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101.
Mechanisms for the land/sea warming contrast exhibited by simulations of climate change 总被引:3,自引:3,他引:0
Manoj M. Joshi Jonathan M. Gregory Mark J. Webb David M. H. Sexton Tim C. Johns 《Climate Dynamics》2008,30(5):455-465
The land/sea warming contrast is a phenomenon of both equilibrium and transient simulations of climate change: large areas
of the land surface at most latitudes undergo temperature changes whose amplitude is more than those of the surrounding oceans.
Using idealised GCM experiments with perturbed SSTs, we show that the land/sea contrast in equilibrium simulations is associated
with local feedbacks and the hydrological cycle over land, rather than with externally imposed radiative forcing. This mechanism
also explains a large component of the land/sea contrast in transient simulations as well. We propose a conceptual model with
three elements: (1) there is a spatially variable level in the lower troposphere at which temperature change is the same over
land and sea; (2) the dependence of lapse rate on moisture and temperature causes different changes in lapse rate upon warming
over land and sea, and hence a surface land/sea temperature contrast; (3) moisture convergence over land predominantly takes
place at levels significantly colder than the surface; wherever moisture supply over land is limited, the increase of evaporation
over land upon warming is limited, reducing the relative humidity in the boundary layer over land, and hence also enhancing
the land/sea contrast. The non-linearity of the Clausius–Clapeyron relationship of saturation specific humidity to temperature
is critical in (2) and (3). We examine the sensitivity of the land/sea contrast to model representations of different physical
processes using a large ensemble of climate model integrations with perturbed parameters, and find that it is most sensitive
to representation of large-scale cloud and stomatal closure. We discuss our results in the context of high-resolution and
Earth-system modelling of climate change. 相似文献
102.
T. P. S. Rawat G. B. Joshi Bhaskar Basu Nurul Absar 《Journal of the Geological Society of India》2010,75(5):709-714
Black shale type uranium deposits, though of low grade (<0.001 to 0.05% U3O8), contain large uranium resources because of their immense volume. The Neoproterozoic-Cambrian Krol-Tal Himalayan sequence
covering a cumulative area of about 1000 sq km in five different synclinal basins from Sirmour district, Himachal Pradesh
in the west to Nainital district, Uttar Pradesh in east contain such black shale horizons. The uranium mineralisation found
in black shale in the Nigalidhar syncline of Himachal Pradesh and its implication of being an indicator for search of such
uranium deposits in Himalayas is discussed. 相似文献
103.
The main objective of this study is to measure the effect of slope and grass-cover on infiltration rate, run-off and sediment
yield under simulated rainfall conditions in a badland area located in the upper Pravara Basin in western India. An automatic
rainfall simulator was designed following Dunne et al (1980) and considering the local conditions. Experiments were conducted on six selected experimental fields of 2 × 2m within
the catchment with distinct variations in surface characteristics — grass-covered area with gentle slope, recently ploughed
gently sloping area, area covered by crop residue (moderate slope), bare badland with steep slope, gravelly surface with near
flat slope and steep slope with grass-cover. The results indicate subtle to noteworthy variations amongst the plots depending
on their slope angle and surface characteristics. An important finding that emerges from the study is that the grass-cover
is the most effective measure in inducing infiltration and in turn minimizing run-off and sediment yield. Sediment yields
are lowest in gently sloping grass-covered surfaces and highest in bare badland surfaces with steep slopes. These findings
have enormous implication for this area, because over 2/3 area is characterized by bare and steep slopes. 相似文献
104.
Temperature and fresh snow are essential inputs in an avalanche forecasting model. Without these parameters, prediction of
avalanche occurrence for a region would be very difficult. In the complex terrain of Himalaya, nonavailability of snow and
meteorological data of the remote locations during snow storms in the winter is a common occurrence. In view of this persistent
problem present study estimates maximum temperature, minimum temperature, ambient temperature and precipitation intensity
on different regions of Indian western Himalaya by using similar parameters of the neighbouring regions. The location at which
parameters are required and its neighbouring locations should all fall in the same snow climatic zone. Initial step to estimate
the parameters at a location, is to shift the parameters of neighbouring regions at a reference height corresponding to the
altitude of the location at which parameters are to be estimated. The parameters at this reference height are then spatially
interpolated by using Barnes objective analysis. The parameters estimated on different locations are compared with the observed
one and the Root Mean Square Errors (RMSE) of the observed and estimated values of the parameters are discussed for the winters
of 2007–2008. 相似文献
105.
106.
Chetana Jain Biswajit Paul Kaustubh Joshi Anjan Dutta Harsha Raichur 《Journal of Astrophysics and Astronomy》2007,28(4):175-184
We report here results from a new search for orbital motion of the accretion powered X-ray pulsar 4U 1626–67 using two different
analysis techniques. X-ray light curve obtained with the Proportional Counter Array of the Rossi X-ray Timing Explorer during
a long observation carried out in February 1996, was used in this work. The spin period and the local period derivative were
first determined from the broad 2–60 keV energy band light curve and these were used for all subsequent timing analysis. In
the first technique, the orbital phase dependent pulse arrival times were determined for different trial orbital periods in
the range of 500 to 10,000 s. We have determined a 3σ upper limit of 13 lt-ms on the projected semimajor axis of the orbit of the neutron star for most of the orbital period range,
while in some narrow orbital period ranges, covering about 10% of the total orbital period range, it is 20lt-ms. In the second
method, we have measured the pulse arrival times at intervals of 100 s over the entire duration of the observation. The pulse
arrival time data were used to put an upper limit on any periodic arrival time delay using the Lomb-Scargle periodogram. We
have obtained a similar upper limit of 10 lt-ms using the second method over the orbital period range of 500–10,000 s. This
puts very stringent upper limits for the mass of the compact object except for the unlikely case of a complete face-on orientation
of the binary system with respect to our line-of-sight. In the light of this measurement and the earlier reports, we discuss
the possibility of this system being a neutron star with a supernovae fall-back accretion disk. 相似文献
107.
We present a study of magnetic fields in umbral dots (UDs) and its consequences on the Joule heating of the UDs. Hamedivafa
(Astron. Astrophys.
407, 761, 2003) studied the Joule heating using the vertical component of the magnetic field. In this paper the magnetic field profile in
the UDs is investigated by including a new azimuthal component of the magnetic field that might explain a relatively large
enhancement of Joule heating causing higher brightness near the circumference of the UDs. 相似文献
108.
Summary The temperature and moisture data from TIROS operational vertical sounder (TOVS) are examined to obtain humidity parameters like, mid and upper tropospheric water vapour, and scale height of water vapour. Their usefulness in characterizing the onset of south-west (SW) monsoon over India is studied. The NOAA satellite data (finished product) with a resolution of 2.5° lat/lon are used to obtain these parameters during and prior to the SW monsoon season over selected regions during 1979 to 1985. The pentad averaged values in the western Indian Ocean showed an increase in scale height of water vapour and mid-tropospheric moisture (700–500 mb) over about 8 to 10 days prior to the onset over Kerala coast. The association of the moisture flux across the Indian Ocean and the rainfall over Kerala coast has also been examined. Results showed that the gradient of middle level moisture is stronger in the case of rainfall deficit years.With 13 Figures 相似文献
109.
During the last few years, a remarkable anomaly between 238U and 234U activities has been observed in the top layers of the coastal sediments along the western region of the Indian sub-continent. Sediment samples from Bombay (19°N, 73°E) to Kottilppad (8°N, 77°E) were leached with saturated ammonium carbonate solution to extract uranium isotopes from the surface layers of the sediment particles without attacking the mineral cores. The 234U/238U activity ratios in these leachates are in the range of 1.12–1.14 while 235U/238U activity ratio is 0.046 which is the same as for other natural uranium.
The surface organic matter from the sediment particles was removed by treatment with hydrogen peroxide in presence of 0.05 M hydrochloric acid. 234U/238U and 235u/238U activity ratios in the extract and the residues were determined.
It is observed that disequilibrium between 238U and 234U exists only on the surface of sediment particles. 234U/238U on the surface of the sediment particles is the same as in the ambient water and as the surface organic matter is removed from the particle surface, the cores show equilibrium activities. 相似文献
110.
A limnological study was carried out in the subtropical Lake Sattal (Kumaun Himalaya) during 1979. The lake was thermally stratified during warm months and a low percentage saturation of dissolved oxygen occurred in the bottom waters. Two maxima of phytoplankton occurred in the Eastern basin in contrast to only one in the Western basin. The peak in the latter developed more than a month (October) after the second peak in the former (August). Bacillariophyceae contributed highest in the Western basin (43.2%) whereas the Dinophyceae had the least share in the Eastern basin (8.0%). Most of the dominant phytoplankters were: Synedra ulna, Fragilaria, Gymnodinium, Crucigenia and Closteridium siamensis. Interestingly, blue-green alga Nostoc, dominated for some time in autumn. A total of 12 genera of rotifers, 6 genera of cladocerans and 1 genus of copepods were found in Lake Sattal basins. Dominant zooplankters included Keratella, Cyclops, Anuraeopsis, Polyarthra and Trichocerca, and there is a high ratio of rotifers to copepods and cladocerans. On comparing the averaged values of both the basins, the Eastern basin showed a 64% larger population of zooplankton than the Western basin. A comparison is made with the plankton of the other subtropical lake-systems of this region. 相似文献