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11.
The genesis potential parameter (GPP) consists of two dynamical variables low-level relative vorticity and vertical wind shear, and two thermodynamic variables middle tropospheric relative humidity and instability are analysed during pre-cyclone watch period over the Bay of Bengal. The pre-cyclone watch period is taken as the period prior to 72-h from the formation of a Depression. The GPP values for 30 tropical disturbances that formed over the Bay of Bengal during the period 2001–2010 are analysed. An independent evaluation of the parameter and possible applications to operational forecasting are presented using data from the year 1998 to 1999. The variables of GPP are calculated using the ECMWF interim reanalysis 1.5° × 1.5° resolution data, averaged within an area of 5° × 5° box on the centre of tropical disturbances and also over the 5° × 5° boxes over the adjacent surrounding areas. The results show that maximum value is observed over the genesis region at 48- and 24-h lead time for both the cases of cyclones and Depressions. The threshold value of GPP is found to be 9.3, 6.3 and 2.7 during pre-cyclone watch period at 24-, 48- and 72-h lead time, respectively. A distinction in GPP values above threshold value for cyclonic and a Depression system is also observed for the cyclogenesis region in 69, 75 and 75 % of cases at 72-, 48- and 24-h lead time, respectively. However, the individual case studies show that the GPP could indicate the genesis of a tropical cyclone with a 2-day lead time. The mean GPP values are 11.8, 8.5 and 3.8 for cyclonic systems and 6.9, 4.2 and 1.6 for Depression systems over an area of a box 5° × 5° on the systems at 24-, 48- and 72-h lead time, respectively, from the stage of Depression. The result of the study is found to be providing probable area of genesis and intensification of a tropical disturbance at a 2 day lead time from the stage Depression. 相似文献
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13.
A. K. Mitra Sankar Nath A. K. Sharma 《Journal of the Indian Society of Remote Sensing》2008,36(3):243-253
Operational meteorology is perceived as a fuzzy environment in which information is vaguely defined. The mesoscale processes
such as fog, stratus and convection are generally dependent on the topography of the place and has always been difficult to
forecast for the meteorologists. The main objective of the present study is to introduce the concept of fuzzy inference system (FIS) in the prediction of fog. This approach uses the concept of a pure fuzzy logic system where the fuzzy rule base
consists of a collection of fuzzy IF-THEN rules. The fuzzy inference engine uses these fuzzy IF-THEN rules to determine a mapping from fuzzy sets in the input universe of discourse to fuzzy sets in the output universe of discourse
based on fuzzy logic principles. Basic weather elements, which affect weather characteristics of fog, are fuzzified. These
are then used in fuzzy weather prediction models based on fuzzy inferences. These models are simulated and the crisp results
obtained using developed defuzzification strategies are compared with the actual weather data. The basis of methodology is
to construct the fuzzy rule base domain from the available daily current weather observations in winter season over New Delhi.
The results reveal that dew point spread and rate of change of dew point spread are the most important parameters for the
formation of fog. The results further indicate that fog formation over New Delhi are dominant when (i) dew point is greater
then 7°C along with dew point spread between 1 and 3°C. (ii) rate of change of dew point spread must be negative and wind
speed should be less than 4 knots. This study presents a technique for predicting the probability of fog over New Delhi for
5–6 hours in advance. The skill score indicates that the performance of FIS is appreciably good. The method is found to be
promising for operational application. 相似文献
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15.
M. Sankar Rao 《Pure and Applied Geophysics》1966,65(1):196-215
Summary In a coordinate system in which the ground is always a coordinate surface, climatic equations for axially asymmetric and symmetric atmospheric motions are derived. These are compared with their counterparts in the pressure coordinate system. Some qualitative predictions regarding solutions are given. 相似文献
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17.
An attempt has been made in this research work to evaluate the concentration of nitrate in groundwater and its management
in Apple town and its environs. Groundwater pollution has been reported in many aquifers because of high concentration of
nitrate in ground water, which is the result of excessive use of fertilizers to cropland. Systematic sampling was done, with
a view to understand the source of nitrate concentration in the study area. Fifteen sample sites were selected and the samples
were taken for a baseline study to understand the geochemistry of the study area and to assess its physicochemical characteristics.
The water quality parameters were investigated for summer (May, 2007) and winter (December, 2007) seasons and were compared
with the standard values given by ICMR / WHO. The hydrochemical data of 15 samples indicates that the concentration of almost
all parameters fall within the permissible limits except nitrate. Linear Trend Analysis on seasonal and annual basis clearly
depicted that nitrate pollution in the study area is increasing significantly. About 85% of samples during summer season and
67% of the samples during winter season were showing a high concentration of nitrate, exceeding permissible limit of WHO (50 mg/l),
which is due to the use of nitrogenous fertilizers in the study area. Appropriate methods for improving the water quality
and its management in the affected areas have been suggested. 相似文献
18.
A S K Nair G Sankar S Nalina Kumar 《Journal of the Indian Society of Remote Sensing》1993,21(3):151-156
The coastal zone of Kerala with moderate energy, monsoonal-storm-dominated wave climate, together with a microtidal range, falls under the major tectonic class of the Amerotrailing edge coasts. In order to have an effective management of this coastal zone, one requires detailed information on various types of coastal landforms and the related processes acting on them. Coastal inlets are one among such landforms, which are relatively short and narrow tidal channels connecting bays and lagoons to the ocean. Coastal inlets and the related landforms form an important type of coastal feature. An examination of coastal maps from any area in the world will reveal that coastal inlets are of migratory and offset in nature. In the present study the migration pattern and offset behaviour of some of the inlets of Kerala coast have been examined using IRS-IA LISS II data and Survey of India topographic sheets. The study reveals that geocoded IRS-IA LISS II data could provide accurate geometrical information which may considerably minimise the field check. 相似文献
19.
Evaluation of groundwater potential zones using Remote Sensing data in upper Vaigai river basin,Tamil Nadu,India 总被引:1,自引:0,他引:1
K Sankar 《Journal of the Indian Society of Remote Sensing》2002,30(3):119-129
The area of upper Vaigai river basin covering parts of Madurai and Theni Districts, in Tamil Nadu, faces acute water scarcity and chronically drought prone. The groundwater resources in the area have not been fully exploited. The present investigation has been made to evaluate the potential zones for groundwater targeting using IRS - ID LISS III geocoded data on 1:50,000 scale. The geology, geomorphology, lineament tectonic maps are generated and integrated to evaluate the hydrogeomorphological characteristics of the upper Vaigai river basin and demarcate the groundwater potential zones. A number of geomorphic units have been observed. Out this the more groundwater prospective units are buried pediment medium, buried pediment deep, flood plain, bajada and lineament and intersection of lineaments. Non potential areas like pediment, pediment inselberg, shallow pediment and pediplain were identified. 相似文献
20.
The concept of fractals is used here for the identification of seismic reflectors with special emphasis on thin‐bed delineation, which is generally overlooked during standard data processing. A new fractal analysis scheme is applied to both synthetic and real field seismic data. The fractal dimensions of the three seismic attributes – amplitude, phase, and instantaneous frequency – have been analysed and evaluated. A change in fractal dimension is found to occur whenever there is a reflection. However, the resolution in the delineation of reflectors varies, depending on the attribute under consideration and the method of fractal dimension estimation used. Fractal analysis is performed on both noise‐free and noisy synthetic data to establish the noise tolerance limit for both the ‘divider method’ and the ‘Hurst method’. It is then tested with different peak frequencies of the source wavelet to establish the criteria for using the divider method and the Hurst method. The divider method is found to be suitable for high peak frequency source wavelets (> 25 Hz), while the Hurst method is best suited for low peak frequency source wavelets (< 25 Hz). Finally, when applied to the digitally processed and migrated field seismic data, it could even delineate reflectors which otherwise went undetected on the migrated time section. 相似文献