全文获取类型
收费全文 | 89篇 |
免费 | 9篇 |
专业分类
大气科学 | 3篇 |
地球物理 | 30篇 |
地质学 | 40篇 |
海洋学 | 17篇 |
天文学 | 5篇 |
综合类 | 1篇 |
自然地理 | 2篇 |
出版年
2021年 | 13篇 |
2020年 | 5篇 |
2019年 | 3篇 |
2018年 | 4篇 |
2017年 | 3篇 |
2016年 | 9篇 |
2015年 | 2篇 |
2014年 | 4篇 |
2013年 | 1篇 |
2012年 | 3篇 |
2011年 | 5篇 |
2010年 | 6篇 |
2009年 | 3篇 |
2008年 | 6篇 |
2007年 | 4篇 |
2006年 | 2篇 |
2005年 | 5篇 |
2004年 | 4篇 |
2003年 | 5篇 |
2002年 | 3篇 |
2001年 | 1篇 |
2000年 | 3篇 |
1998年 | 1篇 |
1993年 | 1篇 |
1980年 | 2篇 |
排序方式: 共有98条查询结果,搜索用时 15 毫秒
71.
Amado LL da Rosa CE Leite AM Moraes L Pires WV Pinho GL Martins CM Robaldo RB Nery LE Monserrat JM Bianchini A Martinez PE Geracitano LA 《Marine pollution bulletin》2006,52(2):199-206
Biomarkers of exposure and effect of pollutants were analyzed in croakers Micropogonias furnieri (Teleostei: Sciaenidae) captured in winter and summer in a polluted and in a non-polluted site at the Patos Lagoon estuary (Southern Brazil). Catalase and glutathione S-transferase activities (exposure biomarkers) and lipid peroxidation (effect biomarker) were analyzed in liver samples. Other two effect biomarkers were also studied: blood cells DNA damage (through comet assay and micronucleus test) and respiratory burst measurements. In a broad view, results point to an important seasonal variation of the biochemical biomarkers analyzed. However, data obtained clearly indicate that croakers collected in winter at the polluted site were subjected to a level of clastogenic agents sufficient to generate irreversible genetic damages (mutations) and impair the fish immune system. 相似文献
72.
Ana G. Elias Virginia M. Silbergleit Alicia L. Clua de Gonzalez 《Journal of Atmospheric and Solar》2011,73(11-12):1492-1499
The long-term variation of the semiannual amplitude in the geomagnetic activity index aa is analyzed with the purpose of contributing to the understanding of solar variability, directly linked to geomagnetic variability. The time series of the semiannual oscillation amplitude, obtained through a wavelet analysis of the daily aa series, presents a long-term variation similar to that shown by solar and geomagnetic indices, like aa itself or Dst. However, the maximum in the semiannual amplitude series occurs around 1947, almost 10 years before it occurs in solar and geomagnetic indices time series. The phase of the semiannual oscillation fluctuates around the values predicted by the equinoctial and Russell–McPherron models, with a predominance of the equinoctial mechanism during the period of maximum semiannual amplitude. A possible source of changes in the equinoctial mechanism would be the secular variation of the Earth's dipole tilt. But, since it does not follow the semiannual amplitude trend, at first sight, it seems not to be responsible for the equinoctial predominance around 1947. The analysis of quiet and disturbed days separately indicates that only disturbed days present the semiannual annual amplitude maximum around 1947, so the 10 year time shift could be due to the mechanism responsible for the semiannual variation in geomagnetically active periods. 相似文献
73.
Katherine B. Lininger Ann V. Rowan Bridget Livers Natalie Kramer Virginia Ruiz-Villanueva Alicia Sendrowski Sallie Burrough 《地球表面变化过程与地形》2021,46(14):2767-2772
Many geomorphologists who are mothers find it challenging to balance field research alongside pregnancy and caring for young children. We offer perspectives on the challenges to conducting fieldwork as mothers and possible solutions, as a means of promoting conversations and highlighting issues that are less commonly considered in field-based geomorphic research. Although every mother's experience and needs are different, we discuss strategies for conducting fieldwork, addressing childcare issues, and dealing with financial considerations. We call for our community to support geomorphologists who are pregnant or caring for young children in carrying out fieldwork to help enhance the diversity of voices and perspectives within our discipline. 相似文献
74.
Alicia M.Soderberg EnricoRamirez-Ruiz 《Monthly notices of the Royal Astronomical Society》2002,330(1):L24-L28
GRB 990123 was a long, complex gamma-ray burst accompanied by an extremely bright optical flash. We find different constraints on the bulk Lorentz of this burst to be consistent with the speculation that the optical light is emission from the reverse shock component of the external shock. Motivated by this currently favoured idea, we compute the prompt reverse shock emission to be expected for bursts in which multiwavelength observations allow the physical parameters to be constrained. We find that for reasonable assumptions about the velocity of source expansion, a strong optical flash mV ≈9 was expected from the reverse shocks, which were usually found to be mildly relativistic. The best observational prospects for detecting these prompt flashes are highlighted, along with the possible reasons for the absence of optical prompt detections in ongoing observations. 相似文献
75.
Mnica Susana Hoffmeyer Menndez María Clara Biancalana Florencia Nizovoy Alicia Mabel Torres Eduardo Ramn 《Estuarine, Coastal and Shelf Science》2009,84(3):181-392
This study focuses on the composition, abundance and distribution of ichthyoplankton in the inner shelf area off Bahía Blanca Estuary on the SW Atlantic Ocean during late spring. Eggs and larvae of Brevoortia aurea, Engraulis anchoita, Parona signata, Sciaenidae spp. – such as Cynoscion guatucupa and Micropogonias furnieri –, and Odontesthes argentinensis were found. Species richness was low probably as a result of season and shallow depths. Ichthyoplankton abundance reached values close to 10 000 per 10 m−3 (eggs) and 4000 per 10 m−3 (larvae) and displayed a spatial distribution pattern with maximum abundance values restricted to a band parallel to the coast. Differences between egg and larval patterns, probably derived from a different displacement and hydrodynamic behavior, were observed. Egg and larvae distribution patterns were found related with spawning areas and to directly depend on salinity and mesozooplankton. The larvae distribution pattern, in particular, was found to inversely depend on particulate organic carbon. In addition, the geographic location of egg and larvae maxima strongly coincided with a saline front reported for this area in springtime, thus suggesting a direct relationship with it. 相似文献
76.
Groundwater flow of freshwater from upland forests into salt marshes is influenced by hydrologic forces that operate over a wide range of temporal scales, including storm events, tidal fluctuations, seasonal variations in rainfall and evapotranspiration (ET). Groundwater salinity can be a useful first order indicator of the balance between these flow processes. A dipole-dipole electrical resistivity survey was conducted approximately monthly during 2005 to measure groundwater salinity across a portion of Crabhaul Creek, a tidal salt marsh basin at the boundary of the upland forest and the North Inlet marsh in South Carolina. The monthly electrical resistivity surveys were designed to provide a detailed, spatially continuous measurement of subsurface conductivity to a depth of 4 m in order to further investigate the seasonal variation in groundwater salinity. Resistivity models were corroborated by simultaneous measurements of salinity in nearby piezometers. The freshwater-brackish water interface was clearly imaged by the resistivity. Movement of this interface occurs on a timescale of months rather than a regular seasonal variation. The average salinity in the marsh basin is highest in late Summer (July–August) when ET is highest, and lowest during the Winter (November–December). The position of the brackish-freshwater interface changes, but is not well correlated to local rainfall or tidal cycles except under specific circumstances. A steady-state hydrological model correctly predicts the average position of the freshwater-brackish interface and suggests a linear relationship between the height of the water table and the location of the interface. These results suggest a complex relationship between precipitation events and groundwater flow from the forest into the marsh. 相似文献
77.
More than half of the surface sediments covering the continental shelves are sandy, which may permit substantial sub-seafloor pore water advection. Knowledge of sediment permeability is required for quantifying advection and associated solute transport, but studies of marine sediments typically report grain size analyses rather than permeability. Here data from 23 studies were examined to determine the range in permeabilities reported for sublittoral marine sands and to assess the utility of permeability–grain size relationships in this setting. In the resulting database, the permeability of small (∼30 cm) undisturbed cores collected from the sea floor all fell between 2 × 10−12 and 4 × 10−10 m2, a range where advective transport induced by wave and current action should be pervasive. The range in grain size was very similar for near-shore (<10 m water depth) and continental shelf samples (>10 m water depth), but the permeability of the continental shelf samples was consistently lower for the same median grain size. Empirical permeability–grain size relationships generated a poor fit (r2 = 0.35) for the aggregate data, but separate relationships for near-shore and continental shelf samples were significantly better, r2 = 0.66 and 0.77, respectively. Permeability–grain size relationships thus may be useful for sublittoral sands, but a larger database needs to be accumulated before reliable fit parameters and variability can be predicted. Thus it is recommended that permeability be routinely determined when characterizing sedimentological properties of marine sand deposits. Concurrent determinations of sediment bulk density and porosity may further improve estimates of permeability. 相似文献
78.
David H. Roberts Elena Grimoldi Louise Callard David J.A. Evans Chris D. Clark Heather A. Stewart Dayton Dove Margot Saher Colm Ó Cofaigh Richard C. Chiverrell Mark D. Bateman Steven G. Moreton Tom Bradwell Derek Fabel Alicia Medialdea 《地球表面变化过程与地形》2019,44(6):1233-1258
During the last glacial cycle an intriguing feature of the British-Irish Ice Sheet was the North Sea Lobe (NSL); fed from the Firth of Forth and which flowed south and parallel to the English east coast. The controls on the formation and behaviour of the NSL have long been debated, but in the southern North Sea recent work suggests the NSL formed a dynamic, oscillating terrestrial margin operating over a deforming bed. Further north, however, little is known of the behaviour of the NSL or under what conditions it operated. This paper analyses new acoustic, sedimentary and geomorphic data in order to evaluate the glacial landsystem imprint and deglacial history of the NSL offshore from NE England. Subglacial tills (AF2/3) form a discontinuous mosaic interspersed with bedrock outcrops across the seafloor, with the partial excavation and advection of subglacial sediment during both advance and retreat producing mega-scale glacial lineations and grounding zone wedges. The resultant ‘mixed-bed’ glacial landsystem is the product of a dynamic switch from a terrestrial piedmont-lobe margin with a net surplus of sediment to a partially erosive, quasi-stable, marine-terminating, ice stream lobe as the NSL withdrew northwards. Glaciomarine sediments (AF4) drape the underlying subglacial mixed-bed imprint and point to a switch to tidewater conditions between 19.9 and 16.5 ka cal BP as the North Sea became inundated. The dominant controls on NSL recession during this period were changing ice flux through the Firth of Forth ice stream onset zone and water depths at the grounding line; the development of the mixed-bed landsystem being a response to grounding line instability. © 2018 John Wiley & Sons, Ltd. 相似文献
79.
Dakhleh Oasis, the largest of the Egyptian Western Desert, presents an opportunity for diachronic study of lithic raw material preferences during the Middle Stone Age (MSA) of the Eastern Sahara. Archaeological aggregates and raw material sources are exposed and easily mapped. Diverse and abundant lithic raw materials derive from sandstone, shale, and limestone sources and are also found in secondary geological contexts. Three main raw materials were used, and there was strong preference for one of these: Tarawan chert. Easily available only in the north‐central oasis, this material was transported substantial distances even when other materials that were known and used by MSA peoples could be found closer at hand. There is little evidence for use of raw materials exogenous to Dakhleh Oasis. This pattern of usage does not appear to change from the older MSA units to the Aterian Dakhleh Unit. © 2002 Wiley Periodicals, Inc. 相似文献
80.
Researchers have described shifting relationships between communities and Protected Areas (PAs), from excluding communities to consultative relationships to participatory models. This research focuses on a PA created on formerly industrial timberland that was the focus of conflict between environmental activists and the timber industry. In a nearby formerly timber-dependent community, we assessed community use and support of the PA, and its perceived purposes and benefits, through a survey of residents and interviews with key stakeholders. Despite intense conflict surrounding its creation, we found support for the PA, and our case suggests a new possible relationship between PAs and communities, which is mitigating and helping to resolve natural resource conflict. We also found that community well-being benefits of the PA were unclear; we suggest that PA management should include cultural, economic, and historical context in objectives and interpretive materials; and should work to create economic opportunities connected to the PA. 相似文献