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   1941篇
  免费   332篇
  国内免费   426篇
测绘学   229篇
大气科学   388篇
地球物理   397篇
地质学   751篇
海洋学   248篇
天文学   119篇
综合类   259篇
自然地理   308篇
  2024年   8篇
  2023年   26篇
  2022年   116篇
  2021年   138篇
  2020年   91篇
  2019年   112篇
  2018年   133篇
  2017年   139篇
  2016年   123篇
  2015年   118篇
  2014年   158篇
  2013年   165篇
  2012年   165篇
  2011年   167篇
  2010年   138篇
  2009年   138篇
  2008年   109篇
  2007年   100篇
  2006年   63篇
  2005年   73篇
  2004年   36篇
  2003年   39篇
  2002年   32篇
  2001年   25篇
  2000年   26篇
  1999年   38篇
  1998年   36篇
  1997年   32篇
  1996年   22篇
  1995年   7篇
  1994年   23篇
  1993年   19篇
  1992年   16篇
  1991年   15篇
  1990年   10篇
  1989年   5篇
  1988年   6篇
  1987年   8篇
  1986年   2篇
  1985年   4篇
  1984年   5篇
  1983年   3篇
  1982年   4篇
  1980年   1篇
  1977年   2篇
  1976年   1篇
  1958年   1篇
  1954年   1篇
排序方式: 共有2699条查询结果,搜索用时 234 毫秒
861.
We report the results from a systematic laboratory investigation on the fundamental properties of hydrous ferric sulfates. The study involves 150 experiments with duration of over 4 years on the stability field and phase transition pathways under Mars relevant environmental conditions for five ferric sulfates: ferricopiapite [Fe4.67(SO4)6(OH)2·20H2O], kornelite [Fe2(SO4)3·7H2O], a crystalline and an amorphous pentahydrated ferric sulfate [Fe2(SO4)3·5H2O], and rhomboclase [FeH(SO4)2·4H2O]. During the processes of phase transitions, we observed the phenomena that reflect fundamental properties of these species and the occurrence of other common hydrous ferric sulfates, e.g. paracoquimbite [Fe2(SO4)3·9H2O]. Based on the results of this set of experiments, we have drown the boundaries of deliquescence zone of five hydrous ferric sulfates and estimated the regions of their stability field in temperature (T) – relative humidity (RH) space. Furthermore, we selected the experimental parameters for a next step investigation, which is to determine the location of the phase boundary between two solid ferric sulfates, kornelite [Fe2(SO4)3·7H2O] and pentahydrated ferric sulfate [Fe2(SO4)3·5H2O]. The experimental observations in ferricopiapite dehydration processes were used to interpret the observed spectral change of Fe-sulfate-rich subsurface soils on Mars after their exposure by the Spirit rover to current martian atmospheric conditions.  相似文献   
862.
With the goal of investigating the degree at which the MIR luminosity in the Wide-field Infrared Survey Explorer (WISE) traces the SFR, we analyse 3.4, 4.6, 12 and 22 ??m data in a sample of ~140,000 star-forming galaxies or star-forming regions covering a wide range in metallicity 7.66 < 12 + log(O/H)<9.46, with redshift z?< 0.4. These star-forming galaxies or star-forming regions are selected by matching the WISE Preliminary Release Catalog with the star-forming galaxy Catalog in SDSS DR8 provided by JHU/MPA1?. We study the relationship between the luminosity at 3.4, 4.6, 12 and 22 ??m from WISE and H?? luminosity in SDSS DR8. From these comparisons, we derive reference SFR indicators for use in our analysis. Linear correlations between SFR and the 3.4, 4.6, 12 and 22 ??m luminosity are found, and calibrations of SFRs based on L(3.4), L(4.6), L(12) and L(22) are proposed. The calibrations hold for galaxies with verified spectral observations. The dispersion in the relation between 3.4, 4.6, 12 and 22 ??m luminosity and SFR relates to the galaxy??s properties, such as 4000 ? break and galaxy color.  相似文献   
863.
为了了解用于预测沿光滑分段均匀混合路径传播的地波时延的Millington经验公式的实用性,对Millington经验公式和用于预测沿光滑分段均匀混合路径传播的地波时延的严格的Wait公式进行了比较。在Wait积分法用计算机软件实现的基础上,用上述2种方法分别计算多条实际路径的地波二次相位因子,并对计算结果进行了比较。比较结果表明,在实际工程应用中用Millington经验公式进行地波时延预测符合应用要求。  相似文献   
864.
本文对高精度轻小型航空遥感系统地对地检校场试验进行了分析,详细介绍集成系统检校原理,简要给出外业实验情况以及内业数据处理的过程,重点给出利用POS获取姿态转换得到的影像外方位元素即直接地理定位、单片后交方法获取外方位元素以及直接利用控制点绝对定向,均匀采集检校场外业检查点,进行精度验证的比较结果.最终实现塔吊模拟飞行条件下高精度的直接地理定位.  相似文献   
865.
杨娜  苏玉扬  关艳玲  左建章 《测绘科学》2013,(4):104-106,103
本文对高精度轻小型航空遥感系统地对地检校场试验进行了分析,详细介绍集成系统检校原理,简要给出外业实验情况以及内业数据处理的过程,重点给出利用POS获取姿态转换得到的影像外方位元素即直接地理定位、单片后交方法获取外方位元素以及直接利用控制点绝对定向,均匀采集检校场外业检查点,进行精度验证的比较结果。最终实现塔吊模拟飞行条件下高精度的直接地理定位。  相似文献   
866.
This paper describes a broad perspective of the application of graph theory to establishment of GPS control networks whereby the GPS network is considered as a connected and directed graph with three components. In this algorithm the gross error detection is undertaken through loops of different spanning trees using the “Loop Law” in which the individual components ΔX, ΔY and ΔZ sum up to zero. If the sum of the respective vector components ΩX, ΩY and ΩZ in a loop is not zero and if the error is beyond the tolerable limit (ε>ω), it indicates the existence of gross errors in one of the baselines in the loop and therefore the baseline must be removed or re-observed. After successful screening of errors by graph theory, network adjustment can be carried out. In this paper, the GPS data from the control network established as refence system for the HP Dam at Baishan county in Liaoning province is presented to illustrate the algorithm.  相似文献   
867.
A method of high accuracy surface modeling (HASM) has been constructed to find a solution for error problems that had long troubled surface modeling in geographical information systems (GIS). It is found that when a preconditioned conjugate gradient (PCG) algorithm is used to solve the large sparse linear system, which HASM can be transferred into, HASM performs best in terms of simulation compared with all other algorithms. But its computing speed is not fast enough for all applications. A multi‐grid method is introduced into HASM to try to shorten its computing time. Both numerical and real‐world tests demonstrate that there is a range of stop error (SE). The multi‐grid method of HASM (HASM‐MG) greatly increases computing speed when SEs are within this range, compared with the PCG algorithm of HASM (HASM‐PCG). HASM‐MG is suitable for applications with a need for less accuracy and a shorter computing time. HASM‐PCG is appropriate for issues needing higher accuracy. HASM‐MG performs better than HASM‐PCG in flat areas, while HASM‐PCG does better in complex terrainm in terms of accuracy and computing time.  相似文献   
868.
采用FSS-3DBH型井下地震计,测量山东省邹城市区域发生的矿震、爆破和天然地震相关事件信息,通过波形分析与波谱分析,对比研究不同类型地震事件特征.结果表明,该区域发生的矿震、爆破和天然地震的波形、幅值及频率等特征指标存在明显差异.通过实时监测该区域地震事件和进行相关的特征分析,可以为研究区域地震的基本规律提供客观数据和科学依据.  相似文献   
869.
利用工具软件对选取的红山地震台波形数据进行分析处理,从波形包含的频率成分特征上可以区分地脉动、干扰、地震;利用Fourier变换、滤波、复时谱分析、高斯小波分析、莫莱小波分析、DB小波分析等手段,综合分析处理可准确标注地震震相.  相似文献   
870.
ABSTRACT

The zone of intersection between land and sea within an urban context has long been viewed as a special type of urban commons. The well-researched port-city interface, however, tells a rather tragic story about the use and management of this valuable resource. This study asks how four major regulatory-institutional issues in the interface – land ownership, activities allowed in port area, planning autonomy, and public access – affect the ability of ports and cities to preserve elements of “commons” in urban coasts? Furthermore, it assesses if and how Elinor Ostrom’s principles for overcoming commons-related tensions, could contribute to the management of port-city conflicts over land-uses in the Mediterranean urban coastline and the various questions that may derive from such an application. For these purposes the study combines a comprehensive literature review with the analysis of planning regulation and in-depth, semi-structured interviews of key-stakeholders in seven port cities across three Mediterranean countries. The common experience in these different cases suggests that through a strategy involving scaling-down spatial decisions or governance, and built-in mechanisms for spatial cooperation, ports and the cities that host them can find a new joint path, which will strengthen local synergies and the quality of urban, public space.  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