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221.
A Neoarchean dismembered ophiolite complex from southern India: Geochemical and geochronological constraints on its suprasubduction origin 总被引:1,自引:0,他引:1
T. Yellappa M. SantoshT.R.K. Chetty Sanghoon KwonChansoo Park P. NageshD.P. Mohanty V. Venkatasivappa 《Gondwana Research》2012,21(1):246-265
Ophiolites, the remnants of ancient oceanic lithosphere, have been described from collisional sutures of various ages with only few examples from Archean terranes. Here we report the discovery of a Neoarchean ophiolite suite from the southern margin of the Dharwar Craton in India, tectonically intercalated within a Neoproterozoic suture zone. The metamorphosed and variably dismembered ophiolite suite, exposed around Devanur, comprises altered ultramafic units, websterite, gabbros, mafic dykes, amphibolites, trondhjemites and pegmatites associated with ferruginous metachert. Structural and petrographic studies indicate that the rocks represent a highly sheared and metamorphosed suite emplaced as a thrust sheet. The major and trace element geochemistry of the mafic dykes indicate derivation from basaltic-andesitic magmas with tholeiitic to calc-alkaline characteristics. The rocks display negative Nb anomalies with enrichment of LILE (K, Rb, Ba, Th) and depletion in HFSE (Ti, Nb, Hf, Tb). The tectonic discrimination of these rocks based on various geochemical plots suggests that they were generated in a suprasubduction zone setting. We present new SHRIMP zircon U-Pb data for two trondhjemite samples from this complex, which yield 238U-206Pb ages of 2528 ± 61 and 2545 ± 56 Ma. The Neoarchean age from the trondhjemites obtained in our study is closely comparable to similar ages obtained in recent studies from magmatic zircons in charnockites and orthogneisses in the area. The suprasubduction zone assemblages and arc magmas suggest a Neoarchean ocean closure along the southern margin of the Dharwar Craton. 相似文献
222.
Markov chain model to study the occurrence of pre-monsoon thunderstorms over Bhubaneswar,India 总被引:1,自引:0,他引:1
Surajit Chattopadhyay Nachiketa Acharya Goutami Chattopadhyay Siripurapu Kiran Prasad Uma Charan Mohanty 《Comptes Rendus Geoscience》2012,344(10):473-482
The present work deals with pre-monsoon thunderstorms over Bhubaneswar belonging to the state of Orissa, India. A Markovian approach has been adopted to discern the probabilistic behavior of the time series of the occurrence and non-occurrence of this hazardous weather event by introducing a dichotomy within the time series. After a painstaking analysis through chi-square tests, we have identified serial independence in a few years and first-order two-state Markovian dependence in a few years (2000, 2001, 2004 and 2006). Finally, for the years of first-order two-state Markovian dependence, it has been observed that the probability of occurrence or non-occurrence of thunderstorm gets higher if the state of the previous day is similar to that of the current day. Furthermore, the probability of getting non-thunderstorm day followed by non-thunderstorm day is higher than the probability of getting thunderstorm day followed by thunderstorm day. It has been also observed that the unconditional climatological probability of the occurrence of severe pre-monsoon thunderstorm implied by the Markov chain is closely in agreement with the observed relative frequencies. However, it could be revealed that Markov chain cannot, in general, be suggested as a predictive tool for pre-monsoon thunderstorms under study without investigating the serial dependence inherent in the time series. 相似文献
223.
Studies on the variations of heavy metals in the marine sediments off Kalpakkam,East Coast of India 总被引:1,自引:1,他引:0
K. K. Satpathy A. K. Mohanty M. V. R. Prasad Usha Natesan S. K. Sarkar 《Environmental Earth Sciences》2012,65(1):89-101
During the last two decades, the coastal environment of southeast India has experienced intense developments in industry,
urbanization and aquaculture. Moreover, the 2004 mega tsunami has devastated this coast, thus affecting the coastal sediment
characteristics. These two phenomena prompted a study to characterize the sediment, to understand the mechanisms influencing
the distribution of heavy metals and to create baseline data for future impact assessment. Results showed that the coastal
sediment was carpeted with a mosaic of sand and silty sand with a minor amount of clay. Heavy metal values showed maximum
variation for Fe and minimum for Cd. Their average values showed the following decreasing trend: Fe > Cu > Zn > Pb > Cr > Ni > Cd.
This study shows that the major source of metals at Kalpakkam coast are land-based anthropogenic ones, such as, discharge
from industrial waste, agricultural waste, urban, municipal and slum sewage into the Buckingham canal, which in turn discharges
into the sea through backwaters, particularly during northeast monsoon period. A clear signature of the role of backwater
discharge increasing the concentration of a few metals in the coastal sediments during monsoon period was observed. Assessments
of the degree of pollution, concentration factor (CF), geoaccumulation index (I
geo) and pollution load index (PLI) have been calculated. CF values and I
geo indicated that the coastal sediment is moderately polluted by Cu and Cd. Increase in Cu, Pb and Zn concentration during the
monsoon period (October–January) compared to the rest of the year was noticed. Factor analysis and correlation among the heavy
metals concluded that Cr, Ni, Cd and Fe are of crustal origin, whereas, Cu, Pb and Zn are from anthropogenic sources. Organic
carbon content in the sediment increased during monsoon period, pointing to the role of land runoff and backwater discharge
in enhancing its content. The study also elucidates the impact of the recent tsunami in depleting metal content in the coastal
sediment as compared to the pre-tsunami period. 相似文献
224.
Sandeep Gupta William K. Mohanty Rajesh Prakash Atindra Kumar Shukla 《Pure and Applied Geophysics》2013,170(4):607-616
To better understand the relationship between crustal heterogeneity and seismotectonics in the National Capital Region (NCR), Delhi, India, we carried out local P- and S-velocity tomography beneath the NCR. First arrival times of the first P- and S-wave from 275 crustal earthquakes recorded by the Seismic Telemetry Network in and around Delhi of the India Meteorological Department, India, are inverted to obtain crustal P-, S-velocity and V P /V S variations in the region. Our tomographic images of the upper crust reflect well the surface geological and tectonic features. The Delhi fold belt is identified as low V P, high V S and low V P/V S. The Sohna hot spring region is appearing as low V P, low V S and high V P /V S correlating with the possible presence of fluid-filled rocks. The crustal seismicity is distributed in both the high- and low-velocity zones, but most distinctly in the low V P /V S region. 相似文献
225.
Abstract Texture is an important spatial feature, useful for identfying objects of regions of interest in an image. There are a number of methods for identification of textural parameters e.g. edgeness, frequency domain analysis, gray tone cooccurrence approach etc. Geologic information in radar images of heavily vegetated areas is contained mostly in the depiction of topography in image texture. Single band SIR/ERS‐1 SAR data posses a problem to the analyst for classification of the various land use/geological classes and generally multidate SAR data are used due to paucity of more number of bands. However, the multidate SAR data classification is not an ideal technique. A new technique, namely, spatial frequency band pass classification technique which generates two or more bands in the Fourier domain using the single band SAR data and then classifies various features of interest using their textural properties has been described here. Result shows higher percentage of classification using Maximum‐Likelihood Classifier (MXL) with two split‐band data as compared to the unsupervised classification of all the bands. 相似文献
226.
In this paper, it is shown that five dimensional LRS Bianchi type-I string cosmological models do not survive for Geometric
and Takabayasi string whereas Barotropic string i.e. ρ=ρ(λ) survives and degenerates string with ρ+λ=0 in scalar tensor theory of gravitation proposed by Saez and Ballester (Phys. Lett. A 113:467, 1986). Further we studied some physical and geometrical properties of the model. 相似文献
227.
A spatially homogeneous anisotropic Bianchi type-I cosmological model in the Barber's second self-creation theory is constructed
when the gravitational field is generated by a mixture of micro and macro matter fields represented by meson field and perfect
fluid respectively. The physical and geometrical features of the micro and macro cosmological model are discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
228.
An anisotropic, homogeneous Bianchi type-I cosmological micro model is obtained in Barber's modified theory of general relativity.
Some properties of the model are discussed. Further, it is found that this theory leads to Einstein theory as the coupling
parameterλ → 0 in micro level (i.e., quantum level) in general.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
229.
Seismic hazard in mega city Kolkata, India 总被引:2,自引:1,他引:1
The damages caused by recent earthquakes in India have been a wake up call for people to take proper mitigation measures,
especially the major cities that lie in the high seismic hazard zones. Kolkata City, with thick sediment deposit (∼12 km),
one of the earliest cities of India, is an area of great concern as it lies over the Bengal Basin and lies at the boundary
of the seismic zones III and IV of the zonation map of India. Kolkata has been affected by the 1897 Shillong earthquake, the
1906 Calcutta earthquake, and the 1964 Calcutta earthquake. An analysis on the maximum magnitude and b-value for Kolkata City region is carried out after the preparation of earthquake catalog from various sources. Based on the
tectonic set-up and seismicity of the region, five seismic zones are delineated, which can pose a threat to Kolkata in the
event of an earthquake. They are broadly classified as Zone 1: Arakan-Yoma Zone (AYZ), Zone 2: Himalayan Zone (HZ), Zone 3:
Shillong Plateau Zone (SPZ), Zone 4: Bay of Bengal Zone (BBZ), and Zone 5: Shield Zone (SZ). The maximum magnitude (m
max) for Zones 1, 2, 3, 4, and 5 are 8.30 ± 0.51, 9.09 ± 0.58, 9.20 ± 0.51, 6.62 ± 0.43 and 6.61 ± 0.43, respectively. A probability
of 10% exceedance value in 50 years is used for each zone. The probabilities of occurrences of earthquakes of different magnitudes
for return periods of 50 and 100 years are computed for the five seismic zones. The Peak Ground Acceleration (PGA) obtained
for Kolkata City varies from 0.34 to 0.10 g. 相似文献
230.