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   464篇
  免费   132篇
  国内免费   603篇
测绘学   1篇
大气科学   2篇
地球物理   139篇
地质学   974篇
海洋学   1篇
天文学   1篇
综合类   73篇
自然地理   8篇
  2017年   4篇
  2016年   6篇
  2015年   1篇
  2013年   11篇
  2011年   45篇
  2010年   25篇
  2009年   57篇
  2008年   17篇
  2007年   32篇
  2006年   114篇
  2005年   111篇
  2004年   121篇
  2003年   116篇
  2002年   58篇
  2001年   65篇
  2000年   54篇
  1999年   36篇
  1998年   50篇
  1997年   44篇
  1996年   32篇
  1995年   24篇
  1994年   12篇
  1993年   45篇
  1992年   52篇
  1991年   14篇
  1990年   12篇
  1989年   17篇
  1988年   4篇
  1987年   10篇
  1986年   6篇
  1982年   1篇
  1959年   1篇
  1950年   2篇
排序方式: 共有1199条查询结果,搜索用时 31 毫秒
991.
INT正ODU**!0厂Nln以la Is located In the nol’th segmentdthe North-southselsnuc Belt,Whlchls thejuncturedthe Qinghai-Xizang(Dbet)block,Alxa block and Odos block.In that region,the tectonic activity。svery strong;。y strong earthquakes occu。d In history,such as the 1739 ingluo M。8.0 earthqu拙eandl920 Halyuan M。8.5 eafthquake,etc.; Merately strongeaFthquakes are still veryactlve atpresent,onlyln the Wuzhong-un斟m area,there have been7 e血hquakes tvlth M。>5.0 to occ…  相似文献   
992.
本系统研究了扬子地台西缘宁蒗泸沽湖地区志留系沉积旋回及海相碳酸盐岩的锶、碳、氧同位素特征,并对同位素曲线演化规律与海平面变化和区域地壳运动的关系进行了探讨。研究结果表明,本区志留系除底部有少量细碎屑岩沉积外,主要为浅海潮坪相碳酸盐岩沉积,其锶、碳、氧同位素值变化范围分别是0.7093~0.7196、-1.28‰~2.74‰和-1.302‰~-10.721‰;平均值分别是0.7114、0.984‰和-7.810‰。由于受区域地壳隆升运动的影响,同位素组成和同位素演化规律与海平面变化的关系并不明显。  相似文献   
993.
The δ18O values of vein quartz of different stages from the Yinshan ore deposit are constant around 16‰ and the calculated δ18OH2O values attain 8‰± ; the δDH2O values of fluid inclu-sions in vein quartz are constant at about-60‰. From the surface down to 1200 m below the δ18O values of altered rocks gradually decrease from 15‰± to 11‰± . Various water-rock inversion calculations indicate that the ore fluids were formed by the interaction between meteoric water and phyllite at 350℃ and the effective W/ R value of around 0.1. When the water-rock exchange in the upper mineralization system took place, the effective W / R value increased to 5.0 or more. As a result, an evolution and mineralization model of a buffered open system with two-stage water-rock interactions is proposed in this study.  相似文献   
994.
桂阳宝山铅锌银矿中部铅锌矿伴生银赋存特征   总被引:6,自引:0,他引:6  
张刚生 《湖南地质》1996,15(3):159-162
宝山中部沿锌矿属中低温热液充填交代型矿床,伴生银平均品位为233g/t。银的主要载体矿物为方铅矿,闪锌矿。银呈独立矿物相为主,(含)银矿物共12种,为一系列复杂的硫盐矿物。银易于随主金属铅锌一起回收,理想回收率达93.77%。  相似文献   
995.
In this paper the author first reviews 6 major advances in the study of Precambrian geologyand tectonics of South China during the last decade, and then proposes the following new modelof Late Precambrian scissors-type opening-closing tectonic evolution in the region. (1) Besidesthe Middle-Late Proterozoic low-grade metamorphic basement, there existed a LateArchaean-Early Proterozoic medium- to high-garde metamorphic basement in South China;both of them formed the united Yangtze-Cathaysia (craton) at the end of the Early Proterozoic,with the Jiangxi-Anhui-Zhejiang palaeogulf extending into the inland and the Jiangxi-Anhui-Jiangsu Peninsula lying on the northern side of the palaeogulf.(2) From the Middle Proterozoic,the present Guangxi-Guizhou-Hunan area in the western-central oldland was subjected toextensional rifting and became a rift trough, thus resulting in counterclockwise rotation of the"Cathaysian block" and clockwise rotation of the "Yangtze block"; moreover, the southwardcompression of the Dabie-Jiaonan block which split from the southern margin of the NorthChina plate and was accreted to the northern margin of the Jiangxi-Anhui-Jiangsu Peninsula ledto the scissors-type closing of the Jiangxi-Anhui-Zhejiang palaeogulf during the Middle-earlyLate Proterozoic, which further influenced the Early Palaeozoic tectonic evolution of the region.  相似文献   
996.
福建郭山高岭土矿床中高岭矿物的研究   总被引:1,自引:0,他引:1  
本文运用X射线衍射、红外吸收光谱、分析电子显微术和化学分析等多种方法对福建郭山高岭土矿床中的高岭矿物(高岭石和埃洛石)的矿物学性质、分布及矿物形成的阶段性变化进行了系统研究。结果表明,根据高岭石和埃洛石相对含量的多少,花岗岩风化剖面全风化带划分的4个矿物段可以反映这两种矿物的分布特点。埃洛石为具有管状和多面体球状的7?型以及10?—7?、7?-高岭石过渡型。高岭石晶体形态和结晶有序度在风化剖面垂直方向上的规律性变化与高岭石的形成经历了初始结晶——强烈高岭土化——风化作用后期的阶段性变化有关。  相似文献   
997.
Based on the new data of isotopic ages and geochemical analyses, three types of Mesozoic granites have been identified for the Xiong'ershan-Waifangshan region in western Henan Province: high-Ba-SrⅠ-type granite emplaced in the early stage (~160 Ma),Ⅰ-type granite in the middle stage (~130 Ma) and anorogenic A-type granite in the late stage (~115 Ma). Geochemical characteristics of the high-Ba-SrⅠ-type granite suggest that it may have been generated from the thickened lower crust by partial melting with primary residues of amphibole and garnet. Gradual increase of negative Eu anomaly and Sr content variations reflect progressive shallowing of the source regions of these granites from the early to late stage. New 40Ar/39Ar plateau ages of the early-stage Wuzhangshan granite (156.0±1.1 Ma, amphibole) and middle-stage Heyu granite (131.8±0.7 Ma, biotite) are indistinguishable from their SHRIMP U-Pb ages previous published, indicating a rapid uplift and erosion in this region. The representative anorogenic A-type granite, Taishanmiao pluton, was emplaced at~115 Ma. The evolution of the granites in this region reveals a tectonic regime change from post-collisional to anorogenic between~160 Ma and~115 Ma. The genesis of the early- and middle-stageⅠ-type granites could be linked to delamination of subducted lithosphere of the Qiniing orogenic belt, while the late-stage A-type granites represent the onset of extension and the end of orogenic process. In fact, along the Qiniing -Dabie-Sulu belt, the Mesozoic granitoids in western Henan, Dabieshan and Jiaodong regions are comparable on the basis of these temporal evolutionary stages and their initial 87Sr/86Sr ratios, which may suggest a similar geodynamic process related to the collision between the North China and Yangtze cratons.  相似文献   
998.
以合成雪硅钙石为晶种回收废水中的磷   总被引:2,自引:0,他引:2  
以合成雪硅钙石为晶种,探索了用结晶法以磷酸钙形式回收废水中磷的适宜条件。结果表明,在实验水质条件下,模拟废水pH=8、n(Ca)/n(P)=2、晶种用量大于1.6g/L、振荡24h后溶液中残留磷可达到国家污水综合排放标准一级(0.5mg/L)以下;在优化条件下证实了合成雪硅钙石的供碱能力,循环利用18次,回收磷的效果仍然很好。运用XRD、FTIR、SEM和EDS等测试手段对在实验条件下重复使用18次的雪硅钙石进行了表征,证明回收的磷主要以结晶度不高的羟基磷灰石形态存在。  相似文献   
999.
亚洲地震委员会(ASC)第四次学术大会暨地震学、地震危险性评估和地震风险管理学术讨论会于2002年11月24-26日在尼泊尔加德满都举行。来自亚洲、大洋洲、美洲和欧洲的22个国家的近200名专家出席了会议,会议共收到约110篇研究报告。文章介绍了大会、学术交流和ASC工作会议等情况。  相似文献   
1000.
对西南地区茅口灰岩生物地层对比和峨眉山玄武岩与茅口灰岩之间的界面特征的研究表明,上扬子西缘茅口灰岩在玄武岩喷发前存在差异剥蚀,自西到东可分为深度剥蚀带(内带)、部分剥蚀带(中带)、古风化壳或短暂沉积间断带(外带)和连续沉积带;整个剥蚀区的范围同峨眉山玄武岩分布区基本一致。差异剥蚀是中二叠世晚期上扬子西缘一次快速地壳抬升和穹状隆起的结果,这说明峨眉山大火成岩省的形成与地幔柱活动有关。根据上升地幔柱地表抬升模型对峨眉山大火成岩省空间展布进行了讨论,并推算出该大火成岩省的规模。  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