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31.
Debashis Chakraborty Dibyendu Dutta H Chandrasekharan 《Journal of the Indian Society of Remote Sensing》2001,29(3):115-128
The vegetation dynamics and land use/land cover types of Birantiya Kalan watershed located in the arid tracts of western Rajasthan have been characterized and evaluated using Remote Sensing and Geographical Information System (GIS). The watershed under study falls in the transitional plain of Luni Basin and is characterized by Aravali ranges in the eastern half and vast alluvial plains in the west. The land use/land cover types, as identified are cropland, fallow, forest, land with scrub, land without scrub, sandy area and the water body. Land with scrub occupied maximum area (39% area of the watershed) in 1996 in place of crop land which was dominant (43% of total area) in the year 1988. During eight years period, seasonal fallow land increased significantly and the areal extent of water body decreased to almost half. Vegetation vigour types have been classified into very poor, poor. moderate, good and very good categories. Moderate vigour type reduced from 62 to 27% and poor type increased from 34 to 68% during the period 1988 to 1996. Other vegetation vigour types have not shown any significant changes. To quantify the changes over the years in both vegetation and land use/land cover, weightages have been given to each type and composite values of both vegetation vigour and land use types for 1996 and 1988 have been calculated. It has been observed that the ratio for vegetation vigour has been found to be 0.85 showing that the overall vegetation have not improved after the treatment. The ratio for land use is found to be 1.01, which indicates negligible change in land use. 相似文献
32.
Hari Sankar Chakraborty 《Pure and Applied Geophysics》1969,76(1):71-78
Summary The problems of radial vibration of a composite orthotropic cylinder subjected to a uniform axial magnetic field forms the chief interest of the paper. 相似文献
33.
R. S. Ross A. Chakraborty A. Chen L. Stefanova S. Sirdas T. N. Krishnamurti 《Meteorology and Atmospheric Physics》2007,98(3-4):137-174
Summary Climate variations in the Caribbean, largely manifest in rainfall activity, have important consequences for the large-scale
water budget, natural vegetation, and land use in the region. The wet and dry seasons will be defined, and the important roles
played by the El Ni?o-Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO) in modulating the rainfall during
these seasons will be discussed.
The seasonal climate forecasts in this paper are made by 13 state of the art coupled atmosphere-ocean general circulation
models (CGCMs) and by the Florida State University Synthetic Superensemble (FSUSSE), whose forecasts are obtained by a weighted
combination of the individual CGCM forecasts based on a training period. The success of the models in simulating the observed
1989–2001 climatology of the various forecast parameters will be examined and linked to the models’ success in predicting
the seasonal climate for individual years. Seasonal forecasts will be examined for precipitation, sea-surface temperature (SST), 2-meter air temperature, and
850 hPa u- and v-wind components during the period 1989–2001. Evaluation metrics include root mean square (RMS) error and Brier skill score.
It will be shown that the FSUSSE is superior to the individual CGCMs and their ensemble mean both in simulating the 1989–2001
climatology for the various parameters and in predicting the seasonal climate of the various parameters for individual years.
The seasonal climate forecasts of the FSUSSE and of the ensemble mean of the 13 state of the art CGCMs will be evaluated for
years (during the period 1989–2001) that have particular ENSO and NAO signals that are known to influence Caribbean weather,
particularly the rainfall. It will be shown that the FSUSSE provides superior forecasts of rainfall, SST, 2-meter air temperature,
and 850 hPa u- and v-wind components during dry summers that are modulated by negative SOI and/or positive NAO indices. Such summers have become
a feature of a twenty-year pattern of drought in the Caribbean region. The results presented in this paper will show that
the FSUSSE is a valuable tool for forecasting rainfall and other atmospheric and oceanic variables during such periods of
drought. 相似文献
34.
Jibamitra Ganguly Weiji Cheng Sumit Chakraborty 《Contributions to Mineralogy and Petrology》1998,131(2-3):171-180
Diffusion couples made from homogeneous gem quality natural pyrope and almandine garnets were annealed within graphite capsules
under anhydrous conditions at 22–40 kbar, 1057–1400 °C in a piston-cylinder apparatus. The concentration profiles that developed
in each couple were modeled to retrieve the self diffusion coefficients [D(I)] of the divalent cations Fe, Mg, Mn and Ca.
Because of their usually low concentrations and lack of sufficient compositional change across the interface of the diffusion
couples, only a few reliable data can be obtained for D(Ca) and D(Mn) from these experiments. However, nine sets of D(Fe)
and D(Mg) data were retrieved in the above P-T range, and cast in the form of Arrhenian relation, D=D
0exp{−[Q(1 bar)+PΔV
+]/RT}. The values of the activation energy (Q) and activation volume (ΔV
+) depend on whether f
O2 is constrained by graphite in the system C-O or held constant. For the first case, we have for Fe:Q(1 bar)=65,532±10,111 cal/mol, D
0=3.50 (±2.30)×10−5 cm2/s, ΔV
+=5.6(±2.9) cm3/mol, and for Mg:Q(1 bar)=60,760±8,257 cal/mol, D
0=4.66 (±2.48)×10−5 cm2/s, ΔV
+=5.3(±3.0) cm3/mol. Here the ΔV
+ values have been taken from Chakraborty and Ganguly (1992). For the condition of constant f
O2, the Q values are ∼9 kcal lower and ΔV
+ values are ∼4.9 cm3/mol larger than the above values. Lower temperature extrapolation of the Arrhenian relation for D(Mg) is in good agreement
with the Mg tracer diffusion data (D
*
Mg) of Chakraborty and Rubie (1996) and Cygan and Lasaga (1985) at 1 bar, 750–900 °C, when all data are normalized to the same
pressure and to f
O2 defined by graphite in the system C-O. The D
*
Mg data of Schwandt et al. (1995), on the other hand, are lower by more than an order of magnitude than the low temperature
extrapolation of the present data, when all data are normalized to the same pressure and to f
O2 defined by the graphite buffer. Comparison of the D(Fe), D(Mg) and D(Mn) data in the pyrope-almandine diffusion couple with
those in the spessartine-almandine diffusion couple of Chakraborty and Ganguly (1992) shows that the self diffusion of Fe
and Mn are significantly enhanced with the increase in Mn/Mg ratio; the enhancement effect on D(Mg) is, however, relatively
small. Proper application of the self diffusion data to calculate interdiffusion coefficient or D matrix elements for the purpose of modeling of diffusion processes in natural garnets must take into account these compositional
effects on D(I) along with the effects of thermodynamic nonideality, f
O2, and pressure.
Received: 8 May 1997 / Accepted: 2 October 1997 相似文献
35.
We have studied string-dust cosmological model in a stationary cylindrically symmetric space-time. A one parameter family of solutions is obtained for the field equations of the system. 相似文献
36.
K. Krishnanunni D. K. Chakraborty A. M. Rakshit T. K. Kurien 《Journal of the Indian Society of Remote Sensing》1979,7(2):23-28
Since snow covered areas in the Himalayas contribute significantly to the discharge of the major rivers of North India, snow monitoring is essential for effective control and management of the available water resources, particularly in the lean period. As accumulation and melting of snow are dynamic processes the need arises for periodic monitoring. Conventional survey methods are time consuming and expensive due to adverse terrain conditions and weather. As such, updating information at reasonably frequent intervals calls for a strategy invoiving remote sensing techniques. Potentials of such techniques such as aerial and orbital photography and multispectral scanning systems as also microwave sensing systems are briefly discussed. Particular emphasis is laid on a Landsat type surveillance system, which is at the operational stage. As a case study demonstrating the system capability an area in the Sutlej catchment has been analysed on Landsat imagery acquired in October and December, 1972. The snow covered area is found to be considerably more in the December, 72 imagery. Such a map overlaid on a contoured 1:250,000 base updated every month can be useful input attempts at watershed modelling incorporating other dynamic features also. 相似文献
37.
S. K. Chakraborty 《Pure and Applied Geophysics》1956,33(1):9-16
Summary The paper deals with the investigations of disturbances in an infinite homogeneous isotropic and perfectly elastic medium
produced by a source operating on a small portion of the inner surface of a cylindrical hole.
Prof.S. K. Chakraborty, M. Sc., Surendranath College, 24 Harrison Road,Calcutta-9, India. 相似文献
38.
Prof. S. K. Chakraborty 《Pure and Applied Geophysics》1956,35(1):25-32
Summary Disturbances generated by pressure on the surface of a spherical cavity inside (i) a dispersive medium, (ii) a medium having transverse isotropy about the radius vector have been considered. Finally, a brief discussion of the propagation of waves in visco-elastic media has been added.I wish to express my gratefulness to Professor B. B.Sen, for his kind help in the preparation of the paper. 相似文献
39.
40.