全文获取类型
收费全文 | 230篇 |
免费 | 3篇 |
国内免费 | 3篇 |
专业分类
测绘学 | 17篇 |
大气科学 | 25篇 |
地球物理 | 38篇 |
地质学 | 88篇 |
海洋学 | 6篇 |
天文学 | 52篇 |
综合类 | 4篇 |
自然地理 | 6篇 |
出版年
2021年 | 4篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 6篇 |
2017年 | 9篇 |
2016年 | 7篇 |
2015年 | 5篇 |
2014年 | 10篇 |
2013年 | 16篇 |
2012年 | 5篇 |
2011年 | 12篇 |
2010年 | 7篇 |
2009年 | 16篇 |
2008年 | 5篇 |
2007年 | 6篇 |
2006年 | 11篇 |
2005年 | 5篇 |
2004年 | 4篇 |
2003年 | 8篇 |
2002年 | 6篇 |
2001年 | 4篇 |
2000年 | 10篇 |
1999年 | 7篇 |
1998年 | 7篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 1篇 |
1994年 | 5篇 |
1993年 | 9篇 |
1992年 | 2篇 |
1991年 | 9篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 5篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1971年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有236条查询结果,搜索用时 15 毫秒
81.
82.
Ashok Kumar Deepak Srivastava Sanjay Kumar Srivastava 《Journal of the Indian Society of Remote Sensing》1994,22(1):57-64
Remotely-sensed satellite data of Landsat 5 (TM) and IRS-1A (LISS II) covering parts of central portion of Chotanagapur plateau have been analysed visually to delineate some prominent lineaments in Ranchi district and its adjoining area. One of the most prominent lineament “Ranchi mega lineament? has been analysed in this paper. This lineament is a potential site for base metal mineralisation at some places, and it acts as good groundwater conduit in the region. No earlier attempt to map this entire structural unit as a separate entity is known. Geophysical bouguer gravity anomaly map, lithological and structural maps have some remarkable correlation with this lineament. In the present paper authors have tried to analyse the lineament with respect to its tectonic, mineralisation and groundwater prospects. Resistivity survey carried in close proximity of this lineament at selected sites, indicate that rocks are well fractured at depth. Available lithological and structural map support this lineament as a shear near Purulia (W.B.) and also having base-metal mineralisation potential in this area. Authors opine that existing gravity anomaly map may be further augmented in the light of present study. 相似文献
83.
This paper is an analysis of the historical change in city size distribution in India from the perspectives provided by Zipf and Jefferson. Rank-size distribution at national level and primate city-size distribution at regional levels are examined. India's national urban system is gradually evolving towards Zipf's rank-size distribution. But primate cities have persisted in three of the four macro-regions in India. The paper also examines, in the Indian context, the relation between rank-size distribution and an integrated urban system, and the normative nature of the latter as a spatial organization of human society. Finally, we have made a modest attempt to locate the research on city-size distribution, especially Berry's system-theoretic interpretation of rank-size distribution, on the realm of the political economy of urbanization. 相似文献
84.
A two-component differentially rotating disk of self-gravitating particles is considered in the hydrodynamical framework. This system is shown to sustain two pairs of density waves, corresponding to the familiar Jeans modes and an acoustic type of modes (similar to ion-acoustic modes in plasmas). As a result of mass and momentum transfer from the gaseous to the stellar component (an accretion process), the acoustic modes suffer a strong damping, whereas the Jeans modes which were oscillatory, now become overstable provided the thermal velocity of stars is larger than that of gaseous component. The waves with frequencies near the corotation have a rather large growth rate. This amplification can explain the maintenance of spiral structure and a selective amplification could even determine the wave-frequency (or pattern velocity). 相似文献
85.
Ashok K. Luhar 《Boundary-Layer Meteorology》2002,102(1):1-38
The mean concentration distributionwithin a plume released from a point source in the atmosphericboundary layer can be greatly influenced by the systematic turningof wind with height (i.e. vertical wind direction shear). Such aninfluence includes a deflection of the plume centroid, with anassociated shearing of the vertical plume cross-section, and anenhancement of dispersion, in the horizontal plane. Wind directionshear is normally not accounted for in coastal fumigation models,although dispersion observations with shear acting as acontrolling parameter are not uncommon. A three-dimensionalLagrangian stochastic model is used to investigate the influenceof uniform wind direction shear on the diffusion of a point-sourceplume within the horizontally homogeneous convective boundarylayer, with the source located at the top of the boundary layer.Parameterisations are developed for the plume deflection andenhanced dispersion due to shear within the framework of aprobability density function (PDF) approach, and compared with theLagrangian model results. These parameterisations are thenincorporated into two applied coastal fumigation models: a PDFmodel, and a commonly used model that assumes uniform andinstantaneous mixing in the vertical direction. The PDF modelrepresents the vertical mixing process more realistically. A moreefficient version of the PDF model, which assumes a well-mixedconcentration distribution in the vertical at large times, isapplied to simulate sulfur dioxide data from the Kwinana CoastalFumigation Study. A comparison between the model results and thedata show that the model performs much better when the wind-sheareffects are included. 相似文献
86.
Near infrared coronal line emission at 1.98 ± 0.02Μm due to [Si VI] detected in the spectrum of Nova Herculis 1991 about 17
days after optical maximum is reported. The early appearance of coronal emission is yet another unusual feature of this fast
nova in which early onset of dust formation processes and X-ray detection five days after outburst have already been reported.
The coronal line observations reported here are consistent with X-ray detection and support a hot shocked circumstellar envelope
at the periphery of the dust formation zone in the nova. 相似文献
87.
High speed photometry during the lunar occultation of a stellar system provides an effective means of achieving high angular
resolution in one dimension at the sub arc second level which is well suited for resolving close binary projected separations
in the range of 10–100 milliarc seconds. An optical fast photometer designed for such a purpose is described and some results
from the initial observations taken with the system including the resolution of a projected separation of 55 milli arcsecond
in one binary system are detailed. 相似文献
88.
The Cretaceous of Afghanistan is marked by great facies diversity. The evolution of Cretaceous basins is part of a complex accretionary history involving three distinct tectonic units namely the Asian (Russian) Block separated from the Indian plate by a rather well defined transcurrent fault (Chaman-Nuski). The southwestern component is representedby the Iran-Afghanistan plate. The Lower Cretaceous of the Asian Block is represented by the Red-Grit Series which isconformable to the underlying Upper Jurassic sequences. The transition is marked by evaporitic facies dominated by salt,gypsum and marl deposits. In south Afghanistan volcanic rocks occur at Farah, with the emplacement of plutonics inwest-central Afghanistan. The Upper Cretaceous of north Afghanistan is marked by richly fossiliferous, lime stone-dominated sequences. The Upper Cretaceous of southern Afghanistan is marked by strong ophiolitic magrmatism. 相似文献
89.
Ashok K. Chugh 《国际地质力学数值与分析法杂志》1981,5(4):449-454
Estimating subsurface pore water pressures in natural slopes along the periphery of rivers and reservoirs for future conditions, created by the operational requiremets to meet increases in energy demand from the observed data of the past and present, operations, is possible with the use of a mathematical model. An effective algorithm for calculating pore water pressure at any location in a slope stability section is to use a complete polynomial and to assure geometric invariance of the calculated results. 相似文献
90.
Infrared observations obtained six years apart of the R CrB type star XX Cam do not show any infrared excess, unlike all the
other members of the class. The observed colours match a 7000 K black body energy distribution quite well. From the year 1898
till todate, apparently XX Cam has undergone only one visual light minimum in 1940. The lack of infrared excess, the abundance
peculiarities and further lack of small amplitude light variations with periods of few tens of days, which are characteristic
of R CrB type stars, are discussed in terms of theoretical pulsation models of helium stars. 相似文献