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31.
32.
A. Aldahan G. Possnert S. J. Johnsen H. B. Clausen E. Isaksson W. Karlen M. Hansson 《Journal of Earth System Science》1998,107(2):139-147
We report in this study the distribution of10Be in the top 40 m of the Renland ice core (East Greenland) and in a 30 m long core from DML (Dronning Maud Land, Antarctica)
for the period 1931–1988. The two sites show differences in10Be content, the Antarctica site showing smaller variance and a lower average10Be annual flux. Similarly, the average accumulation rate (cm water equivalent year−1) is higher in the Renland relative to DML. The variability in accumulation (precipitation) rates seems to explain part of
the difference in10Be flux between the two polar sites. Cyclic fluctuations of10Be flux correlate with the 11-year sunspot number and cosmic ray intensity than with the aa index (perturbation of the geomagnetic
activity by the solar wind). Our data corroborate10Be cyclic fluctuation pattern from the Dye 3 ice core and confirm a promising potential for correlation of global and local
events. 相似文献
33.
V. N. Nijampurkar D. K. Rao H. B. Clausen M. K. Kaul A. Chaturvedi 《Journal of Earth System Science》2002,111(1):39-49
The depth profiles of electrical conductance, δ18O,210Pb and cosmogenic radio isotopes10Be and36Cl have been measured in a 30 m ice core from east Antarctica near the Indian station, Dakshin Gangotri. Using210Pb and δ18O, the mean annual accumulation rates have been calculated to be 20 and 21 cm of ice equivalent per year during the past ∼
150 years. Using these acumulation rates, the volcanic event that occurred in 1815 AD, has been identified based on electrical
conductance measurements. Based on δ18O measurements, the mean annual surface air temperatures (MASAT) data observed during the last 150 years indicates that the
beginning of the 19th century was cooler by about 2‡ C than the recent past and the middle of 18th century. The fallout of
cosmogenic radio isotope10Be compares reasonably well with those obtained on other stations (73‡ S to 90‡ S) from Antarctica and higher latitudes beyond
77‡N. The fallout of36Cl calculated based on the present work agrees well with the mean global production rate estimated earlier by Lal and Peters
(1967). The bomb pulse of36Cl observed in Greenland is not observed in the present studies – a result which is puzzling and needs to be studied on neighbouring
ice cores from the same region. 相似文献
34.
Torben Mikkelsen Hans E. Jørgensen Morten Nielsen Søren Ott 《Boundary-Layer Meteorology》2002,105(3):483-505
Concentration fluctuation data from surface-layer released smokeplumes have been investigated with the purpose of finding suitable scaling parametersfor the corresponding two-particle, relative diffusion process.Dispersion properties have been measured at downwind ranges between 0.1 and 1 km from a continuous, neutrally buoyant ground level source. A combinationof SF6 and chemical smoke (aerosols) was used as tracer. Instantaneous crosswind concentration profiles of high temporal (up to 55 Hz) and spatialresolution (down to 0.375 m) were obtained from aerosol-backscatter Lidar detectionin combination with simultaneous gas chromatograph (SF6) reference measurements. The database includes detailed crosswind concentration fluctuation measurements. Each experiment, typically of 1/2-hour duration, containsplume mean and variance concentration profiles, intermittency profiles andexceedence and duration statistics. The diffusion experiments were accompanied by detailed in-situ micrometeorological mean and turbulence measurements. In this paper, a new distance-neighbour function for surface-released smoke plumes is proposed, accompanied by experimental evidence in its support. The new distance-neighbour function is found to scale with the surface-layer friction velocity,and not with the inertial subrange dissipation rate, over the range of distance-neighbour separations considered. 相似文献
35.
Integrity of Clay Till Aquitards to DNAPL Migration: Assessment Using Current and Emerging Characterization Tools 下载免费PDF全文
Annika S. Fjordbøge Gry S. Janniche Torben H. Jørgensen Bernt Grosen Gary Wealthall Anders G. Christensen Henriette Kerrn‐Jespersen Mette M. Broholm 《Ground Water Monitoring & Remediation》2017,37(3):45-61
Field investigations were carried out to determine the occurrence of tetrachloroethene (PCE) dense nonaqueous phase liquid (DNAPL), the source zone architecture and the aquitard integrity at a 30‐ to 50‐year old DNAPL release site. The DNAPL source zone is located in the clay till unit overlying a limestone aquifer. The DNAPL source zone architecture was investigated through a multiple‐lines‐of‐evidence approach using various characterization tools; the most favorable combination of tools for the DNAPL characterization was geophysical investigations, membrane interface probe, core subsampling with quantification of chlorinated solvents, hydrophobic dye test with Sudan IV, and Flexible Liner Underground Technologies (FLUTe) NAPL liners with activated carbon felt (FACT). While the occurrence of DNAPL was best determined by quantification of chlorinated solvents in soil samples supported by the hydrophobic dye tests (Sudan IV and NAPL FLUTe), the conceptual understanding of source zone architecture was greatly assisted by the indirect continuous characterization tools. Although mobile or high residual DNAPL (S t > 1%) only occurred in 11% of the source zone samples (intact cores), they comprised 86% of the total PCE mass. The dataset, and associated data analysis, supported vertical migration of DNAPL through fractures in the upper part of the clay till, horizontal migration along high permeability features around the redox boundary in the clay till, and to some extent vertical migration through the fractures in the reduced part of the clay till aquitard to the underlying limestone aquifer. The aquitard integrity to DNAPL migration was found to be compromised at a thickness of reduced clay till of less than 2 m. 相似文献
36.
37.
Dissolved organic matter (DOM) export to a temperate estuary: seasonal variations and implications of land use 总被引:1,自引:0,他引:1
Colin A. Stedmon Stiig Markager Morten Søndergaard Torben Vang Anker Laubel Niels Henrik Borch Anders Windelin 《Estuaries and Coasts》2006,29(3):388-400
Inputs of dissolved carbon, nitrogen, and phosphorus were assessed for an estuary and its catchment (Horsens, Denmark). Seasonal
patterns in the concentrations of DOM in the freshwater supply to the estuary differed depending on the soil and drainage
characteristics of the area. In streams draining more natural areas the, patterns observed were largely driven by seasonal
temperature fluctuations. The material exported from agricultural areas was more variable and largely controlled by precipitation
events. Positive exponential relationships were found between the nitrogen and phosphorus loading, and the percentage of catchment
area used for agriculture. Colored DOM (CDOM) loading measurements were found to be a good predictor of dissolved organic
carbon (DOC) loading across the different subcatchments, offering a rapid and inexpensive alternative of operationally monitoring
DOC export. For all the dissolved nutrient inputs to the estuary, dissolved inorganic nitrogen (DIN) and dissolved organic
phosphorus dominated the loadings. Although 81% of the nitrogen annually supplied to the estuary was DIN, 83% of the nitrogen
exported from the estuary was dissolved organic nitrogen (DON). Results show that increasing the area of the catchment covered
by forest and natural pastures would have a positive effect on the trophic status of the estuary, leading to a considerable
decrease in the phosphorus loading and a shift in the nitrogen loading from DIN to DON. Such a change in land use would also
increase the export of DOC and CDOM to the estuary having the potential to increase oxygen consumption and reduce the photic
depth. 相似文献
38.
Ole Rn Clausen Ole Bjrslev Nielsen Mads Huuse Olaf Michelsen 《Global and Planetary Change》2000,24(3-4)
The timing and effect of the Cenozoic uplift of Scandinavia has been investigated using a multi-disciplinary approach involving sedimentological, seismic and biostratigraphic data from the Danish and the adjacent Norwegian parts of the North Sea Basin. It is concluded that significant uplift took place periodically throughout the Palaeogene possibly marking an earlier onset of the so-called “Neogene uplift” of Scandinavia. This conclusion is based on a number of sedimentological observations, including smectite content, grain-size variations, kaolinite thermal stabilities and Tmax values supported by seismic reflection geometries and biostratigraphic data. These data indicate several phases of re-working of Palaeogene and older sediments situated further to the east and northeast during the middle to late Eocene and during the middle to late Oligocene. The tectonic patterns were similar during the late Paleocene and the Oligocene with some inversion taking place, whereas no inversion has been observed during the Eocene. Main provenance areas were to the north and northeast during the Paleocene and Oligocene, whereas the Eocene sediments originate mainly from the British Isles to the west. It is proposed that Palaeogene uplift of Scandinavia was associated with regional tectonic movements along crustal zones of weakness, which were reactivated as they accommodated strain induced by the Alpine Orogeny and the opening of the North Atlantic. 相似文献
39.
Inhabited by humans for over 12,000 calendar years, California's Channel Islands contain thousands of archaeological sites, ranging from dense shell middens and villages to small lithic scatters and camps. Similar to many islands around the world, the Channel Islands have a dearth of burrowing animals and limited historical development leading to generally good preservation of archaeological constituents and relatively high stratigraphic integrity. Despite these favorable preservation conditions, numerous natural and cultural processes have impacted the island's archaeological record. Channel Islands archaeologists, however, have given relatively limited attention to the effects of taphonomic and formation processes. The authors provide an overview of taphonomic and formation processes affecting Channel Islands archaeology, illustrating the importance of regional taphonomic syntheses in the management, preservation, and interpretation of archaeological sites. These data also demonstrate the significance of detailing formation processes in islands and other areas where burrowing rodents and other disturbances are thought to be absent or limited. © 2006 Wiley Periodicals, Inc. 相似文献
40.
Single-frequency single-site VTEC retrieval using the NeQuick2 ray tracer for obliquity factor determination 总被引:1,自引:1,他引:0
A single-frequency single-site GPS/Galileo algorithm for retrieval of absolute total electron content is implemented. A single-layer approximation of the ionosphere is used for data modeling. In addition to a standard mapping function, the NeQuick model (version 2) of the ionosphere is now applied to derive improved mapping functions. This model is very attractive for this purpose, because it implements a ray tracer. We compare the new algorithm with the old one using an effective global height of the ionosphere of 450 km. Combined IGS IONEX gridded data sets serve as reference data. On global average, we find a small improvement of 1 % in precision (standard deviation) of the NeQuick2 mapping method versus the conventional approach on global average. A site-by-site comparison indicates an improvement in the precision for 34 % of the 44 sites under investigation. The level of improvement for these stations is 0.5 TECU on average. No improvement was observed for 41 % of the sites. Further comparisons of the single (code ranges and carrier phases) versus dual-frequency (carrier phases only) single site algorithm show that dual-frequency VTEC estimation is more accurate for the majority of the stations, but only in the range of 0.3 TECU (2.6 %) in average. 相似文献