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   1380篇
  免费   240篇
  国内免费   437篇
测绘学   30篇
大气科学   139篇
地球物理   229篇
地质学   1040篇
海洋学   21篇
天文学   2篇
综合类   96篇
自然地理   500篇
  2024年   8篇
  2023年   14篇
  2022年   40篇
  2021年   55篇
  2020年   69篇
  2019年   64篇
  2018年   70篇
  2017年   69篇
  2016年   79篇
  2015年   68篇
  2014年   105篇
  2013年   91篇
  2012年   105篇
  2011年   107篇
  2010年   81篇
  2009年   95篇
  2008年   74篇
  2007年   118篇
  2006年   117篇
  2005年   86篇
  2004年   77篇
  2003年   87篇
  2002年   54篇
  2001年   36篇
  2000年   33篇
  1999年   42篇
  1998年   24篇
  1997年   33篇
  1996年   25篇
  1995年   21篇
  1994年   29篇
  1993年   17篇
  1992年   20篇
  1991年   8篇
  1990年   9篇
  1989年   13篇
  1988年   5篇
  1987年   5篇
  1985年   1篇
  1984年   1篇
  1982年   1篇
  1954年   1篇
排序方式: 共有2057条查询结果,搜索用时 187 毫秒
891.
甘湫池是翠华山国家地质公园的一个新景点。实地调查发现,整个景区是一座罕见的基岩古滑坡,具有滑坡地貌可观察的景观形态特征。从空间分布和层序关系来看,上覆的崩塌乱石是后期堆积在古滑坡体上,甘湫池应是古滑坡形成的拉伸洼地,并非是由崩塌形成的堰塞湖,同时在景观形态上也与水湫池明显不同,这对于科学认识和开展地质遗迹旅游具有重要的意义。  相似文献   
892.
??????????????????????????仯?????????????????????????? ????????????????????,?????????С?????????????????????????????á??й?????????????硱?????????400???GPS?????????????1999??\,2001???2004?????????????????1999~2001?????????????仯??2001~2004???????1999~2001????????????仯???????????1)????????????????????????????ε????????????????????????2)?????????ε??????????????????????3)2001???????8.1????????????????????????ο?????????????????????????????????????????????4)???????????2001???????8.1???????????????????????????????????????????????????????????????????????????????????????????????  相似文献   
893.
根据最新区域地质调查的代表剖面,在分析研究下二叠统开心岭群、上二叠统乌丽群的岩性组合特征、沉积类型、古生物面貌的基础上,将二叠系建立5个岩石地层单位和相应的5个生物地层单位,代表栖霞期—长兴期地层层序与生物序列;区内生物性质属特提斯动物群和华夏植物群;青南乌丽与藏北双湖及昌都妥坝属同一含煤建造,成煤期为龙潭中期—长兴期。  相似文献   
894.
In this paper predecessorsˊ achievements about the division between subtropical zone and warm temperate zone on the south slope of Funiu Mountain are firstly summarized,and the cause why these viewpoints about the division are different also has been presented.Seven soil profiles at different heights above sea level are dug along the south slope of Funiu Mountain.Many compositions and properties of soil humus have been analyzed in laboratory.A comprehensive study has been made about the division according to the compositions and properties of soil humus with mathematical method.During the analysis process eitht indexes have been used,such as altitude,organic carbon,humic acid(HA),fulvic acid(FA),the ratio of humic acid and fulvic acid(HA/FA),two extinction coefficients(E4,E6), and their ratio (E4/E6).The result indicates that the boundary is at about 1000 meters above sea level.  相似文献   
895.
This study investigated a series of dammed lakes and downstream-adjacent alluvial fans in the upstream to middle reaches of the Golmud River in the eastern Kunlun Mountain, on the north-eastern Qinghai-Tibetan Plateau (QTP). An optically stimulated luminescence (OSL) chronology shows the sediments of five dammed lakes developed from c. 45–40, 30–25, 18–14, and 12–8 ka, corresponding to MIS 3b, late MIS 3a, Last Deglaciation, and early Holocene, respectively. The remote sensing data show these dammed lakes have a total area of 109.4 km2, with the lake volume of more than 4.0 km3. Symmetric alluvial fans from north–south tributary valleys produced OSL ages of c. 61–52, 42–31, 26–20, and 16–10 ka, corresponding to glaciation periods: the MIS 3c and MIS 3a, MIS 2, and the Last Deglaciation. This suggests that glacial activity is responsible for the alluvial fan development, where dammed rivers occurred first, but lake formation did not take place synchronously until later periods of strong hydrologic activity, resulting from northward intrusions of the Indian summer monsoon (ISM) or glacier melt. Thus, the blocking pattern is that river valleys were dammed during periods of glacial activity and lakes formed during wet periods. The lake formation and subsequent drainage may have resulted in: (i) impeded headwater incision and strengthening of downstream dissection; (ii) enriched the halite and potash in the distal Qarhan Salt Lake through hydrologic and hydrochemical processes of abundant water input, the salt lake expansion, salt redissolution from playa and final resedimentation during later dry periods. The alluvial-dammed lake pattern in the mountain-basin systems of eastern Kunlun Mountain offers a model for assessing the linkages between monsoon dynamics, geomorphic processes and distal salt lake evolutions in other arid regions.  相似文献   
896.
大青山发育的石英闪长岩在地球化学上具有埃达克质花岗岩的特点。它们以较高的硅(Si O2一般大于56%,较高的铝(Al2O3一般大于14%),富钠(Na2O通常大于4%),低K2O/Na2O比(分子数)(通常小于0.4)。它们还富大离子亲石元素(如Rb、Sr)、过渡元素(如Cr、Ni)亏损高场强元素(如Nb、Ti)为特征。球粒陨石标准化稀土图谱显示轻稀土富集型,并具有明显的正Eu异常。锆石U-Pb SHRIMP的测年,结合野外地质和前寒武纪消减带花岗岩演化特征,推断埃达克质花岗岩形成于2435±12Ma。表明该区古元古代存在真正意义的板块构造,俯冲作用已经发生。  相似文献   
897.
马震  王玉丽 《内陆地震》2011,25(3):269-274
介绍了利用ArcGIS系统的三维分析模块实现山区水库项目选址的三维可视化。基于GIS、航测、水工设计等基础资料,通过多个软件工具处理数据,在ArcGIS系统下整合与分析。最终实现了库区的三维地形漫游、水库蓄水、淹没等三维动态过程,为论证工程规模与工程选址提供决策依据。  相似文献   
898.
借鉴国内外实际地形条件下的太阳辐射计算方法,基于数字高程模型,建立了任意地形实际天气下30min太阳辐射估算模型。在此基础上利用2008年9月—2009年6月祁连山高山区马粪沟流域实测辐射资料对模型精度进行了验证,并分析了模型误差来源。结果表明,由于DEM数据误差造成30min太阳辐射模型计算的遮蔽度与实际的遮蔽度存在...  相似文献   
899.
Deserts are one of the most important dust sources in the world. Because dust content changes as a function of height at low levels in the atmosphere, this affects long‐term dust transport. In this paper, field data measured above shifting sands in the south‐eastern Tengger Desert were used to analyse the vertical distribution of sediment fluxes in the near‐surface layer (0 to 48 m). It was possible to express horizontal sediment flux as a power function, but aeolian deposition as a function of height could be expressed as an exponential function. There are two curve types for the particle size distributions in the horizontal sediment flux and aeolian deposition: bimodal and unimodal curves. For the horizontal sediment flux and aeolian deposition, heights of 24 m and 32 m, respectively, were the key heights in the size distribution curve; below these heights, the curve was bimodal, whereas above these heights, it was unimodal. At heights of 4 to 16 m, and especially between 8 m and 12 m, the data were particularly interesting because the sediment size, transport mode, degree of sorting, and the skewness and kurtosis change. For the horizontal sediment flux, wind turbulence moved saltating particles higher than expected.  相似文献   
900.
刘祥  郎建军 《地质论评》2011,57(5):650-658
黑龙江五大连池世界地质公园的老黑山、火烧山火山岩屑崩落(debris-avalanche)形成小丘状沉积.老黑山火山西面、东面和东南面有数十座小丘,火烧山火山北面和东北面也有数十座小丘.最大的小丘高约17m,基座直径50m以上.最远的小丘距火山2km.小丘为崩落堆积的岩块相,由巨大的崩落岩块组成.崩落岩块为灰紫色玄武质...  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