全文获取类型
收费全文 | 1616篇 |
免费 | 101篇 |
国内免费 | 31篇 |
专业分类
测绘学 | 38篇 |
大气科学 | 190篇 |
地球物理 | 405篇 |
地质学 | 562篇 |
海洋学 | 117篇 |
天文学 | 281篇 |
综合类 | 4篇 |
自然地理 | 151篇 |
出版年
2024年 | 4篇 |
2023年 | 6篇 |
2022年 | 14篇 |
2021年 | 39篇 |
2020年 | 45篇 |
2019年 | 43篇 |
2018年 | 81篇 |
2017年 | 65篇 |
2016年 | 77篇 |
2015年 | 54篇 |
2014年 | 74篇 |
2013年 | 122篇 |
2012年 | 86篇 |
2011年 | 106篇 |
2010年 | 62篇 |
2009年 | 119篇 |
2008年 | 103篇 |
2007年 | 106篇 |
2006年 | 77篇 |
2005年 | 63篇 |
2004年 | 56篇 |
2003年 | 55篇 |
2002年 | 44篇 |
2001年 | 25篇 |
2000年 | 22篇 |
1999年 | 18篇 |
1998年 | 20篇 |
1997年 | 10篇 |
1996年 | 16篇 |
1995年 | 8篇 |
1994年 | 10篇 |
1993年 | 10篇 |
1992年 | 7篇 |
1991年 | 8篇 |
1989年 | 5篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 11篇 |
1978年 | 6篇 |
1977年 | 6篇 |
1975年 | 3篇 |
1973年 | 3篇 |
1972年 | 2篇 |
排序方式: 共有1748条查询结果,搜索用时 878 毫秒
231.
Social scientists and science communicators are concerned about the apparent discrepancy between the scientific consensus on climate change (Anderegg et al. Proc Natl Acad Sci 107:12107–12109, 2010; Doran and Zimmerman EOS Trans Am Geophys Union 90:22–3, 2009) and the general public’s views (Knight Environ Sociol 2:101–113, 2016; Lee et al. Nat Clim Chang 5:1014–1020, 2015). It is reasoned that increased public awareness and perceived threat of climate change may pressure governments to enact policy to counteract climate change (e.g. setting stringent carbon emissions targets). Despite a logical link between public awareness and government-set emissions targets, this relationship remains untested. We examined the relationship between public awareness about and perceived threat of climate change and governmental emissions targets across 71 countries and 1 region. We found a positive association between the proportions of a country’s population that are aware of climate change and the unconditional emissions reduction targets set by that country in the Paris Agreement (Rogelj et al. Nature 534:631–639, 2016). However, the proportion of people in a country who perceive climate change as a personal threat was not associated with higher emissions reduction targets. Our results suggest that public awareness may be an important part of garnering the public support required for policies designed to mitigate climate change to succeed. 相似文献
232.
233.
Sophie GODIN-BEEKMANN Irina PETROPAVLOSKIKH Stefan REIS Paul NEWMAN Wolfgang STEINBRECHT Markus REX Michelle L. SANTEE Richard S. ECKMAN Xiangdong ZHENG Matthew B. TULLY David S. STEVENSON Paul YOUNG John PYLE Mark WEBER Johanna TAMMINEN Gina MILLS Alkis F. BAIS Clare HEAVISIDE Christos ZEREFOS 《大气科学进展》2017,34(3):283-288
<正>1.Overview The 2016 Quadrennial Ozone Symposium(QOS-2016)was held on 4–9 September 2016 in Edinburgh,UK.The Symposium was organized by the International Ozone Commission(IO3C),the NERC Centre for EcologyHydrology and the University of Edinburgh,and was co-sponsored by the International Union of Geodesy and Geophysics,the International Association of Meteorology and Atmospheric 相似文献
234.
235.
Harvey Karen L. Jones Harrison P. Schrijver Carolus J. Penn Matthew J. 《Solar physics》1999,190(1-2):35-44
Simultaneous measurements of the magnetic fields in the photosphere and chromosphere were used to investigate if magnetic
flux is submerging at sites between adjacent opposite polarity magnetic network elements in which the flux is observed to
decrease or `cancel'. These data were compared with chromospheric and coronal intensity images to establish the timing of
the emission structures associated with these magnetic structures as a function of height. We found that most of the cancelation
sites show either that the bipole is observed longer in the photosphere than in the chromosphere and corona (44%) or that
the timing difference of the disappearance of the bipole between these levels of the atmosphere is unresolved. The magnetic
axis lengths of the structures associated with the cancelation sites are on average slightly smaller in the chromosphere than
the photosphere. These observations suggest that magnetic flux is retracting below the surface for most, if not all, of the
cancelation sites studied. 相似文献
236.
David H.BROMWICH Matthew A.LAZZARA Arthur M.CAYETTE Jordan G.POWERS Kirstin WERNER John J.CASSANO Steven R.COLWELL Scott CARPENTIER Xun ZOU 《大气科学进展》2022,39(3):536-542
1. Overview In June 2021, the 16th Workshop on Antarctic Meteorology and Climate (WAMC) and the 6th Year of Polar Prediction in the Southern Hemisphere (YOPP-SH) Meeting (http://polarmet.osu.edu/WAMC;021/) were held online and hosted by the Polar Meteorology Group at Byrd Polar and Climate Research Center, The Ohio State University, Columbus,Ohio (Fig. 1). 相似文献
237.
Aristides?MoustakasEmail author Matthew?R.?Evans 《Stochastic Environmental Research and Risk Assessment (SERRA)》2017,31(2):315-328
Bovine tuberculosis (TB) poses a serious threat for agricultural industry in several countries, it involves potential interactions between wildlife and cattle and creates societal problems in terms of human-wildlife conflict. This study addresses connectedness network analysis, the spatial, and temporal dynamics of TB between cattle in farms and the European badger (Meles meles) using a large dataset generated by a calibrated agent based model. Results showed that infected network connectedness was lower in badgers than in cattle. The contribution of an infected individual to the mean distance of disease spread over time was considerably lower for badger than cattle; badgers mainly spread the disease locally while cattle infected both locally and across longer distances. The majority of badger-induced infections occurred when individual badgers leave their home sett, and this was positively correlated with badger population growth rates. Point pattern analysis indicated aggregation in the spatial pattern of TB prevalence in badger setts across all scales. The spatial distribution of farms that were not TB free was aggregated at different scales than the spatial distribution of infected badgers and became random at larger scales. The spatial cross correlation between infected badger setts and infected farms revealed that generally infected setts and farms do not coexist except at few scales. Temporal autocorrelation detected a two year infection cycle for badgers, while there was both within the year and longer cycles for infected cattle. Temporal cross correlation indicated that infection cycles in badgers and cattle are negatively correlated. The implications of these results for understanding the dynamics of the disease are discussed. 相似文献
238.
Hierarchically nested river landform sequences. Part 2: Bankfull channel morphodynamics governed by valley nesting structure
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)
Gregory B. Pasternack Dastagir Baig Matthew D. Weber Rocko A. Brown 《地球表面变化过程与地形》2018,43(12):2519-2532
River corridors exhibit landforms nested within landforms repeatedly down spatial scales. In Pasternack et al. ( 2018 ), a new, scale‐independent, hierarchical river classification was developed that uses five landform types to map the domains of a single fluvial process – flow convergence routing – at each of three–five spatial scales. Given those methods, this study investigated the details of how flow convergence routing organizes nested landform sequences. The method involved analyzing landform abundance, sequencing, and hierarchical nesting along the 35 km gravel/cobble lower Yuba River in California. Independent testing of flow convergence routing found that hydraulic patterns at every flow matched the essential predictions from classification, substantiating the process–morphology link. River width and bed elevation sequences exhibit large, nonrandom, and linked oscillations structured to preferentially yield wide bars and constricted pools at base flow and bankfull flow. At a flow of 8.44 times bankfull, there is still an abundance of wide bar and constricted pool landforms, but larger topographic drivers also yield an abundance of nozzle and oversized landforms. The nested structure of flow convergence routing landforms reveals that base flow and bankfull landforms are nested together within specific floodprone valley landform types, and these landform types control channel morphodynamics during moderate to large floods. As a result, this study calls into question the prevailing theory that the bankfull channel of a gravel/cobble river is controlled by in‐channel, bankfull, and/or small flood flows. Such flows may initiate sediment transport, but they are too small to control landform organization in a gravel/cobble river with topographic complexity. Copyright © 2018 John Wiley & Sons, Ltd. 相似文献
239.
Theoretical studies of glacial outburst floods (jökulhlaups) assume that: (i) intraglacial floodwater is transported efficiently in isolated conduits; (ii) intraglacial conduit enlargement operates proportionally to increasing discharge; (iii) floodwater exits glaciers through pre‐existing ice‐marginal outlets; and (iv) the morphology and positioning of outlets remains fixed during flooding. Direct field observations, together with historical jökulhlaup accounts, confirm that these theoretical assumptions are not always correct. This paper presents new evidence for spatial and temporal changes in intraglacial floodwater routing during jökulhlaups; secondly, it identifies and explains the mechanisms controlling the position and morphology of supraglacial jökulhlaup outlets; and finally, it presents a conceptual model of the controls on supraglacial outbursts. Field observations are presented from two Icelandic glaciers, Skeiðarárjökull and Sólheimajökull. Video footage and aerial photographs, taken before, during and after the Skeiðarárjökull jökulhlaup and immediately after the Sólheimajökull jökulhlaup, reveal changes in floodwater routing and the positioning and morphology of outlets. Field observations confirm that glaciers cannot transmit floodwater as efficiently as previously assumed. Rapid increases in jökulhlaup discharge generate basal hydraulic pressures in excess of ice overburden. Under these circumstances, floodwater can be forced through the surface of glaciers, leading to the development of a range of supraglacial outlets. The rate of increase in hydraulic pressure strongly influences the type of supraglacial outlet that can develop. Steady increases in basal hydraulic pressure can retro‐feed pre‐existing englacial drainage, whereas transient increases in pressure can generate hydraulic fracturing. The position and morphology of supraglacial outlets provide important controls on the spatial and temporal impact of flooding. The development of supraglacial jökulhlaup outlets provides a new mechanism for rapid englacial debris entrainment. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
240.
Rill development studies have focused almost exclusively on surface erosion processes and critical threshold hydraulic conditions. Characteristic rill features, such as arcuate headcuts and knickpoints, are morphologically similar to the ‘theatre-headed’ valleys which have been associated with ‘sapping’ processes at various scales. This paper reports on laboratory experiments designed to identify linkages between surface flow hydraulics, subsurface moisture conditions and rill development. Experiments were carried out in a 16·57 m2 flume under simulated rainfall with soil samples up to 0·15 m depth in which moisture conditions were monitored by miniature time-domain reflectometer probes. Tests showed complex responses in which some rill incision reflected surface flow conditions, but major rill system development with markedly enhanced sediment yield was closely associated with high soil moisture contents. It was not possible to measure seepage forces directly, but calculation and observation indicate that these were less important than reduction in soil strength with saturation, which resulted in increased effective runoff erosivity. This caused concentrated undercutting along the water table at rill walls, while slightly stronger surface layers above the water table formed microscarps. These retreated along the water table into interrill surfaces, producing residual pediment transport slopes. The microscarps eventually disappeared when the water table reached the surface, eliminating differential soil strength. The experiments showed complex relationships between surface and subsurface erosional processes in evolving rill systems, strongly influenced by soil moisture dynamics. The very small topographic and hydraulic head amplitudes indicate that seepage forces and ‘sapping’ were minimal. The dominant effect of soil moisture was reduction of soil strength with saturation, and increased runoff entrainment. Experimental conditions were not unusual, either for agricultural fields or natural hillslopes, and the intricate interrelationship of surface and subsurface erosion processes observed is probably not uncommon. Attempts to link specific morphologic features at rill scale to dominance of surface or subsurface processes alone are therefore unlikely to be successful or reliable. © 1998 John Wiley & Sons, Ltd. 相似文献