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91.
G. Mukherjee 《Journal of Astrophysics and Astronomy》1983,4(4):295-300
The Bianchi type I cosmological models have been extensively studied in the past especially as examples of the homogeneous shearing universe. This paper presents a tilted universe solution admitting this group of motion where the velocity field is shear-free but there is an energy flux term. 相似文献
92.
Here we report the spectral characteristics of the high and low states of the pulsar 4U 0114 + 65 and examine the change in
the parameters of the spectral model. A power law and a photoelectric absorption by material along the line of sight together
with a high energy cut-off suffice to describe the continuum spectrum in both the states. A fluorescence iron line at ∼6.4
keV is present in the high as well as in the low state, though it is less intense in the latter. The photon index, cut-off
energy and e-folding energy values hardly show any discernible change over the states. We compare these spectral characteristics
as observed with ASCA with those of other satellites. We also compare the spectral characteristics of 4U 0114 + 650 with other
X-ray sources which show intensity variation at different time scales. 相似文献
93.
U. Mukherjee H. Raichur B. Paul S. Naik N. Bhatt 《Journal of Astrophysics and Astronomy》2006,27(4):411-423
We report here results from detailed timing and spectral studies of the high mass X-ray binary pulsar 4U 1538-52 over several
binary periods using observations made with the Rossi X-ray Timing Explorer (RXTE) and BeppoSAX satellites. Pulse timing analysis
with the 2003 RXTE data over two binary orbits confirms an eccentric orbit of the system. Combining the orbitial parameters
determined from this observation with the earlier measurements we did not find any evidence of orbital decay in this X-ray
binary. We have carried out orbital phase resolved spectroscopy to measure changes in the spectral parameters with orbital
phase, particularly the absorption column density and the iron line flux. The RXTE-PCA spectra in the 3–20 keV energy range
were fitted ∼6.4 keV, whereas the BeppoSAX spectra needed only a power law and Gaussian emission line at ∼6.4 keV in the restricted
energy range of 0.3–10.0 keV. An absorption along the line of sight was included for both the RXTE and BeppoSAX data. The
variation of the free spectral parameters over the binary orbit was investigated and we found that the variation of the column
density of absorbing material in the line of sight with orbital phase is in reasonable agreement with a simple model of a
spherically symmetric stellar wind from the companion star. 相似文献
94.
The problem of electromagnetic radiation from electric and magnetic line sources interacting with a moving uniaxially anisotropic dielectric or plasma half-space is treated. The anisotropy of the plasma is due to an infinitely strong magnetizing field impressedparallel to the motion of plasma. The line source is oriented normal to the direction of medium motion. TheE and theH modes are excited independently in the medium by the magnetic and the electric line sources, respectively. Invoking the saddle-point method of integration, the far-zone radiation field and the radiation pattern are obtained for both line sources. It is found that the radiation from an electric line source is not affected by the anisotropy of the moving medium and that a magnetic line source invacuum has finite components of radiation in directions which are parallel and antiparallel to the direction of motion, for the case of a uniaxial plasma in contrast to the results for a uniaxial dielectric. Numerical results for the far-zone radiation pattern, referring to a magnetic line source, are presented for several values of parameters characterizing the non-dimensional velocity, the anisotropy of the medium, the electron-plasma density and the location of the line source. 相似文献
95.
Priyadarshini Singh Harshita Asthana Vikas Rena Pardeep Kumar Jyoti Kushawaha Saumitra Mukherjee 《Environmental Earth Sciences》2018,77(12):475
Rock–water interaction along with mineral dissolution/ precipitation plays a profound role in the control of fluoride ion concentration within the alluvial groundwater in a part of semi-arid northern India. In the premonsoon season, the alluvial region experiences evaporative processes leading to increase in Na+ ions which through reverse ion exchange processes are adsorbed onto suitable sites within the aquifer matrix in exchange for Ca2+ ion in solution. Increase in Ca2+ ions in solution inhibits fluorite mineral dissolution, thereby controlling premonsoon fluoride ion concentration within alluvial groundwaters (1.40?±?0.5 mg/l). In the postmonsoon season, however, higher average fluoride ion concentration within the alluvial aquifer samples (2.33?±?0.80 mg/l) is observed mainly due to increase in silicate weathering of fluoride-bearing rocks and direct ion exchange processes enabling Ca2+ ion uptake from solution accompanied with the release of fluoride ions. Combined effect of these processes results in average fluoride ion concentration falling above the WHO drinking water permissible limit (1.5 mg/l). Alternatively, the hard rock aquifer samples within the study area have an average fluoride ion concentration falling below the permissible limit in both the seasons. 相似文献
96.
International Journal of Earth Sciences - This short article at first deduces center of gravity (C.G.) for horizontal single-layered and multi-layered rock bodies. Spatial variation of density is... 相似文献
97.
A. K. Jain Puneet Seth Mrinal Shreshtha P. K. Mukherjee Keser Singh 《Journal of the Geological Society of India》2013,82(4):313-318
In the uppermost parts of the Higher Himalayan Crystallines (HHC) of the Great Himalaya, widespread in situ partial melting of sillimanite+K-feldspar gneiss resulted in the formation of migmatite and resultant melt accumulation near the South Tibetan Detachment System (STDS) during various deformation events along the Dhauli Ganga valley in Garhwal. The oldest migmatite phase, designated as the Me1, parallels the main foliation Sm as the stromatite layers and concordant leucogranite bands. Younger melt phases Me2, Me3 and Me5 are recorded along small-scale ductile thrusts, extensional fabric and structureless patches, respectively. It is only the Me4 melting phase that is evidenced by large-scale melt migration along cross-cutting irregular veins. These were possible conduits for migration and accumulation of melt into larger leucogranite bodies like the Malari granite (19.0± 0.5 Ma). 相似文献
98.
Soumyajit Mukherjee 《International Journal of Earth Sciences》2013,102(7):1851-1870
The Higher Himalayan Crystalline (HHC) in the Bhagirathi river section (India) on fieldwork reveals two extensional ductile top-to-N/NE shear sub-zones—the ‘South Tibetan Detachment System’ and the ‘Basal Detachment’—besides a preceding top-to-S/SW ductile shear. A top-to-N/NE brittle shear was identified as backthrusts from the HHC (except its northern portion) that occur repeatedly adjacent to numerous top-to-S/SW brittle shears as fore-thrusts. The northern portion of the HHC—the Gangotri Granite—exhibits infrequent total six extensional and compressional brittle shear senses. The backthrusts could be due to a low friction between the lower boundary of the HHC (i.e. the Main Central Thrust-Zone) and the partially molten hot rock materials of the HHC. Subduction of the Eurasian plate towards S/SW below the Indian plate more extensively in the Garhwal sector could be the second possible reason. Presence of two ductile extensional shear sub-zones may indicate channel flow (or several exhumation mechanisms) of the HHC in a shifting mode (similar to Mukherjee et al. in Int J Earth Sci 101:253–272, 2012). The top-to-S/SW extensional brittle shear exclusively within the upper (northern portion) of the HHC and a top-to-S/SW brittle shear within the remainder of it is a possible indicator of critical taper deformation mechanism. Thus, this work provides the field evidences of possibly both channel flow and critical taper conditions from a Higher Himalayan section, besides that by Larson et al. (Geol Soc Am Bull 122:1116–1134, 2010). 相似文献
99.
100.
Sudeshna Mukherjee Atreyee Chaudhuri Niloy Kundu Sruti Mitra Sumit Homechaudhuri 《Estuaries and Coasts》2013,36(1):192-202
Fish distribution in relation to environmental variables was investigated in the Matla River of Sundarban estuarine system. A total of 64 brackish water species belonging to 38 families showing tropical and subtropical affinities were obtained upon monthly sampling of 1 year. The most abundant species were Harpadon nehereus, Gudusia chapra, Coilia neglecta, Coilia ramcarati and Liza parsia. Fish assemblages showed significant seasonal variation as was revealed from MANOVA. MDS ordination plot based on similarity in the fish assemblages revealed that premonsoonal season was distinguishable from the monsoonal and postmonsoonal seasons. Notable differences were also evident between monsoon and postmonsoon. Canonical correspondence analysis indicated that salinity, acidity, inorganic phosphate concentration and dissolved oxygen were the most important environmental variables in determining the observed variation in fish assemblages. Seasonal succession of fish populations may be related to differences in life cycle and adaptation to prevalent ecological conditions. The study therefore suggests that environmental variations in terms of changing salinity and dissolved oxygen have significant influence in structuring estuarine piscine community in this region. 相似文献