全文获取类型
收费全文 | 237篇 |
免费 | 7篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 16篇 |
地球物理 | 37篇 |
地质学 | 97篇 |
海洋学 | 54篇 |
天文学 | 27篇 |
自然地理 | 11篇 |
出版年
2023年 | 2篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2018年 | 3篇 |
2017年 | 4篇 |
2016年 | 9篇 |
2015年 | 8篇 |
2014年 | 6篇 |
2013年 | 24篇 |
2012年 | 11篇 |
2011年 | 12篇 |
2010年 | 9篇 |
2009年 | 20篇 |
2008年 | 14篇 |
2007年 | 17篇 |
2006年 | 21篇 |
2005年 | 6篇 |
2004年 | 6篇 |
2003年 | 10篇 |
2002年 | 2篇 |
2001年 | 5篇 |
2000年 | 8篇 |
1999年 | 2篇 |
1998年 | 9篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 2篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1978年 | 2篇 |
1974年 | 1篇 |
排序方式: 共有245条查询结果,搜索用时 671 毫秒
51.
52.
53.
54.
An estimate of the total biomass of fish in the North Sea 总被引:2,自引:4,他引:2
55.
56.
Jenny Brunnegrd Sibylle Grandel Henrik Sthl Anders Tengberg Per O.J. Hall 《Progress in Oceanography》2004,63(4):159-181
Rates of transformation, recycling and burial of nitrogen and their temporal and spatial variability were investigated in deep-sea sediments of the Porcupine Abyssal Plain (PAP), NE Atlantic during eight cruises from 1996 to 2000. Benthic fluxes of ammonium (NH4) and nitrate (NO3) were measured in situ using a benthic lander. Fluxes of dissolved organic nitrogen (DON) and denitrification rates were calculated from pore water profiles of DON and NO3, respectively. Burial of nitrogen was calculated from down core profiles of nitrogen in the solid phase together with 14C-based sediment accumulation rates and dry bulk density. Average NH4 and NO3-effluxes were 7.4 ± 19 μmol m−2 d−1 (n = 7) and 52 ± 30 μmol m−2 d−1 (n = 14), respectively, during the period 1996–2000. During the same period, the DON-flux was 11 ± 5.6 μmol m−2 d−1 (n = 5) and the denitrification rate was 5.1 ± 3.0 μmol m−2 d−1 (n = 22). Temporal and spatial variations were only found in the benthic NO3 fluxes. The average burial rate was 4.6 ± 0.9 μmol m−2 d−1. On average over the sampling period, the recycling efficiency of the PON input to the sediment was 94% and the burial efficiency hence 6%. The DON flux constituted 14% of the nitrogen recycled, and it was of similar magnitude as the sum of burial and denitrification. By assuming the PAP is representative of all deep-sea areas, rates of denitrification, burial and DON efflux were extrapolated to the total area of the deep-sea floor (>2000 m) and integrated values of denitrification and burial of 8 ± 5 and 7 ± 1 Tg N year−1, respectively, were obtained. This value of total deep-sea sediment denitrification corresponds to 3–12% of the global ocean benthic denitrification. Burial in deep-sea sediments makes up at least 25% of the global ocean nitrogen burial. The integrated DON flux from the deep-sea floor is comparable in magnitude to a reported global riverine input of DON suggesting that deep-sea sediments constitute an important source of DON to the world ocean. 相似文献
57.
58.
Poul Degnbol Henrik Gislason Susan Hanna Svein Jentoft Jesper Raakjær Nielsen Sten Sverdrup-Jensen Douglas Clyde Wilson 《Marine Policy》2006
Fisheries management benefits from the contribution of several academic disciplines, each with their own perspectives, concerns and solutions. In this essay we argue that the contribution of biology, economics, sociology and other relevant disciplines to fisheries would be improved if they originated from broader, more integrated analytical perspectives that are attuned to the empirical realities of fisheries management. Today, disciplinary boundaries narrow the perspectives of fisheries management, creating tunnel vision and standardized technical fixes to complex and diverse management problems. Having worked separately and together for a number of years in fisheries research and consultancy in many parts of the world we, as a group of biologists, economists and sociologists, feel that the time to rid ourselves from disciplinary dogmatism is long overdue. We claim that improvements in fisheries management will be realized not through the promotion of technical fixes but instead by embracing and responding to the complexity of the management problem. 相似文献
59.
Henrik Lundstedt 《Solar physics》1989,123(1):177-183
Periods of very low solar wind velocity at 1 AU, during the interval from 1977 to 1983, are identified and mapped back to the coronal source surface at 2.5 R
. In total 25 such low-velocity events were found. Inferred source locations were characterized with respect to their position relative to the coronal neutral line. The study showed that in 17 out of 25 cases the slow solar wind originated across a coronal neutral line. In the remaining cases the source was either along the neutral line or insides a warp. A prediction of the IMF polarity to be expected at Earth, from the computed coronal magnetic field, was also done. It failed clearly only in four cases out of 25 events. In three cases the prediction was uncertain because of missing data. Possible explanations of why the potential model sometimes predicts a wrong polarity are discussed. 相似文献
60.