全文获取类型
收费全文 | 708篇 |
免费 | 60篇 |
国内免费 | 46篇 |
专业分类
测绘学 | 28篇 |
大气科学 | 138篇 |
地球物理 | 187篇 |
地质学 | 194篇 |
海洋学 | 68篇 |
天文学 | 104篇 |
综合类 | 1篇 |
自然地理 | 94篇 |
出版年
2024年 | 3篇 |
2023年 | 3篇 |
2022年 | 6篇 |
2021年 | 27篇 |
2020年 | 33篇 |
2019年 | 22篇 |
2018年 | 23篇 |
2017年 | 26篇 |
2016年 | 36篇 |
2015年 | 37篇 |
2014年 | 34篇 |
2013年 | 48篇 |
2012年 | 28篇 |
2011年 | 42篇 |
2010年 | 45篇 |
2009年 | 50篇 |
2008年 | 43篇 |
2007年 | 41篇 |
2006年 | 44篇 |
2005年 | 32篇 |
2004年 | 33篇 |
2003年 | 21篇 |
2002年 | 21篇 |
2001年 | 15篇 |
2000年 | 15篇 |
1999年 | 5篇 |
1998年 | 8篇 |
1997年 | 9篇 |
1996年 | 1篇 |
1995年 | 8篇 |
1994年 | 10篇 |
1993年 | 5篇 |
1992年 | 9篇 |
1991年 | 3篇 |
1990年 | 6篇 |
1989年 | 2篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 6篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有814条查询结果,搜索用时 31 毫秒
771.
ABSTRACT The impact of climate change on runoff characteristics is investigated for the Upper Tisza basin, in eastern Central Europe. For a reliable estimation of uncertainty, an appropriate stochastic weather generator is embedded into a Monte Carlo cycle capable of generating any large number of independent, equally probable, 100-year-long daily sequences of synthetic data with which a hydrological model is driven in order to obtain the hydrological responses to the meteorological data sequences. According to our results, a decrease of daily average runoff is likely to occur in the future in the Upper Tisza basin, especially in July and August. The occurrence of water levels below the critical low level is estimated to increase between July and October. Level-3 flood warnings are projected to be less frequent in the future; however, they will tend to be more severe than in the historical period. 相似文献
772.
The Charisma of Coastal Ecosystems: Addressing the Imbalance 总被引:1,自引:0,他引:1
Carlos M. Duarte William C. Dennison Robert J. W. Orth Tim J. B. Carruthers 《Estuaries and Coasts》2008,31(2):233-238
Coastal ecosystems including coral reefs, mangrove forests, seagrass meadows, and salt marshes are being lost at alarming rates, and increased scientific understanding of causes has failed to stem these losses. Coastal habitats receive contrasting research effort, with 60% of all of the published research carried out on coral reefs, compared to 11–14% of the records for each of salt marshes, mangrove forests, and seagrass meadows. In addition, these highly connected and interdependent coastal ecosystems receive widely contrasting media attention that is disproportional to their scientific attention. Seagrass ecosystems receive the least attention in the media (1.3% of the media reports) with greater attention on salt marshes (6.5%), considerably more attention on mangroves (20%), and a dominant focus on coral reefs, which are the subject of three in every four media reports on coastal ecosystems (72.5%). There are approximately tenfold lower reports on seagrass meadows in the media for every scientific paper published (ten), than the 130–150 media reports per scientific paper for mangroves and coral reefs. The lack of public awareness of losses of less charismatic ecosystems results in the continuation of detrimental practices and therefore contributes to continued declines of coastal ecosystems. More effective communication of scientific knowledge about these uncharismatic but ecologically important coastal habitats is required. Effective use of formal (e.g., school curricula, media) and informal (e.g., web) education avenues and an effective partnership between scientists and media communicators are essential to raise public awareness of issues, concerns, and solutions within coastal ecosystems. Only increased public understanding can ultimately inform and motivate effective management of these ecologically important coastal ecosystems. 相似文献
773.
774.
Which catchment characteristics control the temporal dependence structure of daily river flows?
下载免费PDF全文
![点击此处可从《水文研究》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Andrew Chiverton Jamie Hannaford Ian Holman Ron Corstanje Christel Prudhomme John Bloomfield Tim M. Hess 《水文研究》2015,29(6):1353-1369
Hydrological classification systems seek to provide information about the dominant processes in the catchment to enable information to be transferred between catchments. Currently, there is no widely agreed‐upon system for classifying river catchments. This paper develops a novel approach to classifying catchments based on the temporal dependence structure of daily mean river flow time series, applied to 116 near‐natural ‘benchmark’ catchments in the UK. The classification system is validated using 49 independent catchments. Temporal dependence in river flow data is driven by the flow pathways, connectivity and storage within the catchment and can thus be used to assess the influence catchment characteristics have on moderating the precipitation‐to‐flow relationship. Semi‐variograms were computed for the 116 benchmark catchments to provide a robust and efficient way of characterising temporal dependence. Cluster analysis was performed on the semi‐variograms, resulting in four distinct clusters. The influence of a wide range of catchment characteristics on the semi‐variogram shape was investigated, including: elevation, land cover, physiographic characteristics, soil type and geology. Geology, depth to gleyed layer in soils, slope of the catchment and the percentage of arable land were significantly different between the clusters. These characteristics drive the temporal dependence structure by influencing the rate at which water moves through the catchment and/or the storage in the catchment. Quadratic discriminant analysis was used to show that a model with five catchment characteristics is able to predict the temporal dependence structure for un‐gauged catchments. This method could form the basis for future regionalisation strategies, as a way of transferring information on the precipitation‐to‐flow relationship between gauged and un‐gauged catchments. © 2014 The Authors. Hydrological Processes by published by John Wiley & Sons, Ltd. 相似文献
775.
Peter F. Sale Tundi Agardy Cameron H. Ainsworth Blake E. Feist Johann D. Bell Patrick Christie Ove Hoegh-Guldberg Peter J. Mumby David A. Feary Megan I. Saunders Tim M. Daw Simon J. Foale Phillip S. Levin Kenyon C. Lindeman Kai Lorenzen Robert S. Pomeroy Edward H. Allison R.H. Bradbury Jennifer Corrin Alasdair J. Edwards David O. Obura Yvonne J. Sadovy de Mitcheson Melita A. Samoilys Charles R.C. Sheppard 《Marine pollution bulletin》2014
Over 1.3 billion people live on tropical coasts, primarily in developing countries. Many depend on adjacent coastal seas for food, and livelihoods. We show how trends in demography and in several local and global anthropogenic stressors are progressively degrading capacity of coastal waters to sustain these people. Far more effective approaches to environmental management are needed if the loss in provision of ecosystem goods and services is to be stemmed. We propose expanded use of marine spatial planning as a framework for more effective, pragmatic management based on ocean zones to accommodate conflicting uses. This would force the holistic, regional-scale reconciliation of food security, livelihoods, and conservation that is needed. Transforming how countries manage coastal resources will require major change in policy and politics, implemented with sufficient flexibility to accommodate societal variations. Achieving this change is a major challenge – one that affects the lives of one fifth of humanity. 相似文献
776.
Lava deltas, formed where lava enters the ocean and builds a shelf of new land extending from the coastline, represent a significant local hazard, especially on populated ocean island volcanoes. Such structures are unstable and prone to collapse—events that are often accompanied by small explosions that can deposit boulders and cobbles hundreds of meters inland. Explosions that coincide with collapses of the East Lae ‘Apuki lava delta at Kīlauea Volcano, Hawai‘i, during 2005–2007 followed an evolutionary progression mirroring that of the delta itself. A collapse that occurred when the lava–ocean entry was active was associated with a blast of lithic blocks and dispersal of spatter and fine, glassy tephra. Shortly after delta growth ceased, a collapse exposed hot rock to cold ocean water, resulting in an explosion composed entirely of lithic blocks and lapilli. Further collapse of the delta after several months of inactivity, by which time it had cooled significantly, resulted in no recognizable explosion deposit. Seaward displacement and subsidence of the coastline immediately inland of the delta was measured by both satellite and ground-based sensors and occurred at rates of several centimeters per month even after the lava–ocean entry had ceased. The anomalous deformation ended only after complete collapse of the delta. Monitoring of ground deformation may therefore provide an indication of the potential for delta collapse, while the hazard associated with collapse can be inferred from the level of activity, or the time since the last activity, on the delta. 相似文献
777.
Lisa Johnston Gary S. Wilson Andrew R. Gorman Stuart A. Henrys Huw Horgan Roger Clark Tim R. Naish 《Global and Planetary Change》2008,62(1-2):61-76
Fifty-two kilometres of multi-channel seismic reflection data were acquired from the southern McMurdo Ice Shelf (SMIS) during potential drill site investigations for the Antarctic Drilling (ANDRILL) program. The survey was acquired atop 110 to 220 m of floating ice and extended across ablation and accumulation zones of the ice shelf. Seismic processing was tailored to the ice shelf environment, including: datum static corrections to account for changes in the thickness and average velocity of the near-surface firn layer, and changes in the surface elevation across the survey area; residual static corrections to account for near-surface ice shelf irregularities; and two-step predictive deconvolution to suppress ice and firn layer multiples. A model for the ice shelf thickness was also incorporated in the interval velocity model during depth conversion to ensure that the ice shelf structure did not impose non-static shifts on the seismic section.The depth converted CMP stacked sections reveal several N to NE trending normal faults, that offset reflective horizons by up to 150 m within the lower part of the section and form a broad east-dipping, half-graben structure. The seafloor possesses trough and arch morphology in parallel with the half-graben structure. These features are interpreted as the southern extension of the Terror Rift. The rift succession comprises a dislocated (?)early-Miocene synrift package and a relatively undeformed (?)late-Miocene post-rift package separated by an erosional unconformity. The post-rift package infills and onlaps the rift topography, and drapes over the graben system, reaching a maximum thickness of 400 m. Throughout the post-rift phase, the basin was also influenced by Neogene volcanism, evidenced by three small volcanic features within the seismic profiles, and associated successions of inferred volcanic material. An angular unconformity within the post-rift succession is interpreted as a flexural horizon related to the load of Mount Discovery and/or Mount Morning. Up to 150 m of flexural moat fill occurs above this surface at ~ 20 km from the load centres. The post-rift succession also includes several glacio-geomorphic features, the orientation and morphology of which indicate an approximately SW to NE ice flow direction during a mid-Miocene grounding event and a SE to NW ice flow direction during Quaternary ice sheet grounding events.The thickness and lower extent of the rift succession was not able to be determined because signal-to-noise ratio and vertical resolution were low at these depths. Strata from an earlier, Paleogene, rift episode may underlie the Terror Rift succession, or it may be directly underlain by acoustic basement. A Paleogene rift episode has previously been proposed based on the occurrence of Eocene fossiliferous erratics around the margin of the SMIS and the structural setting revealed by the SMIS seismic reflection profiles is consistent with this hypothesis. 相似文献
778.
A sequence of Late Holocene moraines on the foreland of the Mueller Glacier, Southern Alps, New Zealand, forms part of a local moraine‐age database used to establish a regional glacier chronology and subsequently to investigate potential intra‐hemispheric and global climate forcing mechanisms. We present new sedimentological and geomorphological evidence that a set of these moraine ridges, previously considered to represent individual advances, constitutes a single moraine complex (the ‘Mueller Memorial Moraine’) formed by supraglacial transport of a large volume of landslide debris to the glacier terminus. Because a moraine formed in this way is not necessarily associated with an advance triggered by a climate event, we question the palaeoclimatic significance of the Mueller Memorial Moraine, as well as that of other moraines in comparable settings. Our findings suggest that the mode of formation and glacio‐dynamical context of moraines whose ages contribute to existing palaeoclimate reconstructions need to be re‐examined in order to assess the reliability of these reconstructions. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
779.
Naomi Greenwood Rodney M. Forster Veronique Créach Suzanne J. Painting Anna Dennis Stewart J. Cutchey Tiago Silva David B. Sivyer Tim Jickells 《Ocean Dynamics》2012,62(2):307-320
The seasonal and interannual variability in the phytoplankton community in Liverpool Bay between 2003 and 2009 has been examined
using results from high frequency, in situ measurements combined with discrete samples collected at one location in the bay.
The spring phytoplankton bloom (up to 29.4 mg chlorophyll m−3) is an annual feature at the study site and its timing may vary by up to 50 days between years. The variability in the underwater
light climate and turbulent mixing are identified as key factors controlling the timing of phytoplankton blooms. Modelled
average annual gross and net production are estimated to be 223 and 56 g C m−2 year−1, respectively. Light microscope counts showed that the phytoplankton community is dominated by diatoms, with dinoflagellates
appearing annually for short periods of time between July and October. The zooplankton community at the study site is dominated
by copepods and use of a fine mesh (80 μm) resulted in higher abundances of copepods determined (up to 2.5 × 106 ind. m−2) than has previously reported for this location. There is a strong seasonal cycle in copepod biomass and copepods greater
than 270 μm contribute less than 10% of the total biomass. Seasonal trends in copepod biomass lag those in the phytoplankton
community with a delay of 3 to 4 months between the maximum phytoplankton biomass and the maximum copepod biomass. Grazing
by copepods exceeds net primary production at the site and indicates that an additional advective supply of carbon is required
to support the copepod community. 相似文献
780.
Seismic data are increasingly applied to predict the characteristics of reservoirs, as their quality improves. Since the change
of pressure is a major component in exploitation of reservoirs, a thorough understanding of the influence of pressure on seismic
velocity is also important. In this study we introduce the first results of the developed petrophysical model which describes
the pressure dependence of seismic velocity. The model is based on the idea that microcracks in rocks open and close under
the change of pressure. Laboratory measurements are presented on several sandstone samples. Longitudinal wave velocities were
measured at various incremental pressures increased from 0 to 20 MPa. During the measurements, the pulse transmission technique
was used and the parameters of the model were determined by using a linearized inversion method. The inversion results proved
that the proposed petrophysical model well applies in practice. 相似文献