全文获取类型
收费全文 | 880篇 |
免费 | 73篇 |
国内免费 | 95篇 |
专业分类
测绘学 | 143篇 |
大气科学 | 71篇 |
地球物理 | 152篇 |
地质学 | 274篇 |
海洋学 | 136篇 |
天文学 | 2篇 |
综合类 | 67篇 |
自然地理 | 203篇 |
出版年
2024年 | 4篇 |
2023年 | 18篇 |
2022年 | 36篇 |
2021年 | 41篇 |
2020年 | 37篇 |
2019年 | 49篇 |
2018年 | 27篇 |
2017年 | 37篇 |
2016年 | 41篇 |
2015年 | 32篇 |
2014年 | 38篇 |
2013年 | 61篇 |
2012年 | 32篇 |
2011年 | 37篇 |
2010年 | 39篇 |
2009年 | 45篇 |
2008年 | 54篇 |
2007年 | 58篇 |
2006年 | 50篇 |
2005年 | 30篇 |
2004年 | 36篇 |
2003年 | 24篇 |
2002年 | 27篇 |
2001年 | 29篇 |
2000年 | 17篇 |
1999年 | 13篇 |
1998年 | 18篇 |
1997年 | 16篇 |
1996年 | 14篇 |
1995年 | 11篇 |
1994年 | 1篇 |
1993年 | 15篇 |
1992年 | 8篇 |
1991年 | 12篇 |
1990年 | 5篇 |
1989年 | 3篇 |
1988年 | 7篇 |
1987年 | 10篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1979年 | 1篇 |
1976年 | 2篇 |
1973年 | 1篇 |
排序方式: 共有1048条查询结果,搜索用时 562 毫秒
871.
黄宗捷 《成都信息工程学院学报》2002,17(4):277-280
作为一门综合的交叉学科,《现代物流管理学》有自己的研究对象,它主要讨论现代物流的概念、现代物流构成、物流系统、物流技术基础、物流营销、物流配送、物流运输、供应链管理、企业物流、国际物流及物流成本等内容。 相似文献
872.
WISE EXPLOITATION OF NEWLY GROWING LAND RESOURCES——An Assessment on Land—use Change of Chongming Island Using GIS 总被引:4,自引:1,他引:3
Chongming Island, the third largest island in China and the largest alluvial island in the world, is situated in the north
of Shanghai Municipality at the mouth of the Changjiang (Yangtze) River. Along the fertile and prosperous sea coast there
are a total area of over 120×103ha, with a population of 735 000, accruing some 500ha of new tidal land resources come from silt, sand and mud carried by
the Changjiang River every year, extending about 140m per year. This dynamic process of alluvial growth has run for some 1500
years. Mudflat on Chongming Island at the mouth of the Changjiang River is a resting ground for migratory birds and host more
than a hundred species, including rare cranes and geese. But the local people keep reclaiming the tidal land for economic
development. Obviously, it is crucial to have a well-concerted plan for future exploitation. In this study, we attempted to
investigate the status changes of land use and wild life habitats on Chongming Island in recent 10 years, and then analyzed
different human activities and their effects on wild life habitats using satellite image data (1990, 1997 and 2000) as well
as field survey. Based on the analysis, this study explored the relationships between island growth and land use/cover change
(LUCC), predicted what the habitat would be like in the future and tried to find more effective use of this new growing resource.
At last, this study provided some preliminary management plans for Chongming Island that will coordinate the development of
local economies and the conservation of wild life and their habitats.
Foundation item: Supported by WWF (World Wildlife Fund) China Program (CN0079.08).
Biography: ZHAO Bin (1969 - ), male, a native of Hubei Province, Ph. D., specialized in landscape ecology and biodiversity
information system management. 相似文献
873.
基于数字高程模型(digital elevation model,DEM)高程数据和D8算法实现了湖南中小河流流域子流域划分。利用洪水预报网络传播模型,构建中小河流各子流域径流拓扑结构并提出了空间子流域等效面雨量的概念。基于等效面雨量序列和径流观测序列,构建了基于时空概念的隐马尔可夫降水-径流模型,并利用该模型计算了中小河流各子流域不同时间尺度条件下暴雨致灾临界面雨量阈值,最后利用2010—2015年实况资料对阈值进行检验,结果证明相比传统统计法,新方法的计算结果与传统方法结果一致且具有很好的准确性和稳定性。基于2015年6月的一次暴雨灾害预报,证明了该方法适应于业务化运行。 相似文献
874.
875.
Only few (six) focal mechanism, in CMT Catalog, have been so far known for intraplate shallow events in the Andean chain close to Chile–Argentina state border at latitudes ∼35° S. We add two more mechanisms, depths and moment magnitudes by carefully analyzing full waveforms of weak events recorded by broad-band stations of the Chile Argentina Geophysical Experiment (southern profile). The moment magnitudes of both events (Mw = 3.6 and 3.7) are lower than the duration magnitudes (Md = 4.0 and 4.29) reported by NEIC. The source depth, constrained by waveforms for one of the studied events (5.5–8.5 km) seems to be considerably shallower than the hypocenter depth located by means of arrival times (∼20 km). The waveform analysis was complemented by first-motion polarities which resulted in an uncertainty assessment of the focal mechanism. Event 1 (2001-11-03) has a strike-slip mechanism with a small normal component and almost vertical nodal planes in the north-south and east-west directions. The north-south nodal plane could be related to the Calabozos faults system. Event 2 (2002-02-16) has a strike-slip mechanism with a small thrust component. The latter event (its subhorizontal nodal plane) could be associated with the El Diablo-El Fierro fault system. Dextral strike-slip solutions are consistent with recent studies in the area. 相似文献
876.
经济型连锁酒店的空间布局研究——以北京市如家快捷酒店为例 总被引:1,自引:0,他引:1
以北京市如家快捷酒店为例,基于空间数据探索分析技术,采用全局空间相关性分析其空间聚集程度,并通过局域相关性分析开展热点探测,研究其历年来在北京各区县的空间拓展状况。研究发现:如家快捷酒店的空间拓展可分为前期空间扩散(2002—2006年)、中期集中布点(2007—2010年)和后期的延伸拓展(2011年以后)3个阶段。据此,提出经济型连锁酒店发展的3个阶段:首先,占领商贸、行政中心等重要节点;其次,加大城区的布点密度;最后,再向周边区县延伸扩展。 相似文献
877.
自然灾害发生具有突发性、随机性和链式效应,而且自然灾害拥有庞大的概念体系和灾害事件之间异常复杂的时空关系,由于缺乏对灾害知识的统一描述表达机制,导致灾害领域知识难以实现共享和重用,因此,构建灾害链的统一描述模型并实现灾害知识的共享与重用是当前亟须解决的一个问题。本文提出了一种灾害链领域本体的构建方法,在对比现有方法基础之上,定义了灾害链相关概念、属性,以及概念之间的关系,采用网络本体语言OWL对灾害链领域本体进行建模,并实现了灾害链领域本体的可视化,为灾害知识的共享与重用提供了有效支撑。最后,以暴雨-洪涝灾害链为例验证了该方法的有效性和可靠性。 相似文献
878.
Palaeoenvironmental assessment of past C3 and C4 vegetation distributions relies on end member data from plant analyses. In southwestern Africa, end member data of the carbon number distribution of n-alkanes from leaf waxes and their carbon isotopic composition were available for the rainforest and the savannah. To complement this, we analysed the n-alkane parameters of 41 C3 plants and 11 C4 plants from the transition region, i.e., the wood- and shrubland of Angola. The combined results for the rainforest, the wood- and shrubland and the savannah show an increase in the average chain length (ACL) of C3 and C4 plants and an increasingly enriched carbon stable isotope composition for the C3 plants from the equator towards southern Africa. The enlarged database was applied to the data of a north–south transect of deep-sea surface sediments already used in a previous study, which resulted in the proxies showing a good reflection of the vegetation on the adjacent southwest African continent in terms of %C4 plant cover. Applying end member values for ACL and δ13C obtained from the enlarged database by two different averaging methods (arithmetic average and median) to the n-alkane data from the sediment transect yielded similar vegetation reconstructions. In addition, a correlation between ACL and growth height of the plants is discussed, indicating that the ACL may be useful as a tree abundance parameter. Thus, the enlarged end member database strengthens the n-alkane parameters as tools for palaeoenvironmental studies. 相似文献
879.
铟资源广泛应用于ITO靶材、半导体化合物、焊料及合金等材料的生产制造,是21世纪重要的战略金属。文章基于铟资源全产业链视角,通过分析2000年以来全球铟资源供给与消费格局,并展望未来供需趋势,得出的结论主要有:(1)全球再生铟供给已超过原生铟供给;原生铟供给高度集中在中国、韩国、日本、加拿大四国;再生铟供给集中于日本、韩国。(2)全球铟资源消费量大幅增长,二十年来,翻了两番;日本与韩国是全球铟资源的消费主体;ITO靶材是主要消费领域。(3)2007年以来,全球铟资源总供给量大于总消费量600 t,预判这部分差量进入了国家储备。(4)未来中国增加铟资源供给的途经可以借鉴日本与韩国的经验,从社会存量中再利用铟资源,提高铟全产业链利用效率。 相似文献
880.
为充分利用高光谱遥感影像中丰富的光谱和空间信息,提出了一种基于多核支持向量机(multiple kernel support vector machine,MKSVM)和马尔科夫随机场(markov random field,MRF)的影像分类方法。该方法首先利用MKSVM分类器对影像进行分类处理,再利用MRF对初始分类结果进行空间结构规则化,得到最终分类结果。通过对AVIRIS高光谱影像的分类实验表明,该方法有效地消除了分类结果中同质区域内的"噪声",分类精度提高了3%左右。 相似文献