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151.
Katy R. Wiest Diane I. Doser Aaron A. Velasco James Zollweg 《Pure and Applied Geophysics》2007,164(10):1905-1919
Over the past ~65 years intraslab earthquakes have caused the most significant damage in the western Washington region. This
study examines regional and teleseismic seismograms for four historic, suspected intraslab events of M > 5.5 occurring within
the Cascadia Subduction zone in 1939 (South Seattle), 1946 (Puget Sound), 1949 (Olympia) and 1965 (Sea-Tac) to better determine
the source locations, mechanisms and rupture histories of these events. Our study is aided by digital seismograms of post-1990
intraslab events with well-determined focal depths and focal mechanisms that were recorded in the same locations as the historic
events. Thus the recent events were used as empirical Greens functions to study the historic events. Our results suggest that
the 1946 earthquake is not an intraslab event, that the 1939 event closely resembles the 1965 event, and that the 1949 event
is similar to the 2001 Nisqually earthquake, although the 1949 event appears to have ruptured toward the south, causing significantly
more damage than the Nisqually event. These results suggest that earthquakes periodically rupture along the same or similarly
oriented faults within the subducting slab. 相似文献
152.
Glacial meltwater streams in the McMurdo Dry Valleys, Antarctica exhibit daily cycles in temperature with maxima frequently reaching 10–15 °C, often 10 °C above air temperatures. Hydrologic and biogeochemical processes occurring in these streams and their hyporheic zones strongly influence the flux of water, solutes, and sediment to the ice-covered lakes on the valley bottoms. The purpose of this study was to identify the dominant processes controlling water temperature in these polar desert streams and to investigate in particular the role of hyporheic exchange. In order to do this, we analyzed stream temperature patterns on basin-wide, longitudinal, and reach scales. In the basin-wide study, we examined stream temperature monitoring data for seven streams in the Lake Fryxell Basin. For the longitudinal study, we measured temperatures at seven sites along a 5-km length of Von Guerard Stream. 相似文献
153.
We present first principles calculations for the structural properties of α-berlinite (AlPO4) as a function of pressure. The calculations were performed within the local density approximation using ab initio pseudopotentials and a plane-wave basis. We determined the lattice parameters, cohesive energy, and bulk modulus by minimizing
the enthalpy of the solid with respect to lattice parameters. We find good agreement, within ∼2–3% of the experimentally observed
values, for the structural properties as a function of pressure.
Received: 3 January 1997 / Revised, accepted: 16 April 1997 相似文献
154.
A recent human campsite, occupied in 1973 by members of the Dassanetch tribe of northern Kenya, was observed from its creation through its subsequent burial in flood events 4 months later. The site was excavated as an archeological occurrence in the summer of 1974. Analyses of field and laboratory data yield a detailed picture of sedimentary structures, bone transport and burial, and site preservation in a well-documented depositional situation. Trampling by site occupants was apparently instrumental in burying much small bone prior to the flood events which acted on the site. About 30 cm of sediments accumulated on the site during four or five flood events. Individual sedimentary beds can be related to specific observed flood events in the drainage system. The ultimate preservation of the site as part of the region's archeological record would depend upon the interaction of sediment deflation and the varying local water table. Specific conditions which tend to preserve human sites in water-poor environments may consistently select seasonally biased vestiges of human settlement and economy. 相似文献
155.
Abundant populations of frondose epilithic macroalgae from a variety of carbonate-rich tropical waters were significantly depleted in phosphorus relative to carbon and nitrogen when compared to macroalgae from temperate siliciclastic waters. Percent carbon (C) and percent nitrogen (N) dry weight contents were similar between tissues from the siliciclastic and carbonate environments (means of 22.6% vs. 20.1% and 1.0% vs. 1.2%, respectively), but phosphorus (P) levels were two-fold lower (0.15% vs. 0.07%) in the carbonate-rich systems. Accordingly, the molar C:N tissue ratios were comparable between macroalgae from the siliciclastic and carbonate sites (mean of 29.2 vs. 23.1), whereas large differences were observed for the C:P (mean of 430 vs. 976) and N:P ratios (mean of 14.9 vs. 43.4). In addition, alkaline phosphatase activity was low and often undetectable in the macroalgae from siliciclastic habitats (mean of 7.3 μM PO4 3? released g dry wt?1 h?1) compared to seven-fold higher rates (52.5 μM PO4 3? released g dry wt?1 h?1) observed in the macroalgae from carbonate systems. Seawater samples taken adjacent to benthic macroalgae from the carbonate-rich tropical waters contained relatively high levels of dissolved inorganic nitrogen with low concentrations of soluble reactive phosphorus (SRP), and showed elevated N:SRP ratios (mean=36) compared to siliciclastic environments (mean <3). These data support the precept that availability of N limits the productivity of macroalgae in temperate siliciclastic waters but, conversely, suggest that availability of P, rather than N, may be of paramount importance in limiting primary production of macroalgae in carbonate-rich tropical waters. 相似文献
156.
Matthew P. Miller Bailey E. Simone Diane M. McKnight Rose M. Cory Mark W. Williams Elizabeth W. Boyer 《Aquatic Sciences - Research Across Boundaries》2010,72(3):269-275
In their article, “New light on a dark subject: On the use of fluorescence data to deduce redox states of natural organic
matter,” Macalady and Walton-Day (2009) subjected natural organic matter (NOM) samples to oxidation, reduction, and photochemical transformation. Fluorescence spectra
were obtained on samples, which were diluted “to bring maximum uvvisible absorbance values below 1.0.” The spectra were fit
to the Cory and McKnight (2005) parallel factor analysis (PARAFAC) model, and consistent variation in the redox state of quinone-like moieties was not detected.
Based on these results they concluded that fitting fluorescence spectra to the Cory and McKnight (2005) PARAFAC model to obtain information about the redox state of quinone-like moieties in NOM is problematic. Recognizing that
collection and correction of fluorescence spectra requires consideration of many factors, we investigated the potential for
inner-filter effects to obscure the ability of fluorescence spectroscopy to quantify the redox state of quinone-like moieties.
We collected fluorescence spectra on Pony Lake and Suwannee River fulvic acid standards that were diluted to cover a range
of absorbance wavelengths, and fit these spectra to the Cory and McKnight (2005) PARAFAC model. Our results suggest that, in order for the commonly used inner-filter correction to effectively remove inner-filter
effects, samples should be diluted such that the absorbance at 254 nm is less than 0.3 prior to the collection of fluorescence
spectra. This finding indicates that inner-filter effects may have obscured changes in the redox signature of fluorescence
spectra of the highly absorbing samples studied by Macalady and Walton-Day (2009). 相似文献
157.
158.
Diane J. Brousseau Anna E. Murphy Nicole P. Enriquez Kara Gibbons 《Estuaries and Coasts》2008,31(1):144-151
The Asian shore crab, Hemigrapsus sanguineus, is a recent and particularly successful introduction to the east coast of the USA. Little research has been done on the
utilization of Asian shore crabs for food by native species, a potential form of biocontrol. Over a 4-year period, we examined
the gut contents of cogeners, Fundulus heteroclitus and Fundulus majalis, collected from two embayments in western Long Island Sound for the presence of juvenile H. sanguineus. Frequency (percent) of occurrence of food items in the guts of both species varied over year and study site. Asian shore
crabs were consumed more often by F. heteroclitus than by F. majalis, but predation pressure by both species was low. Only 13% of F. heteroclitus and 7.7% of F. majalis found with food in their guts had ingested Asian shore crab remains. Of those, 1/3 had consumed whole crabs; the rest had
only autotomized appendages in their guts. The mean carapace width of juvenile Asian shore crabs ingested by F. heteroclitus was 3.59 ± 2.22 mm (N = 33). Results of our study on killifish predation support the hypothesis that H. sanguienus abundance is partly explained by reduced impact of native predators (i.e., the “enemy release hypothesis”). Predation pressure
of other potential enemies on both planktonic and benthic stages of the Asian shore crab must be investigated, however, to
understand the full impact of predation on H. sanguineus population dynamics. 相似文献
159.
Spatio‐temporal variations in demersal fish assemblages and diversity in the northern Gulf of St. Lawrence (Canada)
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Species diversity is generally considered one of the key factors of ecosystem resilience in response to anthropogenic pressures, including fishing. In this context, the spatial and temporal changes in demersal fish assemblages and species diversity were investigated in the northern Gulf of St. Lawrence (Canada), over a 20‐year period (1990–2010). Data were obtained from the summer research survey conducted by the Department of Fisheries and Oceans, and include commercial and non‐commercial species. The study covers the period of groundfish fishery collapse, the moratorium period, and the post‐moratorium period, and reflects various modifications in management. Multivariate statistical methods revealed two communities. A coastal community corresponds to strata located above 200 m depth and a deeper community located in the deep channels. Interannual differences in the composition of fish assemblages were observed and are mainly due to the changes in the relative biomass of some dominant species. Three diversity indices (Shannon–Wiener, Simpson's Index of Diversity and Motomura's constant) indicate a slight but significant increase of the diversity over time. This trend is due to the increase of the relative biomass of low‐rank species, which may have been favoured by the prohibition of groundfish trawling after 1997 in that region. The geographical distribution of the Shannon–Wiener index also shows temporal dynamics reflecting the biomass distribution of dominant demersal species. 相似文献