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91.
Extreme localised rainfall events are part of monsoon system occurring every year. Satellite data (TRMM and other geostationary
satellites) together with ground observations will be useful in providing spatial and temporal variability of atmospheric
changes. The short and long term variability is required for better understanding of the local and regional climatic conditions
through detailed modelling. Such information will play a key role in real time data analysis and dissemination system to the
disaster management groups in the country to minimize losses due to these extreme rainfall events. 相似文献
92.
M. R. Ramesh Kumar S. M. Pednekar M. Katsumata M. K. Antony Y. Kuroda A. S. Unnikrishnan 《Theoretical and Applied Climatology》2006,85(1-2):117-122
Summary The diurnal cycle of rainfall over the eastern equatorial Indian Ocean was studied for the period 23rd October 2001 to 31st October 2003 using hourly data from the Triton buoy positioned at 1.5° S and 90° E. An analysis of the active and weak spells
of rainfall for different seasons revealed peaks in the late evening hours in Winter, Summer and Fall and in early morning
hours (in Spring) in 2002. The active spell of rainfall peaked in the afternoon hours, during Winter, Spring and Summer in
2003, which agrees with the previous results of Janowiak et al. (1994). An analysis of rainfall events showed that Fall 2002
had a maximum number of rainfall events (90) and minimum (60) were observed in Spring 2003. Further it was found that the
majority of rain events (>60%) were less than 3 hours in duration throughout the study period. The longer duration rainfall
events (i.e. rain events greater than 6 hour duration) contributed significantly to Spring 2002 (20% of the total rainfall)
and Winter 2003 (21% of the total rainfall). Harmonic analysis of the hourly rainfall data for different seasons revealed
that diurnal harmonic explains more than 80% of the variance for all seasons. Furthermore, the diurnal harmonic has a maximum
amplitude for all seasons except summer, where the semidiurnal and six hourly harmonics are significant. 相似文献
93.
The Gauribidanur Radioheliograph 总被引:1,自引:0,他引:1
A new radio heliograph for obtaining two-dimensional images of the solar corona sequentially at many frequencies in the range 40–150 MHz has been built by the Indian Institute of Astrophysics at the Gauribidanur Radio Observatory (lat. 13°3612 N and long. 77°2707 E) about 100 km north of Bangalore, India. This paper describes various aspects of the antenna system, receiver front end, digital hardware, the data acquisition and the calibration procedure. The performance of the instrument is illustrated with maps of the continuum emission from the undisturbed corona at different frequencies. 相似文献
94.
Prakash Chauhan Shailesh Nayak R Ramesh R Krishnamoorthy S Ramachandran 《Journal of the Indian Society of Remote Sensing》1996,24(2):105-114
Indian Remote Sensing satellite (IRS) 1A & 1B digital data in combination with field measurement were used to map distribution and concentration of suspended sediments along the Tamil Nadu coastal waters for monsoon and non-monsoon periods. Qualitative suspended sediment mapping was done for entire Tamil Nadu coast while quantitative studies were taken at two selected sites (eg. Tuticorin and Ennore). For qualitative mapping both monsoon (17-12-90) and non-monsoon (18-4-90) season data were analysed by level slicing technique and a qualitative scale was assigned to different sediment classes based on tonal variations. The suspended sediment concentration (SSC) samples were collected on April 15, 1992 and March 10, 1992 around Ennore and Tuticorin coastal waters respectively, synchronous to IRS-1A satellite overpass. This data was used for quantitative estimation of SSC using digital chromaticity technique. The study shows that the plumes of high suspended sediment concentration are contributed from the nearshore wetlands and river mouths and were finally dispersing towards Jaffna coast. Different classes of high to low SSC values ranging from less than 5 mg/L in offshore areas to 21 mg/L in nearshore of Tuticorin were also delineated. The dispersal pattern of the sediments on different is discussed. 相似文献
95.
H M Iyer V K Gaur S S Rai D S Ramesh CVR Rao D Srinagesh K Suryaprakasam 《Journal of Earth System Science》1989,98(1):31-60
Analysis of teleseismicP-wave residuals observed at 15 seismograph stations operated in the Deccan volcanic province (DVP) in west central India points
to the existence of a large, deep anomalous region in the upper mantle where the velocity is a few per cent higher than in
the surrounding region. The seismic stations were operated in three deployments together with a reference station on precambrian
granite at Hyderabad and another common station at Poona. The first group of stations lay along a west-northwesterly profile
from Hyderabad through Poona to Bhatsa. The second group roughly formed an L-shaped profile from Poona to Hyderabad through
Dharwar and Hospet. The third group of stations lay along a northwesterly profile from Hyderabad to Dhule through Aurangabad
and Latur. Relative residuals computed with respect to Hyderabad at all the stations showed two basic features: a large almost
linear variation from approximately +1s for teleseisms from the north to—1s for those from the southeast at the western stations,
and persistance of the pattern with diminishing magnitudes towards the east. Preliminary ray-plotting and three-dimensional
inversion of theP-wave residual data delineate the presence of a 600 km long approximately N−S trending anomalous region of high velocity (1–4%
contrast) from a depth of about 100 km in the upper mantle encompassing almost the whole width of the DVP. Inversion ofP-wave relative residuals reveal the existence of two prominent features beneath the DVP. The first is a thick high velocity
zone (1–4% faster) extending from a depth of about 100 km directly beneath most of the DVP. The second feature is a prominent
low velocity region which coincides with the westernmost part of the DVP. A possible explanation for the observed coherent
high velocity anomaly is that it forms the root of the lithosphere which coherently translates with the continents during
plate motions, an architecture characteristic of precambrian shields. The low velocity zone appears to be related to the rift
systems (anomaly 28, 65 Ma) which provided the channel for the outpouring of Deccan basalts at the close of the Cretaceous
period. 相似文献
96.
97.
R. P. Dhir S. K. Tandon B. K. Sareen R. Ramesh T. K. G. Rao A. J. Kailath N. Sharma 《Journal of Earth System Science》2004,113(3):473-515
The calcretes in the Thar desert occur in a variety of settings, including the piedmonts, sheetwash aggraded plains; and this
study adds calcretes in regolith and colluvio-alluvial plains to the group of settings in which calcretes occur in the region.
Field logs, morphological details and analytical data such as petrographic, cathodoluminescence and geochemical characteristics
are described along with a discussion on their implications. Sand dunes and sandy plains dating to < 20 ka have weakly developed
calcretes. The better-developed calcrete horizons occur in piedmonts, interdunes or in areas that have sufficient groundwater.
Deep sections in the region show phases of calcrete development in aeolian sand aggradation at ∼ 150, ∼ 100, ∼ 60 and 27–14
ka. The extensive sheetwash plains have mature calcretes and date to mid-Pleistocene. Our studies indicate that these calcretes
represent a hybrid process, where carbonate enrichment of the originally calcareous host occurred due to periodically raised
groundwaters, and its differentiation into nodules occurred under subaerial environment i.e., after recession of groundwater.
Deep sections also show a stack of discrete calcretes that developed in individual aggradation episodes with hiatuses as indicated
by ESR dating results. Nodules display a multiplicity of carbonate precipi tation events and internal reorganization of calcitic
groundmass. The process is accompanied by degradation and transformation of unstable minerals, particularly clays and with
a neosynthesis of palygorskite.
The ancient calcretes are dated from the beginning of the Quaternary to ∼ 600 ka and show more evolved morphologies marked
by brecciation, dissolution, laminar growth on brecciated surfaces, pisolites and several generations of re-cementation. Mica/chlorite
schists and such other rocks are particularly vulnerable to replacement by carbonate. In an extreme case, replacement of quartzose
sandstone was observed also. The presence of stretches of alluvio-colluvial plains in an area presently devoid of drainage
bespeaks of occasional high-energy fluvial regime, under a semi-arid climate. The mid-Pleistocene period saw a shift towards
more arid climate and this facilitated sheetwash aggradation. Finally, during the late Pleistocene, aggradation of aeolian
sands indicated a progressively drier climate. However, this does not find its reflection in stable isotope data. The amount
of carbonate in the form of calcretes is substantial. The present studies indicate that aeolian dust or rainwater are minor
contributors to the carbonate budget. A more important source was provided by the pre-existing calcretes in the sheetwash
aggraded plains and detrital carbonate in the aeolian sediments. The original source of carbonate in the region, however,
remains unresolved and will need further investigations. Electron spin resonance protocols for the dating of calcretes were
developed as a part of this study and the results accorded well with geological reasoning 相似文献
98.
Ramesh Narayan 《Astronomy& Geophysics》2003,44(6):6.22-6.26
The George Darwin Lecture presented at the Royal Astronomical Society, London, 13 December 2002, by Ramesh Narayan . 相似文献
99.
100.
P Gupta V Khanna T Onong Thirunadha Rao N Dube D Dhar R Ramakrishnan K L Majumder 《Journal of the Indian Society of Remote Sensing》2002,30(1-2):7-13
In this paper, we have described a model to parallelize the resampling routine, which is used in the geometric correction of data provided by remote sensing satellites. Our model is a typical master-slave model consisting of N machines termed as hosts out of which one is designated as the master. The input image data resides on the master. Processing of the input image data is done in parallel on the N machines. Issues related to load-balancing and various error conditions that may occur during execution like one of the machines going down have been studied and are incorporated in the model. It also provides the flexibility to add or delete the hosts during the execution of the resampling routine. The serial version of this routine involves huge amount of computations and takes substantial amount of time even for an image of 473 MB. We have implemented our model with the help of PVM which is most often used in distributed computing environment. Our approach has been tested for geometric correction on LISS-III 4 band data of size 473 MB. It is found that if one uses 2, 3 or 4 hosts the overall execution time is reduced by 33%, 42% and 49%, respectively. 相似文献