全文获取类型
收费全文 | 14557篇 |
免费 | 3121篇 |
国内免费 | 1282篇 |
专业分类
测绘学 | 380篇 |
大气科学 | 425篇 |
地球物理 | 11928篇 |
地质学 | 3097篇 |
海洋学 | 447篇 |
天文学 | 22篇 |
综合类 | 1109篇 |
自然地理 | 1552篇 |
出版年
2024年 | 49篇 |
2023年 | 204篇 |
2022年 | 430篇 |
2021年 | 570篇 |
2020年 | 573篇 |
2019年 | 637篇 |
2018年 | 618篇 |
2017年 | 578篇 |
2016年 | 484篇 |
2015年 | 634篇 |
2014年 | 799篇 |
2013年 | 876篇 |
2012年 | 765篇 |
2011年 | 806篇 |
2010年 | 733篇 |
2009年 | 1011篇 |
2008年 | 749篇 |
2007年 | 852篇 |
2006年 | 821篇 |
2005年 | 790篇 |
2004年 | 730篇 |
2003年 | 715篇 |
2002年 | 561篇 |
2001年 | 508篇 |
2000年 | 473篇 |
1999年 | 397篇 |
1998年 | 393篇 |
1997年 | 381篇 |
1996年 | 377篇 |
1995年 | 317篇 |
1994年 | 305篇 |
1993年 | 246篇 |
1992年 | 190篇 |
1991年 | 107篇 |
1990年 | 75篇 |
1989年 | 55篇 |
1988年 | 48篇 |
1987年 | 24篇 |
1986年 | 20篇 |
1985年 | 12篇 |
1984年 | 11篇 |
1983年 | 5篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 15篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1954年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
水灾遥感实时监测与快速评估的实践与思考 总被引:2,自引:0,他引:2
总结了参加1991 ̄1995年间3次水灾遥感监测与评估科学实验所取得的结果,并结合国情分析,提出进一步发挥航天遥感作用,航天与航空相结合,建立一个花费较少,切实可行,能满足水灾实时监测与快速评估需要的设想。 相似文献
182.
183.
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
184.
分形几何用于岩石损伤扩展过程的研究 总被引:3,自引:2,他引:3
通过对岩石损伤扩展机理的研究,运用分形几何理论,建立了岩石损伤变量ω与分形维数之间关系。 相似文献
185.
We present an overview of our recent results on utilizing small earthquakes in the earthquake engineering practice. Site-specific ground motion time-histories of large earthquakes can be successfully simulated using recordings of small earthquakes which are often referred to as 'empirical Green's functions' in seismology. Another important practical problem is whether and how these observations can be used in seismic risk studies which are based on empirical attenuation relations for ground motion parameters. We study a possibility of extrapolating attenuation relations for small earthquakes, to larger magnitudes using the data from the Garner Valley downhole array in Southern California. Finally we introduce efficient ground motion processing techniques in frequency- and time-domains and apply them to site response estimation. 相似文献
186.
Metropolitan growth and labor markets in Mexico 总被引:1,自引:0,他引:1
Adrian Guillermo Aguilar 《GeoJournal》1997,43(4):371-383
The objective of this paper is to examine the main changes in the metropolitan labor markets associated with economic restructuring in Mexico during the late 1980s and beginning of the 1990s. The analysis refers particularly to the four largest metropoles of the country, Mexico City, Guadalajara, Monterrey and Puebla, looking for common characteristics in their emergent employment structures now strongly differentiated in terms of rewards, stability in employment relations and conditions of access to jobs. The analysis reveals that largest metropolitan areas have been the most profoundly affected by the economic restructuring resulting from globalization, through a rapid de-industrialization and the expansion of the tertiary sector. Metropolitan labor markets in Mexico, at the time that show signs of social polarization in the formal sector, put in evidence a general process of precarization – less labor stability, replacement of permanent by part-time jobs, and increasing subcontracting –, segmentation of the labor force, and an increasing informal conditions of economic activities with small businesses and unskilled, temporarly and poorly paid jobs. The labor force segmentation and its more precarious and casual conditions are mostly explained by the impact of recent neoliberal policies, and recurrent economic crisis during the 1980s and 1990s which highly contributes to social inequality. 相似文献
187.
Dong Ruishu Xiang Hongfa Guo Shunmin Ran Hongliu and Fu ChanghongInstitute of Geology SSB Beijing China Institute of Geophysics SSB Beijing China 《中国地震研究》1997,(4)
There have been 12 possible locations of the earthquakes occurring in the South Yellow Sea since 1505.In this paper,the location of the earthquake that occurred in 1505 has been determined by the collection of more historical data of the influenced field,referring the isoseismal data of earthquakes with the epicentral intensityⅨ and combining geophysical field data with tectonic condition,due to its great influence on seismic safety assessment of some significant engineering. 相似文献
188.
189.
190.
线性度方法在前兆观测数据分析处理中的应用 总被引:3,自引:1,他引:3
利用空间线性度方法,对前兆场中不同台站,不同学科的前兆观测数据从总体形态上进行综合分析,得到关于描述前兆场的新的特征量a(空间线性度)本文给出了空间线性度的具体计算方法,并以华北地区为例,分析处理了区内1970~1994年部分地电阻率和地下水位观测资料,所得结果表明,新的前兆特征量a在中强地震之前一年左右时间内有异常显示。 相似文献