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   74篇
  免费   14篇
  国内免费   10篇
测绘学   4篇
大气科学   11篇
地球物理   10篇
地质学   24篇
综合类   43篇
自然地理   6篇
  2022年   4篇
  2021年   3篇
  2020年   1篇
  2019年   1篇
  2018年   1篇
  2017年   3篇
  2016年   1篇
  2015年   1篇
  2014年   6篇
  2013年   3篇
  2012年   3篇
  2011年   2篇
  2010年   1篇
  2009年   3篇
  2007年   8篇
  2006年   2篇
  2005年   3篇
  2004年   2篇
  2003年   1篇
  2002年   1篇
  2001年   30篇
  2000年   10篇
  1998年   1篇
  1997年   1篇
  1994年   2篇
  1993年   2篇
  1992年   2篇
排序方式: 共有98条查询结果,搜索用时 15 毫秒
41.
通过分析研究当前我省物探工作中存在的问题和困难,提出了如何开展我省物探工作的设想与建议。  相似文献   
42.
从博物馆学角度出发,通过对博物馆标本的典藏、科学研究和社会教育的介绍,阐述了筹建青海省国土资源博物馆的任务及意义,并提出了建馆初步设想,为下一步制定建馆方案奠定了基础。  相似文献   
43.
青海省北部地区NNW(近SN)向断裂十分发育,卫星影像显示为突出的线性构造,并且相隔一定间距成带出现,这些断裂对矿产有着明显的控制作用,已发现的矿产地多生成于NNW向断裂带内或在其旁侧,深入研究这种依附关系或内在联系,可拓宽找矿工作思路,对找矿工作有着重要指导意义。  相似文献   
44.
In this study, the Variable Infiltration Capacity model and Palmer Drought Severity Index (PDSI) were combined for drought identification on the Loess Plateau. The calibration method of climatic characteristic (K j ) in PDSI was improved. Land cover datasets in 1980 and 2005 were used to drive the model. The driest periods over the past four decades of the study region emerged in 1976–1982, 1997–2001 and 2003–2008. Regardless of ranking by duration, spatial extent or severity, most of the prominent droughts occurred in the detected driest periods. The drought severity and area over the upper reaches of the Yellow River were higher than other domains. A total of 53 droughts with area greater than the 25,000 km2 threshold were identified with durations longer than 3 months using clustering algorithm. Most regions of the study area exhibited spatially increasing trends in drought severity and frequency, indicating that the Loess Plateau has experienced apparent drying and warming processes between 1971 and 2010.  相似文献   
45.
Planting structure influences the economic, social, and ecological benefits of crop farming as well as the use efficiency of water and arable land resources, and so crop planning (CP) benefits for agricultural sustainable development and soil resources utilization. The projection pursuit evaluation (PPE) model is put forward to solve the problem of selecting an optimizing scheme for CP by considering the indices of water‐saving and economic, social, and ecological benefits. The real‐coding‐based accelerating genetic algorithm (RAGA) is introduced to accelerate the calculation process. The model can translate multi‐indices into a single index by transforming high‐dimensional data to low‐dimensional space, which helps evaluate CP optimizing schemes. For example, the model is used to evaluate and select an optimal scheme of CP in the middle reaches of the Heihe mainstream basin in the arid area of northwest China. According to four criteria (high efficiency of resources use, economic rationality, social equity, and ecological security) 19 indices were chosen to evaluate 12 optimizing schemes of four kinds (economic‐benefit, food‐security, ecological‐benefit, and water‐saving programs) in 2006, 2020, and 2030. The result shows that, in the 3 years, the water‐saving program is always the optimized scheme in an arid region with water deficiency and fragile ecology. The evaluated results match up to the developmental conditions of crop farming in recent years. Moreover, the direction of the optimal projection could reflect the weight and orientation of indices objectively and accurately.  相似文献   
46.
The impact of climate change and irrigation technology advancement on agricultural water use in China is analyzed for the period of 1949–2005. The Palmer Drought Severity Index (PDSI) is adopted to characterize climate change, and the Gross Irrigation Quota (GIQ) is used to examine the relationship between agricultural water use and climate change in China. The results show that the GIQ correlates well with the PDSI in Chinese irrigated areas for the period of 1949–1990. A quantitative relationship between the GIQ and PDSI is statistically regressed; a new GIQ dataset is generated with the PDSI based on this relationship over the period 1949–2005. The generated GIQ data with climate-only information follow the pattern of the actual GIQ for the period 1949–1990. Since 1991, the actual GIQ becomes much smaller than the generated GIQ, indicating that irrigation technology advancement exerts a dominant impact on reducing agricultural water use intensity in China.  相似文献   
47.
巴颜喀拉残留洋盆的沉积特征   总被引:6,自引:4,他引:6  
巴颜喀拉盆地垂向沉积序列表明:盆地于早古生代被动陆缘的浅海基础上裂陷、拉开,泥盆纪贯通,早石炭世洋盆扩展为成熟大洋,晚石炭世洋盆北部开始消减、南部继续扩张,晚二叠世-中三叠世进入残留洋阶段,晚三叠世转化为周缘前陆盆地.三叠纪末完全闭合,盆地自形成到消亡为一个连续的沉积和地质构造演化过程。其主体由早中三叠世深海沉积、典型浊积岩复理石和晚三叠世浅海复理石、风暴岩沉积、海相磨拉石构成,北部零星出露了中二叠世海山型沉积,昆南结合带以北有早中三叠世岛弧沉积。以盆地为中心具有向南北两侧陆块双向相背俯冲的极性特点,东西两端的碰撞造山不迟于晚二叠世。总体反映了古特提斯晚二叠世-中三叠世的残留洋盆性质和主洋域之所在。  相似文献   
48.
本文主要应用地球物理指标B(布格重力异常梯度值,单位毫伽/公里)值,结合深断裂、地壳结构、布格重力异常特征、莫霍面形态和历史地震分布,对省内区域地壳划分了四个不稳定区;两个次不稳定区;三个基本稳定区和一个稳定区。  相似文献   
49.
In-situ measurement of atmospheric CO_2 was made at the top of the Waliguan Mountain(36°17′N,100°54′E,3816m asl).where the air is not directly affected by the local anthropogenic and natural sources,by using a nondispersiveinfrared(NDIR)analyzer and following the procedures proposed by WMO.The CO_2 in the flask samples collected onthe mountain was also analyzed in a laboratory.The measurements uncover the daily,monthly and seasonal variabilitiesand the baseline level of the CO_2 in the air over the“clean”area of Chinese hinterland.Results suggest that theCO_2 concentration over the East Asia continent has evident periodical variation,similar to that of global distribution.In1992,an annual mean baseline CO_2 concentration of 356.4 ppm over the continent was obtained.The annual mean val-ue was 357.2 ppm for 1993.Some relationships between the CO_2 concentration at Waliguan and the weather conditions,especially,wind speed and direction are found through the observation.  相似文献   
50.
基于黄河源区1∶25万生态环境地质调查新获得的大量实际资料,通过分析和研究发现,黄河源区早更新世—中更新世处于走滑伸展的大陆动力学背景,在整体隆升中,形成断块山与拉分盆地,湖泊广布;晚更新世,大陆动力学机制过渡为挤压收缩,在整体抬升中,断块山显著崛起,湖盆萎缩、变形;全新世,大陆动力学环境反转为走滑挤压,持续隆升,黄河扩展源头到达本区,扎陵湖、鄂陵湖外泄,闭流盆地水环境转向开放。近代,特别是20世纪70年代以来,新构造活化与寒冻风化岩屑坡扩大、沙质荒漠化蔓延、湖泊和沼泽湿地萎缩、区域地下水位下降、源区黄河频繁断流、生态环境日益恶化响应关系密切。因此,新构造运动在黄河源区生态环境恶化中起主导作用,而其他因素则起到促进与加速的作用。  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