全文获取类型
收费全文 | 3761篇 |
免费 | 503篇 |
国内免费 | 844篇 |
专业分类
测绘学 | 178篇 |
大气科学 | 720篇 |
地球物理 | 586篇 |
地质学 | 1887篇 |
海洋学 | 1007篇 |
天文学 | 18篇 |
综合类 | 225篇 |
自然地理 | 487篇 |
出版年
2024年 | 21篇 |
2023年 | 48篇 |
2022年 | 114篇 |
2021年 | 141篇 |
2020年 | 137篇 |
2019年 | 159篇 |
2018年 | 132篇 |
2017年 | 179篇 |
2016年 | 202篇 |
2015年 | 202篇 |
2014年 | 251篇 |
2013年 | 223篇 |
2012年 | 262篇 |
2011年 | 264篇 |
2010年 | 247篇 |
2009年 | 256篇 |
2008年 | 241篇 |
2007年 | 340篇 |
2006年 | 267篇 |
2005年 | 197篇 |
2004年 | 189篇 |
2003年 | 147篇 |
2002年 | 127篇 |
2001年 | 100篇 |
2000年 | 111篇 |
1999年 | 88篇 |
1998年 | 60篇 |
1997年 | 77篇 |
1996年 | 58篇 |
1995年 | 68篇 |
1994年 | 43篇 |
1993年 | 45篇 |
1992年 | 31篇 |
1991年 | 16篇 |
1990年 | 13篇 |
1989年 | 6篇 |
1988年 | 8篇 |
1987年 | 8篇 |
1986年 | 9篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1978年 | 1篇 |
排序方式: 共有5108条查询结果,搜索用时 15 毫秒
31.
南海南部约30 ka来沉积有机质的生物输入特征 总被引:7,自引:4,他引:7
对位于南沙海区的1962柱状样中的有机质进行了热解色谱分析,估算了沉积有机质中水生生物输入和陆源生物输入的变化情况,得出了两种输入的高分辨率的堆积速率曲线,并依此探讨了有关的古海洋事件。发现Younger Dryas、Heinrich及Bond周期事件在本海区皆有表现,说明“西太平洋暖池”在末次冰期是不稳定的。 相似文献
32.
33.
Louis W. Botsford Cathryn A. Lawrence Edward P. Dever Alan Hastings John Largier 《Deep Sea Research Part II: Topical Studies in Oceanography》2006,53(25-26):3116
The production and distribution of biological material in wind-driven coastal upwelling systems are of global importance, yet they remain poorly understood. Production is frequently presumed to be proportional to upwelling rate, yet high winds can lead to advective losses from continental shelves, where many species at higher trophic levels reside. An idealized mixed-layer conveyor (MLC) model of biological production from constant upwelling winds demonstrated previously that the amount of new production available to shelf species increased with upwelling at low winds, but declined at high winds [Botsford, L.W., Lawrence, C.A., Dever, E.P., Hastings, A., Largier, J., 2003. Wind strength and biological productivity in upwelling systems: an idealized study. Fisheries Oceanography 12, 245–259]. Here we analyze the response of this model to time-varying winds for parameter values and observed winds from the Wind Events and Shelf Transport (WEST) study region. We compare this response to the conventional view that the results of upwelling are proportional to upwelled volume. Most new production per volume upwelled available to shelf species occurs following rapid increases in shelf transit time due to decreases in wind (i.e. relaxations). However, on synoptic, event time-scales shelf production is positively correlated with upwelling rate. This is primarily due to the effect of synchronous periods of low values in these time series, paradoxically due to wind relaxations. On inter-annual time-scales, computing model production from wind forcing from 20 previous years shows that these synchronous periods of low values have little effect on correlations between upwelling and production. Comparison of model production from 20 years of wind data over a range of shelf widths shows that upwelling rate will predict biological production well only in locations where cross-shelf transit times are greater than the time required for phytoplankton or zooplankton production. For stronger mean winds (narrower shelves), annual production falls below the peak of constant wind prediction [Botsford et al., 2003. Wind strength and biological productivity in upwelling systems: an idealized study. Fisheries Oceanography 12, 245–259], then as winds increase further (shelves become narrower) production does not decline as steeply as the constant wind prediction. 相似文献
34.
35.
36.
Viability theory for an ecosystem approach to fisheries 总被引:1,自引:1,他引:1
37.
38.
In this paper, we focus on the status and trends of the current Korean fisheries management regime. Specifically, this paper briefly introduces the Korean conventional fisheries management regime (KCFMR) and discusses its problems and limitations. In describing policy evolution, this paper finds reasons why the Korean government has chosen a TAC system, an output control approach, besides input control approaches in force for almost a century. This paper also describes the evolution of the Korean TAC system, which is carrying out a pivotal role in Korean fisheries development, and analyzes problems of the Korean TAC system. Finally, this paper gives a perspective on expanding the Korean TAC system toward Output Control Systems (OCSs) such as Individual Quotas (IQs), Individual Vessel Quotas (IVQs), Individual Transferable Traps (ITTs), Community Quotas (CQs), and Individual Transferable Quotas (ITQs). 相似文献
39.
40.
江苏岸外辐射沙脊群东沙稳定性研究 总被引:8,自引:0,他引:8
东沙是江苏岸外辐射沙脊群中的第二大沙洲,具有独特的地形地貌和水动力条件,对它进行稳定性研究为揭示整个辐射沙洲及其邻近岸滩的动态演变都非常有益。通过利用多年遥感卫片资料、1998年取得的现场水文泥沙观测资料和东沙滩面表层沉积物资料等,对东沙的地形地貌特征、沉积特征和东沙两侧潮汐通道的水流泥沙特征等进行了详细分析。研究结果表明,东沙的沙脊偏于西侧,西侧滩面较窄、高程较高且岸线较为顺直,东侧滩面较宽、高程较低且岸线较为破碎;西洋和陈家坞槽均处于冲刷状态,净输沙的主要方向为输向槽外或输向条子泥;东沙近三十年来面积有所缩小且有外围向中央收缩的趋势,尤其以向东、向南方向的迁移最为明显。 相似文献