全文获取类型
收费全文 | 37646篇 |
免费 | 5124篇 |
国内免费 | 6868篇 |
专业分类
测绘学 | 5608篇 |
大气科学 | 5357篇 |
地球物理 | 8105篇 |
地质学 | 13313篇 |
海洋学 | 4342篇 |
天文学 | 1206篇 |
综合类 | 2789篇 |
自然地理 | 8918篇 |
出版年
2024年 | 144篇 |
2023年 | 414篇 |
2022年 | 1292篇 |
2021年 | 1511篇 |
2020年 | 1696篇 |
2019年 | 2023篇 |
2018年 | 1438篇 |
2017年 | 1869篇 |
2016年 | 1811篇 |
2015年 | 1959篇 |
2014年 | 2287篇 |
2013年 | 2792篇 |
2012年 | 2405篇 |
2011年 | 2517篇 |
2010年 | 1918篇 |
2009年 | 2370篇 |
2008年 | 2326篇 |
2007年 | 2499篇 |
2006年 | 2423篇 |
2005年 | 1960篇 |
2004年 | 1810篇 |
2003年 | 1496篇 |
2002年 | 1209篇 |
2001年 | 997篇 |
2000年 | 912篇 |
1999年 | 790篇 |
1998年 | 789篇 |
1997年 | 671篇 |
1996年 | 559篇 |
1995年 | 482篇 |
1994年 | 420篇 |
1993年 | 405篇 |
1992年 | 296篇 |
1991年 | 220篇 |
1990年 | 165篇 |
1989年 | 165篇 |
1988年 | 123篇 |
1987年 | 75篇 |
1986年 | 64篇 |
1985年 | 72篇 |
1984年 | 40篇 |
1983年 | 21篇 |
1982年 | 25篇 |
1981年 | 26篇 |
1980年 | 23篇 |
1978年 | 13篇 |
1977年 | 22篇 |
1976年 | 25篇 |
1973年 | 17篇 |
1971年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
351.
352.
对于GPS短基线,载波相位双差观测量已基本消除了卫星轨道误差、钟差、大气折射误差等系统偏差的影响,主要包含距离观测量信息及随机测量误差,其中测量误差是高频的测量噪声,小波变换可将GPS载波相位双差观测量中的观测噪声(高频部分)分解出来。本文利用Coiflets小波基函数对GPS快速定位的原始载波相位双差观测量进行5层分解,通过重构第5层低频系数获得去除噪声的"干净"的载波相位双差观测量,然后利用"干净"的双差观测量进行最小二乘参数估计,以减小测量噪声对GPS快速定位病态方程解的扰动。计算结果表明该方法能够显著提高GPS快速定位中模糊度浮点解的精度,仅利用几个观测历元的数据就可以准确地固定模糊度。 相似文献
353.
354.
国内外城市雨水径流水质的研究 总被引:4,自引:0,他引:4
综合国内外综合资料,对城市不同建筑材料屋面和不同路面的雨水径流水质特征进行了对比分析,阐明了影响城市雨水径流水质的三大因素,并论述了城市雨水收集利用的现实意义。 相似文献
355.
356.
357.
R.P. Gupta D.P. Kanungo M.K. Arora S. Sarkar 《International Journal of Applied Earth Observation and Geoinformation》2008
Evaluation of maps generated from different conceptual models or data processing approaches at spatial level has importance in many geoenvironmental applications. This paper addresses the spatial comparison of different landslide susceptibility zonation (LSZ) raster maps of the same area derived from various procedures. 相似文献
358.
This study developed an analytical procedure based upon a spectral unmixing model for characterizing and quantifying urban landscape changes in Indianapolis, Indiana, the United States, and for examining the environmental impact of such changes on land surface temperatures (LST). Three dates of Landsat TM/ETM+ images, acquired in 1991, 1995, and 2000, respectively, were utilized to document the historical morphological changes in impervious surface and vegetation coverage and to analyze the relationship between these changes and those occurred in LST. Three fraction endmembers, i.e., impervious surface, green vegetation, and shade, were derived with an unconstrained least-squares solution. A hybrid classification procedure, which combined maximum-likelihood and decision-tree algorithms, was developed to classify the fraction images into land use and land cover classes. Correlation analyses were conducted to investigate the changing relationships of LST with impervious surface and vegetation coverage. Results indicate that multi-temporal fraction images were effective for quantifying the dynamics of urban morphology and for deriving a reliable measurement of environmental variables such as vegetation abundance and impervious surface coverage. Urbanization created an evolved inverse relationship between impervious and vegetation coverage, and brought about new LST patterns because of LST's correlations with both impervious and vegetation coverage. Further researches should be directed to refine spectral mixture modeling by stratification, and by the use of multiple endmembers and hyperspectral imagery. 相似文献
359.
Hang Li Dahua Li Tangfu Xiao Libin He Zengping Ning Jialong Sun Changsheng Zhu Yan Shuang 《中国地球化学学报》2008,27(1):21-27
The Jinding Pb-Zn deposit in Yunnan Province is the representative of a Cd-enriched area and mining activities lead to the release of Cd into the hypergenic ecosystem, resulting in Cd pollution. The concentrations of Cd vary greatly from one type to another type of rocks in the mining district. In the host rock, Cd concentrations range from 50×10^-6 to 650×10^-6 with an average of 310×10^-6. In primary ores, Cd concentrations range from 14×10^-6 to 2800×10^-6 with an average of 767×10^-6. However, in oxidized ores, Cd concentrations are highest, varying within the range of 110×10^-6 to 8200×10^-6 , averaging 1661×10^-6. It is shown that the oxidized ores are the main carder and environmental source of Cd. Leaching test showed that Pb/Zn ores are easy to oxidize and thereafter release Cd and other harmful elements. These leached elements in the leachate may be precipitated rapidly in the order of Zn〉Pb〉Cd. As for the concentration distribution of Cd in the Bijiang River, it is estimated to be 15.7 μg/L Cd in water, 49.3 mg/L in suspended substances, and 203.7 mg/L in sediments. The average value of Cd in soil from the polluted area is 83.0 mg/kg. Natural weathering of Cd-rich rocks and minerals imposes a potential environmental risk on the aquatic ecosystem of the Bijiang catchment. 相似文献
360.
Three-dimensional modelling from single images remains an interesting topic of investigation in the research community, even though range sensors are becoming a common alternative for the generation of 3D information. The interest in single-image-based modelling is motivated by a wide spectrum of applications such as cultural heritage, civil engineering, urban planning and even criminology. In this paper a complete new production flowline is presented for modelling based on a single image. The modelling process consists of a series of familiar steps in photogrammetry and computer vision: feature extraction, vanishing point computation, camera self-calibration, 3D reconstruction and dimensional analysis. In particular, the methodology developed for single-image-based modelling takes a scientific approach combining several proven techniques with robust estimators. Finally, in order to demonstrate its capabilities, the reported examples include several real situations applied in different contexts. 相似文献