全文获取类型
收费全文 | 250篇 |
免费 | 22篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 36篇 |
地球物理 | 72篇 |
地质学 | 87篇 |
海洋学 | 19篇 |
天文学 | 35篇 |
自然地理 | 24篇 |
出版年
2022年 | 3篇 |
2021年 | 8篇 |
2020年 | 7篇 |
2019年 | 7篇 |
2018年 | 13篇 |
2017年 | 12篇 |
2016年 | 17篇 |
2015年 | 8篇 |
2014年 | 19篇 |
2013年 | 19篇 |
2012年 | 22篇 |
2011年 | 13篇 |
2010年 | 12篇 |
2009年 | 14篇 |
2008年 | 9篇 |
2007年 | 14篇 |
2006年 | 12篇 |
2005年 | 11篇 |
2004年 | 9篇 |
2003年 | 4篇 |
2002年 | 3篇 |
2001年 | 4篇 |
2000年 | 6篇 |
1999年 | 1篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 6篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1991年 | 3篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1979年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有276条查询结果,搜索用时 31 毫秒
131.
Talitha L. F. Costa Michelle P. Araújo Bastiaan A. Knoppers Renato S. Carreira 《Aquatic Geochemistry》2011,17(1):1-19
In the present work, we evaluated the origin of organic matter in the tropical estuarine-lagoon system of Mundaú–Manguaba,
NE Brazil, by considering the bulk (organic carbon and chlorophyll-a) and lipidic (n-alcohols and sterols) composition of suspended particles. Water samples were collected in August 2006 from
24 stations covering the salinity gradient from the rivers down to the sea outlet. Chlorophyll-a (Chl-a) varied from 22.7 to 134.1 μg L−1 in the lagoons, indicating eutrophic to hypertrophic conditions at the time of sampling. The high correlation between Chl-a and phytol together with the molar C:N ratio indicated the presence of fresh and recently produced autochthonous particulate
organic matter throughout the system, except for the river samples. The elevated concentrations of short-chain n-alcohols
and phytosterols, mainly 24-methylcholesta-5,24(28)-dien-3β-ol, also corroborated the predominance of autochthonous organic
matter in the lagoons but were generated by distinct sources: cianobacteria in the freshwater Manguaba lagoon and diatoms
in the brackish Mundaú lagoon compartments. Input of terrestrial organic matter was only detected in the rivers themselves
or at the upper river–lagoon interfaces. Coprostanol indicated contamination by sewage in Mundaú lagoon and in some rivers,
but at lower levels when compared to other Brazilian coastal lagoons and estuaries. 相似文献
132.
133.
Markus Stoffel Michelle Bollschweiler Lorenzo Vázquez‐Selem Osvaldo Franco‐Ramos David Palacios 《地球表面变化过程与地形》2011,36(9):1209-1217
Dynamics and rates of rockfalls have been repeatedly studied in mountain environments with archival records as well as lichenometric, radiocarbon or dendrogeomorphic approaches. In this study, we test the potential of conifers growing at a low‐latitude, high‐elevation site as a dendrogeomorphic tool to reconstruct to calendar dates associated rockfall activity. Analysis is based on tree‐ring records of Mexican mountain pine (Pinus hartwegii Lindl.) growing at timberline [~4000 m above sea level (a.s.l.)] and at the runout fringe of a north–northeast (NNE)‐facing slope of the dormant Iztaccíhuatl volcano (Mexico), which is subject to frequent rockfalls. The potential and limitations of tree‐ring data are demonstrated based on 67 rockfall impacts dated in the increment‐ring series of 24 trees since ad 1836. While findings of this paper are site‐specific, the study clearly shows the potential of dendrogeomorphic approaches in extra‐Alpine, low‐latitude environments and for the understanding of rockfall processes in space and time. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
134.
Jayantha Obeysekera Michelle Irizarry Joseph Park Jenifer Barnes Tibebe Dessalegne 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(4):495-516
Recent climate change projections suggest that negative impacts on flood control and water supply functions and on existing
and future ecosystem restoration projects in south Florida are possible. An analysis of historical rainfall and temperature
data of the Florida peninsula indicates that there were no discernible trends in both the long-term record and during the
more recent period (1950–2007). A comparison of General Circulation Model (GCM) results for the 20th century with the historical
data shows that many of the GCMs do not capture the statistical characteristics of regional rainfall and temperature regimes
in south Florida. Investigation of historical sea level data at Key West finds evidence for an increase in the occurrence
and variance of maximum sea level events for the period 1961–2008 in relation to 1913–1960, along with a shift of energy from
shorter to longer timescales. In order to understand the vulnerability of the water management system in south Florida in
response to changing precipitation and evapotranspiration forcing, a sensitivity analysis using a regional-scale hydrologic
and water management model is conducted. Model results suggest that projected climate change has potential to reduce the effectiveness
of water supply and flood control operations for all water sectors. These findings emphasize that questions on the potential
impacts of climate change need to be investigated with particular attention paid to the uncertainties of such projections. 相似文献
135.
Based on observational meteorological data since A.D. 1864 and tree-ring records of debris-flow activity, this paper assesses changes in rainfall characteristics and their impact on the triggering of geomorphic events in a high-elevation watershed of the Swiss Alps since the end of the Little Ice Age. No trends are visible in the frequency of heavy rainfall events, but we observe a reduced number of heavy, short-lived rainfalls in summer and a concentration of advective storms is recorded in late summer and early fall since the late 1980s. These changes in triggering meteorological conditions resulted in a cluster of debris flows in the early decades of the twentieth century and a lowering of debris-flow activity since the mid 1990s, and may be mirroring the observed changes in persistent high-pressure systems over the Alps. We also observe intra-seasonal differences in debris-flow system response reflecting the state of the permafrost body in the source area of debris flows, allowing for very small debris flows to be released by limited rainfall inputs (<20 mm) in June and July. The same quantities of rain will not trigger debris flows in August or September, when a thick active layer of the permafrost body is capable of absorbing water. With the projected amplitude of climatic change, seasonality, return intervals and volumes of debris flows are likely to be altered. RCM projections based on the IPCC A2 scenario suggest a decrease in heavy summer rainfalls which will most likely result in a (further) reduction of the overall frequency of debris flows, leaving more time for sediment to accumulate in the channel. Such an increase of channel accumulation rates along with the projected destabilization of the steep rock-glacier body is likely, in turn, to exert control ultimately on sediment volumes released from the source areas during future events. Observations from adjacent catchments suggest that extremely large debris flows, beyond historical experience, could occur at the study site and in similar debris-flow systems of the Valais Alps originating from periglacial environments. 相似文献
136.
Joseph Park Jayantha Obeysekera Michelle Irizarry Jenifer Barnes Paul Trimble Winifred Park-Said 《Climatic change》2011,107(1-2):109-128
Water resource management in South Florida faces nearly intractable problems, in part due to weather and climate variability. Rising sea level and coastal storm surge are two phenomena with significant impacts on natural systems, fresh water supplies and flood drainage capability. However, decision support information regarding management of water resources in response to storm surge is not well developed. In an effort to address this need we analyze long term tidal records from Key West, Pensacola and Mayport Florida to extract surge distributions, to which we apply a nonlinear eustatic sea level rise model to project storm surge return levels and periods. Examination of climate connections reveals a statistically significant dependence between surge distributions and the Atlantic Multidecadal Oscillation (AMO). Based on a recent probabilistic model for AMO phase changes, we develop AMO-dependent surge distributions. These AMO-dependent surge projections are used to examine the flood control response of a coastal water management structure as an example of how climate dependent water resource forcings can be used in the formulation of decision support tools. 相似文献
137.
Markus Stoffel Thomas Mendlik Michelle Schneuwly-Bollschweiler Andreas Gobiet 《Climatic change》2014,122(1-2):141-155
This study uses a long dataset of past debris flows from eight high-elevation catchments in the Swiss Alps for which triggering conditions since AD 1864 have been reconstructed. The torrents under investigation have unlimited sediment supply and the triggering of debris flows is thus mainly controlled by climatic factors. Based on point-based downscaled climate scenarios for meteorological stations located next to the catchments and for the periods 2001–2050 and 2051–2100, we study the evolution of temperature and rainfall above specific thresholds (10, 20, 30, 40 and 50 mm) and durations (1, 2 or 3 days). We conclude that the drier conditions in future summers and the wetting of springs, falls and early winters are likely to have significant impacts on the behavior of debris flows. Based on the current understanding of debris-flow systems and their reaction to rainfall inputs, one might expect only slight changes in the overall frequency of events by the mid-21st century, but possibly an increase in the overall magnitude of debris flows due to larger volumes of sediment delivered to the channels and an increase in extreme precipitation events. In the second half of the 21st century, the number of days with conditions favorable for the release of debris flows will likely decrease, especially in summer. The anticipated increase of rainfall during the shoulder seasons (March, April, November, December) is not expected to compensate for the decrease in future heavy summer rainfall over 2 or 3 days. 相似文献
138.
Estuarine sediment deposition during wetland restoration: A GIS and remote sensing modeling approach
Michelle Elizabeth Newcomer Amber Jean Michael Kuss Tyler Ketron Alex Remar Vivek Choksi J. W. Skiles 《国际地球制图》2013,28(4):451-467
Restoration is currently underway in the industrial salt flats of San Francisco Bay, California. Remote sensing of suspended sediment concentration and other GIS predictor variables were used to model sediment deposition within recently restored ponds. Suspended sediment concentrations were calibrated to reflectance values from Landsat TM 5 and ASTER satellite image data using three statistical techniques—linear regression, multivariate regression, and Artificial Neural Network (ANN) regression. Multivariate and ANN regressions using ASTER proved to be the most accurate methods, yielding r2 values of 0.88 and 0.87, respectively. Predictor variables such as sediment grain size and tidal frequency were used in the Marsh Sedimentation (MARSED) model for predicting deposition rates. MARSED results show a root mean square deviation (RMSD) of 66.8 mm (<1σ) between modeled and field observations. This model was applied to a pond breached in November 2010 and indicated that the pond will reach sediment equilibrium levels after 60 months of tidal inundation. 相似文献
139.
Sara Savi Michelle Schneuwly‐Bollschweiler Bastian Bommer‐Denns Markus Stoffel Fritz Schlunegger 《地球表面变化过程与地形》2013,38(9):959-969
The coupling relationships between hillslope and channel network are fundamental for the understanding of mountainous landscapes' evolution. Here, we applied dendrogeomorphic methods to identify the hillslope–channel relationship and the sediment transfer dynamics within an alpine catchment, at the highest possible resolution. The Schimbrig catchment is located in the central Swiss Alps and can be divided into two distinct geomorphic sectors. To the east, the Schimbrig earth flow is the largest sediment source of the basin, while to the west, the Rossloch channel network is affected by numerous shallow landslides responsible for the supply of sediment from hillslopes to channels. To understand the connectivity between hillslopes and channels and between sources and sink, trees were sampled along the main Rossloch stream, on the Schimbrig earth flow and on the Rossloch depositional area. Geomorphic observations and dendrogeomophic results indicate different mechanisms of sediment production, transfer and deposition between upper and lower segments of the channel network. In the source areas (upper part of the Rossloch channel system), sediment is delivered to the channel network through slow movements of the ground, typical of earth flow, shallow landslides and soil creep. Contrariwise, in the depositional area (lower part of the channel network), the mechanisms of sediment transfer are mainly due to torrential activity, floods and debris flows. Tree analysis allowed the reconstruction of periods of high activity during the last century for the entire catchment. The collected dataset presents a very high temporal resolution but we encountered some limitations in establishing the source‐to‐sink connectivity at the catchment‐wide scale. Despite these uncertainties, for decennial timescales the results suggest a direct coupling between hillslopes and neighbouring channels in the Rossloch channel network, and a de‐coupling between sediment sources and sink farther downstream, with connections possible only during extraordinary events. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
140.
William H. McDowell Miguel C. Leon Michelle D. Shattuck Jody D. Potter Tamara Heartsill-Scalley Grizelle González James B. Shanley Adam S. Wymore 《水文研究》2021,35(4):e14146
Catchments in the Luquillo Experimental Forest (LEF) of Puerto Rico are warm, wet and tropical with steep elevational relief creating gradients in temperature and rainfall. Long-term objectives of research at the site are to understand how changing climate and disturbance regimes alter hydrological and biogeochemical processes in the montane tropics and to provide information critical for managing and conserving tropical forest ecosystems globally. Measurements of hydrology and meteorology span decades, and currently include temperature, humidity, precipitation, cloud base level, throughfall, groundwater table elevation and stream discharge. The chemistry of rain, throughfall, and streams is measured weekly and lysimeters and wells are sampled monthly to quarterly. Multiple data sets document the effects of major hurricanes including Hugo (1989), Georges (1998) and Maria (2017) on vegetation, biota and catchment biogeochemistry and provide some of the longest available records of biogeochemical fluxes in tropical forests. Here we present an overview of the findings and the data sets that have been generated from the LEF, highlighting their importance for understanding montane tropical watersheds in the context of disturbance and global environmental change. 相似文献