全文获取类型
收费全文 | 1881篇 |
免费 | 1980篇 |
国内免费 | 608篇 |
专业分类
测绘学 | 69篇 |
大气科学 | 61篇 |
地球物理 | 417篇 |
地质学 | 3430篇 |
海洋学 | 261篇 |
天文学 | 3篇 |
综合类 | 117篇 |
自然地理 | 111篇 |
出版年
2024年 | 10篇 |
2023年 | 32篇 |
2022年 | 128篇 |
2021年 | 233篇 |
2020年 | 178篇 |
2019年 | 181篇 |
2018年 | 179篇 |
2017年 | 178篇 |
2016年 | 195篇 |
2015年 | 209篇 |
2014年 | 248篇 |
2013年 | 234篇 |
2012年 | 250篇 |
2011年 | 271篇 |
2010年 | 206篇 |
2009年 | 218篇 |
2008年 | 175篇 |
2007年 | 184篇 |
2006年 | 126篇 |
2005年 | 132篇 |
2004年 | 108篇 |
2003年 | 101篇 |
2002年 | 77篇 |
2001年 | 92篇 |
2000年 | 72篇 |
1999年 | 76篇 |
1998年 | 67篇 |
1997年 | 43篇 |
1996年 | 76篇 |
1995年 | 37篇 |
1994年 | 45篇 |
1993年 | 24篇 |
1992年 | 25篇 |
1991年 | 15篇 |
1990年 | 8篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1979年 | 3篇 |
1977年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有4469条查询结果,搜索用时 140 毫秒
891.
892.
893.
Three-dimensional analysis of the screening effectiveness of hollow pile barriers for foundation-induced vertical vibration 总被引:2,自引:0,他引:2
The study applies the three-dimensional boundary element method in frequency domain to investigate the screening effectiveness of circular piles in a row for a massless square foundation subject to harmonic vertical loading. Four types of piles were studied: steel pipe piles, concrete hollow piles, concrete solid piles and timber piles. A parametric study was undertaken to examine the effects of pile dimensions, operational frequency, and source distance on the screening effectiveness. The results showed that screening effectiveness of steel pipe piles is generally better than that of solid piles, and that a concrete hollow pile barrier can be ineffective due to its stiffness. The influence of pile length on screening effectiveness is more significant than that of pile spacing and the distance between the vibrating foundation and the pile barrier. 相似文献
894.
Experimental Analysis and Micromechanical Modelling of Dry Granular Flow and Impacts in Laboratory Flume Tests 总被引:7,自引:2,他引:5
Summary. The paper presents the results of a numerical analysis, carried out by using the Discrete Element Method (DEM) and aimed at
reproducing a series of tests on a small-scale laboratory model of a slope. Particular attention is devoted to the validation
of DEM when used for the prediction of the run-out distance and of the impact force on obstacles. The soil used for the small-scale
model is a mono-granular medium sand, which revealed to be particularly suitable to simulate flows like debris or rock avalanches.
The experimental set-up comprises a flume equipped with a system of differently sized instrumented obstacles. The numerical
model of the granular flow has been calibrated on the basis of the displacement measurements, obtained through a photogrammetric
technique.
Author’s address: Roberto Valentino, Department of Civil, Environmental, Territorial Engineering and Architecture, Università
degli Studi di Parma, Parma, Italy 相似文献
895.
896.
Crystallization experiments at 400 MPa, oxidized condition (logfO2= NNO + 1, where NNO is nickel–nickel oxide buffer) andover a range of temperatures (850–950°C) and fluidcomposition (XH2Oin = 0·3–1) have been carriedout to constrain the storage conditions of the sulphur-richmagma of the Huerto Andesite (an anhydrite, pyrrhotite, andS-rich apatite-bearing, post-Fish Canyon Tuff mafic lava). Theresults are used to evaluate the role of fluids released fromthe crystallization of magmas such as the Huerto Andesite onthe remobilization of the largely crystallized dacitic FishCanyon magma body. Experiments were performed using the naturalandesitic bulk composition with and without added sulphur. Thepresence of sulphur slightly affects the phase equilibria bychanging the phase proportions, stability fields of plagioclase,pyroxenes and ilmenite, and also affects the plagioclase composition.Phase equilibria and mineral composition data indicate thatthe magma may have contained 4·5 wt % water in the meltand that the pre-eruptive temperature was 875 ± 25°C.Assuming that the magma was in equilibrium with a fluid phase,the CO2 concentration of the melt is estimated to be in therange 2000–4000 ppm (at 400 MPa). Before eruption, theandesite had an oxidation state very close to, or slightly within,the co-stability field of anhydrite–pyrrhotite at NNO+ 1·1. At these conditions, the sulphur content in themelt is 500 ppm. Assuming open-system degassing resulting fromcontinuing crystallization at depth, most of the CO2 dissolvedin the andesitic melt should be released after the crystallizationof <10 vol. % of the magma, corresponding to a cooling from875 to 825–850°C. Thus, the fluids released owingto crystallization processes should be mainly composed of waterat temperatures below 825°C. KEY WORDS: experimental study; andesite; volatile; Fish Canyon Tuff; Huerto Andesite 相似文献
897.
898.
899.
900.
通过计算对比,说明钻井过程的钻屑量,泥浆泵与钻杆的级配问题及钻井过程团相含量高的危害,对固相含量的要求,提出控制固相含量的措施等。 相似文献