全文获取类型
收费全文 | 1002篇 |
免费 | 23篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 33篇 |
大气科学 | 78篇 |
地球物理 | 196篇 |
地质学 | 310篇 |
海洋学 | 122篇 |
天文学 | 197篇 |
自然地理 | 90篇 |
出版年
2022年 | 5篇 |
2021年 | 11篇 |
2020年 | 11篇 |
2019年 | 13篇 |
2018年 | 9篇 |
2017年 | 17篇 |
2016年 | 24篇 |
2015年 | 21篇 |
2014年 | 26篇 |
2013年 | 50篇 |
2012年 | 25篇 |
2011年 | 61篇 |
2010年 | 32篇 |
2009年 | 48篇 |
2008年 | 40篇 |
2007年 | 43篇 |
2006年 | 47篇 |
2005年 | 30篇 |
2004年 | 36篇 |
2003年 | 34篇 |
2002年 | 38篇 |
2001年 | 35篇 |
2000年 | 27篇 |
1999年 | 19篇 |
1998年 | 18篇 |
1997年 | 15篇 |
1996年 | 17篇 |
1995年 | 15篇 |
1994年 | 17篇 |
1993年 | 14篇 |
1992年 | 9篇 |
1991年 | 17篇 |
1990年 | 12篇 |
1989年 | 8篇 |
1988年 | 13篇 |
1987年 | 11篇 |
1986年 | 6篇 |
1985年 | 21篇 |
1984年 | 18篇 |
1983年 | 11篇 |
1982年 | 10篇 |
1981年 | 10篇 |
1979年 | 15篇 |
1978年 | 6篇 |
1977年 | 7篇 |
1976年 | 5篇 |
1974年 | 5篇 |
1973年 | 5篇 |
1971年 | 5篇 |
1970年 | 4篇 |
排序方式: 共有1026条查询结果,搜索用时 15 毫秒
101.
102.
Yarrow Axford Camilla S. Andresen John T. Andrews Simon T. Belt Áslaug Geirsdóttir Guillaume Massé Gifford H. Miller Sædís Ólafsdóttir Lindsay L. Vare 《第四纪科学杂志》2011,26(6):645-656
Geochemical, mineralogical and biological indicators preserved in sediments are widely used to reconstruct past climate change, but proxies differ in the degree to which their utility as climate indicators has been validated via laboratory experiments, modern spatial calibrations, or down‐core comparisons with instrumental climate data. Multi‐proxy studies provide another means of evaluating interpretations of proxies. This paper presents a multi‐proxy assessment comparing 19 sub‐centennially resolved late Holocene proxy records, covering the period 300–1900 AD, from seven Icelandic marine and lacustrine core sites. We employ simple statistical comparisons between proxy reconstructions to evaluate their correlations over time and, ultimately, their utility as proxies for regional climate. Proxies examined include oxygen isotopic composition of benthic and planktonic foraminifera, abundance of the sea‐ice biomarker IP25, allochthonous quartz in marine sediments (a proxy for drift ice around Iceland), marine carbonate abundance, total organic carbon concentration, chironomid assemblages, lacustrine biogenic silica and carbon/nitrogen ratios in lake sediments. Most of the examined proxy records, including temperature and sea‐ice proxies, correlate strongly with each other over multi‐centennial timescales, and thus do appear to record changes in regional climate. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
103.
104.
105.
The development and transfer of clean energy technologies to achieve universal energy access is challenging due to the inherent complexities of the energy sector, and the energy governance and financial systems in developing economies. Innovation is an essential part of successfully addressing these difficulties. Duplicating the energy infrastructure models of developed countries will not be sufficient to meet the needs of poor consumers. To the extent that innovation can accelerate energy access, it is important to understand the specific types of innovations that are necessary and how they might be facilitated. The general features of existing international clean energy innovation systems, which are predominantly driven by the markets and emissions reduction mechanisms of developed and rapidly growing emerging economies, are reviewed and the alignment of these systems to the innovation processes required to extend energy access globally is evaluated. Drawing on the innovation policy literature, the attributes of effective international and domestic energy innovation systems that are pro-poor and the associated policy approaches are identified. 相似文献
106.
Pulkovo astrometric observations began in the 1840s using the Repsold transit instrument in the prime vertical and Ertel vertical
circle. The first observers on these instruments were W.I. Struve, 1840–1856, and Kh.I. Peters, 1842–1849. In the present
work, we collected and analyzed different series of latitude variations from observations made by M.O. Nuren, B. Wanach, A.A.
Ivanov, I.N. Bonsdorf, and A.Ya. Orlov. In addition, results are given of investigations of a specific behavior of the Chandler
polar motion in this interval, obtained by C. Chandler, Ivanov, Kh. Kimura, Orlov, and N. Sekiguchi. The aim of this paper
is to search for and analyze the earliest series of Pulkovo latitudes, in order to evaluate the possibility of their use to
study the motion of the pole at the maximum available range of observations. Different methods were used to isolate and analyze
the sum of Chandler and annual latitude variations. The annex provides a series of Pulkovo latitude variations for 1840–1848,
which may be used to extend latitude variation back to 1840. 相似文献
107.
Site assessment and monitoring data were analyzed for 26 stream restoration projects in North Carolina where the channel was
reconfigured. Post-project changes in channel capacity were highly variable from site to site, but more than 60% of the projects
underwent, on average at a given site, at least a 20% change in channel capacity. An analysis of site and basin geomorphology
revealed that large post-construction adjustments were associated with highly dynamic stream channels characterized by a combination
of high sediment transport capacity, large sediment supply, and/or easily eroded bank materials. In-stream structures along
dynamic, reconfigured channels also exhibited high incidences of damage. Thus, the design and construction of channels in
a state of equilibrium, which do not exhibit excessive erosion or deposition along highly dynamic rivers is currently problematic.
In light of these findings, a conceptual framework based on geomorphic parameters is put forth to assess the likelihood of
project success early in the design process to (1) eliminate high risk sites from consideration of channel reconfiguration
and (2) improve upon the implemented management strategies that are ultimately used. It is also argued that where space permits
an enhanced natural channel, adjustment approach is likely to be more effective than projects based on natural channel design. 相似文献
108.
Journal of Geographical Systems - The widespread availability of high spatial and temporal resolution public transit data is improving the measurement and analysis of public transit-based... 相似文献
109.
Avalanche and landslide simulation using the material point method: flow dynamics and force interaction with structures 总被引:3,自引:0,他引:3
Carter M. Mast Pedro Arduino Gregory R. Miller Peter Mackenzie-Helnwein 《Computational Geosciences》2014,18(5):817-830
In this paper, the material point method (MPM) is presented as a tool for simulating large deformation, gravity-driven landslides. The primary goal is to assess the interaction of these flow-like events with the built environment. This includes an evaluation of earthen mounds when energy dissipating devices are placed in the path of a snow avalanche. The effectiveness of the embankments is characterized using displacement, velocity, mass, and energy measures. A second example quantifies the force interaction between a landslide and a square rigid column. Multiple slide approach angles are considered, and various aspects of the impact force are discussed. 相似文献
110.
Mineral inclusions in fibrous diamonds: constraints on cratonic mantle refertilization and diamond formation 总被引:1,自引:0,他引:1
We analyzed mineral microinclusions in fibrous diamonds from the Wawa metaconglomerate (Superior craton) and Diavik kimberlites (Slave craton) and compared them with published compositions of large mineral inclusions in non-fibrous diamonds from these localities. The comparison, together with similar datasets available for Ekati and Koffiefontein kimberlites, suggest a general pattern of metasomatic alteration imposed on the ambient mantle by formation of fibrous diamond. Calcium and Fe enrichment of peridotitic garnet and pyroxenes and Fe enrichment of olivine associated with fibrous diamond-forming fluids contributes to refertilization of the cratonic mantle. Saline—carbonatitic—silicic fluid trapped by fibrous diamonds may represent one of the elusive agents of mantle refertilization. Calcium enrichment of peridotitic garnet and pyroxenes is expected in local mantle segments during fibrous diamond production, as Ca in the carbonatitic fluids is deposited into the surrounding mantle when oxidized carbon is reduced to diamond. Harzburgitic garnet evolves towards Ca-rich compositions even when it interacts with Ca-poor saline fluids. An unusual trend of Mg enrichment to Fo95–98 is observed in some olivine inclusions in Wawa fibrous diamonds. The trend may result from the carbonatitic composition of the fluid that promotes crystallization of magnesian olivine and preferentially oxidizes the fayalite component. We propose a generic model of fibrous and non-fibrous diamond formation from carbonatitic fluids that explains enrichment of the mantle in mafic magmaphile and incompatible elements and accounts for locally metasomatized compositions of diamond inclusions. 相似文献