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61.
Arguitxu de la Riva-Caballero H. John B. Birks Anne E. Bjune Hilary H. Birks Torstein Solh?y 《Journal of Paleolimnology》2010,44(1):361-374
Little is known about the relationships between fossil oribatid mite assemblages in lake and mire sediments and the composition,
abundance, and richness of their living communities. Because oribatid mites are a relatively new area of palaeolimnological
study, there is a great lack of knowledge about the taphonomic processes that might affect fossil mite assemblages. The DOORMAT
(Direct Observation Of Recent Macrofossils Across Tree-line) project was designed to study the transport and deposition of
oribatid mites and plant remains in the tree-line area of western Norway. The present study also compares modern oribatid
assemblages with fossil oribatid assemblages in a Holocene lake-sediment sequence from the nearby Trettetj?rn, and considers
the optimal location for studying fossil oribatid mites within a lake basin. Seven novel terrestrial traps (50 × 80 cm Astroturf
doormats) were placed at major vegetational transitions along an altitudinal transect crossing the tree-line ecotone from
633 to 1,120 m a.s.l. at Upsete, west Norway. Three sediment traps were placed in Trettetj?rn (810 m a.sl.) at the inlet,
the middle, and near the outlet. In each terrestrial trap, the oribatid assemblage was found to be characteristic of the surrounding
habitat. The lake-trap analyses showed that aquatic or moist-habitat species had the highest chance of being incorporated
into the lake sediments; the number of terrestrial species decreased considerably from both outlet and inlet traps to the
central trap in the deepest water. The area adjacent to the inlet of Trettetj?rn would therefore be the optimal location for
a sediment core for oribatid analysis. However, this conclusion is not supported when the modern trap results are compared
with the Trettetj?rn sequence from the lake centre. 相似文献
62.
Marianne Presthus Heggen Hilary H. Birks Oliver Heiri John-Arvid Grytnes H. John B. Birks 《Journal of Paleolimnology》2012,48(4):669-691
How representative of the whole-lake fossil assemblage are analyses from a single sediment core taken in the centre of a small lake? This question was addressed in five shallow Norwegian lakes that ranged in location from low-altitude, boreal-deciduous forest to mid-alpine environments. Surface-sediment samples were taken from the deepest part of each lake and in two transects running from the lake centre to shore, and analysed for mites, chironomids, and plant remains. Ordination techniques summarised patterns of variation between and within lakes. Correlations between whole-lake assemblages and water depth and sediment organic content (loss-on-ignition) were investigated. Representativeness of each sample of the whole-lake assemblage was determined by comparing Principal Components Analysis scores of the original data with those of Monte Carlo-simulated data sets, using the actual data as constraints in the simulations. The majority of samples are representative of the whole-lake assemblages. Littoral samples, however, are most frequently unrepresentative or poorly representative samples. Water depth is an important controlling variable. A sediment core from the lake centre has the highest probability of representing the whole-lake assemblage. It may, however, also yield the lowest concentrations of terrestrial remains. A sediment core from the slope is slightly more likely to be unrepresentative of the total plant macrofossil assemblage, but generally has higher concentrations of terrestrial remains. These site differences should be considered when choosing a core location. Overall, the three fossil types are deposited in similar patterns. Therefore they can be satisfactorily analysed using a single core. 相似文献
63.
It is important to understand how phosphate sorption dynamics of coastal carbonate aquifers are affected by seawater intrusion, because many coastal aquifers are composed of carbonate rocks and subject to an increase in saltwater intrusion during relative sea-level rise. Twelve carbonate rock and unconsolidated sediment specimens were acquired from a test corehole spanning the full thickness of the Biscayne aquifer in southeastern Florida. All 12 samples exhibit low phosphorus content but variable contents of iron. Column leaching experiments were conducted with two carbonate aquifer samples, alternating between freshwater and saltwater flow. With the first influx of saltwater, phosphate concentration in leachate increased rapidly from a freshwater value of approximately 0.2 μM to peaks of between 0.8 and 1.6 μM. The phosphate concentration began to diminish as saltwater continued to flow, but sustained desorption continued for over 2 h. Overall, seawater drove sorption behavior much more than chemical composition for the aquifer rocks and sediment from the seven rock samples for which we did isotherm sorption experiments. Our results indicate that an immediate and intense pulse of phosphate desorption from carbonate rock and sediment with low phosphorus content occurs in response to an influx of seawater and that the duration of desorption will vary by layer within a single aquifer. 相似文献
64.
65.
Maureen D. Keller Timothy H. Mague Marguerite Badenhausen Hilary E. Glover 《Estuarine, Coastal and Shelf Science》1982,15(3):301-315
A seasonal study on coastal microplankton was conducted in surface waters near Boothbay Harbor, Maine. Phytoplankton biomass, particulate production and extracellular organic release were examined in conjunction with microheterotrophic biomass and the uptake and respiration of amino acids. In situ dissolved free amino acid (DFAA) concentrations were also determined. Several phytoplankton blooms occurred throughout the year, in mid-summer, late autumn and in mid-winter. Heterotrophic activity and biomass paralleled phytoplankton extracellular release more closely than either phytoplankton particulate production or biomass. DFAA concentrations were not wholly dependent on extracellular release. Heterotrophic uptake did not appear to be dependent on DFAA concentrations but rather on rates of production of DOC by phytoplankton. 相似文献
66.
67.
The excitation of structural components and liquid contents of surface impoundments by seismic waves can generate turbulence
that is large enough to overtop the bounding berms. In cases in which the liquids are wastes from industrial/municipal operations,
their release from impoundments can pose significant risks to the environment. In this analysis, the freeboard magnitudes
that can accommodate liquid head levels in impoundments are determined through linkage of configuration of waves in the liquid
surface to incident seismic wave characteristics, liquid characteristics and impoundment design. For an impoundment site in
a region of ground acceleration levels ranging from 0.2 to 1.0 g and impacted by seismic shear wave velocity of 180 m/s, freeboard
requirements are in the range of 0.004–2.0 m on soft soil; 0.008–0.7 m on medium-dense soil; and 0.002–0.1 m for dense soil.
For the same impoundment design, ground acceleration and incident wave characteristics, freeboard requirements are directly
proportional to the depth of the soil mantle over bedrock. The impoundment slope, which is a key parameter with regards to
liquid holding volumetric capacity of the impoundment, is a less significant parameter than depth to bedrock with regard to
the size of the required freeboard. This implies that siting of an impoundment should be considered to be critical to impoundment
performance in seismic zones. 相似文献
68.
Asbury H. Sallenger Hilary F. Stockdon Laura Fauver Mark Hansen David Thompson C. Wayne Wright Jeff Lillycrop 《Estuaries and Coasts》2006,29(6):880-888
Four hurricanes battered the state of Florida during 2004, the most affecting any state since Texas endured four in 1884.
Each of the storms changed the coast differently. Average shoreline change within the right front quadrant of hurricane force
winds varied from 1 m of shoreline advance to 20 m of retreat, whereas average sand volume change varied from 11 to 66 m3 m−1 of net loss (erosion). These changes did not scale simply with hurricane intensity as described by the Saffir-Simpson Hurricane
Scale. The strongest storm of the season, category 4 Hurricane Charley, had the least shoreline retreat. This was likely because
of other factors like the storm's rapid forward speed and small size that generated a lower storm surge than expected. Two
of the storms, Hurricanes Frances and Jeanne, affected nearly the same area on the Florida east coast just 3 wk apart. The
first storm, Frances, although weaker than the second, caused greater shoreline retreat and sand volume erosion. As a consequence,
Hurricane Frances may have stripped away protective beach and exposed dunes to direct wave attack during Jeanne, although
there was significant dune erosion during both storms. The maximum shoreline change for all four hurricanes occurred during
Ivan on the coasts of eastern Alabama and the Florida Panhandle. The net volume change across a barrier island within the
Ivan impact zone approached zero because of massive overwash that approximately balanced erosion of the beach. These data
from the 2004 hurricane season will prove useful in developing new ways to scale and predict coastal-change effects during
hurricanes. 相似文献
69.
The land use and land cover pattern of a region is a consequence of natural and socio-economic factors and their utilization by man in time and space. In this study, we hypothesized that land use and land cover change patterns in the Lake Chivero catchment, Zimbabwe, were related to its human population dynamics. Using nonparametric correlation coefficients (Spearman’s rho, ρ), we found that bareland, cropland and built-up land had positive relations with human population growth of ρ = 0.7, ρ = 0.9 and ρ = 1, respectively. Grassland/shrubland, water and forest, on the other hand, had a negative relationship with human population growth of ρ = ?0.9, ρ = ?0.7 and ρ = ?0.667, respectively. However, these relationships were only significant (p < 0.05) for cropland, grassland/shrubland and built-up land. Human population dynamics in the Lake Chivero catchment could be one of the major drivers of land use and land cover change in the catchment between 1986 and 2014. 相似文献
70.