全文获取类型
收费全文 | 113篇 |
免费 | 3篇 |
专业分类
测绘学 | 2篇 |
大气科学 | 4篇 |
地球物理 | 13篇 |
地质学 | 23篇 |
海洋学 | 6篇 |
天文学 | 63篇 |
综合类 | 1篇 |
自然地理 | 4篇 |
出版年
2021年 | 2篇 |
2020年 | 2篇 |
2019年 | 1篇 |
2018年 | 7篇 |
2017年 | 6篇 |
2016年 | 12篇 |
2015年 | 4篇 |
2014年 | 19篇 |
2013年 | 14篇 |
2012年 | 9篇 |
2011年 | 10篇 |
2010年 | 7篇 |
2009年 | 2篇 |
2008年 | 1篇 |
2007年 | 2篇 |
2006年 | 3篇 |
2005年 | 1篇 |
2004年 | 1篇 |
2002年 | 1篇 |
2001年 | 4篇 |
2000年 | 1篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1991年 | 1篇 |
1985年 | 1篇 |
排序方式: 共有116条查询结果,搜索用时 46 毫秒
81.
In this paper, we use Visser’s cut and paste approach to construct thin-shell wormholes from charged black string. The dynamics of thin-shell wormholes is analyzed by taking Van der Waals quintessence fluid at the wormhole throat. We investigate the stability of these constructed thin-shell wormholes under linear perturbations preserving the cylindrical symmetry and also study the effects of charge on its stability. It turns out that there exist both unstable and stable wormhole solutions depending on different parameters involved in the equation of state. 相似文献
82.
83.
M. Sharif 《Astrophysics and Space Science》2001,278(4):449-457
We derive matter collineations for some static spherically symmetricspacetimes and compare the results with Killing, Ricci and Curvaturesymmetries. We conclude that matter and Ricci collineations are not,in general, the same. 相似文献
84.
M. J. Abdollahi M. H. Karimpour A. Kheradmand A. R. Zarasvandi 《Natural Resources Research》2009,18(2):137-151
The Muteh gold district with nine gold deposits is located in the Sanandaj-Sirjan metamorphic zone. Gold mineralization occurs
in a pre-Permian complex which mainly consists of green schists, meta-volcanics, and gneiss rocks. Shear zones are the host
of gold mineralization. Gold paragenesis minerals include pyrite, chalcopyrite, pyrrhotite, and secondary minerals. Pyrites
occur as pre-, syn-, and post-metamorphism minerals. To determine the source of the ore-bearing fluids, fifty samples were
selected for petrographical and stable isotope studies. The mean values of 12.4‰, and −42‰ for δ18O and δD isotopes, respectively, and a mean value of 7.75‰ of calculated fractionation factors for δ18O H2O, from quartz veins indicate that metamorphic host rocks are the most important source for the fluids and gold mineralization.
Three generations of pyrite can be distinguished showing a wide range of δ34S. Gold mineralization is closely associated with intense hydrothermal alteration along the ductile shear zones. The characteristics
of the gold mineralization in the study area are similar to those of orogenic gold deposits elsewhere.
An erratum to this article can be found at 相似文献
85.
In this paper, we investigate the behavior of equation of state parameter and energy density for dark energy in the framework of f(T) gravity. For this purpose, we use anisotropic LRS Bianchi type I universe model. The behavior of accelerating universe is discussed for some well-known f(T) models. It is found that the universe takes a transition between phantom and non-phantom phases for f(T) models except exponential and logarithmic models. We conclude that our results are relativity analogous to the results of FRW universe. 相似文献
86.
Syed?Md.?Touhidul?MustafaEmail authorView authors OrcID profile Khodayar?Abdollahi Boud?Verbeiren Marijke?Huysmans 《Hydrogeology Journal》2017,25(5):1357-1375
Groundwater drought is a specific type of hydrological drought that concerns groundwater bodies. It may have a significant adverse effect on the socio-economic, agricultural, and environmental conditions. Investigating the effect of different climatic and anthropogenic factors on groundwater drought provides essential information for sustainable planning and management of (ground) water resources. The aim of this study is to identify the influencing factors on groundwater drought in north-western Bangladesh, to understand the forcing mechanisms. A multi-step methodology is proposed to achieve this objective. The standardised precipitation index (SPI) and reconnaissance drought index (RDI) have been used to quantify the aggregated deficit between precipitation and the evaporative demand of the atmosphere, i.e. meteorological drought. The influence of land-cover patterns on the groundwater drought has been identified by calculating spatially distributed groundwater recharge as a function of land cover. Groundwater drought is defined by a threshold method. The results show that the evapotranspiration and rainfall deficits are determining meteorological drought, which shows a direct relation with groundwater recharge deficits. Land-cover change has a small effect on groundwater recharge but does not seem to be the main cause of groundwater-level decline (depletion) in the study area. The groundwater depth and groundwater-level deficit (drought) is continuously increasing with little correlation to meteorological drought or recharge anomalies. Overexploitation of groundwater for irrigation seems to be the main cause of groundwater-level decline in the study area. Efficient irrigation management is essential to reduce the growing pressure on groundwater resources and ensure sustainable water management. 相似文献
87.
Masoud Rabeti Moghadam Alireza Sadeghi Abdollahi 《Marine Georesources & Geotechnology》2017,35(3):376-396
Breakwaters provide a calm sea basin for ships and protect harbor facilities by reflecting wave energy toward the open sea area. Their performance under environmental loadings is the main concern for coastal engineers. Liquefaction susceptibility of loose sediments of seabed threatens performance of these structures. The article investigates soil liquefaction effects on the seismic performance of Iran liquefied natural gas (LNG) composite breakwater. Performance-based design method, considering both grade of the breakwater and acceptable level of damages, was selected as design philosophy. Liquefaction-induced damages to the breakwater were determined by numerical analysis. Since the obtained level of deformations did not meet allowable damages, soil improvement against liquefaction was considered. Different improvement patterns were proposed based on distribution of pore pressure ratio (ru) beneath the breakwater to control its seismic performance. This investigation revealed that the most important area for soil improvement is located near the toes of breakwater to control the slope instability and performance of the breakwater. 相似文献
88.
Paleoproterozoic granitoids in the basement of Bangladesh: A piece of the Indian shield or an exotic fragment of the Gondwana jigsaw? 总被引:1,自引:0,他引:1
S.M. Mahbubul Ameen Simon A. Wilde Md. Zafrul Kabir Eunuse Akon Khalil R. Chowdhury Md. Sharif Hossain Khan 《Gondwana Research》2007,12(4):380-387
We present the first precise age for Precambrian basement rocks in Bangladesh. These lie within the Dinajpur block, located between the Indian Craton to the southwest and the Shillong Massif to the east. There are no surface outcrops and the rocks were intersected by drill holes. They consist of a suite of tonalitic and granodioritic rocks, variously deformed to granitic gneiss and intruded by younger monzogranite. A tonalite obtained at a depth of 227.48 m in drill hole BH-2 at Maddhapara, in northwestern Bangladesh, records a SHRIMP zircon 207Pb/206Pb magmatic age of 1722 ± 6 Ma. Paleoproterozoic rocks with similar magmatic ages are unknown in the adjacent Indian blocks of the Chotanagpur Plateau (Indian Craton) or Shillong Massif. This lack of comparable ages may be due to the paucity of precise radiometric ages from the Indian terrains or, more likely, because there are real age differences, with the buried rocks at Maddhapara representing a separate and discrete microcontinental fragment (the Dinajpur block) that was trapped by the northward migration of India during Gondwana dispersal. 相似文献
89.
Azadeh Abdollahi Hamed Gharibdoost 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2016,10(3):213-222
The North Qazvin region is a part of the Central Alborz Mountains in Iran and has experienced destructive earthquakes. This region is a popular and industrial zone near Tehran, capital of Iran. To identify the highest and lowest seismic hazard location and consequently the seismic zonation of this region, different parameters, such as topography, geology, tectonics and seismicity, have been focused. Accordingly, the north of Qazvin region can be divided into three subzones: western, eastern and southern. Seismic activity of the western zone is higher than the other ones and seismic potential of the eastern zone is higher than the other two zones. This zoning is also necessary for all seismic active areas to find the most dangerous zone. 相似文献
90.
M.S.Seif M.Askari 《中国海洋工程》2004,18(3):477-484
The paper contains the results of an experimental study on a planing catamaran. The aim of this study is resistance reduction with application of foils. Experiments are performed in different conditions and the results are compared with each other. The foils are used in different configurations and it is concluded that unsuitable design may result in larger resistance. But, it is also shown that, for a good design, the resistance may be reduced considerably. 相似文献