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81.
George Mathew Archana Nair T. K. Gundu Rao Kanchan Pande 《Journal of Earth System Science》2009,118(4):391-404
Thermal infrared spectroscopy is a powerful technique for the compositional analysis of geological materials. The spectral
feature in the mid-IR region is diagnostic of the mineralogy and spectral signatures of mixtures of minerals that add linearly,
and therefore, can be used as an important tool to determine the mineralogy of rocks in the laboratory and remotely for planetary
exploration. The greatest challenge in the emission measurement lies in the measurement of the weak thermal photons emitted
from geological materials in a laboratory setup, and accurately records the temperature of the rock sample. The present work
pertains to the details of a new Thermal Emission Spectrometer (TES) laboratory that has been developed under the ISRO Planetary
Science and Exploration (PLANEX) programme, for emission related mineralogical investigations of planetary surfaces. The focus
of the paper is on the acquisition and calibration technique for obtaining emissivity, and the deconvolution procedure to
obtain the modal abundances of the thermal emission spectra in the range of 6–25 μm using Fourier Transform Infrared (FTIR)
spectroscopy. The basic technique is adopted from the work of Ruff et al (1997). This laboratory at the Department of Earth Sciences, IIT-Bombay is currently developing pure end mineral library
of mineral particulates (<65 μm), and adding new end members to the existing ASU spectral library. The paper argues the need
for considering Lunar Orbiter Thermal Emission Spectrometer (LOTES) for future Indian Moon mission programme (Chandrayan-II)
to determine evidences of varied lithologies on the lunar surface. 相似文献
82.
Evidence for a mantle and/or basaltic component in KT boundary distal ejecta is apparently inconsistent with ejection from Chicxulub Crater since it is located on~35km thick continental crust(De Paolo et al.,1983;Montanari et al.,1983;Hildebrand and Boynton,1988,1990).Evidence for mafic/ultramafic target rocks was reinforced by discovery of chromites,some with shock planar deformation features(PDF),in impact layer samples from sites in southern Colorado and eastern Wyoming(Bohor et al.,1990).However,until now it was unclear whether the chromites originated with an impactor or with terrestrial target rocks.To this end,high-precision 54Cr/52Cr isotope ratios were measured on KT boundary chromites along with known terrestrial chromites.We find a terrestrial 54Cr/52Cr ratio in KT boundary chromites from impact layer samples collected at the above sites over the last several years(Fig.1).Ejected terrestrial chromites suggest the impact sampled terrestrial mafic and/or ultramafic target rocks not known to exist in the Chicxulub target area. 相似文献
83.
Pramit Kumar Deb Burman Dipankar Sarma Mathew Williams Anandakumar Karipot Supriyo Chakraborty 《Journal of Earth System Science》2017,126(7):99
Tropical forests act as a major sink of atmospheric carbon dioxide, and store large amounts of carbon in biomass. India is a tropical country with regions of dense vegetation and high biodiversity. However due to the paucity of observations, the carbon sequestration potential of these forests could not be assessed in detail so far. To address this gap, several flux towers were erected over different ecosystems in India by Indian Institute of Tropical Meteorology as part of the MetFlux India project funded by MoES (Ministry of Earth Sciences, Government of India). A 50 m tall tower was set up over a semi-evergreen moist deciduous forest named Kaziranga National Park in north-eastern part of India which houses a significant stretch of local forest cover. Climatically this region is identified to be humid sub-tropical. Here we report first generation of the in situ meteorological observations and leaf area index (LAI) measurements from this site. LAI obtained from NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS) is compared with the in situ measured LAI. We use these in situ measurements to calculate the total gross photosynthesis (or gross primary productivity, GPP) of the forest using a calibrated model. LAI and GPP show prominent seasonal variation. LAI ranges between 0.75 in winter to 3.25 in summer. Annual GPP is estimated to be \(2.11\,\hbox {kg C m}^{-2} \, \hbox {year}^{-1}\). 相似文献
84.
Boby Mathew B. M. Pathan K. N. Iyer D. R. K. Rao 《Journal of Earth System Science》1991,100(4):331-340
Using simultaneous long-term observations of ionospheric scintillation at equator and anomaly crest region in the same longitude
(Indian) zone comparative features of scintillation occurrence are brought out. The salient features are: (a) predominantly
pre-midnight occurrence of scintillation at equator during winter and equinox seasons, (b) increase of pre-midnight scintillation
occurrence with solar activity (c) shifting of occurrence peak during summer from post-midnight in low to pre-midnight in
high solar activity periods (d) similarity of scintillation behaviour at these locations during winter and equinoxes but dissimilarity
during summer. The solar activity response and magnetic effects indicate that the scintillations at the anomaly crest region
in winter and equinox, particularly during high solar activity periods, are of equatorial origin while the summer events may
be of local or mid-latitude origin. 相似文献
85.
David W. Pierce Tim P. Barnett Robin Tokmakian Albert Semtner Mathew Maltrud JoAnne Lysne Anthony Craig 《Climatic change》2004,62(1-3):13-28
A problem for climate change studies with coupled ocean-atmosphere models has been how to incorporate observed initial conditions into the ocean, which holds most of the `memory' of anthropogenic forcing effects. The first difficulty is the lack of comprehensive three-dimensional observations of the current ocean temperature (T) and salinity (S) fields to initialize to. The second problem is that directly imposing observed T and S fields into the model results in rapid drift back to the model climatology, with the corresponding loss of the observed information. Anthropogenic forcing scenarios therefore typically initialize future runs by starting with pre-industrial conditions. However, if the future climate depends on the details of the present climate, then initializing the model to observations may provide more accurate forecasts. Also, this ~ 130 yr spin up imposes substantial overhead if only a few decades of predictions are desired. A new technique to address these problems is presented. In lieu of observed T and S, assimilated ocean data were used. To reduce model drift, an anomaly coupling scheme was devised. This consists of letting the model's climatological (pre-industrial) oceanic and atmospheric heat contents and transports balance each other, while adding on the (much smaller) changes in heat content since the pre-industrial era as anomalies. The result is model drift of no more than 0.2 K over 50 years, significantly smaller than the forced response of 1.0 K. An ensemble of runs with these assimilated initial conditions is then compared to a set spun up from pre-industrial conditions. No systematic differences were found, i.e., the model simulation of the ocean temperature structure in the late 1990s is statistically indistinguishable from the assimilated observations. However, a model with a worse representation of the late 20th century climate might show significant differences if initialized in this way. 相似文献
86.
S. S. C. Shenoi D. Shankar G. S. Michael J. Kurian K. K. Varma M. R. Ramesh Kumar A. M. Almeida A. S. Unnikrishnan W. Fernandes N. Barreto C. Gnanaseelan R. Mathew K. V. Praju V. Mahale 《Journal of Earth System Science》2005,114(5):475-491
This paper describes the hydrographic observations in the southeastern Arabian Sea (SEAS) during two cruises carried out in
March–June 2003 as part of the Arabian Sea Monsoon Experiment. The surface hydrography during March–April was dominated by
the intrusion of low-salinity waters from the south; during May–June, the low-salinity waters were beginning to be replaced
by the highsalinity waters from the north. There was considerable mixing at the bottom of the surface mixed layer, leading
to interleaving of low-salinity and high-salinity layers. The flow paths constructed following the spatial patterns of salinity
along the sections mimic those inferred from numerical models. Time-series measurements showed the presence of Persian Gulf
and Red Sea Waters in the SEAS to be intermittent during both cruises: they appeared and disappeared during both the fortnight-long
time series. 相似文献
87.
Evidence of paleoearthquakes from trench investigations across Pinjore Garden fault in Pinjore Dun, NW Himalaya 总被引:2,自引:0,他引:2
The Pinjore Garden Fault (PGF) striking NNW-SSE is now considered one of the active faults displacing the younger Quaternary
surfaces in the piggyback basin of Pinjore Dun. This has displaced the older Kalka and Pinjore surfaces, along with the other
younger surfaces giving rise to WSW and SW-facing fault scarps with heights ranging from 2 to 16 m. The PGF represents a younger
branch of the Main Boundary Thrust (MBT) system. An ~ 4m wide trench excavated across the PGF has revealed displacement of
younger Quaternary deposits along a low angle thrust fault. Either side of the trench-walls reveals contrasting slip-related
deformation of lithounits. The northern wall shows displacement of lithounits along a low-angle thrust fault, while the southern
wall shows well-developed fault-related folding of thick sand unit. The sudden change in the deformational features on the
southern wall is an evidence of the changing fault geometry within a short distance. Out of five prominent lithounits identified
in the trench, the lower four units show displacement along a single fault. The basal unit ‘A’ shows maximum displacement
of aboutT
o
= 2.85 m, unit B = 1.8 m and unit C = 1.45 m. The displacement measured between the sedimentary units and retro-deformation
of trench log suggests that at least two earthquake events have occurred along the PGF. The units A and D mark the event horizons.
Considering the average amount of displacement during one single event (2 m) and the minimum length of the fault trace (~
45 km), the behaviour of PGF seems similar to that of the Himalayan Frontal Fault (HFF) and appears capable of producing large
magnitude earthquakes. 相似文献
88.
Production rates of15N by both solar cosmic rays (SCR) and galactic cosmic rays (GCR) have been calculated for moon, as well as meteorites of various
sizes. Our production rates of15N which considered both the reaction channels16O(p, pn)15O and16O(p, 2p)15N separately are about 30% higher than those by Reedy (1981) who considered only the channel16O(p, pn)15O and used an empirical scaling factor to estimate the contribution from16O(p, 2p)15N. Production ratio15N21 Ne is composition dependent and hence is different for various silicate minerals. Additionally the ratio15N/21Ne is very sensitive to the energy spectrum of the cosmic rays. This fact can be made use of in characterizing as well as
in decoupling the SCR and GCR effects in extraterrestrial samples. 相似文献
89.
The short-term variability observed in the near surface meteorological parameters and in the vertical thermal structure of
the upper layers of the northern Bay of Bengal during a weak monsoonal regime is examined with the aid of time series measurements.
The variability of the mixed layer depth is interpreted in terms of forced mixing caused by the surface wind stress and free
mixing by buoyancy flux, Ekman pumping controlled by the curl of the surface wind stress, convergence associated with a clockwise
gyral circulation and stratification caused by freshwater discharges from rivers. The daily-averaged current vectors in the
upper layers indicate the presence of clockwise gyral circulation in the polygon area. 相似文献
90.
Jose Villanueva-Diaz David W. Stahle Brian H. Luckman Julian Cerano-Paredes Mathew D. Therrell Malcom K. Cleaveland Eladio Cornejo-Oviedo 《Climatic change》2007,83(1-2):117-131
The understanding of historic hydroclimatic variability is basic for planning proper management of limited water resources
in northeastern Mexico. The objective of this study was to develop a network of tree-ring chronologies to reconstruct hydroclimate
variability in northeastern Mexico and to analyze the influence of large-scale circulation patterns, such as ENSO. Precipitation
sensitive tree-ring chronologies of Douglas-fir were developed in mountain ranges of the Sierra Madre Oriental and used to
produce winter-spring precipitation reconstructions for central and southern Nuevo Leon, and southeastern Coahuila. The seasonal
winter-spring precipitation reconstructions are 342 years long (1659–2001) for Saltillo, Coahuila and 602 years long (1400–2002)
for central and southern Nuevo Leon. Both reconstructions show droughts in the 1810s, 1870s, 1890s, 1910s, and 1970s, and
wet periods in the 1770s, 1930s, 1960s, and 1980s. Prior to 1800s the reconstructions are less similar. The impact of ENSO
in northeastern Mexico (as measured by the Tropical Rainfall Index) indicated long-term instability of the Pacific equatorial
teleconnection. Atmospheric circulation systems coming from higher latitudes (cold fronts or `nortes’) and others developed
in the Gulf of Mexico (tropical storms, hurricanes) also influence the climatic conditions characterizing this region. The
recent development of new and longer tree-ring chronologies for the region will contribute to a better understanding of the
interannual and multidecadal climatic variability of northeastern Mexico. 相似文献