全文获取类型
收费全文 | 115篇 |
免费 | 0篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 10篇 |
大气科学 | 3篇 |
地球物理 | 4篇 |
地质学 | 23篇 |
海洋学 | 4篇 |
天文学 | 71篇 |
自然地理 | 2篇 |
出版年
2022年 | 1篇 |
2020年 | 1篇 |
2018年 | 5篇 |
2017年 | 8篇 |
2016年 | 8篇 |
2015年 | 6篇 |
2014年 | 3篇 |
2013年 | 5篇 |
2012年 | 4篇 |
2011年 | 10篇 |
2010年 | 8篇 |
2009年 | 5篇 |
2008年 | 2篇 |
2007年 | 3篇 |
2006年 | 5篇 |
2005年 | 7篇 |
2004年 | 3篇 |
2003年 | 1篇 |
2002年 | 5篇 |
2001年 | 3篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1982年 | 2篇 |
1977年 | 1篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1971年 | 2篇 |
1970年 | 2篇 |
1969年 | 2篇 |
排序方式: 共有117条查询结果,搜索用时 31 毫秒
101.
Abstract– Over 4600 Australasian microtektites from 11 sediment cores along an N–S transect in the Central Indian Ocean have been investigated optically for microimpact features on their surfaces. Detailed scanning electron microscope examination of 68 microtektites along this transect shows 4091 such features. These samples are located between approximate distances of 3900–5000 km from the suggested impact site in Indochina and therefore constitute distal ejecta. The morphology of the microimpacts seems to show distinct variations with distance from the source crater. The total number of microcraters on each microtektite decreases drastically from North to South indicating systematic decrease in the spatial density of the ejecta, and decrease in collisional activity between microtektites with distance from the proposed source crater location. Closer to the proposed source crater location, the microcraters are predominantly small (few μm), pit bearing with radial and concentric cracks, suggestive of violent interparticle collisions. The scenario is reverse farther from the source crater with smaller numbers of impacted microtektites due to increased dispersion of the ejecta and the microcraters are large and shallow, implying gentle collisions with larger particles. These observations provide systematic ground truth for the processes that take place as the ejecta of a large oblique impact which generated the Australasian tektite strewn field is emplaced. The microimpacts appear to take place during the descent of the ejecta and their intensity and number density decrease as a function of the spatial density of the ejecta at any given place and with distance from the source region. These features could help understand processes that take place during ejecta emplacement on planets with substantial atmosphere such as Mars and Venus. 相似文献
102.
103.
Anirban Akhand Anirban Mukhopadhyay Abhra Chanda Sandip Mukherjee Abhishek Das Sourav Das Sugata Hazra Debasis Mitra S. B. Choudhury K. H. Rao 《Journal of the Indian Society of Remote Sensing》2017,45(1):147-154
Sundarban, the largest single patch of mangrove forest of the world is shared by Bangladesh (~ 60 %) and India (~ 40 %). Loss of mangrove biomass and subsequent potential emission of carbon dioxide is reported from different parts of the world. We estimated the loss of above ground mangrove biomass and subsequent potential emission of carbon dioxide in the Indian part of the Sundarban during the last four decades. The loss of mangrove area has been estimated with the help of remotely sensed data and potential emission of carbon dioxide has been evaluated with the help of published above ground biomass data of Indian Sundarban. Total loss of mangrove area was found to be 107 km2 between the year 1975 and 2013. Amongst the total loss ~60 % was washed away in the water by erosion, ~ 23 % was converted into barren lands and the rest were anthropogenically transformed into other landforms. The potential carbon dioxide emission due to the degradation of above ground biomass was estimated to be 1567.98 ± 551.69 Gg during this period, which may account to 64.29 million $ in terms of the social cost of carbon. About three-forth of the total mangrove loss was found in the peripheral islands which are much more prone to erosion. Climate induced changes and anthropogenic land use change could be the major driving force behind this loss of ‘blue carbon’. 相似文献
104.
Sandip K. Chakrabarti 《Journal of Astrophysics and Astronomy》1988,9(1):49-61
We compute the metric coefficients and study some properties of the spacetime comprising of a Schwarzschild hole distorted
by a self gravitating thick disc. 相似文献
105.
Subhash Chandra Nandy 《Pure and Applied Geophysics》1970,83(1):56-61
Summary The equations of electricity and the equations of hydrodynamics have been used to solve the problem of unsteady flow of a viscous fluid under variable surface charges. 相似文献
106.
107.
Prasad Basu S. Mondal Sandip K. Chakrabarti 《Monthly notices of the Royal Astronomical Society》2008,388(1):219-226
Gravitational wave signal characteristics from a binary black hole system in which the companion moves through the accretion disc of the primary are studied. We chose the primary to be a super-massive ( M = 108 M⊙ ) Kerr black hole and the companion to be a massive black hole ( M = 105 M⊙ ) to clearly demonstrate the effects. We show that the drag exerted on the companion by the disc is sufficient to reduce the coalescence time of the binary. The drag is primarily due to the fact that the accretion disc on a black hole deviates from a Keplerian disc and becomes sub-Keplerian due to inner boundary condition on the black hole horizon. We consider two types of accretion rates on to the companion. The companion is deeply immersed inside the disc and it can accrete at the Bondi rate which depends on the instantaneous density of the disc. However, an accretion disc can also form around the smaller black hole and it can accrete at its Eddington rate. Thus, this case is also studied and the results are compared. We find that the effect of the disc will be significant in reducing the coalescence time and one needs to incorporate this while interpreting gravitational wave signals emitted from such a binary system. 相似文献
108.
Arun Mondal Deepak Khare Sananda Kundu Sandip Mukherjee Anirban Mukhopadhyay Surajit Mondal 《地学前缘(英文版)》2017,8(3):425-436
Digital Elevation Model (DEM) is one of the important parameters for soil erosion assessment. Notable uncertainties are observed in this study while using three high resolution open source DEMs. The Revised Universal Soil Loss Equation (RUSLE) model has been applied to analysis the assessment of soil erosion uncertainty using open source DEMs (SRTM, ASTER and CARTOSAT) and their increasing grid space (pixel size) from the actual. The study area is a part of the Narmada river basin in Madhya Pradesh state, which is located in the central part of India and the area covered 20,558 km2. The actual resolution of DEMs is 30 m and their increasing grid spaces are taken as 90, 150, 210, 270 and 330 m for this study. Vertical accuracy of DEMs has been assessed using actual heights of the sample points that have been taken considering planimetric survey based map (toposheet). Elevations of DEMs are converted to the same vertical datum from WGS 84 to MSL (Mean Sea Level), before the accuracy assessment and modelling. Results indicate that the accuracy of the SRTM DEM with the RMSE of 13.31, 14.51, and 18.19 m in 30, 150 and 330 m resolution respectively, is better than the ASTER and the CARTOSAT DEMs. When the grid space of the DEMs increases, the accuracy of the elevation and calculated soil erosion decreases. This study presents a potential uncertainty introduced by open source high resolution DEMs in the accuracy of the soil erosion assessment models. The research provides an analysis of errors in selecting DEMs using the original and increased grid space for soil erosion modelling. 相似文献
109.
O. N. Tiwari C. Devadoss M. Pradhan T. Nandy 《International Journal of Environmental Science and Technology》2017,14(1):49-60
In this study, multivariate statistical approaches, namely hierarchical cluster analysis (CA) and principal component analysis (PCA), were employed to understand the impact of copper mining on surface waters located in Central-East India. The data set generated consisted of nine parameters, namely pH, dissolved oxygen (DO), alkalinity, total dissolved solids, copper, iron, manganese, zinc and fluoride, collected in forty sampling points covering all seasons. As delineated by CA, the entire data set for both the surface waters was bifurcated into groups, namely Banjar River inclusion of seepage points (BRISP) and Banjar River exclusion of seepage points (BRESP), Son River inclusion of seepage points (SRISP) and Son River exclusion of seepage points (SRESP). Four latent factors were identified, namely copper, iron, fluoride and manganese, explaining 84.7 % of variance for BRISP, 71.9 % of variance for BRESP, 66.7 % of variance for SRISP and 68 % of variance for SRESP. The extensive application of PCA on BRISP, BRESP, SRISP and SRESP reveals that the main stream of both the rivers remains unaffected by mining operations when seepage points were excluded. Additionally, iron content is considerably significant throughout the stream due to the geogenic sources and it is considered as a major factor for the depletion of DO level in the streams. This study reveals the level of contamination in the studied surface waters and the effectiveness of multivariate statistical techniques for evaluation and interpretation of complex data matrix in understanding the spatial variations and identification of pollution sources. 相似文献
110.
The occurrence of dental/skeletal fluorosis among the people in the study area provided the motivation to assess the distribution, severity and impact of fluoride contamination in groundwater of Bankura district at Simlapal block, West Bengal, India. To meet the desired objective, groundwater samples were collected from different locations of Laxmisagar, Machatora and Kusumkanali regions of Simlapal block at different depths of tube wells in both pre- and post-monsoon seasons. Geochemical results reveal that the groundwaters are mostly moderate- to hard-water type. Of total groundwater samples, 37% are situated mainly in relatively higher elevated region containing fluoride above 1.5 mg/L, indicating that host aquifers are severely affected by fluoride contamination. Machatora region is highly affected by fluoride contamination with maximum elevated concentration of 12.2 mg/L. Several symptoms of fluorosis among the different age-groups of people in Laxmisagar and Machatora areas are indicating consumption of fluoridated water for prolonged period. The groundwater samples were mainly Na–Ca–HCO3 type and rock dominance indicating the dissolution of minerals taking place. Ion exchange between OH? ion and F? ion present in fluoride-bearing mineral is the most dominant mechanism of fluoride leaching. High concentration of Na+ and HCO3 ? increases the alkalinity of the water, providing a favorable condition for fluoride to leach into groundwater from its host rocks and minerals. 相似文献