全文获取类型
收费全文 | 9948篇 |
免费 | 2433篇 |
国内免费 | 3502篇 |
专业分类
测绘学 | 1594篇 |
大气科学 | 1616篇 |
地球物理 | 1805篇 |
地质学 | 5643篇 |
海洋学 | 2605篇 |
天文学 | 243篇 |
综合类 | 860篇 |
自然地理 | 1517篇 |
出版年
2024年 | 87篇 |
2023年 | 299篇 |
2022年 | 727篇 |
2021年 | 793篇 |
2020年 | 643篇 |
2019年 | 640篇 |
2018年 | 640篇 |
2017年 | 675篇 |
2016年 | 660篇 |
2015年 | 665篇 |
2014年 | 656篇 |
2013年 | 857篇 |
2012年 | 827篇 |
2011年 | 858篇 |
2010年 | 875篇 |
2009年 | 743篇 |
2008年 | 791篇 |
2007年 | 734篇 |
2006年 | 689篇 |
2005年 | 556篇 |
2004年 | 455篇 |
2003年 | 353篇 |
2002年 | 390篇 |
2001年 | 404篇 |
2000年 | 275篇 |
1999年 | 157篇 |
1998年 | 84篇 |
1997年 | 58篇 |
1996年 | 40篇 |
1995年 | 20篇 |
1994年 | 26篇 |
1993年 | 23篇 |
1992年 | 32篇 |
1991年 | 9篇 |
1990年 | 18篇 |
1989年 | 11篇 |
1988年 | 10篇 |
1987年 | 12篇 |
1986年 | 18篇 |
1985年 | 9篇 |
1984年 | 11篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1979年 | 7篇 |
1975年 | 3篇 |
1965年 | 2篇 |
1964年 | 2篇 |
1958年 | 4篇 |
1957年 | 3篇 |
1954年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 234 毫秒
21.
22.
Pco2 of air and seawater samples from the East China Sea(ECS) were measured in situ in autumn, 1994,Ocean currents,terrestrial fluviation,biological activities,etc.,Pco2 char-acters in air and seawater were investigated,CO2 flux and its character in the East China Sea are discussed on the basis of the Pco2 profiles of air and seawater,It was clear that the nearshore was the source of CO2;and tht the oulter sea area was the sink of CO2; and that the shelf area of the EXS is a net sink for atmospheric CO2 in autumn. 相似文献
23.
24.
BIAN Jian-min LIN Nian-feng TANG Jie College of Environment Resources Jilin University Changchun Jilin China 《东北亚地学研究》2005,(Z1)
Desertification is an environmental issue in the world. The salt-alkalization desertification land area formed by both primary and secondary salt-alkalization has extended in a large scale, which has become a significant eco-environmental problem. Based on the characteristics of eco-environment and the situation of desertification in western Songnen plain, this paper reports the analyzes of its formation in background and cause. An early warning system on the salt-alkalization desertification is established and the GIS technology is used to abstract the information of desertification evaluation index. Supported by the integrated technology of the GIS and ANN, the orientation and quantitative result of desertification are gained, which is helpful to the eco-environment protection and resource development in western Songnen Plain. 相似文献
25.
林一山 《地球信息科学学报》1996,(2):43-46
随着我国人口日益增多,经济形势的飞速发展,加快开发西部的任务日趋紧迫和重要。而西部南水北调则是开发西部必须先行的关键性工程。这项工程是从青藏高原怒江、澜沧江、金沙江、雅砻江、大渡河等五大水系调水,穿过巴颜喀拉山入黄,以黄河大柳树枢纽为总灌渠渠首,把水引向内蒙西部,直至新疆东部地区。引水路线跨越西藏、四川、青海、甘肃、内蒙、新疆等地。此项工程调水量约800亿立方米,一旦实现,将使那里沙漠变绿洲,可开发那里东部地区稀少的矿产及其它资源。 相似文献
26.
27.
Molecular phylogenetic analysis of attached Ulvaceae species and free-floating Enteromorpha from Qingdao coasts in 2007 总被引:3,自引:1,他引:2
Based on the sequence data of the nuclear ribosomal DNA internal transcribed spacer(ITS) 1,5.8 S,and ITS 2,the molecular phylogeny was analyzed on Ulvaceae species collected from Qingdao coasts in summer of 2007,including 15 attached Ulva and Enteromorpha samples from 10 locations and 10 free-floating Enteromorpha samples from seven locations.The result supported the monophyly of all free-floating Enteromorpha samples,implying the unialgal composition of the free-floating Enteromorpha,and the attached Ulvaceae species from Qingdao coasts were grouped into other five clades,suggesting that they were not the biogeographic origin of the free-floating Enteromorpha in that season. 相似文献
28.
For a Hamiltonian that can be separated into N+1(N\geq 2) integrable parts, four algorithms can be built for a symplectic integrator. This research compares these algorithms for the
first and second order integrators. We found that they have similar local truncation errors represented by error Hamiltonian
but rather different numerical stability. When the computation of the main part of the Hamiltonian, H
0, is not expensive, we recommend to use S
* type algorithm, which cuts the calculation of the H
0 system into several small time steps as Malhotra(1991) did. As to the order of the N+1 parts in one step calculation, we found that from the large to small would get a slower error accumulation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
29.
氢化物发生-原子荧光光谱法直接测定地球化学样品中痕量碲 总被引:2,自引:1,他引:1
采用硝酸-氢氟酸-高氯酸溶解样品,以Fe3+作减缓剂,不需分离富集,用氢化物发生-原子荧光光谱法直接测定地球化学样品中痕量碲。对测定介质、KBH4浓度、铁盐的作用等条件进行试验。方法检出限为0.0031μg/g,精密度(RSD,n=11)<6.10%。方法用于国家一级地球化学标准物质中痕量碲的测定,结果与标准值一致。 相似文献
30.