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121.
Anirban Mukhopadhyay Arun Mondal Sandip Mukherjee Dipam Khatua Subhajit Ghosh Debasish Mitra Tuhin Ghosh 《Journal of Earth System Science》2014,123(6):1349-1360
In the Himalayan states of India, with increasing population and activities, large areas of forested land are being converted into other land-use features. There is a definite cause and effect relationship between changing practice for development and changes in land use. So, an estimation of land use dynamics and a futuristic trend pattern is essential. A combination of geospatial and statistical techniques were applied to assess the present and future land use/land cover scenario of Gangtok, the subHimalayan capital of Sikkim. Multi-temporal satellite imageries of the Landsat series were used to map the changes in land use of Gangtok from 1990 to 2010. Only three major land use classes (built-up area and bare land, step cultivated area, and forest) were considered as the most dynamic land use practices of Gangtok. The conventional supervised classification, and spectral indices-based thresholding using NDVI (Normalized Difference Vegetation Index) and SAVI (Soil Adjusted Vegetation Index) were applied along with the accuracy assessments. Markov modelling was applied for prediction of land use/land cover change and was validated. SAVI provides the most accurate estimate, i.e., the difference between predicted and actual data is minimal. Finally, a combination of Markov modelling and SAVI was used to predict the probable land-use scenario in Gangtok in 2020 AD, which indicted that more forest areas will be converted for step cultivation by the year 2020. 相似文献
122.
We present preliminary kinematic analyses of Taylor–Couette flow. We consider deformation of a Newtonian incompressible ductile material inside rotating horizontal listric (concentric circular) boundaries. The velocity profile is curved indicating non-uniform shear strain but leads to the same shear sense. Each material point on progressive shear keeps increasing shear strain linearly with time. A curve of no movement, the ‘neutral curve’, may exist inside the shear zone. Irregular geometries of initially regular markers and their individual non-matching strain paths indicate inhomogeneous deformaion in such Taylor–Couette flow. 相似文献
123.
Kamal A. Ali Robert J. Stern William I. Manton Peter R. Johnson Sumit K. Mukherjee 《International Journal of Earth Sciences》2010,99(4):705-726
The Neoproterozoic Atud diamictite in Wadi Kareim and Wadi Mobarak in the Eastern Desert of Egypt and the Nuwaybah formation
in NW Saudi Arabia consist of poorly sorted, polymictic breccia, with clasts up to 1 m of granitoid, quartz porphyry, quartzite,
basalt, greywacke, marble, arkose, and microconglomerate in fine-grained matrix. Stratigraphic relations indicate that the
diamictite was deposited in a marine environment. Integrated field investigation, petrographic study and U–Pb SHRIMP zircon
ages demonstrate that the Atud and Nuwaybah are correlative. The distribution of zircon ages indicate that ~750 Ma ages are
dominant with a significant component of older materials, characterized by minor Mesoproterozoic and more abundant Paleoproterozoic
and Neoarchean ages. Some matrix and metasedimentary clast zircons yield ages that are a few 10s of Ma younger than the age
of the youngest clast (754 ± 15 Ma), suggesting Atud/Nuwaybah diamictite deposition ~750 Ma or slightly later, broadly consistent
with being deposited during the Sturtian glaciation (740–660 Ma). The Paleoproterozoic and Neoarchean clasts have no source
within the ensimatic Arabian–Nubian Shield. The distribution of the pre-Neoproterozoic ages are similar to the distribution
of the pre-Neoproterozoic ages in Yemen and Saharan Metacraton, suggesting that these clasts have been transported hundreds
of kilometers, maybe by ice-rafting. The Atud diamictite may represent important evidence for Cryogenian “Snowball Earth”
in the Arabian–Nubian Shield. 相似文献
124.
U. Mukherjee S. Bapna H. Raichur B. Paul S. N. A. Jaaffrey 《Journal of Astrophysics and Astronomy》2006,27(1):25-35
We have investigated the Quasi Periodic Oscillation (QPO) properties of the transient accreting X-ray pulsar XTE J1858 + 034
during the second outburst of this source in April–May 2004. We have used observations made with the Proportional Counter
Array (PCA) of the Rossi X-ray Timing Explorer (RXTE) during May 14–18, 2004, in the declining phase of the outburst. We detected
the presence of low frequency QPOs in the frequency range of 140–185 mHz in all the RXTE-PCA observations. We report evolution
of the QPO parameters with the time, X-ray flux, and X-ray photon energy. Though a correlation between the QPO centroid frequency
and the instantaneous X-ray flux is not very clear from the data, we point out that the QPO frequency and the one day averaged
X-ray flux decreased with time during these observations. We have obtained a clear energy dependence of the RMS variation
in the QPOs, increasing from about 3% at 3 keV to 6% at 25 keV. The X-ray pulse profile is a single peaked sinusoidal, with
pulse fraction increasing from 20% at 3 keV to 45% at 30keV. We found that, similar to the previous outburst, the energy spectrum
is well fitted with a model consisting of a cut-off power law along with an iron emission line. 相似文献
125.
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
126.
Integrating multivariate statistical analysis with GIS for geochemical assessment of groundwater quality in Shiwaliks of Punjab,India 总被引:4,自引:2,他引:2
Chander Kumar Singh Satyanarayan Shashtri Saumitra Mukherjee 《Environmental Earth Sciences》2011,62(7):1387-1405
The dependency of people on groundwater has increased in the past few decades due to tremendous increase in crop production,
population and industrialization. Groundwater is the main source of irrigation in Shiwaliks of Punjab. In the present study
the samples were collected from predetermined location as was located on satellite image on basis of spectral reflectance.
Global positioning system was used to collect samples from specific locations. Principal components analysis (PCA) together
with other factor analysis procedures consolidate a large number of observed variables into a smaller number of factors that
can be more readily interpreted. In the present study, concentrations of different constituents were correlated based on underlying
physical and chemical processes such as dissociation, ion exchange, weathering or carbonate equilibrium reactions. The PCA
produced six significant components that explained 78% of the cumulative variance. The concentration of the few trace metals
was found to be much higher indicating recharge due to precipitation as main transport mechanism of transport of heavy metals
in groundwater which is also confirmed by PCA. Piper and other graphical methods were used to identify geochemical facies
of groundwater samples and geochemical processes occurring in study area. The water in the study area has temporary hardness
and is mainly of Ca–Mg–HCO3 type. 相似文献
127.
The impact of Hurricane Ivan on water quality in Pensacola Bay was investigated by MODIS 250 m remote sensing of chlorophyll-a concentrations at different time slots before and after the hurricane event. Before the hurricane, the mean chlorophyll-a in the Bay was 5.3 μg/L. Heavy rainfall occurred during the hurricane landfall. The 48 h rainfall reached 40 cm and the peak storm surge reached 3 m on 9/16. After the rainstorm and during the storm surge on 9/17/2004, the mean chlorophyll-a concentration substantially increased to 14.7 μg/L. 26.3% water area was in the poor-water-quality condition (chl-a > 20 μg/L). This indicates that heavy nutrient loads from urban stormwater runoff and storm-surge inundation simulated chlorophyll bloom. After the end of the storm surge on 9/18/2004, the mean chlorophyll dropped to 2.0 μg/L, suggesting the effective flushing of polluted water from the bay to the Gulf of Mexico by the storm-surge. The good water quality condition lasted for almost several weeks after the storm surge. The peak river flow, arriving on the 4th day after the peak storm surge, did not alter the good water quality situation in the bay. This indicates that urban stormwater runoff rather than the river inflow is the major pollutant source for water quality in Pensacola Bay during the hurricane. 相似文献
128.
O. P. Mishra D. Zhao Chandan Ghosh Z. Wang O. P. Singh Biman Ghosh K. K. Mukherjee D. K. Saha G. K. Chakrabortty S. G. Gaonkar 《Natural Hazards》2011,57(1):51-64
The Andaman–Nicobar (A–N) Islands region has attracted many geo-scientists because of its unique location and complex geotectonic
settings. The recent occurrence of tsunamis due to the megathrust tsunamigenic north Sumatra earthquake (Mw 9.3) with a series
of aftershocks in the A–N region caused severe damage to the coastal regions of India and Indonesia. Several pieces of evidence
suggest that the occurrence of earthquakes in the A–N region is related to its complex geodynamical processes. In this study,
it has been inferred that deep-seated structural heterogeneities related to dehydration of the subducting Indian plate beneath
the Island could have induced the process of brittle failure through crustal weakening to contribute immensely to the coastal
hazard in the region. The present study based on 3-D P-wave tomography of the entire rupture zone of the A–N region using
the aftershocks of the 2004 Sumatra–Andaman earthquake (Mw 9.3) clearly demonstrates the role of crustal heterogeneity in
seismogenesis and in causing the strong shakings and tsunamis. The nature and extent of the imaged crustal heterogeneity beneath
the A–N region may have facilitated the degree of damage and extent of coastal hazards in the region. The 3-D velocity heterogeneities
reflect asperities that manifest what type of seismogenic layers exist beneath the region to dictate the size of earthquakes
and thereby they help to assess the extent of earthquake vulnerability in the coastal regions. The inference of this study
may be used as one of the potential inputs for assessment of seismic vulnerability to the region, which may be considered
for evolving earthquake hazard mitigation model for the coastal areas of the Andaman–Nicobar Islands region. 相似文献
129.
130.
This work aims to assess the soil microzonation of Agartala city and its surrounding areas based on spectral geophysical signatures. Different spectral resolutions of Landsat TM have been used for assessing the Normalized Difference Vegetative Index, spatial thermal emission representation and plant water moisture representation. Normalized Difference Vegetative Index (NDVI) was measured from band 4 (near-infrared (NIR)) and band 3 (photosynthetically active radiation (PAR)). The Digital Number (DN) values of thermal infrared band (TIR) were used for measuring spatial variation of thermal representation in the city area. A very simple model was developed for measuring thermal emission representative index from NDVI and automated classified TIR band. Overlaid NDVI and classified TIR shows the spatial distribution of thermal emission representative values. Classified mid-wave infrared band (MWIR) was used for measuring the surface geotherm units (τ) which are related with different types of soil. On the basis of spatial distribution of τ value which is clearly visible in a thermal emission representative map overlaid by classified MWIR, the soil microzonation map of the study area was prepared. This soil microzonation map shows that Agartala and its surrounding areas are characterized by four types of soil which are related to different geomorphic and geological units. The soil of this area is classified as dry sandy soil and sandy clay soil of the highland areas and wet sandy alluvium and clayey alluvium of the flood plain area. 相似文献