全文获取类型
收费全文 | 4568篇 |
免费 | 313篇 |
国内免费 | 253篇 |
专业分类
测绘学 | 152篇 |
大气科学 | 128篇 |
地球物理 | 447篇 |
地质学 | 782篇 |
海洋学 | 217篇 |
天文学 | 2775篇 |
综合类 | 63篇 |
自然地理 | 570篇 |
出版年
2024年 | 24篇 |
2023年 | 36篇 |
2022年 | 72篇 |
2021年 | 77篇 |
2020年 | 69篇 |
2019年 | 123篇 |
2018年 | 59篇 |
2017年 | 66篇 |
2016年 | 72篇 |
2015年 | 86篇 |
2014年 | 125篇 |
2013年 | 147篇 |
2012年 | 140篇 |
2011年 | 174篇 |
2010年 | 117篇 |
2009年 | 407篇 |
2008年 | 351篇 |
2007年 | 423篇 |
2006年 | 406篇 |
2005年 | 332篇 |
2004年 | 308篇 |
2003年 | 303篇 |
2002年 | 215篇 |
2001年 | 192篇 |
2000年 | 146篇 |
1999年 | 158篇 |
1998年 | 179篇 |
1997年 | 61篇 |
1996年 | 52篇 |
1995年 | 37篇 |
1994年 | 28篇 |
1993年 | 33篇 |
1992年 | 25篇 |
1991年 | 12篇 |
1990年 | 17篇 |
1989年 | 12篇 |
1988年 | 8篇 |
1987年 | 11篇 |
1986年 | 10篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1971年 | 2篇 |
排序方式: 共有5134条查询结果,搜索用时 15 毫秒
171.
172.
173.
174.
175.
176.
177.
Effects of calculation procedure and sampling site on trap method estimates of sediment resuspension in a shallow lake 总被引:1,自引:0,他引:1
Resuspension estimates given by two different trap methods in a shallow lake were compared. The sensitivity of the methods to errors in estimates of gross sedimentation and organic fraction of trapped material was explored. The methods were label method, in which resuspension is estimated by determining the organic fraction of surface sediment, suspended seston and trapped material, and SPIM/SPM method, where the relationship between settling particulate inorganic matter (SPIM) and total settling particulate matter (SPM) is used. During the whole 111 day study period, according to the label method, at a sheltered station 1949 g m−2 dry weight of sediment was resuspended, whereas SPIM/SPM gave an estimate of 1815 g m−2. The difference in the estimates was probably due to mineralization loss of organic material in the traps during the two week exposure periods. Sensitivity analysis showed that of the two methods, the label method was more sensitive to variations in the organic content of trapped material. At a wind-exposed station, the total amounts of resuspended matter given by the label method and by the SPIM/SPM method were 4966 g m−2 and 4971 g m−2, respectively. Due to wind effects, escape of trapped material took place, which caused underestimation of gross sedimentation and compensated the effects of mineralization loss to diminish the difference between the methods. Of the two methods, the SPIM/SPM method seems thus more suitable for lakes, where bacterial activity is high. If cyanobacterial blooms take place, the label method is probably more reliable, providing that the exposure time of sediment traps is kept adequately short. 相似文献
178.
Roger Guérin 《Hydrogeology Journal》2005,13(1):251-254
179.
沿海地区海底地下水排放在北美和欧洲等发达地区受到了越来越多的重视,被认为是一个重要的海岸带陆海相互作用过程。但这一过程在我国尚未引起足够认识,有关研究极少见。海底地下水排放的研究历史不长,只是近十多年才有了快速的发展,有了越来越多的定量研究成果。其研究方法主要有水文计算法、现场实测法和地球化学示踪法,各种方法之间的对比实验是目前的热点问题。沿海地下水排放具有重要的环境意义,它可以是陆地营养物质和污染物质的一个重要排放通道,可以对海岸带环境产生一定影响。我国沿海地区应该加强有关的研究工作,为海岸带环境管理作出贡献。 相似文献
180.
A multiphase approach for evaluating the horizontal and rocking impedances of pile group foundations
下载免费PDF全文
![点击此处可从《国际地质力学数值与分析法杂志》网站下载免费的PDF全文](/ch/ext_images/free.gif)
This paper advocates the use of a multiphase model, already developed for static or quasi‐static geotechnical engineering problems, for simulating the behaviour of piled raft foundations subject to horizontal as well as rocking dynamic solicitations. It is shown that such a model, implemented in a FEM code, yields appropriate predictions for the foundation impedance characteristics, provided that shear and bending effects in the piles are taken into account, thus corroborating the findings of the asymptotic homogenization theory. Besides, it is notably pointed out that such a multiphase‐based computational tool makes it possible to assess the dynamic behaviour of pile groups in a much quicker way than when using direct numerical simulations, which may face oversized problems when large pile groups are concerned. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献