全文获取类型
收费全文 | 29902篇 |
免费 | 5559篇 |
国内免费 | 7157篇 |
专业分类
测绘学 | 1741篇 |
大气科学 | 6276篇 |
地球物理 | 7796篇 |
地质学 | 14925篇 |
海洋学 | 3648篇 |
天文学 | 1369篇 |
综合类 | 3344篇 |
自然地理 | 3519篇 |
出版年
2024年 | 111篇 |
2023年 | 449篇 |
2022年 | 1262篇 |
2021年 | 1459篇 |
2020年 | 1219篇 |
2019年 | 1386篇 |
2018年 | 1633篇 |
2017年 | 1463篇 |
2016年 | 1756篇 |
2015年 | 1334篇 |
2014年 | 1735篇 |
2013年 | 1727篇 |
2012年 | 1603篇 |
2011年 | 1722篇 |
2010年 | 1651篇 |
2009年 | 1674篇 |
2008年 | 1460篇 |
2007年 | 1421篇 |
2006年 | 1153篇 |
2005年 | 1191篇 |
2004年 | 847篇 |
2003年 | 882篇 |
2002年 | 910篇 |
2001年 | 891篇 |
2000年 | 978篇 |
1999年 | 1448篇 |
1998年 | 1200篇 |
1997年 | 1265篇 |
1996年 | 1197篇 |
1995年 | 975篇 |
1994年 | 858篇 |
1993年 | 769篇 |
1992年 | 626篇 |
1991年 | 474篇 |
1990年 | 379篇 |
1989年 | 300篇 |
1988年 | 284篇 |
1987年 | 179篇 |
1986年 | 166篇 |
1985年 | 110篇 |
1984年 | 84篇 |
1983年 | 61篇 |
1982年 | 72篇 |
1981年 | 39篇 |
1980年 | 52篇 |
1979年 | 39篇 |
1978年 | 22篇 |
1977年 | 17篇 |
1976年 | 15篇 |
1958年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
介绍了近年来河外H2O超脉泽的主要观测结果。H2O超脉泽通常起源于活动星系核中央的拱核盘。它们主要寄生在 Serfert 2星系或低电离核区。至今为止,已有20个星系探测到H2O超脉泽。脉泽辐射的各向同性光度为10~6000L⊙。所有超脉泽星系显示出核的活动,显然,脉泽是由核活动所产生的射电和X射线光子或激波来抽运的。H2O超脉泽倾向存在于高倾斜度的星系,这使得沿视线上的分子柱密度增高,产生足够大的放大光深。最有可能产生H2O超脉泽辐射的星系应有一个包含着射电源的侧向的分子盘以及一个适当的抽运机制。 相似文献
62.
63.
64.
THECONSTRUCTIONANDITSDEVELOPMENTOFTHEOVERSEASTRANSPORTSYSTEMINNORTHEASTCHINAGaoShali(高莎丽)(DepartmentofGeography,NortheastNorm... 相似文献
65.
Relict rock glaciers have considerable potential for contributing to palaeoclimatic reconstruction, but this potential is often undermined by lack of dating control and problems of interpretation. Here we reinvestigate and date four proposed ‘rock glaciers’ in the Cairngorm Mountains and show that the morphology of only one of these appears consistent with that of a true rock glacier produced by creep of underlying ice or ice‐rich sediment. All four features comprise rockslide or rock avalanche runout debris, and the possibility that all four represent unmodified runout accumulations cannot be discounted. Surface exposure dating of the four debris accumulations using cosmogenic 10Be produced uncertainty‐weighted mean ages of 15.4 ± 0.8 ka, 16.2 ± 1.0 ka, 12.1 ± 0.6 ka and 12.7 ± 0.8 ka. All four ages imply emplacement under cold stadial conditions, two prior to the Windermere Interstade of ca. 14.5–12.9 cal. ka BP and two during the Loch Lomond Stade of ca. 12.9–11.5 cal. ka BP. The above ages indicate that paraglacial rock‐slope failure on granite rockwalls occurred within a few millennia after deglaciation. The mean exposure ages obtained for runout debris at two sites – Strath Nethy (16.2 ± 1.0 ka) and Lairig Ghru (15.4 ± 0.8 ka) – are consistent with basal radiocarbon ages from Loch Etteridge, 22 km to the southwest (mean = 15.6 ± 0.3 cal. ka BP) and imply widespread deglaciation of the Cairngorms and adjacent valleys before 15 ka and possibly 16 ka. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
66.
Qinghai Wang Wenliang Xu Dongyan Wang Jingqian LinCollege of Earth Sciences Jilin University Changchun China 《东北亚地学研究》2003,(2)
1IntroductionAdakite has specially sense in the resuming structure background of rock formed,because of its distinctive geochemistry feature and implying partic-ular petrogenesis and ore genesis mechanism (De-fant and Drummond,1990),as a result,it arouses numerous researchers widely concern. After adakite conception was drawn by Chinese (Wang etal.,2000), it was widely concerned by domestic re-searchers (Wang etal.,2000,2001a,2001b;Xu etal.,2000;Pan etal.,2001;Qian,2001;Xu etal.,2001;X… 相似文献
67.
The present paper reports 9 species of pontoniine shrimps collected from Hainan IS-land ,South China Sea ,by the Joint Chinese-German Marine Biology Expeditions,in which Peri-climenaeus arabicus (Calman,1939) and Periclimenaeus hecate (Nobili,1904) are recorded for the first time from Hainan Island. 相似文献
68.
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
69.
LIUXin-wei CHENBai-ming ZHANGDing-xiang 《中国地理科学(英文版)》2004,14(3):209-214
Efficiency and sustainability of grain production are now important in China. In this study, the grain production systems of Jiangsu and Shaanxi Provinces were compared, to analyze their efficiency and sustainability in terms of utilization of natural resources, inputs of purchased energy and materials, and outputs. Flows of energy and materials between environment and human society were identified, and the natural and human work involved in generating inputs as materials or energy were valued in terms of equivalent amount of solar energy required for their production using emergy method. The results showed environmental resources were continually playing a less important role in the systems, when inorganic subsidiary emergy inputs increased drastically while organic ones decreased or increased little. Deterioration of input emergy structure affected the systems‘ efficiency and sustainability, resulting in emergy investment ratios and environmental loading ratios increasing while yield ratios and sustainability indices decreasing. In general, efficiency and sustainability of grain production in Jiangsu are worse than those in Shaanxi. This analysis also suggested that inorganic subsidiary emergy should be introduced properly, and peasants in Jiangsu should utilize natural conditions wisely while those in Shaanxi pay enough attention to soil and surface water conservation. 相似文献
70.
A THREE-DIMENSIONAL ELASTIC NESTED-GRID MESO-(β-γ)SCALE ATMOSPHERIC MODEL——PARTI:MODEL DESCRIPTION 下载免费PDF全文
A three-dimensional elastic nonhydrostatic mesoscale(β-γ)model with nested-grid is presented.It uses a set of fullequations in terrain-following coordinates as its basic dynamic frame,which is solved with a time-splitting algorithmfor acoustic and gravity waves.The model physical parameterization includes a K-theory subgrid eddy mixing for cloudand free atmosphere,a bulk planetary boundary layer parameterization,and three types of sofisticated cloudmicrophysics schemes with double-parameters for hail-bearing clouds,warm clouds and snowing clouds respectively.The model is designed to be used flexibly for simulations of a variety of meso-and small-scale atmospheric processes,and can be improved as a regional and local operational NWP system in future. 相似文献