全文获取类型
收费全文 | 15833篇 |
免费 | 2593篇 |
国内免费 | 4587篇 |
专业分类
测绘学 | 2138篇 |
大气科学 | 3070篇 |
地球物理 | 3584篇 |
地质学 | 6297篇 |
海洋学 | 3017篇 |
天文学 | 1421篇 |
综合类 | 1381篇 |
自然地理 | 2105篇 |
出版年
2024年 | 62篇 |
2023年 | 172篇 |
2022年 | 525篇 |
2021年 | 575篇 |
2020年 | 774篇 |
2019年 | 896篇 |
2018年 | 670篇 |
2017年 | 792篇 |
2016年 | 778篇 |
2015年 | 928篇 |
2014年 | 932篇 |
2013年 | 1103篇 |
2012年 | 1014篇 |
2011年 | 1009篇 |
2010年 | 812篇 |
2009年 | 944篇 |
2008年 | 1056篇 |
2007年 | 1252篇 |
2006年 | 1222篇 |
2005年 | 1071篇 |
2004年 | 889篇 |
2003年 | 743篇 |
2002年 | 687篇 |
2001年 | 510篇 |
2000年 | 634篇 |
1999年 | 608篇 |
1998年 | 475篇 |
1997年 | 356篇 |
1996年 | 298篇 |
1995年 | 223篇 |
1994年 | 201篇 |
1993年 | 183篇 |
1992年 | 162篇 |
1991年 | 103篇 |
1990年 | 66篇 |
1989年 | 89篇 |
1988年 | 49篇 |
1987年 | 43篇 |
1986年 | 37篇 |
1985年 | 17篇 |
1984年 | 16篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1971年 | 2篇 |
1954年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
171.
172.
173.
174.
应用经验模式分解(EMD)将恒电量瞬态响应信号分解为不同时间尺度的内在模函数(IMF)分量。去除其中的小时间尺度的干扰噪声分量。然后经过拉普拉斯变换获得恒电量频谱以研究电化学腐蚀过程。 相似文献
175.
176.
Are invasive species most successful in habitats of low native species richness across European brackish water seas? 总被引:5,自引:0,他引:5
Marjo Paavola Sergej Olenin Erkki Leppkoski 《Estuarine, Coastal and Shelf Science》2005,64(4):738-750
European brackish water seas (Baltic Sea, Black Sea and Sea of Azov, Caspian Sea) are subject to intense invasion of non-indigenous species (NIS). In these seas, salinity is the most important range limiting factor and native species seem to reach a minimum species richness at intermediate salinities. This trend, revealed by Remane in 1934 and later on confirmed by many other scientists, was compared to the salinity range of already established NIS in the European brackish water seas. It turned out that most NIS are well adapted to the salinities holding lowest native species richness, already in their native area, and that NIS richness maximum in brackish water seas occurs in the salinity intervals of native species richness minimum. A predictable pattern in the salinity range of NIS can be used as a tool in initial risk assessment of future invasions in brackish water seas, especially when mapping highly potential donor and recipient areas. A product of empty niches, suitable environmental conditions, and availability of proper vectors might be the most effective predictor for the invasibility of brackish water areas. 相似文献
177.
In recent years, the red tide erupted frequently, and caused a great economic loss. At present, most literatures emphasize the academic research on the growth mechanism of red tide alga. In order to find out the characters of red tide in detail and improve the precision of forecast, this paper gives some new approaches to dealing with the red tide. By the extreme values, we deal with the red tide frequency analysis and get the estimation of T-times red tide level U (T) , which is the level once the consistence of red tide alga exceeds on the average in a period of T times. 相似文献
178.
通过亲贝强化营养和升温促熟培育,提早栉江珧人工育苗时间;合理控制幼虫密度,前期4~5个/mL,后期2~3个/mL,严把饵料质量关,投喂新鲜无污染的饵料,科学换水与充气,及时分级筛选等系列技术措施,克服栉江珧育苗中易发生幼虫粘连的技术难题,使育苗生产顺利进行;开展了多种附着基投放的采苗方法试验,选出了铺砂浮动网箱采苗和网袋装网片附着基和细砂吊在池中采苗2种比较理想的采苗方法,提高稚贝的附着变态率,其附着变态率达30%以上,促进稚贝的生长和成活,在1 000 m3水体中育出2 mm以上的稚贝1.096亿粒。 相似文献
179.
Empirical orthogonal functions (EOFs) or principal components were used to extract the significant modes of shoreline variability from several data sets collected at three very different locations. Although EOFs have proven to be a valuable tool in the analysis of nearshore data, most applications have focused on the ability of the technique to describe cross-shore or profile variability. Here however, EOFs were used to help identify the dominant modes of longshore shoreline variability at Duck, North Carolina, the Gold Coast, Australia, and at several locations within the Columbia River Littoral Cell in the U.S. Pacific Northwest. In part one of this analysis, characteristic patterns of shoreline variability identified by the EOF analysis are described in detail. At each site, the dominant modes consisting of the first four eigenfunctions were found to describe nearly 95% of the total shoreline variability. At both Duck and the Gold Coast, several interesting longshore periodic features suggestive of sand waves were identified, while boundary effects related to natural headlands and navigational structures/entrances dominated the Pacific Northwest data sets. 相似文献
180.