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141.
Thomas Oommen Anupma Prakash Debasmita Misra Sathy Naidu John J. Kelley Sukumar Bandopadhyay 《Marine Georesources & Geotechnology》2008,26(1):1-18
Goodnews Bay, southwest Alaska, is known for platinum (Pt) reserve that extends offshore in the Bering Sea. To assess the nearshore placer potential we first collated marine Pt concentrations available since 1960 in a geographic information system (GIS) database. Subsequently, in 2005, we collected 23 pipe dredge sediment samples and 26 vibracores from unexplored sites and analyzed them for Pt. This sampling was supplemented by magnetic (Sea Spy) and seismic (side scan, geoacoustic and datasonic bubble pulser) surveys. Integrating results of geospatial analysis of Pt concentrations with geophysical analysis using GIS techniques led to delineate four locations encouraging for further Pt exploration. Of these, two locations fall close to paleochannels and drowned ultramafic source, while the other two coincide with high energy environments in the Goodnews Bay and close to the Carter Bay. 相似文献
142.
The space–time structure of the daily atmospheric variability in the South American monsoon system has been studied using multichannel singular spectrum analysis of daily outgoing longwave radiation. The three leading eigenmodes are found to have low-frequency variability while four other modes form higher frequency oscillations. The first mode has the same time variability as that of El Nino-Southern Oscillation (ENSO) and exhibits strong correlation with the Pacific sea surface temperature (SST). The second mode varies on a decadal time scale with significant correlation with the Atlantic SST suggesting an association with the Atlantic multidecadal oscillation (AMO). The third mode also has decadal variability but shows an association with the SST of the Pacific decadal oscillation (PDO). The fourth and fifth modes describe an oscillation that has a period of about 165 days and is associated with the North Atlantic oscillation (NAO). The sixth and seventh modes describe an intraseasonal oscillation with a period of 52 days which shows strong relation with the Madden-Julian oscillation. There exists an important difference in the variability of convection between Amazon River Basin (ARB) and central-east South America (CESA). Both regions have similar variations due to ENSO though with higher magnitude in ARB. The AMO-related mode has almost identical variations in the two regions, whereas the PDO-related mode has opposite variations. The interseasonal NAO-related mode also has variations of opposite sign with comparable magnitudes in the two regions. The intraseasonal variability over the CESA is robust while it is very weak over the ARB region. The relative contributions from the low-frequency modes mainly determine the interannual variability of the seasonal mean monsoon although the interseasonal oscillation may contribute in a subtle way during certain years. The intraseasonal variability does not seem to influence the interannual variability in either region. 相似文献
143.
This paper intends to explore whether there is an important source for monazite beach placer of the Gopalpur-Chhatrapur-Rushikulya
coast, Orissa, in the adjacent Eastern Ghat Mobile Belt (EGMB). Petrographic and mineralogical studies were conducted on all
the rock types constituting the EGMB exposed over a stretch extended up to ∼20 km landward from the estuary of the River Rushikulya
that is believed to transport the major bulk of sand to the Gopalpur-Chhatrapur-Rushikulya beach. Heavy mineral population
was concentrated using bromoform and percentages of each heavy mineral constituting the population were estimated for all
the potential source rock types. Isodynamic separation and XRD techniques were deployed for precision identification of every
heavy mineral present. The study identified the granitoid (or migmatite) basement rock as by far the major contributor of
monazite to the Chhatrapur beach sand. The study also reveals that charnockite is an important contributor of orthopyroxene
as well as garnet, although the sillimanite-garnet-quartz schist (khondalites) is also an important source for the latter.
On the other hand, garnet-quartz schist and garnet-biotite-quartz schist may also contribute substantial quantity of pyroxene
and garnet. The high grade metasedimentary rocks, in general, could be the major sources for rutile, while ilmenite, magnetite
and zircon in the beach sand have their sources perhaps in all the varieties of rocks constituting the EGMB. 相似文献
144.
K. Ramesh Kumar Dheeraj Pande Arpan Misra L. K. Nanda 《Journal of the Geological Society of India》2011,77(1):89-94
The Didwana playa, the second largest playa in the eastern part of the Thar desert, is 5.6 km long and 2.4 km wide and supports
commercial salt production. The thickness of lake sediment package is reported to be 20 m and comprises fine grained clays
and silts, with abundant calcite, gypsum, and halite, associated with hypersaline water. Isolated hills of graphitic phyllite
and quartzite are seen on the western side of the lake. During the course of investigations for uranium in surficial environment
of semi-arid terrain of Rajasthan, ground water sampling defined a NE-SW trending uranium halo encompassing the Didwana playa.
Subsequent sampling of unlined dug wells, up to water table in central part of the playa, indicated uranium values up to 190
ppm and 2072 ppb in lake sediments and brine respectively. These values are of the order of 21 ppm and 192 ppb towards the
southwestern periphery of the lake. The average uranium content, as inferred from 12 samples in the central part of the lake,
is around 60 ppm over a thickness of 5 m. It appears that the uranium is loosely bonded to the sediments in amorphous form
and is, hence, easily leachable. Samples of brine (n=10), from both the central and southwestern portions of the lake, analysed
high (1,67,500–3,00,000 mg/l) TDS, HCO3− (1128–8395 mg/l), and SO4 (30,536–88,000 mg/l). These are of alkaline (pH: 7.2–9.3) and reducing (Eh: −200 to −340 mV) nature. Under these Eh-pH conditions
below the groundwater table, and for such uranium bearing groundwater, precipitation of primary uranium is expected. It is,
therefore, modelled that uranium in lake sediment package above water table is concentrated by evaporation process and by
chemical reduction below the water table. 相似文献
145.
P. K. Misra A. K. Jauhri R. P. Tiwari S. Kishore Ajay Pratap Singh S. K. Singh 《Journal of the Geological Society of India》2011,78(4):355-364
The present paper records nine species of coralline algae from the Prang Formation of middle-late Eocene age from the Jaintia
Hills, Meghalaya. The algae are associated with the larger foraminifera including Nummulites, Alveolina and Discocyclina throughout the succession. The temporal distribution of algal species indicates that seven species are known from the Eocene.
Of the remaining two, one ranges from the Palaeocene to Eocene and the other is Palaeocene in age. The coralline algae and
larger foraminifers are differentiated into two associations, the lower one indicating inner-ramp environment of high energy
and the upper one showing deposition in relatively calm waters of deeper ramp environment. 相似文献
146.
Kuntal Misra Dave Pooley † Poonam Chandra D. Bhattacharya Alak K. Ray Ram Sagar Walter H. G. Lewin 《Monthly notices of the Royal Astronomical Society》2007,381(1):280-292
We present X-ray, broad-band optical and low-frequency radio observations of the bright type IIP supernova SN 2004et. The Chandra X-ray Observatory observed the supernova at three epochs, and the optical coverage spans a period of ∼470 d since explosion. The X-ray emission softens with time, and we characterize the X-ray luminosity evolution as L X ∝ t −0.4 . We use the observed X-ray luminosity to estimate a mass-loss rate for the progenitor star of ∼2 × 10−6 M⊙ yr−1 . The optical light curve shows a pronounced plateau lasting for about 110 d. Temporal evolution of photospheric radius and colour temperature during the plateau phase is determined by making blackbody fits. We estimate the ejected mass of 56 Ni to be 0.06 ± 0.03 M⊙ . Using the expressions of Litvinova & Nadëzhin we estimate an explosion energy of (0.98 ± 0.25) × 1051 erg . We also present a single epoch radio observation of SN 2004et. We compare this with the predictions of the model proposed by Chevalier, Fransson & Nymark. These multiwavelength studies suggest a main-sequence progenitor mass of ∼20 M⊙ for SN 2004et. 相似文献
147.
148.
The 27 April 1975 Kitimat,British Columbia,submarine landslide tsunami: a comparison of modeling approaches 总被引:1,自引:0,他引:1
We present numerical simulations of the April 27, 1975, landslide event in the northern extreme of Kitimat Arm, British Columbia. The event caused a tsunami with an estimated wave height of 8.2 m at Kitimat First Nations Settlement and 6.1 m at Clio Bay, at the northern and southern ends of Kitimat Arm, respectively. We use the nonhydrostatic model NHWAVE to perform a series of numerical experiments with different slide configurations and with two approaches to modeling the slide motion: a solid slide with motion controlled by a basal Coulomb friction and a depth-integrated numerical slide based on Newtonian viscous flow. Numerical tests show that both models are capable of reproducing observations of the event if an adequate representation of slide geometry is used. We further show that comparable results are obtained using estimates of either Coulomb friction angle or slide viscosity that are within reasonable ranges of values found in previous literature. 相似文献
149.
Evapotranspiration (ET) is a vital process in land surface atmosphere research. In this study, Surface Energy Balance Algorithm for Land (SEBAL) for the assessment of ET (for 23 December 2010, 8 January 2011, 24 January 2011, 9 February 2011, 25 February 2011, 29 March 2011 and 14 April 2011) from LANDSAT7-ETM+ and validation with Lysimeter data set is illustrated. It is based on the evaporative fraction concept, and it has been applied to LANDSAT7-ETM + (30 m resolution) data acquired over the Indian Agricultural Research Institute’s agricultural farm land. The ET from SEBAL was compared with Lysimeter ET using four statistical tests (root-mean-square error (RMSE), relative root-mean-square error (R-RMSE), mean absolute error (MAE), and normalized root-mean square error (NRMSE)), and each test showed a good correlation between the predicted and observed ET values. Results from this study revealed that the RMSE of crop-growing period was 0.51 mm d?1 for ETSEBAL, i.e. ETSEBAL having good accuracy with respect to observed ETLysimeter. Results were also validated using R-RMSE test, which also proved that ETSEBAL data are having good accuracy with respect to observed ETLysimeter as R-RMSE of crop-growing period is 0.19 mm d?1. MAE (0.19), NRMSE (0.21) and r2 (0.91) tests indicated that model prediction is significant, and model can be effectively used for the estimation of ET from SEBAL as input of remote sensing data sets. Finally, the SEBAL has been useful for remote agricultural land where ground-based data (Lysimeter data) are not available for daily ET (ET24 h) estimation. The temporal study of the ET24 h values analysed has revealed that the highest ET24 h values are owing to the higher development (high greenness) of crops, whereas the lower values are related to the lower development (low greenness) or null crop. 相似文献
150.
Samaddar Subhajyoti Choi Junho Misra Bijay Anand Tatano Hirokazu 《Natural Hazards》2015,75(2):1531-1554
Natural Hazards - Recent decades have seen an increasing recognition and consensus among researchers and planners in disaster management in the need to foster social learning... 相似文献