全文获取类型
收费全文 | 775篇 |
免费 | 114篇 |
国内免费 | 61篇 |
专业分类
测绘学 | 37篇 |
大气科学 | 25篇 |
地球物理 | 72篇 |
地质学 | 508篇 |
海洋学 | 92篇 |
综合类 | 55篇 |
自然地理 | 161篇 |
出版年
2024年 | 5篇 |
2023年 | 15篇 |
2022年 | 29篇 |
2021年 | 23篇 |
2020年 | 14篇 |
2019年 | 20篇 |
2018年 | 20篇 |
2017年 | 12篇 |
2016年 | 10篇 |
2015年 | 26篇 |
2014年 | 33篇 |
2013年 | 26篇 |
2012年 | 41篇 |
2011年 | 51篇 |
2010年 | 36篇 |
2009年 | 41篇 |
2008年 | 48篇 |
2007年 | 42篇 |
2006年 | 45篇 |
2005年 | 52篇 |
2004年 | 46篇 |
2003年 | 56篇 |
2002年 | 56篇 |
2001年 | 48篇 |
2000年 | 26篇 |
1999年 | 17篇 |
1998年 | 21篇 |
1997年 | 24篇 |
1996年 | 21篇 |
1995年 | 12篇 |
1994年 | 5篇 |
1993年 | 6篇 |
1992年 | 12篇 |
1991年 | 3篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 1篇 |
排序方式: 共有950条查询结果,搜索用时 15 毫秒
441.
荆州市区水环境系统分析 总被引:2,自引:0,他引:2
陈国金 《水文地质工程地质》1998,25(5):21-23
荆州市区水环境系统是一个人工复合系统,并且是不断恶化和不相协调的系统,本文主要是通过构造沉降与大堤约束,洪水位上升与洪涝灾害等一系列矛盾运动的论述,揭示荆州市区水环境还在恶化的发展趋势,支撑荆州市区经济发展是改善和控制荆江洪水位上升。 相似文献
442.
Temporal and spatial distributions of dominant shrimp stocks and their relationship with the hydrological environment in the East China Sea 总被引:3,自引:0,他引:3
To provide a scientific and technological base for fishery administration, holding a moratorium on fishing, and combating habitat degradation, a shrimp stock survey was carried out in May, August, and November 1998 and in February 1999. The study was conducted in the area between 26o00′ N and 33o00′ N and to the west of 127o00′ E in the East China Sea using a multi-sac trawl-net, with 115 stations being sampled. Up to 2001, we had found 121 species, which belong to 63 genera under 22 families, and 41 species are of high economic value and in great abundance. Nine shrimp species were of great economic importance, whose stock accounted for 76.8% of the demersal total. They were Parapenaeus fissuroides, Metapenaeopsis philippi, Palaemon gravieri, Metapenaeopsis barbata, Solenocera koelbeli, Solenocera crassicornis, Trachypenaeus curvirostris, Solenocera melantho and Parapenaeopsis hardwickii (listed in stock order). The nine species belong to the eurythermal and eurysaline community and high thermal and high saline community, had different migration patterns and stocks, and their distribution patterns could be generally classified into three types:(1) dominating in the north or the south;(2) dominating to the north of and in the coast to the south of 30o00′ N;and (3) dominating to the east of 60 m isobath, which were related to six water masses in the ECS near two lines, i.e., the 60 m isobath and 30o00′N latitudinal lines. Densely habited shrimps were found in all four seasons due to temperature and salinity frontiers and upwelling. The general stock density index was relatively higher in spring, summer, and autumn, when it surpassed 10 kg/h, while in winter, it was only 6.8 kg/h which might be caused by overfishing. According to the spawning areas of the nine species and their distribution patterns, to attain sustainable development of the shrimp fishery in the ECS, it is imperative to protect fishing areas and to hold a moratorium on catching to the west of 60 m isobath from April through October, and between 60 m and 100 m isobaths and to the south of 30oN from June through August and to limit fishing in winter. 相似文献
443.
444.
445.
据水文统计和测量数据,借助GIS技术和统计方法,定量研究快速城市化背景下兰州-西宁区域水环境演化,得出:①区域城市经济建设需水与供水矛盾日趋恶化,得到城市化水平与供水之间呈自然对数关系;②流域内用水以农林牧畜用水为主,甘肃段集中了甘肃省主要的工业用水、城镇公共用水及绿化用水;③依据地表水水域环境功能和保护目标,按功能高... 相似文献
446.
447.
448.
449.
450.