全文获取类型
收费全文 | 1732篇 |
免费 | 80篇 |
国内免费 | 28篇 |
专业分类
测绘学 | 66篇 |
大气科学 | 140篇 |
地球物理 | 385篇 |
地质学 | 592篇 |
海洋学 | 132篇 |
天文学 | 366篇 |
综合类 | 8篇 |
自然地理 | 151篇 |
出版年
2022年 | 24篇 |
2021年 | 28篇 |
2020年 | 29篇 |
2019年 | 32篇 |
2018年 | 60篇 |
2017年 | 58篇 |
2016年 | 50篇 |
2015年 | 46篇 |
2014年 | 54篇 |
2013年 | 97篇 |
2012年 | 52篇 |
2011年 | 74篇 |
2010年 | 75篇 |
2009年 | 83篇 |
2008年 | 75篇 |
2007年 | 70篇 |
2006年 | 68篇 |
2005年 | 42篇 |
2004年 | 53篇 |
2003年 | 48篇 |
2002年 | 64篇 |
2001年 | 30篇 |
2000年 | 36篇 |
1999年 | 23篇 |
1998年 | 32篇 |
1997年 | 30篇 |
1996年 | 17篇 |
1995年 | 21篇 |
1994年 | 15篇 |
1993年 | 18篇 |
1992年 | 23篇 |
1991年 | 15篇 |
1990年 | 14篇 |
1989年 | 10篇 |
1987年 | 22篇 |
1986年 | 17篇 |
1985年 | 24篇 |
1984年 | 30篇 |
1983年 | 32篇 |
1982年 | 37篇 |
1981年 | 25篇 |
1980年 | 25篇 |
1979年 | 25篇 |
1978年 | 11篇 |
1977年 | 18篇 |
1976年 | 17篇 |
1975年 | 8篇 |
1974年 | 16篇 |
1973年 | 12篇 |
1971年 | 8篇 |
排序方式: 共有1840条查询结果,搜索用时 15 毫秒
71.
Water levels in cryoconite holes were monitored at high resolution over a 3‐week period on Austre Brøggerbreen (Svalbard). These data were combined with melt and energy balance modelling, providing insights into the evolution of the glacier's near‐surface hydrology and confirming that the hydrology of the near‐surface, porous ice known as the ‘weathering crust’ is dynamic and analogous to a shallow‐perched aquifer. A positive correlation between radiative forcing of melt and drainage efficiency was found within the weathering crust. This likely resulted from diurnal contraction and dilation of interstitial pore spaces driven by variations in radiative and turbulent fluxes in the surface energy balance, occasionally causing ‘sudden drainage events’. A linear decrease in water levels in cryoconite holes was also observed and attributed to cumulative increases in near‐surface ice porosity over the measurement period. The transport of particulate matter and microbes between cryoconite holes through the porous weathering crust is shown to be dependent upon weathering crust hydraulics and particle size. Cryoconite holes therefore yield an indication of the hydrological dynamics of the weathering crust and provide long‐term storage loci for cryoconite at the glacier surface. This study highlights the importance of the weathering crust as a crucial component of the hydrology, ecology and biogeochemistry of the glacier ecosystem and glacierized regions and demonstrates the utility of cryoconite holes as natural piezometers on glacier surfaces. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
72.
Joseph Awetori Yaro 《GeoJournal》2010,75(2):199-214
Land in most of Africa is controlled under the customary tenure system which is governed by well intentioned social and cultural
rules meant to grant equal access to families within groups with common interest in land. Rapid changes in the domestic situation
of countries resulting from both refractions of policies and influences from the global economy and emerging complexities
within the local socio-economic context has altered the traditional land tenure systems in most parts of Africa. In the rural
setting and for agricultural purposes, the customary tenure system seems to be crumbling slowly, while in the urban centres
and for housing, industrial and commercial purposes the system has collapsed in favour of a commoditised one. The emerging
patterns of access in Northern Ghana show growing inequalities in access, control and ownership. There is the need for a new
architecture of land rights negotiated by a participatory process and regulated by both state and traditional institutions. 相似文献
73.
Nicholas P. Dunning Carmen McCane Tyler Swinney Matthew Purtill Jani Sparks Ashley Mann Jon‐Paul McCool Chantal Ivenso 《Geoarchaeology》2015,30(3):167-199
Over the past thirty years, geoarchaeology has moved from the fringe to mainstream status within Mesoamerican archaeological investigations. This review focuses on works published since the year 2000. Five themes are identified as central to recent studies: (1) the correlation of environmental change and cultural history; (2) anthropogenic environmental impacts; (3) ancient land cover, land use, and diet; (4) archaeological prospection; and (5) provenance studies. These themes are often interwoven in the application of complex systems approaches that allow scientists to more accurately model the intricacies of ancient human–environment interactions. 相似文献
74.
75.
A diatom‐inferred record of lake variability during the last 900 years in Lützow–Holm Bay,East Antarctica
下载免费PDF全文
![点击此处可从《第四纪科学杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Rachel C. Rudd Jonathan J. Tyler John Tibby Yusuke Yokoyama Ines Tavernier Elie Verleyen Manabu Fukui Yoshinori Takano 《第四纪科学杂志》2016,31(2):114-125
Decadal–centennial‐scale climate variability in coastal Antarctica remains poorly understood due to the limited number of highly resolved, well‐dated records. We present a 900‐year, decadal‐scale reconstruction based on sedimentary diatoms from Lake Abi in Lützow–Holm Bay, East Antarctica. Hydrological change is inferred from diatom ecological preferences in conjunction with an existing regional training set and implies that lake water specific conductivity, depth and nitrogen availability are the key drivers of diatom assemblage change. Lake Abi underwent a series of subtle environmental changes related to these environmental variables, possibly driven by changes in catchment snow melt and the duration of seasonal ice cover. Ordination is used to trace the major patterns of change in the diatom community, with notable shifts identified between 470 and 400 and at ~350 cal a BP (where present = CE 1950). The frequency of environmental variability at Lake Abi is broadly consistent with a record of the Interdecadal Pacific Oscillation during the last millennium, but contrasts with the apparent climate stability elsewhere in eastern Antarctica. Further research is required to constrain the limnological and ecological responses of lakes in coastal Antarctica to obtain more rigorous palaeoclimate reconstructions from these sites of immense potential. 相似文献
76.
77.
Khan Mohd Yawar Ali Khan Babra Chakrapani Govind Joseph 《Arabian Journal of Geosciences》2016,9(8):1-11
Arabian Journal of Geosciences - A comprehensive study on the chemical considerations of thermal waters (springs and geothermal wells) on the performance of solute geothermometers in predicting the... 相似文献
78.
Tyler R. Bonnell Colin A. Chapman Raja Sengupta 《International journal of geographical information science》2016,30(10):2075-2088
Spatial simulations are a valuable tool in understanding dynamic spatial processes. In developing these simulations, it is often required to make decisions about how to represent features in the environment and how events unfold in time. These spatial and temporal choices have been shown to significantly alter model outcomes, yet their interaction is less well understood. In this paper, we make use of a simple group foraging model and systematically vary how features are represented (cell size of the landscape) as well as how events unfold in time (order in which foragers take action) to better understand their interaction. Our results show similar nonlinear responses to changes in spatial representation found in the literature, and an effect of the order in which agents were processed. There was also a clear interaction between how features are represented and how events unfold in time, where, under certain environmental representations results were found to be more sensitive to the order in which individuals were processed. Furthermore, the effects of feature representation, scheduling of agents, and their interaction were all found to be influenced by the heterogeneity of the spatial surface (food), suggesting that the statistical properties of the underlying spatial variable will additionally play a role. We suggest that navigating these interactions can be facilitated through a better understanding of how these choices affect the decision landscape(s) on which agents operate. Specifically, how changes to representation affect aggregation and resolution of the decision surface, and thereby the degree to which agents interact directly or indirectly. We suggest that the challenges of dealing with spatial representation, scheduling, and their interaction, while building models could also present an opportunity. As explicitly including alternate representations and scheduling choices during model selection can aid in identifying optimal agent–environment representations. Potentially leading to improved insights into the relationships between spatial processes and the environments in which they occur. 相似文献
79.
80.
Assessment of soil erosion in a tropical mountain river basin of the southern Western Ghats,India using RUSLE and GIS 总被引:1,自引:0,他引:1
Revised Universal Soil Loss Equation(RUSLE) model coupled with transport limited sediment delivery(TLSD) function was used to predict the longtime average annual soil loss, and to identify the critical erosion-/deposition-prone areas in a tropical mountain river basin, viz., Muthirapuzha River Basin(MRB; area=271.75 km~2), in the southern Western Ghats, India. Mean gross soil erosion in MRB is 14.36 t ha~(-1) yr~(-1), whereas mean net soil erosion(i.e., gross erosion-deposition) is only 3.60 t ha~(-1) yr~(-1)(i.e., roughly 25% of the gross erosion). Majority of the basin area(~86%) experiences only slight erosion(5 t ha~(-1) yr~(-1)), and nearly 3% of the area functions as depositional environment for the eroded sediments(e.g., the terraces of stream reaches, the gentle plains as well as the foot slopes of the plateau scarps and the terrain with concordant summits). Although mean gross soil erosion rates in the natural vegetation belts are relatively higher, compared to agriculture, settlement/built-up areas and tea plantation, the sediment transport efficiency in agricultural areas and tea plantation is significantly high,reflecting the role of human activities on accelerated soil erosion. In MRB, on a mean basis, 0.42 t of soil organic carbon(SOC) content is being eroded per hectare annually, and SOC loss from the 4th order subbasins shows considerable differences, mainly due to the spatial variability in the gross soil erosion rates among the sub-basins. The quantitative results, on soil erosion and deposition, modelled using RUSLE and TLSD, are expected to be beneficial while formulating comprehensive land management strategies for reducing the extent of soil degradation in tropical mountain river basins. 相似文献