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151.
152.
Restoration of offshore marine habitats is a relatively new concept, with attempts in the European Union being largely instigated by requirements of various strategic directives. In this experiment, we investigate the practicality and effectiveness of gravel seeding, using a commercial aggregate dredging vessel, in order to recreate a gravel habitat. The experimental design consisted of a Treatment and Control site, both within an area of historic dredging characterised by an overburden of sand, and a gravel dominated Reference site. All sites were surveyed, using a combination of acoustic, camera and grab techniques, 2 months before, and then at 0, 12 and 22 months after the deposition of 4444 m3 of gravel dominated sediments within the Treatment site. Although financial and practical constraints limited replication of the Treatment to one area, and so precluded strong statistical conclusions, our results suggested that the technique was both practically feasible, and successful in terms of returning the physical and biological attributes at the Treatment site to a state more representative of gravelly substrata in the wider, un-impacted environment. 相似文献
153.
Differences in physiological response to increased seawater temperature in nearshore and offshore corals in northern Vietnam 总被引:1,自引:0,他引:1
Faxneld S Jörgensen TL Nguyen ND Nyström M Tedengren M 《Marine environmental research》2011,71(3):225-233
Effects of elevated seawater temperature show high spatial heterogeneity and variation within and among coral species. The objective of this study was to investigate how two coral species, Porites lutea and Galaxea fascicularis, from two high latitude reefs differently exposed to chronic disturbance, respond to elevated seawater temperatures. Corals were collected from reefs nearshore (i.e. subjected to high sediment load, higher chlorophyll α concentrations, turbidity etc.) and offshore (i.e. less exposed). The corals were exposed in the lab to gradually increasing temperatures (25.5-33.5?°C) for 72?h after which they were allowed to recover to ambient temperature (25.5?°C) for 24?h. Production and respiration were measured after 24, 48, 72 and 96?h. The results show that P. lutea from nearshore reefs suffered an initial decrease in gross primary production/respiration (GP/R) ratio after 24?h, after only a moderate temperature increase (+2?°C, from 25.5 to 27.5?°C), while there was no difference in GP/R ratio between heat-exposed and controls the other days, indicating that the chronic disturbance in the nearshore reef had no effect on their thermotolerance. Furthermore, P. lutea from the offshore reef showed a decrease in GP/R ratio both after 24?h and 72?h (33.5?°C) of exposure. In comparison, G. fascicularis showed a decrease in GP/R ratio after 48?h, 72?h and 96?h of exposure for the nearshore corals. Also, after 72?h these corals had withdrawn their polyps. There were no differences between heat-treated and controls for the offshore G. fascicularis. This implies that the chronically disturbed G. fascicularis had lower thermotolerance when exposed to a temperature increase. This study, hence, shows that the response of corals to elevated seawater temperature varies with species and environmental background history. 相似文献
154.
155.
Recent observations of brightness variations on the Sun during the solar cycle have motivated us to re-examine the widely held view that cool, dark starspots, covering a significant fraction of the star, are the centers of magnetic activity on BY Dra stars. We propose that the magnetic regions are better described by a bright facular network, and that the dark areas which give rise to photometric rotational modulation are actually regions where the underlying quiet photosphere is seen. This interpretation is consistent with recent observations of late-type stars that show that bright areas covering much of the star have magnetic fields with strengths of several thousand gauss. It resolves several problems with the current model, including the size, location, and stability of the starspots required to match photometric and Doppler-imaging observations. It also has interesting observational implications for the correlation of photometric rotational modulation and long term brightness variations with other surface activity, and for the positions of magnetically active stars in the H-R diagram.Hubble Fellow. 相似文献
156.
Ian J. W. Giesbrecht William C. Floyd Suzanne E. Tank Ken P. Lertzman Brian P. V. Hunt Maartje C. Korver Allison A. Oliver Ray Brunsting Paul Sanborn Santiago G. Gonzalez Arriola Gordon W. Frazer Kyra A. St. Pierre Shawn Hateley James McPhail Colby Owen Stewart Butler Bryn Fedje Emma Myers Lucy Quayle Emily Haughton Isabelle Desmarais Rob White David J. Levy-Booth Colleen T. E. Kellogg Jennifer M. Jackson William W. Mohn Steven J. Hallam Justin Del Bel Belluz 《水文研究》2021,35(6):e14198
The Kwakshua Watersheds Observatory (KWO) is an integrative watersheds observatory on the coastal margin of a rain-dominated bog-forest landscape in British Columbia (BC), Canada. Established in 2013, the goal of the KWO is to understand and model the flux of terrestrial materials from land to sea – the origins, pathways, processes and ecosystem consequences – in the context of long-term environmental change. The KWO consists of seven gauged watersheds and a network of observation sites spanning from land to sea and along drainage gradients within catchments. Time-series datasets include year-round measurements of weather, soil hydrology, streamflow, aquatic biogeochemistry, microbial ecology and nearshore oceanographic conditions. Sensor measurements are recorded every 5 min and water samples are collected approximately monthly. Additional observations are made during high-flow conditions. We used remote sensing to map watershed terrain, drainage networks, soils and terrestrial ecosystems. The watersheds range in size from 3.2 to 12.8 km2, with varying catchment characteristics that influence hydrological and biogeochemical responses. Despite local variation, the overall study area is a global hotspot for yields of dissolved organic carbon, dissolved organic nitrogen and dissolved iron at the coastal margin. This observatory helps fill an important gap in the global network of observatories, in terms of spatial location (central coast of BC), climate (temperate oceanic), hydrology (very high runoff, pluvial regime), geology (igneous intrusive, glacially scoured), vegetation (bog rainforest) and soils (large stores of organic carbon). 相似文献
157.
An idealized model of tidal dynamics in the North Sea: resonance properties and response to large-scale changes 总被引:3,自引:1,他引:2
Pieter C. Roos Jorick J. Velema Suzanne J. M. H. Hulscher Ad Stolk 《Ocean Dynamics》2011,61(12):2019-2035
An idealized process-based model is developed to investigate tidal dynamics in the North Sea. The model geometry consists
of a sequence of different rectangular compartments of uniform depth, thus, accounting for width and depth variations in a
stepwise manner. This schematization allows for a quick and transparent solution procedure. The solution, forced by incoming
Kelvin waves at the open boundaries and satisfying the linear shallow water equations on the f plane with bottom friction, is in each compartment written as a superposition of eigenmodes, i.e. Kelvin and Poincaré waves.
A collocation method is employed to satisfy boundary and matching conditions. First, the general resonance properties of a
strongly simplified geometry with two compartments, representing the Northern North Sea and Southern Bight, are studied. Varying
the forcing frequency while neglecting bottom friction reveals Kelvin and Poincaré resonance. These resonances continue to
exist (but with lower amplification and a modified spatial structure) when adding the Dover Strait as a third compartment
and separating the solutions due to forcing from either the north or the south only. Including bottom friction dampens the
peaks. Next, comparison with tide observations along the North Sea coast shows remarkable agreement for both semi-diurnal
and diurnal tides. This result is achieved with a more detailed geometry consisting of 12 compartments fitted to the coastline
of the North Sea. Further simulations emphasize the importance of Dover Strait and bottom friction. Finally, it is found that
a sea level rise of 1 m, uniformly applied to the entire North Sea, amplifies the M2-elevation amplitudes almost everywhere
along the coast, with an increase of up to 8 cm in Dover Strait. Bed level changes of ±1 m, uniformly applied to the Southern
Bight only, imply weaker changes, with changes in coastal M2-elevation amplitudes below 5 cm. 相似文献
158.
Though the concept of sustainable development originally included a clear social mandate, for two decades this human dimension has been neglected amidst abbreviated references to sustainability that have focused on bio-physical environmental issues, or been subsumed within a discourse that conflated ‘development’ and ‘economic growth’. The widespread failure of this approach to generate meaningful change has led to renewed interest in the concept of ‘social sustainability’ and aspects thereof. A review of the literature suggests, however, that it is a concept in chaos, and we argue that this severely compromises its importance and utility. The purpose of this paper is to examine this diverse literature so as to clarify what might be meant by the term social sustainability and highlight different ways in which it contributes to sustainable development more generally. We present a threefold schema comprising: (a) ‘development sustainability’ addressing basic needs, the creation of social capital, justice and so on; (b) ‘bridge sustainability’ concerning changes in behaviour so as to achieve bio-physical environmental goals and; (c) ‘maintenance sustainability’ referring to the preservation - or what can be sustained - of socio-cultural characteristics in the face of change, and the ways in which people actively embrace or resist those changes. We use this tripartite of social sustainabilities to explore ways in which contradictions and complements between them impede or promote sustainable development, and draw upon housing in urban areas as a means of explicating these ideas. 相似文献
159.
Claudio Marchesi José María González-Jiménez Fernando Gervilla Carlos J. Garrido William L. Griffin Suzanne Y. O’Reilly Joaquín A. Proenza Norman J. Pearson 《Contributions to Mineralogy and Petrology》2011,161(6):977-990
Chromitite pods in the Mayarí-Cristal ophiolitic massif (eastern Cuba) were formed in the Late Cretaceous when island arc
tholeiites and MORB-like back-arc basin basalts reacted with residual mantle peridotites and generated chromite-rich bodies
enclosed in dunite envelopes. Platinum-group minerals (PGM) in the podiform chromitites exhibit important Os-isotope heterogeneities
at the kilometric, hand sample and thin section scales. 187Os/188Os calculated at the time of chromitite crystallization (~90 Ma) ranges between 0.1185 and 0.1295 (γOs = −7.1 to +1.6, relative
to enstatite chondrite), and all but one PGM have subchondritic 187Os/188Os. Grains in a single hand sample have initial 187Os/188Os that spans from 0.1185 to 0.1274, and in one thin section it varies between 0.1185 and 0.1232 in two PGM included in chromite
which are only several millimeters apart. As the Os budget of a single micrometric grain derives from a mantle region that
was at least several m3 in size, the variable Os isotopic composition of PGM in the Mayarí-Cristal chromitites probably reflects the heterogeneity
of their mantle sources on the 10–100 m scale. Our results show that this heterogeneity was not erased by pooling and mingling
of individual melt batches during chromitite crystallization but was transferred to the ore deposits on mineral scale. The
distribution of the Os model ages calculated for PGM shows four main peaks, at ~100, 500, 750 and 1,000 Ma. These variable
Os model ages reflect the presence of different depleted domains in the oceanic (Pacific-related) upper mantle of the Greater
Antilles paleo-subduction zone. The concordance between the age of crystallization of the Mayarí-Cristal chromitites and the
most recent peak of the Os model age distribution in PGM supports that Os in several grains was derived from fertile domains
of the upper mantle, whose bulk Os isotopic composition is best approximated by that of enstatite chondrites; on the other
hand, most PGM are crystallized by melts that tapped highly refractory mantle sources. 相似文献
160.
The Kimberlites and related rocks of the Kuruman Kimberlite Province,Kaapvaal Craton,South Africa 总被引:2,自引:0,他引:2
Cara L. Donnelly William L. Griffin Suzanne Y. O’Reilly Norman J. Pearson Simon R. Shee 《Contributions to Mineralogy and Petrology》2011,161(3):351-371
The Kuruman Kimberlite Province is comprised of 16 small pipes and dikes and contains some of the oldest known kimberlites
(>1.6 Ga). In this study, 12 intrusions are subdivided into three groups with distinct petrology, age, and geochemical and
isotopic compositions: (1) kimberlites with groundmass perovskites defining a Pb–Pb isochron age of 1787 ± 69 Ma, (2) orangeite
with a U–Pb perovskite age of 124 ± 16 Ma, and (3) ultramafic lamprophyres (aillikite and mela-aillikite) with a zircon U–Pb
age of 1642 ± 46 Ma. The magma type varies across the Province, with kimberlites in the east, lamprophyres in the west and
orangeite and ultramafic lamprophyres to the south. Differences in the age and petrogenesis of the X007 orangeite and Clarksdale
and Aalwynkop aillikites suggest that these intrusions are probably unrelated to the Kuruman Province. Kimberlite and orangeite
whole-rock major and trace element compositions are similar to other South African localities. Compositionally, the aillikites
typically lie off kimberlite and orangeite trends. Groundmass mineral chemistry of the kimberlites has some features more
typical of orangeites. Kimberlite whole-rock Sr and Nd isotopes show zoning across the Province. When the kimberlites erupted
at ~1.8 Ga, they sampled a core volume (ca 50 km across) of relatively depleted SCLM that was partially surrounded by a rim
of more metasomatized mantle. This zonation may have been related to the development of the adjacent Kheis Belt (oldest rocks
~2.0 Ga), as weaker zones surrounding the more resistant core section of SCLM were more extensively metasomatized. 相似文献