to its current forest carbon inventory work. We do not comment on WWF's new work. Our principal concern remains on the environmental narratives crafted by WWF that were used to justify attempts to remove Warufiji small-scale rice farmers from the mangrove forests in the Rufiji Delta North. We emphasize the political implications of designating forest areas for carbon forestry and REDD projects in terms of forest dependent people's land and livelihood rights. We argue from environmental historical and social justice perspectives that the Warufiji should be counted among the winners, not the losers, in the green value chains currently under construction.  相似文献   
207.
Reduced Emissions from Deforestation and Degradation (REDD+) is being proclaimed as “a new direction in forest conservation” (Anglesen, 2009: 125). This financial incentives-based climate change mitigation strategy proposed by the UNEP, World Bank, GEF and environmental NGOs seeks to integrate forests into carbon sequestration schemes. Its proponents view REDD+ as part of an adaptive strategy to counter the effects of global climate change. This paper combines the theoretical approaches of market environmentalism and environmental narratives to examine the politics of environmental knowledge that are redefining socio-nature relations in the Rufiji Delta, Tanzania to make mangrove forests amenable to markets. Through a case study of a “REDD-readiness” climate change mitigation and adaptation project, we demonstrate how a shift in resource control and management from local to global actors builds upon narratives of environmental change (forest loss) that have little factual basis in environmental histories. We argue that the proponents of REDD+ (Tanzanian state, aid donors, environmental NGOs) underestimate the agency of forest-reliant communities who have played a major role in the making of the delta landscape and who will certainly resist the injustices they are facing as a result of this shift from community-based resource management to fortress conservation.  相似文献   
208.
A luminescence dating study has been applied to inform the history and archaeology of two early medieval buildings in north western France. Five bricks were sampled from the medieval churches (10th–11th centuries A.D.) of Rugles and Condé-sur-Risle in Normandy. The samples were divided and tested in the luminescence laboratories of the University of Durham (UK) and of Iramat-CRP2A, University of Bordeaux 3 (France). The fine grain and quartz inclusion techniques were applied, and tests included an examination of the anomalous fading of the luminescence signal from fine grain samples and coarse grains of feldspar. With one exception, the dates produced using the fine grain technique, although corrected for fading, were significantly younger than those produced with quartz inclusions. Although most of the corrected fine grain dates were consistent with the medieval construction of the churches, the brick fabric is of Roman type by archaeological assessment, and this is supported by the quartz coarse grain dates. We conclude that the bricks sampled are re-used, likely to be of Roman origin, and that the reliability of measurements with feldspars in brick fabrics requires wider investigation.  相似文献   
209.
The diversity–stability relationship is the subject of a long-standing debate in ecology, but the genetic component of diversity has seldom been explored. In this study, we analyzed the interplay between genetic diversity and demographic responses to environmental pressures. This analysis included 30 meadows formed by the Mediterranean endemic seagrass, Posidonia oceanica, showing a wide range of population dynamics ranging from a near equilibrium state to steep decline due to strong environmental pressures close to aquaculture installations. Our results show that sedimentation rates are much better predictors of mortality than clonal or genetic components. An unexpected positive trend was observed between genotypic diversity and mortality, along with a negative relationship between allelic richness and net population growth. Yet such trends disappeared when excluding the most extreme cases of disturbance and mortality, suggesting the occurrence of a threshold below which no relationship exists. These results contrast with the positive relationship between genotypic diversity and resistance or resilience observed in previous manipulative experiments on seagrass. We discuss the reasons for this discrepancy, including the difficulties in designing experiments reflecting the complexity of natural meadows.  相似文献   
210.
The Katanga province, Democratic Republic of Congo, hosts world-class cobalt deposits accounting for ~50% of the world reserves. They originated from sediment-hosted stratiform copper and cobalt sulfide deposits within Neoproterozoic metasedimentary rocks. Heterogenite, the main oxidized cobalt mineral, is concentrated as “cobalt caps” along the top of silicified dolomite inselbergs. The supergene cobalt enrichment process is part of a regional process of residual ore formation that also forms world-class “manganese cap” deposits in western Katanga, i.e., the “black earths” that are exploited by both industrial and artisanal mining. Here, we provide constraints on the genesis and the timing of these deposits. Ar–Ar analyses of oxidized Mn ore and in situ U–Pb SIMS measurements of heterogenite yield Mio–Pliocene ages. The Ar–Ar ages suggest a multi-phase process, starting in the Late Miocene (10–5 Ma), when the metal-rich substratum was exposed to the action of meteoric fluids, due to major regional uplift. Further oxidation took place in the Pliocene (3.7–2.3 Ma) and formed most of the observed deposits under humid conditions: Co- and Mn-caps on metal-rich substrata, and coeval Fe laterites on barren areas. These deposits formed prior to the regional shift toward more arid conditions in Central Africa. Arid conditions still prevailed during the Quaternary and resulted in erosion and valley incision, which dismantled the metal-bearing caps and led to ore accumulation in valleys and along foot slopes.  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