全文获取类型
收费全文 | 326篇 |
免费 | 19篇 |
国内免费 | 9篇 |
专业分类
测绘学 | 10篇 |
大气科学 | 21篇 |
地球物理 | 92篇 |
地质学 | 136篇 |
海洋学 | 21篇 |
天文学 | 35篇 |
综合类 | 19篇 |
自然地理 | 20篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 6篇 |
2020年 | 4篇 |
2019年 | 9篇 |
2018年 | 21篇 |
2017年 | 17篇 |
2016年 | 28篇 |
2015年 | 25篇 |
2014年 | 25篇 |
2013年 | 37篇 |
2012年 | 17篇 |
2011年 | 20篇 |
2010年 | 14篇 |
2009年 | 18篇 |
2008年 | 10篇 |
2007年 | 12篇 |
2006年 | 9篇 |
2005年 | 8篇 |
2004年 | 13篇 |
2003年 | 12篇 |
2002年 | 5篇 |
2001年 | 4篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1982年 | 1篇 |
1979年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有354条查询结果,搜索用时 46 毫秒
161.
Manoj Yadav M. P. Sharma R. Prawasi Rajeev Khichi Pavan Kumar V. P. Mandal Abdul Salim R. S. Hooda 《Journal of the Indian Society of Remote Sensing》2014,42(2):343-352
Haryana has emerged as an important state for Rice & Wheat production in India contributing significantly in the central pool. Mechanized combine harvesting technologies, which have become common in Rice Wheat System (RWS) in India, leave behind large quantities of straw in the field for open burning of residue. Besides causing pollution, the burning kills the useful micro flora of the soil causing soil degradation. There is no field survey (Girdawari) data available with the Government for the areas where stubble burning is taking place. The present paper describes the methodology and results of wheat and rice residue burning areas for three districts of Haryana namely Kaithal, Kurukshetra and Karnal for the year 2010 using complete enumeration approach of multi-date IRS-P6 AWiFS and LISS-III data. In season ground truth was collected using hand held GPS and used to identify area of burnt wheat/rice residues, associated crops and land features. After geo-referencing the satellite images, district images were masked-out and multi-date image data stacks were created. Normalized Difference Vegetation Index (NDVI) of each date was generated and used at the time of classification along with other spectral bands. The non-agricultural classes in the image included: forest, wasteland, water bodies, urban/settlement and permanent vegetation etc. The vector of these non-agriculture classes were extracted from the land use, imported and mask was generated. During the classification non-agriculture area was excluded by using mask of these classes. From this the agricultural area could be separated out. The area was estimated by computing pixels under the classified image mask. In season multi-date AWiFS data along with available single-date LISS-III data between third week of April to last week of May are found to be useful for estimation of wheat residue burning areas estimation. The data between second week of October to last week of November is useful for estimation of rice residue burning areas estimation at district level. 相似文献
162.
Mohammad Abdul Quader Hemal Dey Md. Abdul Malak Md. Zakiur Rahman 《Singapore journal of tropical geography》2023,44(2):277-299
Floods are a frequently occurring calamity in deltaic Bangladesh. This paper aims to assess the temporal expansion of waterbodies during flooding using geospatial techniques. Several water indices were applied to classify the satellite images at various temporal scales. Among them, the Normalized Difference Water Index (NDWI) showed the highest correlation (r = 0.831; where p = 0.01) with rainfall data. Specifically, the NDWI results showed that perennial waterbodies measured 37 km2 and 60 km2 in Sunamganj District in 2017 and 2019, respectively. The area of waterbodies notably increased 52-fold from March to April (37 km2 to 1958 km2) during the pre-monsoon flash flood of 2017. During the July 2019 monsoon flood, waterbodies started to extend after May and flooded 2784 km2 in area. NDVI analysis showed that in 2019, floodwater submerged 361.7 km2 of vegetation cover. At the same time, the Surma River's flooding resulted in a 73.9 per cent inundation of the total area of the Sunamganj District. We hope that this study will provide better understanding of the varying nature of floods that occur in the low lying bowl shaped Haor region which will in turn assist the government with flood mitigation. 相似文献
163.
FAO 56 Model and Remote Sensing for the Estimation of Crop-Water Requirement in Main Branch Canal of the Bhadra Command area, Karnataka State 总被引:1,自引:0,他引:1
S. N. A. Abdul Karim S. A. Ahmed V. Nischitha Surabhi Bhatt S. Kiran Raj K. N. Chandrashekarappa 《Journal of the Indian Society of Remote Sensing》2013,41(4):883-894
Remote sensing and FAO 56 crop water model are used for estimating crop water requirement for paddy crop located in the main branch canal of Bhadra Command Area in Karnataka, India. The estimation of crop-water requirement depends on the meteorological factors, soil type and crop coefficients. The result obtained showed that water requirements of rabi crops higher than those of the kariff crops. The total irrigated area estimated from the IRS image is 29,353 ha. It is found that the total paddy crop acreage is 18,257 ha covering 62 % in the total irrigated area of the command area, Arecanut 20 %, coconut 15 % and sugarcane with other crops 3 %. The water requirement for paddy is 1180.4 mm for its entire growth period. The total water requirement for irrigation supply for crops in the entire command area is 5,790 at a demand of 0.10501 cusecs per ha. 相似文献
164.
Noor Azlinda Ahmad M. Fernando Z.A. Baharudin V. Cooray H. Ahmad Z. Abdul Malek 《Journal of Atmospheric and Solar》2010,72(5-6):534-540
Narrow bipolar pulses (NBPs) are considered as isolated intracloud events with higher peak amplitude and strong high frequency emission compared to the first return strokes and other intracloud discharges. From 182 NBPs recorded in Malaysia in the tropic, 75 were narrow negative bipolar pulses (NNBPs) while 107 were narrow positive bipolar pulses (NPBPs). The mean duration of NNBPs was 24.6±17.1 μs, while 30.2±12.3 μs was observed for NPBPs. The mean full-width at half-maximum (FWHM) was 2.2±0.7 and 2.4±1.4 μs for NNBPs and NPBPs, respectively. The mean peak amplitude of NPBPs normalized to 100 km was 22.7 V/m, a factor of 1.3 higher than that of NNBPs which is 17.6 V/m. In contrast to the previous studies, it was observed that the electric field change was characterized by a bipolar pulse with a significant amount of fine structures separated by a few tens of nanoseconds intervals, embedded on it. 相似文献
165.
166.
Aws A. Ajaaj Ashok. K. Mishra Abdul A. Khan 《Stochastic Environmental Research and Risk Assessment (SERRA)》2016,30(6):1659-1675
Long-term historical precipitation data are important in developing metrics for studying the impacts of past hydrologic events (e.g., droughts) on water resources management. Many geographical regions around the world often witness lack of long term historical observation and to overcome this challenge, Global Precipitation Climatology Center (GPCC) datasets are found to be useful. However, the GPCC data are available at coarser scale (0.5° resolution), therefore bias correction techniques are often applied to generate local scale information before it can be applied for decision making activities. The objective of this study is to evaluate and compare five different bias correction techniques (BCT’s) to correct the GPCC data with respect to rain gauges in Iraq, which is located in a semi-arid climatic zone. The BCT’s included in this study are: Mean Bias-remove (B) technique, Multiplicative Shift (M), Standardized-Reconstruction (S), Linear Regression (R), and Quantile Mapping (Q). It was observed that the Performance Index (PI) of BCT’s differs in space (i.e., precipitation pattern) and temporal scale (i.e., seasonal and monthly). In general, the PI for the Q and B were better compared to other three (M, S and R) bias correction techniques. Comparatively, Q performs better than B during wet season. However, both these techniques performed equally well during average rainy season. This study suggests that instead of using a single bias correction technique at different climatic regimes, multiple BCT’s needs to be evaluated for identifying appropriate methodology that suits local climatology. 相似文献
167.
Balasubramanian Balamuralikrishnan Vellingiri Balachandar Mohana Devi Subramaniam Karthick Kumar Alagumuthu Shanmugam Sureshkumar Meyyazhagan Arun Sundaramoorthy Arun Krishnan Padmavathi Abdul Hakkim Razeena Mohan Gomathi Palanivel Velmurugan Shahnaz N. Dharwadkar Keshavarao Sasikala 《Stochastic Environmental Research and Risk Assessment (SERRA)》2014,28(7):1801-1814
Chemicals, especially silica, have been suspected to cause genetic alterations in pottery industry workers. The present study aims to analyze the frequency of chromosomal aberrations (CA), micronucleus (MN) and DNA damage (comet assay) in the peripheral blood lymphocytes and the immunological alterations workers chronically exposed to silica and in control subjects. In our study, 50 silica exposed workers and 35 control subjects were recruited and silica level was measured by respirable dust and respirable quartz concentrations of badge dosimeter. The serum immunoglobulins (IgM, IgG, and IgA) of all the subjects were measured by using ELISA method. The individuals exposed to silica have a significant increase in the frequency of CA, MN and the total DNA damage (p < 0.05). Immunoglobulin elevation on silica exposed workers was statistically significant (p < 0.05) on comparison with their respective controls. Investigation of the smoking and alcohol habitats coupled with silica exposure in exposed and control subjects represents alcohol consumption and smoking as additional risk factors and must be avoided. Multiple linear regression analysis obtained for CA, MN and comet assay confirm these tests as biomarkers for silica exposed pottery workers. Some confounding factors also showed significant influence on exposed subjects. These results indicate the mutagenic risk in the working environment has a high probability of association with the silica dust exposure in pottery industries. Nevertheless, the present study will create awareness and public concern not only among the silica exposed workers but also to the welfare of their progeny. 相似文献
168.
Statistical distributions of annual extreme (AE) series and partial duration (PD) series for dry-spell event are analyzed for a database of daily rainfall records of 50 rain-gauge stations in Peninsular Malaysia, with recording period extending from 1975 to 2004. The three-parameter generalized extreme value (GEV) and generalized Pareto (GP) distributions are considered to model both series. In both cases, the parameters of these two distributions are fitted by means of the L-moments method, which provides a robust estimation of them. The goodness-of-fit (GOF) between empirical data and theoretical distributions are then evaluated by means of the L-moment ratio diagram and several goodness-of-fit tests for each of the 50 stations. It is found that for the majority of stations, the AE and PD series are well fitted by the GEV and GP models, respectively. Based on the models that have been identified, we can reasonably predict the risks associated with extreme dry spells for various return periods. 相似文献
169.
The effects of plant density of Melastoma malabathricum on the erosion rate of slope soil at different slope orientations 总被引:2,自引:0,他引:2
Malaysia’s cut slopes,especially for road lines accommodation,are prone to erosions and landslides.These problems mainly occur due to lack of vegetation cover and strong erosive forces.In addition,the topography factors have also become a major factor affecting soil degradation.Thus,this study is aimed at determining the effects of planting density of a selected species,namely Melastoma malabathricum;one,two,and three seedlings per box,on the erosion rate at selected slopes of different orientation(morning and evening sun) at the Guthrie Corridor Expressway,Selangor.In six months of observation,treatment with three seedlings/box on the morning sun slope showed a lower erosion rate by 69.2%than those with the same treatment on the evening sun slope.In addition,the treatment of the three seedlings recorded at month six(final observation) had the highest reduction of soil saturation level(STL),by 23.6%.Furthermore,the physiological values of the species studied,grown on the morning sun slope,were higher in terms of stomatal conductance and photosynthetic rate by 12.1%and 15.8%(three seedlings/box),respectively.The overall results showed that plant density was inversely related to the STL and erosion rate on the slope.In conclusion,a planting density of three seedlings/box and morning sun orientation gave positive effects on the plant’s physiological performance of the slope,reducing the STL,as well as alleviating the erosion rate of slope soils. 相似文献
170.