全文获取类型
收费全文 | 2655篇 |
免费 | 330篇 |
国内免费 | 380篇 |
专业分类
测绘学 | 215篇 |
大气科学 | 297篇 |
地球物理 | 772篇 |
地质学 | 1082篇 |
海洋学 | 413篇 |
天文学 | 127篇 |
综合类 | 172篇 |
自然地理 | 287篇 |
出版年
2024年 | 10篇 |
2023年 | 40篇 |
2022年 | 108篇 |
2021年 | 113篇 |
2020年 | 107篇 |
2019年 | 118篇 |
2018年 | 154篇 |
2017年 | 127篇 |
2016年 | 133篇 |
2015年 | 133篇 |
2014年 | 168篇 |
2013年 | 150篇 |
2012年 | 139篇 |
2011年 | 184篇 |
2010年 | 154篇 |
2009年 | 149篇 |
2008年 | 126篇 |
2007年 | 113篇 |
2006年 | 96篇 |
2005年 | 85篇 |
2004年 | 82篇 |
2003年 | 88篇 |
2002年 | 120篇 |
2001年 | 104篇 |
2000年 | 71篇 |
1999年 | 49篇 |
1998年 | 60篇 |
1997年 | 58篇 |
1996年 | 37篇 |
1995年 | 43篇 |
1994年 | 29篇 |
1993年 | 28篇 |
1992年 | 36篇 |
1991年 | 18篇 |
1990年 | 11篇 |
1989年 | 18篇 |
1988年 | 9篇 |
1987年 | 11篇 |
1986年 | 5篇 |
1985年 | 7篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 7篇 |
1980年 | 10篇 |
1979年 | 7篇 |
1978年 | 8篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1973年 | 3篇 |
排序方式: 共有3365条查询结果,搜索用时 468 毫秒
101.
Chunying Chang Fangbai Li Chengshuai Liu Jianfeng Gao Hui Tong Manjia Chen 《中国地球化学学报》2016,35(4):329-339
Soil secondary minerals are important scavengers of rare earth elements (REEs) in soils and thus affect geochemical behavior and occurrence of REEs. The fractionation of REEs is a common geochemical phenomenon in soils but has received little attention, especially fractionation induced by secondary minerals. In this study, REEs (La to Lu and Y) associated with soil-abundant secondary minerals Fe-, Al-, and Mn-oxides in 196 soil samples were investigated to explore the fractionation and anomalies of REEs related to the minerals. The results show right-inclined chondrite-normalized REE patterns for La–Lu in soils subjected to total soil digestion and partial soil extraction. Light REEs (LREEs) enrichment features were negatively correlated with a Eu anomaly and positively correlated with a Ce anomaly. The fractionation between LREEs and heavy REEs (HREEs) was attributed to the high adsorption affinity of LREEs to secondary minerals and the preferred activation/leaching of HREEs. The substantial fractions of REEs in soils extracted by oxalate and Dithionite-Citrate-Bicarbonate buffer solutions were labile (10 %–30 %), which were similar to the mass fraction of Fe (10 %–20 %). Furthermore, Eu was found to be more mobile than the other REEs in the soils, whereas Ce was less mobile. These results add to our understanding of the distribution and geochemical behavior of REEs in soils, and also help to deduce the conditions of soil formation from REE fractionation. 相似文献
102.
103.
104.
105.
106.
107.
108.
109.
110.
Seonghun Kim Kyounghoon Lee Won Duk Yoon Hyungbeen Lee Kangseok Hwang 《Ocean Science Journal》2016,51(1):59-65
Nemopilema nomurai jellyfish, which are believed to complete their development in the East China Sea, have started migrating into the Yellow Sea in recent years. We obtained biomass estimates of this species in the Yellow Sea using bottom trawl fishing gear and sighting surveys over a 5-year period. These methods are effective for obtaining N. nomurai jellyfish density estimates and information about the community distribution near the bottom or surface of the sea. To verify the vertical distributions of giant jellyfish between, we used hydroacoustic equipment, including an optical stereo camera system attached to a towed sledge and an echo counting method with scientific echosounder system. Acoustic and optical data were collected while the vessel moved at 3 knots, from which the distribution and density of N. nomurai jellyfish were analyzed. Subsequently, the camera system was towed from a 7 m mean depth to sea level, with the detection range of the acoustic system extending from an 8 m depth to the bottom surface. The optical and acoustic methods indicated the presence of vertical distribution of 0.113 (inds/m3) and 0.064 (inds/m3), respectively. However, the vertical distribution indicated that around 93% of individuals occurred at a depth range of 10–40 m; thus, a 2.4-fold greater density was estimated by acoustic echo counting compared to the optical method. 相似文献