全文获取类型
收费全文 | 237篇 |
免费 | 9篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 5篇 |
大气科学 | 25篇 |
地球物理 | 37篇 |
地质学 | 103篇 |
海洋学 | 21篇 |
天文学 | 23篇 |
综合类 | 1篇 |
自然地理 | 35篇 |
出版年
2021年 | 3篇 |
2020年 | 5篇 |
2019年 | 5篇 |
2018年 | 7篇 |
2017年 | 10篇 |
2016年 | 12篇 |
2015年 | 5篇 |
2014年 | 9篇 |
2013年 | 11篇 |
2012年 | 15篇 |
2011年 | 14篇 |
2010年 | 11篇 |
2009年 | 17篇 |
2008年 | 14篇 |
2007年 | 11篇 |
2006年 | 14篇 |
2005年 | 7篇 |
2004年 | 7篇 |
2003年 | 4篇 |
2002年 | 6篇 |
2001年 | 5篇 |
1999年 | 5篇 |
1998年 | 6篇 |
1997年 | 1篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1987年 | 1篇 |
1986年 | 5篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1970年 | 1篇 |
1969年 | 2篇 |
1968年 | 1篇 |
1966年 | 1篇 |
1956年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有250条查询结果,搜索用时 78 毫秒
71.
Katrine K. Andersen Anders Svensson Sigfus J. Johnsen Sune O. Rasmussen Matthias Bigler Regine Rthlisberger Urs Ruth Marie-Louise Siggaard-Andersen Jrgen Peder Steffensen Dorthe Dahl-Jensen Bo M. Vinther Henrik B. Clausen 《Quaternary Science Reviews》2006,25(23-24):3246
The Greenland Ice Core Chronology 2005, GICC05, is extended back to 42 ka b2k (before 2000 AD), i.e. to the end of Greenland Stadial 11. The chronology is based on independent multi-parameter counting of annual layers using comprehensive high-resolution measurements available from the North Greenland Ice Core Project, NGRIP. These are measurements of visual stratigraphy, conductivity of the solid ice, electrolytical melt water conductivity and the concentration of Na+, Ca2+, SO42−, NO3−, NH4+. An uncertainty estimate of the time scale is obtained from identification of ‘uncertain’ annual layers, which are counted as 0.5±0.5 years. The sum of the uncertain annual layers, the so-called maximum counting error of the presented chronology ranges from 4% in the warm interstadial periods to 7% in the cold stadials. The annual accumulation rates of the stadials and interstadials are on average one-third and half of the present day values, respectively, and the onset of the Greenland Interstadials 2, 3, and 8, based on 20 year averaged δ18O values, are determined as 23,340, 27,780, and 38,220 yr b2k in GICC05. 相似文献
72.
Ruth Liepins 《The Australian geographer》1995,26(2):118-126
A gendered consideration of rural geography has been barely discernible within Australian and New Zealand literature. The notable exceptions in this case have illustrated the complexity and merit of studying the gender patterns and relations of rural life. Outside geography, there is an expanding literature on rural women in Australia. These works parallel significant developments in the lives and politics of rural and agricultural women themselves. This paper reports selected findings from a study of the women in agriculture movement in Australia. As such, it illustrates the increased awareness of the gendered conditions of farming. The women in agriculture movement works to increase the recognition of women's contribution to agriculture. In doing so it affirms the legitimacy of women farmers’ voices and perspectives. There will be no sustainable rural systems while half the rural population is unseen or unheard. Women in agriculture demonstrate a social dimension of sustainability. They highlight the need to integrate gender equity and a ‘wider‐than‐economic’ conceptualisation of sustainable agriculture. Their actions can stimulate rural geographers to further consider the social and political aspects of rural sustainability beyond the conventional farm/industry and community service sites we usually consider. 相似文献
73.
Organic-rich (18.2%) Monterey Formation diatomite from California was studied. The organic matter consist of 94% bitumen and 6% kerogen. Biological markers from the bitumen and from pyrolysates of the coexisting asphaltenes and kerogen were analyzed in order to elucidate the relationship between the various fractions of the organic matter. While 17 alpha(H), 18 alpha(H), 21 alpha(H)-28,30-bisnorhopane was present in the bitumen and in the pryolysate of the asphaltenes, it was not detected in the pyrolysates of the kerogen. A C40-isoprenoid with "head to head" linkage, however, was present in pyrolysates of both kerogen and asphaltenes, but not in the bitumen from the diatomite. The maturation level of the bitumen, based on the extent of isomerization of steranes and hopanes, was that of a mature oil, whereas the pyrolysate from the kerogen showed a considerably lower maturation level. These relationships indicate that the bitumen may not be indigenous to the diatomite and that it is a mature oil that migrated into the rock. We consider the possibility, however, that some of the 28,30-bisnorhopane-rich Monterey Formation oils have not been generated through thermal degradation of kerogen, but have been expelled from the source rock at an early stage of diagenesis. 相似文献
74.
It is shown that relatively small errors of the order of 10% in the electron densities, for example derived from polarization brightness measurements, might lead to large errors in the velocities inferred from intensity measurements of the L Hi 1216 spectral line in the inner corona. It is demonstrated that in some cases this effect can result in very high velocities close to the coronal base with subsequent small acceleration with heliocentric distance. It is also pointed out that the errors in the deduced velocities can be reduced if simultaneous observations that place constraints on the mass flux are available, and by ensuring that the mass flux computed from the derived velocities and densities is constant. 相似文献
75.
Long-term changes in salt marsh extent affected by channel deepening in a modified estuary 总被引:2,自引:0,他引:2
The aim of this study is to quantify the long-term (54 years) rates of marsh extension and retreat at two sites in the Westerschelde Estuary, SW Netherlands. Nine sets of aerial photographs were obtained for each of the two salt marsh sites, Zuidgors and Waarde, taken at various times between 1944 and 1998. The seaward edges of the marshes were digitised from rectified images after the photographs had been scanned and georegistered to the Dutch National Grid. Comparison of the extents of the marshes at these nine time points revealed that the areas of both marshes had fluctuated during these 54 years with periods of both extension and retreat of the seaward marsh edges. These periods of extension and retreat appeared to be approximately synchronised until the 1990s, with mean changes in position of marsh front ranging from −7.92 to 6.04 m a−1.The rate of landward retreat and seaward extension of the marsh front is shown to be related to an increase in the tidal prism brought about by dredging operations to maintain or increase the depth of the main navigable channel of the estuary. The consequent greater frequency with which the high tides reach the edge of the fringing marshes increases the risk of erosion. Strong westerly winds may also be a factor in increasing erosion. No relationship between the volume of shipping traffic using the estuary and marsh erosion was found. 相似文献
76.
Ruth Elaine Blake 《Geochimica et cosmochimica acta》2003,67(13):2315-2316
77.
The Arro system is an oblique fold system involving the Eocene sediments of the Graus-Tremp basin. It consists of westward-verging folds, trending NNW–SSE, some of them related with thrusts, in piggyback sequence. Seismic profiles allow to infer the geometry of structures at depth: folds and thrusts are ‘decolled’ over an unconformity between turbiditic and platform sediments. Re-activation of bedding surfaces by folding in the underlying units resulted in folding and thrusting in the upper series. To cite this article: A.M. Casas et al., C. R. Geoscience 334 (2002) 765–772. 相似文献
78.
79.
Ruth Weir 《Transactions in GIS》2019,23(6):1232-1250
Reducing domestic abuse has become a priority for both local and national governments in the UK, with its substantial human, social, and economic costs. It is an interdisciplinary issue, but to date there has been no research in the UK that has focused on neighborhood‐level predictors of domestic abuse and their variation across space. This article uses geographically weighted regression to model the predictors of police‐reported domestic abuse in Essex. Readily available structural and cultural variables were found to predict the domestic abuse rate and the repeat victimization rate at the lower super output area level and the model coefficients were all found to be non‐stationary, indicating varying relationships across space. This research not only has important implications for victims' well being, but also enables policy makers to gain a better understanding of the geography of victimization, allowing targeted policy interventions and efficiently allocated resources. 相似文献
80.
桂林穿山洞穴沉积物物的古地磁解释 总被引:1,自引:1,他引:0
<正> 穿山是桂林峰林平原上一座联座石峰(图1),在其不同高度上发育着许多洞穴。本文所涉及的古地磁样品则主要采集于穿山最西部月岩附近的19、20、21和28号洞内(图2)。与漓江高河漫滩高程相当的洞穴,其中沉积物均是细颗粒的,质地较软粘土。根据未经干扰的残留沉积物来分析,洞内沉积物充填的高度高出附近高河漫滩约13—14米。其它洞穴中残留的水平顶板亦表明曾经受过一个高水位的溶蚀作用。 相似文献