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281.
Xianzhe Duan Hongfu Zhang M. Santosh Hengci Tian He Sun Kaixuan Tan 《International Geology Review》2020,62(4):479-502
ABSTRACTThe lithospheric mantle beneath the South China Block (SCB) underwent a dramatic transformation from depleted to enriched during late Mesozoic. With a view to deeply understand this process, here we investigate the Mesozoic basalts and their melt inclusions from the Daoxian and Ningyuan regions within the central SCB. The geochemical features of the melt inclusions in these basalts suggest that these rocks originated from the lithospheric mantle enriched through interaction with K-rich aqueous fluids released from subducted Palaeo-Pacific oceanic sediments, whereas the Ningyuan basalts were mainly derived from the asthenospheric mantle source. Geochemical modelling indicates that the Daoxian basalts were generated from 15%-25% of partial melting of garnet lherzolite, whereas the Ningyuan basalts originated from 10%-20% of partial melting of garnet pyroxenites. Our data, combined with those from other Jurassic basalts suggest a temporal evolution of the SCB mantle sources during the Late Mesozoic. Diverse crust–mantle interactions through mixing of the asthenospheric melts with variable proportions of subducted Palaeo-Pacific oceanic sediments might account for the spatial heterogeneity of mantle sources observed beneath the SCB. The transition from Tethyan tectonic realm to the Palaeo-Pacific tectonic regime might have played a significant role in the transformation of the lithospheric mantle beneath the SCB. 相似文献
282.
Studies on the soil properties of the apparently flat-lying, but salt-affected Banni mudflat region of arid Kachchh in western India revealed the influence of subtle topographic variations on soil texture and nature and distribution of salts. Six master pedons were investigated to an average depth of 150 cm. The pedons on the upper surfaces showed an abundance of fine sand and a gradual impoverishment of silt and clay, as also lesser amounts of salts in the profiles. Pedons on the successively lower surfaces showed more silt and clay contents, as well as higher amounts of salts. The findings helped to identify the areas suitable for pasture development in this vast degraded rangeland, and to suggest some management practices for improvement. 相似文献
283.
Fuzzy-based method for landslide hazard assessment in active seismic zone of Himalaya 总被引:1,自引:2,他引:1
Landslides in Himalaya cause widespread damage in terms of property and human lives. It the present study, an attempt is made
to derive information on causative parameters and preparation of landslide-susceptible map using fuzzy data integration in
one of the seismically active region of Garhwal Himalaya that was recently devastated by a huge landslide. High-resolution
remotely sensed data products acquired from Indian Remote Sensing Satellite before and after the landslide event were processed
to improve interpretability and derivation of causative parameters. Spatial data sets such as lithology, rock weathering,
geomorphology, lineaments, drainage, land use, anthropogenic factor, soil type and depth, slope gradient, and slope aspect
were integrated using fuzzy gamma operator. The final map was reclassified in to five classes such as highly to lowly susceptible
classes based on cumulative cutoff. The result shows around 72% of known landslide areas including the large Uttarkashi landslide
in the high and very high susceptibility classes comprising of only 37% of the total area. The precipitation data from ground-
and satellite-based observations were compared; the precipitation threshold and the role of seismic activity were analyzed
for initiation of landslide. 相似文献
284.
We report new occurrences of sapphirine- and corundum-bearing granulites intercalated within orthogneisses at Lachmanapatti and Malappatty in the northern part of Madurai Block. Sapphirine in these localities occurs either as needle-like intergrowth with cordierite and corundum in symplectites and medium- to fine-grained euhderal to subhedral crystals associated with cordierite and corundum (Lachmanapatti) or in association with plagioclase, corundum and gedrite (Malappatty). The sapphirine from Lachmanapatti is highly magnesian (XMg = 0.87-0.94) with higher Cr content (up to 0.9 pfu) as compared with those in other localities in the Madurai Block. The sapphirine-corundum association reported in this study has important bearing on the ultrahigh-temperature metamorphism and exhumation history of the northern Madurai Block as well as on the tectonic evolution of the continental deep crust in southern India. 相似文献
285.
Fonarev V. I. Santosh M. Vasiukova O. V. Filimonov M. B. 《Contributions to Mineralogy and Petrology》2003,145(3):339-354
Contributions to Mineralogy and Petrology - In charnockites and host garnet-biotite gneisses of the Trivandrum Granulite Block (TGB), southern India, fluid inclusions are mainly represented by... 相似文献
286.
Jessica M. Bartlett Jon S. Dougherty-Page Nigel B. W. Harris Chris J. Hawkesworth M. Santosh 《Contributions to Mineralogy and Petrology》1998,131(2-3):181-195
The technique of single zircon dating from the thermal evaporation of 207Pb/206Pb (Kober 1986, 1987) provides a means of dating successive periods of growth and nucleation of zircons in polymetamorphic
assemblages. In contrast Nd model ages may provide a measure of the period of crustal residency for the sample or its protolith.
These two techniques have been combined to elucidate the tectonic history of the Proterozoic mobile belt of southern India,
exposed south of the Palghat-Cauvery Shear Zone that marks the southern boundary of the Archaean craton of Karnataka. The
two main tectonic units of this mobile belt comprise the Madurai and Trivandrum Blocks, both of which are characterised by
massive charnockite uplands and low-lying polymetamorphic metasedimentary belts that have undergone a complex tectonic history
throughout the Proterozoic. Evidence for early Palaeoproterozoic magmatism is restricted to the Madurai Block where single
zircon evaporation ages from a metagranite (2436 ± 4 Ma) are similar to model Nd ages from a range of lithologies suggesting
crustal growth at that time. The Trivandrum Block, to the south of the Achankovil shear zone, is comprised of the Kerala Khondalite
Belt, the Nagercoil charnockites and the Achankovil metasediments. Single zircon evaporation ages, together with conventional
zircon and garnet chronometry, suggest that all three units underwent upper-amphibolite facies metamorphism at ∼1800 Ma, an
event unrecorded in the metagranite from the Madurai Block. This implies that the Madurai and Trivandrum blocks represent
distinct terrains throughout the Palaeoproterozoic. Model Nd ages from the Achankovil metasediments are much younger (1500–1200
Ma) than those from the adjacent Kerala Khondalite Belt and Madurai Blocks (3000–2100 Ma), but there is no evidence for zircon
growth in these metasediments during the Mesoproterozoic. Hence the comparatively young model Nd ages of the metasediments
are indicative of a mixed provenance rather than a discrete period of crustal growth. Zircon overgrowths from the Madurai
Block (547 ± 17 Ma) and Achankovil metasediments (530 ± 21 Ma) suggest that all tectonic units of the Proterozoic mobile belt
of South India shared the same metamorphic history from the early Palaeozoic. This event has been recognised in the basement
lithologies of Sri Lanka and East Antarctica, confirming that the constituent terrains of East Gondwana had assembled by this
time.
Received: 10 October 1995 / Accepted: 27 October 1997 相似文献
287.
288.
D.?Bala SubrahamanyamEmail author T.?J.?Anurose Mannil?Mohan M.?Santosh N.?V.?P.?Kiran Kumar S.?Sijikumar 《Pure and Applied Geophysics》2012,169(4):741-753
On 15 January 2010, Thumba (8.5°N, 76.9°E) witnessed one of the longest known noontime annular solar eclipses (ASEs) spanning
a period of about 7 min, centered at 1314 hours local time. In this research article, we present a case study on the behaviour
of the atmospheric boundary layer characteristics and its vertical structure in response to this rare celestial event by making
use of a suite of different in-situ instruments. During the peak period of the ASE, the incoming solar irradiance was dimmed
by about 87% of its normal values, resulting in a significant reduction in the magnitudes of turbulent kinetic energy and
surface-layer turbulent fluxes of heat and momentum. The intensity and vertical thickness of the sea/land breeze circulation
cell over the study domain also weakened. However, the mixed layer heights determined from balloon-borne GPS Radiosonde did
not show any appreciable changes. Analysis of vertical profiles of thermodynamic parameters in association with the wind direction
during ASE indicated the formation of a double mixed layer between 700 and 1500 m and is attributed to horizontal advection
of a different airmass at those altitudes. 相似文献
289.
290.