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51.
Diwakar A Qureshi MH 《Population geography : a journal of the Association of Population Geographers of India》1992,14(1-2):27-36
"Metropolitanisation has been observed by experts as one of the main characteristics of Indian urbanisation. Rural to urban migration has been a major player in urban growth of metropolitan cities, particularly Delhi. Not only Delhi but its hinterland [are] urbanising fast as compared to the hinterlands of other major cities of India. There are several processes of urbanization viz. historical, physical, demographic and economic. In this paper the role of demographic processes in urban expansion of Delhi [is examined]." 相似文献
52.
High-speed solar wind streams (HSWS) were identified for solar cycles 22 and 23 (up to 2004). Preliminarily, HSWS were classified
in three groups according to their continuous period of occurrence. In the declining phase of solar cycle 23, 2003 is found
to be anomalous, showing a very large number of HSWS events of long duration (> ten days). We have studied the effect of HSWS
on the cosmic-ray intensity as well as their relationship with geomagnetic disturbance index Ap on yearly, daily, and hourly bases. The yearly average of solar-wind speed was also found to be maximum in 2003. Being within
the declining phase of solar activity, the occurrence of solar flares in 2003 is quite low. In particular during HSWS, no
solar flares have been observed. Associations with cosmic-ray changes do not support the notion that the HSWS are usually
effective in producing significant cosmic-ray decreases. Out of 12 HSWS events observed during the period 2002 (December)
to 2003, four events of significant cosmic-ray decreases at all the stations have been selected for further analysis. The
cosmic-ray intensity has been found to decrease during the first phase of the event (first five days of HSWS) at all three
neutron-monitor stations situated at different latitudes with different cutoff rigidities. The rigidity spectra of observed
decreases in cosmic-ray intensity for these four cases have been found to be significantly different than that of Fds (Forbush
decrease). In two cases the spectra are softer, whereas in the other two they are harder than that of Fds. However, if the
average of all four events is considered together then the spectra of the decrease in cosmic rays during HSWS exactly match
that of Fds. Such a result implies that initially individual events should be considered, instead of combining them together,
as was done earlier. The Ap index is also found to generally increase in the first phase of the event. However, the four events selected on the basis
of cosmic-ray decrease are not always associated with enhanced values of the Ap index. As such, the significance of our study is that further detailed investigations for much longer periods and on an event-by-event
basis is required to understand the effect of coronal-hole-associated HSWS. 相似文献
53.
The electrostatic ion-cyclotron instability (EICI) in low β (ratio of plasma to magnetic pressure), anisotropic, inhomogeneous
plasma is studied by investigating the trajectories of the particles using the general loss-cone distribution function (Dory-Guest-Harris
type) for the plasma ions. In particular, the role of the loss-cone feature as determined by the loss-cone indices, in driving
the drift-cyclotron loss-cone (DCLC) instability is analysed. It is found that for both long and short wavelength DCLC mode
the loss-cone indices and the perpendicular thermal velocity affect the dispersion equation and the growth rate of the wave
by virtue of their occurrence in the temperature anisotropy. The dispersion relation for the DCLC mode derived here using
the particle aspect analysis approach and the general loss-cone distribution function considers the ion diamagnetic drift
and also includes the effects of the parallel propagation and the ion temperature anisotropy. It is also found that the diamagnetic
drift velocity due to the density gradient of the plasma ions in the presence of the general loss-cone distribution acts as
a source of free energy for the wave and leads to the generation of the DCLC instability with enhanced growth rate. The particle
aspect analysis approach used to study the EICI in inhomogeneous plasma gives a fairly good explanation for the particle energisation,
wave emission by the wave–particle interaction and the results obtained using this particle aspect analysis approach are in
agreement with the previous theoretical findings using the kinetic approach. 相似文献
54.
55.
Manish Tiwari Rengaswamy Ramesh Ravi Bhushan Madavalm S. Sheshshayee Bammidipati L. K. Somayajulu A. J. Timothy Jull George S. Burr 《第四纪科学杂志》2010,25(7):1179-1188
A few studies from the western Arabian Sea indicate that the Indian summer (or southwest) monsoon (ISM), after attaining its maximum intensity at ca. 9 ka, declined during the Holocene, as did insolation. In contrast, earlier and later observations from both the eastern and the western Arabian Sea do not support this inference. Analysis of multiple proxies of productivity in a new sediment core from the western Arabian Sea fails to confirm the earlier, single‐proxy (e.g. abundance of Globigerina bulloides) based, inference of the Holocene weakening of ISM, following insolation. The reason for the observed decreasing trend in foraminiferal abundance – the basis for the earlier inference – could be the favouring of silicate rather than carbonate productivity by the increased ISM wind strength. Although ISM exhibits several multi‐millennial scale fluctuations, there is no evidence from several multi‐proxy data to conclude that it declined during the Holocene; this is consistent with the phase lag analysis of longer time series of monsoon proxies. Thus, on sub‐Milankovitch timescales, ISM did not follow insolation, highlighting the importance of internal feedbacks. A comparison with East Asian summer monsoon (EASM) records suggests that both ISM and EASM varied in unison, implying common forcing factors on such longer timescales. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
56.
The spatial and temporal distribution of total ozone over India and its vertical distribution in theatmosphere during 1964–1969 was studied using Dobson spectrophotometer data at a network of six stations in India, Srinagar (34°N), New Delhi (28°N), Varanasi (24°N), Ahmedabad (23°N), Dum Dum (22°N), and Kodaikanal (10°N). The annual and seasonal variations show a clear phase-shift in the occurrence of the ozone maxima and minima as one proceeds from higher to lower latitudes in the tropics. In the northern stations (north of 25°N) the increase in total ozone during the course of the annual variation is caused by the fractional increase in all layers from the ground to 28 km, the main contribution coming from 10–24 km. Above 28 km the concentration changes roughly in accordance with photochemical production.In lower latitudes (south of 25°N) an increase in total ozone amount during the annual cycle is caused by a gradual increase in all the layers from the ground to 36 km above which the variation is negligible. 相似文献
57.
KP. Tiwari 《Journal of the Indian Society of Remote Sensing》1974,2(2):65-73
The use of panchromatic (black & white) aerial photographs on 1:15,000 scale for forest type mapping and evolving a suitable basis of volume stratification for man-made forests of Haldwani Division of U.P. is discussed. Forest types by species, height and density were identified and ground survey data collected in 0.1 hectare circular plots were used to evolve the basis of volume stratification by statistical analysis. The methodology used for pilot studies before regional surveys are undertaken is presented. 相似文献
58.
Giriraj Tiwari 《Pure and Applied Geophysics》1971,91(1):71-75
Summary Displacement due to impulsive twist in a semi-infinite elastic medium is calculated in the light of Cosserats theory of couple stresses [1, 2]. Numerical results are obtained for a particular 相似文献
59.
The Dhanbad district in Jharkhand faces acute water scarcity and is chronically drought-prone. The groundwater resources in
the area have not been fully exploited. The present study was undertaken to evaluate the groundwater prospective zones. Landsat-5
Multi Spectral Scanner (MSS) data of band 2 and band 4 and false colour composite (FCC) of band 2, 3, 4 were interpreted visually
to differentiate different hydromorphogeological units and to delineate the major trends of lineaments. The different geomorphic
features identified are linear ridges, residual hills, and pediplain, buried pediment and dissected pediplain, besides lineaments.
The study shows that the pediplain and buried pediments are promising zones for groundwater prospecting. The occurrence and
movement of groundwater is restricted to the unconsolidated material, weathered and fractured rocks. For the selection of
tube well sites, geoelectrical resistivity investigations have been carried out at the sites, which were found suitable based
on hydrogeomorphological and hydrogeological studies. Twenty-six Vertical Electrical Soundings (VES) have been carried out
by using Schlumberger electrode configuration, which have brought out 3 to 7 layered sub-surface layers. The resistivity of
water-bearing weathered/fractured rocks varies from 120–150 ohm m. The integrated studies have revealed that the blue colour
zones are most promising for groundwater exploration and dug wells may be dug up to depths of 30±5m. 相似文献
60.
The Walsh power spectral technique has been applied to the non-sinusoidal palaeoclimatic (theGloborotalia menardii climatic curve) and palaeomagnetic intensity variation records of the last 1.2 Myr. The analysis reveals, in the case of palaeomagnetic variations, statistically significant peaks (at 90% confidence level) centered around 150, 60 and 24 kyr. The palaeoclimatic spectrum, however, indicates only two significant peaks of 60 and 24 kyr. The identical periodicities in both the phenomena may suggest a causal link between the geomagnetic intensity variations and climatic changes. 相似文献