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   1331篇
  免费   213篇
  国内免费   714篇
测绘学   229篇
大气科学   300篇
地球物理   94篇
地质学   1122篇
海洋学   173篇
天文学   1篇
综合类   78篇
自然地理   261篇
  2024年   9篇
  2023年   15篇
  2022年   46篇
  2021年   55篇
  2020年   63篇
  2019年   61篇
  2018年   58篇
  2017年   77篇
  2016年   86篇
  2015年   103篇
  2014年   105篇
  2013年   158篇
  2012年   128篇
  2011年   132篇
  2010年   104篇
  2009年   119篇
  2008年   115篇
  2007年   120篇
  2006年   127篇
  2005年   113篇
  2004年   88篇
  2003年   56篇
  2002年   50篇
  2001年   48篇
  2000年   37篇
  1999年   26篇
  1998年   33篇
  1997年   22篇
  1996年   23篇
  1995年   15篇
  1994年   12篇
  1993年   8篇
  1992年   6篇
  1991年   6篇
  1990年   5篇
  1989年   5篇
  1988年   2篇
  1987年   4篇
  1986年   5篇
  1985年   3篇
  1984年   5篇
  1983年   2篇
  1982年   3篇
排序方式: 共有2258条查询结果,搜索用时 26 毫秒
1.
海拉尔盆地乌尔逊凹陷古流体动力场数值模拟   总被引:5,自引:0,他引:5  
首先对地下水动力场进行数学描述,以水动力为主线,建立适合该地区的数学模型,选择正确的地质模型参数,主要采用数值计算和模拟等手段,在恢复出乌尔逊凹陷主要目的层在不同地质历史时期古水动力的基础上又恢复出古流体势的演化历史。整体上,在乌尔逊凹陷,各主要地质时期的油势演化特征为西部地区大于东部地区,乌南大于乌北,且低势区的发育有较好的继承性。最后,依据油气聚集理论,进行油气运移聚集系统的划分、油气运移方向的分析,从而得出有关研究区油气运移聚集条件的认识,主要从流体动力的角度考虑,指出有利聚集区,认为在乌尔逊凹陷苏4~苏18井区、苏132~苏17~铜2井区及巴1~巴2~巴4井区为有利油气运移聚集区。  相似文献   
2.
This study examines the local geological conditions and soil structure as possible causes of the collapse of the Zümrüt Building 2 February 2004. This catastrophe resulted in 92 fatalities and 35 injuries. This study also examines other views which claim weak soil structure, elastic and consolidation settlement of soil and excessive groundwater extraction as well as subsidence resulting from the underground silt erosion as possible factors. Zümrüt Building was constructed on normally consolidated, low plasticity clay. The underground water table was 30 m in depth. The internal friction angle of soil was 8°–30°, its cohesion was between 34 and 127 kN/m2 and standard penetration test numbers varied between 11 and 50. The underground water level beneath Zümrüt Building had risen 4.5 m since its construction. Therefore the claim that subsidence resulting from the decrease of underground water level contributed to the collapse is incorrect. Secondly the settlement, resulting from the filling up of the pores created by the silt receding with the underground water, was 4.4 mm in total, and attributing this as the primary cause of the collapse is also incorrect. Soil properties, in situ and laboratory test results showed that the existing and/or expected settlement and the differential ground settlement in the Zümrüt building vicinity had the potential to cause structural damage. The tensile stresses caused by differential settlements recorded here are thought to be an indicator, but not the main cause contributing to the collapse of the building. The Zümrüt Building collapse was due to several compounding mistakes during the construction phase. These were geotechnical and other project faults and the use of low quality construction materials. The resulting catastrophe caused 92 fatalities, 35 injuries and a material loss of approximately US$7 million.  相似文献   
3.
宁文务 《探矿工程》2008,35(8):44-46
在现行规范中,由于桩基沉降估算模式的不同,压缩层厚度的确定方法也不完全相同。对这些方法进行归纳、总结,并通过具体的工程实例,对由不同估算模式确定的压缩层厚度及沉降估算结果进行探讨与分析,认为对于工程场地地质资料掌握较为翔实的情况下,压缩层厚度可采用变形比法确定,否则,宜根据应力比法确定。  相似文献   
4.
This study aimed to contribute to conservation management of reefs of Serpula vermicularis by increasing understanding of the factors influencing larval settlement. The study was carried out in Loch Creran, which supports the most extensive known development of S. vermicularis reefs in the world. Settlement plates were deployed to examine the influence of season, depth, reef density, substrate type and orientation. Monthly deployment of plates revealed settlement of S. vermicularis to occur predominantly from mid-June to mid-October, peaking in late August to early September. Settlement of Pomatoceros spp. peaked much earlier, in late May to early June. Deployment of plates at different depths revealed a marked reduction in S. vermicularis settlement intensity between 6 and 12 m. As this corresponds with the deeper limit of the peripheral fringe of serpulid reefs in the loch, it is suggested that this limit is imposed by a depth-correlated settlement response, rather than reduction in available substrata. Comparisons of various substrata showed a preference by S. vermicularis larvae for a slate over a scallop substrate and no evidence of enhanced recruitment to occupied or unoccupied tubes of S. vermicularis, suggesting that gregarious attraction is unlikely to be a factor causing reef formation. Settlement onto the upper side of a horizontal scallop substrate was found to be insignificant in comparison with the underside or a vertically orientated scallop. Evidence for the role of light in controlling the depth and substrate-orientation preferences of S. vermicularis larvae is discussed. Based on the results of this study, recommendations are made regarding remediation of areas suffering reef damage.  相似文献   
5.
6.
以上海市向阳圩海塘围堰主堤为工程背景,在大量原位实测的基础上通过对各测试结果的统计分析研究了软土海滩围堰堤坝及地基沉降位移特性。结果表明:围堰堤坝及地基沉降具有显著的时效特性,沉降与时间的相关关系可用负指数时效特性曲线拟合;各测点位移值随时间具有明显突变变化,整个沉降时域可分为快速沉降时域区及缓慢沉降时域区。同时,在充分考察了沉降速率随时间变化特性的前提下提出了用该参量预测堤坝稳定时间及最终沉降位移的建议。  相似文献   
7.
在港口工程建设中,快速加固超软弱的吹填地基,采用真空预压法是一个经济有效的方法,再联合以碎石桩加固则能进一步提高地基的承载力、减少地基工后沉降.通过真空预压联合碎石桩加固地基的现场试验以及观测资料的分析,得出真空预压联合碎石桩加固后地基的承载力特征值由原天然地基的60 kPa左右提高到220 kPa,计算结果表明打碎石桩后的地基变形模量Esp与真空预压后的Ea相比提高了1倍,联合碎石桩加固后的地基沉降量比仅经过真空预压的地基减少1/3.  相似文献   
8.
本文根据1996年“中-法合作东海计划”在冲绳海槽中西部边缘区所取柱状样岩芯沉积物粒度分析资料,对该区沉积物特征进行研究。结果表明,火山沉积和富含生物的半远洋深海软泥沉积是本区的主要特征。以481cm为界,上、下两层沉积物截然不同,可能是沉积物的来源不同或者是水动力条件的差异。该区主要受火山活动的影响,其次是黑潮、大洋风暴  相似文献   
9.
冲绳海槽轴线地质特征   总被引:10,自引:2,他引:10  
冲绳海槽位于东海大陆架与琉球岛弧之间,海槽中发育着一系列平行轴向延伸的地堑型正断层。穿越海槽的地震剖面证实了海槽扩张中心的存在,扩张轴沿海槽轴线方向延伸。由于地堑构造中心的扩张速率较大,由某引起的海槽中心下陷的速率大于沉积作用的补偿速率,使海槽中心海底出现明显的下陷。在轴线的大陆坡一侧,陆源沉积占绝对优势;轴线的岛坡一侧,以火山坡碎屑、浮岩、有孔虫软泥为沉积特征。  相似文献   
10.
- Based on field investigations, this paper analyzes three types of harbour basinns and navigation channel excavated on seabed in Jiaozhou Bay, get a general rule of deposition for excavated trough, it found that pollution is one of crucial factors resulting in the deposition of the excavated trough in the east shore of Jiaozhou Bay. With these results, it predicted the annual deposition thickness for the excavated trough and disclosed the fact that it can't be deposited deadly during one storm. At the same time, with two-dimensional numerical model, it studied the effects of the excavated trough and the reclamation near shore on tidal cureent and said that the excavated trough can decrease the current velocity passing through the trough about 10- 15%, but only limited inside and near the trough and there are no effect on other regions; reclamation can cut off the pollution sources and no obvious effect on the currents of the Jiaozhou Bay. Connecting the deep trough and Cangkou tidal channel with a new  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