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61.
Edmund Penning-Rowsell Clare Johnson Sylvia Tunstall 《Global Environmental Change》2006,16(4):323-339
This paper evaluates policy accelerations after past flood crises in the UK (in 1947, 1953, 1998 and 2000) and explores their value as surrogates or metaphors for how governments might respond with policy changes to the local expressions of global climate and environmental change in the future. We find that these past policy change accelerations were, in general, not based on the development of new ideas but on bringing forward existing ideas that were already the subject of widespread professional or public discourse. We suggest, therefore, that we may be able to detect now, as ‘signals’ within current policy discourse, the embryos of the policy shifts that are likely to come about as part of any crisis-response adaptation to future climate change. If this is the case, then we believe that those with policy responsibilities now may be able to begin carefully and proactively to prepare the ground for such policy changes ahead of the crisis events that will alone trigger their acceleration and adoption. 相似文献
62.
The relationship between the magnetic and strain fabrics of some haematite-bearing Welsh slates 总被引:1,自引:0,他引:1
Sylvia J. Kneen 《Earth and Planetary Science Letters》1976,31(3):413-416
The anisotropy of magnetic susceptibility and the natural remanent magnetization of haematite-bearing Welsh Cambrian slates, showing a gradation in degree of deformation, have been related to the known strain of these rocks. An approximate quantitative relationship between strain and magnetic susceptibility anisotropy has been deduced, which would allow rapid strain estimation in this region by magnetic analysis. 相似文献
63.
Javier Tomasella Martin G. Hodnett Luz Adriana Cuartas Antonio D. Nobre Maarten J. Waterloo Sylvia M. Oliveira 《水文研究》2008,22(13):2133-2147
In humid tropical systems, the large intraseasonal and interannual variability of rainfall can significantly affect all components of the water balance. This variability and the lack of detailed hydrological and meteorological data in both temporal and spatial scales have created uncertainties regarding the closure of the water balance for the Amazon basin. Previous studies in Amazonian micro‐catchments suggested that both the unsaturated and groundwater system, which are not taken into consideration in basin‐wide water budgets published in the literature, play an important role in controlling the timing of runoff generation. In this paper, the components of the water balance and the variations in different storages within the system were examined using 3 years' data from a 6·58 km2 micro‐catchment in central Amazonia. The role and relative importance of the various stores were examined. The results show a strong memory effect in the groundwater system that carries over seasonal climate anomalies from one year to the next and affects the hydrological response well beyond the time span of the anomaly. In addition, the deep unsaturated zone was found to play a key role in reducing most of the intraseasonal variability and also affected the groundwater recharge. This memory effect is crucial for sustaining streamflow and evaporation in years with rainfall deficiency. The memory effect caused by storage in the groundwater and unsaturated systems may also prevent the closure of annual large‐scale water balances, which assume that storage returns to a standard state each year. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
64.
An observational study in the middle reach of Delaware Bay shows that vertical stratification is often enhanced during flood tide relative to ebb tide, contrary to the tidal variability predicted by the tidal straining mechanism. This tidal period variability was more pronounced during times of high river discharge when the tidally mean stratification was higher. This tidal variability in stratification is caused by two reinforcing processes. In the along-channel direction, the upstream advection of a salinity front at mid-depth causes an increase of the vertical stratification during the flood tide and a decrease during the ebb tide. In the cross-channel direction, the tilting of isohalines during the ebb reduces vertical stratification, and the subsequent readjustment of the salinity field during the flood enhances the water column stability. A diagnosis of the cross-channel momentum balance reveals that the lateral flows are driven by the interplay of Coriolis forcing and the cross-channel pressure gradient. During the flood tide, these two forces mostly reinforce each other, while the opposite occurs during the ebb tide. This sets up a lateral circulation that is clockwise (looking landward) during the first half of the flood and then reverses and remains counterclockwise during most of the ebb tide. Past maximum ebb, the cross-channel baroclinic term, overcomes Coriolis and reverses the lateral flows. 相似文献
65.
The ‘Chicken Creek’ artificial catchment area, Welzow-South, E Germany, created to study processes and structures of initial ecosystem development, discharges into a small experimental lake (A=3805 m2, V=3992 m3, zmax=2.4 m). This lake was man-made in 2005 and filled by natural surface runoff until January 2006. In summer 2006 and 2008, the actual development of sediments and the evolution of the phosphorus (P) cycle were studied. 19.7% of the original lake volume was filled by sediment within the first 3 years. A fine-grained sediment representing silt (6.3-63 μm) accumulated at high accretion rates at the deepest point (200 mm a−1, 0-24 mm week−1) due to massive erosion in the catchment. The sediment is low in organic matter (2.5-5.2%) and total P (TP, 0.31-0.97 mg g−1). Low amounts of P associated with degradable organic matter and surplus of metal hydroxides (Fe:P∼40, Al:P∼20) favor an efficient P binding and low dissolved P concentrations in pore water (1-107 μg l−1). Hence, the mineral sediment quality and the low rates of P release (0.06 mg m−2 d−1) revealed that a lake at an initial stage of development has essentially no sedimentary P cycle compared to eutrophic shallow lakes. However, the increasing emersed and submersed macrophyte growth will control further lake succession by intensifying the internal nutrient cycling. The macrophytes drive the evolution of a sedimentary P cycle by mobilizing and translocating P, by accumulating carbon and thus by stimulating microbial and redox processes. 相似文献
66.
Population density in Guangzhou City is characterized by a main single center and considerable differences throughout the
8 districts and 112 neighborhoods and towns. Historically, population density in Guangzhou City rose sharply, and population
distribution was mainly influenced by the attraction of the port. After the founding of the People’s Republic of China (PRC),
a series of large-sized factories were built in suburban areas, which drew in a large amount of population from the areas
outside of Guangzhou. A small part of this population lived in the suburban areas while most resided within the city centre.
As the natural increase rate of population was very high, the population density of both the city centre and suburban areas
rose, the former rose at higher rates. Since reform and the opening up to the outside world, Chinese economy has grown quickly,
the total population of Guangzhou has also increased quickly. Meanwhile, changes in population density within the city is
becoming more and more obvious. Population density in the city centre is falling and in city periphery is rising. From the
analysis of the population density model, it is found that population distribution of Guangzhou is in the process of transition
from an early stage to a mature stage. Population decline within the centre city of Guangzhou City, which reflects a prosperous
economy of the city, is significantly different from the recession of in the western countries. 相似文献
67.
68.
Sylvia Bonilla Daniel Conde Luis Aubriot María del Carmen Pérez 《Estuaries and Coasts》2005,28(6):884-895
A survey was carried out to investigate the relationship of phytoplankton biovolume, structure, and species life strategies
with major abiotic factors in a subtropical choked coastal lagoon (34°33′S, 54°22′W) naturally connecting with the Atlantic
Ocean several times a year. Marine and limnetic influence areas were sampled on a monthly basis during two periods, one of
low rainfall and high conductivity (August 1996 to February 1998) and a second period with the opposite tendency (December
1998 to March 2000). Photosynthetically active radiation availability was high and reached the bottom (>1% of the incident
light), while dissolved inorganic nitrogen (0.6–18.4 μM), soluble reactive phosphorus (<0.3–2.7 μM), and reactive silica (5–386
μM) were highly variable. Life strategies were identified in the phytoplankton as a function of morphology. C-strategists,
invasive planktonic and epipelic species of small size, and R-strategists, mixing-dependent species of medium size, characterized
this permanently mixed system. High frequency of exchange with the ocean prevented high biomass accumulation. Phytoplankton
biomass was lower in the second period of high rainfall (2.3 and 1.1 mm3 1−1 for period 1 and 2 respectively). A canonical correspondence analysis showed that conductivity, nitrogen, phosphorus, and
silica were the main environmental variables explaining phytoplankton species composition patterns. During the first period,
Bacillariophyceae (mostly pennate species) and the potentially toxicPrococentrum minimum were dominant; during the second period a higher contribution of flagellates (Cryptophyceae, Euglenophyceae, Prasinophyceae,
and flagellates <7 μm) was found. Differences of phytoplankton biomass, main taxonomic groups, and strategies were found between
periods but not between limnic and marine areas, suggesting that hydrological dynamic is more relevant than seasonal and spatial
differences. 相似文献
69.
Yan Zhao Carl D. Sayer Hilary H. Birks Michael Hughes Sylvia M. Peglar 《Journal of Paleolimnology》2006,35(2):335-350
We have explored the contemporary spatial relationship between aquatic vegetation and surficial macrofossil and pollen remains
in a small, shallow, English lake. A detailed point-based (n = 87) underwater vegetation survey was undertaken in the middle of the plant-growing season in July 2000. Then following
plant die-back in November 2000, surface sediment samples (upper 1.5 cm) were collected from 30 of these plant survey points
and analysed for plant macro-remains (all 30 samples), and pollen (4 evenly spaced samples). All data were stored as separate
layers in a geographical information system and spatial relationships between the aquatic vegetation and plant remains were
explored. In contrast to pollen types, plant macrofossils were not evenly dispersed across all parts of the lake and, with
the exception of Chara oospores, higher concentrations of remains (particularly for Potamogeton) were found close to areas of source-plant dominance. The spatial pattern of macrophyte–macrofossil relationships revealed
that vegetative remains (particularly leaf fragments) were probably deposited at source, whereas seeds were recovered close
to the shore suggesting slightly wider dispersal. Overall, however, macro-remains best represented local ‘patch-scale’ vegetation
within 20–30 m of the core site. The macro-remains effectively recorded the dominant plants in the lake with 63% of samples
containing a combination of remains of Chara, Elodea, and Potamogeton. However, relationships between macrophytes and fossils were complex. Some species were significantly over-represented by
macrofossils (e.g., Chara spp., Nitella flexilis agg., and Zannichellia palustris), while others were either under-represented (e.g., Potamogeton spp.), or not represented at all (e.g., Lemna trisulca). Pollen represented macrophyte diversity poorly, but some taxa were found (e.g., Myriophyllum spicatum, Ceratophyllum demersum) that were not recorded by macro-remains. We conclude that macrofossil analysis may be very usefully employed to determine
the dominant taxa in past aquatic plant communities of shallow, productive lakes and that the addition of pollen analysis
provides further information on former species richness. 相似文献
70.
Spatial simulation of evapotranspiration of semi-arid Inner Mongolian grassland based on MODIS and eddy covariance data 总被引:4,自引:4,他引:0
Sylvia?H.?VetterEmail author David?Schaffrath Christian?Bernhofer 《Environmental Earth Sciences》2012,65(5):1567-1574
In semi-arid regions of Central Asia, water shortage results from low annual precipitation (P) with high interannual variability. Evapotranspiration (ET) dominates water balance losses entirely. Previous studies showed
large differences between individual grassland sites in the partitioning of ET into evaporation and transpiration, but only
little difference in the evaporative ratio ET/P. The hydrological model BROOK90 was applied to the Xilin river catchment in Inner Mongolia (China) in combination with data
from moderate resolution imaging spectroradiometer (MODIS) and ET measurements. The ET part of the model was parameterised
using several years of eddy covariance (EC) measurements over grasslands differing in grazing intensity and leaf area index
(LAI). Using a relatively well-established relationship of LAI and P as well as LAI and temperature derived from MODIS, the water balance components of a 16 km2 sample area in the catchment
were modelled with a 1 km2 resolution for the vegetation period of 2006. All pixels were modelled assuming a similar ET control
as at the EC sites. Spatial variation in ET as well as in the partitioning of ET between transpiration and evaporation could
be identified. The results indicate the potential of using MODIS data and BROOK90 to upscale ET of semi-arid grasslands from
site to larger grass dominated catchments. 相似文献