全文获取类型
收费全文 | 337篇 |
免费 | 78篇 |
国内免费 | 96篇 |
专业分类
测绘学 | 5篇 |
大气科学 | 69篇 |
地球物理 | 120篇 |
地质学 | 157篇 |
海洋学 | 58篇 |
天文学 | 4篇 |
综合类 | 18篇 |
自然地理 | 80篇 |
出版年
2024年 | 2篇 |
2023年 | 2篇 |
2022年 | 7篇 |
2021年 | 12篇 |
2020年 | 13篇 |
2019年 | 19篇 |
2018年 | 22篇 |
2017年 | 13篇 |
2016年 | 17篇 |
2015年 | 17篇 |
2014年 | 18篇 |
2013年 | 25篇 |
2012年 | 10篇 |
2011年 | 17篇 |
2010年 | 13篇 |
2009年 | 20篇 |
2008年 | 15篇 |
2007年 | 26篇 |
2006年 | 23篇 |
2005年 | 19篇 |
2004年 | 19篇 |
2003年 | 21篇 |
2002年 | 17篇 |
2001年 | 16篇 |
2000年 | 16篇 |
1999年 | 15篇 |
1998年 | 12篇 |
1997年 | 11篇 |
1996年 | 10篇 |
1995年 | 10篇 |
1994年 | 8篇 |
1993年 | 12篇 |
1992年 | 11篇 |
1991年 | 9篇 |
1990年 | 5篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有511条查询结果,搜索用时 484 毫秒
161.
The interaction between groundwater and surface water in northern Shaanxi is quite complicated and frequent under the influence of regional hydrogeological condition and human intervention. These performances bring serious challenges to regional water resources assessment and utilization. The river baseflow process at Gaojiabu Station in windy desert region, Gaoshiya and Caoping Station in loess region were taken as research objects, and their variation trends and change points in the river baseflow series were analyzed in this paper. In addition, to explore the cause of the baseflow change, this research compared their correlations with precipitations in the same area respectively from two aspects of flow variation and multi timescale characteristics. The results show that: ①groundwater recharges for river flow in windy desert region significantly exceed those in loess region; ②baseflows of all the rivers in the study area reducing significantly are mainly determined by human intervention such as the extensive pumping of groundwater; ③periodic changes of baseflow in each station response closely to precipitation change on meso-scale and small-scales; ④precipitation-runoff relationships in windy desert regions are much more complicated and unstable than loess region, which is mainly because of its more significant impact from groundwater storage and the lateral recharge change. Under the changing environment, the water cycle in windy desert regions would be in complexity and variability. Therefore, it is recommended that, groundwater changes need to be considered in regional water resources assessment. 相似文献
162.
Secondary/minor structures occurring along the main fault surfaces are important indicators for judging the kinematic characteristics of faults. However, many factors can lead to the formation of these structures, which results in the difficulty for rapid judgment and application in the fields. A series of secondary faults/fractures developed due to the movement of main faults are the most important and widespread phenomena in the scope of brittle deformation. The morphology of the main fault surfaces is various, and former researchers mainly discussed the structures on the main even fault surfaces. However, the fluctuation of fault surfaces is the intrinsic character of the faults, and the intersection between the main fault and secondary faults/fractures can produce a series of kinematic indicators on the main fault surfaces. Based on previous studies and our observations, i.e. the structural traces of the P, R, R’, T and X shears/faults along the main faults, some indicators which are rarely reported previously, are described in the paper. Furthermore, their reliabilities are also discussed, and more practical and reliable criteria are brought forward. We suggest that the simple application of congruous and incongruous steps without knowing their exact origins should be abandoned in the fields, and several types of indicators along one fault surface should be checked with each other as much as possible. Meanwhile, the origins of some other arcuate indicators on the fault surfaces are also discussed, and new models are brought forward. 相似文献
163.
164.
Groundwater in coastal areas is commonly disturbed by tidal fluctuations. A two‐dimensional analytical solution is derived to describe the groundwater fluctuation in a leaky confined aquifer system near open tidal water under the assumption that the groundwater head in the confined aquifer fluctuates in response to sea tide whereas that of the overlying unconfined aquifer remains constant. The analytical solution presented here is an extension of the solution by Sun for two‐dimensional groundwater flow in a confined aquifer and the solution by Jiao and Tang for one‐dimensional groundwater flow in a leaky confined aquifer. The analytical solution is compared with a two‐dimensional finite difference solution. On the basis of the analytical solution, the groundwater head distribution in a leaky confined aquifer in response to tidal boundaries is examined and the influence of leakage on groundwater fluctuation is discussed. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
165.
166.
《地学前缘(英文版)》2018,9(6):1609-1618
Rock properties exhibit spatial variabilities due to complex geological processes such as sedimentation,metamorphism, weathering, and tectogenesis. Although recognized as an important factor controlling the safety of geotechnical structures in rock engineering, the spatial variability of rock properties is rarely quantified. Hence, this study characterizes the autocorrelation structures and scales of fluctuation of two important parameters of intact rocks, i.e. uniaxial compressive strength(UCS) and elastic modulus(EM).UCS and EM data for sedimentary and igneous rocks are collected. The autocorrelation structures are selected using a Bayesian model class selection approach and the scales of fluctuation for these two parameters are estimated using a Bayesian updating method. The results show that the autocorrelation structures for UCS and EM could be best described by a single exponential autocorrelation function. The scales of fluctuation for UCS and EM respectively range from 0.3 m to 8.0 m and from 0.3 m to 8.4 m.These results serve as guidelines for selecting proper autocorrelation functions and autocorrelation distances for rock properties in reliability analyses and could also be used as prior information for quantifying the spatial variability of rock properties in a Bayesian framework. 相似文献
167.
《International Journal of Digital Earth》2013,6(3):291-303
Abstract The southern part of the Caspian Sea shoreline in Iran with a length of 813 km has different topographic conditions. Owing to sea fluctuation, these zones have various dimensions in different times. During the last years, the Caspian Sea experienced enormous destructive rises. The historical information and tidal gauge measurements showed different ranges of sea rise from ?30 m to ?22 m from the mean sea level. On the other hand, the probable flooding zone is related to slope gradient of coasts. To help the determination of the probable flooding area owing to sea level rises, the coastal zones can be modelled using geographic information system (GIS) environment as vulnerability risk rates. These rates would be useful for making decisions in coastal management programs. This study examined different scenarios of sea rise to determine hazard-flooding rates in the coastal cities of the Mazandaran province and classified them based on vulnerability risk rates. The 1:2000 scale topographic maps of the coastal zones were prepared to extract topographic information and construct the coastal digital elevation model. With the presumption of half-metre sea rise scenarios, the digital elevation models classified eight scenarios from ?26 to ?22 m. The flooding areas in each scenario computed for 11 cities respectively. The vulnerability risk rate in each rise scenario was computed by dividing the flooded area of each scenario to city area. The results showed that in the first four scenarios, from ?26 to ?24 m, the Behshahr, Joibar, Neka and Babolsar cites would be more vulnerable than other cites. Moreover, for the second four scenarios from ?24 to ?22 m sea level rise scenario, only the coastal area of Chalous city would be vulnerable. It was also observed that the coastal region of Behshahr would be critical in total scenarios. Further studies would be necessary to complete this assessment by considering social-economic and land use information to estimate the exact hazardous and vulnerable zones. 相似文献
168.
Abstract This paper develops a new analytical solution for the aquifer system, which comprises an unconfined aquifer on the top, a semi-confined aquifer at the bottom and an aquitard between them. This new solution is derived from the Boussinesq equation for the unconfined aquifer and one-dimensional leaky confined flow equation for the lower aquifer using the perturbation method, considering the water table over-height at the remote boundary. The head fluctuation predicted from this solution is generally greater than the one solved from the linearized Boussinesq equation when the ratio of the tidal amplitude to the thickness of unconfined aquifer is large. It is found that both submarine groundwater discharges from upper and lower aquifers increase with tidal amplitude–aquifer thickness ratio and may be underestimated if the discharge is calculated based on the average head fluctuation. The effects of the aquifer parameters and linearization of the Boussinesq equation on the normalized head fluctuation are also investigated. Editor D. Koutsoyiannis; Associate editor J. Simunek Citation Chuang, M.-H., Mahdi, A.-A. and Yeh, H.-D., 2012. A perturbation solution for head fluctuations in a coastal leaky aquifer system considering water table over-height. Hydrological Sciences Journal, 57 (1), 162–172. 相似文献
169.
动水压力型滑坡对库水位升降作用的响应以三峡库区树坪滑坡为例 总被引:2,自引:0,他引:2
三峡库区涉水型滑坡众多,库水位周期性涨落引起库岸滑坡岩土体物理性质的改变,还使得滑体内渗流场发生变化,进而影响滑坡体稳定性。为研究库水位升降作用对涉水边坡稳定性的影响,基于三峡库区重大涉水滑坡分类,对动水压力型滑坡进行分析。以三峡库区秭归县树坪滑坡为例,利用Geo-Studio软件的SEEP模块及SLOPE分别对滑坡渗流场与稳定性进行计算,分析不同滑体渗透系数及不同库水位升降速率对动水压力型滑坡的影响规律。结果表明:对于动水压力型滑坡,库水位上升过程中,地下水位线有下凹趋势,稳定性系数有所增大; 库水位下降过程中,地下水位线有上凸现象,且稳定性系数明显减小; 库水位升降速率越大,滑体渗透系数越小,库水位变动对滑坡渗流及稳定性影响越明显。 相似文献
170.
The multi-fractal behaviors of relative humidity over China are studied using the multi-fractal detrended fluctuation analysis (DFA) method. Three multi-fractal parameters (the spectrum width Δα, the asymmetry Δα as , and the long-range correlation exponent α 0 ) of the singularity spectrum are introduced to quantify the multi-fractal behaviors. The results show that multi-fractality exists in daily humidity records over most stations in China and is mainly due to the broad distribution of the probability density of the sequence values. Strong multifractal behaviors over some stations in the Yunnan, Guangdong, and Inner Mongolia provinces are obvious. These behaviors are mainly caused by different longrange correlations between large and small fluctuations. The asymmetry of the singularity of relative humidity records is weak, except for a small number of stations in the far east and west of China, where the singularity spectrum is left-skewed. Finally, the long-range correlations in North China are stronger than those in South China, which indicates better predictability in North China. By studying the parameters of the multi-fractal spectrum, various data of long-range power law correlations of the relative humidity records are obtained, which may provide theoretical support for climate prediction. 相似文献