全文获取类型
收费全文 | 541篇 |
免费 | 33篇 |
国内免费 | 7篇 |
专业分类
测绘学 | 18篇 |
大气科学 | 31篇 |
地球物理 | 133篇 |
地质学 | 283篇 |
海洋学 | 33篇 |
天文学 | 40篇 |
综合类 | 8篇 |
自然地理 | 35篇 |
出版年
2022年 | 12篇 |
2021年 | 19篇 |
2020年 | 11篇 |
2019年 | 12篇 |
2018年 | 52篇 |
2017年 | 31篇 |
2016年 | 56篇 |
2015年 | 11篇 |
2014年 | 42篇 |
2013年 | 51篇 |
2012年 | 26篇 |
2011年 | 21篇 |
2010年 | 13篇 |
2009年 | 21篇 |
2008年 | 12篇 |
2007年 | 16篇 |
2006年 | 16篇 |
2005年 | 10篇 |
2004年 | 9篇 |
2003年 | 15篇 |
2002年 | 9篇 |
2001年 | 9篇 |
2000年 | 12篇 |
1999年 | 7篇 |
1998年 | 4篇 |
1996年 | 4篇 |
1995年 | 7篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1981年 | 5篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1971年 | 3篇 |
1969年 | 1篇 |
1968年 | 3篇 |
1964年 | 1篇 |
1960年 | 1篇 |
排序方式: 共有581条查询结果,搜索用时 15 毫秒
491.
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
492.
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
493.
The geological studies of the eastern parts of Harda-Barwah basin covering about 3000 sq. km area on 1∶50,000 scale have been carried out using satellite imagery of IRS (FCC), supplemented by Landsat TM/MSS scences and air photos. The present studies with the aid of satellite imagery and remote sensing techniques have brought out the regional stratigraphy and structure of the area and helped in deciphering the interrelationship of various rock groups in the Narmada lineament zone. The area comprises Archaean/Proterozoic gneisses, the Mahakoshal volcano sedimentary suite, the Harda granitoids, the Bijawar Group and the rocks of Vindhyan Supergroup, Deccan Trap and Quaternary sediments. The Archaean/Proterozoic rocks comprising gneisses and schist form basement. The Mahakoshal Group of rocks occur along the ENE-WSW to E-W trending Narmada lineament zone and comprise foliated quartzite, actinolite-chlorite-sericite phyllite and metabasics. The Harda granitoids showing intrusive relationship with earlier rocks, comprise coarse-grained crudely foliated grey to pink granites, fine to medium grained homogeneous granites and porphyritic granites. The Bijawar Group comprises quarzite, chert breccia and dolomite in the order of younging and shows unconformable relationship with the Mahakoshal and the Harda granitoids. The Bijawar rocks show doubly plunging major synformal structure and numerous sympathetic minor folds along ENE-WSW to E-W axis and cross folds along NW-SW axis. The Bijawar rocks are unconformably overlain by a sequence of sandstone and shales belonging to the Rewa Group of the Vindhyan Supergroup. The Deccan Trap lava flows represent the last igneous activity in the area. The Quaternary deposits comprising a cyclic sequence of sand, silt, clay and rock gravels of the Narmada river represent the youngest formation of the area. 相似文献
494.
Karez is an indigenous method of irrigation in which groundwater is tapped by a tunnel. After running for some distance the tunnel comes out in the open and the water is conducted to the command area. Karez irrigation is practised in 22 countries from China to Chile including Pakistan. In Pakistan it is confined to the province of Balochistan which has a tribal society.Karez is an old and stable irrigation system of Pakistan. It is a community enterprise managed by tribal tradition and run by social control. Spacing of the karez, their types, life, length, discharge, land development and allocation, water distribution and management are important aspects of karez irrigation which have been discussed in this paper. Differences in karez maintenance and management produced by differences in tradition and customs of various tribes inhabiting Balochistan are brought out. Furthermore recent changes in Karez irrigation caused by changes in the socio-economic conditions are also analysed. 相似文献
495.
A three-dimensional mesoscale model was used to study the effect of an urban heat island in a relatively complex situation. A heat emission inventory was carried out for an urban airshed thatincludes sources such as motor vehicles, waste heat from industries and electricity consumption. To demonstrate the relative significance of anthropogenic heat flux and variant surface characteristics, three model simulations were conducted. In the first simulation, anthropogenic heat flux was ignored and non-variant surface properties were considered for the entire modelling domain. In the second simulation, variant surface characteristics were considered. While in the third simulation, gridded anthropogenic heat flux and variant surface characteristic were utilised. From these experiments, it was inferred that an additional source of heat in urban areas can substantially affect the wind and temperature regime under light wind conditions. During the day, the anthropogenic heat flux has minimum effect on the urban temperature, however it magnifies the intensity of the convergence near the urban areas. 相似文献
496.
C. Jeganathan S. A. Khan Ramesh Chandra H. Singh V. Srivastava P. L. N. Raju 《Journal of the Indian Society of Remote Sensing》2001,29(1-2):31-36
As per the World Health Organisation, about 260 million people worldwide are infected with malaria and 1.5 to 2.7 million patients die annually due to this most significant infectious parasite. In this study two important species,Anopheles dints andAnopheles minimus, have been studied in North Lakhimpur and Dibrugarh districts of Assam in the North-Eastern India. Remote sensing has certainly provided a clue in identifying the symptoms of mosquito habitat and Geographical Information System (GIS) has helped us to analyse and identify two species with several environmental parameters. Remote sensing inputs have made a difference in understanding the presence of these species in two districts which are having similar meteorological conditions. It has been found that the nature of the breeding ground for mosquitoes and their spreading patterns are not so complex as generally expected. 相似文献
497.
SONG Shuai LI Fadong LU Yonglong Kifayatullah Khan XUE Jianfang LENG Peifang 《资源与生态学报(英文版)》2018,9(3):290-301
Extreme climate events exhibit an increasing spatio-temporal trend globally, and the increasing intensity and frequency may have severe impacts on the human society and natural ecosystems. This study analyzed the extreme temperature and precipitation variability from 1956 to 2016, and evaluated their potential effects on crop yield in Ethiopia. Relative extreme temperature indices exhibited a decreasing trend with low-temperature events, but a significantly upward trend with extreme high temperature events. The frequency of annual warm nights increased to a greater degree than that of cold days. The total annual wet-day precipitation decreased significantly at a rate of -46 mm/decade. Further, the succession of dry days gradually increased by 5.6 day/decade, while an opposite trend of wet days was found with a decline of 1.4 day/ decade. The correlation between annual precipitation and crop production was 0.422, indicating that extreme precipitation indices may have higher explanatory power than extreme temperature indices in the crop yield variations. Moreover, the extreme climate changes have induced significant adverse impacts on crops yield particularly in Ethiopia where no proper adaptation measures have been implemented. 相似文献
498.
R. M. Vil’fand V. F. Martazinova V. Yu. Tsepelev V. M. Khan N. P. Mironicheva G. V. Eliseev E. K. Ivanova V. A. Tishchenko D. N. Utkuzova 《Russian Meteorology and Hydrology》2017,42(8):485-493
The results of experiments on the integration of synoptic and hydrodynamic forecasts of monthly air temperature for the northwestern part of Eurasia for the period of 2011–2015 are presented. The comprehensive comparison of skill scores of individual and integrated forecasts is provided. It is demonstrated that during the cold season hydrodynamic forecasts have the highest skills among the other forecasts. It is revealed that empirical methods are characterized by the forecast skill increase in summer and by its decrease in winter and during the period of spring transformation of atmospheric circulation. In most cases the integration of diverse methods allows combining their benefits and improving the resultant forecast skill. The synchrony was detected in the forecast skill variations. It is shown that the forecast skill mainly depends on the persistence of macrocirculation patterns. 相似文献
499.
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
500.
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