全文获取类型
收费全文 | 4504篇 |
免费 | 633篇 |
国内免费 | 693篇 |
专业分类
测绘学 | 423篇 |
大气科学 | 611篇 |
地球物理 | 933篇 |
地质学 | 1990篇 |
海洋学 | 752篇 |
天文学 | 7篇 |
综合类 | 258篇 |
自然地理 | 856篇 |
出版年
2024年 | 37篇 |
2023年 | 106篇 |
2022年 | 173篇 |
2021年 | 223篇 |
2020年 | 194篇 |
2019年 | 221篇 |
2018年 | 162篇 |
2017年 | 233篇 |
2016年 | 232篇 |
2015年 | 210篇 |
2014年 | 342篇 |
2013年 | 336篇 |
2012年 | 305篇 |
2011年 | 302篇 |
2010年 | 293篇 |
2009年 | 281篇 |
2008年 | 290篇 |
2007年 | 291篇 |
2006年 | 297篇 |
2005年 | 222篇 |
2004年 | 175篇 |
2003年 | 145篇 |
2002年 | 166篇 |
2001年 | 98篇 |
2000年 | 87篇 |
1999年 | 73篇 |
1998年 | 75篇 |
1997年 | 42篇 |
1996年 | 42篇 |
1995年 | 35篇 |
1994年 | 32篇 |
1993年 | 33篇 |
1992年 | 32篇 |
1991年 | 8篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 8篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1978年 | 3篇 |
1977年 | 1篇 |
排序方式: 共有5830条查询结果,搜索用时 0 毫秒
1.
Roberto Mínguez Fernando Delgado Ignacio Escuder Manuel G. de Membrillera 《国际地质力学数值与分析法杂志》2006,30(10):1019-1037
Empirical criteria have been used successfully to design filters of most embankment large dam projects throughout the world. However, these empirical rules are only applicable to a particular range of soils tested in laboratory and do not take into account the variability of the base material and filter particle sizes. In addition, it is widely accepted that the safety of fill dams is mainly dependent on the reliability of their filter performance. The work herein presented consists in a new general method for assessing the probability of fulfilling any empirical filter design criteria accounting for base and filter heterogeneity by means of first‐order reliability methods (FORM), so that reliability indexes and probabilities of fulfilling any particular criteria are obtained. This method will allow engineers to estimate the safety of existing filters in terms of probability of fulfilling their design criteria and might also be used as a decision tool on sampling needs and material size tolerances during construction. In addition, sensitivity analysis makes possible to analyse how reliabilities are influenced by different sources of input data. Finally, in case of a portfolio risk assessment, this method will allow engineers to compare the safety of several existing dams in order to prioritize safety investments and it is expected to be a very useful tool to evaluate probabilities of failure due to internal erosion. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
2.
3.
4.
珠江三角洲地质灾害种类的多样性与其所处的复杂地质环境和多变的气候条件密切相关。文章选用了地震活动、活动断裂、地壳升降运动、软土地基、地面塌陷以及冲、淤积等6个主要因素作为评价指标,并用模糊数学方法对珠江三角洲内17个小区作了计算,结果表明该区大部分地区属于轻灾害区,只有滨海沿岸地区属于较重灾害区。 相似文献
5.
6.
Video assessment of environmental impacts of salmon farms 总被引:1,自引:0,他引:1
7.
In recent years, bulk carriers have been identified with high risks of catastrophic structural failure and foundering, and with heavy loss of human life. This study, based upon Lloyd's of London casualty records, identified four risk factors that had significant, independent effect upon the likelihood of a bulk carrier foundering. The risk of foundering increased with the age of the ship, and was related to the ship's flag of registration. Most importantly, however, increased risks were found for heavy cargoes of iron ore and scrap steel or iron, and for trading routes to the Far East and from Europe to North America. Additional safety measures, in particular regarding ship design and high-risk trades, may well be necessary to reduce the high casualty rates. 相似文献
8.
9.
A multi-method approach to study the stability of natural slopes and landslide susceptibility mapping 总被引:8,自引:0,他引:8
In this paper, a multi-method approach for the assessment of the stability of natural slopes and landslide hazard mapping applied to the Dakar coastal region is presented. This approach is based on the effective combination of geotechnical field and laboratory works, of GIS, and of mechanical (deterministic and numerical) stability analysis. By using this approach, valuable results were gained regarding instability factors, landslide kinematics, simulation of slope failure and coastal erosion. This led to a thorough assessment and strong reduction in the subjectivity of the slope stability and hazard assessment and to the development of an objective landslide danger map of the SW coast of Dakar. Analysis of the results shows that the slides were influenced by the geotechnical properties of the soil, the weathering, the hydrogeological situation, and the erosion by waves. The landslide susceptibility assessment based on this methodological approach has allowed for an appropriate and adequate consideration of the multiple factors affecting the stability and the optimization of planning and investment for land development in the city. 相似文献
10.
Predicting average annual groundwater levels from climatic variables: an empirical model 总被引:8,自引:0,他引:8
On the basis of one-dimensional theoretical water flow model, we demonstrate that the groundwater level variation follows a pattern similar to recharge fluctuation, with a time delay that depends on the characteristics of aquifer, recharge pattern as well as the distance between the recharge and observation locations. On the basis of a water budget model and the groundwater flow model, we propose an empirical model that links climatic variables to groundwater level. The empirical model is tested using a partial data set from historical records of water levels from more than 80 wells in a monitoring network for the carbonate rock aquifer, southern Manitoba, Canada. The testing results show that the predicted groundwater levels are very close to the observed ones in most cases. The overall average correlation coefficient between the predicted and observed water levels is 0.92. This proposed empirical statistical model could be used to predict variations in groundwater level in response to different climate scenarios in a climate change impact assessment. 相似文献