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91.
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
92.
Landslide zoning in a part of the Garhwal Himalayas 总被引:21,自引:1,他引:20
The Himalayas are undergoing constant rupturing in the thrust belt zone in the Garhwal Himalayas, due to which earthquake
and mass movement activity is triggered. These processes of mass movement and landslides have been constantly modifying the
landscape. Landslides are one of the indicators of the geomorphological modifications taking place in this active and fragile
terrain. This work is aimed at providing another example of landslide susceptibility mapping based on geological and geomorphological
attributes. The data collected from aerial photographs, topographic sheets and the image suggests that there is a correlation
between the distribution of landslides and some of the geological and geomorphological factors, for example, the distance
from an active fault, relative relief and slope. Parameters like factor of safety, altitude, relief, slope and the distance
from the fault lineament have been included in the study. A rating system has been applied to the factors for arriving at
a quantitative estimate of landslide susceptibility for each physiographic unit. Since terrain classification forms the foundation
of this work, the entire study can be grouped into two sequential activities: (1) the terrain classification and (2) landslide
susceptibility mapping. The result is the landslide susceptibility zoning map presented. The landslides have not been classified
with respect to time and may represent the final result of the on-going geological, geomorphological and seismic activity
since the Holocene period or late Pleistocene time when the glaciers retreated.
The area chosen for the study lies between Badri gad and Barni gad in Yamuna valley region of the Garhwal Himalaya where a
very large scale investment is in the pipe line for Hydroelectric power generation.
Received: 12 August 1993 · Accepted: 13 January 1998 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.
Irene Sarkar R. Chander K. N. Khattri V. K. Gaur 《Journal of Earth System Science》1987,96(3):229-238
The paper describes an algorithm for estimating the hypocentral coordinates and origin time of local earthquakes when the
wave speed model to be employed is a layered one with dipping interfaces. A constrained least-squared error problem has been
solved using the penalty function approach, in conjunction with the sequential unconstrained optimization technique of Fiacco
and McCormick. Joint confidence intervals for the computed parameters are estimated using the approach of Bard for nonlinear
problems. These results show that when a hypocentre lies outside the array of recording stations and head waves from a dipping
interface are involved, then its inclination must be taken into account for dip angles exceeding 5°. 相似文献
96.
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
97.
An analysis of the meteorological data collected by the research vessel ORV Sagarkanya for the mean latent and sensible heat
fluxes over the Arabian Sea has indicated appreciable changes between active and weak phases of the southwest monsoon of 1986.
We suggest that: (a) the presence of a core of low level winds associated with the Somali jet and its southward shift during
the season, along with (b) a ridge in surface pressure over the central Arabian Sea could be responsible for the deficit in
monsoon rainfall along the west coast of India in 1986. 相似文献
98.
99.
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
100.
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