全文获取类型
收费全文 | 951篇 |
免费 | 54篇 |
国内免费 | 17篇 |
专业分类
测绘学 | 28篇 |
大气科学 | 75篇 |
地球物理 | 261篇 |
地质学 | 331篇 |
海洋学 | 105篇 |
天文学 | 110篇 |
综合类 | 8篇 |
自然地理 | 104篇 |
出版年
2021年 | 20篇 |
2020年 | 17篇 |
2019年 | 17篇 |
2018年 | 21篇 |
2017年 | 26篇 |
2016年 | 36篇 |
2015年 | 26篇 |
2014年 | 26篇 |
2013年 | 61篇 |
2012年 | 34篇 |
2011年 | 50篇 |
2010年 | 40篇 |
2009年 | 52篇 |
2008年 | 37篇 |
2007年 | 42篇 |
2006年 | 39篇 |
2005年 | 38篇 |
2004年 | 25篇 |
2003年 | 31篇 |
2002年 | 23篇 |
2001年 | 21篇 |
2000年 | 20篇 |
1999年 | 17篇 |
1998年 | 21篇 |
1997年 | 10篇 |
1996年 | 7篇 |
1995年 | 12篇 |
1994年 | 5篇 |
1993年 | 10篇 |
1992年 | 8篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 8篇 |
1988年 | 15篇 |
1987年 | 13篇 |
1986年 | 7篇 |
1985年 | 11篇 |
1984年 | 15篇 |
1983年 | 18篇 |
1982年 | 11篇 |
1981年 | 13篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 13篇 |
1977年 | 10篇 |
1976年 | 10篇 |
1975年 | 17篇 |
1974年 | 7篇 |
1973年 | 9篇 |
1969年 | 5篇 |
排序方式: 共有1022条查询结果,搜索用时 20 毫秒
951.
952.
Julian Saville Marsh 《Contributions to Mineralogy and Petrology》1975,50(2):135-144
Aenigmatite is common in many trachytes, phonolites and agpaitic nepheline syenites. Petrographic evidence suggests that the aenigmatite in these rocks arises by the reaction of Ti-magnetite with a peralkaline silica-undersaturated liquid, and it is postulated that a no-oxide field, where aenigmatite is stable, exists in alkaline undersaturated magmas. This field is similar to that found in silicic liquids but lies below the FMQ buffer curve in
space and is probably confined within narrow limits of temperature and oxygen fugacity. The hydrated equivalent of aenigmatite is possibly astrophyllite and the latter mineral is frequently associated with Na-amphiboles in natural rocks. This suggests that the stability field of astrophyllite is similar to that of Na-amphiboles with respect to temperature and
. 相似文献
953.
Robert N. Clayton Julian R. Goldsmith Karin J. Karel Toshiko K. Mayeda 《Geochimica et cosmochimica acta》1975,39(8):1197-1201
The equilibrium distribution of oxygen isotopes between calcium carbonate and water was determined at 500°C at pressures from 1 to 20 kbar and at 700°C at pressures of 0.5 and 1 kbar. At both temperatures, the pressure-dependence of the fractionation factor was below the limit of detection. The experimental results are consistent with theoretical estimates of the volume change due to isotope substitution. Application of the theory to silicate systems leads to the conclusion that pressure effects on oxygen isotopic fractionation between silicates are < 0.2% at pressures of tens of kilobars. Thus the observed large variations of O18/O16 ratio in kimberlitic eclogites cannot be attributed to the effect of pressure 相似文献
954.
Annie Michard-Vitrac Francis Albarede Christian Dupuis Hugh P. Taylor Jr 《Contributions to Mineralogy and Petrology》1980,72(1):57-72
The Maladeta plutonic complex formed during the latest stages of the Variscan orogeny. It was emplaced into the Paleozoic sedimentary sequence of the Pyrenees. The eastern part, investigated in the present study, consists of an early intrusion of cumulate gabbronorites followed in order of emplacement by the main biotite-hornblende granodiorite, which was itself intruded by two small stocks of two-mica cordierite granite. An 87Rb-87Sr isochron dates the granodiorite at 277±7 m.y. with an initial (87Sr/86Sr)o ratio of 0.7117±3. Gabbroic rocks have lower strontium initial ratios, down to 0.7092, while those of granite range from that of the granodiorite up to about 0.715. The three rock types have distinctive 18O values: 8.7 to 9.6 for the gabbronorites, 9.4 to 10.4 for the granodiorites and 10.3 to 11.8 for the granites. Lead isotopic compositions of rocks and feldspars are all radiogenic. Feldspars give consistent Pb model ages around 280 m.y., with and values of about 9.7 and 4.05, respectively. No pristine, mantle-derived magma was found among the investigated samples and the rocks cannot be related to one another by any simple mechanism of fractional crystallization. Some type of mixing process involving two end members seems to be required: a high-18O, high-87Sr material that is clearly of crustal origin, and a lower-18O, lower-87Sr end member derived from the mantle. Examination of various mixing models does not support magma mixing nor assimilation of crustal rocks by a mafic magma. The most acceptable model involves melting at different levels of a vertically-zoned source in the continental crust; this source was formed by mixing between mantle-derived magmas and crustal metasediments. This material was apparently thickened, tectonically downwarped and partially melted. None of the Maladeta magma-types appear to have been derived at a consuming plate boundary.Contribution Number 3280, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA 相似文献
955.
956.
Dennis Edler Julian Keil Marie-Christin Tuller Anne-Kathrin Bestgen Frank Dickmann 《The Cartographic journal》2020,57(1):6-17
ABSTRACTMap legends are key elements of thematic maps and cartographic communication. The question of how to style map legends is a topic which has often been addressed by cartographic academics and practitioners. Nevertheless, the question of where to position a map legend has only hardly been discussed. Principles of cognitive sciences allow the assumption that a legend positioned to the right of a map field can be read and decoded faster than a legend on the left side. This study investigates the impact of legend positioning on legend decoding. It involves an experiment based on a recognition memory paradigm and the registration of eye-movements. The results show that, in less time, a legend positioned to the right of the map field (compared to a left legend) can be decoded faster. The same accuracy of a cognitive representation of geographic space can be achieved in spatial memory. 相似文献
957.
Crustal structure beneath western and eastern Iceland from surface waves and receiver functions 总被引:1,自引:0,他引:1
958.
959.
Julian P. Hume 《Geology Today》2012,28(4):147-151
The dodo, Raphus cucullatus (Aves, Columbidae), has become one of the most famous birds in the world, a true icon of extinction. Known from a few contemporary illustrations and accounts, probably more has been written about it than any other species, yet we know practically nothing about the bird in life. Recent excavations on Mauritius are now revealing the ecology and habitat of this iconic bird, and providing new information as to why it was so vulnerable to human interference. 相似文献
960.
A self‐limiting bank erosion mechanism? inferring temporal variations in bank form and skin drag from high resolution topographic data
下载免费PDF全文
![点击此处可从《地球表面变化过程与地形》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Julian Leyland Stephen E. Darby Liliana Teruggi Massimo Rinaldi Daniele Ostuni 《地球表面变化过程与地形》2015,40(12):1600-1615
Fluvial bank erosion rates are often quantified by assuming that the erosion rate is a function of the excess (above a critical threshold) boundary shear stress applied by the flow. Research has shown that the form roughness induced by natural topographic bank features, such as slumps, spurs and embayments, is the dominant component of the spatially‐averaged total shear stress, meaning that form roughness provides an important control on bank erosion rates. However, measuring the relative components of the total shear stress for a natural system is not straightforward. In this work we use the method of Kean and Smith to partition the form and skin drag components of river bank roughness using a time series (2005–2011) of high‐resolution topographic surveys of an eroding bank of the Cecina River in central Italy. This method approximates the form drag component of the roughness along a longitudinal bank profile as a series of user‐defined Gaussian curves. The extracted metrics are used in conjunction with an estimate of the outer region flow velocity to partition the form and skin drag components of the total boundary shear stress according to the Kean and Smith analytical solution. The relative magnitude of the form and skin shear stress at each survey date is analysed alongside DEMs of difference to reveal that intense episodes of erosion are followed by periods of quiescence. We show that this is due to the protection offered by increased form drag roughness following erosion. We conceptualise the dynamic feedbacks that exist between river discharge, bank erosion processes and bank form roughness, into a simple model of the self‐limiting nature of river bank erosion. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献