全文获取类型
收费全文 | 1401篇 |
免费 | 273篇 |
国内免费 | 89篇 |
专业分类
测绘学 | 33篇 |
大气科学 | 2篇 |
地球物理 | 532篇 |
地质学 | 641篇 |
海洋学 | 117篇 |
天文学 | 10篇 |
综合类 | 36篇 |
自然地理 | 392篇 |
出版年
2024年 | 4篇 |
2023年 | 5篇 |
2022年 | 20篇 |
2021年 | 62篇 |
2020年 | 69篇 |
2019年 | 75篇 |
2018年 | 60篇 |
2017年 | 75篇 |
2016年 | 66篇 |
2015年 | 66篇 |
2014年 | 76篇 |
2013年 | 154篇 |
2012年 | 63篇 |
2011年 | 69篇 |
2010年 | 51篇 |
2009年 | 97篇 |
2008年 | 81篇 |
2007年 | 66篇 |
2006年 | 71篇 |
2005年 | 64篇 |
2004年 | 60篇 |
2003年 | 34篇 |
2002年 | 46篇 |
2001年 | 36篇 |
2000年 | 46篇 |
1999年 | 30篇 |
1998年 | 28篇 |
1997年 | 33篇 |
1996年 | 24篇 |
1995年 | 23篇 |
1994年 | 11篇 |
1993年 | 12篇 |
1992年 | 8篇 |
1991年 | 10篇 |
1990年 | 8篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1986年 | 11篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1975年 | 1篇 |
排序方式: 共有1763条查询结果,搜索用时 15 毫秒
71.
《水文科学杂志》2013,58(2)
Abstract Abstract The MASONW (MACRO + SOILN + Watershed) model describing nitrogen leaching in watersheds was developed and tested. The model is based on the MACRO and SOILN models. The dual-porosity model MACRO simulates water flow on the field scale. The SOILN model describes turnover and leaching of nitrogen. Two main features of a watershed have been added into these two models: (a) the existence of a river system, and (b) variable thickness of the aeration zone within a watershed. Good agreement between the output of the MASONW model and observed data for water discharge and nitrate concentrations were achieved in the Odense watershed (496 km2) in Denmark. 相似文献
72.
《水文科学杂志》2013,58(5)
Abstract Results of a study on change detection in hydrological time series of annual maximum river flow are presented. Out of more than a thousand long time series made available by the Global Runoff Data Centre (GRDC) in Koblenz, Germany, a worldwide data set consisting of 195 long series of daily mean flow records was selected, based on such criteria as length of series, currency, lack of gaps and missing values, adequate geographical distribution, and priority to smaller catchments. The analysis of annual maximum flows does not support the hypothesis of ubiquitous growth of high flows. Although 27 cases of strong, statistically significant increase were identified by the Mann-Kendall test, there are 31 decreases as well, and most (137) time series do not show any significant changes (at the 10% level). Caution is advised in interpreting these results as flooding is a complex phenomenon, caused by a number of factors that can be associated with local, regional, and hemispheric climatic processes. Moreover, river flow has strong natural variability and exhibits long-term persistence which can confound the results of trend and significance tests. 相似文献
73.
Desert pavements (DPs) are critical for maintaining ecological stability and promoting near-surface hydrological cycling in arid regions. However, few studies have focused on eco-hydrological processes of DPs in the ecological systems of fluvial fans. Although DP surfaces appear to be barren and flat, we found that the surfaces are characterized by surface mosaic patterns of desert pavement (mosaic DP) and bare ground (mosaic BG). We investigated the effects of mosaic DP on water infiltration and vegetation distribution at six sites in fluvial fans (one on a hillside and five within the sectors of fans) along a southwest belt transect in northern Linze County, in the central Hexi Corridor (China). We found significant differences in mosaic DP between the hillside and sector sites in terms of pavement thickness and vesicular horizon thickness (Av thickness), particle composition, and bulk density, although significant differences were absent for mass soil water content, gravel coverage, and surface gravel size. The mosaic DP inhibited water infiltration by the pavement layer, where the sorptivity (S), initial infiltration rate (iint), steady-state infiltration rate (isat) and infiltration time (T) averaged 1.19 cm/min-0.5, 0.64 cm/min, 0.13 cm/min and 12.76 min, respectively. Where the pavement layer was scalped, the S, iint, and isat increased by 0.27 cm/min-0.5, 0.52 cm/min, and 0.40 cm/min, respectively, and the T reduced by 7.42 min. Water infiltration was mainly controlled by the pavement layer thickness (+), Av thickness (−), surface gravel coverage (−), fine earth (+) and fine gravel (−) in the pavement layer. The DP surfaces only had a sparse covering of shrubs, but an abundance of herbs. Few shrubs were present on the mosaic DP, but a greater number of shrubs and herbs grew on the mosaic BG. It can be concluded that DPs can maintain vegetation stability for different surface mosaic patterns. This study deepens our understanding of the eco-hydrological cycle of DP landscapes in arid regions. 相似文献
74.
The understanding of nutrient uptake in streams is impeded by a limited understanding of how geomorphic setting and flow regime interact with biogeochemical processing. This study investigated these interactions as they relate to transient storage and nitrate uptake in small agricultural and urban streams. Sites were selected across a gradient of channel conditions and management modifications and included three 180‐m long geomorphically distinct reaches on each of two streams in north‐central Colorado. The agricultural stream has been subject to historically variable cattle‐grazing practices, and the urban stream exhibits various levels of stabilisation and planform alteration. Reach‐scale geomorphic complexity was characterised using highly detailed surveys of channel morphology, substrate, hydraulics and habitat units. Breakthrough‐curve modelling of conservative bromide (Br?) and nonconservative nitrate (NO3?) tracer injections characterised transient storage and nitrate uptake along each reach. Longitudinal roughness and flow depth were positively associated with transient storage, which was related to nitrate uptake, thus underscoring the importance of geomorphic influences on stream biogeochemical processes. In addition, changes in geomorphic characteristics due to temporal discharge variation led to complex responses in nitrate uptake. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
75.
《水文科学杂志》2013,58(5)
Abstract A revised approach to the calculation of baseflow using the method originally proposed by the United Kingdom Institute of Hydrology is presented. The revisions resolve two aspects of the method that lead to less than optimal results; that is, the calculation of values of baseflow that exceed the corresponding values of streamflow and the dependence of the calculated values on the origin of the five-day segmentation of the input streamflow data. The approach is illustrated using streamflow monitoring information that is typical for areas of southern Ontario, Canada, where baseflow is primarily the result of groundwater discharge. 相似文献
76.
Adrian E. Scheidegger 《Natural Hazards》1988,1(1):5-13
When a study is to be made of seismic risks, the present-day geodynamic conditions are of fundamental importance: Earthquakes do not happen by themselves, they do have a cause. The cause of earthquakes is that the tectonic stresses exceed a critical limit. The build-up of these stresses is conditioned by the geodynamic processes occurring in the region in question. A knowledge of the geodynamics characteristic of a region is therefore fundamental for seismic risk studies. The general methodology for making such a geodynamic study is based on the entire set of manifestations of the plate-tectonic conditions of that region: these include the mechanism of earthquakes, the stresses observed in mines, the orientation of surface joints and even the direction of river valleys. Examples of geodynamic studies and their bearing on seismic risks are shown from various areas of the world, notably from China, India, and Colombia. 相似文献
77.
The geometric signature: Quantifying landslide-terrain types from digital elevation models 总被引:11,自引:0,他引:11
Richard J. Pike 《Mathematical Geology》1988,20(5):491-511
78.
79.
R. M. Dargám 《International Journal of Salt Lake Research》1994,3(2):137-158
This paper reports on hydrochemical features of diluted waters in the source areas and the brine end-members dominant in the playa of the Salinas Grandes Basin, Córdoba, Argentina. Special emphasis was placed on the study of the relationship between geomorphology and the resulting hydrochemical fractionation. Inflow is from springs and mountain streams which disappear before reaching the saline complex. The playa and intermittent saline lakes are mainly fed by groundwater flow and a few moderately saline and perennial springs. Conversely, ephemeral lakes are fed by atmospheric precipitation and groundwater, whereas small ponds are only fed by atmospheric precipitation. The absence of a clear linkage between geomorphological units and water types was evident in the source areas. Up to four types of water were recognized in a given geomorphological unit. From the sandflat downward towards the playa, the correspondence between geomorphological units and water types was clear, coinciding with a decreased hydrochemical heterogeneity. In this subenvironment, I have recognized two dominant types of water (SO
4
2–
–Cl––HCO
3
–
–Na+ and Cl––SO
4
2–
–HCO
3
–
–Na+), which can be considered the original members of the neutral brine in the playa (Cl––SO
4
2–
–Na+ where Ca2++Mg2+ do not surpass 5 meq per cent), and an intermediate type in the mudflat (Cl––SO
4
2–
–Na+ where the contribution of Ca2++Mg2+ reaches up to 15 meq per cent). It seems evident that in the zone between the source areas and the sandflat, hydrochemistry is governed by chemical weathering. In stream floodplains and in the distal alluvial plain, close to the saline complex, the increase in water types as well as the increase of HCO
3
–
with respect to SO
4
2–
, were explained by the mixture of aquifers controlled by the Salinas Grandes-Salinas de Ambargasta fracture. In the saline complex, the more concentrated end-members are the result of evaporation of the two more frequent water-types in the sandflat subenvironment, and salt dissolution of ancient evaporite deposit. 相似文献
80.
Results from a new model of river basin evolution 总被引:1,自引:0,他引:1
This paper briefly describes a model of the erosional development of catchments and their channel networks. The model differentiates between the dominant transport processes in hillslope and channels. The development of channels and hillslopes occurs in an integrated manner as a function of physically observable mechanisms. The growth of a river basin is qualitatively described. The model concepts are used to study the basin during periods of growth (transient periods), as well as during dynamic equilibrium. This leads to hypotheses about the relationship between slopes, relief, tectonic uplift, erodability, runoff, and catchment area. It is shown that the model leads to very reasonable and desirable behaviour of hillslopes during retreat and degradation. 相似文献