全文获取类型
收费全文 | 322篇 |
免费 | 15篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 5篇 |
大气科学 | 7篇 |
地球物理 | 47篇 |
地质学 | 138篇 |
海洋学 | 16篇 |
天文学 | 94篇 |
自然地理 | 32篇 |
出版年
2021年 | 4篇 |
2020年 | 5篇 |
2019年 | 2篇 |
2018年 | 7篇 |
2017年 | 9篇 |
2016年 | 10篇 |
2015年 | 6篇 |
2014年 | 7篇 |
2013年 | 15篇 |
2012年 | 11篇 |
2011年 | 10篇 |
2010年 | 12篇 |
2009年 | 16篇 |
2008年 | 15篇 |
2007年 | 12篇 |
2006年 | 11篇 |
2005年 | 10篇 |
2004年 | 5篇 |
2003年 | 6篇 |
2002年 | 12篇 |
2001年 | 4篇 |
2000年 | 8篇 |
1999年 | 12篇 |
1998年 | 9篇 |
1997年 | 5篇 |
1996年 | 10篇 |
1995年 | 5篇 |
1994年 | 7篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1986年 | 5篇 |
1985年 | 8篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 7篇 |
1980年 | 8篇 |
1979年 | 2篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1974年 | 2篇 |
1973年 | 5篇 |
1968年 | 2篇 |
1934年 | 1篇 |
1882年 | 1篇 |
1877年 | 2篇 |
排序方式: 共有339条查询结果,搜索用时 93 毫秒
101.
Lewis A. Owen Ben Richards Edward J. Rhodes W. Dickson Cunningham Brian F. Windley J. Badamgarav D. Dorjnamjaa 《第四纪科学杂志》1998,13(6):539-547
Relict permafrost structures (ice-wedge casts and cryoturbation structures) are present in the Gobi of southern Mongolia. Luminescence dates of sediments are presented to constrain the age of formation of permafrost structures. These data show that there was a phase of permafrost development during the latter part of the Last Glacial (after about 22 to 15 ka) that resulted in cryoturbated sediments and ice-wedge casts. Furthermore, permafrost degradation occurred during late Pleistocene times (13–10 ka) and was absent during the early Holocene. These permafrost structures mark the southernmost evidence of permafrost in northern Asia during late Quaternary times and indicate that the mean annual air temperature was below approximately −6°C during their formation. © 1998 John Wiley & Sons, Ltd. 相似文献
102.
A New Kingdom spinning bowl from Karnak (Luxor) Egypt is similar in form to spinning bowls commonly found at other Egyptian sites and has a bulk chemical composition in the range for other Egyptian marl vessels. These data support a domestic origin. The matrix of the bowl contains unaltered, sand-sized, mafic rock fragments with volcanic, subophitic textures. Over 20% of the sand-sized grains consist of angular, unweathered rock fragments, and of these ∼20% are volcanic. Apparently they were added as temper. Electron microprobe analyses show that augite, plagioclase, and, where present, pigeonite, in nine of these have compositions typical of mafic igneous rocks. Geothermometry confirms crystallization at ∼1100°C. Pyroxene discrimination diagrams indicate geological sources ranging from within-plate alkali basalts to within-plate, continental tholeiites. Suitable sources for the temper are rare in Egypt. Both alkaline and tholeiitic, postorogenic (unaltered) late Cenozoic basalts occur in the Cairo area, making this the most likely but not the only possible source for the temper. The pottery may have also originated in Cairo because raw rock materials were moved upstream less commonly than down the Nile. A Cairo provenance for the Karnak artifact is consistent with the everyday movement of people and goods along the Nile between the ancient twin capitals of Memphis and Thebes. These results and the common occurrence of volcanic rocks as temper indicate that microbeam analytical techniques may help narrow the provenance of ancient pottery. © 1998 John Wiley & Sons, Inc. 相似文献
103.
Alan W. Owen 《Geological Journal》1984,19(3):304-305
104.
105.
Using the recently completed Giant Meterwave Radio Telescope, we have detected the HI 21 cm-line absorption from the peculiar
galaxy C153 in the galaxy cluster Abell 2125. The HI absorption is at a redshift of 0.2533, with a peak optical depth of 0.36.
The full width at half minimum of the absorption line is 100 km s−1. The estimated column density of atomic Hydrogen is 0.7×1022(T
s
/100) cm−2. The HI absorption is redshifted by ∼400km s−1 compared to the [OIII] emission line from this system. We attribute this to an infalling cold gas or to an out-flowing ionised
gas, or to a combination of both as a consequence of tidal interactions of C153 with either a cluster galaxy or the cluster
potential. 相似文献
106.
Bioerosion by Cliona delitrix and Cliona lampa was assessed at 43 sites along the Florida Reef Tract, USA, in the summer of 2001. Sponge abundances were estimated using rapid visual assessment. Tissue samples of sponges were taken for analysis of delta15N. Comparison samples were taken from Belize. Annual trends in sponge abundance were estimated from archived videos covering the period from 1996 to 2001. Sites with the greatest boring sponge size and cover were in the Backcountry and Lower Keys, where total nitrogen, ammonium, and delta15N levels were highest. The sites with the largest relative increase of C. delitrix and C. lampa over the 5 year period were in the Upper Keys, where the greatest relative decline in stony coral cover has occurred. Florida sponge delta15N values were 5.2(+/-0.1)%, suggesting the influence of human waste; in comparison, offshore Belize samples were 2.1(+/-0.1)%. These results suggest sewage contamination of the Florida Reef Tract, shifting the carbonate balance from construction to destruction. 相似文献
107.
108.
109.
Late Holocene radiocarbon and aspartic acid racemization dating of deep-sea octocorals 总被引:1,自引:0,他引:1
Primnoa resedaeformis is a deep-sea gorgonian coral with a two-part skeleton of calcite and gorgonin (a fibrillar protein), potentially containing long-term records of valuable paleo-environmental information. For various reasons, both radiocarbon and U/Th dating of these corals is problematic over the last few centuries. This paper explores aspartic acid racemization dating of the gorgonin fraction in modern and fossil specimens collected from the NW Atlantic Ocean. Radiocarbon dating of the fossil specimen indicates a lifespan of 700 ± 100 years, the longest yet documented for any octocoral. Gorgonin amino acid compositions were identical in the fossil and modern specimens, indicating resistance to organic diagenesis. Similar to bone collagen, the fibrillar protein of gorgonin may impose conformational constraints on the racemization of Asp at low temperatures. The rate of racemization of aspartic acid (d/l-Asp) was similar to previously published results from an 1800 year old anemone (Gerardia). The age equation was: age (years BP 2000 AD) = [(d/l − 0.020 (±.002))/.0011 (±.0001)]2 (r2 = 0.97, p < .001). The error in an age estimate calculated by d/l-Asp was marginally better than that for 14C dating over the most recent 50-200 years, although the dating error may be improved by inclusion of more samples over a broader time range. These results suggest that d/l-Asp dating may be useful in augmenting 14C dating in cases where 14C calibrations yield two or more intercept ages, or in screening samples for further 14C or U/Th dating. 相似文献
110.
Tobias Owen 《Icarus》1976,29(1):159-163
A brief review of the history of Jovian satellite nomenclature is given to indicate the background for the names proposed for the numbered satellites. The new names are consistent with established tradition and should cause minimal confusion with other named objects in the solar system. 相似文献