全文获取类型
收费全文 | 15433篇 |
免费 | 3214篇 |
国内免费 | 4344篇 |
专业分类
测绘学 | 1410篇 |
大气科学 | 3130篇 |
地球物理 | 3515篇 |
地质学 | 7850篇 |
海洋学 | 3002篇 |
天文学 | 750篇 |
综合类 | 1401篇 |
自然地理 | 1933篇 |
出版年
2024年 | 66篇 |
2023年 | 266篇 |
2022年 | 697篇 |
2021年 | 753篇 |
2020年 | 648篇 |
2019年 | 725篇 |
2018年 | 763篇 |
2017年 | 781篇 |
2016年 | 862篇 |
2015年 | 759篇 |
2014年 | 911篇 |
2013年 | 1011篇 |
2012年 | 942篇 |
2011年 | 1016篇 |
2010年 | 1125篇 |
2009年 | 988篇 |
2008年 | 1005篇 |
2007年 | 963篇 |
2006年 | 859篇 |
2005年 | 774篇 |
2004年 | 598篇 |
2003年 | 524篇 |
2002年 | 487篇 |
2001年 | 578篇 |
2000年 | 508篇 |
1999年 | 614篇 |
1998年 | 516篇 |
1997年 | 448篇 |
1996年 | 457篇 |
1995年 | 380篇 |
1994年 | 318篇 |
1993年 | 305篇 |
1992年 | 263篇 |
1991年 | 200篇 |
1990年 | 156篇 |
1989年 | 130篇 |
1988年 | 131篇 |
1987年 | 74篇 |
1986年 | 74篇 |
1985年 | 52篇 |
1984年 | 41篇 |
1983年 | 30篇 |
1982年 | 42篇 |
1981年 | 32篇 |
1980年 | 22篇 |
1979年 | 20篇 |
1978年 | 8篇 |
1976年 | 9篇 |
1975年 | 8篇 |
1958年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
林一山 《地球信息科学学报》1996,(2):43-46
随着我国人口日益增多,经济形势的飞速发展,加快开发西部的任务日趋紧迫和重要。而西部南水北调则是开发西部必须先行的关键性工程。这项工程是从青藏高原怒江、澜沧江、金沙江、雅砻江、大渡河等五大水系调水,穿过巴颜喀拉山入黄,以黄河大柳树枢纽为总灌渠渠首,把水引向内蒙西部,直至新疆东部地区。引水路线跨越西藏、四川、青海、甘肃、内蒙、新疆等地。此项工程调水量约800亿立方米,一旦实现,将使那里沙漠变绿洲,可开发那里东部地区稀少的矿产及其它资源。 相似文献
43.
44.
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
45.
APPLICATION OF GEOGRAPHICAL PARAMETER DATABASE TO ESTABLISHMENT OF UNIT POPULATION DATABASE 总被引:1,自引:1,他引:0
Now GIS is turning into a good tool in handling geographical, economical, and population data, so we can obtain more and more information from these data. On the other hand, in some cases, for a calamity, such as hurricane, earthquake, flood, drought etc., or a decision-making, such as setting up a broadcasting transmitter, building a chemical plant etc., we have to evaluate the total population in the region influenced by a calamity or a project. In this paper, a method is put forward to evaluate the population in such special region. Through exploring the correlation of geographical parameters and the distribution of people in the same region by means of quantitative analysis and qualitative analysis, unit population database (1km× 1km) is established. In this way, estimating the number of people in a special region is capable by adding up the population in every grid involved in this region boundary. The geographical parameters are obtained from topographic database and DEM database on the scale of 相似文献
46.
吴秋凤 《广东海洋大学学报》2003,23(5):94-98
在阐述西部大开发中科技主导地位的基础上 ,从科技应用成效二重性的视角 ,探讨了关注西部科技伦理的必要性 ,并初步提出了西部大开发战略的科技伦理调控机制 相似文献
47.
1 IntroductionDiscontinuousDeformationAnalysis(DDA)developedbyShiin 1 980’s[1 ,2 ] maybeusedtocalculatethedeformationanddisplacementsinamulti blocksystemandtoanalyzetherelationbe tweenforcesanddisplacementsinthesystem .Ifthesurveydisplacementofeverypointordirectionisknown,alldisplacementsanddeformationsofblocks,eventheglide ,theclosureandthestretchoftheboundary planeofblocks ,canbecalculated .TheresultisoptimallyfittedaccordingtotheLeastSquarePrinciple.DDAismainlyusedinrockblockssystems… 相似文献
48.
49.
CORROSION AND ADHERENCE AT SEA OIL-PLATFORM 总被引:1,自引:0,他引:1
Measurements of the adhesive corrosion and protective potentials of 3 Bohai Sea oilplatforms under different cathodic protection showed corrosion still occurred on these platforms undertheir designed protective potentials. Preliminary conclusions from indoor experiments on the relation betweenadhesive corrosion and cathodic protection showed adhering organisms caused the corrosion onthese platforms. 相似文献
50.
Observation of fluid parcel pathways in the Kuroshio Stream revealed a striking crossstream pattern associated with the Kuroshio‘‘ s meanders. In order to understand the observed pattern, a two-dimensional kinematic model of a meandering jet was developed which could be used to examine the relationship between streamfunction patterns and fluid parcel trajectories. The experiments designed to investigate the dependence of the water exchanges between the Kuroshio water and its surroundings on the characteristics of the Kuroshio‘‘s meanders involved the downstream speed,phase speed and the amplitude of other propagating waves. The results suggested that fluid parcels could cross the meandering jet to and fro; and that the water exchanges between the Kuroshio and its surroundings increased with a) increasing meander amplitude, b) decreasing downstream speed, and c) increasing wave phase speed. The results also showed that when the meandering jet was disturbed by other propagating waves, more effective water exchanges could be induced. 相似文献