全文获取类型
收费全文 | 4087篇 |
免费 | 1052篇 |
国内免费 | 1570篇 |
专业分类
测绘学 | 542篇 |
大气科学 | 704篇 |
地球物理 | 912篇 |
地质学 | 2995篇 |
海洋学 | 608篇 |
天文学 | 77篇 |
综合类 | 337篇 |
自然地理 | 534篇 |
出版年
2024年 | 44篇 |
2023年 | 150篇 |
2022年 | 253篇 |
2021年 | 282篇 |
2020年 | 244篇 |
2019年 | 266篇 |
2018年 | 290篇 |
2017年 | 235篇 |
2016年 | 269篇 |
2015年 | 284篇 |
2014年 | 300篇 |
2013年 | 304篇 |
2012年 | 407篇 |
2011年 | 358篇 |
2010年 | 335篇 |
2009年 | 319篇 |
2008年 | 296篇 |
2007年 | 304篇 |
2006年 | 279篇 |
2005年 | 233篇 |
2004年 | 188篇 |
2003年 | 135篇 |
2002年 | 125篇 |
2001年 | 124篇 |
2000年 | 112篇 |
1999年 | 98篇 |
1998年 | 70篇 |
1997年 | 66篇 |
1996年 | 66篇 |
1995年 | 50篇 |
1994年 | 31篇 |
1993年 | 31篇 |
1992年 | 32篇 |
1991年 | 19篇 |
1990年 | 29篇 |
1989年 | 12篇 |
1988年 | 10篇 |
1987年 | 17篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1958年 | 1篇 |
1954年 | 5篇 |
排序方式: 共有6709条查询结果,搜索用时 15 毫秒
991.
ABSTRACT Spatial heterogeneity represents a general characteristic of the inequitable distributions of spatial issues. The spatial stratified heterogeneity analysis investigates the heterogeneity among various strata of explanatory variables by comparing the spatial variance within strata and that between strata. The geographical detector model is a widely used technique for spatial stratified heterogeneity analysis. In the model, the spatial data discretization and spatial scale effects are fundamental issues, but they are generally determined by experience and lack accurate quantitative assessment in previous studies. To address this issue, an optimal parameters-based geographical detector (OPGD) model is developed for more accurate spatial analysis. The optimal parameters are explored as the best combination of spatial data discretization method, break number of spatial strata, and spatial scale parameter. In the study, the OPGD model is applied in three example cases with different types of spatial data, including spatial raster data, spatial point or areal statistical data, and spatial line segment data, and an R “GD” package is developed for computation. Results show that the parameter optimization process can further extract geographical characteristics and information contained in spatial explanatory variables in the geographical detector model. The improved model can be flexibly applied in both global and regional spatial analysis for various types of spatial data. Thus, the OPGD model can improve the overall capacity of spatial stratified heterogeneity analysis. The OPGD model and its diverse solutions can contribute to more accurate, flexible, and efficient spatial heterogeneity analysis, such as spatial patterns investigation and spatial factor explorations. 相似文献
992.
993.
基于GIS的承德乡村地名文化景观空间分布特征 总被引:2,自引:2,他引:2
将承德地区乡村地名作为离散点,以GIS中移动搜索法的点距离空间平滑分析法为支撑,从地理区域这一角度分析地名文化景观空间分布特征。研究发现:承德地区自然类景观,以“山”、“水文”、“动植物”命名的地名分布主要位于中低海拔高度的平坦地区;承德地区乡村地名文化景观划分为军事活动类、经济活动类、房屋建筑类、美愿与纪念类、满蒙少数民族语言及方言类,其空间分布特征与当地历史时期的军事、生产生活、社会变迁的相对频繁程度以及人口稠密情况基本上相符合。 相似文献
994.
In this paper, the infinite boundary elements developed previously in two and three dimensional problems are reviewed, and the shortcoming and irrationality of interpolation functions of those elements are pointed out. A new interpolation function of infinite boundary element is proposed. The divergent integration on infinite element is also discussed in this paper. 相似文献
995.
996.
In the present paper, inequalities stronger than Sundman's and the best possible zero velocity surfaces of the spatial 3-body problem first obtained by Saari (1987) are deduced using a modified version of the transformation developed by Zare (1976). The notion of inertia ellipsoid is used to show the equivalence of the present authors' result to that of Saari's. 相似文献
997.
In this study,we derived atmospheric profiles of temperature,moisture,and ozone,along with surface emissivity,skin temperature,and surface pressure,from infrared-sounder radiances under clear sky (cloudless) condition.Clouds were detected objectively using the Atmospheric Infrared Sounder under a relatively low spatial resolution and cloud-mask information from the Moderate Resolution Imaging Spectroradiometer under a high horizontal resolution;this detection was conducted using space matching.Newton’s nonlinear physical iterative solution technique is applied to the radiative transfer equation (RTE) to retrieve temperature profiles,relative humidity profiles,and surface variables simultaneously.This technique is carried out by using the results of an eigenvector regression retrieval as the background profile and using corresponding iterative forms for the weighting functions of temperature and water-vapor mixing ratio.The iterative forms are obtained by applying the variational principle to the RTE.We also compared the retrievals obtained with different types of observations.The results show that the retrieved atmospheric sounding profile has great superiority over other observations by accuracy and resolution.Retrieved profiles can be used to improve the initial conditions of numerical models and used in areas where conventional observations are sparse,such as plateaus,deserts,and seas. 相似文献
998.
太原盆地地下水资源模拟研究 总被引:1,自引:0,他引:1
山西省太原盆地由于地下水长期超采,引发了地下水降落漏斗、地面沉降等环境地质问题。通过GMS建立地下水水流三维数值模型,基于模型预测了现状开采条件下地下水水位的变化趋势,并提出合理利用地下水资源的措施,为地下水资源的优化管理提供科学依据。 相似文献
999.
一种新的粒度指标:沉积物粒度分维值及其环境意义 总被引:28,自引:2,他引:28
根据分形理论,对1000个不同类型沉积物样品的粒度分形结构及其分维值作了定量计算。结果表明:各类型沉积物都具有良好的统计自相似性,并且各自有着不同的分维值。粒度分维值的大小与分选好坏密切相关。没有经过外力搬运与分选的风化破碎物质(碎屑物)——断层泥、冻土的粒度分维值接近于碎形体的分维值2.60左右;经过外力搬运但分选作用较弱的冰碛物、水石流、泥石流堆积物的粒度分维值也接近2.60;而经过强烈外力分选作用的河床、湖泊沉积物、潮滩及海底沉积物的分维值明显偏小。鉴于此,本认为分维值可以作为沉积物类型判别的重要参数之一。 相似文献
1000.