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461.
Piero Guilizzoni Aldo Marchetto Andrea Lami Frank Oldfield Marina Manca Claudio A. Belis Anna M. Nocentini Patrizia Comoli Vivienne J. Jones Steve Juggins Christina Chondrogianni Daniel Ariztegui John J. Lowe David. B. Ryves Richard W. Battarbee Tim C. Rolph Julieta Massaferro 《Journal of Paleolimnology》2000,23(2):117-127
We report the results of analyses of pigments (derived from algae and photosynthetic bacteria), diatoms and invertebrate fossil remains (ostracods, cladocerans, chironomids) in two late Pleistocene sediment cores from Lago Albano, a crater lake in Central Italy. The record contains evidence for oscillations in lake biota throughout the period ca. 28 to 17 k yr BP. The earliest of these are contained in the basal 3.5 m of light olive-gray and yellowish-gray spotted muds sampled in core PALB 94-1E from 70 m water depth. The later oscillations are best represented in the more extended sediment sequence recovered from a second core site, PALB 94-6B, in 30 m water depth. The sediments at site 1E, containing the earlier oscillations (ca. 28-24 k yr BP), predate any sedimentation at the shallower site, from which we infer an initially low lake level rising to permit sediment accumulation at site 6B from ca. 24 k yr onwards. At site 6B, massive silts rich in moss remains are interbedded with laminated silts and carbonates. These sediments span the period ca. 24 to 17 k yr and are interpreted as representing, respectively, times of shallow water alternating with higher lake stands, when the lake was stratified and bottom water was stagnant. A range of mutually independent chronological constraints on the frequency and duration of the oscillations recorded in the lake biota indicate that they were aperiodic and occurred on millennial to century timescales. We interpret them as responses to climate forcing through its impact on lake levels and changing aquatic productivity. The time span they occupy, their frequency and their duration suggest that at least some of these changes may parallel both the Dansgaard-Oeschger events recorded in Greenland Ice Cores and the contemporary oscillations in North Atlantic circulation documented in marine sediment cores. 相似文献
462.
Mountaintop removal/valley fill coal mining (MTR/VF) in central Appalachia has buried an estimated 4000 km of headwater streams, but the long-term geomorphic consequences of the anthropogenic valley fills and associated mined landscapes are poorly understood. These anthropogenic landscapes are not intended to be maintained in perpetuity once reclamation is complete. Here we present the first ever field-based study of erosional landforms on this type of mined landscape paired with the subsequent examination of 10 regional LiDAR (light detection and ranging) datasets for gullies and landslides in a transect from eastern Kentucky to central West Virginia. Field observations indicate that overtopping of or intentional discharge from drainage systems and overtopping of valley fill terraces can initiate gullying. We manually extracted 1328 gullies from 512 km2 of mined landscape within the LiDAR datasets. Gullies are predominantly located along the perimeter of the mined landscape with the majority of gullies associated with drainage systems. The number of gullies linearly scales with mined area (R2 = 0.66). We observed 387 landslides along the perimeter of MTR/VF. Within the datasets, landslides per km2 ranged from 0.1 to 3.9. We observed 34 landslides within fully reclaimed valley fills, a heretofore undocumented phenomenon. Over 90% of these landslides were in Kentucky datasets, which covered only 47% of total mined area analyzed. Previously measured regional differences in the angle of friction of mine spoils or construction practices may explain the abundance of gullies and elevated level of landslide occurrence in eastern Kentucky valley fills relative to West Virginia. Observations of erosion on regionally extensive MTR/VF landscapes warrant further study to better ascertain ecological impacts. Large-scale alteration by surface mining in steep landscapes may generally lead to peripheral gully erosion. © 2020 John Wiley & Sons, Ltd. 相似文献
463.
Alexa M. Hinzman Ylva Sjöberg Steve W. Lyon Stefan W. Ploum Ype van der Velde 《水文研究》2020,34(19):3894-3909
The Arctic is warming at an unprecedented rate. We hypothesis that as seasonally frozen soils thaw and recede in extent as a response to this warming, flow path diversity and thus hydrologic connectivity increases. This enhanced hydrologic connectivity then increases the non-linearity of the storage-discharge relationship in a catchment. The objective of this study is to test this hypothesis by quantifying trends and spatio-temporal differences in the degree of linearity in the storage-discharge relationships for 16 catchments within Northern Sweden from 1950 to 2018. We demonstrate a clear increase in non-linearity of the storage-discharge relationship over time for all catchments with 75% showing a statistically significant increase in non-linearity. Spring has significantly more linear storage-discharge relationships than summer for most catchments (75%) supporting the idea that seasonally frozen soils with a low degree of hydrological connectivity have a linear storage-discharge relationship. For the period considered, spring also showed greater change in storage-discharge relationship trends than summer signifying that changes in recessions are primarily occurring during the thawing period. Separate storage-discharge analyses combined with preceding winter conditions demonstrated that especially cold winters with little snow yielded springs and summers with more linear storage-discharge relationships. We show that streamflow recession analysis reflects ongoing hydrological change of an arctic landscape as well as offering new metrics for tracking change across arctic and sub-arctic landscapes. 相似文献
464.
Pump‐and‐Treat Groundwater Remediation Using Chlorine/Ultraviolet Advanced Oxidation Processes 下载免费PDF全文
Comparative studies of the use of chlorine/ultraviolet (Cl2/UV) and hydrogen peroxide/ultraviolet (H2O2/UV) Advanced oxidation processes (AOPs) to remove trichloroethylene (TCE) from groundwater in a pump‐and‐treat application were conducted for the first time at the full‐scale operational level at two water treatment facilities in Northern California. In these studies, aqueous chlorine replaced hydrogen peroxide in the AOP treatment step, where the oxidant is exposed to UV light to produce highly reactive radical species that degrade groundwater contaminants. TCE removal rates as a function of initial chlorine dose and pH were then determined. At the site where the natural pH of the water was 7.1, TCE was removed (to a concentration of less than 0.5 µg/L) for nearly every chlorine dose point tested, and pH adjustment slightly enhanced the treatment process at this facility. The second site had a high natural pH of 7.7, and here, TCE was not completely removed for any chlorine dose up to 5.7 mg/L, although TCE removal did increase when the chlorine dose increased between 0.9 and 3.6 mg/L. Residual TCE remaining in the water post‐Cl2/UV was readily removed using active carbon filtration, which is part of the overall treatment train at this facility. These studies also verified that Cl2/UV AOP did not interfere with the photolysis of N‐nitrosodimethylamine or result in an effluent acutely toxic toward Ceriodaphnia dubia. Comparative economic analysis revealed that the chemical costs associated with Cl2/UV AOP were 25 to 50% of the costs associated with in place H2O2/UV AOP treatment. 相似文献
465.
466.
Scott G. Johnston Richard T. Bush Leigh A. Sullivan Edward D. Burton Douglas Smith Michelle A. Martens Angus E. McElnea Col R. Ahern Bernard Powell Luisa P. Stephens Steve T. Wilbraham Simon van Heel 《Estuarine, Coastal and Shelf Science》2009
This study examines the remediation of surface water quality in a severely degraded coastal acid sulfate soil landscape. The remediation strategy consisted of partial restoration of marine tidal exchange within estuarine creeks and incremental tidal inundation of acidified soils, plus strategic liming of drainage waters. Time-series water quality and climatic data collected over 5 years were analysed to assess changes in water quality due to this remediation strategy. A time-weighted rainfall function (TWR) was generated from daily rainfall data to integrate the effects of antecedent rainfall on shallow groundwater levels in a way that was relevant to acid export dynamics. Significant increases in mean pH were evident over time at multiple monitoring sites. Regression analysis at multiple sites revealed a temporal progression of change in significant relationships between mean daily electrical conductivity (EC) vs. mean daily pH, and TWR vs. mean daily pH. These data demonstrate a substantial decrease over time in the magnitude of creek acidification per given quantity of antecedent rainfall. Data also show considerable increase in soil pH (2–3 units) in formerly acidified areas subject to tidal inundation. This coincides with a decrease in soil pe, indicating stronger reducing conditions. These observations suggest a fundamental shift has occurred in sediment geochemistry in favour of proton-consuming reductive processes. Combined, these data highlight the potential effectiveness of marine tidal inundation as a landscape-scale acid sulfate soil remediation strategy. 相似文献
467.
Implementation of marine ecosystem-based management requires improved understanding of existing governance, including gaps and overlaps resulting from fragmented management. Focusing on overlaps, this paper presents a technique using text analysis to assist in the identification of agencies and laws involved in overlaps from a system perspective. The overlaps analysis uses term frequency counts on ocean laws and regulations in conjunction with relevant agency authority. Such information delivered in a transparent user-friendly presentation can help policymakers and other constituents of ecosystem-based management to find existing overlaps as a step to facilitate improved coordination. 相似文献
468.
Nicholas Williamson Atsuki Komiya Shigenao Maruyama Masud Behnia Steve W. Armfield 《Journal of Oceanography》2009,65(3):349-359
The transport of nutrient-rich, deep sea water from an artificial upwelling pipe has been simulated. A numerical model has
been built within a commercial Computational Fluid Dynamics (CFD) package. The model considers the flow of the deep sea water
after it is ejected from the pipe outlet in a negatively buoyant plume (densimetric Froude number = −2.6), within a stably
stratified ocean environment subject to strong ocean current cross flow. Two cross-flow profiles were tested with momentum
flux ratios equal to 0.92 and 3.7. The standard k-ε turbulence model has been employed and a range of turbulent Schmidt and Prandtl numbers tested. In all cases the results
show that the rapid diffusion of heat and salinity at the pipe outlet causes the plume to attain neutral buoyancy very rapidly,
preventing strong fountain-like behavior. At the higher momentum flux ratio fountain-like behavior is more pronounced close
to the pipe outlet. The strong cross-current makes horizontal advection the dominant transport process downstream. The nutrient
plume trajectory remains largely within one relatively thin stratified layer, making any ocean cross-flow profile less important.
Very little unsteady behavior was observed. The results show that the nutrient is reduced to less than 2% of its inlet concentration
10 meters downstream of the inlet and this result is largely independent of turbulent Prandtl or Schmidt number. Initial results
would suggest that if such an artificial upwelling were to be viable for an ocean farming project, a large number of upwelling
pipes would be necessary. Further work will have to determine the minimum nutrient concentration required to sustain a viable
phytoplankton population and the required spacing between upwelling pipes. 相似文献
469.
Jason Microwave Radiometer Performance and On-Orbit Calibration 总被引:2,自引:0,他引:2
Results are presented from the on-orbit calibration of the Jason Microwave Radiometer (JMR). The JMR brightness temperatures (TBs) are calibrated at the hottest and coldest ends of the instrument's dynamic range, using Amazon rain forest and vicarious cold on-Earth theoretical brightness temperature references. The retrieved path delay values are validated using collocated TOPEX Microwave Radiometer and Radiosonde Observation path delay (PD) values. Offsets of 1-4 K in the JMR TBs and 8-12 mm in the JMR PDs, relative to TMR measurements, were initially observed. There were also initial TB offsets of 2 K between the satellite's yaw state. The calibration was adjusted by tuning coefficients in the antenna temperature calibration algorithm and the antenna pattern correction algorithm. The calibrated path delay values are demonstrated to have no significant bias or scale errors with consistent performance in all nonprecipitating weather conditions. The uncertainty of the individual path delay measurements is estimated to be 0.74 cm ± 0.15, which exceeds the mission goal of 1.2 cm RMS. 相似文献
470.
To provide coastal engineers and scientists with a detailed inter-comparison of widely used parametric wave transformation models, several models are tested and calibrated with extensive observations from six field experiments on barred and unbarred beaches. Using previously calibrated (“default”) values of a free parameter γ, all models predict the observations reasonably well (median root-mean-square wave height errors are between 10% and 20%) at all field sites. Model errors can be reduced by roughly 50% by tuning γ for each data record. No tuned or default model provides the best predictions for all data records or at all experiments. Tuned γ differ for the different models and experiments, but in all cases γ increases as the hyperbolic tangent of the deep-water wave height, Ho. Data from two experiments are used to estimate empirical, universal curves for γ based on Ho. Using the new parameterization, all models have similar accuracy, and usually show increased skill relative to using default γ. 相似文献