全文获取类型
收费全文 | 84篇 |
免费 | 1篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 1篇 |
地球物理 | 8篇 |
地质学 | 24篇 |
天文学 | 50篇 |
自然地理 | 4篇 |
出版年
2021年 | 1篇 |
2020年 | 2篇 |
2018年 | 5篇 |
2017年 | 3篇 |
2016年 | 5篇 |
2015年 | 1篇 |
2014年 | 4篇 |
2013年 | 3篇 |
2012年 | 1篇 |
2011年 | 6篇 |
2009年 | 9篇 |
2008年 | 2篇 |
2007年 | 4篇 |
2006年 | 7篇 |
2005年 | 2篇 |
2004年 | 4篇 |
2003年 | 4篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1994年 | 1篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
排序方式: 共有87条查询结果,搜索用时 18 毫秒
51.
52.
53.
Calibration of the Regional Crustal Waveguide and the Retrieval of Source Parameters Using Waveform Modeling 总被引:5,自引:0,他引:5
v--vRegional crustal waveguide calibration is essential to the retrieval of source parameters and the location of smaller (M < 4.8) seismic events. This path calibration of regional seismic phases is strongly dependent on the accuracy of hypocentral locations of calibration (or master) events. This information can be difficult to obtain, especially for smaller events. Generally, explosion or quarry blast generated travel-time data with known locations and origin times are useful for developing the path calibration parameters, but in many regions such data sets are scanty or do not exist. We present a method which is useful for regional path calibration independent of such data, i.e. with earthquakes, which is applicable for events down to Mw = 4 and which has successfully been applied in India, central Asia, western Mediterranean, North Africa, Tibet and the former Soviet Union. These studies suggest that reliably determining depth is essential to establishing accurate epicentral location and origin time for events. We find that the error in source depth does not necessarily trade-off only with the origin time for events with poor azimuthal coverage, but with the horizontal location as well, thus resulting in poor epicentral locations. For example, hypocenters for some events in central Asia were found to move from their fixed-depth locations by about 20 km. Such errors in location and depth will propagate into path calibration parameters, particularly with respect to travel times. The modeling of teleseismic depth phases (pP, sP) yields accurate depths for earthquakes down to magnitude Mw = 4.7. This Mw threshold can be lowered to four if regional seismograms are used in conjunction with a calibrated velocity structure model to determine depth, with the relative amplitude of the Pnl waves to the surface waves and the interaction of regional sPmP and pPmP phases being good indicators of event depths. We also found that for deep events a seismic phase which follows an S-wave path to the surface and becomes critical, developing a head wave by S to P conversion is also indicative of depth. The detailed characteristic of this phase is controlled by the crustal waveguide. The key to calibrating regionalized crustal velocity structure is to determine depths for a set of master events by applying the above methods and then by modeling characteristic features that are recorded on the regional waveforms. The regionalization scheme can also incorporate mixed-path crustal waveguide models for cases in which seismic waves traverse two or more distinctly different crustal structures. We also demonstrate that once depths are established, we need only two-stations travel-time data to obtain reliable epicentral locations using a new adaptive grid-search technique which yields locations similar to those determined using travel-time data from local seismic networks with better azimuthal coverage. 相似文献
54.
M. V. D. Sitaram George John P. G. Rao M. M. Saikia 《Studia Geophysica et Geodaetica》1990,34(2):96-109
Summary Based on 90 accurately localized earthquakes in and around North-East India and the local crustal velocity model of Gupta
et al. [4], the travel times of P-waves have been determined from the foci of these earthquakes at arbitrarily selected depths
of 5, 13, 25, 41 and 50 km to the sites of the seismic stations operated by the Regional Research Laboratory, Jorhat and the
National Geophysical Research Institute, Hyderabad, and also to the sites of the Shillong and Tura seismic stations run by
the India Meteorological Department, New Delhi. The travel times of P-waves fit a straight line very well with velocities
of 5·97 ± 0·31, 6·18 ± 0·01, 6·41 ± 0·03, 7·82 ± 0·07 and 7·95 ± 0·01 km/sec at each of the depths under study. Similar investigations
of P* and Pg-waves of 16 earthquakes at a depth of 10 km have revealed velocities of 6·53 ± 0·31 and 5·64 ± 0·34 km/sec, respectively.
A simplified two-layered crustal model consisting of an average crustal thickness of 41·5 km with 22·2 and 19·3 km thick layers
has been obtained. 相似文献
55.
Bhabesh C. Sarkar Bashab N. Mahanta Kalyan Saikia Pradip R. Paul Gurdeep Singh 《Environmental Geology》2007,51(7):1177-1196
A study on geo-environmental quality assessment in Jharia coalfield, India, has been attempted using multivariate statistical
analysis and geographic information system (GIS) modelling techniques. Water quality index, calculated for each sample network
station in the study area to assess the suitability of water for human consumption, revealed very poor to poor quality surface
water and mine water. Air quality indexing indicated that there is no sample station with clean air as per the Indian standards,
which indicate the hazardous air quality. Multi-criteria evaluation (MCE), a potential GIS tool, has been applied to the delineation
of various degrees of stressed villages in terms of quality of life (QoL). The role of various geo-environmental parameters
such as quality of groundwater, surface water, mine water and air together with village population densities has been emphasized
for delineation of the environmentally stressed villages in Jharia coalfield. The integrated cluster analysis and MCE approach
provide an improved means to geo-environmental quality assessment in Jharia coalfield in terms of QoL. The assessment study
is aimed to be used for future coal mining, ensuring ecologically sustainable industrial development, particularly in a coalfield. 相似文献
56.
Binoy K.Saikia Jyotilima Saikia Shahadev Rabha Luis F.O.Silva Robert Finkelman 《地学前缘(英文版)》2018,9(3):863-875
Coal is the most abundant fossil fuel in the world. Because of the growth of coal mining, coal-fired power plants and coal-burning industries, the increase of the emission of particulates(coarse, fine or ultrafine)is of great concern. There is a relationship between increasing human morbidity and mortality and progressive environmental air pollution caused by these types of particles. Thus, the knowledge of the physico-chemical composition and ambient concentrations of coal-derived nanoparticles will improve pollution control strategy. Given the current importance of this area of research, the advanced characterization of this coal combustion-derived nanoparticles/nanominerals as well as hazardous elements is likely to be one of the hottest research fields in coming days. In this review, we try to compile the existing knowledge on coal-derived nanoparticles/nanominerals and discuss the advanced level of characterization techniques for future research. This review also provides some of aspects of health risks associated with exposure to ambient nanoparticles. In addition, the presence of some of the hazardous elements in coal and coal combustion activities is also reviewed. 相似文献
57.
Sowrav Saikia Santanu Baruah Sumer Chopra Upendra K. Singh Bibhuti Gogoi Himanata B. Gohain 《Journal of Seismology》2018,22(1):229-249
It is noticed that few geophysical studies have been carried out to decipher the crustal structure of southwestern part of the Northeast India comprising of Tripura fold belt and Bengal basin as compared to the Shillong plateau and the Brahmaputra basin. This region has a long history of seismicity that is still continuing. We have determined first-order crustal features in terms of Moho depths (H) and average VP/VS ratios (κ) using H-κ stacking technique. The inversion of receiver functions data yields near surface thick sedimentary layer in the Bengal basin, which is nearly absent in the Shillong plateau and Tripura fold belt. Our result suggests that the crust is thicker (38–45 km) in the Tripura fold belt region with higher shear-wave velocity in the lower crust than the Shillong plateau. The distribution of VP/VS ratio indicates heterogeneity throughout the whole region. While low to medium value of Poisson’s ratio (1.69–1.75) indicates the presence of felsic crust in the Shillong plateau of the extended Indian Archean crust. The medium to high values of VP/VS ratio (> 1.780) in the Bengal basin and the Tripura fold belt region represent mafic crust during the formation of the Bengal delta and the Tripura fold belt creation in the Precambrian to the Permian age. The depth of the sediments in the Bengal basin is up to 8 km on its eastern margin, which get shallower toward its northeastern and southeastern margins. 相似文献
58.
C. Konar M. Jamrozy M. J. Hardcastle J. H. Croston S. Nandi D. J. Saikia J. Machalski 《Journal of Astrophysics and Astronomy》2011,32(4):477-486
Relativistic and magnetized plasma ejected by radio loud AGNs through jets form the diffuse lobes of radio galaxies. The radiating
particles (electron/electron–positron) in lobes emit in radio via the synchrotron process and X-ray via inverse-Compton scattering
of cosmic microwave background photons. The thermal environment around radio galaxies emits X-rays via the thermal bremsstrahlung
process. By combining information from these processes we can measure physical conditions in and around the radio lobes and
thus study the dynamics of radio galaxies, including double–double radio galaxies. 相似文献
59.
The Bayana Basin forms the eastern most limit of north Delhi fold belt covering parts of northeastern Rajasthan. The deposition
of sediments took place during middle Proterozoic in fluvial and shallow marine environments. The rocks are mainly clastics
and include conglomerate, sandstone and shale. During mechanical compaction rearrangement of grains took place and point and
long contacts were formed. The sandstones are cemented by iron oxide, silica, carbonate and barite. The porosity has developed
due to dissolution of iron, carbonate cement and feldspar grains. Dissolution of quartz along grain boundaries and silica
rich compaction pore water seems to be the main source of silica. These observations suggest progressive compaction which
initiated at the sediment water interface and continued till deep burial diagenesis in a rapidly subsiding basin. 相似文献
60.
C. Konar D. J. Saikia M. Jamrozy J. Machalski 《Monthly notices of the Royal Astronomical Society》2006,372(2):693-702
We present new radio observations at frequencies ranging from 240 to 4860 MHz of the well-known, double–double radio galaxy (DDRG), J1453+3308, using both the Giant Metrewave Radio Telescope (GMRT) and the Very Large Array (VLA). These observations enable us to determine the spectra of the inner and outer lobes over a large frequency range and demonstrate that while the spectrum of the outer lobes exhibits significant curvature, that of the inner lobes appears practically straight. The break frequency, and hence the inferred synchrotron age of the outer structure, determined from 16-arcsec strips transverse to the source axis, increases with distance from the heads of the lobes. The maximum spectral ages for the northern and southern lobes are ∼47 and 58 Myr, respectively. Because of the difference in the lengths of the lobes, these ages imply a mean separation velocity of the heads of the lobes from the emitting plasma of 0.036 c for both the northern and southern lobes. The synchrotron age of the inner double is about 2 Myr which implies an advance velocity of ∼0.1 c , but these values have large uncertainties because the spectrum is practically straight. 相似文献