全文获取类型
收费全文 | 2778篇 |
免费 | 471篇 |
国内免费 | 791篇 |
专业分类
测绘学 | 273篇 |
大气科学 | 738篇 |
地球物理 | 336篇 |
地质学 | 1398篇 |
海洋学 | 654篇 |
天文学 | 11篇 |
综合类 | 220篇 |
自然地理 | 410篇 |
出版年
2024年 | 11篇 |
2023年 | 41篇 |
2022年 | 74篇 |
2021年 | 83篇 |
2020年 | 126篇 |
2019年 | 126篇 |
2018年 | 102篇 |
2017年 | 126篇 |
2016年 | 137篇 |
2015年 | 163篇 |
2014年 | 213篇 |
2013年 | 235篇 |
2012年 | 206篇 |
2011年 | 236篇 |
2010年 | 164篇 |
2009年 | 193篇 |
2008年 | 161篇 |
2007年 | 165篇 |
2006年 | 180篇 |
2005年 | 164篇 |
2004年 | 148篇 |
2003年 | 149篇 |
2002年 | 116篇 |
2001年 | 105篇 |
2000年 | 96篇 |
1999年 | 87篇 |
1998年 | 81篇 |
1997年 | 61篇 |
1996年 | 43篇 |
1995年 | 50篇 |
1994年 | 40篇 |
1993年 | 32篇 |
1992年 | 31篇 |
1991年 | 20篇 |
1990年 | 13篇 |
1989年 | 7篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1983年 | 7篇 |
1982年 | 12篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有4040条查询结果,搜索用时 296 毫秒
51.
52.
The seasonal variability of tropical cyclones (CTCs) generated over the South China Sea (SCS) from 1948 to 2003 is analyzed. It peaks in occurrence in August and few generate in late winter (from January to March). The seasonal activity is attributed to the variability of atmosphere and ocean environments associated with the monsoon system. It is found that the monsoonal characteristics of the SCS basically determine the region of tropical cyclone (TC) genesis in each month. 相似文献
53.
Seasonal dynamics of elemental sulfur in two coastal sediments 总被引:1,自引:0,他引:1
A spectrophotometric method for elemental sulfur (S0) analysis without interference from other reduced sulfur compounds was adapted for the use in reducing sediments. The S0 distribution in two coastal sediments was studied regularly from summer to winter and compared to factors regulating the S0 accumulation, such as redox potentials, the rate of bacterial sulfide production and the general sulfur chemistry. Dense coatings of sulfur bacteria developed on the sediment surface of a sulfuretum which had an S0 concentration of up to 41 μmol S cm?3. The 2·5-mm thick bacterial coating contained 40% of all S0 in the sediment. A more typical marine sediment with a few cm thick oxidized surface layer had an S0 maximum of 1–3 μmol S cm?3 at 2–4 cm depth. The S0 maximum in both sediments increased from summer to winter as the sediments gradually became more oxidized. The deeper layers maintained a low S0 concentration. Most of the S0 in the upper few mm of a laboratory sulfuretum was present inside sulfur bacteria and actively migrated up and down with the bacteria depending upon the changing light and oxygen conditions. 相似文献
54.
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
55.
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
56.
57.
58.
59.
60.