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61.
M. O'Regan K. Moran C. D. P. Baxter J. Cartwright C. Vogt M. Kölling 《Basin Research》2010,22(2):215-235
The Integrated Ocean Drilling Program's Expedition 302, the Arctic Coring Expedition (ACEX), recovered the first Cenozoic sedimentary sequence from the central Arctic Ocean. ACEX provided ground truth for basin scale geophysical interpretations and for guiding future exploration targets in this largely unexplored ocean basin. Here, we present results from a series of consolidation tests used to characterize sediment compressibility and permeability and integrate these with high‐resolution measurements of bulk density, porosity and shear strength to investigate the stress history and the nature of prominent lithostratigraphic and seismostratigraphic boundaries in the ACEX record. Despite moderate sedimentation rates (10–30 m Myr?1) and high permeability values (10?15–10?18 m2), consolidation and shear strength measurements both suggest an overall state of underconsolidation or overpressure. One‐dimensional compaction modelling shows that to maintain such excess pore pressures, an in situ fluid source is required that exceeds the rate of fluid expulsion generated by mechanical compaction alone. Geochemical and sedimentological evidence is presented that identifies the Opal A–C/T transformation of biosiliceous rich sediments as a potential additional in situ fluid source. However, the combined rate of chemical and mechanical compaction remain too low to fully account for the observed pore pressure gradients, implying an additional diagenetic fluid source from within or below the recovered Cenozoic sediments from ACEX. Recognition of the Opal A–C/T reaction front in the ACEX record has broad reaching regional implications on slope stability and subsurface pressure evolution, and provides an important consideration for interpreting and correlating the spatially limited seismic data from the Arctic Ocean. 相似文献
62.
Roberto Oyarzun Paloma Cubas Pablo Higueras Javier Lillo Willians Llanos 《Environmental Geology》2009,58(4):761-777
The Rodalquilar mineral deposits (SE Spain) were formed in Miocene time in relation to caldera volcanic episodes and dome
emplacement phenomena. Two types of ore deposits are recognized: (1) the El Cinto epithermal, Au–As high sulphidation vein
and breccia type; and (2) peripheral low sulphidation epithermal Pb–Zn–Cu–(Au) veins. The first metallurgical plants for gold
extraction were set up in the 1920s and used amalgamation. Cyanide leaching began in the 1930s and the operations lasted until
the mid 1960s. The latter left a huge pile of ~900,000–1,250,000 m3 of abandoned As-rich tailings adjacent to the town of Rodalquilar. A frustrated initiative to reactivate the El Cinto mines
took place in the late 1980s and left a heap leaching pile of ~120,000 m3. Adverse mineralogical and structural conditions favoured metal and metalloid dispersion from the ore bodies into soils and
sediments, whereas mining and metallurgical operations considerably aggravated contamination. We present geochemical data
for soils, tailings and wild plant species. Compared to world and local baselines, both the tailings and soils of Rodalquilar
are highly enriched in As (mean concentrations of 950 and 180 μg g−1, respectively). Regarding plants, only the concentrations of As, Bi and Sb in Asparagus horridus, Launaea arborescens, Salsola genistoides, and Stipa tenacissima are above the local baselines. Bioaccumulation factors in these species are generally lower in the tailings, which may be
related to an exclusion strategy for metal tolerance. The statistical analysis of geochemical data from soils and plants allows
recognition of two well-differentiated clusters of elements (As–Bi–Sb–Se–Sn–Te and Cd–Cu–Hg–Pb–Zn), which ultimately reflect
the strong chemical influence of both El Cinto and peripheral deposits mineral assemblages. 相似文献
63.
64.
Deming Drake Jennings Donald E. McCabe George Moran Thomas Loewenstein Robert 《Solar physics》1998,182(2):283-291
We determined the limb profile of the extremely Zeeman-sensitive emission line of Mg i at 12.32 m (811.58 cm–1) during the May 1994 annular eclipse, using the 3.5-m ARC telescope at the Apache Point site on Sacramento Peak, New Mexico. Spectra were recorded at 0.1 cm–1 spectral resolution and 1 s time resolution using a cryogenic grating spectrometer. The time derivatives of the observed line energy and continuum intensity were used to infer high-resolution profiles of the solar limb. Data were obtained at second contact only, since clouds prevented observations at third contact. We find that the emission line energy peaks very close to the 12 m continuum limb. This agrees with our result from the 1991 total eclipse over Mauna Kea, and also with non-LTE radiative transfer theory for this line, which predicts an upper-photospheric origin. However, in 1991, line emission remained observable as high as 2000 km above the continuum limb, whereas the 1994 data show observable emission to only 500 km. This difference greatly exceeds any applicable errors, or sensitivity differences in either data set, and must be attributed to spatial and/or temporal inhomogeneities in the solar limb emission of this line. We discuss possible causes of these inhomogeneities, and implications for observations at far-IR and submillimeter wavelengths. 相似文献
65.
High resolution sediment physical properties, measured on gravity and piston cores collected during cruises to Lake Winnipeg, include bulk density, acoustic velocity, magnetic susceptibility, shear strength and colour reflectance. The high resolution data are used here to construct complete stratigraphic (composite) sections of Lake Winnipeg sediments from a series of individual, discontinuous cores for the North and South Basins. These composite sections are used to evaluate basin-wide glacial and post-glacial depositional histories and to compare the northern and southern basin histories. In addition, these sections provide a baseline depth reference for interpretation of the biostratigraphy, paleomagnetic record and rock magnetic stratigraphy. Some of the data (density and shear strength) are also be used to estimate sediment stress history for the two major lithostratigraphic units and their variations across the basin. 相似文献
66.
67.
High resolution seismic profiles from the Canadian Beaufort Sea continental slope characteristically show a surficial 50 m
thick conformably stratified unit overlying an irregular erosion surface. This stratified unit appears to be compressionally
folded and associated with minor faults. At the shelf break, there are numerous indicators of a tensional regime, such as
a large, slope-parallel graben and numerous mud diapirs. Although a large-scale slide-scar was mapped in one area, most of
the slope is interpreted to be deforming by a creep mechanism. Preliminary calculations can provide reasonable values for
the fold wave length and rate of deformation, supporting the suggestion that time dependent creep deformation has occurred
in this area. 相似文献
68.
Lee W. Cooper Ingvar L. Larsen Jacqueline M. Grebmeier S. Bradley Moran 《Deep Sea Research Part II: Topical Studies in Oceanography》2005,52(24-26):3452
During three icebreaker cruises in the Arctic Ocean under different sea-ice conditions in 2002, undisturbed benthic surface sediments were collected and assayed for the presence of a short-lived (t1/2=53 d), particle-reactive cosmogenic radionuclide, 7Be, that is solely derived from atmospheric deposition. Under largely ice-covered conditions in May–June 2002, we did not detect this radionuclide in benthic surface sediments, despite significant inventories present in ice-rafted snow on the overlying sea ice (mean=86.8 Bq m−2±32.0 SD; n=9). During the July–August 2002 Shelf–Basin Interactions (SBI) cruise aboard the USCGC Healy and during a simultaneous cruise of the CCGS Sir Wilfrid Laurier on the Bering and Chukchi Shelf, which occupied the same general region following retreat and dissolution of Arctic ice cover, the 7Be present in this snow as well as surface deposition on to the sea ice-free water surface was detected in many benthic surface sediments, including some as deep as 945 m in Barrow Canyon. Inventories of 7Be in sediments were as high (60 Bq m−2) as the entire decay-corrected inventory present earlier in some snow samples collected on the sea-ice cover. Other deposition indicators such as the inventories of sediment chlorophyll, sediment oxygen respiration rates and 234Th-derived export fluxes also showed post-ice melt particle deposition and vertical transport, but in most cases the 7Be deposition was not tightly correlated with these other indicators, suggesting that 7Be sedimentation may not be controlled by the same processes. Our observations indicate that materials in sea ice, including contaminants, particulate organic, and mineral matter originating from atmospheric deposition or entrained in continental shelf sediments and rafted onto sea ice, can be rapidly transported to depth. The re-distribution of these materials as sea-ice drifts and eventually melts has the potential for impacting Arctic Ocean biogeochemical cycles and contaminant concentrations in areas of the Arctic remote from the original point of deposition. 相似文献
69.
We investigate further the interpretation of dark magnetic faculae observed in previous imaging of the solar photosphere at 1.63 m. We show that their contrast at 1.63 m increases with magnetic flux beyond a threshold value of 2 × 1018 Mx and blends smoothly with the contrast vs flux relation measured at this wavelength for larger structures of sunspot size. Not all facular structures that are bright in Ca K are dark at 1.63 m, apparently because their magnetic flux is not large enough. After correction for blurring, the contrast of the dark faculae observed near the disc center at 1.63 m is approximately 4%. But our observations at 1.23 m, which probe slightly higher photospheric levels, do not show these dark faculae. These results indicate that magnetic flux tubes of diameter as small as 500 km significantly inhibit convective heat flow to the photosphere, much as do sunspot flux tubes of much larger diameter. They also suggest that, in even smaller flux tubes, the inhibition becomes rapidly less significant. Finally, we show that the sunspot-size dependence of umbral infrared contrast versus wavelength that we observe can probably be explained in terms of instrumental blurring. Observations with lower scattered light will be required to determine whether a real decrease of contrast with diameter also plays a role. 相似文献
70.