全文获取类型
收费全文 | 2746篇 |
免费 | 468篇 |
国内免费 | 828篇 |
专业分类
测绘学 | 30篇 |
大气科学 | 120篇 |
地球物理 | 447篇 |
地质学 | 2217篇 |
海洋学 | 481篇 |
天文学 | 9篇 |
综合类 | 83篇 |
自然地理 | 655篇 |
出版年
2024年 | 15篇 |
2023年 | 46篇 |
2022年 | 103篇 |
2021年 | 105篇 |
2020年 | 163篇 |
2019年 | 159篇 |
2018年 | 154篇 |
2017年 | 133篇 |
2016年 | 167篇 |
2015年 | 154篇 |
2014年 | 162篇 |
2013年 | 218篇 |
2012年 | 180篇 |
2011年 | 197篇 |
2010年 | 158篇 |
2009年 | 161篇 |
2008年 | 146篇 |
2007年 | 185篇 |
2006年 | 185篇 |
2005年 | 154篇 |
2004年 | 143篇 |
2003年 | 148篇 |
2002年 | 106篇 |
2001年 | 121篇 |
2000年 | 98篇 |
1999年 | 96篇 |
1998年 | 64篇 |
1997年 | 68篇 |
1996年 | 52篇 |
1995年 | 46篇 |
1994年 | 37篇 |
1993年 | 26篇 |
1992年 | 20篇 |
1991年 | 11篇 |
1990年 | 13篇 |
1989年 | 12篇 |
1988年 | 9篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 3篇 |
1984年 | 5篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1978年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有4042条查询结果,搜索用时 31 毫秒
991.
介绍了芜湖长江大桥北岸接线工程约2.1km软土地基的特征及物理力学性质,采用袋装砂井及砂垫层联合使用的处理方法,技术可行,经济合理,效果良好,提高了地基强度,保证了工程质量,具有施工周期短、施工速度快等优点. 相似文献
992.
993.
根据土壤化学特征划分伏牛山亚热带北界 总被引:1,自引:0,他引:1
The boundary between subtropical zone and temperate zone is not only important in physical geography, but also attractive in agricultural production. Seven soil profiles studied in this paper are placed along the southern slope of Funiu Mountain at different heights above sea level.Many compositions and properties of these soils have been determined in laboratory. In this paper,the laws of migration and accumulation of soil materials on the southern slope of Funiu Mountain are discussed first, then the division of the boundary between subtropical zone and temperate zone in this area according to soil geochemistry is discussed with qualitative methods and mathematical classification method in which twelve selected indexes such as Km, Saf, Ba, β, Feo/Fet, Mno/Mnt and so on are used. The result indicates that the boundary between subtropical zone and temperate zone on the southern slope of Funiu Mountain is about 950 m above sea level. 相似文献
994.
995.
AyadMohammedFadhil 《中国地质大学学报(英文版)》2002,13(1):67-72
This study was carried out at Sand Dunes Stabilization Researches Station in Baiji district (230km north of Baghdad,Iraq) to evaluate the effects of local soil conditioners manufactured from oil derivatives and plant residuals on sand dunes fixation as the first step for sand dunes stabilization.The results indicate that the fuel oil has the first place in improving wind erosion parameters in the study area,such as increasing mean weight diameter,dry aggregates percentage,the needed time for complete disaggregation by dry sieving,and decreasing the disaggregation rates.Bitumen emulsion occupies the second place ,while the plant residuals occupies the third place and has slight effects on the studied pa-rameters.Effects of conditioners on natural vegetation cover are negative in oil derivatives treatments,while positive in plants residuals treatments. 相似文献
996.
历史时期我国沙尘暴东渐的原因分析 总被引:6,自引:4,他引:6
对历史时期我国沙尘暴发生的特点进行初步总结的结果显示:自汉代之后,沙尘暴发生的范围开始向东扩展,至元明清时期,其发生范围扩展到几乎整个华北地区.这一发展趋势虽与气候的冷暖干湿变化密切相关,但农业经济开发活动向西北地区的转移也是重要原因之一. 相似文献
997.
提供了土工格栅加筋砂土上的偏心受压条形基础极限承载力的室内模型试验结果。试验中只使用了一种相对压实密度的砂土和一种土工格栅,基础深度由0变化至B(基础宽度)。基于室内试验结果,提出了一个称为折减系数的经验关系,将偏心受压基础的极限承载力与中心受压基础的极限承载力联系起来。 相似文献
998.
999.
Michael Wiedenbeck 《Geostandards and Geoanalytical Research》2008,32(4):489-494
Secondary ion mass spectrometry (SIMS or ion microprobe) remains one of the most powerful tools available to the analytical geochemist. Despite the impressive progress witnessed by other competing laboratory methods over recent years, SIMS remains unsurpassed in its combination of small sampling volumes with low analytical uncertainties. Although the current SIMS analytical design has existed for over three decades, the period 2006–2007 saw significant advances in instrumentation, analytical methodology and, not least, the characterisation of new reference materials upon which all analyses depend. As of the end of 2007 the SIMS geoscience literature was reporting total sampling masses down to the 10 fg range, spatial resolution of better than 100 nm and uncertainties on major element isotope ratio determinations of better than ± 0.2‰ (1s). This article intends to synthesise the progress made by the geo‐SIMS community during this two year period and will also highlight some specific research results that were only possible due to the unique capabilities provided by SIMS. 相似文献
1000.
Total Sulfur Concentration in Geological Reference Materials by Elemental Infrared Analyser 总被引:1,自引:0,他引:1
L. Paul Bédard Dany Savard Sarah-Jane Barnes 《Geostandards and Geoanalytical Research》2008,32(2):203-208
Total sulfur is an analyte for which there are few determinations published, despite the fact that it is a very important element (e.g., a major element in most ores, an important gas constituent in global warming, an active participant in acid drainage). Most geological reference materials have very poor quality sulfur results, that is with relative standard deviations (RSD) in the range of 30–50%, even for concentrations over 100 μg g−1 S, which compromises their use as calibrators. In order to provide modern results with low RSD, sulfur was determined in twenty-nine geological reference materials with a state-of-the-art elemental S/C analyser using metal chips (certified reference materials with a traceability link) and analytical grade sulfur for high concentration samples. Analytical parameters (sample mass, crucible degassing, calibration strategy, etc.) were optimised by testing. Our results agreed with reference material values provided by issuing bodies. Results for CCRMP SY-2 (129 ± 13 μg g−1 S), which has been proposed as a sulfur reference material, were in agreement with the proposed modern value of 122 ± 3.7 μg g−1 S. 相似文献