全文获取类型
收费全文 | 364篇 |
免费 | 21篇 |
国内免费 | 10篇 |
专业分类
测绘学 | 2篇 |
大气科学 | 50篇 |
地球物理 | 77篇 |
地质学 | 120篇 |
海洋学 | 53篇 |
天文学 | 38篇 |
综合类 | 1篇 |
自然地理 | 54篇 |
出版年
2023年 | 2篇 |
2022年 | 1篇 |
2021年 | 4篇 |
2020年 | 11篇 |
2019年 | 8篇 |
2018年 | 13篇 |
2017年 | 19篇 |
2016年 | 21篇 |
2015年 | 11篇 |
2014年 | 16篇 |
2013年 | 19篇 |
2012年 | 18篇 |
2011年 | 22篇 |
2010年 | 27篇 |
2009年 | 16篇 |
2008年 | 18篇 |
2007年 | 24篇 |
2006年 | 22篇 |
2005年 | 15篇 |
2004年 | 20篇 |
2003年 | 8篇 |
2002年 | 9篇 |
2001年 | 1篇 |
2000年 | 13篇 |
1999年 | 6篇 |
1998年 | 13篇 |
1997年 | 1篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1988年 | 2篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1980年 | 1篇 |
排序方式: 共有395条查询结果,搜索用时 234 毫秒
301.
302.
Lisa E. Osterman Richard Z. Poore Peter W. Swarzenski David B. Senn Steven F. DiMarco 《Geo-Marine Letters》2009,29(6):405-414
Since systematic measurements of Louisiana continental-shelf waters were initiated in 1985, hypoxia (oxygen content <2 mg
L−1) has increased considerably in an area termed the dead zone. Monitoring and modeling studies have concluded that the expansion
of the Louisiana shelf dead zone is related to increased anthropogenically derived nutrient delivery from the Mississippi
River drainage basin, physical and hydrographical changes of the Louisiana Shelf, and possibly coastal erosion of wetlands
in southern Louisiana. In order to track the development and expansion of seasonal low-oxygen conditions on the Louisiana
shelf prior to 1985, we used a specific low-oxygen foraminiferal faunal proxy, the PEB index, which has been shown statistically
to represent the modern Louisiana hypoxia zone. We constructed a network of 13 PEB records with excess 210Pb-derived chronologies to establish the development of low-oxygen and hypoxic conditions over a large portion of the modern
dead zone for the last 100 years. The PEB index record indicates that areas of low-oxygen bottom water began to appear in
the early 1910s in isolated hotspots near the Mississippi Delta and rapidly expanded across the entire Louisiana shelf beginning
in the 1950s. Since ~1950, the percentage of PEB species has steadily increased over a large portion of the modern dead zone.
By 1960, subsurface low-oxygen conditions were occurring seasonally over a large part of the geographic area now known as
the dead zone. The long-term trends in the PEB index are consistent with the 20th-century observational and proxy data for
low oxygen and hypoxia. 相似文献
303.
A program of geophysical mapping and vibracoring was conducted to better understand the geologic evolution of Apalachicola
Bay. Analyses of the geophysical data and sediment cores along with age control provided by 34 AMS 14C dates on marine shells and wood reveal the following history. As sea level rose in the early Holocene, fluvial deposits
filled the Apalachicola River paleochannel, which extended southward under the central part of the bay and seaward across
the continental shelf. Sediments to either side of the paleochannel contain abundant wood fragments, with dates documenting
that those areas were forested at 8,000 14C years b.p. As sea level continued to rise, spits formed of headland prodelta deposits. Between ∼6,400 and ∼2,500 14C years b.p., an Apalachicola prodelta prograded and receded several times across the inner shelf that underlies the western part of
the bay. An eastern deltaic lobe was active for a shorter time, between ∼5,800 and 5,100 14C years b.p. Estuarine benthic foraminiferal assemblages occurred in the western bay as early as 6,400 14C years b.p., and indicate that there was some physical barrier to open-ocean circulation and shelf species established by that time.
It is considered that shoals formed in the region of the present barrier islands as the rising sea flooded an interstream
divide. Estuarine conditions were established very early in the post-glacial flooding of the bay. 相似文献
304.
Stephen E. Watkins Alexander C. Whittaker Rebecca E. Bell Sam A. S. Brooke Vamsi Ganti Robert L. Gawthorpe Lisa C. McNeill Casey W. Nixon 《Basin Research》2020,32(6):1600-1625
The volume and grain-size of sediment supplied from catchments fundamentally control basin stratigraphy. Despite their importance, few studies have constrained sediment budgets and grain-size exported into an active rift at the basin scale. Here, we used the Corinth Rift as a natural laboratory to quantify the controls on sediment export within an active rift. In the field, we measured the hydraulic geometries, surface grain-sizes of channel bars and full-weighted grain-size distributions of river sediment at the mouths of 47 catchments draining the rift (constituting 83% of the areal extent). Results show that the sediment grain-size increases westward along the southern coast of the Gulf of Corinth, with the coarse-fraction grain-sizes (84th percentile of weighted grain-size distribution) ranging from approximately 19 to 91 mm. We find that the median and coarse-fraction of the sieved grain-size distribution are primarily controlled by bedrock lithology, with late Quaternary uplift rates exerting a secondary control. Our results indicate that grain-size export is primarily controlled by the input grain-size within the catchment and subsequent abrasion during fluvial transport, both quantities that are sensitive to catchment lithology. We also demonstrate that the median and coarse-fraction of the grain-size distribution are predominantly transported in bedload; however, typical sand-grade particles are transported as suspended load at bankfull conditions, suggesting disparate source-to-sink transit timescales for sand and gravel. Finally, we derive both a full Holocene sediment budget and a grain-size-specific bedload discharged into the Gulf of Corinth using the grain-size measurements and previously published estimates of sediment fluxes and volumes. Results show that the bedload sediment budget is primarily comprised (~79%) of pebble to cobble grade (0.475–16 cm). Our results suggest that the grain-size of sediment export at the rift scale is particularly sensitive to catchment lithology and fluvial mophodynamics, which complicates our ability to make direct inferences of tectonic and palaeoenvironmental forcing from local stratigraphic characteristics. 相似文献
305.
Celeste Benham Alison M. Cawood Geoffrey S. Cook Ange Darnell Peter C. Davison Miriam C. Goldstein Ayana Elizabeth Johnson Talina Konotchick Elisa M. Maldonado Alexis L. Pasulka Jennifer C. Prairie Serena M. Moseman Vera Tai Christina A. Tanner Tali Vardi Tara S. Whitty & Lisa A. Levin 《Marine Ecology》2008,29(2):319-320
306.
Lisa Cheong Christoph Kinkeldey Ingrid Burfurd Susanne Bleisch 《International journal of geographical information science》2020,34(5):1022-1050
ABSTRACT This paper reports on a controlled experiment evaluating how different cartographic representations of risk affect participants’ performance on a complex spatial decision task: route planning. The specific experimental scenario used is oriented towards emergency route-planning during flood response. The experiment compared six common abstract and metaphorical graphical symbolizations of risk. The results indicate a pattern of less-preferred graphical symbolizations associated with slower responses and lower-risk route choices. One mechanism that might explain these observed relationships would be that more complex and effortful maps promote closer attention paid by participants and lower levels of risk taking. Such user considerations have important implications for the design of maps and mapping interfaces for emergency planning and response. The data also highlights the importance of the ‘right decision, wrong outcome problem’ inherent in decision-making under uncertainty: in individual instances, more risky decisions do not always lead to worse outcomes. 相似文献
307.
ABSTRACT Urban greening, the improvement or increase of green spaces in cities, has purported environmental, individual, social and cultural benefits. The extent and qualities of urban green spaces, and our opportunities to engage with them, reflect and shape human responses to those spaces. Planning scholars recognise the traditional role and obligation of planning to help reduce social problems and see the potential for the public to be leaders in defining responses. However, use of technical, scientific and economic approaches by urban land managers can limit recognition of diverse connections to urban green and advance narrow conceptions of nature. We sample people’s responses to different forms of urban green and greening in three case studies from Melbourne, Australia. We show that modern connections and expressions are personal, social and dynamic. Human experiences are embedded in nature and connections develop from interactions with and about nature, in formal and informal spaces. Diverse connections prompt responses to nature, and actions affecting nature itself. Accordingly, we propose ways to develop more receptive, responsive, inclusive and connected forms of urban greening. These include recognising diverse connections and expressions, encouraging dynamic relationships with nature, and providing varied ways of engaging with urban green spaces that foster stewardship. 相似文献
308.
309.
310.