全文获取类型
收费全文 | 1904篇 |
免费 | 309篇 |
国内免费 | 369篇 |
专业分类
测绘学 | 257篇 |
大气科学 | 284篇 |
地球物理 | 161篇 |
地质学 | 1419篇 |
海洋学 | 119篇 |
天文学 | 15篇 |
综合类 | 125篇 |
自然地理 | 202篇 |
出版年
2024年 | 5篇 |
2023年 | 24篇 |
2022年 | 53篇 |
2021年 | 46篇 |
2020年 | 74篇 |
2019年 | 84篇 |
2018年 | 58篇 |
2017年 | 68篇 |
2016年 | 95篇 |
2015年 | 94篇 |
2014年 | 146篇 |
2013年 | 134篇 |
2012年 | 138篇 |
2011年 | 161篇 |
2010年 | 117篇 |
2009年 | 128篇 |
2008年 | 99篇 |
2007年 | 101篇 |
2006年 | 109篇 |
2005年 | 98篇 |
2004年 | 100篇 |
2003年 | 94篇 |
2002年 | 79篇 |
2001年 | 78篇 |
2000年 | 58篇 |
1999年 | 63篇 |
1998年 | 55篇 |
1997年 | 42篇 |
1996年 | 36篇 |
1995年 | 34篇 |
1994年 | 27篇 |
1993年 | 26篇 |
1992年 | 14篇 |
1991年 | 11篇 |
1990年 | 10篇 |
1989年 | 4篇 |
1988年 | 6篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1974年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有2582条查询结果,搜索用时 17 毫秒
21.
This article introduces the most advanced form of electronic chart display and information systems (ECDIS) which complies with the performance standards for ECDIS established by the International Maritime Organization (IMO) and International Hydrographic Organization (IHO). It also describes the key features and the important functions of ECDIS, which we developed. This system is different from the productions developed by C-map, Seven-cs, offshore, and others. It is more suitable for China Marine Safety Administration Bureau to manage the navigation marks real-time. Using this system charts were located and accessed rapidly, and displayed smoothly. This article also discusses in ECDIS application system how to dynamically access and desert charts data in a limited memory (limited computer memory and resource). We constructed a tridimensional structure to manage a large amount of charts data. Vertically, according to the scale range, all charts were divided into eight levels, and a data structure called as “Multiple Scale Quad-tree” was constructed. And horizontally, a grid (every unit has a fixed size) was given to a certain scale level. We call this data structure a “Regular Page.” We explore the implementation of such a structure on the worldwide charts management utilizing quad-trees. Then we discuss the future development of ECDIS and its application system in marine agencies in China. 相似文献
22.
J.G.P.W. Clevers L. KooistraM.E. Schaepman 《International Journal of Applied Earth Observation and Geoinformation》2008
Canopy water content (CWC) is important for mapping and monitoring the condition of the terrestrial ecosystem. Spectral information related to the water absorption features at 970 nm and 1200 nm offers possibilities for deriving information on CWC. In this study, we compare the use of derivative spectra, spectral indices and continuum removal techniques for these regions. Hyperspectral reflectance data representing a range of canopies were simulated using the combined PROSPECT + SAILH model. Best results in estimating CWC were obtained by using spectral derivatives at the slopes of the 970 nm and 1200 nm water absorption features. Real data from two different test sites were analysed. Spectral information at both test sites was obtained with an ASD FieldSpec spectrometer, whereas at the second site HyMap airborne imaging spectrometer data were also acquired. Best results were obtained for the derivative spectra. In order to avoid the potential influence of atmospheric water vapour absorption bands the derivative of the reflectance on the right slope of the canopy water absorption feature at 970 nm can best be used for estimating CWC. 相似文献
23.
24.
25.
26.
27.
28.
29.
以耿皇勘探区钻孔资料为基础,对该区煤系地层沉积环境及成煤条件进行分析,简述了本区煤系地层是在海退基础上,以三角洲为主体的三角洲相与泻湖海湾潮坪相相互交替的沉积体系,通过对该特点的分析研究,为今后地质勘探和煤矿开采提供了借鉴和依据。 相似文献
30.
利用井田勘探资料及野外地质资料,对井田构造基本形态、断层发育特征及其分布规律进行分析,总结出该井田的构造模式、构造成因、构造组合特征及其演化规律。研究认为井田的构造格局是多期构造运动综合作用、相互叠加的结果。井田构造形态为一略有起伏的平缓单斜,区内NE向的高角度正断层,多属张扭性,EW向构造早于NE向构造,构造复合部位较复杂,其余区段较简单;伸展构造是井田构造的主体样式,这一结论对下一步继续勘探及煤矿开采具有指导意义。 相似文献