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151.
F. Rahaman S. Chakraborty S. Das R. Mukherjee M. Hossain N. Begam 《Astrophysics and Space Science》2003,288(4):379-387
We have presented in homogeneous cosmological models within the framework of Lyra geometry. We have considered an inhomogeneous
spherically symmetric higher dimensional model in presence of a mass less scalar field whose potential has a flat part. The
scalar field is considered to be inhomogeneous. Also an inhomogeneous cosmological model is derived in a Kaluza-Klein type
of space time. The matter field is taken as an inhomogeneous distribution of fluid. It is observed that there is no singularity
at finite past in our model and the desirable feature of dimensional reduction is also possible for the extra space.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
152.
Frequency of global axisymmetric oscillations of a perfect fluid disk rotating around a compact object is investigated by trial function method. A formula for the frequency of local radial oscillation is presented. 相似文献
153.
Ritabrata Biswas Nairwita Mazumder Subenoy Chakraborty 《Astrophysics and Space Science》2011,335(2):603-609
In this paper we deal with accretion of dark energy in the holographic dark energy model for a general non-rotating static
spherically symmetric black hole. The mass of the black hole increases or decreases depending on the nature of the holographic
dark energy (quintessence or phantom) as well as on some integration parameters. It is to be illustrated that the enhancement
or reduction of mass of a black hole is independent of the mass or size of the black hole itself. Rather it depends only upon
the radius of the event horizon of the universe. Finally, the generalized second law of thermodynamics has been studied on
the event horizon to be assured that the law holds even if when the black hole mass is decreasing though it is engrossing
some mass. 相似文献
154.
T. N. Krishnamurti Ruby Krishnamurti Anitha D. Sagadevan Arindam Chakraborty William K. Dewar Carol Anne Clayson James F. Tull 《Meteorology and Atmospheric Physics》2009,105(1-2):69-83
Using the United States Geological Survey global daily data sets for 31 years, we have tabulated the earthquake intensities on a global latitude longitude grid and represented them as a finite sum of spherical harmonics. An interesting aspect of this global view of earthquakes is that we see a low frequency modulation in the amplitudes of the spherical harmonic waves. There are periods when these waves carry larger amplitudes compared to other periods. A power spectral analysis of these amplitudes clearly shows the presence of a low frequency oscillation in time with a largest mode around 40 days. That period also coincides with a well-know period in the atmosphere and in the ocean called the Madden Julian Oscillation. This paper also illustrates the existence of a spatial oscillation in strong earthquake occurrences on the western rim of the Pacific plate. These are like pendulum oscillations in the earthquake frequencies that swing north or south along the western rim at these periods. The spatial amplitude of the oscillation is nearly 10,000 km and occurs on an intraseasonal time scale of 20–60 days. A 34-year long United States Geological Survey earthquake database was examined in this context; this roughly exhibited 69 swings of these oscillations. Spectral analysis supports the intraseasonal timescale, and also reveals higher frequencies on a 7–10 day time scale. These space-time characteristics of these pendulum-like earthquake oscillations are similar to those of the MJO. Fluctuations in the length of day on this time scale are also connected to the MJO. Inasmuch as the atmospheric component of the MJO will torque the solid earth through mountain stresses, we speculate the MJO and our proposed earthquake cycle may be connected. The closeness of these periods calls for future study. 相似文献
155.
Daily solar radio flux at six different frequencies in dm, cm and mm wavelength regions has been studied for 182 days from December 1, 1970 to May 30, 1971. It is found that the slowly varying component of the centimeter wave emission correlates well with the physical model of the coronal active regions derived by Sengupta (Sengupta, 1971b) from which, as he showed earlier, most of the solar soft X-rays of wavelength less than 20 Å comes. It is also found that the cm wave emission is consistent with the assumption that the emitting regions are optically thin in this wavelength range.Emissions in dm and mm wavelength ranges, however, show poor correlation with the physical model of the soft X-ray emitting regions.It is concluded that the preferred regions of cm wave emission are located in the same region of solar corona from where most of the soft X-rays comes, but are different from the preferred regions of mm and dm emission. 相似文献
156.
D. K. Chakraborty † Parijat Thakur 《Monthly notices of the Royal Astronomical Society》2000,318(4):1273-1276
The projected properties of a triaxial generalization of the modified Hubble mass model are investigated. The projected surface density can be evaluated analytically, allowing us to investigate its properties in analytic forms. The profiles of axis ratio and position angle of the major axis of constant density elliptical contours, as a function of viewing angles, can be compared with observations. 相似文献
157.
Copper and zinc uptake by rice and accumulation in soil amended with municipal solid waste compost 总被引:5,自引:0,他引:5
P. Bhattacharyya A. Chakraborty K. Chakrabarti S. Tripathy M.A. Powell 《Environmental Geology》2006,49(7):1064-1070
Effect of addition of municipal solid waste compost (MSWC) on two metals viz. copper (Cu) and zinc (Zn) contents of submerged
rice paddies were studied. Experiments were conducted during the three consecutive wet seasons from 1997 to 1999 on rice grown
under submergence, at the Experimental Farm of Calcutta University, India. A sequential extraction method was used to determine
the metal (Cu and Zn) fractions in MSWC and cow dung manure (CDM). Both metals were significantly bound to the organic matter
and Fe and Mn oxides in MSWC and CDM. Metal content in rice straw was higher than in rice grain. Metal bound with Fe and Mn
oxides in MSWC and CDM best correlated with straw and grain metal followed by exchangeable and water soluble fractions. Carbonate,
organic matter bound and residual fractions in MSWC and CDM did not significantly correlate with rice straw and grain metal.
The MSWC would be a valuable resource for agriculture if it can be used safely, but long-term field experiments with MSWC
are needed to assess by regular monitoring of the metal loads and accumulation in soil and plants. 相似文献
158.
The disastrous Mw 9.3(seismic moment 1.0×1030 dyn/cm) earthquake that struck northwest Sumatra on 26 December 2004 and triggered~30 m high tsunami has rejuvenated the quest for identifying the forcing behind subduction related earthquakes around the world.Studies reveal that the strongest part(elastic core) of the oceanic lithosphere lie between 20 and 60 km depth beneath the upper (~7 km thick) crustal layer,and compressive stress of GPa order is required to fail the rock-layers within the core zone.Here we present evidences in favor of an intraplate origin of mega-earthquakes right within the strong core part(at the interface of semi-brittle and brittle zone),and propose an alternate model exploring the flexing zone of the descending lithosphere as the nodal area for major stress accumulation. We believe that at high confining pressure and elevated temperature,unidirectional cyclic compressive stress loading in the flexing zone results in an increase of material yield strength through strain hardening, which transforms the rheology of the layer from semi-brittle to near-brittle state.The increased compressive stress field coupled with upward migration of the neutral surface(of zero stress fields) under noncoaxial deformation triggers shear crack.The growth of the shear crack is initially confined in the near-brittle domain,and propagates later through the more brittle crustal part of the descending oceanic lithosphere in the form of cataclastic failure. 相似文献
159.
Shah?Wali?FaryadEmail author Sumit?Chakraborty 《Contributions to Mineralogy and Petrology》2005,150(3):306-318
Rocks from the Micaschist–Marble Complex of the Wölz Tauern, which are part of the middle Austroalpine unit, contain large (up to 2 cm) garnet crystals that show clear evidence of multistage growth. Isotopic dating indicates that a Variscan (~270 Ma) garnet core was overgrown by new garnet formed during Eo-Alpine metamorphism at Cretaceous times. P-T paths for the Eo-Alpine metamorphism were obtained using the method of pseudosections (Powell and Holland in Metam Geol 16:309–343, 1998) and are consistent with earlier results from independent thermobarometry. Due to the large size of the garnets, growth zoning was preserved during amphibolite facies metamorphism at both Variscan and Alpine times. Full multicomponent diffusion modeling of compositional zoning at the interface of the Alpine and Pre-Alpine garnets in conjunction with the retrieved P-T paths allow average subduction/exhumation as well as heating/cooling rates to be retrieved. The modeling suggests that a minimum subduction/exhumation rate of ~4 cm/a and heating/cooling rates on the order of 100–260°C/Ma for a 60°C subduction angle are required to preserve the observed compositional zoning overall while modifying the zoning at the interface between two garnets to the extent observed. Such rapid rates of burial/exhumation are consistent with the results of direct GPS measurements of convergence rates at several orogenic belts as well as with inferred rates from modeling in the Alps and other areas. In combination, this indicates that such rapid rates are commonplace during metamorphism in collisional orogens and places important constraints on the rheological behavior of crustal blocks in such orogens. 相似文献
160.
Evidence of lacustrine sedimentation in the Upper Permian Bijori Formation, Satpura Gondwana basin: Palaeogeographic and tectonic implications 总被引:1,自引:0,他引:1
The Upper Permian Bijori Formation of the Satpura Gondwana basin comprising fineto coarse-grained sandstone, carbonaceous
shale/mudstone and thin coal bands was previously interpreted as the deposits of meandering rivers. The present study documents
abundance of wave ripples, hummocky and swaley cross-stratification and combined flow bedforms in the Bijori Formation, suggesting
that a significant part of the formation was deposited in a wave-agitated environment. Evidence of near-emergent depositional
conditions provided by repeated occurrence of rootlet beds and hydromorphic paleosols, local flooding surfaces denoting rapid
fluctuation of water level, occurrences of temnospondyl vertebrate fossils, and absence of tidal signatures and marine fossils
suggest a lacustrine rather than marine depositional regime. Five facies associations recognised within the Bijori Formation
are inferred to represent fluvial channels and associated floodplains (FA1), lake shorelines (FA2), subaqueous distributary
channels and associated levees (FA3), waveand storm-affected delta front (FA4), and open lacustrine/lower shoreface (FA5)
deposits. The planoconcave fluvial channel-fill sandbodies with unidirectional cross-beds are clearly distinguishable from
the delta front bars that show a convexo-plan or bi-convex sandbody geometry and dominance of wave and combined flow bedforms.
Some of the distributary channels record interaction of fluvial and wave-dominated basinal processes. Major distributary sandbodies
show a north to northwest flow direction while wave-affected delta front sandbodies show very complex flow patterns reflecting
interaction between fluvial discharge and wave processes. Wave ripple crest trends show that the lake shoreline had an overall
east-northeast to west-southwest orientation. The lack of documented contemporaneous lacustrine or marine sediments in the
Satpura Gondwana basin posed a major problem of basin-scale palaeogeographic reconstruction. The existence of Bijori lake
solves the problem and the lake is inferred to have acted as repository for the contemporaneous alluvial drainage. Development
of the large Bijori lake body implies generation of accommodation space exceeding the rate of sediment supplied and thus represents
locus of high tectonic subsidence. Transition of fluvial sediments with red mudstone and calcareous soil profile in the lower
part of the succession to carbonaceous shale and coal-bearing lacustrine sediments in the upper part, denote a change from
a warm semi-arid climate with seasonal rainfall to a more humid one. 相似文献