全文获取类型
收费全文 | 441篇 |
免费 | 26篇 |
国内免费 | 13篇 |
专业分类
测绘学 | 11篇 |
大气科学 | 44篇 |
地球物理 | 125篇 |
地质学 | 145篇 |
海洋学 | 40篇 |
天文学 | 65篇 |
综合类 | 1篇 |
自然地理 | 49篇 |
出版年
2021年 | 15篇 |
2020年 | 11篇 |
2019年 | 6篇 |
2018年 | 13篇 |
2017年 | 18篇 |
2016年 | 19篇 |
2015年 | 14篇 |
2014年 | 15篇 |
2013年 | 27篇 |
2012年 | 15篇 |
2011年 | 17篇 |
2010年 | 14篇 |
2009年 | 21篇 |
2008年 | 21篇 |
2007年 | 21篇 |
2006年 | 17篇 |
2005年 | 22篇 |
2004年 | 13篇 |
2003年 | 17篇 |
2002年 | 16篇 |
2001年 | 8篇 |
2000年 | 22篇 |
1999年 | 6篇 |
1998年 | 9篇 |
1997年 | 6篇 |
1996年 | 4篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1991年 | 2篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1984年 | 5篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1974年 | 3篇 |
1972年 | 2篇 |
1969年 | 2篇 |
1899年 | 1篇 |
1897年 | 1篇 |
1895年 | 1篇 |
排序方式: 共有480条查询结果,搜索用时 15 毫秒
61.
R. A. L. Osborne 《Australian Journal of Earth Sciences》2019,66(6):767-778
In order of impact, the main anthropogenic threats to caves in eastern Australia are and have been for the European history of Australia: mining, inundation, vandalism, wear and tear, lampenflora, lint and dust, scientists and poorly informed decisions. Destruction of caves by natural processes is not a focus of this paper as it occurs over a geological time scale and there are few historical accounts of natural catastrophic cave failure. Saving and protecting caves are difficult due to the reliance and insistence on conservation by secrecy used by cavers and the organisations that represent them. Other issues that inhibit cave conservation are: limited public exposure, perceptions of land managers and farmers about caves, a shortage of research-based information on caves and difficulties with establishing the significance of a cave. Cave monitoring and the education of managers and cave guides are known to enhance the conservation of show caves. Actions that would help to save and conserve caves throughout Australia include: changes to planning legislation, establishment of a cave conservation organisation, introduction of specific cave protection legislation and the establishment of a Research Centre for Caves, Karst and Geoheritage. 相似文献
62.
63.
Maria Karbon Robert Heinkelmann Julian Mora-Diaz Minghui Xu Tobias Nilsson Harald Schuh 《Journal of Geodesy》2017,91(7):755-765
The radio sources within the most recent celestial reference frame (CRF) catalog ICRF2 are represented by a single, time-invariant coordinate pair. The datum sources were chosen mainly according to certain statistical properties of their position time series. Yet, such statistics are not applicable unconditionally, and also ambiguous. However, ignoring systematics in the source positions of the datum sources inevitably leads to a degradation of the quality of the frame and, therefore, also of the derived quantities such as the Earth orientation parameters. One possible approach to overcome these deficiencies is to extend the parametrization of the source positions, similarly to what is done for the station positions. We decided to use the multivariate adaptive regression splines algorithm to parametrize the source coordinates. It allows a great deal of automation, by combining recursive partitioning and spline fitting in an optimal way. The algorithm finds the ideal knot positions for the splines and, thus, the best number of polynomial pieces to fit the data autonomously. With that we can correct the ICRF2 a priori coordinates for our analysis and eliminate the systematics in the position estimates. This allows us to introduce also special handling sources into the datum definition, leading to on average 30 % more sources in the datum. We find that not only the CPO can be improved by more than 10 % due to the improved geometry, but also the station positions, especially in the early years of VLBI, can benefit greatly. 相似文献
64.
65.
Climate change adaptation of coffee production in space and time 总被引:1,自引:0,他引:1
Peter Läderach Julian Ramirez–Villegas Carlos Navarro-Racines Carlos Zelaya Armando Martinez–Valle Andy Jarvis 《Climatic change》2017,140(1):47-61
Savannas constitute the most fire-prone vegetation type on earth and are a significant source of greenhouse gas emissions. Most savanna fires are lit by people for a variety of livelihood applications. ‘Savanna burning’ is an accountable activity under the Kyoto Protocol, but only Australia, as a developed economy, accounts for emissions from this source in its national accounts. Over the past decade considerable effort has been given to developing savanna burning projects in northern Australia, combining customary indigenous (Aboriginal) approaches to landscape-scale fire management with development of scientifically robust emissions accounting methodologies. Formal acceptance by the Australian Government of that methodology, and its inclusion in Australia’s developing emissions trading scheme, paves the way for Aboriginal people to commercially benefit from savanna burning projects. The paper first describes this Australian experience, and then explores options for implementing community-based savanna burning emissions reduction projects in other continental savanna settings, specifically in Namibia and Venezuela. These latter examples illustrate that savanna fire management approaches potentially have broader application for contributing to livelihood opportunities in other fire-prone savanna regions. 相似文献
66.
Julian?WittmerEmail author Cornelius?ZetzschEmail author 《Journal of Atmospheric Chemistry》2017,74(2):187-204
The photochemical activation of chlorine by dissolved iron in artificial sea-salt aerosol droplets and by highly dispersed iron oxide (Fe2O3) aerosol particles (mainly hematite, specific surface ~150 m2 g?1) exposed to gaseous HCl, was investigated in humidified air in a Teflon simulation chamber. Employing the radical-clock technique, we quantified the production of gaseous atomic chlorine (Cl) from the irradiated aerosol. When the salt aerosol contained Fe2O3 at pH 6, no significant Cl production was observed, even if the dissolution of iron was forced by “weathering” (repeatedly freezing and thawing for five times). Adjusting the pH in the stock suspension to 2.6, 2.2, and 1.9 and equilibrating for one week resulted in a quantifiable amount of dissolved iron (0.03, 0.2, and 0.6 mmol L?1, respectively) and in gaseous Cl production rates of ~1.6, 6, and 8?×?1021 atoms cm?2 h?1, respectively. In a further series of experiments, the pure Fe2O3 aerosol was exposed to various levels of gaseous hydrogen chloride (HCl). The resulting Cl production rates ranged from 8?×?1020 Cl atoms cm?2 h?1 (at ~4 ppb HCl) to 5?×?1022 Cl atoms cm?2 h?1 (at ~350 ppb HCl) and confirmed the uptake and conversion of HCl to atomic Cl (at HCl to Cl conversion yields of 2–5 %, depending on the relative humidity). The Fe2O3 experiments indicate that iron-induced Cl formation may be important for highly soluble combustion-aerosol particles in marine environments in the presence of gaseous HCl. 相似文献
67.
Remote sensing and GIS based determination of groundwater dependent ecosystems in the Western Cape, South Africa 总被引:4,自引:0,他引:4
Finding the location of groundwater dependent ecosystems (GDEs) is important in determining the extent of restrictions that
need to be placed upon the abstraction of groundwater. Remote sensing was combined with geographical information system (GIS)
modelling to produce a GDE probability rating map for the Sandveld region, South Africa. Landsat TM imagery identified the
areas indicating the probable presence of GDEs and GIS assisted in their delineation. Three GIS models were generated: a GIS
model predicting landscape wetness potential (LWP model) based on terrain morphological features; the LWP model was modified
to highlight groundwater generated landscape wetness potential (the resulting GglWP model); and a groundwater elevation model
was interpolated, combining groundwater level measurements in boreholes in the region with digital elevation model data. Biomass
indicators generated from Landsat were classified and combined with the GIS models, followed by field verification of riverine
and wetland GDEs. The LWP model provided the most accurate results of the three models tested for GDEs in this region.
相似文献
Zahn MünchEmail: |
68.
Correlation-coefficient fields are widely used in short-term climate prediction research. The most frequently used significance test method for the correlation-coefficient field was proposed by Livezey, in which the number of significantcorrelation lattice(station) points on the correlation coherence map is used as the statistic. However, the method is based on two assumptions:(1) the spatial distribution of the lattice(station) points is uniform;and(2) there is no correlation between the physical quantities in the correlation-coefficient field. However, in reality, the above two assumptions are not valid.Therefore, we designed a more reasonable method for significance testing of the correlation-coefficient field. Specifically, a new statistic, the significant-correlation area, is introduced to eliminate the inhomogeneity of the grid(station)-point distribution, and an empirical Monte Carlo method is employed to eliminate the spatial correlation of the matrix.Subsequently, the new significance test was used for simultaneous correlation-coefficient fields between intensities of the atmospheric activity center in the Northern Hemisphere and temperature/precipitation in China. The results show that the new method is more reasonable than the Livezey method. 相似文献
69.
70.
Osborne Alfred R. Resio Donald T. Costa Andrea Ponce de León Sonia Chirivì Elisabetta 《Ocean Dynamics》2019,69(2):187-219
Ocean Dynamics - We analyze surface wave data taken in Currituck Sound, North Carolina, during a storm on 4 February 2002. Our focus is on the application of nonlinear Fourier analysis (NLFA)... 相似文献