全文获取类型
收费全文 | 777篇 |
免费 | 20篇 |
国内免费 | 28篇 |
专业分类
测绘学 | 35篇 |
大气科学 | 61篇 |
地球物理 | 152篇 |
地质学 | 285篇 |
海洋学 | 97篇 |
天文学 | 118篇 |
综合类 | 15篇 |
自然地理 | 62篇 |
出版年
2022年 | 7篇 |
2020年 | 9篇 |
2019年 | 8篇 |
2018年 | 24篇 |
2017年 | 26篇 |
2016年 | 22篇 |
2015年 | 34篇 |
2014年 | 39篇 |
2013年 | 49篇 |
2012年 | 28篇 |
2011年 | 28篇 |
2010年 | 31篇 |
2009年 | 23篇 |
2008年 | 38篇 |
2007年 | 24篇 |
2006年 | 18篇 |
2005年 | 14篇 |
2004年 | 17篇 |
2003年 | 14篇 |
2002年 | 11篇 |
2001年 | 14篇 |
2000年 | 12篇 |
1999年 | 13篇 |
1998年 | 11篇 |
1997年 | 15篇 |
1995年 | 8篇 |
1994年 | 7篇 |
1993年 | 14篇 |
1992年 | 8篇 |
1991年 | 8篇 |
1990年 | 11篇 |
1989年 | 12篇 |
1988年 | 14篇 |
1987年 | 16篇 |
1985年 | 17篇 |
1984年 | 18篇 |
1983年 | 15篇 |
1982年 | 8篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1974年 | 5篇 |
1973年 | 7篇 |
1972年 | 5篇 |
1929年 | 4篇 |
1921年 | 4篇 |
1920年 | 4篇 |
1918年 | 4篇 |
排序方式: 共有825条查询结果,搜索用时 31 毫秒
801.
Sagar S Salunkhe A K Bera S S Rao V Raghu Venkataraman Uday Raj Y V N Krishna Murthy 《Journal of Earth System Science》2018,127(8):116
Desertification has emerged as a major economic, social and environmental problem in the western part of India. The best way of dealing with desertification is to take appropriate measures to arrest land degradation, especially in areas prone to desertification. This requires an early warning system for desertification based on scientific inputs. Hence, in the present study, an attempt has been made to develop a comprehensive model for the assessment of desertification risk in the Jodhpur district of Rajasthan, India, using 23 desertification indicators. Indicators including soil, climate, vegetation and socio-economic parameters were integrated into a GIS environment to get environmental sensitive areas (ESAs) to desertification. Desertification risk index (DRI) was calculated based on ESAs to desertification, the degree of land degradation and significant desertification indicators obtained from the stepwise multiple regression model. DRI was validated by using independent indicators such as soil organic matter content and cation exchange capacity. Multiple regression analysis shows that 16 indicators out of 23 were found to be significant for assessing desertification risk at a 99% confidence interval with \(R^{2}=0.83\). The proposed methodology provides a series of effective indicators that would help to identify where desertification is a current or potential problem, and what could be the actions to alleviate the problem over time. 相似文献
802.
Parameter estimation of SWAT and quantification of consequent confidence bands of model simulations 总被引:1,自引:0,他引:1
Soil and Water Assessment Tool (SWAT) is a river basin scale model widely used to study the impact of land management practices in large, complex watersheds. Even though model output uncertainties are generally recognized to affect watershed management decisions, those uncertainties are largely ignored in model applications. The uncertainties of SWAT simulations are quantified using various methods, but simultaneous attempt to calibrate a model so as to reduce the uncertainty are seldom done. This study aims to use an uncertainty reduction procedure that helps calibrate the SWAT model. The shuffled complex evolutionary metropolis algorithm for uncertainty analysis is employed for this purpose, and is demonstrated using the data from the St. Joseph River basin, USA. The values of the performance indices, the r2 and the Nash–Sutcliffe efficiency (NSE) for the simulations during calibration period was found to be 0.81 (same for r2 and NSE) and 0.79 for validation period indicating a good simulation by the model. The results also indicate that the algorithm helps reduce the uncertainty (percentage of coverage?=?62% and average width?=?19.2 m3/s), and also identifies the plausible range of parameters that simulate the processes with less uncertainty. The confidence bands of simulations are obtained that can be employed in making uncertainty-based decisions on watershed management practices. 相似文献
803.
Landslide Susceptibility Mapping along Bhalubang–Shiwapur Area of Mid-Western Nepal Using Frequency Ratio and Conditional Probability Models 总被引:3,自引:3,他引:0
Amar Deep Regmi Kohki Yoshida Hamid Reza Pourghasemi Megh Raj DhitaL Biswajeet Pradhan 《山地科学学报》2014,11(5):1266-1285
Roads constructed in fragile Siwaliks are prone to large number of instabilities. Bhalubang–Shiwapur section of Mahendra Highway lying in Western Nepal is one of them. To understand the landslide causative factor and to predict future occurrence of the landslides, landslide susceptibility mapping(LSM) of this region was carried out using frequency ratio(FR) and weights-of-evidence(W of E) models. These models are easy to apply and give good results. For this, landslide inventory map of the area was prepared based on the aerial photo interpretation, from previously published/unpublished reposts, and detailed field survey using GPS. About 332 landslides were identified and mapped, among which 226(70%) were randomly selected for model training and the remaining 106(30%) were used for validation purpose. A spatial database was constructed from topographic, geological, and land cover maps. The reclassified maps based on the weight values of frequency ratio and weights-of-evidence were applied to get final susceptibility maps. The resultant landslide susceptibility maps were verified andcompared with the training data, as well as with the validation data. From the analysis, it is seen that both the models were equally capable of predicting landslide susceptibility of the region(W of E model(success rate = 83.39%, prediction rate = 79.59%); FR model(success rate = 83.31%, prediction rate = 78.58%)). In addition, it was observed that the distance from highway and lithology, followed by distance from drainage, slope curvature, and slope gradient played major role in the formation of landsides. The landslide susceptibility maps thus produced can serve as basic tools for planners and engineers to carry out further development works in this landslide prone area. 相似文献
804.
Arthur J. Askew 《水文科学杂志》2013,58(1):195-196
Abstract A snowmelt runoff model is derived for relatively small rivers. The model involves the main components of the catchment water budget, physiographical and some other factors: water equivalent of snow cover, precipitation, antecedent moisture content, daily snowmelt, non-uniformity of snow cover, retention capacity of the basin, and percentage of forest area. The model structure includes calculations of the daily values of snowmelt excess and the transformation of these values into discharges at the outlet of the basin based on meteorological observations and appropriate distribution functions. Both calculations are made separately for open and forest areas. The parameters of the model were derived by optimization methods. The linear model based on the superposition principle is used to transform the discharges of a small river into total inflow into a large reservoir. The combined model was used to forecast for five days in advance daily mean inflows into the Gorky and Kuibyshev reservoirs (on the River Volga), using the observed and forecast discharges of the small rivers as input. 相似文献
805.
Accurate benthic habitat maps are critical for resource management in coastal waters with competing uses. We used a 500 kHz
phase-measuring bathymetric sonar (PMBS) and 900 kHz side-scan sonar to acquire seafloor data in estuarine and shelf environments.
Grab samples and remotely operated vehicle video created geological and biological classifications for segmented maps produced
by a backscatter clustering program. PMBS improves regional map resolution (<1 m), reduces the need for direct sampling, extends
information on sediment–biological relationships to larger areas, and allows measurements of bedforms. Auto-segmentation was
successful in environments with highly contrasting acoustic signatures and meters-scale homogeneity. Patchier communities
are identifiable in PMBS data. Species preferences for sediment (i.e., tubeworm preference for sediment without shell hash)
allowed us to determine potential habitat without identifying individual organisms in acoustic data. PMBS with sufficient
ground-truthing offers an efficient way to map seafloor characteristics, which is critical in marine spatial planning efforts. 相似文献
806.
The focus of the present study is the assessment of the impact of wind forcing on the spectral wave model MIKE 21 SW in the Indian Ocean region. Three different wind fields, namely the ECMWF analyzed winds, the ECMWF blended winds, and the NCEP blended winds have been used to drive the model. The wave model results have been compared with in-situ observations and satellite altimeter data. This study also evaluated the performance of the wind products during local phenomenon like sea breeze, since it has a significant impact on the wave prediction in the Indian coastal region. Hence we explored the possibility of studying the impact of diurnal variation of winds on coastal waves using different wind fields. An analysis of the model performance has also been made during high wind conditions with the inference that blended winds generate more realistic wave fields in the high wind conditions and are able to produce the growth and decay of waves more realistically. 相似文献
807.
Numerical simulation of a typical tropical thunder storm event at Pune (18.53°N, 73.85°E), India, has been performed using the three nested domain configuration of Weather Research and Forecasting-Advanced Research Weather Model (version 3.2). The model simulations have been compared with observations. Sensitivity to cumulus parameterization schemes, namely Betts–Miller (BM), Grell–Devenyi (GD), and Kain–Fritsch (KF), for simulation of vertical structure and time evolution of weather parameters has been evaluated using observations from automatic weather station and global positioning system radiosonde ascents. Comparison of spatial distribution of 24-h accumulated rain with Tropical Rainfall Measuring Mission data shows that BM scheme could simulate better rain than GD and KF schemes. The BM scheme could well simulate the development of storm and heavy rain as it could generate sufficiently humid and deep layer in the lower and middle atmosphere, along with co-existence of updrafts and downdrafts and frozen hydrometeors at the middle level and rain water near the surface. 相似文献
808.
809.
Amar Deep Regmi Kohki Yoshida Megh Raj Dhital Biswajeet Pradhan 《Environmental Earth Sciences》2014,71(6):2711-2727
Sangrumba landslide is one of the largest and the most active landslides in Nepal Himalaya. Geologically the landslide belongs to the Higher Himalaya and consists of Pre-Cambrian biotite–garnet and sillimanite gneiss with some quartzite. The present paper aims at describing various degrees of rock weathering and their effect in Sangrumba landslide. Field study followed by mineralogical, geochemical and geotechnical analyses of the collected rock and soil samples from the landslide zone were used in characterizing weathering degree. The gneisses are intensely weathered while quartzite is unweathered. Petrographical and X-ray diffraction analyses showed that the rocks in the landslide zone had undergone weathering process with the formation of different types of clay minerals as kaolinite, vermiculite, smectite and chlorite. This was further confirmed by the Scan Electron Microscope and Energy Dispersive X-ray analyses. These clay minerals drastically reduced the rock strength facilitating the extensive failure of the Sangrumba landslide. The major and trace element composition of the rock and soil samples was calculated from the XRF analyses. The geochemical analyses and weathering indexes of rocks showed that they are significantly weathered and had a major influence in the formation of the Sangrumba landslide. In addition, mechanical strength measurement of rock/soil showed that the strength drastically decreases as the weathering intensity increases. Rainfall followed by the rock type are the most dominant parameters influencing the weathering process which leads to the formation of large landslide as the present one. These findings can be used in other areas with similar geological and topographical conditions. 相似文献
810.
The North Indian Ocean exhibits profound impact of variation in lower tropospheric winds. In the present study climatological monthly winds are used to force a nonlinear reduced gravity model of the North Indian Ocean to simulate climatological surface circulation and sea level anomaly for all 12 months of the year. The sea level anomalies agree reasonably well with satellite altimeter derived sea level anomalies. The model successfully simulates the varying eddy structure and current pattern of the North Indian Ocean. Finally, the kinetic energy variation in the North Indian Ocean with special reference to equatorial region and the boundaries is analyzed in detail. 相似文献