首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   60篇
  免费   4篇
  国内免费   1篇
测绘学   2篇
大气科学   3篇
地球物理   17篇
地质学   35篇
海洋学   1篇
天文学   3篇
综合类   2篇
自然地理   2篇
  2022年   5篇
  2021年   7篇
  2020年   7篇
  2019年   1篇
  2018年   10篇
  2017年   6篇
  2016年   4篇
  2015年   2篇
  2014年   3篇
  2013年   8篇
  2012年   3篇
  2011年   1篇
  2010年   2篇
  2009年   1篇
  2008年   3篇
  2007年   2篇
排序方式: 共有65条查询结果,搜索用时 15 毫秒
1.
Spatial downscaling methods are widely used for the production of bioclimatic variables(e.g. temperature and precipitation) in studies related to species ecological niche and drainage basin management and planning. This study applied three different statistical methods, i.e. the moving window regression(MWR), nonparametric multiplicative regression(NPMR), and generalized linear model(GLM), to downscale the annual mean temperature(Bio1) and annual precipitation(Bio12) in central Iran from coarse scale(1 km × 1 km) to fine scale(250 m ×250 m). Elevation, aspect, distance from sea and normalized difference vegetation index(NDVI) were used as covariates to create downscaled bioclimatic variables. Model assessment was performed by comparing model outcomes with observational data from weather stations. Coefficients of determination(R2), bias, and root-mean-square error(RMSE) were used to evaluate models and covariates. The elevation could effectively justify the changes in bioclimatic factors related to temperature and precipitation. Allthree models could downscale the mean annual temperature data with similar R2, RMSE, and bias values. The MWR had the best performance and highest accuracy in downscaling annual precipitation(R2=0.70; RMSE=123.44). In general, the two nonparametric models, i.e. MWR and NPMR, can be reliably used for the downscaling of bioclimatic variables which have wide applications in species distribution modeling.  相似文献   
2.
Feizi  Atabak  Vahabzadeh  Zahra  Maleki  Vahid 《Water Resources》2022,49(4):689-698
Water Resources - Monitoring and reviewing vegetation changes are one of the important strategies for multi-year planning in an area regarding the environmental problems of the last decade. The...  相似文献   
3.
This study attempted to examine the effects of biochar amendment together with bio-fertilizer on soybean yield and its qualitative properties, as well as a few chemical properties of soil through a factorial randomized complete block design at three replications in east of Golestan Province (Iran) during 2014. The two factors under study included the following: (1) biochar amendment (in four levels of 0, 2.5, 8, and 16 tons per hectare), (2) bio-fertilizer containing phosphorus and sulfur growth-promoting rhizobacteria (in two levels of inoculation and non-inoculation) applied through foliar feeding. The results of analysis of variance indicated that interactions of biochar amendment and bio-fertilizer on harvest index and grain yield were significant (p ≤?0.01). According to the results of this study, the highest harvest index and oil content were 56.9, and 17.7%, respectively, in the treatment of 8 tons per hectare biochar and inoculation with bio-fertilizer. The lowest harvest index and the lowest oil content were in the control treatment. The interaction of biochar and bio-fertilizer on bulk density and cation exchange capacity was significant (p ≤?0.01). The results of this study demonstrated that biochar affected the amount of residual nitrogen in the soil after harvest, cation exchange capacity (CEC), acidity (pH), and electrical conductivity (EC). The highest grain yield (3440 kg/ha) was in the 8-ton biochar treatment with inoculated bio-fertilizer. Our study concludes that the biochar and bio-fertilizers can improve grain yield of soybean till 51% relative to the control.  相似文献   
4.
5.
6.
International Journal of Earth Sciences - Quantitative vorticity analyses in orogenic belts are essential for studying the kinematics of deformation and can be performed using a range of methods....  相似文献   
7.
8.
In this work, we study static spherically symmetric wormhole solutions in f(R) gravity. We explore wormhole solutions for anisotropic and isotropic fluids as well as barotropic equation of state with radial pressure. The behavior of weak and null energy conditions is investigated in each case. It is found that these energy conditions are violated for both the anisotropic and isotropic case but are satisfied for barotropic fluids in particular regions. This confirms the existence of wormholes obeying the energy conditions in these regions.  相似文献   
9.
Roads and buildings constitute a significant proportion of urban areas. Considerable amount of research has been done on the road and building extraction from remotely sensed imagery. However, a few of them have been concentrating on using only spectral information. This study presents a comparison between three object-based models for urban features’ classification, specifically roads and buildings, from WorldView-2 satellite imagery. The three applied algorithms are support vector machines (SVMs), nearest neighbour (NN) and proposed rule-based system. The results indicated that the proposed rules in this study, despite the spectral complexity of land cover types, performed a satisfactory output with an overall accuracy of 92.92%. The advantages offered by the proposed rules were not provided by other two applied algorithms and it revealed the highest accuracy compared to SVM and NN. The overall accuracy for SVM was 76.76%, which is almost similar to the result achieved by NN (77.3%).  相似文献   
10.
The purpose of this study is to analyze the dynamical role of a radiation field on the growth rate of the unstable Kelvin-Helmholtz (KH) perturbations. As a first step toward this purpose, the analyze is done in a general way, irrespective of applying the model to a specific astronomical system. The transition zone between the two layers of the fluid is ignored. Then, we perform a linear analysis and by imposing suitable boundary conditions and considering a radiation field, we obtain appropriate dispersion relation. Unstable modes are studied by solving the dispersion equation numerically, and then growth rates of them are obtained. By analyzing our dispersion relation, we show that for a wide range of the input parameters, the radiation field has a destabilizing effect on KH instability. In eruptions of the galaxies or supermassive stars, the radiation field is dynamically important and because of the enhanced KH growth rates in the presence of the radiation; these eruptions can inject more momentum and energy into their environment and excite more turbulent motions.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号