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   181篇
  免费   24篇
  国内免费   67篇
测绘学   5篇
大气科学   13篇
地球物理   34篇
地质学   147篇
海洋学   20篇
天文学   6篇
综合类   10篇
自然地理   37篇
  2023年   2篇
  2022年   5篇
  2021年   9篇
  2020年   1篇
  2019年   2篇
  2018年   5篇
  2017年   4篇
  2016年   3篇
  2015年   6篇
  2014年   15篇
  2013年   8篇
  2012年   10篇
  2011年   8篇
  2010年   11篇
  2009年   16篇
  2008年   18篇
  2007年   13篇
  2006年   14篇
  2005年   12篇
  2004年   9篇
  2003年   15篇
  2002年   12篇
  2001年   22篇
  2000年   15篇
  1999年   16篇
  1998年   1篇
  1997年   4篇
  1996年   6篇
  1994年   2篇
  1993年   1篇
  1991年   1篇
  1988年   2篇
  1986年   1篇
  1985年   1篇
  1983年   1篇
  1981年   1篇
排序方式: 共有272条查询结果,搜索用时 15 毫秒
1.
疏散星团在天文学和天体物理学研究中有着多方面的重要性。近年来在观测和理论工作上都取得了显著的进展。综述了疏散星团的研究现状,对成员判别、基本参数确定、团与恒星的演化、团的结构和动力学进行了详细评述。  相似文献   
2.
科学大洋钻探与深部生物圈   总被引:1,自引:0,他引:1  
从深海钻探计划(DSDP)在20世纪70年代最早提出海洋沉积物中细菌活动性的证据到90年代大洋钻探计划(ODP)获得了令人信服的海底深部生物的存在证据,并成为即将启动的综合大洋钻探计划(IODP)的一个优先研究领域,深部生物圈成为科学大洋钻探近年来最为重大的发现之一,同时它也将有效地促进地球科学和生物学等其他学科的交叉。  相似文献   
3.
滇西沘江流域水体中重金属元素的地球化学特征   总被引:6,自引:1,他引:5  
通过测定流经兰坪金顸铅锌矿区的沘江水体中Pb、Zn、Cd、As的含量和底泥中重金属元素的化学形态的含量,分析了重金属元素的分布和化学形态的变化。结果表明,沘江水遭到了Cd污染,底泥已经成为重金属元素的蓄积库,以国家土壤环境质量标准(Ⅲ级)衡量,Pb、Zn、Cd和舡分别超标3.4倍、15.8倍、106倍和2.6倍。沘江水中重金属元素含量的峰值在矿山附近的下游,而底泥中重金属元素的峰值在矿山下游30-50km的地方,矿业活动、水流变缓、pH等水体环境条件的变化都能影响水和底泥中重金属元素的含量。底泥中的Pb以碳酸盐结合态为主,Zn和Cd以铁锰氧化物结合态为主,而As以残渣态为主。Pb、Cd、Zn三种元素的环境有效态含量比较高,对沘江流域生态环境具有潜在的巨大的危害。  相似文献   
4.
分析了求解变分不等式Newton方法的半局部收敛性,建立了类似于Kantorovich定理的收敛性结果。该结果不仅为判断Newton方法的收敛性提供了可计算的充分条件,也给出了Newton方法的收敛域以及问题解的存在区域。同时,文章也得到了Newton方法的若干收敛性质,包含收敛阶以及可计算的误差估计式等。  相似文献   
5.
Using methods of discontinuous deformation analysis and finite element (DDA+FEM), this paper simulates dynamic processes of the Tangshan earthquake of 1976, which occurred in the northern North China where its internal blocks apparently interacted. Studies focus upon both the movement and deformation of the blocks, in particular, the Ordos block, and variations of stress states on the boundary faults. The Tangshan earthquake was composed of three events: slipping motions of NNE-striking major fault, NE-striking fault near the northeastern end of the NNE-striking fault, and NW-striking fault on the southeastern side of the NNE-striking fault. Compared with previous studies, our model yields a result that is more agreeable with the configuration of aftershock distributions. A number of data are presented, such as the principle stress field during the earthquake, contours of the maximum shear stress, the strike-slip deformation between blocks near the earthquake focus, time-dependent variations of slips of earthquake-triggered faulting, the maximum slip distance, and stress drops. These results are in accord with the earthquake source mechanism, basic parameters from earthquake wave study, macro-isoseismic line, observed horizontal displacement vectors, etc. The Tangshan earthquake exerted different influences on the adjacent blocks and boundary faults between them, thus resulting in differential movement and deformation. The Ordos block seems to have experienced the small-scale counterclockwise rotation and deformation, but its northeast part, bounded on the east by the Taihangshan and on the north by the Yanshan and Yinshan belts, underwent relatively stronger deformation. The Tangshan earthquake also changed the stress state of boundary faults of the North China, leading to an increase in shear stress and a decrease in normal stress in the NW-trending Zhangjiakou-Penglai fault through Tangshan City and the northern border faults of the Ordos block, and therefore raises the potential risk of earthquake occurrence. This result is supported by the facts that a series of Ms ≥ 6 earthquakes took place at the northern margin of the Ordos block after the Tangshan earthquake.  相似文献   
6.
试论会东大银厂铅锌矿找矿模式   总被引:2,自引:0,他引:2  
对大银厂铅锌矿点分布区的地层、构造和成矿地质背景进行了论述,并与大梁子铅锌矿床作了对比,提出了寻找该类矿床的模式及找寻工业矿体最有希望的地段。找矿方法宜先化探后钻探。  相似文献   
7.
图像配准和融合及其在医学影像中的应用   总被引:2,自引:2,他引:2  
图像配准和融合是图像分析和处理的基本问题,在医学影像、遥感、计算机视觉等领域有着广泛的应用。本文研究它们在多模态医学影像技术中的应用。本文提出并实现了基于Fourier变换的图像配准和基于子波变换的图像融合方法,在图像融合中,我们采用特征选择的取大原则,这种准则更适合于来自不同图像中的明显特征  相似文献   
8.
文章选择龙首山隆起区金川、塔马子沟、毛草泉、小口子、藏布台几个镁铁-超镁铁质岩体进行地质、地球化学比较研究,发现岩体普遍具有橄榄石堆晶特征,中段金川岩体以二辉橄榄岩为主要特征,外围岩体以单辉橄榄岩为特征.地球化学数据显示,这些镁铁-超镁铁质岩体处于相同的岩石系列,源区具有相似性,岩体含矿差异主要源自岩浆演化.结合地质综合场模型,提出金川外围岩体在龙首山隆起区,沿构造带东西长约80~100km范围存在金川深部岩浆房响应的产物.  相似文献   
9.
In order to study the migration and transformation mechanism of Hg content and occurrence form in subsurface flow zone of gold mining area in Loess Plateau and its influence on water environment, the field in-situ infiltration test and laboratory test were carried out in three typical sections of river-side loess, alluvial and proluvial strata in Tongguan gold mining area of Shaanxi Province, and the following results were obtained: (1) The source of Hg in subsurface flow zone is mainly caused by mineral processing activities; (2) the subsurface flow zone in the study area is in alkaline environment, and the residual state, iron and manganese oxidation state, strong organic state and humic acid state of mercury in loess are equally divided in dry and oxidizing environment; mercury in river alluvial or diluvial strata is mainly concentrated in silt, tailings and clayey silt soil layer, and mercury has certain stability, and the form of mercury in loess is easier to transform than the other two media; (3) under the flooding condition, most of mercury is trapped in the silt layer in the undercurrent zone where the sand and silt layers alternate with each other and the river water and groundwater are disjointed, and the migration capacity of mercury is far less than that of loess layer and alluvial layer with close hydraulic connection; (4) infiltration at the flood level accelerates the migration of pollutants to the ground; (5) the soil in the undercurrent zone is overloaded and has seriously exceeded the standard. Although the groundwater monitoring results are safe this time, relevant enterprises or departments should continue to pay attention to improving the gold extraction process, especially vigorously rectify the small workshops for illegal gold extraction and the substandard discharge of the three wastes, and intensify efforts to solve the geological environmental problems of mines left over from history. At present, the occurrence form of mercury in the undercurrent zone is relatively stable, but the water and soil layers have been polluted. The risk of disjointed groundwater pollution can not be ignored while giving priority to the treatment of loess and river alluvial landform areas with close hydraulic links. The research results will provide a scientific basis for water conservancy departments to groundwater prevention and control in water-deficient areas of the Loess Plateau.  相似文献   
10.
以蓬莱西海岸西庄至栾家口岸段作为研究区,利用机载成像高光谱数据,对比航空垂直影像图和野外调查结果,通过分析砂质、黑泥砂质和黄泥砂质3种海岸类型的光谱特征,建立分类识别模型,完成了对3种海岸类型的分类处理,确定出湿滩和干滩范围,并进一步提取出高潮潮位线和低潮潮位线。  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