全文获取类型
收费全文 | 373篇 |
免费 | 17篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 18篇 |
大气科学 | 28篇 |
地球物理 | 89篇 |
地质学 | 184篇 |
海洋学 | 16篇 |
天文学 | 29篇 |
综合类 | 6篇 |
自然地理 | 25篇 |
出版年
2022年 | 9篇 |
2021年 | 15篇 |
2020年 | 6篇 |
2019年 | 15篇 |
2018年 | 27篇 |
2017年 | 27篇 |
2016年 | 38篇 |
2015年 | 22篇 |
2014年 | 23篇 |
2013年 | 41篇 |
2012年 | 18篇 |
2011年 | 18篇 |
2010年 | 13篇 |
2009年 | 23篇 |
2008年 | 6篇 |
2007年 | 14篇 |
2006年 | 12篇 |
2005年 | 7篇 |
2004年 | 4篇 |
2003年 | 6篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 3篇 |
1993年 | 2篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1979年 | 1篇 |
1976年 | 2篇 |
排序方式: 共有395条查询结果,搜索用时 15 毫秒
91.
The first aim of the present work is to compute a more accurate and recent model for the Earth’s magnetic field. The second
aim is to determine the effects of the Earth’s magnetic field on the motion of a charged artificial satellite to evaluate
the variations of the orbital elements of the satellite due to these effects. The magnetic field and its variation with time
have been studied at different heights, longitudes and latitudes. The geomagnetic field is considered as a multiple potential
field and the electrical charge of the satellite is assumed to be constant. A new computer code has been constructed to follow
the components of the magnetic field in spherical harmonic models. The Gauss equations are solved numerically. The results
concentrate on the computation of the numerical values of orbital perturbation for the case of a low Earth satellite. RS-1
satellite and space craft gravity probe B (GPB) are chosen as cases of studies for a detailed numerical analysis. 相似文献
92.
Boutheina Farhat Abdallah Ben Mammou Lamia Kouzana Ismail Chenini Francesca Podda Giovanni De Giudici 《Resource Geology》2010,60(4):377-388
The present paper investigates hydrochemical processes and water quality in the Mornag aquifer in NE Tunisia. Groundwater samples were collected during a field campaign, and were analysed for major and trace elements. The collected waters have a chemical facies rich in Ca2+, Na+ and Cl-. Piper diagram shows a progressive increase in chloride ions along with increasing salinity. Saturation indexes calculated by using PHREEQC (USGS) show that the Mornag waters are slightly saturated with respect to carbonates (calcite and dolomite), while undersaturated with respect to gypsum, halite and other evaporitic minerals. The current composition of waters takes place via dissolution of halite and Ca-sulfates, where the increase in calcium is partially balanced by possible calcite precipitation. The relevant recorded pollutant is nitrate, which was likely dispersed from agricultural soils, while heavy metals were generally far below values of pollution thresholds, indicating no influence by mining activity. 相似文献
93.
Colby Loucks Shannon Barber-Meyer Md. Abdullah Abraham Hossain Adam Barlow Ruhul Mohaiman Chowdhury 《Climatic change》2010,98(1-2):291-298
The Sundarbans mangrove ecosystem, shared by India and Bangladesh, is recognized as a global priority for biodiversity conservation. Sea level rise, due to climate change, threatens the long term persistence of the Sundarbans forests and its biodiversity. Among the forests’ biota is the only tiger (Panthera tigris) population in the world adapted for life in mangrove forests. Prior predictions on the impacts of sea level rise on the Sundarbans have been hampered by coarse elevation data in this low-lying region, where every centimeter counts. Using high resolution elevation data, we estimate that with a 28 cm rise above 2000 sea levels, remaining tiger habitat in Bangladesh’s Sundarbans would decline by 96% and the number of breeding individuals would be reduced to less than 20. Assuming current sea level rise predictions and local conditions do not change, a 28 cm sea level rise is likely to occur in the next 50–90 years. If actions to both limit green house gas emissions and increase resilience of the Sundarbans are not initiated soon, the tigers of the Sundarbans may join the Arctic’s polar bears (Ursus maritimus) as early victims of climate change-induced habitat loss. 相似文献
94.
ABSTRACTGrowth in water use and threatened shortages of water have become increasingly important in the modern world system. Natural resources are exploited extensively by capitalist interests in industrially advanced nations, while the lower strata of the world system, the underdeveloped societies, are left with limited access to natural resources for their productive processes, particularly water resources. We contribute to socio-hydrological research by examining underlying socio-structural factors that play a part in the process of deteriorating conditions of global water resources. Drawing on a world-systems perspective, this study examines how socio-structural forces – world-system position, per capita beef consumption, per capita energy consumption, and urbanization – affect per capita water footprint, which includes an accounting of “virtual water” consumption. We find that per capita beef consumption and per capita energy consumption have significant positive direct effects, and the world-system position has a significant indirect and total effect on per capita water footprint. 相似文献
95.
96.
Ahmad Ismail Chee Kong YAP Fong Fei Chan 《湿地科学》2004,2(4):248-258
1 INTRODUCTIONKelanaJayaMunicipalParkcoveredatotallandareaof40hectaresandabout 70 %oftheareasarelakes(Mohkeri,2 0 0 2 ) .KelanaJayaLakes ,locatedwithinthePark ,areex miningpondsattheDamansaraRiverBasininSelangorandthelakesarebeingmanagedbythePetalingJayaMunicipalCouncil (MPPJ)solelyasfloodretentionareasuntil1 996,werethendevelopedasapublicpark .SomeofthemajorproblemsthreateningKelanaJayaLakeswerehighwayrunoffs,untreatedsewagefromthenearbyoxidationpondsandsemi treatedortreateddome… 相似文献
97.
98.
99.
E. M. Abdelrahman H. M. El-Araby B. El-Hakim A. I. Bayoumi A. M. Ismail 《Studia Geophysica et Geodaetica》1993,37(3):302-314
Summary This paper discusses an approach to determining the least-squares optimum order of a polynomial fit to temperature-gradient data. The optimum is reached when two successive least-squares regional maps are sufficiently similar. This similarity is measured by the correlation factor between the polynomials.The approach was applied to the available deep bore-hole temperature data in the central part of the Northern Western Desert of Egypt. The fitting polynomial was found to be of the second degree. Assuming the thermal conductivity to be uniformly 2·2 Wm–1K–1 for the stratigraphic section in the Western Desert, the heat-flow density ranges between 35 and 70 mW/m2.Presented at the International Meeting on Terrestrial Heat Flow and the Structure of Lithosphere, Bechyn Castle, Czech Republic, September 2 – 7, 1991. 相似文献
100.
Angelo Minissale Mohamed A. Mattash Orlando Vaselli Franco Tassi Ismail N. Al-Ganad Enrico Selmo Nasr M. Shawki Dario Tedesco Robert Poreda Abdassalam M. Ad-Dukhain Mohammad K. Hazzae 《Applied Geochemistry》2007
Most thermal springs of continental Yemen (about 65 emergences at 48 sampling sites) and a couple of fumaroles and boiling water pools have been sampled and analyzed for chemical and isotopic composition in the liquid phase and the associated free-gas phase. Whatever the emergence, all the water discharges have an isotopic signature of meteoric origin. Springs seeping out from high altitudes in the central volcanic plateau show a prevalent Na–HCO3-composition, clearly affected by an anomalous flux of deep CO2 deriving from active hydrothermal systems located in the Jurassic Amran Group limestone sequence and/or the Cretaceous Tawilah Group, likely underlying the 2000–3000 m thick volcanic suite. At lower elevations, CO2 also affects the composition of some springs emerging at the borders of the central volcanic plateau. 相似文献