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61.
We report the size, abundance, and distribution (horizontal, vertical) of northern rock sole, Lepidopsetta polyxystra, larvae collected from ichthyoplankton surveys on the southeastern Bering Sea shelf near Unimak Island, in Unimak Pass, and in the Gulf of Alaska south of Unimak Island. The greatest abundances of larvae occurred within Unimak Pass and in the Bering Sea northeast of Unimak Island. Larvae were smaller and more abundant in 2002 than in 2003. Larval abundance and size varied with depth. Highest abundances were at depths of 10-30 m during the day, and larger fish appeared to migrate from below 20 m to 0-10 m at night. There was evidence of multiple spawning locales and larval dispersal pathways that were depth- and area-specific. Northern rock sole larvae spawned west of Unimak Pass along the Aleutian Islands may be transported northward by the Bering Slope Current. Larvae spawned in the Gulf of Alaska and advected through Unimak Pass are differentially dispersed, primarily to the middle and outer shelves along the 100 m and 200 m isobaths, or along the Alaska Peninsula. Larvae spawned along the Alaska Peninsula east of Unimak Island appear to have the greatest chance of being transported to nursery areas in the coastal domain. Dispersal of near-surface northern rock sole larvae in any of these locations is likely influenced by wind-driven advection, but below-surface (>10 m) northern rock sole larval transport is probably more affected by factors that modulate geostrophic flow rather than wind-driven surface currents. 相似文献
62.
Warren B. White Kathryn A. Gloersen Francis Marsac Yves M. Tourre 《Journal of Oceanography》2004,60(3):531-541
Interannual coupled Rossby waves in the extratropical Indian Ocean propagate westward in covarying pycnocline depth, sea surface
temperature, and meridional surface wind anomalies from the west coast of Australia between 15°S and 35°S, taking 3–4 years
to transit the interior ocean to Madagascar. In the interior subtropical gyre, where the tuna longline catch (TLC) mainly
concerns two species (albacore and bigeye), these waves have been observed to affect year-to-year changes in catch, with wave
crests (troughs) in the main pycnocline associated with high (low) TLC anomalies. This suggested that tuna longline catch
is associated with the entrainment of nutrient-rich pycnocline water into the photic zone and a subsequent increase in primary
productivity there. Here, this hypothesis is examined within the context of SeaWiFS chlorophyll concentration (CC). We find
the situation the opposite of that expected, with wave crests (troughs) in the main pycnocline associated with low (high)
CC anomalies averaged over the photic zone. These results are shown to be consistent with a model relating the anomalous CC
tendency to upper-layer divergence in the wave, not unlike that relating surface slicks to upper-layer divergence in internal
gravity waves. Thus, the connection between interannual coupled Rossby waves and TLC in the interior subtropical gyre does
not appear to derive from wave-induced modulation of the pelagic food web.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
63.
Anja Guhl Pascal Bertran Christoph Zielhofer Kathryn E. Fitzsimmons 《Boreas: An International Journal of Quaternary Research》2013,42(2):317-332
Two sand wedge structures and their host sediments, from Jonzac in SW France, were successfully dated using Optically Stimulated Luminescence (OSL) measurements on both small aliquots and single grains of quartz from the 180–212 μm size fraction. One of the sand wedges clearly contains primary infilling. However, grain‐size analysis and field observations do not clearly indicate whether the other feature represents a primary sand wedge or a composite sand wedge with primary and secondary infilling. OSL results and the geological setting justify using the Central Age Model (CAM) for the calculation of age estimates. Grain‐size analysis and detailed investigations of OSL results revealed the contamination of one sand wedge sample with host sediment. However, age calculation using the Finite Mixture Model (FMM) provided what is considered to be a reliable age estimate for the contaminated sample. The age estimates for all samples correspond to Marine Isotope Stage (MIS) 3. While fine‐grained sediments were deposited in the middle of MIS 3 (c. 43–55 ka), the sand wedges unexpectedly correspond to the end of this period (c. 33 ka) or the onset of MIS 2 (c. 27 ka). The sand wedges were probably formed during intense but short cold periods, possibly correlated with a Heinrich event (H2 and/or H3). The results help us to assess how effective luminescence dating is on sand wedges and the limitations involved in correlating sand wedge ages with Heinrich events, and contribute to the debate on the timing of cryogenic formation processes and the permafrost distribution in SW France. 相似文献
64.
Jordan S. Oestreicher Karina Benessaiah Maria C. Ruiz-Jaen Sean Sloan Kate Turner Johanne Pelletier Bruno Guay Kathryn E. Clark Dominique G. Roche Manfred Meiners Catherine Potvin 《Global Environmental Change》2009,19(2):279-291
Reducing greenhouse gas emissions from deforestation and forest degradation (REDD) is likely to be central to a post-Kyoto climate change mitigation agreement. As such, identifying conditions and factors that will shape the success or failure of a reduced deforestation scheme will provide important insights for policy planning. Given that protected areas (PAs) are a cornerstone in forest conservation, we draw on interviews and secondary data to analyze the effects of available PA resources, governance ability, the level of community involvement, and provincial deforestation rates on land-cover change in nine PAs in Panama. Our results illustrate that coupling surveillance measures with greater funding and strong governance are paramount to reducing deforestation. Alone, however, these factors are insufficient for forest protection. We argue that conservation approaches that complement effective surveillance with community participation and equitable benefit sharing will address the wider issues of leakage and permanence. 相似文献
65.
The Keisarhjelmen detachment records Silurian–Devonian extensional collapse in Northern Svalbard
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At the junction of the Atlantic and Arctic margins, the crustal‐scale Keisarhjelmen detachment of north‐west Svalbard records previously unrecognised magnitudes of extension. The detachment separates a corrugated metamorphic core complex in the footwall from a mantling Devonian supradetachment basin in the hangingwall. The detachment has a top‐N displacement of more than 50 km, which is aligned with the map‐scale corrugations, and an upwards ductile to brittle transition with shear related footwall retrogression. This configuration has striking similarities to extensional collapse detachments in the paired Scandinavian–Greenland Caledonides, but orientation and position link the detachment with the Ellesmerian orogen. 相似文献
66.
Mary Gleason Scott McCreary Melissa Miller-Henson John Ugoretz Evan Fox Matt Merrifield Will McClintock Paulo Serpa Kathryn Hoffman 《Ocean & Coastal Management》2010,53(2):52-68
The planning process for California's Marine Life Protection Act in north central California represents a case study in the design of a regional component of a statewide network of marine protected areas (MPAs) for improved ecosystem protection. We describe enabling factors, such as a legislative mandate, political will, and adequate capacity and funding that fostered a successful planning process. We identify strategic principles that guided the design of a transparent public planning process that delivered regional MPA network proposals, which both met science guidelines and achieved a high level of support among stakeholders. We also describe key decision support elements (spatial data, planning tools, and scientific evaluation) that were essential for designing, evaluating, and refining alternative MPA network proposals and for informing decision-makers. 相似文献
67.
Community geography emphasizes the centrality of community engagement to socially transformative research. This introduction to a special issue of GeoJournal on community geography outlines how this growing subfield provides a model for collaborative action with the crises of our time, from white supremacy through climate change. As the co-editors of this special issue, we summarize the contents of these 14 articles, grouping them by the shared themes of power, institutional partnerships, pedagogy, and methods.
相似文献68.
Louis J. Maher 《Quaternary Research》1977,7(1):14-44
Lake Superior sediments contain pollen whose changes through time can be corelated with dated pollen diagrams from small lakes in the region. A core collected in 1972 from the deep trough (265 m) off Silver Bay (47° 09′N, 91°20′W) penetrated 6.25 cm of taconite tailings, 55 cm of postglacial silty clay, and 93.5 cm of late-glacial varves. Seven levels in the core were dated by stratigraphic and palynological techniques. The varves stopped forming about 9000 years ago, probably when glacial ice retreated to the north shore. The last 100 varves accumulated at about 10 mm/yr, but the average net sedimentation rate subsequently slowed to 0.05 mm/yr until the time of settlement about 1890. The sedimentation rate then increased by a factor of 10, to 0.5 mm/yr until 1956 when taconite processing began. The postsettlement interval can be recognized by marked increases of ragweed and chenopod pollen that result from land disturbance caused by forest clearance and agriculture. The postsettlement interval is also present at the top of six cores from four other sites in western Lake Superior, collected in water from 25–140 m deep. The postsettlement sedimentation rate varies from 0.1–0.8 mm/yr, suggesting that man has greatly increased sediment yield to the lake in the last 80 years. 相似文献
69.
70.
We analyzed the isotopic patterns found in the tooth enamel of modern feral horses from Shackleford Banks, North Carolina (USA), which has a temperate climate and supports primarily C4 grasslands. Enamel δ13C values averaged −4.1‰ with a standard deviation (1σ) of 1.7‰, which corresponds to an average diet of 66 ± 12% C4 plants. Our results differ from dietary reconstructions from 1978 to 1981, which found that horses consumed 91% C4 plants. This suggests that horses have increased their consumption of C3 forbs, likely as a result of the removal of cattle, sheep, and goats from the island. Shackleford surface waters had δ18O values that averaged −3.3 ± 0.5‰ and −1.3 ± 1.8‰ on the western and eastern ends of the island, respectively. Tooth enamel samples averaged 27.3 ± 1.5‰ and displayed the same range of δ18O values as surface waters. The variability of both δ18O and the δ13C values among individuals within this population demonstrates that horses from relatively homogenous temperate environments can display a wide range of isotopic values. Given the observed range of isotopic values for modern horses, we suggest that researchers use the mean values of multiple (≥9) equids when attempting to reconstruct average paleodiets and/or paleoenvironmental conditions. 相似文献