全文获取类型
收费全文 | 803篇 |
免费 | 162篇 |
国内免费 | 343篇 |
专业分类
测绘学 | 128篇 |
大气科学 | 142篇 |
地球物理 | 131篇 |
地质学 | 513篇 |
海洋学 | 216篇 |
天文学 | 10篇 |
综合类 | 80篇 |
自然地理 | 88篇 |
出版年
2024年 | 6篇 |
2023年 | 27篇 |
2022年 | 71篇 |
2021年 | 78篇 |
2020年 | 49篇 |
2019年 | 56篇 |
2018年 | 71篇 |
2017年 | 47篇 |
2016年 | 61篇 |
2015年 | 67篇 |
2014年 | 49篇 |
2013年 | 62篇 |
2012年 | 68篇 |
2011年 | 98篇 |
2010年 | 67篇 |
2009年 | 65篇 |
2008年 | 52篇 |
2007年 | 59篇 |
2006年 | 70篇 |
2005年 | 51篇 |
2004年 | 40篇 |
2003年 | 18篇 |
2002年 | 20篇 |
2001年 | 20篇 |
2000年 | 8篇 |
1999年 | 4篇 |
1998年 | 6篇 |
1997年 | 4篇 |
1996年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 1篇 |
1987年 | 2篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 1篇 |
排序方式: 共有1308条查询结果,搜索用时 0 毫秒
41.
基于GIS的震害空间分布图集的设计与编制 总被引:2,自引:0,他引:2
快速地生成震害分布预测图,对提高减灾救灾能力有着重要意义。本研究采用3S(地理信息系统—G IS、全球定位系统—GPS和遥感—RS)技术,设计了一套全方位、多角度、综合自然环境、社会经济和人文要素的震害空间分布图集。本文将G IS强大的空间分析和数据管理能力与GPS、RS和地震科学相结合,从设计思想、图集内容、表现形式等方面介绍了专题图集的设计与编制。经过多次地震应急演练,该图集在制图规范化和出图速度方面有了较大的改善,能为应急指挥和辅助决策提供有力的技术保障。 相似文献
42.
CT断层重建中滤波函数设计的新方法 总被引:1,自引:0,他引:1
滤波函数在CT图像重建过程中起着非常重要的作用,直接关系到重建图像质量。为了提高CT重建图像质量,本文从加权平均的思想出发,根据FBP重建算法的理论基础,提出一种设计滤波函数的新思路,并分析了五点加权平均滤波函数性能比较。最后针对Shepp-Logan模型数据和实际的海螺投影数据,设计出一种新的滤波函数并与S-L和R-L滤波函数的重建效果进行了比较。从比较结果可以看出,新设计的滤波函数重建的图像效果在整体性能上最好,在局部地方,其密度分辨率有所提高。本文为滤波函数的设计提出了一种新的想法和思路。 相似文献
43.
校园作为城市高密度地区的典型区域,建筑密度高、道路错综曲折、灾后疏散难度大。以南京中心城区某高校为实证研究案例,展开问卷调查;采用皮尔逊卡方检验法,对校园人群安全意识及疏散行为和性别、年龄、受教育程度及参加疏散演练次数等人员特性信息进行交叉分析,得到存在相关性的变量组;基于Logistic回归模型,建立了人群特征、安全意识评价指标对校园人群疏散行为及心理影响的评价模型,识别疏散行为影响因素,以及各因素的影响程度大小。结果表明:年龄、性别以及参加过疏散演练的次数是影响人群安全意识及疏散行为的显著相关因素,学历是相关因素;地震灾害下受访人群对避难场所的选择偏好为:场地型避难场所>建筑型避难场所>地下空间;参加疏散演练的次数,安全意识、风险认知对灾害发生时的人群疏散行为有显著影响。 相似文献
44.
Effects of precipitation and landuse on runoff during the past 50 years in a typical watershed in the Loess Plateau, China 总被引:2,自引:0,他引:2
Huaxing BI Bin LIU Jie WU Lei YUN Zhihan CHEN Zhewei CUI Prof. in hydrology College of soil water conservation Box Beijing Forestry University Qinghua East Road Haidian District Beijing China Researcher in hydrology Xifeng station of soil water conservation Xifeng Gansu Province China Graduate Assis. 《国际泥沙研究》2009,24(3):352-364
In the past century, great progress has been made worldwide in our understanding of forest-water relationship. The successful forestation programs implemented in China-which have improved the ecological environmental conditions-have gained the attention of many researchers and highlighted the relationship between forestation and water yields. The arid and semi-arid Loess Plateau has received attention from water engineers and eco-hydrological researchers in China because of a shortage in water resources. We selected one of the oldest stations conducting soil and water conservation experiments, the Xifeng soil and water conservation station, and chose the Nanxiaohe catchment and its paired catchments (Yangjiagou catchment and Dongzhuanggou catchment) as our research areas. Trends in precipitation, air temperature, streamflow over the past 50 years, and the effect of changing land use on streamflow were analyzed. The Mann-Kendall test showed that precipitation had a negative trend (downward trend), whereas air temperature showed a positive trend (upward trend) from the past to present in the Nanxiaohe catchment. However, the trends seen in precipitation, air temperature did not contain any "jumping points." The paired catchment approach is used to detect the effects of land cover change on hydrology in the Yangjiagou and the contrast catchment, i.e., Dongzhuanggou catchment in our study. The results showed a large change in land use in the Yangjiagou catchment from 1954 to 2008. An increase in forested land (from 0% to 40.08% from 1954 to 2008) and a reduction of bare land (from 51.26% to 5.50% from 1954 to 2008) accounted for a large part of the change in land use. However, the land use changed little in the contrast catchment. The comparison of streamfiow in the paired catchments showed that forestation reduced streamflow by 49.63% (or 6.5 mm) each year. 相似文献
45.
对滇西南1970年以来所有M≥4.6级地震前的空间活动图像进行研究,用地震频度作为参数描述地震前区域的地震活动增强与平静现象,用空区、条带描述地震的孕震过程,得到以下认识:①地震频度增加是滇西南地区5级以上地震前的共性特征;②滇西南地区M≥4.6级地震前出现空区的比例随着地震震级的增加而有所增加,4.6~4.9级地震前只有60%的地震出现空区,5.0~5.9级地震前有90.9%的地震出现空区,而6.0级以上地震前全部出现空区;③空区平均持续时间也随着震级的加大而增加,空区平均持续时间为13.58个月,最短为3个月,最长为37个月;④主震位置(27/33)多发生在空区边缘(含长轴端12次、短轴端8次)。震前出现条带的规律则不明显。 相似文献
46.
通过1:50000水系沉积物测量、1:25000土壤地球化学测量工作,在安徽上金山地区圈定出多个强度大、峰值高、组合好的W、Mo组合异常,经工程验证,在AP-4、AP-5、AP-8异常范围内发现了钨钼矿体,经过勘查工作最终探获一大型层控矽卡岩型钨钼矿床,实现了江南隆起带东段找矿的重大突破.依据成矿地质条件、地球化学异常及工程验证成果对比研究认为,矿区内AP-3、AP-7化探异常仍有较大的找矿潜力,若进一步开展勘查工作,钨钼资源量将显著增加. 相似文献
47.
High quality marine source rock (HQMSR) is the key prerequisite for medium to large hydrocarbon accumulations. However, the forming mechanism remains unclear. On the basis of the in-vestigation for the geodynamic setting of the Middle-Upper Yangtze during the Early Cambrian in dif-ferent spatial scales and the analysis of trace elements, the main controlling factors of the development of high quality marine source rock are discussed, with specific consideration of the burial rate of the organic matter. The ... 相似文献
48.
XU Bin-bin ZHANG Dong-li ZHANG Pei-zhen ZHENG Wen-jun BI Hai-yun TIAN Qing-ying ZHANG Yi-peng XIONG Jian-guo LI Zhi-gang 《地震地质》2019,41(3):587-602
Slip rate is one of the most important parameters in quantitative research of active faults. It is an average rate of fault dislocation during a particular period, which can reflect the strain energy accumulation rate of a fault. Thus it is often directly used in the evaluation of seismic hazard. Tectonic activities significantly influence regional geomorphic characteristics. Therefore, river evolution characteristics can be used to study tectonic activities characteristics, which is a relatively reliable method to determine slip rate of fault. Based on the study of the river geomorphology evolution process model and considering the influence of topographic and geomorphic factors, this paper established the river terrace dislocation model and put forward that the accurate measurement of the displacement caused by the fault should focus on the erosion of the terrace caused by river migration under the influence of topography. Through the analysis of the different cases in detail, it was found that the evolution of rivers is often affected by the topography, and rivers tend to migrate to the lower side of the terrain and erode the terraces on this side. However, terraces on the higher side of the terrain can usually be preserved, and the displacement caused by faulting can be accumulated relatively completely. Though it is reliable to calculate the slip rate of faults through the terrace dislocation on this side, a detailed analysis should be carried out in the field in order to select the appropriate terraces to measure the displacement under the comprehensive effects of topography, landform and other factors, if the terraces on both sides of the river are preserved. In order to obtain the results more objectively, we used Monte Carlo method to estimate the fault displacement and displacement error range. We used the linear equation to fit the position of terrace scarps and faults, and then calculate the terrace displacement. After 100, 000 times of simulation, the fault displacement and its error range could be obtained with 95%confidence interval. We selected the Gaoyan River in the eastern Altyn Tagh Fault as the research object, and used the unmanned air vehicle aerial photography technology to obtain the high-resolution DEM of this area. Based on the terrace evolution model proposed in this paper, we analyzed the terrace evolution with the detailed interpretation of the topography and landform of the DEM, and inferred that the right bank of the river was higher than the left bank, which led to the continuous erosion of the river to the left bank, while the terraces on the right bank were preserved. In addition, four stages of fault displacements and their error ranges were obtained by Monte Carlo method. By integrating the dating results of previous researches in this area, we got the fault slip rate of(1.80±0.51)mm/a. After comparing this result with the slip rates of each section of Altyn Tagh Fault studied by predecessors, it was found that the slip rate obtained in this paper is in line with the variation trend of the slip rate summarized by predecessors, namely, the slip rate gradually decreases from west to east, from 10~12mm/a in the middle section to about 2mm/a at the end. 相似文献
49.
应用热重-质谱(TG-MS)联用技术对风化煤(WC)及其腐植酸提取后残渣(WCR)的热解行为进行了研究,分析了非烃类(H2、H2O、CO和CO2)、低碳烃类(CH4、C3H6和C3H7)和芳烃类(C6H6)的实验结果,并利用Coast-Redfern积分法对其热解和烃类生成动力学进行了探讨,获得了热解过程和烃类生成动力学参数。结果表明:热解过程中风化煤的质量损失率(38.9%)略大于其腐植酸提取后残渣(36.6%);除CO和CO2外,残渣中非烃类、低碳烃类和芳烃类产物的逸出量都稍微或显著多于风化煤中各类组分的逸出量。用Coast-Redfern积分法求得的动力学参数很好地解释了这一结果。 相似文献
50.
介绍了线路工程中断链的知识,描述了自由设站法曲线测设平面坐标计算及竖曲线高程计算原理,利用Java语言编写了Android应用程序,可实现含有断链的线路上任意点坐标和高程的快速计算。 相似文献