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151.
James R. Hein Ann E. Gibbs David A. Clague Michael Torresan 《Marine Georesources & Geotechnology》2013,31(2):177-203
This is the first article to describe mineralization of midplate submarine rift zones and hydrothermal manganese oxide mineralization of midplate volcanic edifices. Hydrothermal Mn oxides were recovered from submarine extensions of two Hawaiian rift zones, along Haleakala and Puna Ridges. These Mn oxides form two types of deposits, metallic stratiform layers in volcaniclastic rocks and cement for clastic rocks; both deposit types are composed of todorokite and bimessite. Thin Fe‐Mn crusts that coat some rocks formed by a combination of hydrogenetic and hydrothermal processes and are composed of δ‐MnO2. The stratiform layers have high Mn contents (mean 40%) and a large fractionation between Mn and Fe (Fe/Mn = 0.04). Unlike most other hydrothermal Mn oxide deposits, those from Hawaiian rift zones are enriched in the trace metals Zn, Co, Ba, Mo, Sr, V, and especially Ni (mean 0.16%). Metals are derived from three sources: mafic and ultramafic rocks leached by circulating hydrothermal fluids, clastic material (in Mn‐cemented sandstone), and seawater that mixed with the hydrothermal fluids. Mineralization on Haleakala Ridge occurred sometime during the past 200 to 400 ka, when the summit was at a water depth of more than 1,000 m. Hydrothermal circulation was probably driven by heat produced by intrusion of dikces, magma reservoirs, and flow of magma through axial and lateral conduits. The supply of seawater to ridge interiors must be extensive because of their high porosity and permeability. Precipitation of Mn oxide below the seafloor is indicated by its occurrence as cement, growth textures that show mineralizing fluids were introduced from below, and pervasive replacement of original matrix of clastic rocks. 相似文献
152.
In recent years, a substantial reduction of the sea ice in the Arctic has been observed. At the same time, the near-surface
air in this region is warming at a rate almost twice as large as the global average—this phenomenon is known as the Arctic
amplification. The role of the ice-albedo feedback for the Arctic amplification is still a matter of debate. Here the effect
of the surface-albedo feedback (SAF) was studied using a coupled climate model CCSM3 from the National Center for Atmospheric
Research. Experiments, where the SAF was suppressed by locking the surface albedo in the entire coupled model system, were
conducted. The results reveal polar temperature amplification when this model, with suppressed albedo, is forced by a doubling
of the atmospheric CO2 content. Comparisons with variable albedo experiments show that SAF amplifies the surface-temperature response in the Arctic
area by about 33%, whereas the corresponding value for the global-mean surface temperature is about 15%. Even though SAF is
an important process underlying excessive warming at high latitudes, the Arctic amplification is only 15% larger in the variable
than in the locked-albedo experiments. It is found that an increase of water vapour and total cloud cover lead to a greenhouse
effect, which is larger in the Arctic than at lower latitudes. This is expected to explain a part of the Arctic surface–air-temperature
amplification. 相似文献
153.
A. Koschinsky P. Halbach J. R. Hein A. Mangini 《International Journal of Earth Sciences》1996,85(3):567-576
Hydrogenetic ferromanganese crusts reflect the chemical conditions of the sewater from which they formed. Fine-scale geochemical
analysis of crust layers in combination with age determinations can therefore be used to investigate paleoceanographic changes
which are recorded in geochemical gradients in the crusts. At Tropic seamount (off northwest Africa), uniform crust growth
influenced by terrigenous input from the African continent occurred during approximately the past 12 Ma. Phosphatization of
these crusts is minor. In contrast, crusts from Lion seamount, located between Madeira and the Portuguese coast, display a
much more variable growth history. A pronounced increase in Ni, Cu, and Zn is observed in some intervals of the crusts, which
probably reflects increased surface productivity. A thick older phosphatized generation occurs in many samples. Hydrographic
profiles indicate that Mediterranean outflow water (MOW) may play an important role in the composition of these crusts.10Be dating of one sample confirms that the interruption of the MOW during the Messinian salinity crisis (6.2–5 Ma ago) resulted
in changes in element composition. Sr-isotope dating of the apatite phase of the old crust generation has been carried out
to obtain a minimum age for the older generation of Atlantic crusts and to determine whether crust phosphatization in the
Atlantic can be related to phosphatization episodes recorded in Pacific crusts. The preliminary data show that the old phosphatized
crust generation might be as old as approximately 30–40 Ma. 相似文献
154.
Pisces submersible dives within Baffin Island fjords have revealed the common occurrence of pits on the sea floor, at water depths
between 40 and 326 m. The size of these pits are in the decimeter to meter range. Through indirect evidence (by comparison
of morphologic features to pits or gouges of known origin) they are believed to be feeding traces of narwhal, beluga, or bowhead
whales. If so, they are the deepest mammalian feeding traces yet reported. Bioerosion by large foraging mammals may be a more
common sea floor process than previously thought. 相似文献
155.
156.
Influence of atmospheric inputs on the iron distribution in the subtropical North-East Atlantic Ocean 总被引:3,自引:0,他引:3
Graldine Sarthou Alex R. Baker Jurjen Kramer Patrick Laan Agathe Laës Simon Ussher Eric P. Achterberg Hein J.W. de Baar Klaas R. Timmermans Stphane Blain 《Marine Chemistry》2007,104(3-4):186-202
Aerosol (soluble and total) iron and water-column dissolved (DFe, < 0.2 μm) and total dissolvable (TDFe, unfiltered) iron concentrations were determined in the Canary Basin and along a transect towards the Strait of Gibraltar, in order to sample across the Saharan dust plume. Cumulative dust deposition fluxes estimated from direct aerosol sampling during our one-month cruise are representative of the estimated deposition fluxes based on near surface water dissolved aluminium concentrations measured on board. Iron inventories in near surface waters combined with flux estimates confirmed the relatively short residence time of DFe in waters influenced by the Saharan dust plume (6–14 months). Enhanced near surface water concentrations of DFe (5.90–6.99 nM) were observed at the Strait of Gibraltar mainly due to inputs from metal-rich rivers. In the Canary Basin and the transect towards Gibraltar, DFe concentrations (0.07–0.76 nM) were typical of concentrations observed in the surface North Atlantic Waters, with the highest concentrations associated with higher atmospheric inputs in the Canary Basin. Depth profiles showed that DFe and TDFe were influenced by atmospheric inputs in this area with an accumulation of aeolian Fe in the surface waters. The sub-surface minimum of both DFe and TDFe suggests that a simple partitioning between dissolved and particulate Fe is not obvious there and that export may occur for both phases. At depths of around 1000–1300 m, both regeneration and Meddies may explain the observed maximum. Our data suggest that, in deep waters, higher particle concentrations likely due to dust storms may increase the scavenging flux and thus decrease DFe concentrations in deep waters. 相似文献
157.
158.
Simulating search behaviour of fish towards bait 总被引:2,自引:0,他引:2
Vabo Rune; Huse Geir; Ferno Anders; Jorgensen Terje; Lokkeborg Svein; Skaret Georg 《ICES Journal of Marine Science》2004,61(7):1224-1232
159.
Monsoon-induced upwelling off the Vietnamese coast 总被引:1,自引:0,他引:1
Joachim W. Dippner Kim Vinh Nguyen Hartmut Hein Thomas Ohde Natalie Loick 《Ocean Dynamics》2007,57(1):46-62
During the southwest monsoon from July 8 to 28, 2003, an interdisciplinary cruise took place in the central area of Vietnamese upwelling with “MV Nghien Cuu Bien” in the South China Sea. Physical observations in the upwelling area are analyzed with respect to local/regional wind forcing and far field forcing. Nutrients and phytoplankton measurements are discussed with respect to exchange processes between different water masses. The wind-induced coastal upwelling by local wind forcing is much weaker than in the previous years due to weaker-than-normal winds. This can be attributed to the far field forcing of the 2002/2003 El Niño event which modulates the upwelling intensity. The atmospheric conditions reflect the typical situation after an El Niño event which weakens the wind-induced coastal upwelling, reduces the latent heat flux, and results in higher-than-normal sea-surface temperatures. The general circulation pattern during SW monsoon is driven by the spatial asymmetry in the monsoon forcing. The flow pattern is characterized by an upwelling-induced northward undercurrent and a recently detected southward countercurrent. The resulting stretching deformation of this flow pattern forms an offshore jet between ~12°N and 12.5°N and causes a local enhancement of the upwelling intensity. The upwelling due to stretching deformation is a peculiarity, which makes the Vietnamese upwelling area different to other upwelling areas. A budget of the upwelling components is presented: the strongest contribution in 2003 to the Vietnamese upwelling is the dynamical upwelling due to the clockwise rotation of the northward undercurrent. The internal radius of deformation separates the upwelling area from the offshore area as well as different water masses. Mekong River and the Gulf of Thailand waters which are offshore show nutrient depletion. Therefore, high chlorophyll maxima cannot be explained by nutrient supply from river runoff. The dynamical upwelling brings in nutrient-rich Maximum Salinity Water into the euphotic zone. This causes a subsurface chlorophyll maximum between 20 and 40 m water depth along the northward undercurrent. Deflection from the Redfield ratio in the C:N ratio and negative excess nitrogen identifies the region as nitrogen-limited which may favor cyanobacteria blooms. The consequence is a unique feature in new production: in the upwelling area, new production is based on upwelled nitrate, whereas offshore in the nutrient-depleted Mekong and Gulf of Thailand water, new production is based in addition on nitrogen fixation. 相似文献
160.
Rare earth elements in the Pacific and Atlantic Oceans 总被引:1,自引:0,他引:1