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   1247篇
  免费   92篇
  国内免费   136篇
测绘学   706篇
大气科学   41篇
地球物理   113篇
地质学   359篇
海洋学   87篇
天文学   65篇
综合类   84篇
自然地理   20篇
  2024年   2篇
  2023年   12篇
  2022年   37篇
  2021年   77篇
  2020年   91篇
  2019年   58篇
  2018年   32篇
  2017年   97篇
  2016年   64篇
  2015年   79篇
  2014年   86篇
  2013年   84篇
  2012年   69篇
  2011年   67篇
  2010年   66篇
  2009年   54篇
  2008年   54篇
  2007年   65篇
  2006年   62篇
  2005年   45篇
  2004年   30篇
  2003年   37篇
  2002年   37篇
  2001年   46篇
  2000年   22篇
  1999年   18篇
  1998年   23篇
  1997年   12篇
  1996年   9篇
  1995年   5篇
  1994年   10篇
  1993年   7篇
  1992年   6篇
  1991年   3篇
  1990年   5篇
  1988年   2篇
  1981年   1篇
  1954年   1篇
排序方式: 共有1475条查询结果,搜索用时 381 毫秒
51.
利用RS技术发现耕地损毁,网络RTK测量耕地损毁范围及面积,GIS提取耕地被损毁前的分类面积和等别,以及利用网络RTK配合Maptek I-Site8810三维激光扫描仪重构损毁耕地三维模型。  相似文献   
52.
在利用三维激光扫描仪进行测量工作前,我们首先应了解其实际测量精度是否符合标称精度,而可靠的评价方式对得到精确的数据结果至关重要。本文利用北京卓立汉光TSA50-C型电动位移台作为评价标准,通过其精确的位移功能,准确地评价了RIGEL VZ-400三维激光扫描仪在测量单点位移时的误差,从而得到了其最佳工作距离。  相似文献   
53.
利用地面三维激光扫描仪对目标物体表面进行多方位、多角度的扫描,可以获取其表面大量且密集的高精度点的三维坐标信息以及反射率信息,将这些信息存储到电脑中,使用专业软件进行处理,再使用建模软件生成建筑物的三维模型。本文所研究的是使用地面三维激光扫描仪,通过高速激光测量方式,快速、全面、精确地获取建筑物表面的三维信息,经过一系列的点云数据处理及模型处理,最终完成曲面模型三维重建的过程。  相似文献   
54.
针对城市电力隧道结构、走向多变、电缆设施多、电磁干扰大等因素,常规的监测方法难以顺利完成的现状,对目前先进的3种隧道结构自动化监测系统进行深入的研究比较,光纤传感自动技术解决了电力隧道结构监测点布设困难,数据受电磁干扰大的问题,能实时有效、可靠、高精度地监控电力隧道,及时掌握隧道的应力、应变及振动等主要结构参数,确保隧道结构安全。研究对类似的城市电力隧道自动化监测具有一定的参考意义。  相似文献   
55.
传统基于GPS和全站仪的地表变形监测手段由于监测点少,难以对滑坡体进行整体监测,本文提出基于点云所成模型间比较的变形信息提取方法,结合试验验证了算法的效果。结果表明,地面三维激光扫描技术应用于变形监测领域是完全可行的,虽然其在测量精度上略低于GPS、全站仪等传统监测手段,但对大范围区域快速、连续、全方位监测的优势是其他监测手段所不具备的。  相似文献   
56.
As an important canopy structure indicator, leaf area index (LAI) proved to be of considerable implications for forest ecosystem and ecological studies, and efficient techniques for accurate LAI acquisitions have long been highlighted. Airborne light detection and ranging (LiDAR), often termed as airborne laser scanning (ALS), once was extensively investigated for this task but showed limited performance due to its low sampling density. Now, ALS systems exhibit more competing capacities such as high density and multi-return sampling, and hence, people began to ask the questions like—“can ALS now work better on the task of LAI prediction?” As a re-examination, this study investigated the feasibility of LAI retrievals at the individual tree level based on high density and multi-return ALS, by directly considering the vertical distributions of laser points lying within each tree crown instead of by proposing feature variables such as quantiles involving laser point distribution modes at the plot level. The examination was operated in the case of four tree species (i.e. Picea abies, Pinus sylvestris, Populus tremula and Quercus robur) in a mixed forest, with their LAI-related reference data collected by using static terrestrial laser scanning (TLS). In light of the differences between ALS- and TLS-based LAI characterizations, the methods of voxelization of 3D scattered laser points, effective LAI (LAIe) that does not distinguish branches from canopies and unified cumulative LAI (ucLAI) that is often used to characterize the vertical profiles of crown leaf area densities (LADs) was used; then, the relationships between the ALS- and TLS-derived LAIes were determined, and so did ucLAIs. Tests indicated that the tree-level LAIes for the four tree species can be estimated based on the used airborne LiDAR (R2 = 0.07, 0.26, 0.43 and 0.21, respectively) and their ucLAIs can also be derived. Overall, this study has validated the usage of the contemporary high density multi-return airborne LiDARs for LAIe and LAD profile retrievals at the individual tree level, and the contribution are of high potential for advancing forest ecosystem modeling and ecological understanding.  相似文献   
57.
在建筑物立面重建中,窗户提取、结构识别是学者们研究的热点。针对建筑物特征提取的应用需求,文中提出一种基于局部搜索算法——爬山法的窗户信息提取方法,介绍研究中采用的一些原理、方法,从而可以准确有效地从激光扫描数据中提取出建筑物的窗户信息。利用本方案对地面激光扫描系统获取的建筑物实验数据进行具体的处理,并给出可视化表达结果。  相似文献   
58.
The LA‐ICP‐MS U‐(Th‐)Pb geochronology international community has defined new standards for the determination of U‐(Th‐)Pb ages. A new workflow defines the appropriate propagation of uncertainties for these data, identifying random and systematic components. Only data with uncertainties relating to random error should be used in weighted mean calculations of population ages; uncertainty components for systematic errors are propagated after this stage, preventing their erroneous reduction. Following this improved uncertainty propagation protocol, data can be compared at different uncertainty levels to better resolve age differences. New reference values for commonly used zircon, monazite and titanite reference materials are defined (based on ID‐TIMS) after removing corrections for common lead and the effects of excess 230Th. These values more accurately reflect the material sampled during the determination of calibration factors by LA‐ICP‐MS analysis. Recommendations are made to graphically represent data only with uncertainty ellipses at 2s and to submit or cite validation data with sample data when submitting data for publication. New data‐reporting standards are defined to help improve the peer‐review process. With these improvements, LA‐ICP‐MS U‐(Th‐)Pb data can be considered more robust, accurate, better documented and quantified, directly contributing to their improved scientific interpretation.  相似文献   
59.
LA‐ICP‐MS is increasingly applied to obtain quantitative multi‐element data with minimal sample preparation, usually achieved by calibration using reference materials (RMs). However, some ubiquitous RMs, for example the NIST SRM 61× series glasses, suffer from reported value uncertainties for certain elements. Moreover, no long‐term data set of analyses conducted over a range of ablation and tuning conditions exists. Thus, there has been little rigorous examination of the extent to which offsets between measured and reported values are the result of error in these values rather than analytically induced fractionation. We present new software (‘LA‐MINE’), capable of extracting LA‐ICP‐MS data with no user input, and apply this to our system, yielding over 5 years of data (~ 5700 analyses of ten glass and carbonate RMs). We examine the relative importance of systematic analytical bias and possible error in reported values through a mass‐specific breakdown of fourteen of the most commonly determined elements. Furthermore, these data, obtained under a wide range of different ablation conditions, enable specific recommendations of how data quality may be improved, for example the role of diatomic gas, the effect of differential inter‐glass fractionation factors and choice of transport tubing material. Finally, these data demonstrate that the two‐volume Laurin ablation cell is characterised by no discernible spatial heterogeneity in measured trace element ratios.  相似文献   
60.
现代地球科学研究的重大突破在很大程度上取决于观测和分析技术的创新。新世纪以来,我国地球科学领域引进了一批高性能新型微束分析仪器设备,建立了一批高规格的实验室。本文回顾了近十年来微束分析技术与方法的主要进展及其在地球科学研究中的应用实例,包括电子探针、扫描电镜、透射电镜、大型离子探针、纳米离子探针、飞行时间二次离子质谱、激光剥蚀等离子体质谱、激光诱导原子探针、原子探针技术、显微红外光谱、同步辐射等,这些分析技术的进步和广泛应用极大地提高了我们对地球和行星演化历史及许多地质过程的理解。今后,应加快微束分析的新技术、新方法和新标准的开发,特别是高水平人才队伍建设,提高创新能力并在国际学术舞台上发挥重要作用。  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