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51.
The possible influences of the Emperor Seamounts (ESs) upon the subarctic gyre of the North Pacific (NPSAG) were investigated
by a series of numerical experiments. In the experiments, a two-layer ocean with a meridional mountain ridge was forced by
seasonally varying wind stress. We focused on how the return ratio, the ratio of the boundary transport along the eastern
side of the ridge to the interior Sverdrup transport, changes with ridge height, width and density stratification. It was
found that the return ratio can be large if the ridge width is greater than the width of the viscous boundary layer. In this
case, the bottom pressure torque determines the return ratio; the return ratio is almost proportional to the ridge height
when the ridge height is small and some contours of planetary potential vorticity pass over the ridge. However, the return
ratio is independent of the ridge height and decreases with the stratification when the ridge height is large and all the
contours of planetary potential vorticity are closed. These dependences of the return ratio were understood in terms of barotropic
and baroclinic components of the bottom pressure torque. Implications for the bathymetric influences of ESs on the actual
NPSAG are also discussed. 相似文献
52.
Evidence and Implications of Recent Climate Change in Northern Alaska and Other Arctic Regions 总被引:19,自引:0,他引:19
Larry D. Hinzman Neil D. Bettez W. Robert Bolton F. Stuart Chapin Mark B. Dyurgerov Chris L. Fastie Brad Griffith Robert D. Hollister Allen Hope Henry P. Huntington Anne M. Jensen Gensuo J. Jia Torre Jorgenson Douglas L. Kane David R. Klein Gary Kofinas Amanda H. Lynch Andrea H. Lloyd A. David McGuire Frederick E. Nelson Walter C. Oechel Thomas E. Osterkamp Charles H. Racine Vladimir E. Romanovsky Robert S. Stone Douglas A. Stow Matthew Sturm Craig E. Tweedie George L. Vourlitis Marilyn D. Walker Donald A. Walker Patrick J. Webber Jeffrey M. Welker Kevin S. Winker Kenji Yoshikawa 《Climatic change》2005,72(3):251-298
The Arctic climate is changing. Permafrost is warming, hydrological processes are changing and biological and social systems
are also evolving in response to these changing conditions. Knowing how the structure and function of arctic terrestrial ecosystems
are responding to recent and persistent climate change is paramount to understanding the future state of the Earth system
and how humans will need to adapt. Our holistic review presents a broad array of evidence that illustrates convincingly; the
Arctic is undergoing a system-wide response to an altered climatic state. New extreme and seasonal surface climatic conditions
are being experienced, a range of biophysical states and processes influenced by the threshold and phase change of freezing
point are being altered, hydrological and biogeochemical cycles are shifting, and more regularly human sub-systems are being
affected. Importantly, the patterns, magnitude and mechanisms of change have sometimes been unpredictable or difficult to
isolate due to compounding factors. In almost every discipline represented, we show how the biocomplexity of the Arctic system
has highlighted and challenged a paucity of integrated scientific knowledge, the lack of sustained observational and experimental
time series, and the technical and logistic constraints of researching the Arctic environment. This study supports ongoing
efforts to strengthen the interdisciplinarity of arctic system science and improve the coupling of large scale experimental
manipulation with sustained time series observations by incorporating and integrating novel technologies, remote sensing and
modeling. 相似文献
53.
Kazuyuki Saito Sergei Marchenko Vladimir Romanovsky Amy Hendricks Nancy Bigelow Kenji Yoshikawa John Walsh 《Boreas: An International Journal of Quaternary Research》2014,43(3):733-749
A high‐resolution map of potential frozen ground distribution in NE Asia (90–150°E, 25–60°N) at the period of the Last Permafrost Maximum (LPM, c. 21 000 years ago) was dually reconstructed by means of a statistical classification using air freezing and thawing indices and a topographical downscaling using a digital relief model (ETOPO1). Background LPM climate data were derived from global climate model simulations of the Paleoclimate Model Intercomparison Project, Phase II (PMIP2). The reconstructed LPM map shows the southward shift of the southern limit of climate‐driven permafrost by 400–1500 km, with the greatest advance in the western sector (90–110°E), encompassing an area from central Siberia to most of the Altai area. The advance of environmentally conditional permafrost and seasonally frozen ground was greatest in the eastern sector (110–150°E), with an average shift of about 450 km. The descent of the lower limit of LPM alpine permafrost was in the range of 400–800 m. A comparison of the reconstructed map with published literature shows that this method, simplistically constructed yet effectively recognizing seasonality, continentality and topography, captures local features better than more elaborate methods. The sensitivity examination of a constant atmospheric lapse rate shows that altitudes of 2000–5000 m a.s.l. were most sensitive, though with only a limited effect on overall LPM distribution. 相似文献
54.
Ohtsuka Katsuhito Shimoda Chikara Yoshikawa Makoto Watanabe Jun-Ichi 《Earth, Moon, and Planets》1997,77(2):83-91
The detailed activity profile of the Sextandids - one of the day-time meteor showers - is poorly known and still unclear.
Using the forward-scatter radio technique we have successfully been able to obtain further detailed overall activity profile
of the Sextantids for seven consecutive years: 1991–1997. Analysis confirmed the Sextantid activity duration in solar longitude
(J2000) of at least 184–193° and the maximum solar longitude at 188.35 ± 0.10° with a full width at half maximum (FWHM) of
2.0 ± 0.2°. Performing the numerical integrations, we also substantiated a possibility of the association between Apollo-type
asteroid (3200) Phaethon and the Sextantids. Furthermore, we roughly estimated relative maximum flux rate of Sextantids :
Geminids as 1 : 3 amplitude ratio. Depending upon the flux rates and the time lags of the orbital evolution with Phaethon,
we conclude that the Sextantids are at a more progressive stage of orbital evolution than the Geminids if both meteor streams
are really associated with Phaethon.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
55.
Ichiro Yoshikawa Junya Ono Go Murakami Shingo Kameda 《Planetary and Space Science》2008,56(13):1676-1680
A rare, but normal, astronomical event occurred on November 9th 2006 (JST) as Mercury passed in front of the Sun from the perspective of the Earth. The abundance of the sodium vapor above the planet limb was observed by detecting an excess absorption in the solar sodium line D1 during this event. The observation was performed with a 10-m spectrograph of Czerny-Turnar system at Domeless Solar Tower Telescope at the Hida Observatory in Japan. The excess absorption was red-shifted by 10 pm relative to the solar line, and was measured at the dawnside (eastside) and duskside (westside) of Mercury. Between the dawn and dusksides, an asymmetry of total sodium abundance was clearly identified. At the dawnside, the total sodium column density was 6.1×1010 Na atoms/cm2, while it was 4.1×1010 Na atoms/cm2 at the duskside. The investigation of dawn-dusk asymmetry of the sodium exosphere of Mercury is a clue to understand the release mechanism of sodium from the surface rock. Our result suggests that a thermal desorption is a main source process for sodium vapor in the vicinity of Mercury. 相似文献
56.
Isotope analyses of lavas from the Hyblean Plateau (SE Sicily) provided first order constraints for the characterization of the relative magma sources, contributing to a better understanding of the tectono-magmatic evolution of the northernmost part of the African plate. To integrate this research, we are currently studying ultramafic xenoliths of mantle provenance exhumed by the Hyblean alkaline volcanics. These mainly consist of anhydrous spinel-facies peridotites and subordinate pyroxenites/websterites. The paragenesis of the latter is extremely variable in terms of modal proportions and mineral composition, with clinopyroxene composition ranging from Cr-diopside to Al-augite, and variable amount of spinel ± garnet. New Sr-Nd isotopic analyses carried out on hand-picked (and leached) clinopyroxenes indicate that peridotites have 87Sr/86Sr ranging from 0.70288 to 0.70309, and 143Nd/144Nd from 0.51287 to 0.51292. This Sr-Nd isotopic fingerprint approaches that of the HIMU mantle end-member, regionally referred as EAR (European Astenospheric Reservoir) to emphasize a connection with a sub-lithospheric metasomatic component ubiquitous throughout Europe, the Mediterranean area and North Africa. The Sr-Nd analyses of pyroxenites also reveal an EAR affinity, but are slightly distinct from those of peridotites. They display 87Sr/86Sr ranging between 0.70305–0.70326 and 143Nd/144Nd between 0.51292–0.51299, overlapping the composition typical of the Hyblean alkaline lavas. This possibly implies that pyroxene-rich domain significantly contributed to the genesis of the Hyblean magmas. Therefore, the presented Sr-Nd isotopic ratios suggest that the role of the pyroxene-rich mantle portions was more important than commonly considered in the petrogenetic models of Hyblean magmas. This scenario would be coherent with recent evidences highlighting the importance of pyroxenites (together with peridotites) as contributing sources to basalt generation. 相似文献
57.
Various types of endocrine disruptors or environmental hormones flow from their sources down into harbours through rivers and other watercourses, and are accumulated in sediment on the sea bottom. Tributyltin, which has been used as paint for ship bottoms, is considered one of the endocrine disruptors.In close cooperation with the other ministries and agencies, the Ports and Harbours Bureau of the Ministry of Land, Infrastructure and Transport carried out an investigation in 1999 to determine the actual condition of 12 endocrine disruptors in the sediment of 39 harbours, in order to gather fundamental data to be used in future examinations of policy. Furthermore, in 2000 the bureau chose seven harbours out of the above 39 harbours as subjects of an additional investigation regarding the surface distribution of endocrine disruptors in the harbour areas and the synchronistic change of accumulation of dioxin and other substances. As the result of the investigation regarding the surface distribution of endocrine disruptors accumulated in seven harbours, relatively high concentrations were measured in the innermost parts of harbours and the mouths of rivers. Synchronistic changes in the amount of dioxin and other substances accumulated in sediments of five harbours were determined. Small amounts of dioxin and other substances, including an especially small amount of coplanar-PCBs, were found in the layers formed before or around 1950. Relatively large amounts of these substances were measured in the upper layers formed during roughly 1960-1990, though no significant yearly differences in concentration could be identified. This result coincides with the facts that, during roughly 1960-1980, PCP and CNP were used as agricultural chemicals and full-scale production of PCBs started in 1960. 相似文献
58.
STOIC: a study of coupled model climatology and variability in tropical ocean regions 总被引:13,自引:4,他引:13
M. Davey M. Huddleston K. Sperber P. Braconnot F. Bryan D. Chen R. Colman C. Cooper U. Cubasch P. Delecluse D. DeWitt L. Fairhead G. Flato C. Gordon T. Hogan M. Ji M. Kimoto A. Kitoh T. Knutson M. Latif H. Le Treut T. Li S. Manabe C. Mechoso G. Meehl S. Power E. Roeckner L. Terray A. Vintzileos R. Voss B. Wang W. Washington I. Yoshikawa J. Yu S. Yukimoto S. Zebiak 《Climate Dynamics》2002,18(5):403-420
59.
60.
Insight into nitrous oxide production processes in the western North Pacific based on a marine ecosystem isotopomer model 总被引:2,自引:0,他引:2