全文获取类型
收费全文 | 4636篇 |
免费 | 890篇 |
国内免费 | 1427篇 |
专业分类
测绘学 | 221篇 |
大气科学 | 1277篇 |
地球物理 | 783篇 |
地质学 | 2495篇 |
海洋学 | 771篇 |
天文学 | 465篇 |
综合类 | 381篇 |
自然地理 | 560篇 |
出版年
2024年 | 25篇 |
2023年 | 73篇 |
2022年 | 139篇 |
2021年 | 141篇 |
2020年 | 168篇 |
2019年 | 237篇 |
2018年 | 160篇 |
2017年 | 178篇 |
2016年 | 183篇 |
2015年 | 202篇 |
2014年 | 255篇 |
2013年 | 271篇 |
2012年 | 279篇 |
2011年 | 326篇 |
2010年 | 286篇 |
2009年 | 346篇 |
2008年 | 307篇 |
2007年 | 358篇 |
2006年 | 359篇 |
2005年 | 272篇 |
2004年 | 276篇 |
2003年 | 242篇 |
2002年 | 198篇 |
2001年 | 204篇 |
2000年 | 171篇 |
1999年 | 175篇 |
1998年 | 146篇 |
1997年 | 164篇 |
1996年 | 136篇 |
1995年 | 118篇 |
1994年 | 100篇 |
1993年 | 101篇 |
1992年 | 73篇 |
1991年 | 80篇 |
1990年 | 48篇 |
1989年 | 42篇 |
1988年 | 43篇 |
1987年 | 19篇 |
1986年 | 14篇 |
1985年 | 8篇 |
1984年 | 6篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 7篇 |
1977年 | 1篇 |
1973年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有6953条查询结果,搜索用时 705 毫秒
91.
92.
93.
Micro-spectroscopic investigations of highly heterogeneous waste repository materials 总被引:1,自引:0,他引:1
A.M. Scheidegger D. Grolimund C.R. Cheeseman R.D. Rogers 《Journal of Geochemical Exploration》2006,88(1-3):59
Assuring safe disposal and long-term storage of radioactive and toxic wastes corresponds to a primary environmental task of present societies. To improve any technical limitation, a mechanistic understanding of the processes governing the binding of heavy metals and radionuclides is required. In this study, the significance of synchrotron-based X-ray microprobes for elucidating the spatial distribution and the speciation of radionuclides in highly heterogeneous waste repository materials will be outlined. A case study on the uptake process of Co in cementitious engineered barrier materials exposed to microbial degradation will be presented. 相似文献
94.
Janet M. Hergt L. Paul Bédard Etienne Deloule Klaus Peter Jochum Kathryn L. Linge Paul J. Sylvester Matthias Willbold Jon D. Woodhead 《Geostandards and Geoanalytical Research》2006,30(3):141-142
In 2005 Geostandards and Geoanalytical Research embarked upon a new initiative for its readers. Key researchers in various fields of geoanalytical technique development and their application were identified and invited to provide reviews pertinent to their expertise. As noted in the first of these publications "…instead of revisiting the historical context or decades of development in each analytical technique, the goal here has been to capture a snapshot of "hot topics" across a range of fields as represented in the… literature" (Hergt et al . 2005). Rather than prepare an annual review, a decision was taken earlier this year to provide a biennial summary of progress and accomplishments, in this case for the years 2004–2005. The principal techniques employed in Earth and environmental sciences are covered here, and include laser ablation and multicollector ICP-MS, ICP-AES, thermal ionisation and secondary ion mass spectrometry, as well as neutron activation analysis, X-ray fluorescence and atomic absorption spectrometry. A comprehensive review of the development of reference materials, often essential to these techniques, is also provided. The contributions assembled serve both to keep readers informed of advances they may be unfamiliar with, but also as a means of showcasing examples of the breadth and depth of work being conducted in these fields. 相似文献
95.
WANG Lei ZHANG Guang-Xin 《湿地科学》2006,4(3):193-197
1 INTRODUCTIONNitrogen and phosphorus in the water are the nu-trients limited in natural wetlands,which seriously in-fluence on the ecosystem production and the biodiver-sity(Mitsch,Grosselin,2000).Nitrogen and phos-phorus recycles have been interrupted b… 相似文献
96.
97.
采用密闭室红外气体分析仪法(IRGA法)观测了中亚热带红壤侵蚀裸地植被恢复后不同季节土壤呼吸速率的日动态变化,并比较了IRGA法与碱吸收法(AA法)测定的土壤呼吸速率.结果表明:侵蚀裸地植被恢复后土壤呼吸速率日动态呈单峰曲线,与土壤温度的昼夜变化基本一致,最高值一般出现在午后13∶00~17∶00,最低值出现在凌晨3∶00~7∶00;植被恢复显著提高了土壤日呼吸速率,但明显降低了土壤呼吸速率日变化幅度;马尾松林对土壤呼吸速率日变化幅度降低程度高于板栗园和百喜草地,且对夏季的降低程度影响最大.而IRGA法和AA法测定的土壤呼吸速率具有显著的幂函数关系,AA法测定的土壤呼吸速率为IRGA法的27.5%~218%,平均为76.2%.当土壤呼吸速率较低时,AA法比IRGA法高估了土壤呼吸速率;反之,AA法则低估了土壤呼吸速率. 相似文献
98.
99.
100.
Re-evaluation of focal depths and source mechanisms of selected earthquakes in the Afar depression 总被引:1,自引:0,他引:1
We present a stepwise inversion procedure to assess the focal depth and model earthquake source complexity of seven moderate-sized earthquakes (6.2 > M w > 5.1) that occurred in the Afar depression and the surrounding region. The Afar depression is a region of highly extended and intruded lithosphere, and zones of incipient seafloor spreading. A time-domain inversion of full moment tensor was performed to model direct P and SH waves of teleseismic data. Waveform inversion of the selected events estimated focal depths in the range of 17–22 km, deeper than previously published results. This suggests that the brittle–ductile transition zone beneath parts of the Afar depression extends more than 22 km. The effect of near-source velocity structure on the moment tensor elements was also investigated and was found to respond little to the models considered. Synthetic tests indicate that the size of the estimated, non-physical, non-isotropic source component is rather sensitive to incorrect depth estimation. The dominant double couple part of the moment tensor solutions for most of the events indicates that their occurrence is mainly due to shearing. Parameters associated with source directivity (rupture velocity and azimuth) were also investigated. Re-evaluation of the analysed events shows predominantly normal faulting consistent with the relative plate motions in the region. 相似文献