全文获取类型
收费全文 | 136篇 |
免费 | 7篇 |
专业分类
测绘学 | 5篇 |
大气科学 | 21篇 |
地球物理 | 32篇 |
地质学 | 41篇 |
海洋学 | 7篇 |
天文学 | 28篇 |
自然地理 | 9篇 |
出版年
2021年 | 6篇 |
2020年 | 1篇 |
2019年 | 3篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2016年 | 11篇 |
2015年 | 11篇 |
2014年 | 5篇 |
2013年 | 10篇 |
2012年 | 3篇 |
2011年 | 9篇 |
2010年 | 9篇 |
2009年 | 8篇 |
2008年 | 8篇 |
2007年 | 4篇 |
2006年 | 9篇 |
2005年 | 3篇 |
2004年 | 6篇 |
2003年 | 6篇 |
2002年 | 4篇 |
2001年 | 3篇 |
2000年 | 5篇 |
1999年 | 5篇 |
1998年 | 2篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1984年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有143条查询结果,搜索用时 15 毫秒
71.
72.
The influence of leaf litter diversity and soil fauna on initial soil erosion in subtropical forests 总被引:4,自引:0,他引:4 下载免费PDF全文
Steffen Seitz Philipp Goebes Pascale Zumstein Thorsten Assmann Peter Kühn Pascal A. Niklaus Andreas Schuldt Thomas Scholten 《地球表面变化过程与地形》2015,40(11):1439-1447
Although the protective role of leaf litter cover against soil erosion is known for a long time, little research has been conducted on the processes involved. Moreover, the impact of soil meso‐ and macrofauna within the litter layer on erosion control is not clear. To investigate how leaf litter cover and diversity as well as meso‐ and macrofauna influence sediment discharge in subtropical forest ecosystems, a field experiment has been carried out in Southeast China. A full‐factorial random design with 96 micro‐scale runoff plots and 7 domestic leaf species was established and erosion was triggered by a rainfall simulator. Our results demonstrate that leaf litter cover protects soil from erosion (?82 % sediment discharge on leaf covered plots) by rainfall and this protection is removed as litter decomposes. The protective effect is influenced by the presence or absence of soil meso‐ and macrofauna. Fauna presence increases soil erosion rates significantly by 58 %, while leaf species diversity shows a non‐significant negative trend. We assume that the faunal effect arises from arthropods slackening and processing the soil surface as well as fragmenting and decomposing the protecting leaf litter covers. Even though the diversity level did not show a significant influence, single leaf species in monocultures show rather different impacts on sediment discharge and thus, erosion control. In our experiment, runoff plots with leaf litter from Machilus thunbergii showed the highest sediment discharge (68.0 g m?2) whereas plots with Cyclobalanopsis glauca showed the smallest rates (7.9 g m?2). Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
73.
We have used GLONASS P-code measurements from different geodetic GPS/GLONASS receivers involved in the IGEX campaign to perform
frequency/time transfer between remote clocks. GLONASS time transfer is commonly based on the clock differences between GLONASS
system time and the local clock computed by a time transfer receiver. We choose to analyze the raw P-code data available in
the RINEX files. This also allows working with the data from geodetic receivers involved in the IGEX campaign. As a first
point, we show that the handling of the external frequency in some of the IGEX receivers is not suited for time transfer applications.
We also point out that the GLONASS broadcast ephemerides give rise to a considerable number of outliers in the time transfer,
compared to the precise IGEX ephemerides. Due to receiver clock resets at day boundaries, which is a characteristic of the
R100 receivers from 3S-Navigation, continuous data sets exceeding one day are not available. Invthis context, it is therefore
impossible to perform RINEX-based precise frequency transfer with GLONASS P-codes on a time scale longer than one day. Because
the frequencies used by GLONASS satellites are different, the time transfer results must be corrected for the different receiver
hardware delays. After this correction, the final precision of our time transfer results corresponds to a root-mean-square
(rms) of 1.8 nanoseconds (ns) (maximum difference of 11.8 ns) compared to a rms of about 4.4 ns (maximum difference of 31.9
ns) for time transfer based on GPS C/A code observations. ? 2001 John Wiley & Sons, Inc. 相似文献
74.
Jeffrey L Bada Mark A Sephton Pascale Ehrenfreund Richard A Mathies Allison M Skelley Frank J Grunthaner Aaron P Zent Richard C Quinn Jean-Luc Josset François Robert Oliver Botta Daniel P Glavin 《Astronomy& Geophysics》2005,46(6):6.26-6.27
If we are to find unequivocal evidence for life on Mars, we will need new ways to search for it. Jeff L Bada and the MOD team describe the innovative strategy developed for the ExoMars mission. 相似文献
75.
Dawsonite synthesis and reevaluation of its thermodynamic properties from solubility measurements: Implications for mineral trapping of CO2 总被引:1,自引:0,他引:1
Pascale Bénézeth Donald A. Palmer Juske Horita 《Geochimica et cosmochimica acta》2007,71(18):4438-4455
Over the last decade, a significant research effort has focused on determining the feasibility of sequestering large amounts of CO2 in deep, permeable geologic formations to reduce carbon dioxide emissions to the atmosphere. Most models indicate that injection of CO2 into deep sedimentary formations will lead to the formation of various carbonate minerals, including the common phases calcite (CaCO3), dolomite (CaMg(CO3)2), magnesite (MgCO3), siderite (FeCO3), as well as the far less common mineral, dawsonite (NaAlCO3(OH)2). Nevertheless, the equilibrium and kinetics that control the precipitation of stable carbonate minerals are poorly understood and few experiments have been performed to validate computer codes that model CO2 sequestration.In order to reduce this uncertainty we measured the solubility of synthetic dawsonite according to the equilibrium: , from under- and oversaturated solutions at 50-200 °C in basic media at 1.0 mol · kg−1 NaCl. The solubility products (Qs) obtained were extrapolated to infinite dilution to obtain the solubility constants (. Combining the fit of these values and fixing at 25 °C, which was derived from the calorimetric data of Ferrante et al. [Ferrante, M.J., Stuve, J.M., and Richardson, D.W., 1976. Thermodynamic data for synthetic dawsonite. U.S. Bureau of Mines Report Investigation, 8129, Washington, D.C., 13p.], the following thermodynamic parameters for the dissolution of dawsonite were calculated at 25 °C: , and . Subsequently, we were able to derive values for the Gibbs energy of formation (, enthalpy of formation ( and entropy ( of dawsonite. These results are within the combined experimental uncertainties of the values reported by Ferrante et al. (1976). Predominance diagrams are presented for the dawsonite/boehmite and dawsonite/bayerite equilibria at 100 °C in the presence of a saline solution with and without silica-containing minerals. 相似文献
76.
77.
Improving the resilience of existing built assets to earthquake induced liquefaction disaster events
Jones Keith G. Morga Mariantonietta Wanigarathna Nadeeshani Pascale Federica Meslem Abdelghani 《Bulletin of Earthquake Engineering》2021,19(10):4145-4169
Bulletin of Earthquake Engineering - LIQUEFACT was a EU H2020 funded project to investigate earthquake induced liquefaction potential across Europe and develop a series of tools to understand... 相似文献
78.
Noam Shani Vasantha Aravinthan Pierre Rossi Guillaume Laulan Pascale Ducommun Christof Holliger 《Ground Water Monitoring & Remediation》2013,33(2):31-37
Groundwater microbial community samples are traditionally collected using pumping techniques optimized for groundwater chemistry assessment, although the impact of groundwater pumping parameters on apparent bacterial community structures (BCSs) is not really known. We therefore studied the impact of pumping lift, flow regime, and tubing material on BCS, which were analyzed by terminal‐restriction fragment length polymorphism (T‐RFLP). Ruzicka dissimilarity coefficients were calculated between T‐RFLP profiles to assess disparities between BCS. Variations in pumping lift, flow regime, and tubing material did not affect the apparent BCS in experiments using a homogenous water system under laboratory conditions showing that the conditions within the tube had no detectable effect on BCS. However, pumping groundwater from aquifer monitoring wells at different flow rates in the field revealed a significant impact on the apparent BCS. Water samples collected from fine sediment were the most affected by the pumping flow rate. 相似文献
79.
Masa Kageyama Pascale Braconnot Laurent Bopp Véronique Mariotti Tilla Roy Marie-Noëlle Woillez Arnaud Caubel Marie-Alice Foujols Eric Guilyardi Myriam Khodri James Lloyd Fabien Lombard Olivier Marti 《Climate Dynamics》2013,40(9-10):2469-2495
The climates of the mid-Holocene (MH, 6,000 years ago) and the Last Glacial Maximum (LGM, 21,000 years ago) have been extensively documented and as such, have become targets for the evaluation of climate models for climate contexts very different from the present. In Part 1 of the present work, we have studied the MH and LGM simulations performed with the last two versions of the IPSL model: IPSL_CM4, run for the PMIP2/CMIP3 (Coupled Model Intercomparion Project) projects and IPSL_CM5A, run for the most recent PMIP3/CMIP5 projets. We have shown that not only are these models different in their simulations of the PI climate, but also in their simulations of the climatic anomalies for the MH and LGM. In the Part 2 of this paper, we first examine whether palaeo-data can help discriminate between the model performances. This is indeed the case for the African monsoon for the MH or for North America south of the Laurentide ice sheet, the South Atlantic or the southern Indian ocean for the LGM. For the LGM, off-line vegetation modelling appears to offer good opportunities to distinguish climate model results because glacial vegetation proves to be very sensitive to even small differences in LGM climate. For other cases such as the LGM North Atlantic or the LGM equatorial Pacific, the large uncertainty on the SST reconstructions, prevents model discrimination. We have examined the use of other proxy-data for model evaluation, which has become possible with the inclusion of the biogeochemistry morel PISCES in the IPSL_CM5A model. We show a broad agreement of the LGM–PI export production changes with reconstructions. These changes are related to the mixed layer depth in most regions and to sea-ice variations in the high latitudes. We have also modelled foraminifer abundances with the FORAMCLIM model and shown that the changes in foraminifer abundance in the equatorial Pacific are mainly forced by changes in SSTs, hence confirming the SST-foraminifer abundance relationship. Yet, this is not the case in all regions in the North Atlantic, where food availability can have a strong impact of foraminifer abundances. Further work will be needed to exhaustively examine the role of factors other than climate in piloting changes in palaeo-indicators. 相似文献
80.
Pascale M. Biron Antoine Richer Alistair D. Kirkbride Andr G. Roy Sangsoo Han 《地球表面变化过程与地形》2002,27(9):913-928
Understanding flow structures in river confluences has largely been the product of interpretations made from measured flow velocity data. Here, we turn the attention to the investigation of the patterns of both the average and standard deviations of the micro‐topography of the water surface at an asymmetrical natural discordant confluence for different flow conditions. Water surface topography is measured using a total station to survey the position of a reflector mounted on a custom‐built raft. To limit error problems related to changes in the water level, measurements are taken and analysed by cross‐stream transects where five water surface profiles are taken before moving to the next transect. Three‐dimensional numerical simulations of the flow dynamics at the field site are used to examine predicted water surface topography for a steady‐state situation. The patterns are interpreted with respect to flow structure dynamics, visual observations of boils, and bed topography. Results indicate that coherent patterns emerge at the water surface of a discordant bed confluence for different flow conditions. The zone of stagnation and the mixing layer are characterized by super‐elevation, a lateral tilt is present at the edge of the mixing layer, and a zone of super‐elevation is present on the tributary side at the downstream junction corner. The latter seems associated with periodical upwelling and is not present in the numerical simulations that do not take into account instantaneous velocity fluctuations. Planform curvature, topographic steering related to the tributary mouth bar, and turbulent structures associated with the mixing layer all play a key role in the pattern of both the average and standard deviation of the water surface topography at confluences. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献