全文获取类型
收费全文 | 687篇 |
免费 | 27篇 |
国内免费 | 12篇 |
专业分类
测绘学 | 29篇 |
大气科学 | 27篇 |
地球物理 | 164篇 |
地质学 | 354篇 |
海洋学 | 35篇 |
天文学 | 66篇 |
综合类 | 20篇 |
自然地理 | 31篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 21篇 |
2020年 | 28篇 |
2019年 | 23篇 |
2018年 | 70篇 |
2017年 | 53篇 |
2016年 | 70篇 |
2015年 | 36篇 |
2014年 | 56篇 |
2013年 | 73篇 |
2012年 | 29篇 |
2011年 | 39篇 |
2010年 | 35篇 |
2009年 | 28篇 |
2008年 | 20篇 |
2007年 | 21篇 |
2006年 | 12篇 |
2005年 | 11篇 |
2004年 | 14篇 |
2003年 | 5篇 |
2002年 | 4篇 |
2001年 | 7篇 |
2000年 | 5篇 |
1999年 | 4篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 6篇 |
1994年 | 2篇 |
1993年 | 5篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1989年 | 1篇 |
1988年 | 5篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1977年 | 4篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有726条查询结果,搜索用时 388 毫秒
611.
This paper presents a technique to reproduce compatible seismogran3s involving permanent displacen3ent effects at sites close to the fault source. A multi-objective evolutionary algorithm is used to minimize the differences between the response spectra and multi-tapered power spectral delsilies corresponding to the recorded and simulated wavelbrms. The multi-taper method is used to reduce the spectral leakage that is inherent in the Fourier rams formed form ofwavelbrms, ieading to a reduction of variance in power spectral amplitudes, thus permitting the calibration of the two sets of data. The technique is implemented using the 1998-Fandoqa (lran) earthquake data and the results are compared with the actual observed data. Additionally, a comparison is made with a SAR interfcrometry study leading to fair agreement with the reported dislocation along the main fault. The simulation procedure and results are discussed and assessed concluding that, although the technique may be associated with uncertainties, it can still be used to reproduce wavelbnns at near source sites that include permanent dislocation, and can be used for seismic pertbrmance evaluation of structures in the region under study. 相似文献
612.
EFFECTS OF SEASONALITY ON STREAMFLOW AND WATER QUALITY OF THE PINANG RIVER IN PENANG ISLAND, MALAYSIA 总被引:1,自引:0,他引:1
AhmadJailaniMuhamedYUNUS NobukazuNAKAGOSHI 《中国地理科学(英文版)》2004,14(2):153-161
For the Pinang River, originating in the western highlands of Penang Island, the nature, sources and extent of pollution were studied. The river water samples collected at five selected sites were analyzed for various physical and chemical parameters, namely temperature, DO, BOD, COD, SS, pH, ammoniac nitrogen (AN), and conductance. Long-term data of rainfall and temperature were analyzed to determine the seasonal variations of the streamflow.The streamflow during the dry season is extremely low compared to the wet season, thus concentrations of contaminants derived from point pollution source increase due to lack of rainfall and runoff events. On the contrary, in the predominantly urban and agricultural catchments, non-point pollution source increases during rainy season through seepage and runoff. Effects of seasonal variations consequently deterrnine the quantity and quality of the water parameters.The Jelutong River, the Dondang River and the Air Itam River carry the seepage from widely urban and residential areas to the main Pinang River systems. Water quality of the Pinang River at different points assessed by the water quality indices was compared. According to the quality indices during the study period, water quality in the upper reaches of the river is medium to good. It dwindled in the plains, due to the seepage from urban areas and discharges from the industrial and agricultural lands. 相似文献
613.
In this study, an earth levee model is constructed to investigate the impact of animal burrows on the integrity and performance of earthen structures. A series of centrifuge experiments are conducted on homogenous scaled-down 1H:1V levee models built from the natural Kasama soil. Both intact and deteriorated models were subject to a 35g acceleration level. Invasive animal intrusions were introduced in the form of horizontal array of idealized cylindrical burrows at the mid-height of the levee. The water level was gradually increased during the centrifuge flight, and the response of the levee was monitored throughout the test. Pore pressures were recorded using pressure transducers placed at preselected locations within the model. Surface displacements were measured using laser LVDTs and supplemented with three digital cameras for tracking the overall deformation pattern of the levee model. A summary of the test procedure and selected results is presented herewith. The observed deformation mechanism due to the presence of animal burrows is also described. As compared with the intact levee, the presence of burrows is found to alter the pattern of the water flow through the deteriorated levee structure—leading to a notable increase in the exit hydraulic gradient, internal erosion, and subsequently slope failure. 相似文献
614.
Mohammad Imran Malik M. Sultan Bhat Shahnaz Ahmad Najar 《Journal of the Geological Society of India》2016,87(6):716-726
The valley of Kashmir is blessed with abundant water resources. However, high population growth and concentration of population at favorable locations have resulted in increased demand for water. The problem is further aggravated in Lidder catchment where unplanned tourism development has resulted in deterioration of water quality. Multi-Criteria Evaluation (MCE) approach is adopted using IRS P6 LISS III satellite data 2010, geological map published by Geological Survey of India, toposheets prepared by Survey of India, 1961 and field observation. Seven thematic layers (slope, lineament density, drainage density, soil, geology, geomorphology and land use land cover) are generated in GIS environment and weighted according to their relative relevance to groundwater occurrence. Knowledge-based weights and ranks are normalized, and a weighted linear combination technique is adopted to determine the groundwater potential (GWP). The catchment is divided into five zones of very high, high, medium, low and very low GWP. The results show that 50.22% of the total catchment area, which is uninhabited, has very low GWP. However, the densely populated southern part of the catchment has moderate to very high GWP. The study demonstrates that MCE using remote sensing and GIS technology could be efficiently employed as a very useful tool for the assessment and management of groundwater resources especially in regions where data is poor. 相似文献
615.
Geochemistry and petrogenesis of Proterozoic granitic rocks from northern margin of the Chotanagpur Gneissic Complex (CGC) 总被引:1,自引:0,他引:1
Bhupendra S Yadav Nishchal Wanjari Talat Ahmad Rajesh Chaturvedi 《Journal of Earth System Science》2016,125(5):1041-1060
This study presents the geochemical characteristics of granitic rocks located on the northern margin of Chotanagpur Gneissic Complex (CGC), exposed in parts of Gaya district, Bihar and discusses the possible petrogenetic process and source characteristics. These granites are associated with Barabar Anorthosite Complex and Neo-proterozoic Munger–Rajgir group of rocks. The granitic litho-units identified in the field are grey, pink and porphyritic granites. On the basis of geochemical and petrographic characteristics, the grey and pink granites were grouped together as GPG while the porphyritic granites were named as PG. Both GPG and PG are enriched in SiO2, K2O, Na2O, REE (except Eu), Rb, Ba, HFSE (Nb, Y, Zr), depleted in MgO, CaO, Sr and are characterised by high Fe* values, Ga/Al ratios and high Zr saturation temperatures (GPGavg~ 861 °C and PGavg~ 835 °C). The REE patterns for GPG are moderately fractionated with an average (La/Yb)N~ 4.55 and Eu/Eu* ~ 0.58, than PG which are strongly fractionated with an average (La/Yb)N~ 31.86 and Eu/Eu* ~ 0.75. These features indicate that the granites have an A-type character. On the basis of geochemical data, we conclude that the granites are probably derived from a predominant crustal source with variable mantle involvement in a post-collisional setting. 相似文献
616.
Soil complexity and its multivariable nature restrict the precision of soil maps that are essential tools for soil sustainable management. Most methods developed for reducing impurities of soil map units focus on soil external properties. Taking into account the soil internal properties like geochemical weathering indices could increase the map unit’s purity. However, the compatibility of these indices with Soil Taxonomic Classes has not been studied yet. This study has been performed in a hilly region with different soil types, vegetation and diverse topographic attributes to illustrate the spatial variability of soil weathering indices and their compatibility with Soil Taxonomic Classes. The grid sampling is at 100 m interval. Physico-chemical and total elemental analyses were performed on 184 and 56 soil samples respectively. Eight topographic attributes and 14 common soil development indices were determined. Principal components analysis (PCA) was done to identify the most important components. The results indicated that Morphological Index (MI) was the best index to show the degree of soil development in the studied region. Spatial distribution of Soil Taxonomic Classes showed relatively good compatibility with the first principal component (PC1), Vogt (V) and morphological indices. This study showed that using soil development indices with the conventional methods could be helpful tools in soil survey investigations 相似文献
617.
Komeil Rokni Tajul Ariffin Musa Sharifeh Hazini Anuar Ahmad Karim Solaimani 《Natural Hazards》2015,78(1):219-230
The aim of this paper was to investigate the suitability of the pixel-level and product-level image fusion approaches to detect surface water changes. In doing so, firstly, the principal component analysis technique was applied to Landsat TM 2010 multispectral image to generate the PC components. Several pixel-level image fusion techniques were then performed to merge the Landsat ETM+ 2000 panchromatic with the PC1PC2PC3 band combination of Landsat TM 2010 imagery to highlight the surface water changes between the two images. The suitability of the resulting fused images for surface water change detection was evaluated quantitatively and visually. Finally, the support vector machine (SVM) technique was applied to the qualified fused images to map the highlighted changes. Furthermore, a product level fusion (PLF) approach based on various satellite-derived indices was employed to detect the surface water changes between ETM+ 2000 and TM 2010 images. The accuracy of the resulting change maps was assessed based on a reference change map produced using visual interpretation. The results demonstrated the effectiveness of the proposed approaches for surface water change detection, especially using the Gram Schmidt-SVM, PLF-NDWI, and PLF-NDVI methods which improved the accuracy of change detection over 99.70 %. 相似文献
618.
Arabian Journal of Geosciences - The gravimetric geoid model can be used as vertical reference in surveying and other related technologies. It is being developed by NESCOM in collaboration with the... 相似文献
619.
Feizabadi Sajjad Rafati Yashar Ghodsian Masoud Akbar Salehi Neyshabouri Ali Abdolahpour Maryam Mazyak Ahmad Rezaee 《Ocean Dynamics》2022,72(6):421-442
Ocean Dynamics - The climatic change has led to the sea-level rise (SLR), which is expected to continue based on the current industrial and human activities. Previous studies indicated that most of... 相似文献
620.
Hydrogeology Journal - Significant urbanization and industrialization, combined with strong population growth, have been witnessed in the Arabian Peninsula (Oman, United Arab Emirates, Saudi... 相似文献