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排序方式: 共有164条查询结果,搜索用时 62 毫秒
51.
Roberto De Propris Matthew Colless Simon P. Driver Warrick Couch John A. Peacock Ivan K. Baldry Carlton M. Baugh Joss Bland-Hawthorn Terry Bridges Russell Cannon Shaun Cole Chris Collins Nicholas Cross Gavin B. Dalton George Efstathiou Richard S. Ellis Carlos S. Frenk Karl Glazebrook Edward Hawkins Carole Jackson Ofer Lahav Ian Lewis Stuart Lumsden Steve Maddox Darren S. Madgwick Peder Norberg Will Percival Bruce Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2003,342(3):725-737
52.
Steep schlieren and associated enclaves in the Vinalhaven granite,Maine: possible indicators for granite rheology 总被引:2,自引:1,他引:2
R. A. Wiebe M. Jellinek M. J. Markley D. P. Hawkins D. Snyder 《Contributions to Mineralogy and Petrology》2007,153(2):121-138
Schlieren that form above the solidus are potentially diagnostic of the rheology of crystallizing granitic magmas and could
provide insights into magma chamber structure. Here we focus on steep schlieren associated with comagmatic enclaves in the
Vinalhaven granite. Steep schlieren extend 1–3 m upward from the sides of enclaves and appear to have steep cylindrical shapes
in 3D. Analyses of schlieren widths and the sizes of associated enclaves suggest that granitic crystal mush in which they
occur had a plastic rheology probably characterized by a yield strength. The enclaves, now enclosed in coarse-grained granite,
must have existed at higher levels in a crystal-poor part of a magma chamber and settled downward until reaching material
with a yield strength exceeding the buoyancy of the enclaves. In addition to constraining the local rheology of the granite,
their relative positions may indicate vertical rheological variations and possibly the chamber floor. 相似文献
53.
John H. Trefry Robert P. Trocine Michelle L. McElvaine Robert D. Rember Lucas T. Hawkins 《Environmental Geology》2007,53(2):375-385
Concentrations of total Hg in sediments near six drilling sites in the Gulf of Mexico were elevated well above average background
values of 40–80 ng/g. The excess Hg was associated with barite from discharged drilling mud. In contrast with total Hg, concentrations
of methylmercury (MeHg) in these sediments did not vary significantly at nearfield (<100 m) versus farfield (>3 km) distances
from the drilling sites. Observed variability in concentrations of MeHg were related to local differences in redox state in
the top 10 cm of sediment. Low to non-detectable concentrations of MeHg were found in nearfield sediments that were anoxic,
highly reducing and contained abundant H2S. At most drilling sites, nearfield samples with high concentrations of total Hg (>200 ng/g) had similar or lower amounts
of MeHg than found at background (farfield) stations. Higher values of MeHg were found in a few nearfield sediments at one
site where concentrations of TOC were higher and where sediments were anoxic and moderately reducing. Overall, results from
this study support the conclusion that elevated concentrations of MeHg in sediments around drilling sites are not a common
phenomenon in the Gulf of Mexico. 相似文献
54.
The Vinalhaven intrusive complex provides field and petrographic evidence for multiple replenishments of mafic and silicic
magmas, mingling and limited mixing, and rejuvenation of granite. Quartz in granitic rocks preserves a record of those processes,
in the form of cathodoluminescence (CL) zoning, which is related to concentration of titanium, and to temperature of crystallization
using the new TitaniQ (Ti in quartz) geothermometer. Injection of mafic melts into partly crystalline Vinalhaven granite resulted
in partial quartz resorption followed by higher-temperature growth from H2O-undersaturated melt. This is shown by steep, rimward increases in CL intensity and Ti content across discordant boundaries
that truncate older growth zones. Quartz zoning in granite affected by mafic magmas displays large rimward jumps in Ti content,
whereas quartz in granitic feeders and in granite far from mafic rocks typically displays broad rims with decreasing Ti contents,
consistent with slow cooling without thermal disruptions due to mafic recharge. 相似文献
55.
Rare earth elements (REE) concentrations of Archean and Proterozoic chemical sediments are commonly used as proxies to study secular trends in the geochemistry of Precambrian seawater. In addition, similarities in the REE signatures of Archean chemical sediments and modern seawater have led researchers to argue that some Archean rocks originated as biochemical precipitates (i.e., microbial carbonates) in shallow marine (e.g., peritidal) environments. However, terrestrial waters, including river water and groundwater, also commonly exhibit REE fractionation patterns that resemble modern seawater. Here, we present the seawater-like REE data for groundwaters from central México as additional evidence that these patterns are not unique to the marine environment. The shale-normalized REE patterns of the groundwaters are compared to those of modern seawater (open ocean and nearshore), Holocene reefal microbial carbonates and corals, and Archean chemical sediments using statistical means (i.e., ANOVA and Wilcoxon analyses) in order to quantify the similarities and/or differences in the REE patterns. Shale-normalized (SN) Ce anomalies and measures of REE fractionation [i.e., (La/Yb)SN, (Pr/Yb)SN, (Nd/Yb)SN, and (Gd/Yb)SN] of the central México groundwater samples are statistically indistinguishable from those of modern seawater. Moreover, except for differences in the Ce anomalies, which are lacking in Archean chemical sediments, the REE patterns of the central México groundwaters are also statistically similar to REE patterns of Archean chemical sediments, especially those of the 3.45 Ga Strelley Pool Chert. Consequently, we suggest that without additional information, it may be premature to unequivocally conclude that Archean chemical sediments record REE signatures of an Archean ocean. 相似文献
56.
57.
The technique of instrumental neutron activation analysis (INAA) has been used to analyze chip samples of geological material for 12 elements. Discriminant analysis has been used to classify the unknown chip samples to the correct stratum in a sedimentary succession. 相似文献
58.
W. Saunders W. J. Sutherland S. J. Maddox O. Keeble S. J. Oliver M. Rowan-Robinson R. G. McMahon G. P. Efstathiou H. Tadros S. D. M. White C. S. Frenk A. Carramiñana M. R. S. Hawkins 《Monthly notices of the Royal Astronomical Society》2000,317(1):55-64
We present the catalogue, mask, redshift data and selection function for the PSC z survey of 15 411 IRAS galaxies across 84 per cent of the sky. Most of the IRAS data are taken from the Point Source Catalog, but this has been supplemented and corrected in various ways to improve the completeness and uniformity. We quantify the known imperfections in the catalogue, and we assess the overall uniformity, completeness and data quality. We find that overall the catalogue is complete and uniform to within a few per cent at high latitudes and 10 per cent at low latitudes. Ancillary information, access details, guidelines and caveats for using the catalogue are given. 相似文献
59.
Jin Ba Noel S. Keenlyside Wonsun Park Mojib Latif Ed Hawkins Hui Ding 《Climate Dynamics》2013,41(7-8):2133-2144
Atlantic Multidecadal Variability (AMV) is investigated in a millennial control simulation with the Kiel Climate Model (KCM), a coupled atmosphere–ocean–sea ice model. An oscillatory mode with approximately 60 years period and characteristics similar to observations is identified with the aid of three-dimensional temperature and salinity joint empirical orthogonal function analysis. The mode explains 30 % of variability on centennial and shorter timescales in the upper 2,000 m of the North Atlantic. It is associated with changes in the Atlantic Meridional Overturning Circulation (AMOC) of ±1–2 Sv and Atlantic Sea Surface Temperature (SST) of ±0.2 °C. AMV in KCM results from an out-of-phase interaction between horizontal and vertical ocean circulation, coupled through Irminger Sea convection. Wintertime convection in this region is mainly controlled by salinity anomalies transported by the Subpolar Gyre (SPG). Increased (decreased) dense water formation in this region leads to a stronger (weaker) AMOC after 15 years, and this in turn leads to a weaker (stronger) SPG after another 15 years. The key role of salinity variations in the subpolar North Atlantic for AMV is confirmed in a 1,000 year long simulation with salinity restored to model climatology: No low frequency variations in convection are simulated, and the 60 year mode of variability is absent. 相似文献
60.