全文获取类型
| 收费全文 | 2355篇 |
| 免费 | 803篇 |
| 国内免费 | 1395篇 |
专业分类
| 测绘学 | 106篇 |
| 大气科学 | 36篇 |
| 地球物理 | 503篇 |
| 地质学 | 3178篇 |
| 海洋学 | 495篇 |
| 天文学 | 11篇 |
| 综合类 | 97篇 |
| 自然地理 | 127篇 |
出版年
| 2024年 | 6篇 |
| 2023年 | 30篇 |
| 2022年 | 92篇 |
| 2021年 | 103篇 |
| 2020年 | 144篇 |
| 2019年 | 171篇 |
| 2018年 | 169篇 |
| 2017年 | 138篇 |
| 2016年 | 213篇 |
| 2015年 | 175篇 |
| 2014年 | 230篇 |
| 2013年 | 262篇 |
| 2012年 | 227篇 |
| 2011年 | 240篇 |
| 2010年 | 218篇 |
| 2009年 | 204篇 |
| 2008年 | 221篇 |
| 2007年 | 213篇 |
| 2006年 | 242篇 |
| 2005年 | 181篇 |
| 2004年 | 161篇 |
| 2003年 | 134篇 |
| 2002年 | 105篇 |
| 2001年 | 110篇 |
| 2000年 | 86篇 |
| 1999年 | 80篇 |
| 1998年 | 62篇 |
| 1997年 | 74篇 |
| 1996年 | 66篇 |
| 1995年 | 41篇 |
| 1994年 | 30篇 |
| 1993年 | 28篇 |
| 1992年 | 13篇 |
| 1991年 | 18篇 |
| 1990年 | 18篇 |
| 1989年 | 8篇 |
| 1988年 | 8篇 |
| 1987年 | 9篇 |
| 1986年 | 6篇 |
| 1985年 | 5篇 |
| 1984年 | 5篇 |
| 1983年 | 1篇 |
| 1982年 | 2篇 |
| 1978年 | 1篇 |
| 1977年 | 1篇 |
| 1974年 | 1篇 |
| 1972年 | 1篇 |
排序方式： 共有4553条查询结果，搜索用时 15 毫秒
11.
土壤聚合物对几种重金属离子固化效果的研究 总被引：2，自引：0，他引：2
土壤聚合物是一种新型的无机聚合物,其分子链由Si、O、Al等以共价键或离子键连接而成,形成网络结构,对重金属有较强的固定作用.本文试图利用土壤聚合物固化铜、锌、铅三种重金属离子,实现资源化利用.实验以固化体抗压强度和浸出毒性作为性能表征量,结果表明:土壤聚合物对不同重金属的固化有各自的极限浓度,Cu2 、Zn2 、Pb2 的理想固化量分别为0.9%、1%、2%;若固化过程中添加一定量的高炉矿渣,则可以提高固化体的抗压强度.本文通过土壤聚合物固化体SEM分析,从固化体微观结构的形态来阐述土壤聚合物宏观上的优越表现. 相似文献
12.
Effect of Cyclic Loading Frequency on Undrained Behaviors of Undisturbed Marine Clay 总被引：2，自引：0，他引：2
Based on a series of cyclic triaxial tests, the effect of cyclic frequency on the undrained behaviors of undisturbed marine clay is investigated. For a given dynamic stress ratio, the accumulated pore water pressure and dynamic strain increase with the number of cycles. There exists a threshold value for beth the accumulated pore water pressure and dynamic strain, below which the effect of cyclic frequency is very small, but above which the accumulated pore water pressure and dynamic strain increase intensely with the decrease of cyclic frequency for a given number of cycles. The dynamic strength increases with the increase of cyclic frequency, whereas the effect of cyclic frequency on it gradually diminishes to zero when the number of cycles is large enough, and the dynamic strengths at different frequencies tend to the same limiting minimum dynamic strength. The test results demonstrate that the reasons for the frequency effect on the undrained soil behaviors are beth the creep effect induced by the loading rate and the decrease of sample effective confining pressure caused by the accumulated pore water pressure. 相似文献
13.
14.
1 .IntroductionThe lifting systemis composed of pipes andtheir connectors .It is not onlythe lifting channel formanganese nodule betweenthe miningship andintermediate bin,but alsothe supporting massfor deepsea miningequipment and cables .Sothe reliability… 相似文献
15.
In this paper, a new definition of structure system redundancy is proposed in view of the various measures for structure redundancy. By introducing the terms of structure system failure at the mechanism level and equivalent reliability index, the safety for existing offshore platforms can be evaluated by the semi-probabilistic method presented in this paper. Some numerical examples are given and satisfactory results have been obtained. 相似文献
16.
Yu Xiaodong Yan Shuwang Sun Wanhe
Postgraduate Student Tianjin University Tianjin Professor Tianjin University Tianjin Senior Engineer Tianjin Port Engineering Institute Tianjin 《中国海洋工程》1997,(2)
At pesent,it is very popular to estimate pile bearing capacity by use of empirical formula andphysical indexes of soil provided in the design codes for civil construction in China.This paper attempts toapply mechanical indexes of soil and semi-empirical formulas,which are based on soil mechanical theoriesand were summarized and presented by Meyerhof in 1976,to calculate the axial pile bearing capacity.Lo-ading test results of 24 single piles in Tianjin area have been collected and compared with the proposed cal-ulation approach. 相似文献
17.
Li Runpei Chen Weigang Gu Yongning
Professor Shanghai Jiao Tong University Shanghai Assistant Shanghai Jiao Tong University Shanghai 《中国海洋工程》1996,(1)
In this paper a numerical analysis method combining FEM incemental technique with limit analysis concept is proposed for the study of the static strength of offshore platform in collision. Large deformation and plasticity are accounted for and the limit yield surface expressed by generalized stress for a tubular section is derived. The modified stiffness matrix of space beam element is formulated by Plastic Node Method. The buckling behavior of beam columns can also be taken into account. It can trace the generation of plastic hinges during loading and finally the ultimate strength of offshore platform against collision is obtained. 相似文献
18.
19.
20.