全文获取类型
收费全文 | 12952篇 |
免费 | 3081篇 |
国内免费 | 4196篇 |
专业分类
测绘学 | 592篇 |
大气科学 | 3280篇 |
地球物理 | 3979篇 |
地质学 | 7665篇 |
海洋学 | 1897篇 |
天文学 | 272篇 |
综合类 | 803篇 |
自然地理 | 1741篇 |
出版年
2024年 | 73篇 |
2023年 | 225篇 |
2022年 | 537篇 |
2021年 | 572篇 |
2020年 | 565篇 |
2019年 | 742篇 |
2018年 | 619篇 |
2017年 | 571篇 |
2016年 | 617篇 |
2015年 | 739篇 |
2014年 | 897篇 |
2013年 | 913篇 |
2012年 | 900篇 |
2011年 | 963篇 |
2010年 | 807篇 |
2009年 | 1038篇 |
2008年 | 999篇 |
2007年 | 1105篇 |
2006年 | 978篇 |
2005年 | 786篇 |
2004年 | 783篇 |
2003年 | 635篇 |
2002年 | 595篇 |
2001年 | 483篇 |
2000年 | 473篇 |
1999年 | 459篇 |
1998年 | 403篇 |
1997年 | 354篇 |
1996年 | 302篇 |
1995年 | 220篇 |
1994年 | 235篇 |
1993年 | 164篇 |
1992年 | 142篇 |
1991年 | 71篇 |
1990年 | 55篇 |
1989年 | 47篇 |
1988年 | 39篇 |
1987年 | 30篇 |
1986年 | 17篇 |
1985年 | 19篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1981年 | 7篇 |
1980年 | 3篇 |
1979年 | 14篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1971年 | 3篇 |
1954年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 742 毫秒
51.
52.
Behavior of Pile Groups under Lateral Load 总被引:2,自引:0,他引:2
Yang Keji Li Qixin Wang Fuyuan
Associate Proferssor Hehai University Nanjing Engineer Hehai University Nanjing 《中国海洋工程》1991,(2)
Based on investigation and model tests, and in combination with the research work on group effect for pile groups under lateral loads relating to the code of fixed offshore platforms, a series of studies have been performed on the behavior and failure mechanism of laterally loaded pile groups, critical pile spacing inducing group effect, lateral bearing capacity of pile groups and its main influence factors, the stress-strain relationship for single piles and pile groups and so on. Some new laws about non-uniformity of load distribution in the longitudinal direction of pile groups and load-deflection (p - y) curves for pile groups have been discovered, and an empirical formula is presented in order to remedy the defect of current calculating methods at home and abroad. These results can be used for reference in the design of pile foundation under lateral loads. 相似文献
53.
青海湖全新世植被演变及气候变迁:QH85—14C孔孢粉数值分析 总被引:20,自引:3,他引:20
本文应用青海湖QH85-14C孔取得的具有~(14)C测年数据所支持的原始孢粉资料,进行数值分析(有序聚类、主成份分析、滑动平均和回归分析)。从而对青海湖区11000年以来的植被和气候变化进一步讨论。 相似文献
54.
E.R. Jefferys 《Applied Ocean Research》1984,6(1):31-39
Classical frequency and time domain models of a single degree of freedom wave power device are presented. In the time domain, a convolution integral is conventionally used to represent the fluid dynamic radiation force, characterised by added mass and damping in the frequency domain. This integral is replaced by an approximate ordinary differential equation (ODE) model which is faster and more convenient in simulations. A time domain model of the fluid dynamics of an oscillating water column (OWC) device is derived to illustrate the technique. Digital simulations of the OWC are used to compare the accuracy of the classical and ODE models. The simulation of the ODE model runs about six times as fast as the classical model based on convolution, yet characterises the fluid dynamics accurately. 相似文献
55.
The VOF method and the k–ε model, combined with the equation of state of air at constant temperature, have been used to calculate the total horizontal wave force caused by monochromatic waves acting on a perforated caisson with a top cover. From comparison of various parameters, such as the total horizontal force, the pressure difference on the front wall, the pressure on the back wall and the pressure on the top cover, between the numerical results and test data, it can be seen that the numerical results agree well with the test data. It is concluded that the method described in this paper can be utilized to calculate wave forces acting on perforated caissons with a top cover in the case of nonovertopping, nonbreaking waves. A simplified method to calculate the total horizontal force has been developed, based on test data, using a least-squares method. A comparison between the numerical results and the values calculated from the simplified equations shows good agreement. Therefore the simplified equations can be used in engineering applications to evaluate the total horizontal force on a perforated caisson with a top cover. 相似文献
56.
57.
58.
依据黄、东海环流的的动力学模型 ,运用“流速分解法”对黄、东海正压环流进行了数值模拟。计算结果表明冬季黄海正压环流主要受风应力影响 ,基本形态为黄海暖流由济州岛西南进入南黄海中部 ,其东西两侧分别为两支向南流动的沿岸流 ;夏季主要受到潮致体力的影响 ,为一逆时针涡旋。东海环流主要是边界力作用驱动的结果 ,东海黑潮、台湾暖流和对马暖流较稳定。冬季风应力对东海环流表层流场有消弱作用 ,在夏季则有一定增强作用。 相似文献
59.
Amodeloftheformationanddevelopmentofoceanshearwave¥QiaoFangliandZhangQinghua(FirstInstituteofOceanography,stateoceanicAdminis... 相似文献
60.
Yu Yuxiu Liu Shuxue Li Li Professor Dept. of Civil Engineering Dalian University of Technology Dalian
Research Assistant Dept. of Civil Engineering Dalian University of Technology Dalian 《中国海洋工程》1991,(3)
Multi-directional irregular waves are simulated on the basis of the given directional spectrum using a double summation model, a single direction per frequency model and a single summation model. Their results are compared. It is shown that the single direction per frequency model proposed in this paper can generate a realistic wave field. The effects of the model parameters on the simulated results are also studied in this paper and corresponding suggestions are given. 相似文献