全文获取类型
收费全文 | 54328篇 |
免费 | 13482篇 |
国内免费 | 18888篇 |
专业分类
测绘学 | 9695篇 |
大气科学 | 7808篇 |
地球物理 | 10331篇 |
地质学 | 35239篇 |
海洋学 | 9860篇 |
天文学 | 916篇 |
综合类 | 4591篇 |
自然地理 | 8258篇 |
出版年
2024年 | 373篇 |
2023年 | 1181篇 |
2022年 | 3268篇 |
2021年 | 3965篇 |
2020年 | 3131篇 |
2019年 | 3586篇 |
2018年 | 3355篇 |
2017年 | 3096篇 |
2016年 | 3242篇 |
2015年 | 3774篇 |
2014年 | 3702篇 |
2013年 | 4531篇 |
2012年 | 5134篇 |
2011年 | 5062篇 |
2010年 | 5036篇 |
2009年 | 4756篇 |
2008年 | 4579篇 |
2007年 | 4265篇 |
2006年 | 4168篇 |
2005年 | 3383篇 |
2004年 | 2529篇 |
2003年 | 1800篇 |
2002年 | 1865篇 |
2001年 | 1783篇 |
2000年 | 1427篇 |
1999年 | 819篇 |
1998年 | 463篇 |
1997年 | 366篇 |
1996年 | 339篇 |
1995年 | 248篇 |
1994年 | 219篇 |
1993年 | 184篇 |
1992年 | 177篇 |
1991年 | 105篇 |
1990年 | 125篇 |
1989年 | 84篇 |
1988年 | 74篇 |
1987年 | 77篇 |
1986年 | 79篇 |
1985年 | 48篇 |
1984年 | 53篇 |
1983年 | 29篇 |
1982年 | 30篇 |
1981年 | 20篇 |
1980年 | 12篇 |
1979年 | 36篇 |
1978年 | 9篇 |
1976年 | 9篇 |
1957年 | 18篇 |
1954年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
科技进步是测绘事业发展的动力 ,讨论运用科技进步的评价指标 ,对测绘单位的科技进步速度和对经济增长的贡献等进行测算和分析 ,可以为测绘规划管理及决策提供参考。 相似文献
102.
南水北调西线工程(简称西线调水)是从长江上游引水至黄河上游的跨流域调水工程。其重要目标是开发西北,繁荣发展中西部经济和改良生态环境。 本世纪末;下世纪初,我国经济建设的重点将转向大西北,实现区域资源开拓的重点转移。显然这对振兴大西北,实现区域持续发展是一项重大的战略决策。 相似文献
103.
104.
The sand–loess transition zone in north China is sensitive to climate change, and is an ideal place to investigate past environmental changes. However, past climate change at millennial–centennial timescales in this region has not been well reconstructed because of limited numerical dating. Alternations of sandy loam soils with aeolian sand layers in the Mu Us and Otindag sand fields, which lie along the sand–loess transition zone, indicate multiple intervals of dune activity and stability. This change is probably a response to variations of the East Asian monsoon climate during the late Quaternary. The single aliquot regeneration (SAR) optically stimulated luminescence (OSL) dating protocol, which has been successfully applied to aeolian deposits worldwide, is applied to these two sand fields in this study. The OSL ages provide reliable constraints for reconstruction of past climate changes at suborbital timescale. Sections in both sand fields contain aeolian sand beds recording millennial‐scale episodes of dry climate and widespread dune activation, including episodes at about the same time as Heinrich Event 5 and the Younger Dryas in the North Atlantic region. These results demonstrate the potential of aeolian sediments in semi‐arid north China to record millennial‐scale climatic events, and also suggest that dry–wet climate variation at the desert margin in China may be linked to climatic change elsewhere in the Northern Hemisphere, through atmospheric circulation. This article was published online on 27 November 2008. An error was subsequently identified. This notice is included in the online and print versions to indicate that both have been corrected (16 December 2008). Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
105.
106.
Molecular phylogenetic analysis of attached Ulvaceae species and free-floating Enteromorpha from Qingdao coasts in 2007 总被引:3,自引:1,他引:2
Based on the sequence data of the nuclear ribosomal DNA internal transcribed spacer(ITS) 1,5.8 S,and ITS 2,the molecular phylogeny was analyzed on Ulvaceae species collected from Qingdao coasts in summer of 2007,including 15 attached Ulva and Enteromorpha samples from 10 locations and 10 free-floating Enteromorpha samples from seven locations.The result supported the monophyly of all free-floating Enteromorpha samples,implying the unialgal composition of the free-floating Enteromorpha,and the attached Ulvaceae species from Qingdao coasts were grouped into other five clades,suggesting that they were not the biogeographic origin of the free-floating Enteromorpha in that season. 相似文献
107.
STUDY ON BEIJING''''S EMERGING MOBILE COMMUNICATION INDUSTRIAL CLUSTER AND ITS POLICY IMPLICATIONS 总被引:1,自引:0,他引:1
1INTRODUCTIONClusters,definedasgeographicallyproximategroupsofinterconnectedcompaniesandassociatedinstitutionsinparticularfields,linkedbycommonalitiesandcomple-mentarities(PORTER,2000),havearousedanintenseinterestofurbanandregionalplanningresearchersandpolicymakersoverthepastdecades.Itiswidelyrecog-nizedthatclusterscanpromoteproductivityandinno-vation,developlocalcompetitiveadvantages.Popular-izedbyMichaelPORTERinhisbook“TheCompetitiveAdvantageofNationsin1990,theclusterisnotanewcon… 相似文献
108.
Afforestation has been suggested as a means of improving soil and water conservation in north‐western China, especially on the Loess Plateau. Understanding of the hydrological responses to afforestation will help us develop sustainable watershed management strategies. A study was conducted during the period of 1956 to 1980 to evaluate runoff responses to afforestation in a watershed on the Loess Plateau with an area of 1·15 km2, using a paired watershed approach. Deciduous trees, including locust (locusta L.), apricot (praecox L.) and elm (ulmus L.), were planted on about 80% of a treated watershed, while a natural grassland watershed remained unchanged. It was estimated that cumulative runoff yield in the treated watershed was reduced by 32% as a result of afforestation. A significant trend was also observed that shows annual runoff reduction increases with the age of the trees planted. Reduction in monthly runoff occurred mainly from June to September, which was ascribed to greater rainfall and utilization by trees during this period. Afforestation also resulted in reduction in the volume and peak flow of storm runoff events in the treated watershed with greater reduction in peak flow. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
109.
110.
报表服务是大地测量信息系统的一项基本功能,但往往会因为格式的微小调整而导致系统的整体重构。首先分析了当前报表生成方法的缺点,提出了基于XML相关技术生成报表的新思路;然后介绍了以XML为基本语法的统一数据交换接口,屏蔽了各种报表数据源的差异;重点讨论了如何运用XSL技术将接口文件变换成通用的HTML,并对报表中的图形信息用SVG进行描述,从而将报表转换成通用浏览器可以识别的信息模型;最后对此技术进行了实践。通过在系统外部更改报表样式文件,能够实现报表服务的个性化,增强系统的扩展性。 相似文献