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81.
The effect of bulk viscosity on the evolution of the spatially flat Friedmann-Robertson-Walker models in the context of open
thermodynamical systems, which allow particle creation, is analyzed within the framework of Brans-Dicke theory. Particle creation
and bulk viscosity have been considered as separated irreversible processes. To accommodate the viscous pressure and creation
pressure, which is associated with creation of matter out of gravitational field, the energy-momentum tensor is modified.
Dynamical behaviour of the models have been discussed. 相似文献
82.
C.Indrani A. A.Deshpande V.Balasubramanian 《Monthly notices of the Royal Astronomical Society》1998,295(2):397-400
We report timing observations on 16 pulsars obtained using the Ooty Radio Telescope operating at 327 MHz. Using these observations, spanning over a year, we have obtained values of period derivatives for the first time and refined the estimates of the periods for all pulsars in this sample. We also report improved positions for all cases where the earlier position estimates had an uncertainty of a few arcmin. 相似文献
83.
Malkiat Singh H S Gurm M R Deshpande R G Rastogi G Sethia A R Jain A V Janve R K Rai V M Patwari B S Subbarao 《Journal of Earth System Science》1978,87(3):47-55
Radio beacon from ATS-6 at 140 MHz was used to measure the changes in the polarization angle (Faraday rotation) at Bombay,
Rajkot, Ahmedabad, Udaipur and Patiala during October 1975 to July 1976. In this paper, results of diurnal, seasonal and latitudinal
variations in total electron content (TEC) derived from these measurements are reported. The amplitude of diurnal peak is
found to be higher at Rajkot, Ahmedabad and Udaipur as compared to that at Patiala or Bombay, indicating that the peak of
Appleton anomaly in the latitudinal variation of TEC was close to the latitude of Ahmedabad. The diurnal maximum of TEC occurs
around the same time during summer and winter months. The peak electron content shows a semiannual variation at all the stations
with large values in equinoxes as compared to winter and summer. The TEC at Bombay shows a seasonal anamoly with high values
in winter as compared to summer. The paper describes the development of latitudinal anomaly with the time of the day for different
seasons. This anomaly is maximum during 1000 to 1800 LT and is located between 12° and 14° N (dip latitude) in summer and
equinoxes and at about 10°N in winter. 相似文献
84.
D P Agrawal M N Deshpande S N Rajaguru Bhaskar Roy 《Journal of Earth System Science》1978,87(3):23-28
There is considerable controversy regarding the mode of deposition of the OCP culture-associated sediments in the Gangetic
valley and their ecological implications. SEM and sedimentologic studies show a fluvial mode of deposition of sediments originally
derived from a glacial environment. 相似文献
85.
Journal of Earth System Science - Isolated ionospheric irregularities produce oscillating (ringing) diffraction patterns on the ground. Typical physical properties such as density, size, etc. of... 相似文献
86.
Turbulent flow structures in alluvial channels with curved cross‐sections under conditions of downward seepage
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Experimental investigations have been done to analyze turbulent structures in curved sand bed channels with and without seepage. Measures of turbulent statistics such as time‐averaged near‐bed velocities, Reynolds stresses, thickness of roughness sublayer and shear velocities were found to increase with application of downward seepage. Turbulent kinetic energy and Reynolds normal stresses are increased in the streamwise direction under the action of downward seepage, causing bed particles to move rapidly. Analysis of bursting events shows that the relative contributions of all events (ejections, sweeps and interactions) increase throughout the boundary layer, and the thickness of the zone of dominance of sweep events, which are responsible for the bed material movement, increases in the case of downward seepage. The increased sediment transport rate due to downward seepage deforms the cross‐sectional geometry of the channel made of erodible boundaries, which is caused by an increase in flow turbulence and an associated decrease in turbulent kinetic energy dissipation and turbulent diffusion. 相似文献
87.
K. S. Dwarakanath A. A. Deshpande N. Udaya Shankar 《Journal of Astrophysics and Astronomy》1990,11(3):311-322
A simple but effective modification to the conventional CLEAN algorithm is suggested. This modification ensures both stability
and speed when CLEAN is applied to maps containing a mixture of point sources and extended structures. The method has been
successfully applied to the recently-completed sky survey at 34.5 MHz (Dwarakanath & Udaya Shankar 1990). This survey was
made using the Gauribidanur T array (GEETEE)1 in 1-D aperture synthesis mode. Since in this case the ‘dirty beam’ (point spread
function) cannot be directly computed, a method to obtain this is discussed in detail. The results of this deconvolution procedure
have been encouraging in terms of reduced computing time and improved dynamic range in our maps. This algorithm should find
wider application in deconvolving maps which have both extended structures and point sources
This telescope is jointly operated by the Indian Institute of Astrophysics, Bangalore & the Raman Research Institute, Bangalore. 相似文献
88.
The estimates of quiescent and flare time temperatures of soft X-ray emitting regions on the Sun are obtained for flares observed during March–August 1967 from X-ray observations in two soft X-ray bands, 2–12 Å (Explorer-33 data) and 8–12 Å (OSO-3 data). It is concluded that hot coronal condensation, originally at 2–3 × 106 K, is raised to the temperature of about 4–5 × 106 K and is responsible for soft X-ray enhancement.On leave from Physics Department, College of Engineering, Aurangabad, India. 相似文献
89.
In this paper, we describe pulsar observations at decametric wavelengths using the Gauribidanur Radio Telescope made subsequent
to our earlier measurements (Deshpande & Radhakrishnan 1992). To improve the time-resolution in our measurements of pulse
profiles, we have used the ‘swept-frequency dedispersion’ method with some modifications to suit its application at such low
radio frequencies. We also present a new scheme that simplifies the calibration of the receiver gain characteristics. We present
average profiles on four pulsars from these improved measurements at 34.5 MHz. 相似文献
90.
A. A. Deshpande F. D’Alessandro P. M. McCulloch 《Journal of Astrophysics and Astronomy》1996,17(1-2):7-16
Spectral analysis of the residual pulsearrival times of pulsars is a useful tool in understanding the nature of the underlying
processes that may be responsible for the timing noise observed from pulsars. Power spectra of pulsar timing residuals may
be described by one or a combination of powerlaws. As these spectra are expected to be very steep, it is important to ensure
a high dynamic range in the estimation of the spectrum. This is difficult in practice since one is, in general, dealing with
timing measurements made at unevenly placed epochs. In this paper, we present a technique based on, ‘CLEAN’ to obtain high
dynamic range spectra from unevenly sampled data. We compare the performance of this technique with other techniques including
some that were used earlier for estimation of power spectra of pulsar timing residuals. 相似文献