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   5229篇
  免费   1005篇
  国内免费   571篇
测绘学   1728篇
大气科学   268篇
地球物理   839篇
地质学   2516篇
海洋学   599篇
天文学   158篇
综合类   382篇
自然地理   315篇
  2024年   8篇
  2023年   56篇
  2022年   217篇
  2021年   335篇
  2020年   275篇
  2019年   268篇
  2018年   140篇
  2017年   252篇
  2016年   221篇
  2015年   258篇
  2014年   398篇
  2013年   324篇
  2012年   363篇
  2011年   333篇
  2010年   247篇
  2009年   268篇
  2008年   304篇
  2007年   348篇
  2006年   314篇
  2005年   248篇
  2004年   243篇
  2003年   225篇
  2002年   177篇
  2001年   131篇
  2000年   121篇
  1999年   122篇
  1998年   102篇
  1997年   100篇
  1996年   110篇
  1995年   80篇
  1994年   52篇
  1993年   34篇
  1992年   34篇
  1991年   19篇
  1990年   15篇
  1989年   18篇
  1988年   11篇
  1987年   10篇
  1986年   8篇
  1985年   2篇
  1984年   5篇
  1983年   2篇
  1982年   4篇
  1980年   1篇
  1954年   2篇
排序方式: 共有6805条查询结果,搜索用时 18 毫秒
1.
本文在已有数据处理方法的基础上,利用近代数值逼近理论,给出了从时空域角度描述地壳垂直运动过程的一种具体的函数解析形式。最后给出了一个实际算例。  相似文献   
2.
UV and X-ray space-based interferometry will open unprecedented possibilities for spectral and spatial studies of a wide range of currently unresolvable interacting systems. Ultra-high angular resolution direct imaging of individual} components and transport processes in interacting binary systems is essential for detailed studies and modeling of accretion and activity. Understanding the mass loss characteristics of both components, and the dynamics of the system as a function of time, will provide key inputs to evolutionary models and will revolutionize our view and understanding of the Universe.  相似文献   
3.
The Munich Near-IR Cluster Survey (MUNICS) is a wide-area, medium-deep, photometric survey selected in the K' band. The project's main scientific aims are the identification of galaxy clusters up to redshifts of unity and the selection of a large sample of field early-type galaxies up to z < 1.5 for evolutionary studies. We created a Large Scale Structure catalog, using a new structure finding technique specialized for photometric datasets, that we developed on the basis of a friends-of-friends algorithm. We tested the plausibility of the resulting galaxy group and cluster catalog with the help of Color-Magnitude Diagrams (CMD), as well as a likelihood- and Voronoi-approach. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
4.
Ashok  N. M.  Chandrasekhar  T.  Ragland  Sam  Bhatt  H. C. 《Experimental Astronomy》1994,4(3-4):177-188
A recently developed near infrared high speed photometer intended for lunar oc-cultation studies is described. The primary scientific objective is to reach milli arc second levels of angular resolution so that circumstellar structure of the occulted sources can be resolved. Near infrared sky brightness close to the lunar limb is also studied. Angular diameter derived from the observed occultation of IRC +20169 is presented and system performance discussed.  相似文献   
5.
We have analysed short-exposure high-resolution images obtained on the William Herschel Telescope (WHT), Big Telescope Azimuthal (BTA) and CanadaFranceHawaii Telescope (CFHT) in order to investigate mechanical vibrations that are capable of reducing the high angular resolution allowed by speckle-interferometric methods. After filtering the photon noise we have computed power spectra of the image centres of gravity. In these spectra we have found vibration features that differ from one telescope to another and that vary in particular with the zenith angle. In the case of the WHT we discuss these results in terms of possible causes and in terms of degradation of the transfer function. We present some means to improve the data.  相似文献   
6.
利用三峡地区多年的地形变观测资料,分析了该区的地形变特征。结果表明,各断层活动性甚微或基本不活动,区域地壳相对稳定  相似文献   
7.
鱼卡煤田大煤沟组高分辨率层序地层特征及聚煤规律   总被引:1,自引:0,他引:1  
利用高分辨率层序地层学理论和技术方法,综合地震、测井、岩芯和煤质资料对柴达木盆地北缘鱼卡煤田中下侏罗统大煤沟组地层河湖三角洲沉积体系进行高分辨率层序地层学分析,从中识别出短期、中期、长期3个级别的基准面旋回层序,划分出向上"变深"非对称型、向上"变浅"非对称型及对称型3种短期基准面旋回基本结构类型。依据等时地层对比法则进行不同级次基准面旋回层序的联井对比,建立了大煤沟组的等时地层格架,在等时地层格架内进行了煤层对比,并在等时地层格架内分析了聚煤规律。  相似文献   
8.
车镇凹陷上古生界高分辨率层序地层研究   总被引:2,自引:0,他引:2  
以高分辨率层序地层学原理为指导,利用测井、岩芯和录井等资料,对车镇凹陷上古生界不同级次基准面旋回进行了高分辨率层序划分。将上古生界划分为2个超长期、7个长期、16个中期和45个短期基准面旋回,精细对比研究了短期、中期和长期基准面旋回。其中,短期基准面旋回可分为2大类3种亚类,并区别出A型、B型不对称短期基准面旋回和C型对称性短期基准面旋回,总结了它们的结构特征、形成条件、岩性岩相组成;通过研究不同沉积体系下中期、长期基准面旋回特点,得出中期、长期基准面旋回的特点和发育特征,区别出不同沉积环境下层序界面特点;分析了研究区内超长期基准面旋回特征,综合分析认为车镇凹陷超长期基准面旋回以下降半旋回为主。  相似文献   
9.
This paper presents a new contact calculating algorithm for contacts between two polyhedra with planar boundaries in the three-dimensional discontinuous deformation analysis (3-D DDA). In this algorithm, all six type contacts in 3-D (vertex-to-face, vertex-to-edge, vertex-to-vertex, face-to-face, edge-to-edge, and edge-to-face) are simply transformed into the form of point-to-face contacts. The presented algorithm is a simple and efficient method and it can be easily coded into a computer program. In this paper, formulations of normal contact, shear contact and frictional force submatrices based on the new method are derived and the algorithm has been programmed in VC++. Examples are provided to demonstrate the new contact rule between two blocks.  相似文献   
10.
Comparing satellite data derived map products are affected by differences in data characteristics, image acquisition dates, processing techniques, and classification schemes used for assigning pixels to a thematic class. By comparing two forest maps generated from Landsat Enhanced Thematic Mapper Plus (ETM+) and Advanced Very High Resolution Radiometer (AVHRR) images acquired on the same day, and processed using identical classification scheme and methods these differences were minimized. The ETM+ derived map had higher classification accuracy values and more precise area estimates than the AVHRR derived map. In the ETM+ derived map, 87 of the 599 verification data were misclassified, whereas in the AVHRR derived map, 155 of the 469 verification data were misclassified. Detailed error analyses by land cover class revealed that a land use based definition of forest accounted for 74% (64 out of 87) and 57% (89 out of 155) of the classification errors in ETM+ and AVHRR derived maps, respectively.  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