全文获取类型
收费全文 | 27081篇 |
免费 | 4432篇 |
国内免费 | 6568篇 |
专业分类
测绘学 | 6120篇 |
大气科学 | 4738篇 |
地球物理 | 6285篇 |
地质学 | 11158篇 |
海洋学 | 3628篇 |
天文学 | 271篇 |
综合类 | 2202篇 |
自然地理 | 3679篇 |
出版年
2024年 | 163篇 |
2023年 | 442篇 |
2022年 | 920篇 |
2021年 | 1108篇 |
2020年 | 1284篇 |
2019年 | 1394篇 |
2018年 | 1157篇 |
2017年 | 1387篇 |
2016年 | 1492篇 |
2015年 | 1643篇 |
2014年 | 1736篇 |
2013年 | 2020篇 |
2012年 | 1868篇 |
2011年 | 1869篇 |
2010年 | 1487篇 |
2009年 | 1675篇 |
2008年 | 1758篇 |
2007年 | 1821篇 |
2006年 | 1705篇 |
2005年 | 1491篇 |
2004年 | 1347篇 |
2003年 | 1132篇 |
2002年 | 1043篇 |
2001年 | 877篇 |
2000年 | 805篇 |
1999年 | 697篇 |
1998年 | 650篇 |
1997年 | 552篇 |
1996年 | 481篇 |
1995年 | 448篇 |
1994年 | 396篇 |
1993年 | 335篇 |
1992年 | 201篇 |
1991年 | 183篇 |
1990年 | 118篇 |
1989年 | 92篇 |
1988年 | 93篇 |
1987年 | 65篇 |
1986年 | 32篇 |
1985年 | 32篇 |
1984年 | 17篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1978年 | 9篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1972年 | 1篇 |
1954年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
172.
Mesoscale features in the eastward extension of the Kuroshio were investigated using assimilation of TOPEX/POSEIDON (T/P)
data into a three-layer quasi-geostrophic model. The T/P data exhibited an elongated state of the southern recirculation gyre
in 1993–95 and 1997, between whose two periods the gyre had a contracted state in 1995–96. A few stationary eddies were located
in the southern gyre during the contracted state. The baroclinic instability, which was indicated by the phase shift from
the uppermost-to the lowest-layer anomalies toward the downstream side, was evident near the Kuroshio Extension (KE) path.
Since the instability never appeared in the artificial model without bottom topography, the topographic barrier for the eastward
flow in the lowest layer was a necessary condition for the instability. The instability synchronized with the transition in
the western region of the KE axis from the elongated to the contracted states. This evolution was interpreted as if the baroclinic
instability played some part in the KE states and was a trigger for the transition from the elongated to the contracted states. 相似文献
173.
Among the assumptions upon which linear time-invariant models of floating bodies are based is that the body motions are so small that any change in the body’s angular position can be disregarded. However, it is often a major design requirement of a wave energy conversion device that the response amplitude is large, thereby invalidating one of the assumptions of the linear model. In particular, the immersed geometry of a body undergoes considerable variation when it is moved in pitch. With regard to this we investigate the difference in performance between a quasi-linear model in which the change of immersed surface is modelled by time-varying parameters and a basic linear model in which the immersed surface is time-invariant. The time-varying parameter model is realized by interpolation between the appropriate parameter values of a set of linear time-invariant (LTI) models derived for the different immersed surfaces that occur at discrete body displacements. It is shown that the responses predicted using the time-varying parameter model are closer to those measured experimentally than those of a standard frequency-domain model. Particular improvement occurs when the responses are large, such as at or near the resonance frequency. A problem which may limit the general use of the model is also discussed. 相似文献
174.
湍流数值模拟中封闭模式应用的局限性 总被引:1,自引:0,他引:1
通过对琼州海峡的潮流场特征进行数值模拟,指出了选择不同的特征混合长度表达式对数值模拟结果的影响,表明了基于特征混合长度理论的流封闭模式在近海湍流数值模拟中应用的局限性。 相似文献
175.
176.
海洋交通运输业碳排放研究对制定行之有效的低碳海洋交通政策具有重要意义。本文首先对2006—2015年中国沿海11个省(区、市)的海洋交通运输业碳排放量进行估算,然后运用超效率SBM模型对碳排放效率进行测度,最后运用Tobit模型探究碳排放效率的影响因素。结果表明:①中国海洋交通运输业碳排放效率整体上处于低效率状态,且各省(区、市)间差异明显,但差异正在逐渐缩小。②2006—2015年沿海各省(区、市)市海洋交通运输业碳排放效率变动呈现出“M”形波动上升趋势。③将各省(区、市)海洋交通运输业碳排放效率水平划分为不同类型,其中上海和天津属于高效率型,河北属于中效率型,其余省(区、市)市属于低效率型。④货运距离和能源结构对海洋交通运输业碳排放效率具有显著的正向作用,而能源强度对其具有显著的负向作用。 相似文献
177.
Morphodynamic modeling is employed in the present work to predict the long-term evolution (over the next 100 years) of typical sedimentary coasts in the western Russian Arctic. The studied objects are the coasts of Varandey (the Barents Sea), Baydaratskaya Bay and Harasavey (the Kara Sea). The model developed takes into account both the short-term processes (storm events) and long-term factors (for example, changes in sea level, inter-annual variations in gross sediment flux, lack or excess of sediment supply). Predicted and observed morphological changes in coastal profiles are shown to agree well for time scales ranging from weeks to decades. It is revealed that under given environmental conditions, the morphological evolution is strongly influenced by storm surges and associated wind-driven circulation. The water level gradient created by a surge generates a seaward flow at the bed. This outflow is shown to be an important destructive mechanism contributing to the erosion and recession of Arctic coasts. The rate of change is found to depend on both the exposure of the coast (relative to the direction of dominant winds) and its height above the sea. The open coast of Varandey is expected to retreat as much as 300–500 m over 100 years, while recession of the less exposed coasts of Baydaratskaya Bay would not exceed about 100 m/century. If long-term sediment losses are insignificant, the rate of erosion decays with time and the morphodynamic system may tend toward equilibrium. It is concluded that the expected relative sea-level rise (up to 1 m over the nearest 100 years) is non-crucial to the future coastal evolution if an erosion activity is already high enough. 相似文献
178.
179.
180.
本文分析了厦门海沧海岸地区花岗岩资源开发利用现状和存在的问题,运用生态恢复理论讨论了矿山采石高难度地生态恢复技术途径和模式。 相似文献