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   4948篇
  免费   742篇
  国内免费   796篇
测绘学   1703篇
大气科学   715篇
地球物理   524篇
地质学   1585篇
海洋学   558篇
天文学   464篇
综合类   553篇
自然地理   384篇
  2024年   19篇
  2023年   60篇
  2022年   168篇
  2021年   204篇
  2020年   197篇
  2019年   231篇
  2018年   139篇
  2017年   255篇
  2016年   260篇
  2015年   253篇
  2014年   318篇
  2013年   445篇
  2012年   337篇
  2011年   372篇
  2010年   281篇
  2009年   299篇
  2008年   283篇
  2007年   311篇
  2006年   247篇
  2005年   258篇
  2004年   221篇
  2003年   212篇
  2002年   141篇
  2001年   160篇
  2000年   121篇
  1999年   97篇
  1998年   110篇
  1997年   96篇
  1996年   77篇
  1995年   64篇
  1994年   55篇
  1993年   43篇
  1992年   30篇
  1991年   27篇
  1990年   19篇
  1989年   14篇
  1988年   16篇
  1987年   11篇
  1986年   12篇
  1985年   5篇
  1984年   5篇
  1983年   1篇
  1982年   1篇
  1980年   2篇
  1978年   1篇
  1977年   2篇
  1975年   1篇
  1954年   3篇
  1882年   1篇
  1875年   1篇
排序方式: 共有6486条查询结果,搜索用时 328 毫秒
991.
Abstract

Sources of heterogeneous geospatial data such as the elevation, the slope, the aspect, the water network and the current settlements related to the known Neolithic archaeological sites of Magnesia, are used in an attempt to confirm the existence and allow for the prediction of other archaeological sites using predictive modelling theory. Predictive modelling allows the update of the problem solving strategy as soon as new data layers are available. The Dempster–Shafer Theory also commonly referred to as evidential reasoning (ER) is used to compose probability maps of areas of archaeological interest from physiographical and historical data. The advantage of this theory is that the ignorance is quantified and used to compose the probability maps named as belief, plausibility and belief interval for the archaeological sites. The final digital probability maps show that the Neolithic archaeological sites can be detected in the prefecture of Magnesia. This research study forms a methodological tool for the prediction of new archaeological sites in other areas of archaeological interest according to the physiographical and historical characteristics of the archaeological period being examined. It also contributes to the digital earth modelling and archaeological site protection, one of the most critical and challenging global initiatives.  相似文献   
992.
Abstract

Cultures throughout the world are associating with the rivers. People depend upon the rivers and their tributaries for food, water, transport, and many other aspects of their daily lives. Unfortunately, human beings have not calculated the accurate lengths for the great rivers even today. The lengths of the rivers are very different in popular textbooks, magazines, atlases and encyclopedias, etc. To accurately determine the lengths of the principal rivers of the world, the combination of satellite image analysis and field investigations to the source regions is proposed in this paper. The lengths of the Nile, Amazon, Yangtze, Mississippi, Yellow, Ob, Yenisey, Amur, Congo and Mekong, with lengths over or close to 5000 km, were calculated using the proposed method. The results may represent the most reliable and accurate lengths of the principal rivers of the world that are currently achievable.  相似文献   
993.
Abstract

Historical soil survey paper maps are valuable resources that underpin strategies to support soil protection and promote sustainable land use practices, especially in developing countries where digital soil information is often missing. However, many of the soil maps, in particular those for developing countries, are held in traditional archives that are not easily accessible to potential users. Additionally, many of these documents are over 50 years old and are beginning to deteriorate. Realising the need to conserve this information, the Joint Research Centre (JRC) and the ISRIC-World Soil Information foundation have created the European Digital Archive of Soil Maps (EuDASM), through which all archived paper maps of ISRIC has been made accessible to the public through the Internet. The immediate objective is to transfer paper-based soil maps into a digital format with the maximum possible resolution and to ensure their preservation and easy disclosure. More than 6,000 maps from 135 countries have been captured and are freely available to users through a user-friendly web-based interface. Initial feedback has been very positive, especially from users in Africa, South America and Asia to whom archived soil maps were made available to local users, often for the first time. Link: http://eusoils.jrc.ec.europa.eu/library/maps/country_maps/list_countries.cfm  相似文献   
994.
ABSTRACT

While impressive direct geolocation accuracies better than 5.0?m CE90 (90% of circular error) can be achieved from the last DigitalGlobe’s Very High Resolution (VHR) satellites (i.e. GeoEye-1 and WorldView-1/2/3/4), it is insufficient for many precise geodetic applications. For these sensors, the best horizontal geopositioning accuracies (around 0.55?m CE90) can be attained by using third-order 3D rational functions with vendor’s rational polynomial coefficients data refined by a zero-order polynomial adjustment obtained from a small number of very accurate ground control points (GCPs). However, these high-quality GCPs are not always available. In this work, two different approaches for improving the initial direct geolocation accuracy of VHR satellite imagery are proposed. Both of them are based on the extraction of three-dimensional GCPs from freely available ancillary data at global coverage such as multi-temporal information of Google Earth and the Shuttle Radar Topography Mission 30?m digital elevation model. The application of these approaches on WorldView-2 and GeoEye-1 stereo pairs over two different study sites proved to improve the horizontal direct geolocation accuracy values around of 75%.  相似文献   
995.
Abstract

Since the publication of the first waterway map in 1990, the Inland Waterways of Britain series has expanded to a total of twenty three individual maps, a national route planning map, the first ring atlas and a directory of the inland waterways which explores aspects of preservation, restoration and heritage. Many of the titles have featured in walking guides, directories, promotional literature and web sites. This paper outlines the development of the series from the first map, describing the maps themselves, tracking the evolution of production methodologies, defining marketing and sales strategies and discussing the decision-making processes behind the publication and introduction of new titles.  相似文献   
996.
Abstract

Using examples from the governmental, commercial and educational sectors, the development of photo maps and mapping using satellite imagery is outlined. The emphasis of this paper is on the design possibilities and limitations which are evident in these products. Contrast and legibility problems and image clutter are considered, but it is concluded that the institutional impediments to the collaboration of specialists in researching and designing such maps may be of most importance in determining progress in the use of such maps.  相似文献   
997.
Abstract

Maps which are created on demand by combining geospatial data from different Web Map Services integrate conflicting portrayals and do not satisfy the requirements of effective cartographic communication. A significant improvement is achieved by selecting clearly distinguishable colours which are determined by solving an optimisation problem. Cartographic guidelines and user characteristics (e.g. colour vision impairment) can be incorporated into the optimisation model as constraints which guide the selection of colours.  相似文献   
998.
GPS卫星精密定轨中的摄动力分析   总被引:1,自引:0,他引:1  
王琰  宋力杰  黄令勇 《测绘工程》2013,(5):16-20,24
在介绍各种摄动模型的基础上,将IGS提供的SP3精密星历作为几何轨道,应用不同的摄动模型进行几何轨道平滑,求得卫星轨道的动力学参数,再用动力学参数积分求定卫星的轨道,将其与IGS提供的SP3精密星历进行比较,从而详细分析每一种摄动力对GPS轨道影响的量级,而且说明建立的GPS卫星轨道的摄动模型是比较准确的。  相似文献   
999.
利用MTSAT-2静止气象卫星数据开展了中国区域的雪盖监测研究,结合MODIS雪盖产品及站点雪深观测数据对判识结果进行对比分析和验证。首先,根据MTSAT-2静止气象卫星数据特点,进行角度效应校正及多时相数据合成,以减少云对图像的影响;其次,根据多个雪盖判识因子建立中国区域雪盖判识算法;最后,对比分析2011年1月份MTSAT-2和MODIS雪盖判识结果,并使用站点观测数据进行精度验证。研究表明:(1)MTSAT-2雪盖判识受云影响比例约30%,MODIS雪盖产品受云影响比例约60%,MTSAT-2去云效果明显。(2)无云情况下,MTSAT-2雪盖判识和MODIS雪盖产品判识精度均高于92%;有云覆盖时,MTSAT-2判识精度约65%,优于MODIS雪盖产品35%的判识精度。(3)MTSAT-2静止气象卫星在保持高积雪判识精度的前提下,可以更有效减少云对雪盖判识影响,实时获取更多地表真实信息。该研究对中国区域雪盖信息准确监测、气候变化研究以及防灾减灾等具有重要意义。  相似文献   
1000.
介绍了GRACE重力卫星,并对GRACE重力卫星数据在陆地水储量变化中的应用现状进行分析,总结了GRACE重力卫星数据在陆地水储量变化检测中的数据获取、计算方法和精度分析,以及Grace数据在不同区域尺度陆地水储量变化估算中的应用情况,最后,指出GRACE在水储量应用中的不足和未来的研究方向。  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