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491.
Prosanta Kumar Khan Manoj Ghosh Partha Pratim Chakraborty Debdeep Mukherjee 《Pure and Applied Geophysics》2011,168(10):1693-1706
Seismicity data of northeast India, recorded between 1986 and 1999 by a local network, are analysed for estimation of b-values. Based on the obtained values, viz. low (b ≤ 0.5), moderate (0.5 < b ≤ 0.7) and high (b > 0.7), the study area is classified into different seismic-domains. An assessment of stress level is also carried out in
identifying seismic-domains. Seismic activities, though mostly confined in some sectors, are presumably triggered by mutual
interaction of the Shillong Plateau, Mikir Hills, Indo-Burman Ranges and the easternmost part of the Himalayas, and the contributions
from deep-seated fractures cannot be ignored. The results resemble the seismic character of a foreland setting adjacent to
a convergent margin. The b-values estimated for 240 square grids of dimension 0.6° × 0.6° over five seismic domains indicate wide variation. An analysis
of cumulative seismic moment release (M
O) in different layers also indicates an anomaly in reference to the total seismic-energy budget of the five zones. The lower
b-value and higher M
O recorded at relatively lower depth (~30 km) towards the southwest of the study area might be associated with upward bulging
of a strong lithosphere. The bulging is perhaps regionally compensated by the downward flexing of the descending Indian lithosphere
beneath the Upper Assam area; features unequivocally observed in any foreland setup. Towards the north and east of the study
area, random variations of in both b-value and M
O along the converging zone suggest a varied tectonic environment with active interaction between the tectonic elements in
these areas. 相似文献
492.
Analysis of flood causes and associated socio-economic damages in the Hindukush region 总被引:1,自引:0,他引:1
Pakistan is exposed to numerous hazards, but the problem of recurrent floods has been causing massive losses to lives and
other properties. Swat valley is no exception to it. In this paper, an attempt has been made to analyse the causes and associated
socio-economic impacts of floods on the Swat valley, Pakistan. Swat valley falls in the Hindukush region, North-west-Pakistan.
The valley has been studied with special reference to its physical and socio-economic environment. Similarly, three-sample
villages were also randomly selected from the active floodplain for micro-level analysis. The sample villages include Ningolai,
Delay and Ghureijo. All the three-sample communities are located on the right bank of river Swat. This area is located in
the active flood zone of Swat valley. The analysis revealed that in the study area, floods occur during summer season, which
is mainly caused by heavy rainfall as well as rapid melting of snow and glacier. Besides these, there are some floods intensifying
factors, which accelerate intensity of floods and enhance resultant damages in the valley. It was found that during flood
season, water overflows the natural levees and trigger tremendous loses to housing, agricultural land, standing crops and
other properties. The flood-related Government Departments have only implemented limited structural mitigation measures. However,
in addition to structural measure, land-use zoning and flood abatement strategies would largely help in reducing the adverse
consequences of this recurrent phenomenon. 相似文献
493.
The quantitative relationships between lithological variables from the Late Paleozoic coal bearing cycles have been investigated using factor analysis in an attempt to analyze net subsidence during the deposition of these cycles. The results suggest that there are only two non-zero eigenvalues in varimax matrix which indicate that the hyper ellipsoid enclosing the data points have seven axes of zero length and exists an ordinary two dimensional ellipsoid. The data points can be located with reference to two mutually perpendicular axes. Loading on thickness of sandstones, thickness of shale, number of sandstone beds and number of shale beds are extremely high on RF-I and low on the other factor. This would lead to the interpretation that a balance was maintained throughout the Barakar sedimentation between the rate of deposition and the rate of subsidence. On the other hand, loading on number of coal beds is high on ‘ suggesting that the development of peat swamps (coal beds) is not a normal feature during the Late Paleozoic Barakar sedimentation in this Gondwana sub-basin. 相似文献
494.
Muhammad Umar Henrik Friis Abdul Salam Khan Akhtar Muhammad Kassi Aimal Khan Kasi 《Journal of Asian Earth Sciences》2011,40(2):622-635
The Maastrichtian Pab Formation in the southern part of Pakistan is composed of fine- to very coarse-grained texturally mature quartz arenite and subordinate sublitharenite varieties. The sandstones have undergone intense and complex diagenetic episodes due to burial and uplift. Diagenetic modifications were dependent mainly on the clastic composition of sandstone, burial depth and thrust tectonics. Diagenetic events identified include compaction, precipitation of calcite, quartz, clay minerals and iron oxide/hydroxide, dissolution and alteration of unstable clastic grains as feldspar and volcaniclithic fragments as well as tectonically induced grain fracturing. The unstable clastic grains like feldspar and lithic volcanic fragments suffered considerable alteration to kaolinite and chlorite. Dissolution and alteration of feldspar and volcanic lithic fragments and pressure solution were the main sources of quartz cements. Mechanical compaction and authigenic cements like calcite, quartz and iron oxide/hydroxide reduced the primary porosity, whereas dissolution of clastic grains and cements has produced secondary porosity. Chlorite coatings on clastic grains have prevented quartz cementation. Coarse-grained, thick bedded packages of fluviodeltaic, shelf delta lobe and submarine channels facies have higher average porosity than fine-grained, thin bedded and bioturbated sandstone of deeper shelf and abyssal plain environments and these facies are concluded to be possible future hydrocarbon prospects. 相似文献
495.
In recent years, the United Arab Emirates (UAE) has experienced an unprecedented growth which is coupled with the increase in seismic activity in the surroundings. Previous studies presents significant variations in their results whereas some recent studies although very detailed focus on only few cities. This study reviews the results of previous studies and presents new findings for the whole of UAE based on the improved source model and use of next generation attenuation (NGA) equations. The peak ground accelerations, spectral accelerations and deaggregation of hazard for major cities are presented. Moreover, the breakdown of the range of mapped spectral accelerations (S 0.2 and S 1) is proposed to form the basis for the development of site amplification factors in subsequent studies. The results of this study indicate almost similar values of ground motion compared to some recently published studies and smaller values compared to some earlier studies. 相似文献
496.
Simulation of a flood producing rainfall event of 29 July 2010 over north-west Pakistan has been carried out using the Weather Research and Forecasting (WRF) model. This extraordinary rainfall event was localized over north-west Pakistan and recorded 274 mm of rainfall at Peshawar (34.02°N, 71.58°E), within a span of 24 h on that eventful day where monthly July normal rainfall is only 46.1 mm. The WRF model was run with the triple-nested domains of 27, 9, and 3 km horizontal resolution using Kain–Fritsch cumulus parameterization scheme having YSU planetary boundary layer. The model performance was evaluated by examining the different simulated parameters. The model-derived rainfall was compared with Pakistan Meteorological Department–observed rainfall. The model suggested that this flood producing heavy rainfall event over north-west region of Pakistan might be the result of an interaction of active monsoon flow with upper air westerly trough (mid-latitude). The north-west Pakistan was the meeting point of the southeasterly flow from the Bay of Bengal following monsoon trough and southwesterly flow from the Arabian Sea which helped to transport high magnitude of moisture. The vertical profile of the humidity showed that moisture content was reached up to upper troposphere during their mature stage (monsoon system usually did not extent up to that level) like a narrow vertical column where high amounts of rainfall were recorded. The other favourable conditions were strong vertical wind shear, low-level convergence and upper level divergence, and strong vorticity field which demarked the area of heavy rainfall. The WRF model might be able to simulate the flood producing rainfall event over north-west Pakistan and associated dynamical features reasonably well, though there were some spatial and temporal biases in the simulated rainfall pattern. 相似文献
497.
Evaluation of coal as adsorbent for phosphate removal 总被引:1,自引:1,他引:0
Sabir Khan M. Ishaq Imtiaz Ahmad Sajjad Hussain Hameed Ullah 《Arabian Journal of Geosciences》2013,6(4):1113-1117
This paper reports the adsorption of phosphate ions on coal, charcoal, and coal ash. The influences of factors such as contact time, and initial adsorbate concentration have been studied. Adsorption of phosphate ions on virgin coal was significant compared to charcoal, coal and coal ash evacuated at 200°C. The significant adsorption capability of coal is due to the porosity as well as due to organic carbon and inorganic elements present in coal. The evacuation of coal proved to be ineffective in enhancing its capability for phosphate ions retention. The adsorption behaviors of all the three adsorbent used was conformed using Freundlich’s adsorption model. The results suggest that coal could be used as an efficient adsorbent for removing phosphate ions from wastewater. 相似文献
498.
Forecasting flood risk in the Indus River system using hydrological parameters and its damage assessment 总被引:1,自引:1,他引:0
Hydrological parameters are among the widely used parameters in assessing flood risk. On the other hand, anticipated flood damages, in case of flooding, are estimated with the help of expected losses in areas nearer to the watercourse. The major source of almost every-year flooding in Pakistan is the Indus River system that comprises the major rivers of Pakistan. We first use observed data to construct simulated data models based on various probability distributions namely normal, lognormal, Weibull, largest extreme value, gamma-3, and log-Pearson type-3 distributions and thereby compute probable maximum flood. Secondly, we perform log-Pearson type-3 analysis with and without historic adjustment on the observed data series of 17 years to forecast floods with return periods T of 2, 5, 10, 25, 50, 100, and 200 years. We also categorize the river structures based on the risk of flooding. Lastly, we estimate risk of flood damages in terms of expected losses based on observed data. The present study reveals that the log-Pearson type-3 distribution is relatively better for estimating probable maximum flood. We use exceedence probability to assess the risk of flooding in the various structures of the said rivers. The analysis shows that flood damages in Pakistan may be reduced by increasing the design capacity of the structures and also by giving awareness to people about the flood-generating factors. 相似文献
499.
500.
Closed basins such as the Caspian Sea rapidly respond to variations in atmospheric and geological events. This study has been
conducted to deduce the role of natural and anthropogenic influences on the Caspian Sea mean water level fluctuations for
the period of 1998–2005. It is recognized that climate is the primary mechanism of the Caspian Sea mean water level variations
based on the relatively small differences of the Caspian Sea hydrologic budget residuals and the Caspian Sea mean water level
fluctuations. This is further supported by the similarity in water-level variations of the Caspian Sea with those of Lake
Van and Lake Urmia. On the other hand, the Caspian Sea needed to lose some of its water to attain water balance equilibrium
in 2000 and 2001. The year 2000 showed anomalous seismic activity particularly in the southwestern part of the Caspian Sea.
Two significant earthquakes with magnitudes of 6.8 and 6.5 Mw occurred on November 25, 2000. The focal mechanisms of these earthquakes and numerous aftershocks indicated normal faulting
and, therefore, caused the Caspian Sea lake level to decline in 2000. The contribution of submarine mud volcano eruptions
to the Caspian Sea lake level could be insignificant based on the comparison of water budget residuals and the mean water
level variations. Neither crustal deformation (based on the GPS measurements) nor the offshore oil and natural gas production
activities in the Caspian Sea are responsible for noticeable changes to the level of the Caspian Sea. 相似文献