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   117篇
  免费   31篇
  国内免费   66篇
测绘学   19篇
大气科学   23篇
地球物理   26篇
地质学   96篇
海洋学   17篇
综合类   18篇
自然地理   15篇
  2023年   3篇
  2022年   6篇
  2021年   8篇
  2020年   4篇
  2019年   5篇
  2018年   6篇
  2017年   2篇
  2016年   8篇
  2015年   8篇
  2014年   6篇
  2013年   7篇
  2012年   7篇
  2011年   11篇
  2010年   8篇
  2009年   5篇
  2008年   14篇
  2007年   14篇
  2006年   5篇
  2005年   6篇
  2004年   12篇
  2003年   1篇
  2002年   4篇
  2001年   4篇
  2000年   9篇
  1999年   14篇
  1998年   4篇
  1997年   6篇
  1996年   7篇
  1995年   4篇
  1994年   7篇
  1993年   4篇
  1992年   1篇
  1991年   2篇
  1989年   1篇
  1987年   1篇
排序方式: 共有214条查询结果,搜索用时 500 毫秒
101.
The chemical and isotopic characteristics of the water and suspended particulate materials(SPM)in the Yellow River were investigated on the samples collected from 29 hydrological monitoring stations in the mainstem and several major tributaries during 2004 to 2007.TheδD andδ~(18)O values of the Yellow River water vary in large ranges from-32‰to-91‰and from-3.1‰to-12.5‰,respectively.The characters of H and O isotope variations indicate that the major sources of the Yellow River water are meteoric water and snow melting water,and water cycle in the Yellow River basin is affected strongly by evaporation process and human activity.The average SPM content(9.635g/L)of the Yellow River is the highest among the world large rivers.Compared with the Yangtze River,the Yellow River SPM has much lower clay content and significantly higher contents of clastic silicates and carbonates.In comparison to the upper crust rocks,the Yellow River SPM contains less SiO_2,CaO,K_2O and Na_2O,but more TFe_2O_3,Co,Ni,Cu,Zn,Pb and Cd.The abnormal high Cd contents found in some sample may be related to local industrial activity.The REE contents and distribution pattern of the Yellow River SPM are very close to the average value of the global shale.The averageδ~(30)Si_(SPM)in the Yellow River(-0.11‰)is slightly higher than the average value(-0.22‰)of the Yangtze River SPM.The major factors controlling theδ~(30)Si_(SPM)of the Yellow River are the soil supply,the isotopic composition of the soil and the climate conditions.The TDS in the Yellow River are the highest among those of world large rivers.Fair correlations are observed among Cl~-,Na~+,K~+,and Mg~(2+)contents of the Yellow River water,indicating the effect of evaporation.The Ca~(2+)and Sr~(2+)concentrations show good correlation to the SO_4~(2-)concentration rather than HCO_3~-concentration,reflecting its origin from evaporates.The NO_3~-contents are affected by farmland fertilization.The Cu,Zn and Cd contents in dissolved load of the Yellow River water are all higher than those of average world large rivers,reflecting the effect of human activity.The dissolved load in the Yellow River water generally shows a REE distribution pattern parallel to those for the Yangtze River and the Xijiang River.Theδ~(30)Si values of the dissolved silicon vary in a range from 0.4‰to 2.9‰,averaging1.34‰.The major processes controlling the D_(Si)andδ~(30)Si_(Diss)of the Yellow River water are the weathering process of silicate rocks,growth of phytolith in plants,evaporation,dissolution of phytolith in soil,growth of fresh water diatom,adsorption and desorption of aqueous monosilicic acid on iron oxide and human activities.The averageδ~(30)Si_(Diss)value of the Yellow River is significantly lower than that of the Nile River,Yangtze River and Siberia rivers,but higher than those of other rivers,reflecting their differences in chemical weathering and biological activity.Theδ~(34)S_(SO4)values of the Yellow River water range from-3.8‰to 14.1‰,averaging 7.97‰.There is some correlation between SO_4~(2-)content andδ~(34)S_(SO4).The factors controlling theδ~(34)S_(SO4)of the Yellow River water are the SO_4 in the meteoric water,the SO_4 from gypsum or anhydrite in evaporite rocks,oxidation and dissolution of sulfides in the mineral deposits,magmatic rocks and sedimentary rocks,the sulfate reduction and precipitation process and the sulfate from fertilizer.The~(87)Sr/~(86)Sr ratios of all samplesrange from 0.71041 to 0.71237,averaging 0.71128.The variations in the~(87)Sr/~(86)Sr ratio and Sr concentration of river water are primarily caused by mixing of waters of various origins with different~(87)Sr/~(86)Sr ratios and Sr contents resulting from water-rock interaction with different rock types.  相似文献   
102.
获取全球环境与气候变化记录是世界科学钻探发展的必然趋势.白垩纪作为地质历史时期"温室气候"的典型范例时期,提供了温室气候条件下地球气候系统运作和变化的良好档案.但是目前国际上针对白垩纪地层的科学钻探主要限于海相地层,对陆相白垩系的科学钻探尚属空白.在我国松辽盆地北部新近完成的中国白垩纪大陆科学钻探工程——松科1井项目有望在此方面取得重要的突破.该项目经过一年多的努力,钻探工程已经全都结束,总计获取岩心长2485.89 m,收获率达96.46%,是目前为止所获取的国际上第一条最长而且连续的白垩系陆相沉积记录.针对岩心的全面研究工作正在开展并已取得初步成果.相关研究工作进展突出表现在通过厘米级样品的取样与分析,将传统地质学百万年的时间分辨率提高到万年尺度,预计其研究结果可为解决当今的全球变暖问题提供重要的参照.利用松科1井科学钻探工程的原始科学资料和研究成果,对岩心已经和在建的包括岩石地层、古生物、沉积相、古地磁、有机地化、旋回地层、地微生物等十大剖面系列,进行科学钻探成果的集成.初步研究在沉积学和有机地球化学、旋回地层学、松辽古湖泊温度变化、地微生物和古大气中CO2浓度定量重建方面已取得重要进展."松科1井"全部岩心剖切后,38%将馆藏保存,其余将用于现阶段研究,并向全世界科学家开放.后续工程"松科2井"也已经被列入国际大陆钻探计划(ICDP)候选项目.  相似文献   
103.
Qualitative representation of spatial locations and their similarity measurements are essential for the analysis of linguistic term‐based data. Existing methods have focused on the similarities of spatial relations and spatial scenes but have not considered the variations in geometrical representations and relations over scales. This study developed some new measures to assess the similarities of both single‐ and multi‐scale qualitative locations. Region‐ and cell‐based models were used to formalize qualitative locations of spatial objects with respect to multi‐scale frames of reference. The similarities were assessed by integrating the similarities of frames and qualitative relations. The frame similarity measures how two objects are compared considering the common elements that they occupy in the reference frames. Moreover, the similarity of qualitative relation measures how two relations relate two objects to the corresponding elements in the frames. The location similarities at a single level integrate the similarities of the frames and qualitative relations, whereas the location similarities at multiple scales incorporate the variations in qualitative locations over scales. These methods were used to assess location similarities concerning residential areas, roads, and lakes. The results indicated that the location‐based measurements can disclose the distributions of the similarities and that the cell‐based model is more accurate than the region‐based model.  相似文献   
104.
直流场和交变场对泥岩磁化率的影响   总被引:1,自引:0,他引:1  
磁化率值不仅受控于天然岩石和环境物质中磁性颗粒的组合特征,还与实验室内的处理过程有关,包括热处理过程和加场处理过程.热处理过程通常改变磁性矿物的类型,使样品的磁化率值发生明显变化,因而备受关注.但加场处理过程对样品磁化率的影响在于改变其中所含磁性颗粒的磁畴结构,这种变化是微观的,目前尚未受到应有的重视.本文选择8块泥岩样品进行了加场处理对其磁化率影响的研究.样品取自松辽盆地松科1井青山口组一段,主要携磁矿物为准单畴( PSD)或多畴(MD)磁铁矿.在逐步获得等温剩磁直至饱和的过程中,逐步测量样品的磁化率值.随后对其进行单轴系统交变退磁,逐步测量剩磁后,完成磁化率测量.结果发现:1)直流场使样品的磁化率值增大.在低于50mT的外加场中,随外加场的增强,样品的磁化率值快速增大;之后,随外加场的增强,样品的磁化率值基本不变,直到600mT; 600mT ~ 1T之间样品的磁化率值又大幅增大;最终,样品的磁化率较初始值(x0)增大0.84% ~ 3.40%.这种磁化率值的增大受控于样品内PSD或MD磁铁矿磁畴结构的改变,与磁铁矿的含量无关.2)样品获得SIRM后进行的逐步交变退磁使其磁化率值有所降低,随交变场的增强,其降低的幅度也增大,但是,交变场达到100mT时,样品的磁化率值仍较x0高.经逐步交变退磁后,样品的磁化率较x0增加0.03% ~ 2.42%.因而,天然样品在进行磁化率测量之前,不能将其置于任何直流场或交变场中处理.  相似文献   
105.
The characteristics of internal waves (IWs) observed during the Asian Sea International Acoustics Experiment 2001 in the East China Sea are presented in this paper. Temperature data from a 17-element thermistor chain exhibit clear IW features in shallow water. Large-amplitude oscillations, up to 35 m, are noted due to the semi-diurnal internal tides. High-frequency (HF) and narrow-bandwidth IW trains around 6 c/h ride on semi-diurnal IWs. The spectrum of vertical displacement of the IWs, calculated from the thermistor chain data, falls as /spl omega//sup -1.6/ in the frequency band of 0.1-4 c/h. For higher frequencies (>6 c/h), the spectrum falls as /spl omega//sup -3.0/. Vertical coherence of the IWs for both semi-diurnal internal tides and HF IWs is analyzed. Comparisons of our observations with other data, obtained from SWARM95, the Barents Sea, and the Gulf of Mexico, display some common characteristics of shallow-water IWs.  相似文献   
106.
黄河水氢、氧同位素组成的空间变化特征及其环境意义   总被引:5,自引:1,他引:4  
2005年7月从黄河源头到渤海人海口沿黄河干流系统采集了24个水样,对水的氢氧同位素组成进行了分析.黄河水δD和δ18O值的变化范围分别为-91‰~-44‰和-12.4‰~-4.2‰,并且二者都表现出从上游到下游整体逐渐上升的趋势,但青海玛多样品除外.黄河水δ18O和δD的线性关系方程为δD=5.69×δ18O-15....  相似文献   
107.
提出地球重力场中不平衡地壳固体环压、环拉定位集中原理新概念。由于这一新概念的确立,关于地壳斜向滑力最大集中量的物质质量来源理论上可以达到纯固体地壳全部质量的量级。从而找到了地质演化力源中尚未找到的第一力源。指出在斜向滑力等诸力作用下地球壳、幔中固、液环流的存在,论证了基于固、液环流的地质演化的6种地质区型,进而划定了9种地震成因的地质界线。  相似文献   
108.
对商丘市代表站各标准层等压面水汽含量计算分析结果表明:商丘春季空中水资源呈逐月递增趋势,秋季空中水资源呈逐月递减趋势;5月和9月是干旱的关键季节,实施人工增雨的潜力较大;春季的增雨潜力大于秋季.  相似文献   
109.
安徽铜陵矿集区冬瓜山矿床:一个叠加改造型铜矿   总被引:28,自引:4,他引:24  
通过对安徽铜陵地区冬瓜山大型铜矿床详细的野外观察和室内分析对比 ,笔者认为 ,冬瓜山矿床是一个海西期同生沉积的块状硫化物被燕山期岩浆成矿作用叠加而形成的大型铜矿床。经过岩浆叠加改造 ,底部的纹层状含燧石富水高镁碳酸盐岩变为蛇纹石 (滑石 )岩 ;胶黄铁矿、黄铁矿大部分变为磁黄铁矿。这种变质过程是在一种近于封闭的等化学条件下完成的 ,类似角岩化。在有岩浆加入的条件下形成交代夕卡岩 ,这类夕卡岩明显地晚于封闭条件下形成的层状“夕卡岩”。通过岩浆的叠加改造 ,在温度场作用下产生的排金效应使金向上部温度较低的场所富集 ,使矿床中金品位由下而上显著增大 (下部 0 .15× 10 - 6 ,上部 16 .4 7× 10 - 6 ) ,岩浆叠加改造过程中 ,排金效应是金矿床形成的机制之一。同时 ,海西期沉积喷流型块状硫化物矿床与燕山期岩浆成矿作用的叠加是形成大型—超大型铜 (金 )矿床的前提条件之一。也是铜陵地区夕卡岩能形成大型铜矿床的内在原因之一。  相似文献   
110.
<正>Objective The potassic and ultrapotassic rocks relating to the India-Eurasia collision and continual plate convergence are widely distributed in the Lhasa terrane.These rocks are very important to understand the deep processes of the India-Eurasia collision and the uplift and evolution of the Tibetan Plateau.Although high-potassic volcanic rocks are also exposed in the western Lhasa terrane,their formation  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