全文获取类型
收费全文 | 2371篇 |
免费 | 450篇 |
国内免费 | 652篇 |
专业分类
测绘学 | 285篇 |
大气科学 | 627篇 |
地球物理 | 767篇 |
地质学 | 723篇 |
海洋学 | 603篇 |
天文学 | 8篇 |
综合类 | 281篇 |
自然地理 | 179篇 |
出版年
2024年 | 20篇 |
2023年 | 41篇 |
2022年 | 86篇 |
2021年 | 108篇 |
2020年 | 113篇 |
2019年 | 161篇 |
2018年 | 117篇 |
2017年 | 139篇 |
2016年 | 114篇 |
2015年 | 132篇 |
2014年 | 161篇 |
2013年 | 191篇 |
2012年 | 164篇 |
2011年 | 162篇 |
2010年 | 145篇 |
2009年 | 169篇 |
2008年 | 131篇 |
2007年 | 176篇 |
2006年 | 123篇 |
2005年 | 112篇 |
2004年 | 125篇 |
2003年 | 82篇 |
2002年 | 73篇 |
2001年 | 79篇 |
2000年 | 70篇 |
1999年 | 58篇 |
1998年 | 54篇 |
1997年 | 55篇 |
1996年 | 55篇 |
1995年 | 50篇 |
1994年 | 38篇 |
1993年 | 37篇 |
1992年 | 35篇 |
1991年 | 19篇 |
1990年 | 13篇 |
1989年 | 22篇 |
1988年 | 14篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 10篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1981年 | 2篇 |
1978年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有3473条查询结果,搜索用时 0 毫秒
101.
Li Yucheng Wang Fenglong Professor Dalian University of Technology Dalian Senior Engineer Dalian University of Technology Dalian 《中国海洋工程》1993,(1)
- The wave-current forces on vertical piles in side-by-side arrangement induced by irregular waves with opposing current are investigated experimentally in this paper. The characteristics in both time and frequency domain of in-line, lift and resultant forces are analyzed. The grouping effect coefficients of inline, lift and resultant forces on piles related to KC number and relative spacing parameters are given. These results are compared with those in the case of irregular waves combined with following currents. It is found that the results in these two cases are quite different. The range of KC number tested is 10- 60, the range of Reynolds number is (0.55-3.43) ×104. 相似文献
102.
回顾了近年来国内外河口、近岸海域三维斜压水流数值模式研究的进展,着重讨论了不同垂向坐标下三维水流模式的发展状况以及存在的问题。地形拟合坐标(σ坐标)模式可以很好地拟合床面地形和自由面,已在物理海洋学中被广泛使用。但在地形变化剧烈,尤其在密度层结效应明显的海域,σ坐标模式中的水平压强梯度力误差会引起伪密度流。寻求高精度的数值模式以及更加有效的拟合坐标变换将是值得努力的方向。 相似文献
103.
The mixing agents and their role in the dynamics of a shallow fjord are elucidated through an Eulerian implementation of artificial tracers in a three-dimensional hydrodynamic model. The time scales of vertical mixing in this shallow estuary are short, and the artificial tracers are utilized in order to reveal information not detectable in the temperature or salinity fields. The fjord's response to external forcing is investigated through a series of model experiments in which we quantify vertical mixing, transport time scales of fresh water runoff and estuarine circulation in relation to external forcing.Using age tracers released at surface and bottom, we quantify the time scales of downward mixing of surface water and upward mixing of bottom water. Wind is shown to be the major agent for vertical mixing at nearly all depth levels in the fjord, whereas the tide or external sea level forcing is a minor agent and only occasionally more important just close to the bottom. The time scale of vertical mixing of surface water to the bottom or ventilation time scale of bottom water is estimated to be in the range 0.7 h to 9.0 days, with an average age of 2.7 days for the year 2004.The fjord receives fresh water from two streams entering the innermost part of the fjord, and the distribution and age of this water are studied using both ageing and conservative tracers. The salinity variations outside this fjord are large, and in contrast to the salinity, the artificial tracers provide a straight forward analysis of river water content. The ageing tracer is used to estimate transport time scales of river water (i.e. the time elapsed since the water left the river mouth). In May 2004, the typical age of river water leaving the fjord mouth is 5 days. As the major vertical mixing agent is wind, it controls the estuarine circulation and export of river water. When the wind stress is set to zero, the vertical mixing is reduced and the vertical salinity stratification is increased, and the river water can be effectively exported out of the fjord.We also analyse the river tracer fields and salinity field in relation to along estuary winds in order to detect signs of wind-induced straining of the along estuary density gradient. We find that events of down estuary winds are primarily associated with a reduced along estuary salinity gradient due to increased surface salinity in the innermost part of the fjord, and with an overall decrease in vertical stratification and river water content at the surface. Thus, our results show no apparent signs of wind-induced straining in this shallow fjord but instead they indicate increased levels of vertical mixing or upwelling during down estuary wind events. 相似文献
104.
Bathymetric segregation of sea urchins on reefs of the Canarian Archipelago: Role of flow-induced forces 总被引:1,自引:0,他引:1
F. Tuya J. Cisneros-Aguirre L. Ortega-Borges R.J. Haroun 《Estuarine, Coastal and Shelf Science》2007,73(3-4):481-488
We examined whether adults of three species of sea urchins species (Diadema antillarum, Arbacia lixula, and Paracentrotus lividus) exhibit a consistent depth-dependent partitioning pattern on rocky reefs of the Canarian Archipelago (eastern Atlantic). Hydrodynamic experiments were carried out to quantify the resistance to flow-induced dislodgement in these three species. We tested the model that different morphology can result in habitat partitioning among these sea urchins. Abundances of D. antillarum increased with depth. In contrast, A. lixula and P. lividus showed the opposite zonation pattern, coexisting in high abundances in the shallowest depths (<5 m), and occurring in low densities in the deepest part of reefs (>7 m). Both A. lixula and P. lividus had greater adhesion-surface to body-height ratios than D. antillarum. Similarly, A. lixula and P. lividus showed a greater ability to resist flow-induced dislodgement compared with D. antillarum. The mean “velocity of dislodgement” was 300% and 50% greater for A. lixula and P. lividus, respectively, relative to D. antillarum, for any particular size. As a result, A. lixula and P. lividus are better fitted to life in high-flow environments than D. antillarum. We conclude that the risk of dislodgement by water motion likely play a relevant role in the vertical distribution patterns of these sea urchins in the eastern Atlantic. 相似文献
105.
研究具有窄谱和Weibull波高分布的波群对非线性桩柱系统作用力的统计性质。求得了桩桩的波浪峰力的各种特征值及其比值。指出这些数值不仅是阻力一惯性力参数bH的函数,也随着波群因子而变化。本文模式更具广泛性。文中给出了一系列计算图表,可从理论计算波群作用于桩柱的波浪峰力。 相似文献
106.
直立式防波堤堤头在斜向波浪作用下波浪力的计算在现行的技术规范中尚属空白。通过物理模型试验给出了堤头结构设计所需的波压分布图,指出了波浪入射方向和地形对堤头所受波浪力的贡献有时可以超过波高和波周期,根据现行规范按波浪正向入射计算堤头所受的波浪力偏于安全。 相似文献
107.
Zooplankton diel vertical migration is evident on the mixed isothermal side of the western Irish Sea frontal system but is often influenced by large tides and persistent geostrophic currents. On the stratified side of the front, temperature acts as a controlling factor with most of the zooplankton occurring above the thermocline and carrying out pronounced vertical migration when chlorophyll a levels are low and diffuse. At higher chlorophyll levels, when discrete chlorophyll a maxima form, zooplankton vertical movement may be greatly modified with a large number of species and stages concentrating within these maxima at all times of the diel light cycle. 相似文献
108.
109.
110.