全文获取类型
收费全文 | 28703篇 |
免费 | 4593篇 |
国内免费 | 6043篇 |
专业分类
测绘学 | 3467篇 |
大气科学 | 4552篇 |
地球物理 | 7313篇 |
地质学 | 12669篇 |
海洋学 | 3799篇 |
天文学 | 1120篇 |
综合类 | 2026篇 |
自然地理 | 4393篇 |
出版年
2024年 | 85篇 |
2023年 | 325篇 |
2022年 | 826篇 |
2021年 | 1022篇 |
2020年 | 1196篇 |
2019年 | 1331篇 |
2018年 | 1053篇 |
2017年 | 1337篇 |
2016年 | 1346篇 |
2015年 | 1450篇 |
2014年 | 1805篇 |
2013年 | 2136篇 |
2012年 | 1862篇 |
2011年 | 2003篇 |
2010年 | 1555篇 |
2009年 | 1996篇 |
2008年 | 1958篇 |
2007年 | 2028篇 |
2006年 | 1971篇 |
2005年 | 1569篇 |
2004年 | 1461篇 |
2003年 | 1225篇 |
2002年 | 958篇 |
2001年 | 867篇 |
2000年 | 773篇 |
1999年 | 730篇 |
1998年 | 720篇 |
1997年 | 626篇 |
1996年 | 518篇 |
1995年 | 459篇 |
1994年 | 390篇 |
1993年 | 393篇 |
1992年 | 267篇 |
1991年 | 206篇 |
1990年 | 161篇 |
1989年 | 158篇 |
1988年 | 131篇 |
1987年 | 66篇 |
1986年 | 58篇 |
1985年 | 63篇 |
1984年 | 33篇 |
1983年 | 17篇 |
1982年 | 26篇 |
1981年 | 19篇 |
1980年 | 23篇 |
1979年 | 16篇 |
1977年 | 22篇 |
1976年 | 26篇 |
1973年 | 17篇 |
1971年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 468 毫秒
81.
Qin Chengzhi 《中国地震研究》2004,18(2):178-187
The migration of strong earthquakes is an important research topic because the migration phenomena reflect partly the seismic mechanism and involve the prediction of tendency of seismic activity. Research on migration of strong earthquakes has mostly focused on finding the phenomena. Some attempts on getting regularity were comparatively subjective. This paper suggests that there should be indices of migration in earthquake dataset and the indexes should have statistical meaning if there is regularity in the migration of strong earthquakes. In this study, three derivative attributes of migration, i.e., migration orientation, migration distance and migration time interval, were statistically analyzed. Results in the North China region show that the migration of strong earthquakes has statistical meaning. There is a dominant migration orientation (W by S to E by N), a dominant distance (≤100km and on the confines of 300~700km), and a dominant time interval (≤1a and on the confines of 3~4a). The results also show that the migration will differ slightly with different magnitude range or earthquake activity phase. 相似文献
82.
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
83.
84.
85.
Aimed at promoting regional coalitions and expanding the approach to economic links, this paper puts forward some new concepts
such as link intensity and receiving coefficient, expounds the indexes of quantitative analysis of economic links and establishes
the quantitative-analysis model of economic links. With help of the model, this paper calculates the values of the link intensities
between Su-Xi-Chang (Suzhou-Wuxi-Changzhou) region and Shanghai, and analyzes the regional difference of the economic links. 相似文献
86.
MAO Duan-qian ZHANG Jie BAO Hao-sheng 《中国地理科学(英文版)》2005,15(3):275-280
1IN T R O D U C T IO NAn image isa setofbelief,s ideasand impressionsthatapersonholdsaboutan object(KOTLER,1991).Similar-lydefinitionistheimage of a destinationas thesum ofbelief,sideasand impressionsthatpeoplehave ofa placeor destination(CROMPTON,1979;KO… 相似文献
87.
沉积物粒度分析在厦门市第四纪环境研究和地层划分对比中的应用 总被引:6,自引:0,他引:6
采用MS2000型激光粒度分析仪进行测试,利用计算机粒度分析软件对数据进行整理和计算,绘制出样品的频率曲线、概率累积曲线以及粒度众数位值曲线等图件并进行沉积环境分析。厦门地区第四纪环境演化经历了中更新世同安组(含泥中粗砂、含泥细中砂、砂为主)海积一冲积一更新统上部龙海组(含泥粗中砂、含泥细中砂、含泥粗砂、粗砂、细中砂、含细砾中粗砂、中细砂等)冲积一洪冲积一更新世上部东山组(砂、砂砾、含泥中粗砂、粗砂、泥质中细砂、细砂、中粗砂等)冲洪积及部分海积(粉砂、细粉砂、含碳质泥、粘土、淤泥质粘土、粉砂质粘土等)一全新世长乐组(粉砂,淤泥质粘土、粉砂质粘土、碳质粘土、含砂淤泥质粘土,粉砂质亚粘土、粉细砂亚粘土等)海湾沉积。在解释环境变化的同时,说明粒度变化曲线在一定程度上可以作为地层划分的依据之一,并以此对研究区地层进行了详细划分。 相似文献
88.
89.
In this paper, the currently accepted correlation of the Early Pleistocene Ludhamian stage of England with the Tiglian‐A sub‐stage of the Netherlands is challenged. Recent investigations of Early Pleistocene marine North Sea deposits from a borehole near Noordwijk (the Netherlands) yielded evidence from molluscs, dinoflagellate cysts and sporomorphs for an alternation of warm‐temperate and arctic intervals within the Praetiglian and Tiglian stages. Marine equivalents of the terrestrial‐based pollen sub‐stages Tiglian A and B have been recognised in the upper part of the sequence. A Praetiglian age can be assigned to the lower part of the sequence on the basis of mollusc analysis. Within the Praetiglian, an alternation of warm and cold phases has been recognised from both the dinoflagellate cyst and molluscan records. Three cold phases within the Praetiglian are tentatively correlated with marine isotope stages (MIS) 96–100. The molluscan assemblages provide evidence for climate forcing of the sea level: highest sea levels are reached in the warm‐temperate intervals. Within the Praetiglian, an interval with an acme zone of the dinoflagellate cyst Impagidinium multiplexum, is correlated with the Ludhamian and tentatively linked to MIS 97 and/or MIS 96. The cold molluscan assemblages from the Noordwijk borehole include an acme zone of Megayoldia thraciaeformis, the first and only occurrence of this North Pacific bivalve in the North Sea Basin. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
90.