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61.
62.
Summary The wind regime of the Lake Tekapo Basin is examined with reference to the interaction of multi-scale local, regional and synoptic circulations. Analysis of the historical wind direction record from Mt John identifies airflow from three principal directions to most frequently affect the study area. Both seasonal and diurnal trends in the frequency of each directional category are identified, which reflect the influence of local thermal forcings and seasonal changes in synoptic circulation on the Lake Tekapo windfield. Meteorological observations from a network of automatic weather stations and anemographs within the study area identified Lake Tekapo to generate its own circulation system, a lake/land breeze. This combines with the larger scale valley wind, which during ideal conditions continues after sunset in the upper reaches of the lake catchment. During light to moderate foehn northwesterly conditions, the combined lake breeze/valley wind system remains decoupled from the prevailing synoptic airstream. Towards evening when local thermal circulations weakened, a channelised foehn airstream often becomes dominant over the entire field area. Observations made during this investigation have a number of applied implications with respect to air pollution dispersion modelling and forecasting within alpine lake basins.With 7 Figures 相似文献
63.
Integrating uncertainty: Canyon Creek hyperconcentrated flows of November 1989 and 1990 总被引:1,自引:0,他引:1
Canyon Creek drains a 79 km2 watershed in northwestern Washington State. Extensive logging occurred from the mid-1960s to 1980s, which resulted in numerous
slope instabilities and a several order of magnitude increase in sediment supply to the creek. On November 9, 1989, a hyperconcentrated
flow with a peak discharge of 450 m3/s destroyed one house on the fan. A forensic investigation of the event suggests that a temporary landslide dam may have
formed at two coalescing earthflows about 4 km above the fan apex. The 1989 hyperconcentrated flow caused significant aggradation
on the fan. One year later to the day, a significant flood occurred, which ran over the aggraded fan surface from the 1989
event. This latter event destroyed four more homes mostly through bank erosion and rendered a section of county road impassable.
FLDWAV, a flood routing model capable of simulating unsteady flow conditions, was used to model landslide dam breaches for
a number of different dam heights at the earthflows. Modeling results were then combined with historic air photograph interpretation,
dendrochronology, and eyewitness accounts to construct a frequency–magnitude relationship for hyperconcentrated flows at Canyon
Creek. FLDWAV results were combined with a hyperconcentrated flow runout model (FLO-2D) on the fan to estimate maximum flow
depth and flow velocity for the design event, a 500-year return period with a predicted peak discharge of 710 m3/s. A large range of mitigation measures were reviewed, but it was concluded that buy-outs would be the most effective risk
reduction measure. Property acquisition commenced in 2004. 相似文献
64.
65.
The objective of moveout parameter inversion is to derive sets of parameter models that can be used for moveout correction and stacking at each common midpoint location to increase the signal-to-noise ratio of the data and to provide insights into the kinematic characteristics of the data amongst other things. In this paper, we introduce a data-driven user-constrained optimization scheme that utilizes manual picks at a point on each reflector within a common midpoint gather to constrain the search space in which an optimization procedure can search for the optimal parameter sets at each reflection. The picks are used to create boundary curves which can be derived approximately via an optimization technique or analytically via the derivation of an analytical bounds function. In this paper, we derive analytical forms of bounds functions for four different moveout cases. These are normal moveout, non-hyperbolic moveout, azimuthally dependent normal moveout and azimuthally dependent non-hyperbolic moveout. The optimization procedure utilized here to search for the optimal moveout parameters is the particle swarm optimization technique. However, any metaheuristic optimization procedure could be modified to account for the constraints introduced in this paper. The technique is tested on two-layer synthetic models based on three of the four moveout cases discussed in this paper. It is also applied to an elastic forward modelled synthetic model called the HESS model, and finally to real 2D land data from Alaska. The resultant stacks show a marked improvement in the signal-to-noise ratio compared to the raw stacks. The results for the normal moveout, non-hyperbolic moveout and azimuthally dependent normal moveout tests suggest that the method is viable for said models. Results demonstrate that our method offers potential as an alternative to conventional parameter picking and inversion schemes, particularly for some cases where the number of parameters in the moveout approximation is 2 or greater. 相似文献
66.
67.
C. Alcock R. A. Allsman D. R. Alves T. S. Axelrod A. C. Becker D. P. Bennett P. A. Charles K. H. Cook A. J. Drake K. C. Freeman M. Geha K. Griest P. Groot † M. J. Lehner S. L. Marshall K. E. McGowan ‡ D. Minniti C. A. Nelson B. A. Peterson P. Popowski M. R. Pratt P. J. Quinn W. Sutherland A. B. Tomaney T. Vandehei J. van Paradijs 《Monthly notices of the Royal Astronomical Society》2000,316(4):729-733
Using the exceptional long-term monitoring capabilities of the MACHO project, we present here the optical history of LMC X-2 for a continuous 6-yr period. These data were used to investigate the previously claimed periodicities for this source of 8.15 h and 12.54 d: we find upper limits of 0.10 mag and 0.09 mag, respectively. 相似文献
68.
Vivianite is a bluish mineral sometimes encountered in archaeological deposits. It is notable for its tendency to change color from white or grayish to blue on exposure to air. Vivianite requires specific conditions for its formation—sources of iron, phosphate, and water, as well as low levels of oxygen and sulfide. Microbial activity is also thought to play a part in vivianite formation. The majority of archaeological texts do not discuss vivianite to any great degree, preventing a more detailed interpretation of site conditions and features. Vivianite was found in 25 exhumed burials from the North Brisbane Burial Ground, Queensland, Australia. Research indicated that bone or tissue samples for DNA analysis are best taken from areas distant from vivianite encrustations and that presence of vivianite has implications for artifact conservation. Vivianite at the North Brisbane Burial Grounds helped protect some skeletal and dental elements, preserved the impressions of metal coffin lacing, and also corroborated the oral history of temporary waterlogging and acted as a measure of pollution levels across the site. © 2006 Wiley Periodicals, Inc. 相似文献
69.
H. A. McGowan A. P. Sturman M. Kossmann P. Zawar-Reza 《Meteorology and Atmospheric Physics》2002,79(3-4):215-230
Summary Local scale windfield and air mass characteristics during the onset of two foehn wind events in an alpine hydro-catchment
are presented. Grounding of the topographically modified foehn was found to be dependent on daytime surface heating and topographic
channelling of flow. The foehn front was observed to advance down-valley until the valley widened significantly. The foehn
wind appeared to decouple from the surface downstream of the accelerated flow associated with the valley constriction, and
to be lifted above local thermally generated circulations including a lake breeze. Towards evening, the foehn front retreated
up valley in response to reduced surface heating and the intrusion into the study area of a deep and cool air mass associated
with a regional scale mountain-plain circulation. Differences in the local windfield observed during both case study events
reflect the importance of different thermal and dynamic forcings on airflow in complex terrain. These are the result of variation
in surface energy exchanges, channelling and blocking of airflow. Observations presented here have both theoretical and applied
implications with regard to forecasting foehn onset, wind hazard management, recreational activities and air quality management
in alpine settings.
Received January 23, 2001 Revised October 17, 2001 相似文献
70.
Anh Duc Trinh Thu Nga Do Virginia N. Panizzo Suzanne McGowan Melanie J. Leng 《水文研究》2020,34(22):4239-4250
The young water fraction of streamflow (Fyw), an important hydrological variable, has been calculated for the first time, for a monsoon-fed coastal catchment in northern Vietnam. Oxygen stable isotopes (δ18O) from six river sites in the Day River Basin (DRB) were analysed monthly, between January 2015 and December 2018. River δ18O signatures showed sine wave variability, reflecting the amount effect and tropical (dry-rainy) seasonality of the region. The δ18O composition of precipitation ranged from −12.67 to +1.68‰, with a mean value of −5.14‰, and in-streamflow signatures ranged from −11.63 to −1.37‰ with a mean of −5.02‰. Fractions of young water (Fyw) were calculated from the unweighted and flow-weighted δ18O composition of samples. Unweighted Fyw ranged between 29 ± 8% and 82 ± 21% with a mean value of 51 ± 19%, and was not significantly different from flow-weighted Fyw (range between 33 ± 25% and 92 ± 73%, mean 52 ± 36%). Both unweighted and flow-weighted Fyw were highest in the middle of stream and lowest in downstream sites, capturing the impacts of landuse changes, hydrology and human activities in the catchment. Our calculations imply that more than a half of rainwater reaches the DRB river mainstream within the first 3 months. The Fyw is much higher than the global average (of one-third) and insensitive to discharge due to the combination of a humid catchment with high rainfall, low storage capacity, flat landscape and an intensive drainage system in the DRB. Also the low discharge sensitivity of Fyw in the DRB implies that the regional hydrology is severely altered by humans. 相似文献