首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   44篇
  免费   2篇
  国内免费   2篇
测绘学   1篇
大气科学   5篇
地球物理   10篇
地质学   23篇
海洋学   4篇
天文学   4篇
自然地理   1篇
  2022年   4篇
  2021年   1篇
  2020年   2篇
  2019年   4篇
  2018年   4篇
  2017年   5篇
  2016年   6篇
  2015年   2篇
  2014年   5篇
  2013年   2篇
  2012年   3篇
  2011年   4篇
  2009年   5篇
  2008年   1篇
排序方式: 共有48条查询结果,搜索用时 31 毫秒
41.
In this paper, we report a detailed study of helium (He) incorporation and diffusion pathways in the perfect and defective zircon lattice. Ab initio methods based on Density Functional Theory (DFT) were used to calculate the structural features, the solution energies in interstitial sites in the perfect zircon and in vacancy sites of the defective lattice and He diffusion pathways in these systems. We show that the mode of He incorporation in the perfect zircon is influenced mainly by the topological features of the lattice, promoting site preference of He towards accommodation in the interstitial sites present in the middle of c cylinder channels. The presence of defect species in the form of lattice vacancies and interstitials has a significant effect on He solubility and diffusivity in the lattice, where the ability of lattice vacancies to act as physical traps or repulsive sites depends greatly on the electronic nature of the vacancy, which can enhance solubility of He in the lattice and affect the kinetics of He mobility in zircon mineral.  相似文献   
42.
We report the results of an atomistic computational study of He accommodation and diffusion in the Pu4+- and U4+-doped zircon (ZrSiO4). The He-cation potentials derived for this work give results of comparable accuracy to DFT calculations. We have calculated the structural features of doped lattices as well as He solution energies in interstitial sites in the perfect and doped zircon and its diffusion in these lattices. The mode of He accommodation in the perfect zircon is influenced mainly by the topological features of the lattice, promoting site preference of He towards accommodation in the interstitial sites present in the middle of c cylinder channels, whereas the presence of Pu4+ and U4+ dopants in the zircon lattice significantly affects the energetics of He accommodation and diffusion in the lattice. Doping causes strong local structural distortions, extending to next nearest-neighbour atoms of the dopants to a radius of up to ∼4 Å, in agreement with experimental results. The presence of dopants in the vicinity of He enhances the solubility of He in the lattice compared to the perfect lattice. The mechanism of diffusion is also affected, where the dopants can create a He trap along the most energetically favourable pathway in the (0 0 1) direction, which may slow down the movement of He along the c direction. The dopants also lower the energy barriers by ∼50% in the octahedral sites.  相似文献   
43.
Rostamsowlat  Iman  Richard  Thomas  Evans  Brian 《Acta Geotechnica》2019,14(2):519-534
Acta Geotechnica - A vast majority of experimental researches focuses on the cutting action of a sharp cutter, while there has been limited experimental work devoted to the study of the contact...  相似文献   
44.
Using measured radial velocity data of nine double lined spectroscopic binary systems NSV 223, AB And, V2082 Cyg, HS Her, V918 Her, BV Dra, BW Dra, V2357 Oph, and YZ Cas, we find corresponding orbital and spectroscopic elements via the method introduced by Karami and Mohebi (Chin. J. Astron. Astrophys. 7:558, 2007a) and Karami and Teimoorinia (Astrophys. Space Sci. 311:435, 2007). Our numerical results are in good agreement with those obtained by others using more traditional methods.  相似文献   
45.
2010年玉树超剪切破裂地震破裂过程反演   总被引:1,自引:0,他引:1       下载免费PDF全文
为探讨玉树地震是否为超剪切破裂事件,利用Yagi的方法重新进行了此次地震震源破裂过程的反演。通过给定不同的破裂速度进行对比,发现当破裂速度为4.7km/s时,理论与实际观测结果拟合残差最小,且反演结果更符合实际。另据P波高频辐射能量包络反演,破裂传播速度在4.7~5.8km/s范围内,而该地区的剪切波速度则为3.0~3.6km/s,从而证明了此次地震超剪切破裂现象的存在。反演结果表明,此次地震在玉树段的NW和SE段形成了19和31km的地表破裂,而震中所在的中段由于隆宝湖拉分盆地的存在,造成了15km的未破裂区。超剪切破裂是造成SE段玉树县城遭受严重破坏的原因之一。  相似文献   
46.
Ferdosian  Iman  Haie  Naim 《Water Resources》2016,43(1):200-206
Water Resources - There are two significant reasons for the uncertainties of water demand. On one hand, an evolving technological world is plagued with accelerated change in lifestyles and...  相似文献   
47.
Indian monsoon is the most prominent of the world’s monsoon systems which primarily affects synoptic patterns of India and adjacent countries such as Iran in interaction with large-scale weather systems. In this article, the relationship between the withdrawal date of the Indian monsoon and the onset of fall precipitation in Iran has been studied. Data included annual time series of withdrawal dates of the Indian monsoon prepared by the Indian Institute for Tropical Meteorology, and time series of the first date of 25 mm accumulated precipitation over Iran’s synoptic weather stations in a 10-day period which is the basis for the cultivation date. Both time series were considered in Julian calendar with the starting date on August 1. The studied period is 1960–2014 which covers 55 years of data from 36 meteorological stations in Iran. By classifying the withdrawal dates of the Indian monsoon in three stages of late, normal, and early withdrawals, its relation with the onset of fall precipitation in western, southwestern, southern, eastern, central, and northern regions of Iran was studied. Results demonstrated that in four out of the six mentioned regions, the late withdrawal of the Indian monsoon postpones the onset of fall precipitation over Iran. No significant relation was found between the onset of fall precipitation in central region of Iran and the monsoon’s withdrawal date. In the western, southwestern, southern, and eastern regions of Iran, the late monsoon delays the onset of fall’s precipitation; while in the south Caspian Sea coastal area, it causes the early onset of autumnal precipitation. The lag in onset of fall precipitation in Iran which is coordinated with the late withdrawal of monsoon is accompanied with prolonged subtropical high settling over Iran’s plateau that prevents the southward movement of polar jet frontal systems. Such conditions enhance northerly wind currents over the Caspian Sea which, in turn, increase the precipitation in Caspian coastal provinces, which has a different behavior from the overall response of Iran’s climate to the late withdrawal of monsoon. In the phase of early monsoon withdrawal, the subtropical jet is located at the 200 hPa level in 32.5° north latitude; compared with the late withdrawal date, it shows a 2° southward movement. Additionally, the 500 hPa trough is also located in the Eastern Mediterranean, and the MSL pressure anomaly is between ? 4 to ? 7 hPa. The Mediterranean trough in the late withdrawal phase is located in its central zones. It seems that the lack of significant correlation between late withdrawal date of Indian monsoon and late fall’s precipitation onset in the central region of Iran depends on three reasons:1. Lack of adequate weather stations in central region of Iran.2. Precipitation standard deviations over arid and warm regions are high.3. Central flat region of Iran without any source of humidity is located to the lee side of Zagros mountain range. So intensification or development of frontal systems is almost prohibited over there.  相似文献   
48.
Evaluation of fractures and their parameters, such as aperture and density, is necessary in the optimization of oil production and field development. The purpose of this study is the calculation of fracture parameters in the Asmari reservoir using two electrical image logs (FMI, EMI), and the determination of fracture parameters’ effect on the porosity and permeability using thin sections and velocity deviation log (VDL). The results indicate that production in the Asmari reservoir is a combination of fractures and rock matrix. Fracture aperture (VAH) and fracture porosity (VPA) are only measurable with core and image logs directly. However, regarding core limitations, the image log has been recognized as the best method for fracture parameter determination due to their high resolution (2.5 mm). In this study, VDL log and thin sections have been used as auxiliary methods which may be available in all wells. The VDL log provides a tool to obtain downhole information about the predominant pore type in carbonates. Results indicate that between fracture parameters, VAH is considered as the most important parameter for determining permeability. For well No. 3, VAH ranges from minimum 51 × 10?5 mm to maximum 0. 047 mm and VPA changes from min 10?5% to maximum 0.02056%. For well No. 6, VAH varies from 5 × 10?4 to 0.0695 mm and VPA varies from 10?5 to 0.015%. Therefore, due to high fracture density and fracture aperture, it seems that most of effective porosity originates from fractures especially in well No. 3. However, VDL for well No. 6 indicates that intercrystalline and vuggy porosity are the dominant porosity. This result may be an indication for fracture set diversity in the two studied wells. While in well No. 3, they related to the folding and active faults, in well No. 6 they are only of folding type. Furthermore, results indicate the high capability for both of EMI and FMI image logs for calculation of fracture and vug parameters in the carbonate reservoirs.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号