全文获取类型
收费全文 | 2356篇 |
免费 | 539篇 |
国内免费 | 974篇 |
专业分类
测绘学 | 55篇 |
大气科学 | 66篇 |
地球物理 | 933篇 |
地质学 | 1991篇 |
海洋学 | 345篇 |
天文学 | 12篇 |
综合类 | 125篇 |
自然地理 | 342篇 |
出版年
2024年 | 2篇 |
2023年 | 23篇 |
2022年 | 58篇 |
2021年 | 68篇 |
2020年 | 98篇 |
2019年 | 126篇 |
2018年 | 129篇 |
2017年 | 92篇 |
2016年 | 132篇 |
2015年 | 136篇 |
2014年 | 162篇 |
2013年 | 178篇 |
2012年 | 179篇 |
2011年 | 173篇 |
2010年 | 167篇 |
2009年 | 204篇 |
2008年 | 205篇 |
2007年 | 241篇 |
2006年 | 249篇 |
2005年 | 202篇 |
2004年 | 186篇 |
2003年 | 123篇 |
2002年 | 103篇 |
2001年 | 83篇 |
2000年 | 87篇 |
1999年 | 92篇 |
1998年 | 77篇 |
1997年 | 58篇 |
1996年 | 38篇 |
1995年 | 31篇 |
1994年 | 35篇 |
1993年 | 28篇 |
1992年 | 28篇 |
1991年 | 16篇 |
1990年 | 11篇 |
1989年 | 12篇 |
1988年 | 9篇 |
1987年 | 10篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 4篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1976年 | 1篇 |
排序方式: 共有3869条查询结果,搜索用时 15 毫秒
61.
根据宜兴抽水蓄能站的地应力资料以及厂房区的地质构造条件,通过边界位移的大量调整,模拟出构造应力以及厂房区的三维地应力场,运用Ansys软件单元的生与死,模拟洞室开挖效应引起的围岩稳定性,然后运用等效概化原理,考虑锚杆的作用,对围岩进行加固,结果表明锚固作用明显。 相似文献
62.
63.
Shear‐wall dominant multistorey reinforced concrete structures, constructed by using a special tunnel form technique are commonly built in countries facing a substantial seismic risk, such as Chile, Japan, Italy and Turkey. In spite of their high resistance to earthquake excitations, current seismic code provisions including the Uniform Building Code (International Conference of Building Officials, Whittier, CA, 1997) and the Turkish Seismic Code (Specification for Structures to be Built in Disaster Areas, Ankara, Turkey, 1998) present limited information for their design criteria. In this study, consistency of equations in those seismic codes related to their dynamic properties are investigated and it is observed that the given empirical equations for prediction of fundamental periods of this specific type of structures yield inaccurate results. For that reason, a total of 80 different building configurations were analysed by using three‐dimensional finite‐element modelling and a set of new empirical equations was proposed. The results of the analyses demonstrate that given formulas including new parameters provide accurate predictions for the broad range of different architectural configurations, roof heights and shear‐wall distributions, and may be used as an efficient tool for the implicit design of these structures. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
64.
S. H. Ju 《地震工程与结构动力学》2003,32(9):1431-1442
This paper discusses how to use the three‐dimensional (3D) time‐domain finite‐element method incorporating the least‐squares method to calculate the equivalent foundation mass, damping and stiffness matrices. Numerical simulations indicate that the accuracy of these equivalent matrices is acceptable when the applied harmonic force of 1+sine is used. Moreover, the accuracy of the least‐squares method using the 1+sine force is not sensitive to the first time step for inclusion of data. Since the finite‐element method can model problems flexibly, the equivalent mass, damping and stiffness matrices of very complicated soil profiles and foundations can be established without difficulty using this least‐squares method. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
65.
岩溶地区长桩存在着遇洞率的问题。为了研究岩溶地区桩的受力特点,采用有限元法模拟岩溶地区桩基的工作方式,分析了岩层厚度对桩的影响以及桩的受力状态,并研究了去桩的可能性。计算结果表明:岩层厚度对桩的影响较大,岩层的位置对桩的应力不产生影响,仅对桩的位移产生影响。 相似文献
66.
67.
68.
69.
我国热带亚热带部分地区花岗岩和片麻岩中黑云母风化研究 总被引:5,自引:0,他引:5
综合应用X射线衍射、扫描电镜、透射电镜及偏光显微镜等技术手段研究了我国热带、亚热带部分地区花岗岩和片麻岩中黑云母的风化现象。结果表明,化学风化产物主要有黑云母/蛭石不规则间层矿物、水黑云母、蛭石、0.7nm埃洛石及铁的氢氧化物(氧化物)等。影响黑云母风化及次生产物形成的主要因素包括黑云母的晶体结构和化学成分、气候、风化壳母岩的矿物成分等。 相似文献
70.
Summary Pseudo-static and dynamic non-linear finite element analyses have been performed to assess the dynamic behaviour of gravity retaining walls subjected to horizontal earthquake loading. In the pseudo-static analysis, the peak ground acceleration is converted into a pseudo-static inertia force and applied as a horizontal incremental gravity load. In the dynamic analysis, an actual measured earthquake acceleration time history has been scaled to provide peak ground acceleration values of 0.1 g and 0.3 g. Good agreement is obtained between the pseudo-static analysis and analytical methods for the calculation of the active coefficient of earth pressure. However, the results from the dynamic analysis require careful interpretation. In the pseudo-static analysis, the increase in the point of application of the resultant active force with the horizontal earthquake coefficient k
h from the one-third point to the mid-height of the wall is clearly observed. In the dynamic analysis, the variation in the point of application is shown to be a function of the type of wall deformation. Both finite element analyses indicate the importance of determining the magnitude of the predicted displacements when assessing the behaviour of the wall to seismic loading. 相似文献