全文获取类型
| 收费全文 | 330篇 |
| 免费 | 97篇 |
| 国内免费 | 42篇 |
专业分类
| 测绘学 | 3篇 |
| 地球物理 | 152篇 |
| 地质学 | 239篇 |
| 海洋学 | 7篇 |
| 天文学 | 2篇 |
| 综合类 | 14篇 |
| 自然地理 | 52篇 |
出版年
| 2024年 | 2篇 |
| 2023年 | 2篇 |
| 2022年 | 3篇 |
| 2021年 | 18篇 |
| 2020年 | 21篇 |
| 2019年 | 18篇 |
| 2018年 | 13篇 |
| 2017年 | 20篇 |
| 2016年 | 21篇 |
| 2015年 | 21篇 |
| 2014年 | 7篇 |
| 2013年 | 40篇 |
| 2012年 | 16篇 |
| 2011年 | 20篇 |
| 2010年 | 24篇 |
| 2009年 | 17篇 |
| 2008年 | 21篇 |
| 2007年 | 18篇 |
| 2006年 | 12篇 |
| 2005年 | 15篇 |
| 2004年 | 12篇 |
| 2003年 | 16篇 |
| 2002年 | 11篇 |
| 2001年 | 14篇 |
| 2000年 | 12篇 |
| 1999年 | 7篇 |
| 1998年 | 12篇 |
| 1997年 | 15篇 |
| 1996年 | 6篇 |
| 1995年 | 11篇 |
| 1994年 | 8篇 |
| 1993年 | 3篇 |
| 1992年 | 1篇 |
| 1991年 | 2篇 |
| 1990年 | 1篇 |
| 1989年 | 1篇 |
| 1988年 | 3篇 |
| 1986年 | 2篇 |
| 1985年 | 1篇 |
| 1979年 | 2篇 |
排序方式： 共有469条查询结果，搜索用时 500 毫秒
81.
Bimlesh Kumar 《水文科学杂志》2013,58(5):956-966
Abstract Bed material load, which comprises bed load and suspended load, has been extensively studied in the past few decades and many equations have been developed, but they differ from each other in derivation and form. If a process can be related to various flow conditions on a general basis, a proper understanding of bed material load movement can be ascertained. As the process is extremely complex, obtaining a deterministic or analytical form of it is too difficult. Neural network modelling, which is particularly useful in modelling processes about which knowledge of the physics is limited, is presented here as a complimentary tool for modelling bed material load transport. The developed model demonstrated a superior performance compared to other traditional methods based on different statistical criteria, such as the coefficient of determination, Nash-Sutcliffe coefficient and discrepancy ratio. The significance of the different input parameters has been analysed in the present work to understand the influence of these parameters on the transport process. Editor D. Koutsoyiannis Citation Kumar, B., 2012. Neural network prediction of bed material load transport. Hydrological Sciences Journal, 57 (5), 956–966. 相似文献
82.
ABSTRACTFloodplains are composed of complex depositional patterns of ancient and recent stream sediments, and research is needed to address the manner in which coarse floodplain materials affect stream–groundwater exchange patterns. Efforts to understand the heterogeneity of aquifers have utilized numerous techniques typically focused on point-scale measurements; however, in highly heterogeneous settings, the ability to model heterogeneity is dependent on the data density and spatial distribution. The objective of this research was to investigate the correlation between broad-scale methodologies for detecting heterogeneity and the observed spatial variability in stream/groundwater interactions of gravel-dominated alluvial floodplains. More specifically, this study examined the correlation between electrical resistivity (ER) and alluvial groundwater patterns during a flood event at a site on Barren Fork Creek, in the Ozark ecoregion of Oklahoma, USA, where chert gravels were common both as streambed and as floodplain material. Water table elevations from groundwater monitoring wells for a flood event on 1–5 May 2009 were compared to ER maps at various elevations. Areas with high ER matched areas with lower water table slope at the same elevation. This research demonstrated that ER approaches were capable of indicating heterogeneity in surface water–groundwater interactions, and that these heterogeneities were present even in an aquifer matrix characterized as highly conductive. Portions of gravel-dominated floodplain vadose zones characterized by high hydraulic conductivity features can result in heterogeneous flow patterns when the vadose zone of alluvial floodplains activates during storm events.
EDITOR D. Koutsoyiannis; ASSOCIATE EDITOR X. Chen 相似文献
83.
AbstractLittle is known about the salt intrusion behaviour in Malaysian estuaries. Study of salt intrusion generally requires large amounts of data, especially if 2-D or 3-D numerical models are used; thus, in data-poor environments, 1-D analytical models are more appropriate. A fully analytical 1-D salt intrusion model, which is simple to implement and requires minimal data, was tested in six previously unsurveyed Malaysian estuaries (Kurau, Perak, Bernam, Selangor, Muar and Endau). The required data can be collected during a single day of observations. Site measurements were conducted during the dry season (June–August 2012 and February–March 2013) near spring tide. Data on cross-sections (by echo-sounding), water levels (by pressure loggers) and salinity (by moving boat) were collected as model input. A good fit was demonstrated between the simulated and observed salinity distribution for all six estuaries. Additionally, the two calibration parameters (the Van der Burgh coefficient and the boundary condition for the dispersion) were compared with the existing predictive equations. Since gauging stations were only present in some nested catchments in the drainage basins, the river discharge had to be up-scaled to represent the total discharge contribution of the catchments. However, the correspondence between the calibration coefficients and the predictive equations was good, particularly in view of the uncertainty in the river discharge data used. This confirms that the predictive salt intrusion model is valid for the cases studied in Malaysia. The model provides a reliable, predictive tool, which the water authority of Malaysia can use for making decisions on water abstraction or dredging.
Editor D. Koutsoyiannis; Associate editor A. Fiori 相似文献
84.
William T. Corcoran 《自然地理学》2013,34(2):148-159
The climatic causes of the major forest/grassland ecotone in the south central United States (Kansas, Missouri, Oklahoma, Texas) are still poorly understood. Grassland and forest vegetation types differ markedly in their ability to withstand water stress induced by vapor pressure deficit (VPD), the difference between saturation vapor pressure and actual vapor pressure in the atmosphere. VPD is an airmass characteristic induced by ambient temperatures higher than dewpoint temperature. Mean summer airmass movement is from the Gulf of Mexico onto the continent in the central states area, but mean VPD displays a strong gradient approximately parallel to the ecotone. A subset of days having the strongest VPD gradients across the ecotone also had a 500 mb pressure height pattern identical to the long-term mean (modal) pattern. This 500 mb pattern, with a ridge over the Rocky Mountains and a trough over the Great Lakes, induces subsidence, stability, warming, and high VPD in Great Plains airmasses. Farther east, away from the zone of maximum subsidence, VPD is much lower. The grassland region coincides with the area of highest VPD. Because of the importance of the daily configuration of mid-tropospheric windflow patterns in controlling the distribution of VPD, moisture, and precipitation, more frequent occurrence of the modal 500 mb pattern is one mechanism for the occurrence of drought. 相似文献
85.
86.
通过样品采集和室内分析,研究了成都平原区土壤中Cd高含量区的区域分布特征和第四纪分布的空间响应关联。在绵远河、石亭江流域冲积物中存在Cd含量高值区。在同一流域Ⅰ、Ⅱ级阶地→Ⅲ级阶地→Ⅳ级或Ⅴ级阶地冲积物中Cd含量逐渐降低。发育于龙门山的河流(绵远河、石亭江)沉积物Cd含量显著高于其他水系沉积物。Cd高含量分布区与不同级次的阶地相吻合的特征表明其控制因素显著,属于地质作用的产物。这一结论与多数研究者认为的人为因素引起的具有根本区别。 相似文献
87.
浊水溪冲积扇为台湾目前最严重的地层下陷区,已设置包括DInSAR、GPS、水准测量、磁环分层式监测井与地下水位井等多元监测系统。大范围监测地层下陷方法中的水准测量有取样性不足之缺点,而DInSAR也易受相位不相关与大气误差影响而致精度降低。本研究利用2006~2008年期间共20幅ENVISAT卫星影像,搭配PSI技术,有效降低DInSAR的误差影响,同时获得107.6像素/km2的取样密度,弥补了水准测量取样密度仅0.2个/km2的取样性不足,透过295个监测点交叉验证,PSI与水准测量的成果显示两者的均方根误差为0.6cm。本研究亦发展了资料融合方法,有效结合水准测量与PSI成果,实验结果显示融合后的成果更能精确展现下陷的范围与下陷中心的变化,同时该成果与水准测量之均方根误差降至0.4cm。 相似文献
88.
平面SV波在层状半空间中沉积谷地周围的散射 总被引：2，自引：0，他引：2
采用间接边界元方法求解了入射平面SV波在层状半空间中沉积谷地周围的散射问题.问题的解答包含自由场和散射场两部分.自由场可由直接刚度法求得,散射场由层状半空间中斜线荷载动力格林函数来模拟.文中以入射平面SV波在基岩上单一土层中沉积谷地周围散射为例研究了土层和沉积谷地周围的影响.结果表明,由于考虑了土层的动力特性,平面SV... 相似文献
89.
90.
Research on colluvial depositional systems has recently emphasized periglacial and high‐altitude settings, and the relations between Quaternary slope stratigraphy and climate change. This article examines the role of variable slope morphology, surface hydrology and microclimate in controlling colluvial sedimentation along a coastal tract of the hyperarid Atacama Desert in northern Chile. Direct accessibility of active surfaces is accompanied by uninterrupted stratigraphic exposures along the base of slopes, allowing direct comparisons between surface processes and the resulting sedimentary record. Four slope sectors are identified, based on differences in morphology and processes over active surfaces. Colluvial sedimentation is controlled by complex interactions of slope gradients and profiles, exposure to dominant winds, and potential runoff pathways, which vary considerably between different sectors. Major differences are evident between these hyperarid deposits and slope sedimentation in periglacial and temperate settings, including the complete absence of pedogenic activity and clay minerals; the volume of aeolian deposits and their role in controlling processes which redistribute sediment downslope, extending colluvial aprons; and the occurrence of runoff processes only where favoured by particular topographic configurations. Depositional surfaces range from steep talus cones, to debris‐flow‐dominated and aeolian‐dominated colluvial aprons, to an aeolian ramp subject to reworking by mass flows and flash floods. Consequently, facies associations and architectures at outcrop are highly variable and highlight the importance of spatial variations in slope morphology and processes in producing distinct, coeval colluvial stratigraphies within a single environmental context. Discrepancies between active processes and the corresponding stratigraphic signatures are also evident in some sectors; for example, preservation of alluvial and aeolian facies in stratigraphic sections does not always reflect the dominant processes over active slopes. Together with the spatial variability in processes and deposits along these slopes, this suggests that caution is required when extracting palaeoenvironmental information from analyses of colluvial successions. 相似文献