全文获取类型
收费全文 | 9127篇 |
免费 | 2042篇 |
国内免费 | 2619篇 |
专业分类
测绘学 | 935篇 |
大气科学 | 2117篇 |
地球物理 | 2052篇 |
地质学 | 4284篇 |
海洋学 | 1905篇 |
天文学 | 305篇 |
综合类 | 1027篇 |
自然地理 | 1163篇 |
出版年
2024年 | 73篇 |
2023年 | 177篇 |
2022年 | 487篇 |
2021年 | 578篇 |
2020年 | 493篇 |
2019年 | 557篇 |
2018年 | 590篇 |
2017年 | 578篇 |
2016年 | 567篇 |
2015年 | 555篇 |
2014年 | 577篇 |
2013年 | 651篇 |
2012年 | 727篇 |
2011年 | 724篇 |
2010年 | 709篇 |
2009年 | 636篇 |
2008年 | 550篇 |
2007年 | 569篇 |
2006年 | 496篇 |
2005年 | 444篇 |
2004年 | 270篇 |
2003年 | 252篇 |
2002年 | 240篇 |
2001年 | 263篇 |
2000年 | 281篇 |
1999年 | 327篇 |
1998年 | 203篇 |
1997年 | 230篇 |
1996年 | 156篇 |
1995年 | 169篇 |
1994年 | 141篇 |
1993年 | 128篇 |
1992年 | 97篇 |
1991年 | 69篇 |
1990年 | 56篇 |
1989年 | 37篇 |
1988年 | 28篇 |
1987年 | 29篇 |
1986年 | 8篇 |
1985年 | 6篇 |
1984年 | 7篇 |
1983年 | 13篇 |
1982年 | 8篇 |
1981年 | 7篇 |
1980年 | 3篇 |
1979年 | 8篇 |
1959年 | 1篇 |
1958年 | 4篇 |
1957年 | 4篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Song Jinming 《海洋学报(英文版)》2003,22(1):57-68
Carbon cycle is connected with the most important environmental issue of Global Change.As one of the major carbon reservoirs, oceans play an important part in the carbon cycle. In recent years, iron seems to give us a good news that oceanic iron fertilization could stimulate biological productivity as CO2 sink of human-produced CO2. Oceanic iron fertilization experiments have verified that adding iron into high nutrient low chlorophyll (HNLC) seawaters can increase phytoplankton production and export organic carbon, and hence increase carbon sink of anthropogenic CO2, to reduce global warming. In sixty days, the export organic carbon could reach 10 000 times for adding iron by model prediction and in situ experiment, i.e. the atmospheric CO2 uptake and inorganic carbon drawdown in upper seawaters also have the same magnitude. Therefore, oceanic iron fertilization is one of the strategies for increasing carbon sink of anthropogenic CO2. The paper is focused on the iron fertilization, especially in situ o 相似文献
42.
河口环流和盐水入侵Ⅱ--径流量和海平面上升的影响 总被引:1,自引:0,他引:1
本文利用本序列上篇论文建立的理想河口数值模式,研究径流量和海平面上升对河口环流和盐水入侵的影响.在径流量增大的情况下,口门内表层向海的流速增大,底层向陆的密度流减弱,滞流点下移.口门外侧向口门的密度流增大,上升流趋于增强.口门内盐水入侵减弱,口外盐度减小、冲淡水扩展范围增大.在口门上游北岸底层盐度下降明显,口门处南岸表层盐度下降明显.径流量变化对盐水入侵影响十分巨大.在海平面上升的情况下,拦门沙区域向陆的密度流增强,滞流点上移,表层向海的流动增大.口门内盐水入侵增强,口外盐度增大,冲淡水扩展范围减小.海平面上升对盐水入侵影响十分明显,北岸底层盐度增大尤为特出. 相似文献
43.
鲽形目3亚目8科51属142种。鲀形目2亚目9科57属143种。海蛾鱼目1科2属3种,鮟鱇目3亚目11科23属41种。 相似文献
44.
Full-rangenonlinearanalysisoffatiguebehaviorsofreinforcedconcretestructuresbyfiniteelementmethod¥SongYupu;ZhaoShunbo;WangRuim... 相似文献
45.
Qiu Dahong Zang Jun Jia Ying
Academician of the Chinese Academy of Sciences Professor the State Key Laboratory of Coastal Offshore Engineering 《中国海洋工程》1996,(2)
Based on the 2nd order cnoidal wave theory, the characters of shallow water standing waves and their action on vertical walls are studied in this paper. The theoretical expressions of the wave surface elevation in front of and the wave pressure on the vertical wall are obtained. In order to verify the theoretical results, model tests were made in the State Key Laboratory of Coastal and Offshore Engineering at DUT. For the wave surface elevation in front of the wall and the wave forces on the wall at the moment when the wave surface at the wall surface goes down to the bottom of the wave trough, the calculated results coincide quite well with the experimental results. For the wave forces on the wall at the moment when the wave surface at the wall surface goes up to the top of the wave crest, the theoretical expressions are modified by the experimental results. For the convenience of practical use, calculations are made for the wave conditions which usually occur in enginering practice by use of the inves 相似文献
46.
采用Wilbert蛋白银法及Chatton—Lwoff银浸法对一种附生于栉孔扇贝鳃丝上的寄生车轮虫进行了光镜水平下的研究。依据其形态学和纤毛图式特征,该种被鉴定为TrichodinajadranicaRaabe,1958.此为我国新记录,同时也是第一例有关外寄生于扇贝鳃表纤毛虫原生动物的报道。 相似文献
47.
48.
Under the artificial condition the 59Fe morphology in sea water, its concentration in sediment and phytoplankton, its distribution and metabolism in tissue organs of marine animals were studied. The results showed that the morphology of 59Fe was in a particulate state in sea water. The adsorption rule of 59Fe by three kinds of sediments was similar. The concentration ability of 59Fe by phytoplankton was very strong. The critical concentration organs of S9Fe by marine animals were viscera. The gross radioactivity of 59Fe was mainly concentrated in protein. The concentration factor of 59Fe by DNA was the highest one. After excretion experiment, 59Fe of all the tissue organs was not detected. Small part of59Fe remained in the organic acid and protein state. There was a redistribution process in sediment for59Fe. 相似文献
49.
Song H. Kuperman W.A. Hodgkiss W.S. Gerstoft P. Jea Soo Kim 《Oceanic Engineering, IEEE Journal of》2003,28(2):250-261
Adaptive-array beamforming achieves high resolution and sidelobe suppression by producing sharp s in the adaptive beampattern. Large-aperture sonar arrays with many elements have small resolution cells; interferers may move through many resolution cells in the time required for accumulating a full-rank sample covariance matrix. This leads to "snapshot-deficient" processing. In this paper, the -broadening technique originally developed for an ideal stationary problem is extended to the snapshot-deficient problem combined with white-noise constraint (WNC) adaptive processing. Null broadening allows the strong interferers to move through resolution cells and increases the number of degrees of freedom, thereby improving the detection of weak stationary signals. 相似文献
50.
地形坡度对多金属结核分布的控制作用 总被引:3,自引:3,他引:3
选取我国东太平洋多金属结核开辟区内的一个区域作为研究区,利用人工神经网络中应用最为广泛的BP网络,建立控制多金属结核分布的地质因素与多金属结核分布之间的映射关系,探讨地形坡度对多金属结核分布的控制作用.结果表明,在经度、纬度、水深、坡度四个因素中,坡度对结核分布影响程度最大;多金属结核主要分布于坡度小于5°的地方;当坡度小于5°时,丰度与地形坡度呈正相关,品位与地形坡度呈负相关,丰度与品位呈负相关;品位与坡度似呈指数关系,坡度增大,品位降低. 相似文献