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   1272篇
  免费   605篇
  国内免费   1200篇
测绘学   52篇
大气科学   168篇
地球物理   714篇
地质学   1819篇
海洋学   72篇
天文学   91篇
综合类   93篇
自然地理   68篇
  2024年   1篇
  2021年   2篇
  2016年   1篇
  2015年   4篇
  2013年   9篇
  2012年   4篇
  2011年   183篇
  2010年   101篇
  2009年   166篇
  2008年   43篇
  2007年   114篇
  2006年   224篇
  2005年   266篇
  2004年   506篇
  2003年   297篇
  2002年   235篇
  2001年   176篇
  2000年   115篇
  1999年   79篇
  1998年   91篇
  1997年   102篇
  1996年   67篇
  1995年   56篇
  1994年   40篇
  1993年   92篇
  1992年   59篇
  1991年   18篇
  1990年   3篇
  1989年   11篇
  1988年   1篇
  1987年   8篇
  1986年   1篇
  1982年   1篇
  1979年   1篇
排序方式: 共有3077条查询结果,搜索用时 234 毫秒
981.
采用中子活化分析方法(INAA)测定了鄂尔多斯盆地东北部东胜煤田侏罗系延安组煤中稀土元素(REE)的含量,绘制了稀土元素分布类型曲线并计算了多种化学参数.在对REE的地球化学环境和地球化学特征分析的基础上,得出以下结论:①侏罗纪低灰低硫煤中REE的含量较低,且普遍低于华北盆地石炭二叠纪低灰低硫煤中的REE含量.②侏罗纪煤中的REE主要来自于物源区的陆源碎屑.东胜煤田北部靠近物源区,因此REE含量较南部高,且REE含量与灰分产率和SiO2含量有一定的相关性.③侏罗纪煤中REE的分布类型主要取决于母岩.除两个样品外,其他煤样普遍存在Eu负异常,无正Ce异常存在.④与其他岩石相比,煤中REE的分布类型极其复杂,原因在于开放盆地体系的煤中物质不断的改变和再分配.  相似文献   
982.
库马苏金多金属矿床是最近在进行1∶2.5万土壤化探异常检查过程中发现的,位于新疆阿尔泰山北部诺尔特断陷盆地内。矿体产于下石炭统红山嘴组下亚组第一岩性段的凝灰质细—粉砂岩中,呈NW向带状展布,已控制矿体长逾500m,宽超过200m,矿体有北西翘起而向南东隐伏的可能,目前已控制储量金、铅、锌矿均达小型规模。矿体所在地区地球化学异常、矿化蚀变发育,矿点、矿化点密集,部分矿点已具有一定规模,只是限于地形和工作条件未进行系统的工程控制和详细检查,仅已评价过的20号矿点中就发现相当规模的矿体。通过与同一大地构造位置的哈萨克斯坦块状硫化物矿床特征的初步对比,并对区内地球化学异常、矿化蚀变带及其矿点分布情况进行综合分析,认为本区成矿条件优越,具有较好的找矿前景。  相似文献   
983.
近10年来城市地质学研究和城市地质工作进展述评   总被引:3,自引:0,他引:3  
金江军  潘懋 《地质通报》2007,26(3):366-370371
首先回顾了近10年来城市地质学研究的进展。国际上,城市地质学研究主要集中在城市地质与城市规划的结合、城市地质环境和灾害风险评价等方面,国内则集中在城市地质调查方法、城市地质灾害防治方法等方面。然后回顾了近10年来城市地质工作的情况。国际上,建立城市地质环境动态监测体系是一个新动向。在国内,城市地质调查仍然是今后很长一段时间的工作重点。最后针对目前存在的问题提出了若干对策:城市地质学研究要结合城市发展过程中面临的重大问题,积极运用现代信息技术,大力培养专业人才,主动为城市规划建设服务,编制城市地质工作专项规划,建立城市地质工作成果流通机制等。  相似文献   
984.
Different scales of structural data reveal a complex deformation history of ultrahigh- pressure (UHP) rocks exposed in the Weihai-Rongcbeng area, NE Sulu (northern Jiangsu-eastern Shandong), eastern China. Excluding pre-UHP deformations, at least five major sequential deformational stages (D1-Ds) are recognized. The first deformation (DO produced a weak foliation and lineation in massive eclogites. The foliated eclogite with a dominant foliation containing a stretching and mineral lineation was developed during the I)2 deformation. Both the D1 and D2 deformations occurred under UHP metamorphic conditions, and are well preserved in the eclogite bodies. D3 structures which developed shortly after the formation of granulite/amphibolite facies symplectites are characterized by imbricated associations marked by a regional, steeply dipping foliation, compositional layering, eclogite boudinage, isoclinal folds and reverse ductile shear zones. The D3 deformation was accompanied by decompressional partial melting. A regional, gently dipping amphibolite facies foliation and stretching lineation, low-angle detachments, and dome- and arc-shaped structures formed during the D4 deformation stage dominate to some degree the map pattern of the Weihai-Rongcbeng UHP domain. The last stage of deformation (Ds) gave rise to the final exhumation of the UHP rocks. Ds is characterized by development of brittle-dominated high-angle faulting associated with emplacement of large volmnes of undeformed granite plutons and dykes dated at 134-100 Ma. The deformational and metamorphic sequence followed by the UHP rocks in the Weihai-Rongcheng area is similar to that studied in the entire Dabie-Sulu UHP and HP metamorphic belts from microscopic to mapping scale. Based on structural data, combined with available petrographic, metamorphic and geochronological data, a speculative tectonic evolutionary model for the Dabie-Sulu UHP and IIP belts is proposed, involving continental subduction/collision between the Sino-Korean and Yangtze cratons and subsequent polyphase exhumation histories of the UHP and IIP metamorphic rocks.  相似文献   
985.
An incomplete specimen of Sinosauropteryx prima collected from the Early Cretaceous Yixian Formation of the Dawangzhangzi area in Lingyuan, western Liaoning is depicted. It represents the first systematically described material of this feathered compsognathid outside the Sihetun area in Beipiao. This specimen shows some diagnostic features of Sinosauropteryx prima, such as the very short forelimb in relation to hindlimb with the length ratio of humerus plus radius to femur plus tibia just around 30%, and the long and massive first manual ungual subequal in length to radius. The presence of Sinosauropteryx prima only at Sihetun and Dawangzhangzi supports the suggestion that the fossil-bearing beds in the Sihetun and Dawangzhangzi areas are equivalent to each other within the Yixian Formation.  相似文献   
986.
The Ordos Basin is well-known for the coexistence of oil, natural gas, coal and uranium. However, there has been little research to discuss the genetic relationship between them. In this paper, a case study of the Zaohuohao area in Dongsheng, Inner Mongolia, China, is conducted to investigate the genetic relationship between the natural gas and the uranium accumulation. Fluid inclusion data from the uranium-bearing sandstone samples indicate that the fluid inclusions formed in a gas-water transition zone. Using the homogeneous temperatures of aqueous inclusions coeval with hydrocarbon-bearing inclusions, combined with the buried history and paleo-temperature data, the gas-water transition zone reached the area at about 110 Ma. On the basis of this, the contents of Uranium (U) and Total Organic Carbon (TOC) of the samples were analyzed, and there was no obvious relation between them. With regard to the available data from both publications and this study, it is found that the U mineralization has a spatiotemporal accordance with the gas-water dispersal zone. Thus, it is believed that the natural gas in the gas-water zone is an effective reducer to the U-bearing ground water abundant in oxygen, which is the main factor to U accumulation. This result can be used as the reference to the U mines predicting and prospecting.  相似文献   
987.
塔河地区奥陶系油田水分布与运动学特征研究   总被引:1,自引:0,他引:1       下载免费PDF全文
塔河油田是我国最大的陆上整装碳酸盐岩油田,其油田水分布与运动特征反映了油气运移规律。该区奥陶系油田水现今总体矿化度高,南北向存在从低到高再到低的3个矿化带,各带内平面分割性强,纵向层间差异大。塔河油田奥陶系的流体经历了多期次活动,奥陶系储层共捕获了4~5期盐水包裹体,其均一温度范围集中在60~80℃,90~105℃,110~140℃和145~170℃,盐度集中在0.5%~4%、5%~10%、10%~13%、14%~18%、>18%,反映出奥陶系储层曾经历过了4~5期热流体活动,对照埋藏史与油气运移史,高盐度流体活动与油气运移具有良好的匹配关系,油田水化学指标(油田水变质系数、碳酸盐岩平衡系数等)反映出塔河油区现今保存条件良好。井剖面包裹体纵向温度、盐度纵向不规则变化表明流体的活动以侧向运移为主。流体势分析说明运移方向不仅包括塔河东、南面是烃源岩方向,而且具有高流体势的西面也可能是油气来源方向。  相似文献   
988.
The Heihe River drainage basin is one of the endangered ecological regions of China. The shortage of water resources is the bottleneck,which constrains the sustainable development of the region. Many scholars in China have done researches concerning this problem. Based on previous researches,this paper analyzed characteristics,tendencies,and causes of annual runoff variations in the Yingluo Gorge (1944-2005) and the Zhengyi Gorge (1954-2005),which are the boundaries of the upper reaches,the middle reaches,and the lower reaches of the Heihe River drainage basin,by wavelet analysis,wavelet neural network model,and GIS spatial analysis. The results show that: (1) annual runoff variations of the Yingluo Gorge have principal periods of 7 years and 25 years,and its increasing rate is 1.04 m3/s·10y; (2) annual runoff variations of the Zhengyi Gorge have principal periods of 6 years and 27 years,and its decreasing rate is 2.25 m3/s·10y; (3) prediction results show that: during 2006-2015,annual runoff variations of the Yingluo and Zhengyi gorges have ascending tendencies,and the increasing rates are respectively 2.04 m3/s·10y and 1.61 m3/s·10y; (4) the increase of annual runoff in the Yingluo Gorge has causal relationship with increased temperature and precipitation in the upper reaches,and the decrease of annual runoff in the Zhengyi Gorge in the past decades was mainly caused by the increased human consumption of water resources in the middle researches. The study results will provide scientific basis for making rational use and allocation schemes of water resources in the Heihe River drainage basin.  相似文献   
989.
康定群(康定杂岩)在扬子地台前寒武纪地质研究中具有非常重要的意义,但对其具体的形成时代存在不同认识。本文选择位于德昌茨达—大六槽之间康定群咱里组中斜长角闪岩、斜长片麻岩和花岗质片麻岩进行了较为系统的岩石学和地球化学研究。斜长角闪岩的主、微量元素主要具有N-MORB特征,一个斜长角闪岩样品的地球化学特征介于E-MORB和OIB之间,而斜长片麻岩地球化学具有岛弧岩浆特征。斜长角闪岩的εNd(t)为 3.65~ 12.65,具有亏损地幔岩浆特征,综合分析认为其形成于弧后盆地环境,与盐边群类似。斜长角闪岩和斜长片麻岩的离子探针(SHRIMPⅡ)定年结果表明,康定群玄武岩的形成时代约为830Ma,为新元古代,同时经历了约700Ma的变质作用。本文研究不支持扬子地台西缘存在新太古代—古元古代的古老结晶基底,同时研究表明扬子地台西缘新元古代为岛弧环境。  相似文献   
990.
本文以北京市突发性地质灾害预警预报信息系统为研究对象,讨论了系统设计原则,研究和设计系统的总体架构和详细架构,提出了功能模块、数据库,对比分析了预警预报模型与GIS集成的几种方式。  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