全文获取类型
收费全文 | 797篇 |
免费 | 95篇 |
国内免费 | 96篇 |
专业分类
测绘学 | 265篇 |
大气科学 | 59篇 |
地球物理 | 114篇 |
地质学 | 258篇 |
海洋学 | 90篇 |
天文学 | 31篇 |
综合类 | 69篇 |
自然地理 | 102篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 16篇 |
2021年 | 27篇 |
2020年 | 22篇 |
2019年 | 23篇 |
2018年 | 22篇 |
2017年 | 39篇 |
2016年 | 29篇 |
2015年 | 35篇 |
2014年 | 32篇 |
2013年 | 36篇 |
2012年 | 41篇 |
2011年 | 49篇 |
2010年 | 38篇 |
2009年 | 50篇 |
2008年 | 46篇 |
2007年 | 51篇 |
2006年 | 52篇 |
2005年 | 42篇 |
2004年 | 45篇 |
2003年 | 38篇 |
2002年 | 34篇 |
2001年 | 31篇 |
2000年 | 24篇 |
1999年 | 22篇 |
1998年 | 13篇 |
1997年 | 25篇 |
1996年 | 14篇 |
1995年 | 13篇 |
1994年 | 11篇 |
1993年 | 16篇 |
1992年 | 10篇 |
1991年 | 8篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有988条查询结果,搜索用时 218 毫秒
1.
张赤军 《大地测量与地球动力学》2002,22(4):31-34
介绍当今确定天文大地垂偏差的新仪器-CCD自动天体测量仪和确定两点间高程异常差的新方法,该方法用单极坐标代替繁琐的双极坐标进行计算,讨论了天文重力水准的误差及垂线偏差非线性影响等问题,估计在不久的将来,用这一手段施测山区似大地水准面的精度可望达到厘米级。 相似文献
2.
In this paper the tidal phenomena on the Earth are concisely specified, including solid tides, ocean tides and atmospheric tides due to the luni-solar tide-generating force, and the Earth pole tide due to the motion of the Earth's rotation axis (polar motion); as well as their effects on the Earth rotation. The outcomes of scientific researches of Chinese astronomers on these topics are described in some detail. These researches deal with the mechanisms responsible for tidal effects on the earth rotation, and on the measurements of the Earth rotation parameters. Finally, the effects discovered by Chinese researchers on the measurements of the period and change in period of pulsars are discussed. These effects are very small in magnitude but not negligible. 相似文献
3.
4.
Juerg M. Brunnschweiler 《Marine Ecology》2006,27(1):89-94
It is not known whether sharksuckers have positive or negative effects on their hosts, partly because this association is difficult to study in free‐ranging fish. I observed the behaviour of sharks with and without sharksuckers, to determine whether the hosts actively avoid sharksuckers. Wild blacktip sharks, Carcharhinus limbatus, took evasive actions when sharksuckers, Echeneis naucrates, attached to them, presumably to escape from skin irritation or hydrodynamical drag caused by the sharksuckers. Sharksuckers were most often attached to the belly or back of the shark, and sharks reacted most strongly to sharksuckers on their heads, sides, and dorsal fins. Observations of two captive bull sharks, Carcharhinus leucas, indicated that swimming speed increased when sharksuckers were attached. This paper supports the hypothesis that sharksucker attachment irritates sharks, and that the relationship between the two is best viewed as a subtle host–parasite interaction. 相似文献
5.
K. G. Robertson 《Marine Geophysical Researches》1990,12(1-2):3-8
Accurate navigation forms an essential part of all research at sea and the deep ocean imposes it's own unique problems. This chapter discusses several of the techniques in current use on the research vessels of the Natural Environment Research Council (NERC), concentrating on those systems which provide global navigation facilities, as opposed to the more localised, coastal aids. Whilst most of the systems rely on surface propagation of radio waves, the use of acoustics and sea-bed mapping instruments constitute accurate alternatives for some sub-sea applications. 相似文献
6.
7.
Variations of the Kuroshio Axis South of Kyushu in Relation to the Large Meander of the Kuroshio 总被引:1,自引:0,他引:1
The characteristics of the Kuroshio axis south of Kyushu, which meanders almost sinusoidally, are clarified in relation to
the large meander of the Kuroshio by analyzing water temperature data during 1961–95 and sea level during 1984–95. The shape
of the Kuroshio axis south of Kyushu is classified into three categories of small, medium, and large amplitude of meander.
The small amplitude category occupies more than a half of the large-meander (LM) period, while the medium amplitude category
takes up more than a half of the non-large-meander (NLM) period. Therefore, the amplitude and, in turn, the curvature of the
Kuroshio axis is smaller on average during the LM period than the NLM period. The mean Kuroshio axis during the LM period
is located farther north at every longitude south of Kyushu than during the NLM period, with a slight difference west of the
Tokara Islands and a large difference to the east. A northward shift of the Kuroshio axis in particular east of the Tokara
Islands induces small amplitude and curvature of the meandering shape during the LM period. During the NLM period, the meandering
shape and position south of Kyushu change little with Kuroshio volume transport. In the LM formation stage, the variation
of the Kuroshio axis is small west of the Tokara Islands but large to the east due to a small meander of the Kuroshio. In
the LM decay stage, the Kuroshio meanders greatly south of Kyushu and is located stably near the coast southeast of Kyushu.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
双船中层拖网网位控制的静力学解析 总被引:1,自引:0,他引:1
中层拖网是开发利用中上层鱼类资源的重要工具之一,能否有效实施对拖网作业水层的控制,是实现瞄准捕捞和提高捕捞生产效率的关键。本文提出了1种基于有限元原理的拖网曳纲形状与张力的理论计算方法,以期依据中层拖网拖曳过程中不同拖速、曳纲长度和重锤配备条件下曳纲响应的计算机模拟结果,预测拖网可能的作业水层,以实现中层拖网网位控制,为中层拖网曳纲设计和网位调整提供理论依据。 相似文献
9.
在洋浦近岸海域计算潮流场基础上,计算预选排污口附近海水质点运动轨迹及预测污染物浓度分布,最后,从环保角度出发,推荐了洋浦地区各开发区的排污口位置,为洋浦近岸海域污染控制规划方案的制定及其优化提供了依据。 相似文献
10.