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751.
Jean Delteil Jean-Yves Collot Ray Wood Richard Herzer Stéphane Calmant David Christoffel Mike Coffin Jacky Ferrière Geoffroy Lamarche Jean-Frédéric Lebrun Alain Mauffret Bernard Pontoise Michel Popoff Etienne Ruellan Marc Sosson Ruppert Sutherland 《Marine Geophysical Researches》1996,18(2-4):383-399
The Geodynz-sud cruise on board the R/V l'Atalante collected bathymetric, side-scan sonar and seismic reflection data along the obliquely convergent boundary between the Australian and Pacific plates southwest of the South Island, New Zealand. The survey area extended from 44°05 S to 49°40 S, covering the transition zone between the offshore extension of the Alpine Fault and the Puysegur Trench and Puysegur Ridge. Based on variations in the nature and structure of the crust on either side of the margin, the plate boundary zone can be divided into three domains with distinctive structural and sedimentary characteristics. The northern domain involves subduction of probably thinned continental crust of the southern Challenger Plateau beneath the continental crust of Fiordland. It is characterized by thick sediments on the downgoing slab and a steep continental slope disrupted by fault scarps and canyons. The middle domain marks the transition between subduction of likely continental and oceanic crust defined by a series of en echelon ridges on the downgoing slab. This domain is characterized by a large collapse terrace on the continental slope which appears to be due to the collision of the en echelon ridges with the plate margin. The southern domain involves subduction of oceanic crust beneath continental and oceanic crust. This domain is characterized by exposed fabric of seafloor spreading on the downgoing slab, a steep inner trench wall and linear ridges and valleys on the Puysegur ridge crest. The data collected on this cruise provide insights into the nature and history of both plates, and factors influencing the distribution of strike-slip and compressive strain and the evolution of subduction processes along a highly oblique convergent margin. 相似文献
752.
The Kerguelen Province, consisting of two oceanic plateaus (Kerguelen, Broken Ridge) and three basins (Enderby, Labuan and
Diamantina), covers a large area of ocean floor in the southeast Indian Ocean. As very few magnetic anomalies have been identified
in this area and only a few basement ages from the Kerguelen Plateau are known, reconstruction models of the Kerguelen Province
are not well constrained. In an effort to gain more understanding about the evolution of this area, we have used satellite
gravity to identify additional fracture zones. As they are likely to be associated with high frequency and low amplitude gravity
anomalies, we have computed the vertical derivative map instead of the regular satellite gravity map. Using this approach,
we have identified a series of fracture zones in the Enderby Basin, which are aligned with the Mesozoic fracture zones in
the Perth Basin and converge to the Kerguelen Fracture Zone. In the conjugate Bay of Bengal, we traced an equivalent pattern
of fracture zones which, together, better constrain the early evolution of this part of the Indian Ocean. Synthesis of these
images and the other available data from the Kerguelen Province, suggests that the spreading of India from both Australia
and Antarctica is closely related. Spreading between the three continents appears to have begun about the same time, in the
early Cretaceous and thus, the accretion of some parts of the Kerguelen Province must have occurred before the onset of the
quiet magnetic period at 118 Ma. At about 96–99 Ma, when the spreading direction in the Indian Ocean had changed into a N-S
direction, it also took place throughout the Kerguelen Province. We find that previously proposed slow spreading in the Diamantina
Zone and Labuan Basins, between 96–99 Ma and the initiation of the Southeast Indian Ridge at 43 Ma, could not have taken place.
Furthermore, we suggest that there is growing evidence that the same is true for spreading in the eastward continuation of
the Diamantina Zone and Labuan Basin, between Australia and Antarctica. Initiation of spreading in this area is likely to
be contemporaneous with the spreading in the Kerguelen Province and, thus, older than 96–99 Ma.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
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Morphological and chronological studies have been carried out on coralline algal buildups (“coralligène”) situated between 10 and 60 m depth near Marseilles, and in Corsica (France). Despite the presence of occasionally sizeable quantities of iron hydroxide, these constructions prove to be a reliable material for radiocarbon dating. Ages obtained using this method range from 640±120 yrs B.P. (Corsica, Scandola Natural Reserve, −15 m) to 7760±80 yrs B.P. (Marseilles, Grand Congloue, −52 m). Internal erosion surfaces within the buildups give evidence of discontinuous development. The accumulation rate of the coralligène constructions is very low (0.006–0.83 mm yr−1 according to the depth and time period). The higher values (0.53–0.83 mm yr−1) were recorded for the deeper constructions. They correspond to a period between 8000 and 6000 yrs B.P. After 6000 yrs B.P., the only appreciable accumulation rates (0.11–0.42 mm yr−1) were recorded for constructions situated between 10 and 35 m depth, whereas the accumulation rates of deep coralligène (> 50 m) appear to be low or zero. The age of the large constructions (overhang: 80 cm in width) is positively correlated with depth (r = 0.95; p < 0.005). Their development occurred during the Flandrian transgression. The oldest structures, today situated at 50 to 60 m depth, started to develop when water depth was probably no greater than 10 to 15 m. Apart from in strongly shaded fissures on rocky coasts and areas subjected to heavy sedimentation, the main framework building algal species was initially Mesophyllum lichenoides (Ellis) Lemoine, a high tolerant species to light, hydrodynamic energy and temperature. With the rise in sea level, the coralligène structure gradually became available to other less tolerant algal species (Lithophyllum, Lithothamnion), and the crustforming population diversified. Because of the good preservation of coralligène structures, the reliability of radiocarbon dating and the correlation between the age and bathymetric position of the large coralligène structures (except in areas of heavy sedimentation and fissures in shallow rocky coasts), these buildups are considered to be of use as biological indicators of variations in sea level. 相似文献
756.
Scott T. Larned Jonathan Moores Jenni Gadd Brenda Baillie Marc Schallenberg 《新西兰海洋与淡水研究杂志》2020,54(3):551-591
ABSTRACT To meet the challenges of preventing and reversing adverse effects of land use on ecosystems, management actions need to be founded on strong evidence. We used the pressure-state-impact (PSI) framework to assess evidence of land-use effects on New Zealand freshwater ecosystems. The evidence consisted of published quantitative and categorical associations linking land-use pressures to state changes and ecological impacts in rivers, lakes and aquifers. There was substantial evidence of land-use effects, particularly where land use/land cover (LULC) classes were used as pressure variables. Proportions of catchment area in urban and pastoral LULC were consistently, positively correlated with contaminant levels in water bodies and negatively correlated with ecological-health indicators. Other consistent PSI associations included positive correlations between cattle stocking rates and river contaminant levels, increased fine sediment and decreased ecological-health scores in rivers following forest harvest, and increased river contaminant levels at sites with stock access. Despite these consistent associations, the evidence base has four general shortcomings that should be addressed: (1) inadequate integration of data and models that link land use and contaminant loss to state changes and impacts in freshwater ecosystems; (2) weak inferences based on LULC; (3) reliance on categorical PSI associations; (4) gaps in reported PSI associations. 相似文献
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Jitsangiam Peerapong Pra-ai Suriyavut Boulon Marc Jenck Orianne Chen Xiaobin Techavorasinsakul Supot 《Acta Geotechnica》2022,17(5):1829-1845
Acta Geotechnica - This paper aims to investigate the effects of cyclic shear amplitudes and loading sequences on a soil–structure interface using direct shear tests under a large number of... 相似文献
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