全文获取类型
收费全文 | 114篇 |
免费 | 5篇 |
专业分类
测绘学 | 2篇 |
大气科学 | 13篇 |
地球物理 | 28篇 |
地质学 | 22篇 |
海洋学 | 9篇 |
天文学 | 35篇 |
综合类 | 1篇 |
自然地理 | 9篇 |
出版年
2021年 | 2篇 |
2020年 | 2篇 |
2019年 | 1篇 |
2018年 | 2篇 |
2017年 | 4篇 |
2016年 | 3篇 |
2015年 | 2篇 |
2014年 | 3篇 |
2013年 | 12篇 |
2012年 | 4篇 |
2011年 | 8篇 |
2010年 | 14篇 |
2009年 | 6篇 |
2008年 | 2篇 |
2007年 | 1篇 |
2006年 | 2篇 |
2004年 | 11篇 |
2003年 | 3篇 |
2002年 | 3篇 |
2000年 | 3篇 |
1998年 | 2篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 1篇 |
1992年 | 1篇 |
1989年 | 1篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1981年 | 1篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 3篇 |
1970年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有119条查询结果,搜索用时 156 毫秒
11.
Eric F. Lambin Sarah Ann Lise D’haen Ole Mertz Jonas Østergaard Nielsen Kjeld Rasmussen 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2014,114(1):76-83
In an attempt to anticipate possible futures of drylands of West Africa in the face of rapid socio-economic and environmental changes, we developed four scenarios based on recent survey data, the literature and our knowledge of the region. The four scenarios are inspired by those developed by the Millennium Ecosystem Assessment: (1) ‘downward spiral’ characterized by rapid climate change, expansion of agriculture and chaotic urban growth; (2) ‘integrated economy’ with integrated land management, food production for local markets and rural–urban exchanges; (3) ‘open doors’ characterized by large-scale out-migrations, land grabbing by foreign companies and development aid and (4) ‘climate change mitigation’ with an increase in biofuel crops, land management for carbon capture and development of off-farm activities. We conclude that the Sahel region is most likely moving away from being a highly climate-dependent region based on agriculture towards a more open and diversified economy. West African countries have to find a balance between the new opportunities and risks created by economic globalization. 相似文献
12.
Knut Jørgen Røed Ødegaard 《Astrophysics and Space Science》1996,238(1):107-111
New computations of massive stars follow the evolution up to advanced stages and include: -A large and flexible nuclear network consisting of 174 nuclear species that are linked by 1742 nuclear reactions. -Semiconvection, overshooting and mass loss. -Modern rates for both strong and weak interaction processes as well as the latest rates for the neutrino processes. -Improved grid distribution and a large number of grid points. The nuclear network and the diffusion equation are solved for each time step during the whole evolution. In this way the accuracy of nuclear yields and chemical abundances are mainly limited by uncertainties in the diffusion coefficient found from the convection theories. Several instability mechanisms may affect the mass loss rates of massive stars and thereby the structure and abundances of WR stars. Due to heavy mass loss at the LBV and WR stages, the masses at the pre-SN stage may be less than 5M ⊙. Yields and abundances throughout the stars are discussed together with the amount of all elements expelled. 相似文献
13.
Dennis Stello Hans Kjeldsen Timothy R. Bedding Joris De Ridder Conny Aerts Fabien Carrier SØren Frandsen 《Solar physics》2004,220(2):207-228
The discovery of solar-like oscillations in the giant star ξ Hya (G7 III) was reported by Frandsen et al. (2002). Their frequency analysis was very limited due to alias problems in the data set (caused by single-site observations).
The extent to which the aliasing affected their analysis was unclear due to the unknown damping time of the stellar oscillation
modes. In this paper we describe a simulator created to generate time series of stochastically excited oscillations, which
takes as input an arbitrary window function and includes both white and non-white noise. We also outline a new method to compare
a large number of simulated time series with an observed time series to determine the damping time, amplitude, and limited
information on the degree of the stochastically excited modes. For ξ Hya we find the most likely amplitude to be ∼ 2 m s−1, in good agreement with theory (Houdek and Gough, 2002), and the most likely damping time to be ∼ 2 days, which is much shorter
than the theoretical value of 15–20 days calculated by Houdek and Gough (2002). 相似文献
14.
Solar Physics - A curved filament in a decaying active region (AR&;nbsp;8329) was observed on 9 September 1998 with a combination of several instruments. The main data base is a 4-hour long time... 相似文献
15.
16 lines of Pr ii possibly present in the solar photospheric spectrum have been studied. When including hyperfine structure in synthetic calculations, investigations of 9 lines result in an abundance A
Pr = 0.71 ± 0.08 in the log A
H = 12.00 scale. 相似文献
16.
17.
Öivind Hauge 《Solar physics》1972,22(2):263-275
Photoelectric measurements of photospheric velocity fields have been carried out with the Sacramento Peak Doppler Zeeman Analyzer. Emphasis was given to long periods and low spatial wavenumbers in deep photospheric layers, where the 5-min oscillations are less dominant.Multiple or double peaks cannot be detected in power spectra of the 5-min oscillations, provided that a sufficient number of physically independent points on the solar surface are observed.The most frequent wave-numbers in the spectra of 5-min oscillations (as well as of the low frequency field) agree with those derived from a model assuming statistically independent oscillators of 10 to 20 diameter. These two velocity fields are anti-correlated spatially.Kinetic power in the 20-to-50-min range of periods is closely linked to brightness changes in the same layer, an increase of brightness lagging about 250 sec behind rising motion. Granules can be excluded as a possible source for the appearance of low frequency flow patterns. Different explanations are suggested.On leave from Fraunhofer Institut, Freiburg, Germany. 相似文献
18.
Challenges in global ballast water management 总被引:3,自引:0,他引:3
Endresen Ø Lee Behrens H Brynestad S Bjørn Andersen A Skjong R 《Marine pollution bulletin》2004,48(7-8):615-623
Ballast water management is a complex issue raising the challenge of merging international regulations, ship's specific configurations along with ecological conservation. This complexity is illustrated in this paper by considering ballast water volume, discharge frequency, ship safety and operational issues aligned with regional characteristics to address ecological risk for selected routes. A re-estimation of ballast water volumes gives a global annual level of 3500 Mton. Global ballast water volume discharged into open sea originating from ballast water exchange operations is estimated to approximately 2800 Mton. Risk based decision support systems coupled to databases for different ports and invasive species characteristics and distributions can allow for differentiated treatment levels while maintaining low risk levels. On certain routes, the risk is estimated to be unacceptable and some kind of ballast water treatment or management should be applied. 相似文献
19.
20.