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141.
Based on maps of the extragalactic radio sources Cyg A, Her A, Cen A, 3C 277.3 and others, arguments are given that the twin-jets
from the respective active galactic nucleus ram their channels repeatedly through thin, massive shells. The jets are thereby
temporarily choked and blow radio bubbles. Warm shell matter in the cocoon shows up radio-dark through electron-scattering. 相似文献
142.
Lakshmi H. Kantha 《Dynamics of Atmospheres and Oceans》1979,3(1):39-46
Turbulent fluctuations in active mixed layers can excite internal waves in stably stratified fluid regions adjoining them. Expressions are derived for the energy and momentum fluxes radiated away by internal waves from an oceanic mixed layer, in terms of the spectrum of the static pressure fluctuations imposed at the base of the mixed layer by the turbulent eddies. The role of these internal wave fluxes in questions such as the determination of the rate of deepening of the layer due to an applied surface stress and the origin of internal waves in the deep ocean is discussed. 相似文献
143.
A. K. Mitra L. Stefanova T. S. V. Vijaya Kumar T. N. Krishnamurti 《Pure and Applied Geophysics》2005,162(8-9):1431-1454
Seasonal climate prediction for the Indian summer monsoon season is critical for strategic planning of the region. The mean features of the Indian summer monsoon and its variability, produced by versions of the ‘Florida State University Coupled Ocean-Atmosphere General Circulation Model’ (FSUCGCM) hindcasts, are investigated for the period 1987 to 2002. The coupled system has full global ocean and atmospheric models with coupled assimilation. Four member models were created by choosing different combinations of parameterizations of the physical processes in the atmospheric model component. Lower level wind flow patterns and rainfall associated with the summer monsoon season are examined from this fully coupled model seasonal integrations. By comparing with observations, the mean monsoon condition simulated by this coupled model for the June, July and August periods is seen to be reasonably realistic. The overall spatial low-level wind flow patterns and the precipitation distributions over the Indian continent and adjoining oceanic regions are comparable with the respective analyses. The anomalous below normal large-scale precipitation and the associated anomalous low-level wind circulation pattern for the summer monsoon season of 2002 was predicted by the model three months in advance. For the Indian summer monsoon, the ensemble mean is able to reproduce the mean features better compared to individual member models. 相似文献
144.
In this study, the Florida State University Global Spectral Model (FSUGSM), in association with a high-resolution nested regional
spectral model (FSUNRSM), is used for short-range weather forecasts over the Indian domain. Three-day forecasts for each day
of August 1998 were performed using different versions of the FSUGSM and FSUNRSM and were compared with the observed fields
(analysis) obtained from the European Center for Medium Range Weather Forecasts (ECMWF). The impact of physical initialization
(a procedure that assimilates observed rain rates into the model atmosphere through a set of reverse algorithms) on rainfall
forecasts was examined in detail. A very high nowcasting skill for precipitation is obtained through the use of high-resolution
physical initialization applied at the regional model level. Higher skills in wind and precipitation forecasts over the Indian
summer monsoon region are achieved using this version of the regional model with physical initialization.
A relatively new concept, called the ‘multimodel/multianalysis superensemble’ is described in this paper and is applied for
the wind and precipitation forecasts over the Indian subcontinent. Large improvement in forecast skills of wind at 850 hPa
level over the Indian subcontinent is shown possible through the use of the multimodel superensemble. The multianalysis superensemble
approach that uses the latest satellite data from the Tropical Rainfall Measuring Mission (TRMM) and the Defense Meteorological
Satellite Program (DMSP) has shown significant improvement in the skills of precipitation forecasts over the Indian monsoon
region. 相似文献
145.
The Southern Granulite Terrain with exposed Archean lower crustal rocks is studied using various geophysical tools. The crustal structure derived from seismic reflection and refraction/wide-angle reflection studies is used to understand the tectonic evolution of the region. Deep seismic reflection section along the Kolattur–Palani segment shows an oppositely dipping reflection fabric near the Moyar–Bhavani shear zone, which is interpreted as a signature of collision between the Dharwar craton and another crustal block in the south. The thickened crust due to collision was delaminated during the orogenic collapse and modified the central part, covering the Cauvery Shear Zone system, located between the Moyar–Bhavani and Karur–Oddanchatram shear zones. The delaminated lower crust is altered by magmatic underplating as evidenced by the high velocity layer just above the Moho. The velocity model of the region indicates crustal thickening at the boundary of the Dharwar craton and Moyar–Bhavani shear zone and thinning further south. Back-scattered seismic wave field with negative moveout and the Moho-offset indicate the spatial location and strike-slip nature of the shear zones. Present study suggests that the late Archean collision and suturing of the Dharwar craton with the southern crustal block at the Moyar–Bhavani shear zone may be responsible for the evolution of late Archean granulites. Late Neoproterozoic rifting is observed along the paleo-fault zones. The seismic studies constrained by gravity, magnetic and magnetotelluric data suggest that the Moyar–Bhavani and Karur–Oddanchatram shear zones of the Cauvery Shear Zone system mark terrane boundaries/suture zones. 相似文献
146.
Gaurav J. Kokandakar Sachin S. Ghodke K. Rathna Laxman B. More B. Nagaraju Munjaji V. Bhosle K. Vijaya Kumar 《Journal of the Geological Society of India》2018,91(2):135-146
Three distinct alkaline magmas, represented by shonkinite, lamprophyre and alkali basalt dykes, characterize a significant magmatic expression of rift-related mantle-derived igneous activity in the Mesoproterozoic Prakasam Alkaline Province, SE India. In the present study we have estimated emplacement velocities (ascent rates) for these three varied alkaline magmas and compared with other silicate magmas to explore composition control on the ascent rates. The alkaline dykes have variable widths and lengths with none of the dykes wider than 1 m. The shonkinites are fine- to medium-grained rocks with clinopyroxene, phologopite, amphibole, K-feldspar perthite and nepheline as essential minerals. They exhibit equigranular hypidiomorphic to foliated textures. Lamprophyres and alkali basalts characteristically show porphyritic textures. Olivine, clinopyroxene, amphibole and biotite are distinct phenocrysts in lamprophyres whereas olivine, clinopyroxene and plagioclase form the phenocrystic mineralogy in the alkali basalts. The calculated densities [2.54–2.71 g/cc for shonkinite; 2.61–2.78 g/cc for lamprophyre; 2.66–2.74 g/cc for alkali basalt] and viscosities [3.11–3.39 Pa s for shonkinite; 3.01–3.28 Pa s for lamprophyre; 2.72–3.09 Pa s for alkali basalt] are utilized to compute velocities (ascent rates) of the three alkaline magmas. Since the lamprophyres and alkali basalts are crystal-laden, we have also calculated effective viscosities to infer crystal control on the velocities. Twenty percent of crystals in the magma increase the viscosity by 2.7 times consequently decrease ascent rate by 2.7 times compared to the crystal-free magmas. The computed ascent rates range from 0.11–2.13 m/sec, 0.23–2.77 m/sec and 1.16–2.89 m/sec for shonkinite, lamprophyre and alkali basalt magmas respectively. Ascent rates increase with the width of the dykes and density difference, and decrease with magma viscosity and proportion of crystals. If a constant width of 1 m is assumed in the magma-filled dyke propagation model, then the sequence of emplacement velocities in the decreasing order is alkaline magmas (4.68–15.31 m/sec) > ultramafic-mafic magmas (3.81–4.30 m/sec) > intermediate-felsic magmas (1.76–2.56 m/sec). We propose that SiO2 content in the terrestrial magmas can be modeled as a semi-quantitative “geospeedometer” of the magma ascent rates. 相似文献
147.
Continental flood basalt provinces (CFBs) are important hosts for large-scale Cu-sulfide deposits. However, sulfide mineralization is yet to be discovered, if any, in the end-Cretaceous Deccan volcanic province, India. In the present study, geochemical evidences for the possible absence of Cu-sulfide deposits associated with the Deccan basalts by analyzing and comparing the geochemistries of the Deccan and Siberian CFBs are provided. The Fe-rich nature and high fO2 conditions did not favour sulfide saturation at any stage of magma evolution in the Deccan province. Crustal contamination of the Deccan magmas also did not increase the sulfur budget. The most contaminated basalts of Bushe and Poladpur formations of the Deccan province do not show any depletion in the copper contents compared to other formations. In the absence of sulfide saturation, copper behaved as an incompatible element in the Deccan magmas in contrast to the Siberian basalts, in which copper behaved as a compatible element during magma evolution due to sulfide saturation consequently formed world-class copper sulfide deposits. It is demonstrated that the lithosphere- and asthenosphere-derived Deccan magmas have similar Cu abundances thereby suggesting that the Cu-sulfide deposits associated with the CFBs are process-controlled rather than source-controlled. Although Cu-sulfide deposits may not have formed, the geochemical patterns suggest favourable conditions for native copper mineralization in the Deccan volcanic province. In the present study, a set of geochemical proxies that can be utilized as preliminary exploration tools for Cu-sulfide mineralization in the CFBs is proposed. 相似文献
148.
The very severe cyclonic storm Nargis of 2008 was a strong tropical cyclone that caused the deadliest natural disaster in the history of Myanmar. The time tested NCAR/PSU MM5 model has been used to simulate the Nargis cyclone, which is designed to have two domains covering the Bay of Bengal with horizontal resolutions of 90 and 30?km. The physics options chosen are Kain?CFritsch 2 for convection, Blackadar (BLA), Burk?CThompson, medium range forecast (MRF), Eta Mellor?CYamada (Eta MY) and Gayno?CSeaman (GS) for Planetary Boundary Layer (PBL) and Simple Ice for explicit cloud physics processes. The experiment was conducted with the model integration starting from April 27, 2008, to May 3, 2008. The performance of the five PBL schemes is evaluated in terms of radius height cross-section of the three component winds, surface heat fluxes of sensible heat and latent heat, equivalent potential temperature (?? e ), precipitation, track and variation of Central Surface Pressure and wind speed with time. The numerical results show a large impact of the PBL schemes on the intensity and movement of the system. The intensity of the storm is examined in terms of pressure drop, strength of the surface wind and rainfall associated with the storm. The results are compared to the India Meteorological Department observations. These experiments indicate that the intensity of the storm is well simulated with the Eta MY and BLA with finer resolution. The simulated track with MRF compared well with the Joint Typhoon Warning Center observation at landfall position both with the 90 and 30?km resolutions. 相似文献
149.
This study has investigated the possible relation between the Indian summer monsoon and the Pacific Decadal Oscillation (PDO) observed in the sea surface temperature (SST) of the North Pacific Ocean. Using long records of observations and coupled model (NCAR CCSM4) simulation, this study has found that the warm (cold) phase of the PDO is associated with deficit (excess) rainfall over India. The PDO extends its influence to the tropical Pacific and modifies the relation between the monsoon rainfall and El Niño-Southern Oscillation (ENSO). During the warm PDO period, the impact of El Niño (La Niña) on the monsoon rainfall is enhanced (reduced). A hypothesis put forward for the mechanism by which PDO affects the monsoon starts with the seasonal footprinting of SST from the North Pacific to the subtropical Pacific. This condition affects the trade winds, and either strengthens or weakens the Walker circulation over the Pacific and Indian Oceans depending on the phase of the PDO. The associated Hadley circulation in the monsoon region determines the impact of PDO on the monsoon rainfall. We suggest that knowing the phase of PDO may lead to better long-term prediction of the seasonal monsoon rainfall and the impact of ENSO on monsoon. 相似文献
150.
Unnikrishnan C. K. Rajeevan M. Vijaya Bhaskara Rao S. 《Theoretical and Applied Climatology》2017,129(3-4):949-963
The spatial and temporal trends of 11 (7) temperature (precipitation) extreme indices are examined for the Loess Plateau Region (LPR) and its southeast and northwest sub-regions based on daily observations at 214 meteorological stations. Results show widespread significant warming trends for all the temperature extremes except for the diurnal temperature range (DTR) and the lowest daily maximum temperature in each year (TXn) during 1961–2010. When regionally averaged, a significant warming trend is detected for all the indices except for DTR and TXn in the past 50 years. Compared with the entire LPR, a significant warming trend is detected for all the indices except for DTR and TXn over the southeast sub-region of LPR; while it is observed for all the indices over the northwest. The trends for these indices are generally stronger in the northwest than in the southeast in the past 50 years. In contrast, for precipitation indices, only a small percentage of areas show significant drying or wetting trends and, when regionally averaged, none of them displays significant trends during the past 50 years. On the sub-regional scale, however, a larger percentage of areas show significant drying trends for precipitation indices generally over the southeast relative to the entire LPR, and noticeably, the sub-regional average heavy precipitation (R10mm) and wet day precipitation (PRCPTOT) display significant decreasing trends during the past 50 years; whereas only a slightly larger percentage of areas show significant wetting trends for these indices over the northwest compared with the entire LPR, and when sub-regionally averaged, none of the indices have significant trends during the past 50 years. 相似文献