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   471篇
  免费   20篇
  国内免费   34篇
测绘学   207篇
大气科学   18篇
地球物理   21篇
地质学   86篇
海洋学   48篇
天文学   61篇
综合类   37篇
自然地理   47篇
  2024年   1篇
  2023年   2篇
  2022年   16篇
  2021年   20篇
  2020年   35篇
  2019年   27篇
  2018年   9篇
  2017年   25篇
  2016年   11篇
  2015年   17篇
  2014年   23篇
  2013年   45篇
  2012年   27篇
  2011年   20篇
  2010年   17篇
  2009年   20篇
  2008年   27篇
  2007年   24篇
  2006年   23篇
  2005年   22篇
  2004年   21篇
  2003年   18篇
  2002年   12篇
  2001年   11篇
  2000年   14篇
  1999年   10篇
  1998年   6篇
  1997年   4篇
  1996年   1篇
  1995年   2篇
  1994年   3篇
  1993年   3篇
  1992年   2篇
  1990年   2篇
  1989年   1篇
  1988年   2篇
  1984年   1篇
  1983年   1篇
排序方式: 共有525条查询结果,搜索用时 15 毫秒
521.
武强  刘金韬等 《地质学报》2001,75(4):554-561
采用现场地应力实测、室内不同含水量情况下的断裂带物质的单轴、三轴常规和流变力学试验以及弹塑性三维可视化数值仿真模拟(FLAC^3D)等研究,获得了断裂带物质弱化效应力学参数,阐述了其弱化机理和主要控制因素,提出了煤层底板断裂构造突水时间弱化效应的新概念。对赵各庄矿13水平(-1100m)F8断层破碎带穿越的首采区安全回采方案做出了预测和评价。  相似文献   
522.
四川盆地灯影组白云岩岩溶孔洞储层发育,在四川盆地威远、资阳及高石梯-磨溪地区发现了大型气田。但是该套储层非均质强,储层预测困难,需要进一步从岩溶地质理论出发,恢复岩溶古地貌、古水系,从而掌握该套储层发育分布规律,指导进一步勘探开发。本文选用印模法恢复了高石梯地区灯四顶岩溶古地貌,并结合现代岩溶学和岩溶动力学理论,划分了岩溶台地、岩溶缓坡地和岩溶盆地3类二级地貌单元。应用现代岩溶分类方法,根据微地貌组合形态,对二级地貌作精细刻画,划分了6种三级地貌单元,最后根据岩溶动力学、岩溶水文地质学在高石梯地区刻画出北部、西部和东南部三大水系。认为岩溶缓坡,位于径流区,水动力条件最强,孔洞最发育,是储层勘探方向。精细的古地貌、古水系的刻画对促进高石梯地区灯影组油气勘探开发具有重要实际意义。   相似文献   
523.
本文叙述应用计算机自动识别分类技术在航天遥感图像中对森林资源进行分类的一些探索研究。本文介绍了采用自编程序“地理坐标系和图像坐标系的精密仿射变换”、“识别型增强技术”、“多光谱信息的特征提取”、“多光谱模糊算法聚类分析”等一系列算法后所取得的分类图像结果,与实地及目视解译相比较,森林分类相对精度达90%。  相似文献   
524.
We present relative astrometric measurements of visual binaries, made in 2012 with the speckle camera PISCO at the 102‐cm Zeiss telescope of Brera Astronomical Observatory, in Merate. Our observing list contains orbital couples as well as binaries whose motion is still uncertain. We obtained 355 new measurements of 344 visual binary stars, with angular separations in the range 0′.14–6′.9, and an average accuracy of 0.′02. The mean error on the position angles is 0°.5. Most of the position angles were determined without the usual 180° ambiguity with the application of triple‐correlation techniques and/or by inspection of the long integration files. We also present new revised orbits for ADS 10786 BC, 12144, 12515, 16314, and 16539, partly derived from PISCO observations. The corresponding estimated values for the masses of those systems are compatible with the spectral types. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   
525.
We present relative astrometric and photometric measurements of visual double stars made in 2013–2015, with PISCO2 installed at the 76-cm refractor of Côte d'Azur Observatory in Nice (France). Our observing list contains orbital couples as well as double stars whose motion is still uncertain. Most of the observations were done in 2015, but some other observations of wide couples were done in 2013–2014 (0.3% of the total of the observations). Three different techniques were used for obtaining measurements: lucky imaging, speckle interferometry and the direct vector autocorrelation method. From our observations of 2837 multiple stars, we obtained 5182 new measurements with angular separations in the range of 0 $$ {}^{{\prime\prime} } $$ .1–32 $$ {}^{{\prime\prime} } $$ and an average accuracy of 0 . 018 $$ {0}^{{\prime\prime} }.018 $$ . The mean error on the position angles is 0°.8. Most of the position angles were determined without the usual 180° ambiguity with the application of the direct vector autocorrelation technique and/or by inspection of the Lucky images or the long integration files. We managed to routinely monitor faint systems ( m V 9 11 $$ {m}_V\approx 9-11 $$ ) with large magnitude difference (up to Δ m V 4 . 5 $$ \Delta {m}_V\approx 4.5 $$ ). We have thus been able to measure 21 systems containing red dwarf stars that had been poorly monitored since their discovery, from which we estimated the stellar masses thanks to Gaia measurements. We also measured the magnitude difference of the two components of 1079 double stars with an estimated error of 0.2 mag. Except for a few objects that are discussed, our measurements are in good agreement with the ephemerides computed with published orbital elements, even for the double stars whose separation is smaller than the diffraction limit. Thanks to good seeing images and with the use of high-contrast numerical filters, we have also been able to obtain 196 measurements with an angular separation smaller than the diffraction limit of our instrumentation, and consistent with those obtained with larger telescopes. We also report measurements of the 164 new double stars that we found in the files obtained during the observations. Finally, from a study of the DR3 Gaia release, it is shown that all the objects of the Tycho Double Star Catalog that we did not resolve in 2015 are probably false detections by Tycho.  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