全文获取类型
收费全文 | 47篇 |
免费 | 2篇 |
专业分类
测绘学 | 1篇 |
大气科学 | 3篇 |
地球物理 | 15篇 |
地质学 | 12篇 |
海洋学 | 2篇 |
天文学 | 11篇 |
自然地理 | 5篇 |
出版年
2019年 | 1篇 |
2017年 | 1篇 |
2016年 | 3篇 |
2015年 | 2篇 |
2014年 | 2篇 |
2013年 | 3篇 |
2012年 | 1篇 |
2010年 | 3篇 |
2009年 | 4篇 |
2008年 | 1篇 |
2007年 | 1篇 |
2006年 | 2篇 |
2005年 | 1篇 |
2004年 | 3篇 |
2003年 | 6篇 |
2002年 | 3篇 |
2000年 | 2篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1994年 | 1篇 |
1992年 | 1篇 |
1990年 | 2篇 |
1988年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有49条查询结果,搜索用时 15 毫秒
11.
ABSTRACTGlobally, population ageing is one of the most pressing social and policy issues faced today. Over the next two decades, Australian society will face dramatic increases in the proportion of the population aged 65 years and over, as the baby boomers move into older age and fertility levels remain low. Yet population ageing is not a surprising or new trend—demographic changes in the age profile of a population tend to occur incrementally rather than suddenly. As a demographer and geographer, Graeme Hugo drew attention to this trend in Australia’s population more than three decades ago. Throughout Graeme Hugo’s vast breadth of work over the past 40 years, there has been a consistent thread of demographic analysis and academic thought associated with the ageing of Australia’s population. This paper focuses on Hugo’s contributions to academic thought and policy on Australia’s ageing population and the challenges associated with this for both service delivery and health policy as Australian society moves into an unprecedented era of population ageing. 相似文献
12.
The TLP configuration in this paper comes from the case study of the ISSC Derived Loads Committee I.2 in 1985. Two models, Model 1 and Model 2, are created aiming at developing a computational tool to handle hydro-dynamic and structural aspects together to help the TLP designer. Another objective is to generate relevant information for a non-linear static local stress analysis of TLP components from a dynamic hydro-structural global analysis. Model 2 is developed for LUSAS, a general purpose, well established, FE software, to validate the in-house program DCATLP. Model 1 and Model 2 are purposely made slightly different in the tether modelling so that the non-linear formulations in DCATLP to treat a TLP as a coupled system with the hull and tethers can be verified with a straightforward linear step-by-step dynamic analysis in LUSAS. The code in DCATLP has advanced features to account for some complex aspects of TLPs, such as compliant characteristics. The results from DCATLP can be directly used in the reliability based structural design of TLP components and subsequent optimisation studies. 相似文献
13.
Have applications of continuous rainfall–runoff simulation realized the vision for process‐based flood frequency analysis?
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)
Keith Beven was amongst the first to propose and demonstrate a combination of conceptual rainfall–runoff modelling and stochastically generated rainfall data in what is known as the ‘continuous simulation’ approach for flood frequency analysis. The motivations included the potential to establish better links with physical processes and to avoid restrictive assumptions inherent in existing methods applied in design flood studies. Subsequently, attempts have been made to establish continuous simulation as a routine method for flood frequency analysis, particularly in the UK. The approach has not been adopted universally, but numerous studies have benefitted from applications of continuous simulation methods. This paper asks whether industry has yet realized the vision of the pioneering research by Beven and others. It reviews the generic methodology and illustrates applications of the original vision for a more physically realistic approach to flood frequency analysis through a set of practical case studies, highlighting why continuous simulation was useful and appropriate in each case. The case studies illustrate how continuous simulation has helped to offer users of flood frequency analysis more confidence about model results by avoiding (or exposing) bad assumptions relating to catchment heterogeneity, inappropriateness of assumptions made in (UK) industry‐standard design event flood estimation methods, and the representation of engineered or natural dynamic controls on flood flows. By implementing the vision for physically realistic analysis of flood frequency through continuous simulation, each of these examples illustrates how more relevant and improved information was provided for flood risk decision‐making than would have been possible using standard methods. They further demonstrate that integrating engineered infrastructure into flood frequency analysis and assessment of environmental change are also significant motivations for adopting the continuous simulation approach in practice. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
14.
Tillamook Bay, Oregon, is a drowned river estuary that receives freshwater input from 5 rivers and exchanges ocean water through
a single channel. Similar to other western United States estuaries, the bay exhibits a strong seasonal change in river discharge
in which there is a pronounced winter maximum and summer minimum in precipitation and runoff. The behavior of major inorganic
nutrients (phosphorus, nitrogen, and silica) within the watershed is examined over seasonal cycles and under a range of river
discharge conditions for October 1997–December 1999. Monthly and seasonal sampling stations include transects extending from
the mouth of each river to the mouth of the estuary as well as 6–10 sites upstream along each of the 5 major rivers. Few studies
have examined nutrient cycling in Pacific Northwest estuaries. This study evaluates the distributions of inorganic nutrients
to understand the net processes occurring within this estuary. Based upon this approach, we hypothesize that nutrient behavior
in the Tillamook Bay estuary can be explained by two dominant factors: freshwater flushing time and biological uptake and
regeneration. Superimposed on these two processes is seasonal variability in nutrient concentrations of coastal waters via
upwelling. Freshwater flushing time determines the amount of time for the uptake of nutrients by phytoplankton, for exchange
with suspended particles, and for interaction with the sediments. Seasonal coastal upwelling controls the timing and extent
of oceanic delivery of nutrients to the estuary. We suggest that benthic regeneration of nutrients is also an important process
within the estuary occurring seasonally according to the flushing characteristics of the estuary. Silicic acid, nitrate, and
NH4
+ supply to the bay appears to be dominated by riverine input. PO4
−3 supply is dominated by river input during periods of high river flow (winter months) with oceanic input via upwelling and
tidal exchange important during other times (spring, summer, and fall months). Departures from conservative mixing indicate
that internal estuarine sources of dissolved inorganic phosphorus and nitrogen are also significant over an annual cycle. 相似文献
15.
The inability to detect the presence of viable Helicobacter pylori bacteria in environmental waters has hindered the public health community in assessing the role water may play in the transmission of this pathogen. This work describes a cultural enrichment method coupled with an H. pylori‐specific PCR to identify these bacteria in water. While far from perfected at the present time, this represents an exciting new approach to studying the significance of water as a transmission mechanism for H. pylori. Evidence is presented that indicates culturable H. pylori bacteria were found using this enrichment/PCR method in a local groundwater source. 相似文献
16.
Francesca Vergari Francesco Troiani Hazel Faulkner Maurizio Del Monte Marta Della Seta Sirio Ciccacci Paola Fredi 《地球表面变化过程与地形》2019,44(1):273-286
This paper explores the effectiveness of the widely-used functional relationship between drainage area (A in m2) and slope (S in m/m) to identify local process domains and aid interpretation of process interactions in a complex badland landscape. In order to perform this investigation, a series of sub-basins tributary to the Formone River in the Orcia catchment (central Italy) were selected as a suitable study area within which to explore our questions, given these basins' general representativeness of local terrain, the availability of a high resolution digital terrain model and previous extensive geomorphological research. Eroding basins containing both calanchi and landslides are common in the sub-humid badland landscape of central Italy, where field observation identifies a complex pattern of erosive processes associated with a history of uplift, despite which parts of the local landscape appear disconnected. Results reveal that the shape of all S–A curves (plotted using S data binned on log A) is comparable with that described in the literature, although sub-basins containing calanchi generally plot with higher S values than non-calanchi ones, except in the ‘fluvial’ section of the plots. Second, when viewed on total data (non-binned) S–A plots, landslide source area domains and calanchi domains are entirely coincident in all basins, supporting a cause–effect relationship. Additional plotting of the frequency characteristics of the raw data in a new way supports the interpretation that calanchi frequently initiate in landslide scars. In general though, although the S–A plots can contribute to the disentanglement of geomorphological behaviour in some complex erosional landscapes, it became apparent that in this landscape, process domains do not separate out with clarity along the A axis as suggested by theory. Despite this, an alternative, broader-scale morphoevolutive model can be proposed for the development of within-landslide calanchi, driven by changes to basin connectivity to the base channel. © 2018 John Wiley & Sons, Ltd. 相似文献
17.
P.J. Armitage R.H. Worden D.R. Faulkner A.C. Aplin A.R. Butcher J. Iliffe 《Marine and Petroleum Geology》2010
Fine-grained siliciclastic lithologies commonly act as sealing caprocks to both petroleum fields and host reservoirs for carbon capture (CO2 sequestration) projects. Fine-grained lithologies are thus of great importance in controlling fluid flow and storage in the subsurface. However, fine-grained rocks are rarely characterised in terms of primary sedimentary characteristics, diagenesis and how these relate to their flow properties (i.e. sealing or caprock quality). Seventeen samples from Lower Carboniferous estuarine caprock to a gas field (also to be used as a carbon capture site), have been analysed using a range of petrological and petrophysical techniques. The rock unit that represents the caprock to this gas field was found to be predominantly silt grade with porosity values as low as 1.8%. In these rocks, caprock quality (porosity) is controlled by intrinsic and extrinsic factors linked to primary mineralogy and diagenetic processes. Depositional mineralogy was dominated by quartz, detrital mica, detrital clay (likely Fe-rich 7Å clay and illite–smectite) with minor feldspar and oxide phases. Diagenetic processes included compaction, minor feldspar dissolution and kaolinite growth and the more important processes of chlorite, siderite and quartz cementation, as well as the likely transformation of smectite into illite. Caprock quality is controlled by the primary quantity of illite-muscovite in the sediment and also by the localised extent of chlorite and quartz cementation. Deposition in an estuarine environment led to highly heterogeneous distribution of primary and diagenetic minerals, and thus caprock quality, between and within the samples. 相似文献
18.
This paper investigates the controls of vegetation on runoff and erosion dynamics in the dryland environment of Jornada, New Mexico, USA. As the American southwest has seen significant shifts in the dominant vegetation species in the past 150 years, an understanding of the vegetation effects on hydrological and erosional processes is vital for understanding and managing environmental change. Small‐scale rainfall simulations were carried out to identify the hydrological and erosional processes resulting from the grassland and shrubland vegetation species. Results obtained using tree‐regression analysis suggested that the primary vegetation control on runoff and erosion is the shrub type and canopy density, which directly affects the local microtopographic gradient of mounds beneath the shrubs. Significant interactions and feedbacks were found to occur among the local mound gradient, crust cover, soil aggregate stability and antecedent soil moisture between the different vegetation species for both the runoff and erosion responses. Although some of the shrub species were found to produce higher sediment yields than the grass species, the distinguishing feature of the grassland was the significantly higher enrichment in the fine sediment fraction compared to all other surface cover types. This enrichment in fines has important implications for nutrient movement in such environments. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
19.
The surfaces for the three strongest secular resonances have been located as a function of proper semimajor axis, eccentricity, and inclination for semimajor axes between 1.25 and 3.5 AU. The results are presented graphically. The ν5 resonance only occurs at high inclinations (?23°). The ν6 resonance passes through both the main belt and Mars-crossing space. The ν16 resonance starts near the inner edge of the belt and, at low inclinations at least, folds around a portion of the Mars-crossing space until it runs nearly parallel with the Earth-crossing boundary. 相似文献
20.
Robert L. Paris Jeffery D. Ray James R. Smith Debbie L. Boykin 《Natural Resources Research》2009,18(4):259-266
Protein and oil are the most important components of soybean [Glycine max (L.) Merr.], and they have been shown to have an inverse relationship. As there is a growing demand for soybean oil-based
diesel as an alternative fuel source, a better understanding of the protein–oil inverse relationship in conjunction with seed
yield could be useful in determining the potential of soybean as a source of biodiesel. We retrospectively examined advanced
soybean breeding lines from multiple breeding programs across the southern USA to determine associations between protein and
oil and seed yield. The data analyzed were a subset of the Uniform Soybean Tests and consisted of 31 different soybean breeding
lines and four checks grown at 10 locations in 2000, six locations in 2001, and eight locations in 2002. A progressive multiple
regression analysis was used to develop a single equation describing seed yield over all entries, locations, and years as
a function of five traits: oil content, protein content, maturity, lodging, and plant height. From this equation, the optimum
plant type for maximum seed yield in the southern USA had either high oil (225 g kg−1) and low protein (385 g kg−1), or high protein (437 g kg−1) and low oil (190 g kg−1). Seed yield continues to be the dominant trait of selection in soybean breeding programs. This study demonstrates that high
yield can be achieved with either high protein or high oil. Hence, there is potential for maintaining yield while improving
soybean cultivars for oil production. Given the energy balance between fossil-derived and soy-derived diesel, if soy-based
biodiesel is to be a significant option, an increased focus on developing high-oil/high-yield soybean needs to occur. 相似文献