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51.
Sisir K. Mondal 《Journal of the Geological Society of India》2009,73(1):36-51
The Archaean cratonic nuclei of the continents are important as they contain the most significant evidences for the evolution
of Earth e.g. the greenstone sequences. In the Indian Shield, one of the important cratons is the Singhbhum craton, where
nearly 95% of the Indian chromite deposits and only PGE deposits are located which are hosted within Mesoarchaean ultramafic-mafic
rock sequences. The ultramafic units occur as sill like intrusions within the Iron Ore Group (IOG) greenstone belts and often
associated with gabbroic intrusions. In the Nuasahi and Sukinda mining districts of these occurrences, detailed petrological,
geochemical and isotopic studies have been carried out in the last decades. Petrological and geochemical studies indicate
a supra-subduction zone (SSZ) tectonic settings in Archaean for the origin of these ultramafic-mafic sequences. The Os isotopic
and platinum group element (PGE) geochemical studies of chromites from the two mining districts indicate presence of a subchondritic
source mantle domain beneath and within the Singhbhum craton similar to the Zimbabwean craton of southern African continent.
The Os model age calculation indicates melt extraction from a subcontinental lithospheric mantle (SCLM) before 3.7 Ga which
is similar to the other ancient cratons. As a whole the study supports the premise that India was part of the African continent
in pre-Gondwana times and even in early Archaean and suggest possible amalgamation and building up of a supercontinent during
late Archaean. However, in comparison with other occurrences, the Singhbhum craton of the Indian Shield and the Zimbabwean
craton in southern Africa are characterized by the presence of subchondritic lithospheric mantle domains within the SCLM,
which were developed prior to 3.7 Ga. 相似文献
52.
S. Mondal J.D.A. Piper L. Hunt G. Bandyopadhyay S. Basu Mallik 《Journal of Asian Earth Sciences》2009,34(4):493-506
Palaeomagnetic and magnetomineralogical results are reported from charnockites in basement terrane at the eastern sector of the WSW–ENE granulite belt of South India. Magnetite is the dominant ferromagnet identified by rock magnetic and optical study; it is present in several phases including large homogeneous titanomagnetites and disseminated magnetite in microfractures linked to growth stages ranging from primary charnockite formation to uplift decompression and exhumation within the interval ~2500–2100 Ma. Several components of magnetization are resolved by thermal demagnetization and summarized by four pole positions; in the northern (Pallavaram) sector these are P1 (33°N, 99°E, dp/dm = 8/9°) and P2 (79°N, 170°E, dp/dm = 3/6°), and in the southern (Vandallur) sector they are V1 (23°N, 116°E, dp/dm = 8/9°) and V2 (26°S, 136°E, dp/dm = 5/10°). These magnetizations are linked to uplift cooling of the basement and unblocking temperature spectra suggest acquisition sequences P1 → P2 and V1 → V2 in each case implying movement of the shield from higher to lower palaeolatitudes sometime between 2500 and 2100 Ma. Palaeomagnetic poles from the cratonic nuclei of Africa, Australia and India all identify motion from higher to lower palaeolatitudes in Early Palaeoproterozoic times, and this is dated ~2400 and ~2200 Ma in the former two shields. The corresponding apparent polar wander (APW) segments match the magnetization record within the charnockite basement terranes of southern India to yield a preliminary reconstruction of the ‘Ur’ protocontinent, the oldest surviving continental protolith with origins prior to 3000 Ma. Although subject to later relative movements these nuclei seem to have remained in proximity until the Mesozoic break-up of Gondwana. 相似文献
53.
Aquifer characteristics and its modeling around an industrial complex,Tuticorin, Tamil Nadu,India: A case study 总被引:3,自引:0,他引:3
Anthropogenic pollution of shallow groundwater resources due to industrial activities is becoming a cause of concern in the
east coastal belt of the state of Tamil Nadu, India. Integrated hydrogeological, geophysical and tracer studies were carried
out in the coastal region encompassing an industrial complex. The objective has been to gain knowledge of aquifer characteristics,
ascertaining groundwater movement and its flow direction, which would in turn reveal the possibility of contamination of groundwater
regime and its better management. The results of multi-parameters and model study indicate that the velocity of groundwater
flow ranges from 0.013 m/d to 0.22m/d in and around the industrial complex in upstream western part of the catchment and 0.026
m/d to 0.054m/d in the downstream eastern part, near the coast. These parameters are vital for the development of groundwater
management scheme. 相似文献
54.
S. N. Tandon J. B. Hutchings S. K. Ghosh A. Subramaniam G. Koshy V. Girish P. U. Kamath S. Kathiravan A. Kumar J. P. Lancelot P. K. Mahesh R. Mohan J. Murthy S. Nagabhushana A. K. Pati J. Postma N. Kameswara Rao K. Sankarasubramanian P. Sreekumar S. Sriram C. S. Stalin F. Sutaria Y. H. Sreedhar I. V. Barve C. Mondal S. Sahu 《Journal of Astrophysics and Astronomy》2017,38(2):28
The performance of the ultraviolet telescope (UVIT) on-board AstroSat is reported. The performance in orbit is also compared with estimates made from the calibrations done on the ground. The sensitivity is found to be within \(\sim \)15% of the estimates, and the spatial resolution in the NUV is found to exceed significantly the design value of \(1.8^{\prime \prime }\) and it is marginally better in the FUV. Images obtained from UVIT are presented to illustrate the details revealed by the high spatial resolution. The potential of multi-band observations in the ultraviolet with high spatial resolution is illustrated by some results. 相似文献
55.
Improvement of groundwater quality due to fresh water ingress in Potharlanka Island, Krishna delta, India 总被引:1,自引:0,他引:1
Hydrochemical study had been carried out on the groundwater resources of Potharlanka Island, Krishna delta, India. Groundwater
samples were collected and analyzed at 42 sites in December 2001 and October 2006. A comparative study of hydrochemical data
indicates: groundwater is mildly alkaline with a pH of 7.0–8.2; electrical conductivity (EC) varies from 605 to 5,770 μS/cm
in December 2001, and 652–5,310 μS/cm in October 2006. More than 62% of the groundwater samples in 2006 have TDS value <2,000 mg/l,
which is within permissible limit of potable water, but 57% of the samples in 2001, are higher than the maximum permissible
limit. Extremely low HCO3/Cl and variable high Mg/Ca (molar ratios) had been indicated the transformation of the fresh groundwater aquifer systems
to saline in 2001. Groundwater of this Island is mainly classified as Na–Cl and mixed types. A high percentage of Na–Cl type
of these waters indicates the possibility of seawater ingression/intrusion process during 2001 and comparatively mixed water
type indicates the dilution activities of groundwater. Excessive withdrawal of groundwater has caused the increase of saline
water intrusion. Improvement of groundwater quality in this Island due to artificial recharge structures made by NGRI under
RGNDWM project and affects of the flood due to heavy rainfall of the months of September–October 2005 are discussed in this
paper. 相似文献
56.
Md. Surabuddin Mondal A. C. Pandey R. D. Garg 《Journal of the Indian Society of Remote Sensing》2008,36(1):69-76
Water is the most important natural resource which forms the core of the ecological system. The advent of remote sensing has
opened up new vistas in groundwater prospect evaluation, exploration and management. The groundwater resources of the study
area, Rishikesh region of Garhwal Himalayas, are under threat due to population pressure caused by expanding tourism in this
region. This entails sustainable and judicious use of this precious resource. The groundwater prospect evaluation in Rishikesh
region has been attempted based on hydrogeomorphological mapping of the area consisting of thematic maps of hydrogeomorphology,
geology, drainage, lineament, slope and relief using high resolution IRS-1C LISS III and PAN merged satellite images. The
Rishikesh region exhibits diverse hydrogeomorphological conditions where the groundwater regime is controlled mainly by topography
and geology. A probability-weighted approach has been applied during overlay analysis in ArcMap GIS environment. The overlay
analysis allows a linear combination of weights of each thematic map with respect to ground water potential. Good groundwater
prospects dominate in the area with more than 50% of the study area showing moderate to excellent potential. The study shows
that the remote sensing and geoinformatics techniques can be applied effectively for groundwater prospect evaluation. 相似文献
57.
The variation of temporal fractal dimension D2 (t) value may be well applied for understanding the future large earthquakes. In this present analysis the time series of inter-occurrence of earthquakes of consecutive hundred events window in Himalayan region is analyzed. We observed the variation in D2 (t) values in the range of 0.19 to 0.68 indicating the variation of clustering of events with respect to time. The multifractal nature of earthquakes is also investigated by plotting Dq(t) versus q. The result shows the temporal distribution of earthquakes have multifractal structure of definitive pattern rather than random pattern. 相似文献
58.
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
59.
Fractal study of seismicity in order to characterize the various tectonic blocks of North-east Himalaya,India 总被引:1,自引:1,他引:0
Three major projects initiated by the European Commission within its 7th Framework Programme that have studied the weather phenomena and their projections to the future in relation to their impacts and implications to the European transport systems have recently been concluded. All of the transport modes were covered, as well as all of the critical phenomena present within the European area. The three projects (that ran from 2009 and 2012) are as follows: (1) EWENT (Extreme Weather impacts on European Networks of Transport—www.ewent.vtt.fi); (2) ECCONET (Effects of climate change on the inland waterway networks—www.ecconet.eu); (3) WEATHER (Weather Extremes: Assessment of Impacts on Transport and Hazards for European Regions—www.weather-project.eu). In this Foreward to the Special Issue on “Vulnerability of Transportation to Extreme Weather and Climate Change,” the key results of the above three projects are addressed concisely, offering the reader a broader view of their findings; since some of these are enveloped in the research papers hosted in this volume, they will not be covered in detail. However, the rich output of these projects in the form of “Project Deliverables” and “Reports” is also an important source of information on the findings and results from these three projects which are publicly available on the projects’ Web sites. The purpose of this Foreward is to bring to the attention of the interested reader these sources and overview briefly some of the projects’ outcomes. Also, a short comparative discussion on selected findings is made, outlining agreements and disagreements between the projects. 相似文献
60.
T. K. Biswal V. Thirukumaran Kamleshwar Ratre Krishanu Bandyapadhaya K. Sundaralingam Amit Kumar Mondal 《Journal of the Geological Society of India》2010,75(1):128-136
The E-W running Salem-Attur shear zone demarcates the tectonic boundary between Archaean Dharwar Craton in the north and Proterozoic
Southern granulite terrane in the south. This study reveals that the shear zone is a low angle thrust. The thrust zone is
around 10 m thick and it merges with the main shear zone along the strike. The thrust is developed on charnockite near Odyarpatti,
which is retrograded into schists. Further, it is marked by gently dipping mylonitic foliation and subhorizontal lineation.
The S-C fabric, mantled porphyroclasts and intragranular faults indicate northeasterly slip along the thrust. Recumbent shear
folds SF1 are developed within the thrust zone. The thrust has been folded by late stage F2 fold which has brought variation in the orientation of the mylonitic foliation from subhorizontal to vertical attitude; the
mylonitic lineations have been rotated to subvertical orientation also. Additionally, the F2 crenulations and shear cleavages and intersection lineations are superimposed on the mylonitic fabric. Thrusting along the
Salem-Attur shear zone is probably the cause for upliftment of the charnockites to the upper crust. Post-upliftment stage
has witnessed brittle deformation in the form of development of shear fractures in NNE-SSW and E-W directions. Pseudotachylites
are emplaced along these fractures. 相似文献