全文获取类型
收费全文 | 1832篇 |
免费 | 198篇 |
国内免费 | 434篇 |
专业分类
测绘学 | 49篇 |
大气科学 | 33篇 |
地球物理 | 332篇 |
地质学 | 580篇 |
海洋学 | 939篇 |
天文学 | 13篇 |
综合类 | 179篇 |
自然地理 | 339篇 |
出版年
2024年 | 10篇 |
2023年 | 36篇 |
2022年 | 55篇 |
2021年 | 68篇 |
2020年 | 81篇 |
2019年 | 54篇 |
2018年 | 83篇 |
2017年 | 93篇 |
2016年 | 106篇 |
2015年 | 85篇 |
2014年 | 112篇 |
2013年 | 157篇 |
2012年 | 95篇 |
2011年 | 127篇 |
2010年 | 111篇 |
2009年 | 105篇 |
2008年 | 121篇 |
2007年 | 108篇 |
2006年 | 125篇 |
2005年 | 106篇 |
2004年 | 95篇 |
2003年 | 59篇 |
2002年 | 62篇 |
2001年 | 41篇 |
2000年 | 60篇 |
1999年 | 44篇 |
1998年 | 39篇 |
1997年 | 44篇 |
1996年 | 27篇 |
1995年 | 25篇 |
1994年 | 23篇 |
1993年 | 16篇 |
1992年 | 27篇 |
1991年 | 14篇 |
1990年 | 11篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 1篇 |
排序方式: 共有2464条查询结果,搜索用时 48 毫秒
131.
Tang Lilian Li Fanglin 《地球科学》1986,(1)
本文以526个岩石样品的Hg、Zn测定及闪锌矿单矿物Hg的热释温度测定为基础,探讨了甲生盘层控硫铅锌矿床Hg的岩石地球化学异常特征,提出了以Hg×100/Zn为指标研究成矿后侵入体的热力对Hg的驱赶作用的可能性。从岩体向外250m的距离内,该比值逐渐从2升高到7。原生Hg异常的研究有利于解释该地壤中汞气异常的形成。已经证实,壤中汞气测量对寻找这类矿床是有效的。 相似文献
132.
中国西北C-3植物的碳同位素组成与年降雨量关系初探 总被引:2,自引:0,他引:2
本文对不同年降雨量环境下生长的藜、独行菜、魁蓟和平车前这4种常见C-3植物的δ13C进行了分析,发现这4种C-3植物的δ13C组成都表现出随年降雨量减少而变重的趋势,其中藜和独行菜的碳同位素组成对降水变化的响应相对要较其它2种植物强烈得多。藜、独行菜和魁蓟的δ13C组成与年降雨量有显著的线性关系,平车前碳同位素组成与年降雨量没有显著的相关性,表明藜、独行菜和魁蓟的δ13C组成可作为年降雨量的替代性指标,平车前的δ13C组成不能作为年降水的替代性指标。 相似文献
133.
Mercury in the Tinto-Odiel Estuarine System (Gulf of Cádiz, Spain): Sources and Dispersion 总被引:1,自引:0,他引:1
The Tinto and Odiel are small rivers draining one of the largest sulphide deposits in the world. As a result of these deposits and a large industrial complex, the adjacent marine area receives a high amount of metal input. Mercury distribution in the Tinto-Odiel estuary, the Huelva Ría and the Gulf of Cádiz was assessed in water and suspended particulatematter (SPM) and sediments. In the rivers and estuaries, dissolved (HgD)and particulate (HgP) mercury showed wide variations (13 to 200 pM and0.3 to 330 nmol g-1 respectively) depending on the presence or notof sulphidic waters, phosphogypsum deposits, detrital pyrite and oxyhydroxides.In the Ría, concentrations were lower than 10 pM and 4.5 nmol g-1 for HgD and HgP respectively. In surface waters of the Gulf of Cádiz, the average HgD concentration (pm standard deviation) was 2.9 pm 0.9 pM, which is similar to that of North Atlantic Central Waters. The surface sediments collected in the rivers, the Ría and the Gulf showed systematically enriched mercury compared to pre-industrial levels. Vertical mercury profiles in dated sediment cores were typical of anthropogenically influenced environments starting in the early Roman age. These distribution features suggest that most of the Hg discharged by the Huelva Ría is trapped in the sediments of the Gulf of Cádiz. 相似文献
134.
135.
应用大气光化学模式研究了日间影响NOx光化学转化率的主要物理化学因子.探讨了在不同NMHC/NOx比值时,NOx光化学特征及其转化产物的变化规律.结果表明,影响NOx转化率的主要因子是阳光辐射强度和NMHC/NOx比值.但在NMHC/NOx比值很低时,光强的增加并不能显著提高NOx转化率.温度和初始臭氧浓度对NOx转化率的影响次之.相对湿度对NOx转化率的影响较小.在不同NMHC/NOx比值下,NOx转化特征和产物有很大区别.NMHC/NOx比值高时,产物中PAN>HNO3.NMHC/NOx比值中(低)时,产物主要是HNO3,PAN等有机氮不到10%(1%).最后初步比较了模拟和观测的NOy组成. 相似文献
136.
137.
Responses of herbaceous and suffrutescent species to fire, grazing, and presence of Prosopis glandulosa were examined in a Chihuahuan desert grassland in south-central New Mexico. Treatments were assigned randomly to eight 12×8 m plots within each of two blocks. Following fires in June 1995, unfenced plots were exposed to livestock grazing over 4 years. Plots were established that either included or excluded P. glandulosa. Perennial grass cover, primarilyBouteloua eriopoda , decreased by 13% in burned plots but increased 5% in unburned areas. Conversely, perennial forb cover was 4% greater after fire. Perennial grass frequency decreased 30% more and perennial forb frequency increased 10% more following burning. Further, increases in evenness after fire resulted in a 225% increase in species diversity. Grazing also resulted in a decrease in perennial grass cover while frequency decreased 22% more in grazed than ungrazed plots. Only frequency and not cover of perennial forbs and annual grasses increased more following grazing. Presence of P. glandulosa had no differential effect on responses of non-shrub species. Fires were conducted during near drought conditions while grazing occurred during years of precipitation equivalent to the long-term average. Precipitation immediately following fire may be critical for recovery of B. eriopoda -dominated desert grasslands; relationships between fire and post-fire precipitation patterns require future investigation. 相似文献
138.
植物响应气候变化模型模拟研究进展 总被引:9,自引:0,他引:9
尽管温室气体的增温效应及幅度大小具有很大的不确定性 ,存在许多分歧 ,然而植物对于气候变化的响应研究仍然成为众多学者关注的热点。近十年来 ,国内外学者从模型模拟的角度进行了多层面定量研究。归纳起来 ,已有的模型可以归并为生物地理相关模型、生态响应面模型、立地模型、植物生理模型以及统计模型等五类。本文逐一进行了评述 ,分析了它们的优势与不足 ,最后对模型模拟的发展趋势进行了展望。 相似文献
139.
应用壤中气汞量测量找金的效果——以湖南青京寨、三德堂金矿为例 总被引:2,自引:0,他引:2
湖南青京寨和三德堂分别为破碎带蚀变岩型,残积红土型金矿床。地表存在较厚的残(坡)积覆盖层,应用壤中气汞量测量法寻找隐伏含Au构造蚀变带及金矿体。区内气汞异常带及其峰值与隐伏含Au构造蚀变带及金矿体具有较好的对应性,利用这种对应性并结合区内地质,地球化学特征,施工适当的工程进行验证。在青京寨对6条气汞异常带进行工程揭露验证,各带均发现含Au蚀变带。三德常矿区圈定的金异异常与气汞异常基本一致。壤中气汞量测量法不仅适有于寻找中代温热液型金矿床,而且也适于寻找刚化残积型金矿床。 相似文献
140.
Gianpaolo Coro Pasquale Pagano Anton Ellenbroek 《International Journal of Digital Earth》2020,13(5):567-585
ABSTRACTForecasting environmental parameters in the distant future requires complex modelling and large computational resources. Due to the sensitivity and complexity of forecast models, long-term parameter forecasts (e.g. up to 2100) are uncommon and only produced by a few organisations, in heterogeneous formats and based on different assumptions of greenhouse gases emissions. However, data mining techniques can be used to coerce the data to a uniform time and spatial representation, which facilitates their use in many applications. In this paper, streams of big data coming from AquaMaps and NASA collections of 126 long-term forecasts of nine types of environmental parameters are processed through a cloud computing platform in order to (i) standardise and harmonise the data representations, (ii) produce intermediate scenarios and new informative parameters, and (iii) align all sets on a common time and spatial resolution. Time series cross-correlation applied to these aligned datasets reveals patterns of climate change and similarities between parameter trends in 10 marine areas. Our results highlight that (i) the Mediterranean Sea may have a standalone ‘response’ to climate change with respect to other areas, (ii) the Poles are most representative of global forecasted change, and (iii) the trends are generally alarming for most oceans. 相似文献