首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   48318篇
  免费   936篇
  国内免费   458篇
测绘学   1266篇
大气科学   3388篇
地球物理   10041篇
地质学   17414篇
海洋学   3958篇
天文学   11053篇
综合类   204篇
自然地理   2388篇
  2022年   319篇
  2021年   516篇
  2020年   562篇
  2019年   564篇
  2018年   1306篇
  2017年   1194篇
  2016年   1510篇
  2015年   856篇
  2014年   1502篇
  2013年   2563篇
  2012年   1556篇
  2011年   1968篇
  2010年   1780篇
  2009年   2416篇
  2008年   1982篇
  2007年   1959篇
  2006年   1821篇
  2005年   1375篇
  2004年   1339篇
  2003年   1240篇
  2002年   1181篇
  2001年   1080篇
  2000年   977篇
  1999年   849篇
  1998年   874篇
  1997年   822篇
  1996年   675篇
  1995年   735篇
  1994年   671篇
  1993年   568篇
  1992年   519篇
  1991年   527篇
  1990年   591篇
  1989年   498篇
  1988年   467篇
  1987年   595篇
  1986年   497篇
  1985年   625篇
  1984年   710篇
  1983年   680篇
  1982年   597篇
  1981年   616篇
  1980年   526篇
  1979年   493篇
  1978年   495篇
  1977年   451篇
  1976年   430篇
  1975年   445篇
  1974年   418篇
  1973年   459篇
排序方式: 共有10000条查询结果,搜索用时 21 毫秒
1.
Geomagnetism and Aeronomy - Additional horizontal traces of ground reflections were observed in a studied series of high-latitude, Kp sounding ionograms from the Interkosmos-19 satellite. The...  相似文献   
2.
Water Resources - An Information–Modeling Complex has been developed for the information support of managerial decision making in the field of rational use, protection, and restoration of...  相似文献   
3.
Natural Resources Research - Ecosystems and their services are essential to human well-being, but mining activities often cause adverse impacts on these services. Although impact of mining...  相似文献   
4.
Wuyep  E. O.  Oluyemi  G. F.  Yates  K.  Akisanya  A. R. 《Natural Resources Research》2020,29(2):1239-1258
Natural Resources Research - Sand failure and production occurs when the formation stress exceeds the strength of the formation, which is derived majorly from the natural material that cements the...  相似文献   
5.
Natural Resources Research - In the present study, ground subsidence in the Aliabad plain (central Iran) was investigated using differential synthetic aperture radar interferometry. The data used...  相似文献   
6.
Ali  Moamen  Abdelmaksoud  Ahmed  Essa  M. A.  Abdelhady  A.  Darwish  M. 《Natural Resources Research》2020,29(4):2575-2597
Natural Resources Research - Two main reservoirs are producing in Komombo Basin: the first one belongs to the C Member of the Six Hills Formation, and the second belongs to the Albian/Cenomanian...  相似文献   
7.
A decision support process is presented to accommodate selecting and scaling of earthquake motions as required for the time domain analysis of structures. Code-compatible suites of seismic motions are provided being, at the same time, prequalified through a multi-criterion approach to induce response parameters with reduced variability. The latter is imperative to increase the reliability of the average response values, normally required for the code-prescribed design verification of structures. Structural attributes like the dynamic characteristics as well as criteria related to variability of seismic motions and their compliance with a target spectrum are quantified through a newly introduced index, δ svsc , which aims to prioritize motions suites for response history analysis. To demonstrate the applicability of the procedure presented, the structural model of a multi-story building was subjected to numerous suites of motions that were highly ranked according to both the proposed approach (δ svsc ) and the conventional one (δ conv ), that is commonly used for earthquake records selection and scaling. The findings from numerous linear response history analyses reveal the superiority of the proposed multi-criterion approach, as it extensively reduces the intra-suite structural response variability and consequently, increases the reliability of the design values. The relation between the target reliability in assessing structural response and the size of the suite of motions selected was also investigated, further demonstrating the efficiency of the proposed selection procedure to achieve higher response reliability levels with smaller samples of ground motion.  相似文献   
8.
9.
A review on the historical evolution of seismic hazard maps in Turkey is followed by summarizing the important aspects of the updated national probabilistic seismic hazard maps. Comparisons with the predecessor probabilistic seismic hazard maps as well as the implications on the national design codes conclude the paper.  相似文献   
10.
Fragility functions are derived for low-rise code compliant & non-compliant special moment resisting frames (SMRFs). Non-compliant SMRFs those built in low strength concrete and lacking confining ties in joint panel zones, commonly found in developing countries. Shake table tests were performed on single-storey and two-storey 1:3 reduced scale representative frames to understand the damage mechanism and develop deformation-based damage scale. The non-compliant SMRF experienced column flexure cracking, longitudinal bar-slip in beam and observed with cover concrete spalling from the joint panels. The code compliant SMRF experienced flexure cracks in beam/column, and experienced joint cracking under extreme shaking. Numerical modeling technique is developed for inelastic modeling of reinforced concrete frame with beam bar-slip and joint damageability using SeismoStruct. Natural accelerograms were used to analyze the considered frames through incremental dynamic analyses in SeismoStruct. A probabilistic based approach was used to derive fragility functions for the considered frames. An example case study is presented for damageability evaluation of structures for earthquakes of various return periods (43, 72, 475, 2475 years).  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号