全文获取类型
收费全文 | 455篇 |
免费 | 36篇 |
国内免费 | 60篇 |
专业分类
测绘学 | 5篇 |
大气科学 | 5篇 |
地球物理 | 33篇 |
地质学 | 34篇 |
海洋学 | 427篇 |
综合类 | 24篇 |
自然地理 | 23篇 |
出版年
2024年 | 3篇 |
2023年 | 1篇 |
2022年 | 10篇 |
2021年 | 14篇 |
2020年 | 10篇 |
2019年 | 14篇 |
2018年 | 8篇 |
2017年 | 31篇 |
2016年 | 18篇 |
2015年 | 24篇 |
2014年 | 22篇 |
2013年 | 34篇 |
2012年 | 28篇 |
2011年 | 17篇 |
2010年 | 24篇 |
2009年 | 25篇 |
2008年 | 18篇 |
2007年 | 32篇 |
2006年 | 28篇 |
2005年 | 29篇 |
2004年 | 21篇 |
2003年 | 15篇 |
2002年 | 12篇 |
2001年 | 20篇 |
2000年 | 41篇 |
1999年 | 12篇 |
1998年 | 7篇 |
1997年 | 3篇 |
1996年 | 6篇 |
1995年 | 4篇 |
1994年 | 3篇 |
1992年 | 7篇 |
1990年 | 1篇 |
1989年 | 5篇 |
1987年 | 1篇 |
1984年 | 2篇 |
1980年 | 1篇 |
排序方式: 共有551条查询结果,搜索用时 15 毫秒
511.
We present a conceptual model for the analysis of the costs and benefit aspects of the risk inherent in illegal, unreported and unregulated (IUU) activity. We then develop and present a map of IUU incidences as reported in the Fisheries Centre's Sea Around Us project IUU global database. This map shows that IUU activities are quite widespread geographically. We next present an analysis of the cost and benefit aspects of risks of IUU fishing. A key result of the study is that for the cases analyzed as a group; the expected benefits from IUU fishing far exceed the expected cost of being apprehended. For an assumed 1 in 5 chance of being apprehended, our calculations show that reported fines for the vessels apprehended will have to be increased by 24 times for the expected cost to be at least as much as the expected benefits. 相似文献
512.
Hull forms and hydrodynamic characteristics of small catamarans are studied. The results of model tests and numerical simulations are cross-examined to carefully investigate the shallow water behaviors of the boats as well as the influence of spacing between demi-hulls on the resistance characteristics. A 12 m long 9.77 ton class catamaran has been developed and several ships have already been produced and deployed as pleasure fishing boats along the west coast of the Korean peninsula. The boats are made of fiber-reinforced plastics and are equipped with a pair of 280 hp diesel engines and water jet propulsion systems. The maximum speed of a fully loaded catamaran exceeds 25 knot. The results of sea trials are compared with those predicted from the model tests. 相似文献
513.
Fulton Elizabeth A.; Smith Anthony D.M.; Punt Andre E. 《ICES Journal of Marine Science》2005,62(3):540-551
514.
515.
Subsistence in coastal fisheries policy: What's in a word? 总被引:1,自引:2,他引:1
Consideration of subsistence fishing activities seems particularly relevant to coastal fisheries policy, yet formal recognition of subsistence fishing is often absent from associated policy frameworks. A critical problem is the very meaning of the term “subsistence.” A review of the literature on subsistence, dominated until recently by North American research, reveals a schism between interpretations emphasizing material aspects of subsistence and interpretations highlighting cultural aspects. The North American literature on the subject is heavily influenced by a focus on Arctic indigenous populations emphasizing cultural survival. Ultimately, subsistence can be a matter of survival in the belly, the soul, or both. International case studies suggest that different interpretations of subsistence are appropriate in different circumstances, and that appropriate policy can be fashioned only after the local context of subsistence is understood. 相似文献
516.
Piet G. J.; Quirijns F. J.; Robinson L.; Greenstreet S. P. R. 《ICES Journal of Marine Science》2007,64(1):110-121
517.
518.
爆破振动对铁厂沟村房屋选择性破坏的调查与分析 总被引:2,自引:1,他引:1
乌鲁木齐矿务局露天矿的剥离爆破对距爆点1km外的铁厂沟材房屋产生了选择性破坏,振动对个体房屋的破坏呈现出鲜明的选择性,不同房屋遭受的破坏程度差异极大。 相似文献
519.
The regolith studied here is located at the defunct Areachap mine and the newly discovered Kantienpan Cu–Zn volcanic-hosted massive sulfide (VHMS) deposit, located in the Areachap Group of the eastern part of Mesoproterozoic Namaqua Metamorphic Province. This area is highly prospective for further VHMS discoveries. Paleo and recent weathering of the upper most parts of massive sulfide deposits led to the formation of a gossan zone. Due to semi-arid climatic conditions during the late Cretaceous, affecting the African Land surface, the lowermost units of the Kalahari Group and the underlying floor rocks were calcretized. An approximately 6 m thick calcrete layer formed above the gossan zone and this was later covered by eolian Kalahari sand. Samples were collected from the eolian sand cover in the study areas to determine the best analytical method that would enable recognition of the concealed ore deposits and detect the widest secondary dispersion halo.Mobile metal ions from the finest fraction of the eolian sand samples (< 75 μm) were extracted with a NH4EDTA (EDTA) solution. The solution was analysed for Cu, Zn, Pb and Mn by inductively coupled plasma mass spectrometry (ICP-MS). The same grainsize fraction of the original samples was also analysed for comparison purposes by means of X-ray fluorescence (XRF).Results indicate that the ore zone in both areas may be recognized by both partial and total analyses of the eolian sand samples collected, although the calcrete layer, below the sand cover, acts as a partial geochemical barrier. The recognition of the ore zone depends on the regolith forming processes and the thickness of the eolian sand cover. In the Areachap area, with a relatively thick sand cover (in excess of 1 m) above the calcrete layer, the detectable geochemical halo is related to the distribution of the mobile metal ions, and partial extraction (EDTA solution) results define a larger dispersion halo than that, that could be detected by total analysis (XRF). Whereas, in the Kantienpan area with a very thin sand cover (< 50 cm) dispersion appears to be related more to the secondary redistribution of gossaniferous clasts released by recent weathering out of the calcrete, than to dispersion of mobile metal ions on the surface of sand particles. In this area, the XRF results reveal a wider dispersion of the elements of interest. 相似文献
520.