全文获取类型
收费全文 | 73篇 |
免费 | 1篇 |
专业分类
测绘学 | 9篇 |
大气科学 | 4篇 |
地球物理 | 9篇 |
地质学 | 33篇 |
海洋学 | 4篇 |
天文学 | 13篇 |
自然地理 | 2篇 |
出版年
2023年 | 1篇 |
2022年 | 3篇 |
2021年 | 2篇 |
2020年 | 2篇 |
2019年 | 2篇 |
2018年 | 5篇 |
2017年 | 1篇 |
2016年 | 3篇 |
2015年 | 3篇 |
2014年 | 8篇 |
2013年 | 14篇 |
2012年 | 3篇 |
2011年 | 6篇 |
2010年 | 1篇 |
2009年 | 3篇 |
2008年 | 3篇 |
2007年 | 4篇 |
2006年 | 4篇 |
2005年 | 1篇 |
2004年 | 1篇 |
2003年 | 1篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有74条查询结果,搜索用时 31 毫秒
41.
Performance evaluation of retrofitting strategies for non-seismically designed RC buildings using steel braces 总被引:1,自引:1,他引:0
H. Varum F. Teixeira-Dias P. Marques A. V. Pinto A. Q. Bhatti 《Bulletin of Earthquake Engineering》2013,11(4):1129-1156
Recent major earthquakes around the world have evidenced that research in earthquake engineering must be directed to the vulnerability assessment of existing constructions lacking appropriate seismic resisting characteristics. Their retrofit or replacement should be made in order to reduce vulnerability, and consequent risk, to currently accepted levels. In this work, the efficiency of ductile steel eccentrically-braced systems in the seismic retrofitting of existing reinforced concrete (RC) buildings is studied. The retrofit technique studied consists in a bracing system with an energy dissipation device, designed to dissipate energy by shear deformation. The numerical model was calibrated with cyclic test results on a full-scale structure. The models used for the RC frame and masonry represent their real behavior and influence in the global structural response. The steel bracing system was modeled with strut rigid elements. The model for the energy dissipater device reproduces rigorously the behavior of the shear-link observed in the cyclic tests, namely in terms of shear, drift and energy dissipation. With the calibrated numerical model, a series of non-linear dynamic analyses were performed, for different earthquake input motions, intending to study: the influence of the retrofitting system in the response of bare and infilled structures; the influence of the location and strength of the retrofitting system. 相似文献
42.
Toshio Koike Petra Koudelova Patricia Ann Jaranilla-Sanchez Asif Mumtaz Bhatti Cho Thanda Nyunt Katsunori Tamagawa 《中国科学:地球科学(英文版)》2015,58(1):76-95
This paper introduces the process of development and practical use implementation of an advanced river management system for supporting integrated water resources management practices in Asian river basins under the framework of GEOSS Asia water cycle initiative (AWCI). The system is based on integration of data from earth observation satellites and in-situ networks with other types of data, including numerical weather prediction model outputs, climate model outputs, geographical information, and socio-economic data. The system builds on the water and energy budget distributed hydrological model (WEB-DHM) that was adapted for specific conditions of studied basins, in particular snow and glacier phenomena and equipped with other functions such as dam operation optimization scheme and a set of tools for climate change impact assessment to be able to generate relevant information for policy and decision makers. In situ data were archived for 18 selected basins at the data integration and analysis system of Japan (DIAS) and demonstration projects were carried out showing potential of the new system. It included climate change impact assessment on hydrological regimes, which is presently a critical step for sound management decisions. Results of such three case studies in Pakistan, Philippines, and Vietnam are provided here. 相似文献
43.
This paper examines the effect of a constant κ of a particular integral of the Gylden-Meshcherskii problem on the stability of the triangular points in the restricted three-body
problem under the influence of small perturbations in the Coriolis and centrifugal forces, together with the effects of radiation
pressure of the bigger primary, when the masses of the primaries vary in accordance with the unified Meshcherskii law. The
triangular points of the autonomized system are found to be conditionally stable due to κ. We observed further that the stabilizing or destabilizing tendency of the Coriolis and centrifugal forces is controlled
by κ, while the destabilizing effects of the radiation pressure remain unchanged but can be made strong or weak due to κ. The condition that the region of stability is increasing, decreasing or does not exist depend on this constant. The motion
around the triangular points L
4,5 varying with time is studied using the Lyapunov Characteristic Numbers, and are found to be generally unstable. 相似文献
44.
Rashid Umar Izrar Ahmed Fakhre Alam Mohammad Muqtada Khan 《Environmental Geology》2009,58(6):1295-1300
The present study was undertaken to assess major ion chemistry of groundwater in parts of the Central Ganga Plain and observe
seasonal variations in its chemical quality. Systematic sampling was carried out during November 2005 and June 2006. The major
ion chemistry of groundwater shows large variations, so much so that at times the meteoric signature seems to be completely
obliterated. In many samples the concentrations of SO4, NO3 and F are above the permissible limit for human consumption. The graphical treatment of major ion chemistry helps in identifying
four types of groundwater. All possible ionic species such as NaCl, KCl, NaHCO3, NaSO4, KNO3, NaNO3, CaHCO3, MgHCO3, MgSO4 are likely to occur in groundwater system. The observed chemical variations may be attributed to sediment water interaction,
ion exchange, dissolution mechanisms and anthropogenic influences such as application of fertilizers and effluents from sugar
factories and paper mills. A general increase in TDS is observed in samples during June 2006. The increase in salinity is
attributed to evaporation from water table, irrigation return flows, anthropogenic activities and below average rainfall in
2005 and 2006.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
45.
Hydrogeological and hydrochemical framework of regional aquifer system in Kali-Ganga sub-basin, India 总被引:5,自引:0,他引:5
The central Ganga Basin is one of the major groundwater reservoirs in India. The Kali-Ganga sub-basin is a micro watershed
of the central Ganga Basin, containing a number of productive aquifers. A detailed hydrogeological investigation was carried
out, which reveals the occurrence of a single-tier aquifer system down to 163 m bgl (metres below ground level), but at places
it is interleaved with clay layers; thus imparting it a two-to three-tier aquifer system. These aquifers are unconfined to
confined in disposition. The transmissivity, storage coefficient and hydraulic conductivity are determined as 2178 m2/day, 1.12×10–5 and 120 m/day, respectively. The groundwater of the basin is fresh, of an alkali-bicarbonate type and is suitable for irrigation
and domestic use. However, in certain areas, extensive agricultural activities, and domestic and industrial effluents have
caused some deterioration of groundwater quality. This study contains data of where the concentration of Fe, Pb, Cd, Cr and
Ni are higher than the permissible limits, which may be hazardous to public health.
Received: 2 March 2000 · Accepted: 3 July 2000 相似文献
46.
Stocks, Chemistry, and Sensitivity to Climate Change of Dead Organic Matter Along the Canadian Boreal Forest Transect Case Study 总被引:6,自引:0,他引:6
Improving our ability to predict the impact of climate change on the carbon (C) balance of boreal forests requires increased understanding of site-specific factors controlling detrital and soil C accumulation. Jack pine (Pinus banksiana) and black spruce (Picea mariana) stands along the Boreal Forest Transect Case Study (BFTCS) in northern Canada have similar C stocks in aboveground vegetation and large woody detritus, but thick forest floors of poorly-drained black spruce stands have much higher C stocks, comparable to living biomass. Their properties indicate hindered decomposition and N cycling, with high C/N ratios, strongly stratified and depleted δ13C and δ15N values, high concentrations of tannins and phenolics, and 13C nuclear magnetic resonance (NMR) spectra typical of poorly decomposed plant material, especially roots and mosses. The thinner jack pine forest floor appears to be dominated by lichen, with char in some samples. Differences in quantity and quality of aboveground foliar and woody litter inputs are small and unlikely to account for the contrasts in forest floor accumulation and properties. These are more likely associated with site conditions, especially soil texture and drainage, exacerbated by increases in sphagnum coverage, forest floor depth, and tannins. Small changes in environmental conditions, especially reduced moisture, could trigger large C losses through rapid decomposition of forest floor in poorly drained black spruce stands in this region. 相似文献
47.
Naseemus Saba Rashid Umar Ahsan Absar 《Journal of the Geological Society of India》2018,91(6):711-716
The present work has been carried out in Moradabad, one of the important cities in the state of Uttar Pradesh. The main focus of the study is to estimate the extent of anthropogenic contamination in shallow groundwater of the area. For this purpose, total 188 groundwater samples collected from handpumps in pre- and post monsoon period of 2012 and 2013 (47 in each season) were analyzed for physico-chemical parameters such as pH, EC, TDS, major cations (Ca, Mg, Na, and K) and anions (Cl, HCO3, SO4, NO3 and F). The results of the analysis suggested that groundwater is slightly alkaline, hard to very hard in nature, average TDS values were found to be more than 1000 mg/l, which gives a clear evidence of anthropogenic influences. To estimate the extent of contamination, the information on relatively unpolluted groundwater systems occurring in different terrains including Ganga plain where the groundwater was relatively unaffected by anthropogenic activities is used. The estimated pristine chemical composition of groundwater of different terrains used in the present study was compared with the groundwater of Moradabad city. This comparison showed that Moradabad city with the highest Na, K, Cl, SO4 and NO3 values being 440 mg/l, 96 mg/l, 537 mg/l, 537 mg/ l and 244 mg/l, respectively, is one of the most polluted urban centres within the Ganga plain. It may be suggested that values of > 50 mg/l for Na, > 10 mg/l for K, > 25 mg/l for Cl, > 50 mg/l for SO4 and > 10 mg/l for NO3 have their respective sources in anthropogenic activities such as agricultural in the peripheral region, human and animal wastes, leakages from drains and septic tanks, landfill leachates and industrial effluents. 相似文献
48.
Omer Aziz Tahir Hussain Matee Ullah Asher Samuel Bhatti Aamir Ali 《Marine Geophysical Researches》2018,39(4):491-508
The exploration and production of unconventional resources has increased significantly over the past few years around the globe to fulfill growing energy demands. Hydrocarbon potential of these unconventional petroleum systems depends on the presence of significant organic matter; their thermal maturity and the quality of present hydrocarbons i.e. gas or oil shale. In this work, we present a workflow for estimating Total Organic Content (TOC) from seismic reflection data. To achieve the objective of this study, we have chosen a classic potential candidate for exploration of unconventional reserves, the shale of the Sembar Formation, Lower Indus Basin, Pakistan. Our method includes the estimation of TOC from the well data using the Passey’s ΔlogR and Schwarzkofp’s methods. From seismic data, maps of Relative Acoustic Impedance (RAI) are extracted at maximum and minimum TOC zones within the Sembar Formation. A geostatistical trend with good correlation coefficient (R2) for cross-plots between TOC and RAI at well locations is used for estimation of seismic based TOC at the reservoir scale. Our results suggest a good calibration of TOC values from seismic at well locations. The estimated TOC values range from 1 to 4% showing that the shale of the Sembar Formation lies in the range of good to excellent unconventional oil/gas play within the context of TOC. This methodology of source rock evaluation provides a spatial distribution of TOC at the reservoir scale as compared to the conventional distribution generated from samples collected over sparse wells. The approach presented in this work has wider applications for source rock evaluation in other similar petroliferous basins worldwide. 相似文献
49.
Ansar Khan Soumendu Chatterjee Hashem Akbari Saad Saleem Bhatti Apurba Dinda Chandana Mitra 《国际地球制图》2019,34(5):504-527
The extraction of urban built-up areas is an important aspect of urban planning and understanding the complex drivers and biophysical mechanism of urban climate processes. However, built-up area extraction using Landsat data is a challenging task due to spatio-temporal dynamics and spatially intermixed nature of Land Use and Land Cover (LULC) in the cities of the developing countries, particularly in tropics. In the light of advantages and drawbacks of the Normalized Difference Built-up Index (NDBI) and Built-up Area Extraction Method (BAEM), a new and simple method i.e. Step-wise Land-class Elimination Approach (SLEA) is proposed for rapid and accurate mapping of urban built-up areas without depending exclusively on the band specific normalized indices, in order to pursue a more generalized approach. It combines the use of a single band layer, Normalized Difference Vegetation Index (NDVI) image and another binary image obtained through Logit model. Based on the spectral designation of the satellite image in use, a particular band is chosen for identification of water pixels. The Double-window Flexible Pace Search (DFPS) approach is employed for finding the optimum threshold value that segments the selected band image into water and non-water categories. The water pixels are then eliminated from the original image. The vegetation pixels are similarly identified using the NDVI image and eliminated. The residual pixels left after elimination of water and vegetation categories belong either to the built-up areas or to bare land categories. Logit model is used for separation of the built-up areas from bare lands. The effectiveness of this method was tested through the mapping of built-up areas of the Kolkata Metropolitan Area (KMA), India from Thematic Mapper (TM) images of 2000, 2005 and 2010, and Operational Land Imager (OLI) image of 2015. Results of the proposed SLEA were 95.33% accurate on the whole, while those derived by the NDBI and BAEM approaches returned an overall accuracy of 83.67% and 89.33%, respectively. Comparisons of the results obtained using this method with those obtained from NDBI and BAEM approaches demonstrate that the proposed approach is quite reliable. The SLEA generates new patterns of evidence and hypotheses for built-up areas extraction research, providing an integral link with statistical science and encouraging trans-disciplinary collaborations to build robust knowledge and problem solving capacity in urban areas. It also brings landscape architecture, urban and regional planning, landscape and ecological engineering, and other practice-oriented fields to bear together in processes for identifying problems and analyzing, synthesizng, and evaluating desirable alternatives for urban change. This method produced very accurate results in a more efficient manner compared to the earlier built-up area extraction approaches for the landscape and urban planning. 相似文献
50.
This paper is devoted to investigate the spherically symmetric wormhole models in f(R, T) gravity, where T and R are trace of stress energy tensor and the Ricci scalar, respectively. In this context, we discuss three distinct cases of fluid distributions viz, anisotropic, barotropic and isotropic matter contents. After considering the exponential f(R, T) model, the behavior of energy conditions are analyzed that will help us to explore the general conditions for wormhole geometries in this gravity. It is inferred that the usual matter in the throat could obey the energy conditions but the gravitational field emerging from higher order terms of modified gravity favor the existence of the non-standard geometries of wormholes. The stability as well as the existence of wormholes are also analyzed in this theory. 相似文献