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961.
962.
The importance of long‐term storage of heavy metals in groyne fields, functioning over 150 years, is investigated for the River Odra (Oder), western Poland. Construction of groynes along the Odra preceded rapid development of heavy industrialization in the largest coal mine districts in Poland and the Czech Republic that resulted in persistent riverine pollution. The 187 km long Middle Odra reach was repeatedly channelized from the first half of the eighteenth century to the turn of the twentieth century, during which time partially filled groyne fields were dissected by new bank lines and groyne systems, with older groyne fields partially keyed into the floodplain. Consequently, concentrations of zinc, lead, cadmium, and copper within historically deposited groyne field sediments exceed local geochemical background levels by more than 60, 40, 15 and 10 times, respectively. Sediments contaminated with heavy metals occur within three distinctive geomorphic zones: zone I is up to 250 m wide and furthest from the present channel, comprising decimeter‐thick polluted sediments, overlying eighteenth century sand and gravel bars; zone II represents the former nineteenth century groyne fields, with widths between 10 and 100 m, filled with as much as 3 m of polluted sediments; zone III represents the twentieth century groyne fields, which are several to a dozen metres wide and filled with polluted sediments averaging depths of more than 2 m. This investigation indicates that large and extensive sediment quantities of moderately polluted sediments are stored immediately along the banks of the River Odra. These sediments could be a significant secondary pollution source and therefore careful maintenance of contemporary bank protection structures is required. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
963.
Kristen M. Reifel Scott C. Johnson Paul M. DiGiacomo Michael J. Mengel Nikolay P. Nezlin Jonathan A. Warrick Burton H. Jones 《Continental Shelf Research》2009,29(15):1821-1835
The effects from two winter rain storms on the coastal ocean of the Southern California Bight were examined as part of the Bight ‘03 program during February 2004 and February–March 2005. The impacts of stormwater from fecal indicator bacteria, water column toxicity, and nutrients were evaluated for five major river discharges: the Santa Clara River, Ballona Creek, the San Pedro Shelf (including the Los Angeles, San Gabriel, and Santa Ana Rivers), the San Diego River, and the Tijuana River. Exceedances of bacterial standards were observed in most of the systems. However, the areas of impact were generally spatially limited, and contaminant concentrations decreased below California Ocean Plan standards typically within 2–3 days. The largest bacterial concentrations occurred in the Tijuana River system where exceedances of fecal indicator bacteria were noted well away from the river mouth. Maximum nitrate concentrations (~40 μM) occurred in the San Pedro Shelf region near the mouth of the Los Angeles River. Based on the results of general linear models, individual sources of stormwater differ in both nutrient concentrations and the concentration and composition of fecal indicator bacteria. While nutrients appeared to decrease in plume waters due to simple mixing and dilution, the concentration of fecal indicator bacteria in plumes depends on more than loading and dilution rates. The relationships between contaminants (nutrients and fecal indicator bacteria) and plume indicators (salinity and total suspended solids) were not strong indicating the presence of other potentially important sources and/or sinks of both nutrients and fecal indicator bacteria. California Ocean Plan standards were often exceeded in waters containing greater than 10% stormwater (<28–30 salinity range). The median concentration dropped below the standard in the 32–33 salinity range (1–4% stormwater) for total coliforms and Enterococcus spp. and in the 28–30 salinity range (10–16% stormwater) for fecal coliforms. Nutrients showed a similar pattern with the highest median concentrations in water with greater than 10% stormwater. Relationships between colored dissolved organic matter (CDOM) and salinity and between total suspended solids and beam attenuation indicate that readily measurable, optically active variables can be used as proxies to provide at least a qualitative, if not quantitative, evaluation of the distribution of the dissolved, as well as the particulate, components of stormwater plumes. In this context, both CDOM absorption and the beam attenuation coefficient can be derived from satellite ocean color measurements of inherent optical properties suggesting that remote sensing of ocean color should be useful in mapping the spatial areas and durations of impacts from these contaminants. 相似文献
964.
A fluid dynamics approach to modelling the 18th March 2007 lahar at Mt. Ruapehu,New Zealand 总被引:2,自引:0,他引:2
Lahars are water-sediment mass flows from a volcanic source. They can be triggered by a variety of mechanisms and span a continuum
of flow rheology and hydraulic properties, even within the same event. Lahars are extremely powerful landscaping agents and
represent a considerable hazard potential. However, this highly dynamic character and a lack of direct measurements has made
modelling lahars difficult. This study therefore applies a fluid dynamics model; Delft3D, to analyse the 18th March 2007 dam
break lahar at Mount Ruapehu, New Zealand. The modelled lahar routed through the Whangaehu gorge in ~30 min, crossed the Whangaehu
fan in ~60 min, and then over a further 3 h travelled an additional ~22 km distance along the Whangaehu River to the Tangiwai
bridge. The modelled mean frontal velocity was 6.5 m s−1 along the gorge although peak velocity reached up to 19.6 m s−1. The modelled lahar flow front progressively slowed across the fan but along the River it accelerated from 2.1–3.3 m s−1. Calculated peak velocity along the River was <4.5 m s−1. These results generally compare well with gauged records, with historical records, and with other modelling approaches.
However, discrepancies in frontal velocity and time to peak stage arise due to (1) specifying roughness, which arises from
slope variations between adjacent computational nodes, and which is stage-dependant, and (2) due to rapid topographic changes
that produce frequent hydraulic jumps, which are inadequately accommodated in the numerical scheme. The overall pattern of
discharge attenuation, and of relationships between topographic and hydraulic variables, is similar to that calculated for
lahars on other volcanoes. This modelling method could be applied at other similar sites where a likely source hydrograph
and high-resolution topographic data are available. These results have important implications for hazard management at Ruapehu
and for examining geomorphic and sedimentary impacts of this lahar. 相似文献
965.
Thermal characterization of the Vulcano fumarole field 总被引:1,自引:1,他引:0
Andrew J. L. Harris Luigi Lodato Jonathan Dehn Letizia Spampinato 《Bulletin of Volcanology》2009,71(4):441-458
Ground-based thermal infrared surveys can contribute to complete heat budget inventories for fumarole fields. However, variations
in atmospheric conditions, plume condensation and mixed-pixel effects can complicate vent area and temperature measurements.
Analysis of vent temperature frequency distributions can be used, however, to characterise and quantify thermal regions within
a field. We examine this using four thermal infrared thermometer and thermal image surveys of the Vulcano Fossa fumarole field
(Italy) during June 2004 and July 2005. These surveys show that regions occupied by low temperature vents are characterised
by distributions that are tightly clustered around the mean (i.e., the standard deviation is low), highly peaked (positive
kurtosis) and skewed in the low temperature direction (negative skewness). This population is associated with wet fumaroles,
where boiling controls maximum temperature to cause a narrow distribution with a mode at 90–100°C. In contrast, high temperature
vent regions have distributions that are widely spread about the mean (i.e., the standard deviation is high), relatively flat
(negative kurtosis) and skewed in the high temperature direction (positive skewness). In this dry case, fumaroles are water-free
so that maximum temperatures are not fixed by boiling. As a result greater temperature variation is possible. We use these
results to define two vent types at Vulcano on the basis of their thermal characteristics: (1) concentrated (localized) regions
of high temperature vents, and (2) dispersed low temperature vents. These occur within a much larger region of diffuse heat
emission across which surfaces are heated by steam condensation, the heat from which causes elevated surface temperatures.
For Vulcano's lower fumarole zone, high and low temperature vents occupied total areas of 3 and 6 m2, respectively, and occurred within a larger (430 m2) vent-free zone of diffuse heat emission. For this lower zone, we estimate that 21–43 × 103 W of heat was lost by diffuse heat emission. A further 4.5 × 103 W was lost by radiation from high temperature vents, and 6.5 × 103 W from low temperature vents. Thus, radiative heat losses from high and low temperature vents within Vulcano's lower fumarole
zone respectively account for 10% and 15% of the total heat lost from this zone. This shows that radiation from open vents
can account for a non-trivial portion of the total fumarole field heat budget. 相似文献
966.
Estimating depths of buried lava tubes is important for determining the thermal budgets and effusion rates of basaltic volcanic
systems. This research used a laboratory experiment scaled to a lava tube system to measure the 3D temperature field surrounding
a hot viscous fluid flowing through a buried glass tube while varying conditions such as flow rate and temperature. The depth
of the glass tube was changed for different experimental runs. Numerical techniques were applied to model the laboratory experiment.
The surface thermal distributions from 166 thermal traverses, constrained to a depth to width ratio of 0.6 to 1.6, were analyzed
to empirically derive a depth estimation function using regression techniques. This “Linear Anomaly Surface Transect (LAST)”
depth function is a scaleable depth estimation technique which can be solved with thermal imaging data alone. The minimum
temperature, maximum temperature and width of a Lorentzian distribution fit to a surface thermal transect, are the only inputs
required for the LAST function to estimate the depths of the hot source. The input parameters were then applied to non-laboratory
situations including the Kuhio lava tube system in Hawai’i. The LAST function produced depth estimates of ∼ 0.3 m for the
Kuhio lava tube in Hawai’i, which did not agree with observations on the ground. This is the result of the complex composition
and geometry of an actual lava tube where heat transfer is controlled by more than a simple fluid filling a tube, but also
by convection of gasses and fluids in a partially filled passage. Though not effective for lava tubes at this time, the model
provides promising results for simple cases applied to engineering and underground coal fires. 相似文献
967.
River temperature regimes of England and Wales: spatial patterns,inter‐annual variability and climatic sensitivity 下载免费PDF全文
Identification of the most sensitive hydrological regions to a changing climate is essential to target adaptive management strategies. This study presents a quantitative assessment of spatial patterns, inter‐annual variability and climatic sensitivity of the shape (form) and magnitude (size) of annual river/stream water temperature regimes across England and Wales. Classification of long‐term average (1989–2006) annual river (air) temperature regime dynamics at 88 (38) stations within England and Wales identified spatially differentiable regions. Emergent river temperature regions were used to structure detailed hydroclimatological analyses of a subset of 38 paired river and air temperature stations. The shape and magnitude of air and water temperature regimes were classified for individual station‐years; and a sensitivity index (SI, based on conditional probability) was used to quantify the strength of associations between river and air temperature regimes. The nature and strength of air–river temperature regime links differed between regions. River basin properties considered to be static over the timescale of the study were used to infer modification of air–river temperature links by basin hydrological processes. The strongest links were observed in regions where groundwater contributions to runoff (estimated by basin permeability) were smallest and water exposure time to the atmosphere (estimated by basin area) was greatest. These findings provide a new large‐scale perspective on the hydroclimatological controls driving river thermal dynamics and, thus, yield a scientific basis for informed management and regulatory decisions concerning river temperature within England and Wales. © 2013 The Authors. Hydrological Processes published by John Wiley & Sons, Ltd. 相似文献
968.
AbstractThe societal impacts of flash floods are more significant than any other weather-related hazard. They are often manifested in the form of damage to infrastructure, flooding of roadways and bridges, creating deadly hazards to motorists and inundation of crops and pasture. Some of these hazards can be anticipated and thus mitigated given effective warning systems. This study describes the tools proposed over recent decades in the USA to predict flash flooding and evaluates them using a common observational data set. Design recommendations for flash-flood forecasting systems are provided, taking into account today's availability of high-resolution rainfall data at scales commensurate with flash flooding, their archives, spatial data sets to describe physiographic properties, and ever-increasing computational resources.
Editor D. Koutsoyiannis; Guest editor R.J. MooreCitation Gourley, J.J., Flamig, Z.L., Hong, Y., and Howard, K.W., 2014. Evaluation of past, present and future tools for radar-based flash-flood prediction in the USA. Hydrological Sciences Journal, 59 (7), 1377–1389. http://dx.doi.org/10.1080/02626667.2014.919391 相似文献
969.
970.
The focus of this paper is the recent preparation of the Third National Physical Development Plan for Barbados. Interestingly, this blueprint for the future development of the country was prepared by Canadian consultants, under the auspices of Inter-American Development Bank funding, and thereby ostensibly represents the rolling back of the State in the context of physical development planning. The paper briefly examines the origins of town and country planning in Barbados and the wider Caribbean before critiquing the Third Plan produced in 1998. Emphasis is placed on salient issues such as operationalising sustainable development, the involvement of local stakeholders, the role of Environmental Impact Assessments (EIA) in the planning process, and the production of Community Plans. Throughout, it is shown that whilst the State appears to have been "rolled back", government has retained its strong-hold over the course of physical development planning, principally by "tactics" which have served to minimise the degree to which members of the public and non-governmental organisations (NGOs) have been able to participate. 相似文献