全文获取类型
收费全文 | 478篇 |
免费 | 41篇 |
国内免费 | 68篇 |
专业分类
测绘学 | 2篇 |
大气科学 | 18篇 |
地球物理 | 59篇 |
地质学 | 372篇 |
海洋学 | 26篇 |
天文学 | 6篇 |
综合类 | 18篇 |
自然地理 | 86篇 |
出版年
2023年 | 4篇 |
2022年 | 9篇 |
2021年 | 5篇 |
2020年 | 6篇 |
2019年 | 12篇 |
2018年 | 6篇 |
2017年 | 11篇 |
2016年 | 10篇 |
2015年 | 13篇 |
2014年 | 30篇 |
2013年 | 26篇 |
2012年 | 25篇 |
2011年 | 23篇 |
2010年 | 30篇 |
2009年 | 40篇 |
2008年 | 21篇 |
2007年 | 25篇 |
2006年 | 22篇 |
2005年 | 33篇 |
2004年 | 25篇 |
2003年 | 21篇 |
2002年 | 28篇 |
2001年 | 31篇 |
2000年 | 16篇 |
1999年 | 12篇 |
1998年 | 12篇 |
1997年 | 11篇 |
1996年 | 11篇 |
1995年 | 15篇 |
1994年 | 6篇 |
1993年 | 9篇 |
1992年 | 15篇 |
1991年 | 12篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 4篇 |
1985年 | 1篇 |
1978年 | 1篇 |
排序方式: 共有587条查询结果,搜索用时 578 毫秒
581.
W. Roland Gehrels 《Quaternary Research》1999,52(3):350
A relative sea-level history is reconstructed for Machiasport, Maine, spanning the past 6000 calendar years and combining two different methods. The first method establishes the long-term (103 yr) trend of sea-level rise by dating the base of the Holocene saltmarsh peat overlying a Pleistocene substrate. The second method uses detailed analyses of the foraminiferal stratigraphy of two saltmarsh peat cores to quantify fluctuations superimposed on the long-term trend. The indicative meaning of the peat (the height at which the peat was deposited relative to mean tide level) is calculated by a transfer function based on vertical distributions of modern foraminiferal assemblages. The chronology is determined from AMS 14C dates on saltmarsh plant fragments embedded in the peat. The combination of the two different approaches produces a high-resolution, replicable sea-level record, which takes into account the autocompaction of the peat sequence. Long-term mean rates of sea-level rise, corrected for changes in tidal range, are 0.75 mm/yr between 6000 and 1500 cal yr B.P. and 0.43 mm/yr during the past 1500 years. The foraminiferal stratigraphy reveals several low-amplitude fluctuations during a relatively stable period between 1100 and 400 cal yr B.P., and a sea-level rise of 0.5 m during the past 300 years. 相似文献
582.
区内中生代火山岩—次火山岩发育,铅银矿脉(囊)成群集中分布,具有“小、浅、富”的特点,成因为“火山—次火山含气热液”成矿,矿石类型为块状硫化物型。在斜歪背斜北侧,为一构造与火山—次火山复合作用的沉降凹陷区,弱磁异常规模较大,锰矿化发育,可与特富矿脉部位的弱磁异常、锰矿化相类比,可能存在具一定规模的银、铅(铜、锌、硫)矿体。 相似文献
583.
584.
Luminescence ages are calculated by dividing an absorbed dose by the dose rate to which the natural dosimeter has been exposed. In practice, one measures an equivalent dose, De; in the absence of an alpha dose contribution, this should be indistinguishable from the dose absorbed in nature. Here we first review the relationship between absorbed dose, equivalent dose and dose rate, and the measurements that lead to their estimation; we restate that, in contrast to recent suggestions, an equivalent dose is not a physically different quantity from a beta or gamma dose absorbed by quartz grains. Statistical analysis of OSL data is of great importance when dealing with single grain data, since such data commonly exhibit significant scatter. However, dose rate measurements provide an arithmetic mean of dose rates absorbed by individual grains; in this article, we propose a new model to estimate the average dose absorbed by the grains. We thus introduce a new model for OSL age estimates: the Average Dose Model (ADM). We argue that ADM ages should be more accurate than Central Age Model (CAM) based ages, and we provide experimental evidence supporting this expectation. We also argue that the use of the Finite Mixture Model should be avoided. Finally, we discuss the implications for multi-grain age estimates derived from well-bleached samples. 相似文献
585.
586.
R. C. Chiverrell 《第四纪科学杂志》2001,16(1):9-29
Quantitative reconstruction of changes in mire surface wetness has been used to reconstruct proxy climate from an upland ombrotrophic blanket mire on the North York Moors in northeast England (May Moss). Testate amoebae, plant macrofossil and humification analyses were carried out for six peat profiles. Transfer functions are used to generate estimates of water table levels from the testate amoebae stratigraphy, which complement the semi‐quantitative indications of changing surface wetness provided by plant macrofossil and humification analysis. 14C dates provide the chronology for the stratigraphy. Differences were encountered between AMS 14C dates on pure Sphagnum remains and radiometric dates on bulk peat from the same horizon, which perhaps arise from the heterogeneity of peat. Replicate palaeoecological analysis of adjacent cores identifies consistency within testate amoebae and plant macrofossil stratigraphies, and reveals a strong agreement between the water table level proxies. The record of hydrological changes at sites across May Moss are in synchrony, and so climate change is the most likely cause of the moisture fluctuations. Changes to a wetter or cooler climate were identified cal. ad 260–540, ca. ad 550–650, cal. ad 670–980, ca. ad 1350–1450, cal. ad 1400–1620 and ca. ad 1700–1800. Periods with a drier or warmer climate precede all of these wet shifts, with particularly dry periods between cal. ad 650–860 and 690–980 and between cal. ad 1290–1410 and 1400–1620. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
587.
埃达克岩与Cu-Au成矿作用:有待深入研究的岩浆成矿关系 总被引:29,自引:19,他引:29
研究表明,环太平洋地区新生代斑岩铜矿和浅成热液金矿与同期的埃达克质岩浆活动存在密切的时空与成因联系。埃达克岩是许多世界级的斑岩铜矿的容矿岩,也是许多浅成热液矿化系统的成矿母岩浆。根据目前的研究,二者成因联系可能在于埃达克质岩浆的富流体、高氧逸度和基性源岩等固有属性,有利于Cu、Au等深源金属元素的萃取与富集成矿一因此,这可能是一种潜在的岩浆成矿专属性关系,但对产生这种关系的原因与机制仍然不十分清楚。这有待于今后深入开展成矿与无矿的埃达克岩、成矿的埃达克岩与非埃达克岩、无矿的埃达克岩与非埃达克岩等方面的对比研究,以揭示这种成矿专属性的本质。 相似文献