全文获取类型
收费全文 | 7621篇 |
免费 | 1152篇 |
国内免费 | 1876篇 |
专业分类
测绘学 | 435篇 |
大气科学 | 1948篇 |
地球物理 | 1875篇 |
地质学 | 3502篇 |
海洋学 | 1025篇 |
天文学 | 372篇 |
综合类 | 709篇 |
自然地理 | 783篇 |
出版年
2024年 | 28篇 |
2023年 | 112篇 |
2022年 | 307篇 |
2021年 | 347篇 |
2020年 | 281篇 |
2019年 | 349篇 |
2018年 | 367篇 |
2017年 | 321篇 |
2016年 | 421篇 |
2015年 | 354篇 |
2014年 | 426篇 |
2013年 | 453篇 |
2012年 | 348篇 |
2011年 | 379篇 |
2010年 | 348篇 |
2009年 | 417篇 |
2008年 | 331篇 |
2007年 | 308篇 |
2006年 | 278篇 |
2005年 | 280篇 |
2004年 | 208篇 |
2003年 | 234篇 |
2002年 | 205篇 |
2001年 | 222篇 |
2000年 | 278篇 |
1999年 | 417篇 |
1998年 | 322篇 |
1997年 | 322篇 |
1996年 | 322篇 |
1995年 | 273篇 |
1994年 | 227篇 |
1993年 | 203篇 |
1992年 | 164篇 |
1991年 | 136篇 |
1990年 | 113篇 |
1989年 | 116篇 |
1988年 | 101篇 |
1987年 | 55篇 |
1986年 | 60篇 |
1985年 | 44篇 |
1984年 | 39篇 |
1983年 | 20篇 |
1982年 | 20篇 |
1981年 | 24篇 |
1980年 | 18篇 |
1979年 | 11篇 |
1978年 | 8篇 |
1976年 | 6篇 |
1973年 | 7篇 |
1958年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
Wang Chunzhen Huang Hanming and Wang BiquanInstitute of Geophysics CSB Beijing China 《中国地震研究》1998,(3)
We propose the pseudo-periodicity method and its quantitative prediction indexes for the occurrence time of earlier strong aftershock. We conducted tests of regressive prediction, and the R-value of the tests is 0.45, indicating that this method is effective for prediction. 相似文献
93.
Occurrence of brackish water phytoplankton species at a closed coral reef in Nansha Islands, South China Sea 总被引:1,自引:0,他引:1
Ping-Ping Shen Liang-Min Huang Jian-Lin Zhang Jian-Qiang Yin 《Marine pollution bulletin》2010,60(10):1718-1725
The phytoplankton assemblage of Zhubi Reef, a closed coral reef in Nansha Islands (South China Sea, SCS) was studied in June 2007. A total of 92 species belonging to 53 genera and four phyla have been identified. The dominant taxa in the lagoon were the diatom Chaetoceros and cyanobacteria Nostoc and Microcystis, while in reef flats were cyanobacteria Trichodesmium erythraeum, dinoflagellates Gymnodinium and Prorocentrum. The species richness and diversity were consistently lower in the lagoon than in reef flats. Classification and nMDS ordination also revealed significant dissimilarity in phytoplankton community structure between the reef flat and lagoon, with statistical difference in species composition and abundance between them (ANOSIM, p = 0.025). Nutrient concentrations also spatially varied, with ammonium-enrichment in the lagoon, while high Si-concentration existed in reef flat areas. Both nutrient levels and currents in SCS may play important roles in determining the composition and distribution of microalgae in Zhubi Reef and SCS. 相似文献
94.
95.
西南印度洋63.5°E热液区是在超慢速扩张洋脊发现的首个超镁铁质岩热液系统。对取自该区的热液硫化物样品进行了系统的矿物学和地球化学分析,矿物学分析结果表明:该热液区硫化物为富Fe型高温硫化物,且经历了较深程度的氧化蚀变,大量中间态的Fe氧化物充填在硫化物矿物间的孔隙及内部解理中;这些硫化物相以白铁矿为主,其次是等轴古巴矿和少量铜蓝,缺乏黄铁矿、闪锌矿。据推断,该区的热液成矿作用分为4个阶段:低温白铁矿阶段→高温等轴古巴矿阶段→自形白铁矿阶段→后期海底风化阶段(少量铜蓝以及大量的Fe的羟氧化物)。与之相对应,地球化学分析结果表明这些硫化物的Fe含量较高(31.57%~44.59%),Cu含量次之(0.16%~7.24%),而Zn含量普遍较低(0.01%~0.11%);微量元素较为富集Co(328×10-6~2 400×10-6)和Mn(48.5×10-6~1 730×10-6)。该区硫化物中较高含量的Fe、Co与超镁铁质岩热液系统相似,明显高于镁铁质岩热液系统。独特的热液硫化物矿物学特征和元素组成可能与该区普遍出露的地幔岩、橄榄岩蛇纹石化作用以及拆离断层的广泛发育的环境有关。 相似文献
96.
97.
Although the middle section of the Bangong-Nujiang suture zone has been intensively investigated, its tectonic framework and evolution is still controversy. The Pungco ophiolite has a relative complete ophiolitic complex, which is an ideal specimen for studying this tricky problem. LA-ICP-MS U-Pb dating of zircons from the diabasic rock yielded an age of 159.0±2.1 Ma. This age suggests that the Pungco ophiolite was formed in the Late Jurassic, indicating the development of the Late Jurassic ophiolite in the third ophiolitic subzone. The whole-rock major and trace element compositions of diabasic and basaltic rocks exhibit mixed arc and N-MORB geochemical characteristics. Two diabasic samples have (87Sr/86Sr)i values of 0.7055 and 0.7063 and εNd(t) values of 11.28 and 11.84, respectively. The geochemical signatures and formation age of the Pungco ophiolite suggest that this ophiolite was probably produced in an active continental fore-arc setting. It originated from a N-MORB-like depleted mantle source with the involvement of subducted-slab fluids. Considering the regional geological background, the Pungco ophiolite was likely generated during the southward subduction of the Bangong-Nujiang Tethyan oceanic lithosphere beneath the Lhasa terrane, and belongs to a regional archipelagic arc-basin system together with the other Early Jurassic-Early Cretaceous ophiolites from the northern Tibet Lake district. © 2018, Science Press. All right reserved. 相似文献
98.
99.
Natural gas generation model and its response in accumulated fluids in the Yinggehai basin 总被引:2,自引:0,他引:2
The generation of natural gases is much more complicated in comparison with liquid petro-leum in that natural gases could be generated from both humic and sapropelic organic matter at different stages and that natural gases could be organic and inorganic … 相似文献
100.
ABSTRACT Eighty percent of big data are associated with spatial information, and thus are Big Spatial Data (BSD). BSD provides new and great opportunities to rework problems in urban and environmental sustainability with advanced BSD analytics. To fully leverage the advantages of BSD, it is integrated with conventional data (e.g. remote sensing images) and improved methods are developed. This paper introduces four case studies: (1) Detection of polycentric urban structures; (2) Evaluation of urban vibrancy; (3) Estimation of population exposure to PM2.5; and (4) Urban land-use classification via deep learning. The results provide evidence that integrated methods can harness the advantages of both traditional data and BSD. Meanwhile, they can also improve the effectiveness of big data itself. Finally, this study makes three key recommendations for the development of BSD with regards to data fusion, data and predicting analytics, and theoretical modeling. 相似文献