全文获取类型
收费全文 | 21950篇 |
免费 | 4499篇 |
国内免费 | 6671篇 |
专业分类
测绘学 | 2913篇 |
大气科学 | 3892篇 |
地球物理 | 4467篇 |
地质学 | 12219篇 |
海洋学 | 3981篇 |
天文学 | 697篇 |
综合类 | 1954篇 |
自然地理 | 2997篇 |
出版年
2024年 | 200篇 |
2023年 | 572篇 |
2022年 | 1208篇 |
2021年 | 1357篇 |
2020年 | 1188篇 |
2019年 | 1381篇 |
2018年 | 1305篇 |
2017年 | 1206篇 |
2016年 | 1358篇 |
2015年 | 1339篇 |
2014年 | 1454篇 |
2013年 | 1586篇 |
2012年 | 1642篇 |
2011年 | 1676篇 |
2010年 | 1654篇 |
2009年 | 1532篇 |
2008年 | 1551篇 |
2007年 | 1437篇 |
2006年 | 1432篇 |
2005年 | 1085篇 |
2004年 | 892篇 |
2003年 | 659篇 |
2002年 | 726篇 |
2001年 | 687篇 |
2000年 | 605篇 |
1999年 | 525篇 |
1998年 | 376篇 |
1997年 | 366篇 |
1996年 | 295篇 |
1995年 | 261篇 |
1994年 | 306篇 |
1993年 | 229篇 |
1992年 | 186篇 |
1991年 | 137篇 |
1990年 | 109篇 |
1989年 | 80篇 |
1988年 | 101篇 |
1987年 | 64篇 |
1986年 | 50篇 |
1985年 | 49篇 |
1984年 | 48篇 |
1983年 | 45篇 |
1982年 | 42篇 |
1981年 | 30篇 |
1980年 | 8篇 |
1979年 | 19篇 |
1978年 | 8篇 |
1958年 | 7篇 |
1957年 | 5篇 |
1954年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Ocean current forecasting is still in explorative stage of study. In the study, we face some problems that have not been met before. The solving of these problems has become fundamental premise for realizing the ocean current forecasting. In the present paper are discussed in depth the physical essence for such basic problems as the predictability of ocean current, the predictable currents, the dynamical basis for studying respectively the tidal current and circulation, the necessity of boundary model, the models on regions with different scales and their link. The foundations and plans to solve the problems are demonstrated. Finally a set of operational numerical forecasting system for ocean current is proposed. 相似文献
82.
Zhang Furan Zhao Jun Zhang Xueqin Assistant Researcher Tianjin Research Institute of Water Transport Engineering Tianjin Assistant Engineer Tianjin Research Institute of Water Transport Engineering Tianjin 《中国海洋工程》1993,(2)
In respect of an offshore berthing pillar, the test study result of current force acting on mooring ships is described in this paper. Empirical and semi-empirical relationships of current force coefficient are given according to the angle between the flow direction and the ship's longitudinal axis, which are coincident with the result of theoretical analysis. 相似文献
83.
84.
Preliminary research on sea-level changes of the South China coast since late Epipleistocene 总被引:1,自引:0,他引:1
Several views on sea-level changes of the South China coast are briefly introduced in this paper. On the basis of 236 samples whose ages are determined by 14C chronological method and their sites are corrected with ancient water depth and crustal deformation, a basic model about sea-level changes of the South China coast since late Epipleistocene is set up. This model basically accords with the general cognitions of predecessors, i. e. it not only represents the common characteristics of sea-level changes of the East China coast but has some features of the South China coast itself. In general, this model is relatively close to the Fairbridge's curve, indicating that the sea-level undulations exist since 6 ka ago but the ranges of undulations are slightly larger than those of Fairbridge's curve. 相似文献
85.
The distribution of wave height in front of a vertical breakwater, the range of wave pressure fluctuation at different subsurface levels, and the wave periods have shown that they are practically invariable with depth and can be determined theoretically. The distribution of crest and trough of total pressures is the same as that of wave height. As far as different subsurface levels are concerned, the spectral constitution of wave pressure field and the regularity of attenuation of spectral components are analyzed at the vertical breakwater, and a new expression describing the equilibrium range of wave pressure spectrum obtained. 相似文献
86.
在室内水池中观察了黑鲷(Sparusmacrocephalus)和青石斑鱼(Epinephelusawoara)对孔径0.5mm、孔距5.0cm,空气压力0.25kg/cm2固定气泡幕的反应。结果表明,气泡幕对两种海水鱼都有显著的阻拦作用,平均阻拦率分别为黑鲷75.1%、青石斑鱼82.4%。分析显示,气泡幕对两种鱼的阻拦率间无显著差异。在本实验中,该两种鱼对气泡幕均无明显的适应现象 相似文献
87.
描述中国对虾中枢神经系统神经元细胞体的细胞学结构:神经元细胞体分布在神经节的皮质,每个神经元外都有神经胶质细胞和其突起形成的鞘包裹着,细胞体质膜内陷分枝形成胞管系;尼氏体在各神经节神经元细胞体中都呈细颗粒状均匀分布,其数量随生理状况而改变;内质网膜外表面附有少量核糖体,内质网池不规则,均匀分布在细胞质中;高尔基体呈孤状、圈状和U状;线粒体丰富,为圆形和短棒形,嵴不规则,缺少基粒;细胞体中有糖元和其他碳水化合物存在 相似文献
88.
One new species of free-living marine nematodes (Enoplida,Anticomidae, Cephalanticoma) from the Huanghai Sea 总被引:1,自引:0,他引:1
One new species of free-living marine nematodes Cephalanticoma filicaudata sp. nov. from the Huanghai Sea, China is described and illustrated. Cephalanticoma filicaudata sp. nov. is characterized by well developed cephalic capsule, three teeth at the anterior of oesophagus, excretory pore opens posterior to cervical setae, only two cervical setae per file, body length longer than 5 200 μm, tail long and no ventral-lateral seta between the supplement and the cloacal opening. Types are deposited in the College of Marine Life Sciences, Ocean University of China. 相似文献
89.
90.