全文获取类型
收费全文 | 11853篇 |
免费 | 1811篇 |
国内免费 | 1642篇 |
专业分类
测绘学 | 362篇 |
大气科学 | 1009篇 |
地球物理 | 2665篇 |
地质学 | 5334篇 |
海洋学 | 1721篇 |
天文学 | 45篇 |
综合类 | 573篇 |
自然地理 | 3597篇 |
出版年
2024年 | 50篇 |
2023年 | 171篇 |
2022年 | 460篇 |
2021年 | 498篇 |
2020年 | 461篇 |
2019年 | 512篇 |
2018年 | 440篇 |
2017年 | 504篇 |
2016年 | 499篇 |
2015年 | 564篇 |
2014年 | 718篇 |
2013年 | 773篇 |
2012年 | 662篇 |
2011年 | 723篇 |
2010年 | 609篇 |
2009年 | 770篇 |
2008年 | 861篇 |
2007年 | 874篇 |
2006年 | 830篇 |
2005年 | 634篇 |
2004年 | 582篇 |
2003年 | 532篇 |
2002年 | 358篇 |
2001年 | 329篇 |
2000年 | 315篇 |
1999年 | 258篇 |
1998年 | 198篇 |
1997年 | 176篇 |
1996年 | 168篇 |
1995年 | 168篇 |
1994年 | 147篇 |
1993年 | 115篇 |
1992年 | 98篇 |
1991年 | 67篇 |
1990年 | 56篇 |
1989年 | 36篇 |
1988年 | 27篇 |
1987年 | 10篇 |
1986年 | 10篇 |
1985年 | 10篇 |
1984年 | 10篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 9篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Although the Yellow River Delta and Bohai Sea coastal zone are long distance and different environment with Po River Delta and Adriatic Sea coastal zone, the comparison of data of two different areas and the evolution trend of two areas are quite similar. The influence of natural climatic changes on the evolution of the deltas and coastal zones exists both in ancient and modern times. The cold/wet period occurred in 1300—1400A. D. and 1550 —1850 A.D. within this"large scale" climatie cycle, and shorter periods (10— 35 years) of cold rainy weather alternated with warm/dry period are known as "Bruckner cycles" which have influence on the evolution of the deltas and coastal zones. 相似文献
62.
珠江口现代沉积速率及其反映的沉积特征 总被引:2,自引:0,他引:2
文章分析了珠江河口海区泥沙来源及淤积动态,采用以历史海图分析对比为主,~(210)Pb测年数据校核等方法,参考有关沉积速率定性方面的标志,推算出珠江口不同地段的现代沉积速率,并相应划分出高速率沉积、快速率沉积、中速率沉积和慢速率沉积或稍有侵蚀等4个分区.进而,还论述了沉积作用的特征. 相似文献
63.
Variation of reactivity of particulate and sedimentary organic matter along the Zhujiang River Estuary 总被引:3,自引:0,他引:3
To investigate organic matter source and reactivity in the Zhujiang River (Pearl River)Estuary and its adjacent areas, particulate organic carbon (POC), particulate hydrolysable amino acids (PHAA), and Chl a during two cruises in July 1999 and July 2000 were measured. The highest POC and PHAA concentration was observed in the waters with maximum Chl a. The spectra distribution,relative content (dry weight in milligram per gram), PHAA-C% POC and other indicators such as the ratios of amino acids vs. amino sugars (AA/AS) and glucosamine vs. galactosamine (Glum/Gal) suggested that particulate amino acids in the water column and sediments in the Zhujiang River Estuary were mainly derived from biogenic processes rather than transported from terrestrial erosion. In inner estuary where high turbidity was often observable, organic matter was mainly contributed by re-suspension of bottom sediments with revealed zooplankton, microbial reworked characteristics, which suggest that these organic matters were relatively “old“. In the estuarine brackish region, organic matter in water column is mainly contributed by relatively fresh, easily degradable phytoplankton derived organic matter.During physical - biological processes within the eastuary, organic matter derived from phytoplankton was subjected to alteration by zooplankton grazing and bacterial reworking. 相似文献
64.
65.
1985年5、8月中法联合调查黄河口海域的营养盐,其样品采用常规的分光光度法测定。营养盐的分布总趋势是河口附近浓度高,外海浓度低,河口与外海浓度之比达数百倍。在河口及其邻近海域营养盐的分布梯度与盐度的分布一致。在河口控制营养盐含量的主要因素是河水和海水的混合过程。在119°30′~50′E,37°25′~38°5′N,PO_4—P,SiO_3—Si出现低值区。在此范围附近恰恰浮游植物的总量比较高。对8月份的02站进行了25h的连续观测,其结果是底层营养盐与盐度有良好的负相关性,而表层的相关性较差 黄河具有很高的氮磷比值,这很可能是农业上用氮肥量增多引起的。 相似文献
66.
67.
68.
69.
The abandoned Yellow River Delta coast is a typical erodible silty and muddy coast in China. The paper analyses the marine dynamic characteristics and the mechanism of beach erosion of this area. Analysis and calculation show that in this sea area wave and tidal current action should be considered. Based on the above analysis, an equilibrium beach profile calculation model is developed, in which the wave-current interaction is considered while sediment supply and sediment re-deposition are neglected. The model consists of four parts: (1) calculation of wave parameters, (2) calculation of velocity due to wave-current interaction at different water depth, (3) calculation of friction velocity and shear stress at different water depths, and (4) calculation of the amount of sediment erosion, erosion intensity and variation of beach profile. Calculated results are in good agreement with observed data. Finally, the evolution tendency is discussed and the equilibrium beach profile of this coast is calculated. B 相似文献
70.
黄河三角洲地貌环境体系 总被引:4,自引:0,他引:4
黄河三角洲是由三角洲上部冲积平原一下部冲积海积平原(超潮滩)─周边潮滩三个区带的地貌系列构成.它们之间形成三条地貌环境岸线,是一个复杂而统一的陆上─潮滩堆积地貌体系.该体系研究对三角洲发育.环境及其开发利用有一定理论和实践意义. 相似文献