全文获取类型
收费全文 | 211篇 |
免费 | 8篇 |
专业分类
测绘学 | 13篇 |
大气科学 | 28篇 |
地球物理 | 52篇 |
地质学 | 60篇 |
海洋学 | 11篇 |
天文学 | 34篇 |
自然地理 | 21篇 |
出版年
2021年 | 2篇 |
2020年 | 2篇 |
2019年 | 3篇 |
2018年 | 4篇 |
2017年 | 5篇 |
2016年 | 15篇 |
2015年 | 12篇 |
2014年 | 9篇 |
2013年 | 7篇 |
2012年 | 23篇 |
2011年 | 13篇 |
2010年 | 6篇 |
2009年 | 12篇 |
2008年 | 10篇 |
2007年 | 12篇 |
2006年 | 6篇 |
2005年 | 15篇 |
2004年 | 11篇 |
2003年 | 9篇 |
2002年 | 8篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1976年 | 1篇 |
1970年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有219条查询结果,搜索用时 703 毫秒
71.
Johannes Korsawe Eugen Perau Susanne Potthoff Gerhard Starke 《Computers and Geotechnics》2003,30(8):695-705
A new model for two-phase flow of water and air in soil is presented. This leads to a system of two mass balance equations and two equations representing conservation of momentum of fluid and gas, respectively. This paper is concerned with the verification of this model for the special case of a rigid soil skeleton by computational experiments. Its numerical treatment is based on the Raviart–Thomas mixed finite element method combined with an implicit Euler time discretization. The feasibility of the method is illustrated for some test examples of one- and two-dimensional two-phase flow problems. 相似文献
72.
Martin Gude Gerhard Daut Susanne Dietrich Roland Mäusbacher Christer Jonasson Annett Bartsch & Dieter Scherer 《Geografiska Annaler: Series A, Physical Geography》2002,84(3-4):205-212
The analysis of Holocene geomorphic process activity demands long–term data sets, which are available for the Kärkevagge catchment due to 50 years of intensive geomorphologic field studies. This data set is used in combination with additional field measurements, remote sensing and digital elevation model (DEM) analysis to provide input data for modelling Holocene valley development. On the basis of this information, geomorphic process units (GPUs) are defined by means of GIS modelling. These units represent areas of homogeneous process composition that transfer sediments. Since the data base enables the quantification of single processes, the interaction of processes within the units can also be quantified. Applying this concept permits calculation of recent sediment transfer rates and hence leads to a better understanding of actual geomorphic landscape development activity. To extrapolate these data in time and space the process–related sediments in the valley are analysed for depth and total volume, primarily using geophysical methods. In this fashion the validity of measured process rates is evaluated for the Holocene time scale. Results from this analysis are exemplified in a cross–profile showing some of the principal sediment units in the valley. For example, the measured modern rates on a slush torrent debris fan seem to represent the Holocene mean rate. This approach should also be suitable for revealing Holocene geomorphic landscape development in terms of climate change. 相似文献
73.
Pascal Richet Alan Whittington François Holtz Harald Behrens Susanne Ohlhorst Max Wilke 《Contributions to Mineralogy and Petrology》2000,138(4):337-347
A review of published and newly measured densities for 40 hydrous silicate glasses indicates that the room-temperature partial
molar volume of water is 12.0 ± 0.5 cm3/mol. This value holds for simple or mineral compositions as well as for complex natural glasses, from rhyolite to tephrite
compositions, prepared up to 10–20 kbar pressures and containing up to 7 wt% H2O. This volume does not vary either with the molar volume of the water-free silicate phase, with its degree of polymerization
or with water speciation. Over a wide range of compositions, this constant value implies that the volume change for the reaction
between hydroxyl ions and molecular water is zero and that, at least in glasses, speciation does not depend on pressure. Consistent
with data from Ochs and Lange (1997, 1999), systematics in volume expansion for SiO2–M2O systems (M=H, Li, Na, K) suggests that the partial molar thermal expansion coefficient of H2O is about 4 × 10−5 K−1 in silicate glasses.
Received: 30 June 1999 / Accepted: 5 November 1999 相似文献
74.
75.
Susanne Bleisch Matt Duckham Antony Galton Patrick Laube Jarod Lyon 《International journal of geographical information science》2014,28(2):363-382
In many applications, the environmental context for and drivers of movement patterns are just as important as the patterns themselves. This article adapts standard data mining techniques, combined with a foundational ontology of causation, with the objective of helping domain experts identify candidate causal relationships between movement patterns and their environmental context. In addition to data about movement and its dynamic environmental context, our approach requires as input definitions of the states and events of interest. The technique outputs causal and causal-like relationships of potential interest, along with associated measures of support and confidence. As a validation of our approach, the analysis is applied to real data about fish movement in the Murray River in Australia. The results demonstrate that the technique is capable of identifying statistically significant patterns of movement indicative of causal and causal-like relationships. 相似文献
76.
77.
Claudia Hellmann Carola Winkelmann Susanne Worischka Jürgen Benndorf 《Limnologica》2011,41(3):256-265
Many predation experiments in streams are carried out in enclosures. Hence, the relevance of their results to predict population dynamics is often unclear due to the relatively small spatial and temporal scale of the experiments. To enhance the transferability of experimental results on the ecosystem scale the impact of fish predators on a prey population was observed in a reach scale approach over 2 years in a natural stream. A 400-m reach inhabited by the small benthivorous fishes gudgeon (Gobio gobio) and stone loach (Barbatula barbatula) was compared with a fishless reference reach.It was shown that fish predation may affect the population of the grazing mayfly Rhithrogena semicolorata on the ecosystem scale. Although the larvae grew slower in the fish reach than in the fishless reach, the adults reached the same size and fecundity because they emerged 2–3 weeks later. By this compensation, the prey species avoided a reduction of their individual fecundity. On the other hand, the extended exposure to the fish predators resulted in an enhanced mortality and a reduced density of adult mayflies. Thus, there was obviously a trade-off between maximising fecundity and minimising mortality from fish predation.The observed differences were almost certainly caused be fish predation and not by natural differences of the reaches. This was concluded from results gained after eliminating all benthivorous fish from the former fish reach.With the help of scenario analyses based on our empirical data and simple model assumptions we could demonstrate that compensating the potential loss in fecundity by extending development time led to higher average fitness of the prey population than emerging at an earlier fixed time to avoid additional predation losses. Therefore, we concluded that this strategy was adaptive in the presence of benthivorous fish. 相似文献
78.
Susanne M. Moskalski Christopher K. Sommerfield Kuo-Chuin Wong 《Estuaries and Coasts》2011,34(4):800-813
Influences of tides, freshwater discharge, and winds on water properties in the St. Jones River estuary (USA), a Delaware
National Estuarine Research Reserve, were investigated using multiyear records of sea level, salinity, and turbidity, supplemented
by a current profiler time series in 2007. Results demonstrate that instantaneous properties fluctuate with semidiurnal tides
and resonant overtides, whereas tidal mean variations are forced by seasonal freshwater inflow and offshore winds. Mean sea
level and salinity are highest in summer and vary with seasonal water temperature and rainfall, whereas sea level variability
and turbidity are highest in winter on account of storm effects. Salinity and discharge modeling suggest that much (43–65%)
of the freshwater resident in the estuary is derived from non-point sources below the head of tide. This diffuse freshwater
inflow produces a seaward surface slope and weak mean current, which temporarily reverses under the influence of storm–wind
setup within Delaware Bay. 相似文献
79.
França S Vasconcelos RP Tanner S Máguas C Costa MJ Cabral HN 《Marine environmental research》2011,72(4):204-215
Stable carbon and nitrogen isotopes (δ13C, δ1?N) were used to analyse food web dynamics of two of the main estuaries of the Portuguese coast: Tejo and Mira. The ultimate sources of organic matter supporting production of some of the most abundant and commercially important fish species were determined; and seasonal, inter- and intra- estuarine differences in the trophic relations among producers and consumers were identified. Stable isotope analysis was performed in different producers, primary consumers (main prey items for fish) and fish species (Solea solea, Solea senegalensis, Pomatoschistus microps, Dicentrarchus labrax, Liza ramada, Diplodus vulgaris and Atherina presbyter) of two areas in each estuary, in July and October 2009. Model calculations showed that the main prey for the fish species in the Tejo estuary used mostly salt marsh-derived organic matter as nutritional sources, with no marked differences between the sampled months. Trophic levels of fish species from the same estuary differed at multiple scales: inter-species, seasonally and spatially (both between and within estuaries). Significant differences in isotopic composition of fish species were more pronounced spatially (between the two sampled areas in the estuary) than seasonally (between sampled months). Trophic relationships in both estuaries demonstrated that organic matter is transferred to higher trophic positions mainly through benthic pathways. This shows the flexibility of these species to share resources and to exploit temporary peaks in prey populations. The present results showed that extensive disturbance in intertidal habitats from both estuaries may potentially change the balance of organic matter in the base of these complex food webs. 相似文献
80.
Climate and weather are important for tourism and leisure as they impact on destination attractiveness and subsequent visitation. Through an archive analysis of media articles and a content analysis of Regional Tourism Organisation (RTO) websites, this paper explores perceived deficiencies in the currently available climate and weather information for tourists in New Zealand. While media reports focused on concern by many RTOs over the poor regional images generated by inaccurate and poorly presented climate and weather data, the RTO websites were found to contain limited climate and weather information. There is considerable potential for RTOs to improve in this respect. 相似文献