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31.
Observed positions of minor planets from 1977 and 1978 at the Zeiss-Sonnefeld astrograph 300/1500 of Lohrmann Observatory at Dresden-Gönnsdorf are given. 相似文献
32.
Merryl Alber Erick M. Swenson Susan C. Adamowicz Irving A. Mendelssohn 《Estuarine, Coastal and Shelf Science》2008
This paper provides an overview of the marsh dieback events that have been observed along the east and gulf coasts of the U.S. over the past decade. It is likely that some of the recently reported changes in marsh vegetation were affected by physical or biotic disturbances that are known to generate bare areas, such as overgrazing or wrack smothering. Other areas may be experiencing a state change such as that caused by long-term changes in sea level. However, sites in many areas are not readily explained by these causes and are considered to have experienced “sudden dieback.” In such cases, there are observations that the above-ground plant material thinned or browned or, in some cases, failed to re-emerge in the spring; the dieback occurred over a period of months and usually affected multiple sites within the area; and there is evidence that these events are transient (through successful transplants or natural regrowth/recovery), although some areas take years to recover. We explored the potential linkage of dieback with drought (as characterized by the Palmer Severity Drought Index), and found that there is evidence for an association in the southeast (GA and SC) and the Gulf (LA), but not in the mid-Atlantic (DE, VA) or northeast (ME, RI, CT). We also review the evidence for potential causes of sudden dieback, including changes in soil chemistry, fungal pathogens, top–down consumer controls, and multiple stressors. There is currently no single explanation that can be applied to recent dieback. We highlight the need for the development of improved diagnostics that will allow us to better classify dieback areas and provide evidence for (or against) potential causes. 相似文献
33.
Erick R. Burns Laurence R. Bentley Masaki Hayashi Stephen E. Grasby Anthony P. Hamblin Derald G. Smith Paul R. J. Wozniak 《Hydrogeology Journal》2010,18(6):1375-1390
Fluvial systems tend to deposit sediment in well-defined relational geometries and in vertically and laterally repeating patterns. These sedimentary deposits are preserved to varying degrees depending on how much the fluvial system reworks the deposits. The Paskapoo bedrock aquifer system in southern Alberta, Canada, was deposited in a foreland depositional basin during uplift of the Rocky Mountains, and both the geomorphic model and field evidence indicate that the upper 100 m of the local aquifer system contains well-preserved, highly connected paleo-channels and associated overbank deposits. In order to evaluate the value of different types of data, a simplified stochastic-numerical groundwater flow model was developed to examine the sensitivity of results to model parameters. Parameters examined include: fraction of the formation made up of channel sands; meander and sinuosity factors; width-to-depth ratios of preserved channels; and crevasse splay conductivity. In all cases examined, the system exhibited anisotropic behavior with the along-channel flow direction being the most permeable and the vertical direction being least permeable. In general, the strongest control on the resulting effective anisotropic hydraulic conductivities was channel fraction, but geometric factors that control between-channel connectivity (e.g., channel sinuosity) had an appreciable effect on the across-channel flow direction effective permeability. 相似文献
34.
Fractured bedrock and saprolite hydrogeologic controls on groundwater/surface-water interaction: a conceptual model (Australia) 总被引:1,自引:1,他引:0
Edward W. Banks Craig T. Simmons Andrew J. Love Roger Cranswick Adrian D. Werner Erick A. Bestland Martin Wood Tania Wilson 《Hydrogeology Journal》2009,17(8):1969-1989
Hydrologic conceptual models of groundwater/surface-water interaction in a saprolite-fractured bedrock geological setting often assume that the saprolite zone is hydraulically more active than the deeper bedrock system and ignore the contribution of deeper groundwater from the fractured bedrock aquifer. A hydraulic, hydrochemical, and tracer-based study was conducted at Scott Creek, Mount Lofty Ranges, South Australia, to explore the importance of both the deeper fractured bedrock aquifer system and the shallow saprolite layer on groundwater/surface-water interaction. The results of this study suggest that groundwater flow in the deeper fractured bedrock zone is highly dynamic and is an important groundwater flow pathway along the hillslope. Deep groundwater is therefore a contributing component in streamflow generation at Scott Creek. The findings of this study suggest that hydrologic conceptual models, which treat the saprolite-fractured bedrock interface as a no-flow boundary and do not consider the deeper fractured bedrock in hydrologic analyses, may be overly simplistic and inherently misleading in some groundwater/surface-water interaction analyses. The results emphasise the need to understand the relative importance of subsurface flow activity in both of these shallow saprolite and deeper bedrock compartments as a basis for developing reliable conceptual hydrologic models of these systems. 相似文献
35.
36.
The efficiency of Australian laterites in arsenic adsorption has been examined using three laterite samples collected from
different locations in South Australia. The characteristics such as electrical conductivity, pH, mineral compositions, and
isoelectric point of laterite samples have been measured. The laterite samples are mainly composed of iron and aluminum oxides,
and rutile (TiO2). Two batch experiments have been performed to compare the efficiencies of different laterites to remove AS (III) from water
at two different doses, and to examine whether pH influences arsenic adsorption. For 50 mg/l arsenic solution, at doses 1,000 g
(laterite)/l (arsenic solution) and 200 g/l, the laterites removed more than 97% and 87–97%, respectively. At the dose of
200 g/l, adsorption capacity has been found to be 200–243 mg/kg. Out of the laterite samples from three localities, the Kangaroo
Island laterite performed the best. This is probably related to its high content of gibbsite. It has been found that arsenic
adsorption by laterite is not significantly affected at the examined pH ranges of 4.7–10.0. 相似文献
37.
This paper refers to the formulation of a macroconstitutive law for elastoplastic multilayered media, using both thermodynamical approach and homogenization procedure. The latter shows that both the microstress and strain tensors are constant in each constituent. This result permits the formulation of a macroconstitutive law involving the microplastic strains as internal parameters. Both the macrofree energy and dual dissipation potential are computed and used to derive explicit expressions for the macrocompliance tensor, yield surface and hardening rule. Finally, this law is used to analyse the behavior of a reinforced earth material under various loading paths. 相似文献
38.
39.
Erick T. Young 《Experimental Astronomy》2000,10(2-3):415-418
The Infrared Space Observatory successfullycarried out a wide range of astronomical observations in thewavelength range 2.4 m to nearly 200 m. To coverthis extremely broad range, a variety of detector technologies wereused by the instruments teams. As such ISO also proved to bean important test bed for the operation of these detectors ina low-background space environment. Over the two year mission,all the detector types have proven to be quite stable, withonly the Si:As IBC showing any long term degradation.Significant effort has been expended to cope with thebehaviour of the detectors under the space conditions bothoperationally and in ground processing. The main undesirableeffect can be classified as either transient responseanomalies or radiation effects. Overall sensitivity of theISO detectors was generally worse than predicted fromground-based measurements due to combinations of these twoclasses of phenomena. Splinter meetings were held to exchangespecific strategies for dealing with glitches, radiation curing,and transient effects. Plans for future actions were initiated. 相似文献
40.
R. Eugene Turner Charles S. Milan Erick M. Swenson 《Estuarine, Coastal and Shelf Science》2006,69(3-4):352
Salt marsh sediment volume decreases from organic decomposition, compaction of solids, and de-watering, and each of these processes may change with age. Variability in the vertical accretion rate within the upper 2 m was determined by assembling results from concurrent application of the 137Cs and 210Pb dating techniques used to estimate sediment age since 1963/1964, and 0 to ca 100+ years before present (yBP), respectively. The relationship between 210Pb and the 137Cs dated accretion rates (Sed210 and Sed137, respectively) was linear for 45 salt marsh and mangrove environments. Sed210 averaged 75% of Sed137 suggesting that vertical accretion over the last 100+ years is driven by soil organic matter accumulation, as shown for the pre 137Cs dated horizon. The ratio of Sed210/Sed137 declines with increasing mineral content. A linear multiple regression equation that includes bulk density and Sed137 to predict Sed210 described 97% of the variance in Sed210. Sediments from Connecticut, Delaware and Louisiana coastal environments dated with 14C indicate a relatively constant sediment accretion rate of 0.13 cm year−1 for 1000–7000 yBP, which occurs within 2 m of today's marsh surface and equals modern sea level rise rates. Soil subsidence is not shown to be distinctly different in these vastly different coastal settings. The major reason why the Sed137 measurements indicate higher accretion rates than do the Sed210 measurements is because the former apply to younger sediments where the effects of root growth and decomposition are greater than in the latter. The most intense rates of change in soil volume in organic-rich salt marshes sediments is, therefore, neither in deep or old sediments (>4 m; >1000 years), but within the first several hundreds of years after accumulation. The average changes in organic and inorganic constituents downcore are nearly equal for 58 dated sediment cores from the northern Gulf of Mexico. These parallel changes downcore are best described as resulting from compaction, rather than from organic matter decomposition. Thus most of the volumetric changes in these salt marsh sediments occurs in the upper 2 m, and declines quickly with depth. Extrapolation forwards or backwards, using results from the 210Pb and the 137Cs dating technique appear to be warranted for the types of samples from the environments described here. 相似文献