全文获取类型
收费全文 | 3052篇 |
免费 | 649篇 |
国内免费 | 960篇 |
专业分类
测绘学 | 222篇 |
大气科学 | 725篇 |
地球物理 | 895篇 |
地质学 | 1521篇 |
海洋学 | 466篇 |
天文学 | 257篇 |
综合类 | 248篇 |
自然地理 | 327篇 |
出版年
2024年 | 23篇 |
2023年 | 75篇 |
2022年 | 148篇 |
2021年 | 170篇 |
2020年 | 143篇 |
2019年 | 136篇 |
2018年 | 143篇 |
2017年 | 161篇 |
2016年 | 163篇 |
2015年 | 171篇 |
2014年 | 170篇 |
2013年 | 180篇 |
2012年 | 167篇 |
2011年 | 204篇 |
2010年 | 175篇 |
2009年 | 180篇 |
2008年 | 156篇 |
2007年 | 145篇 |
2006年 | 131篇 |
2005年 | 127篇 |
2004年 | 125篇 |
2003年 | 150篇 |
2002年 | 160篇 |
2001年 | 169篇 |
2000年 | 128篇 |
1999年 | 126篇 |
1998年 | 85篇 |
1997年 | 115篇 |
1996年 | 89篇 |
1995年 | 72篇 |
1994年 | 75篇 |
1993年 | 54篇 |
1992年 | 46篇 |
1991年 | 30篇 |
1990年 | 24篇 |
1989年 | 26篇 |
1988年 | 32篇 |
1987年 | 26篇 |
1986年 | 17篇 |
1985年 | 11篇 |
1984年 | 15篇 |
1983年 | 10篇 |
1982年 | 10篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 9篇 |
1977年 | 7篇 |
1975年 | 8篇 |
1974年 | 5篇 |
1973年 | 6篇 |
排序方式: 共有4661条查询结果,搜索用时 31 毫秒
11.
12.
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
13.
On September 14–18, 2000, a medium-small solar active region was observed at Ganyu Station of Purple Mountain Observatory. Its spots were not large, but it had a peculiar active filament. On Sep.16, a flare of importance IIIb with rather intense geophysical effects was produced. Our computation of the magnetic structure of the active region reveals that the rope-shaped filament was concerned with a low magnetic arc close to magnetic neutral line. An intense shear of magnetic field occurred near magnetic rope. The QSL analysis shows that a 3-D magnetic reconnection might appear in the vicinity of filament, and this can be used to interpret the formation of a large flare. 相似文献
14.
Huijun Jin Zhi Wei Shaoling Wang Qihao Yu Lanzhi Lü Qingbai Wu Yanjun Ji 《Engineering Geology》2008,101(3-4):96-109
The Qinghai–Tibet Highway and Railway (the Corridor) across the Qinghai–Tibet Plateau traverses 670 km of permafrost and seasonally frozen-ground in the interior of the Plateau, which is sensitive to climatic and anthropogenic environmental changes. The frozen-ground conditions for engineering geology along the Corridor is complicated by the variability in the near-surface lithology, and the mosaic presence of warm permafrost and talik in a periglacial environment. Differential settlement is the major frost-effect problem encountered over permafrost areas. The traditional classification of frozen ground based on the areal distribution of permafrost is too generalized for engineering purposes and a more refined classification is necessary for engineering design and construction. A proposed classification of 51 zones, sub-zones, and sections of frozen ground has been widely adopted for the design and construction of foundations in the portion of the Corridor studied. The mean annual ground temperature (MAGT), near-surface soil types and moisture content, and active faults and topography are most commonly the primary controlling factors in this classification. However, other factors, such as local microreliefs, drainage conditions, and snow and vegetation covers also exert important influences on the features of frozen ground. About 60% of the total length of the Corridor studied possesses reasonably good frozen-ground conditions, which do not need special mitigative measures for frost hazards. However, other sections, such as warm and ice-rich or -saturated permafrost, particularly in the sections in wetlands, ground improvement measures such as elevated land bridges and passive or proactive cooling techniques need to be applied to ensure the long-term stability of thermally unstable, thick permafrost subsoils, and/or refill with non-frost-susceptible soils. Due to the long-history of the construction and management of the Corridor by various government departments, adverse impacts of construction and operation on the permafrost environment have been resulted. It is recommended that an integrated, executable plan for the routing of major construction projects within this transportation corridor be established and long-term monitoring networks installed for evaluating and mitigating the impact from anthropogenic and climatic changes in frozen-ground conditions. 相似文献
15.
详细介绍了SD7535型水平定向钻机的技术特点、性能参数、结构原理、钻机机、电、液一体,工程实践证明该机自控能力强,自动化程度高,操作轻便灵活,作业效率高. 相似文献
16.
17.
中国全新世大暖期哺乳动物与气候波动 总被引:13,自引:0,他引:13
计宏祥 《海洋地质与第四纪地质》1996,16(1):5-16
中国全新世哺乳动物群有众多地点,并已作了详细研究,绝大多数地点有^14C的年代测定,全新世一更新世的界线,作者根据哺乳动物及^14C年代测定,在12-10kaB.P之间,可作为二者之间的过渡层位,在10kaB.P。可作为全新世的开始,中国的全新世大暖期出现于8.5-3.0kaB.P。在此期间内的哺乳动物偏南种类似为明显,如亚洲象,苏门犀及爪哇犀等,在5.6-3.0kaB.P。这一时期内的气候波动剧 相似文献
18.
19.
20.