全文获取类型
收费全文 | 839篇 |
免费 | 137篇 |
国内免费 | 263篇 |
专业分类
测绘学 | 41篇 |
大气科学 | 201篇 |
地球物理 | 216篇 |
地质学 | 483篇 |
海洋学 | 101篇 |
天文学 | 45篇 |
综合类 | 62篇 |
自然地理 | 90篇 |
出版年
2024年 | 5篇 |
2023年 | 9篇 |
2022年 | 30篇 |
2021年 | 32篇 |
2020年 | 27篇 |
2019年 | 40篇 |
2018年 | 39篇 |
2017年 | 37篇 |
2016年 | 35篇 |
2015年 | 38篇 |
2014年 | 49篇 |
2013年 | 42篇 |
2012年 | 55篇 |
2011年 | 58篇 |
2010年 | 57篇 |
2009年 | 57篇 |
2008年 | 54篇 |
2007年 | 50篇 |
2006年 | 33篇 |
2005年 | 29篇 |
2004年 | 23篇 |
2003年 | 20篇 |
2002年 | 23篇 |
2001年 | 35篇 |
2000年 | 32篇 |
1999年 | 39篇 |
1998年 | 46篇 |
1997年 | 38篇 |
1996年 | 26篇 |
1995年 | 24篇 |
1994年 | 24篇 |
1993年 | 20篇 |
1992年 | 30篇 |
1991年 | 19篇 |
1990年 | 13篇 |
1989年 | 11篇 |
1988年 | 15篇 |
1987年 | 8篇 |
1986年 | 3篇 |
1985年 | 4篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1958年 | 1篇 |
排序方式: 共有1239条查询结果,搜索用时 15 毫秒
181.
云南腾冲新期火山岩矿物及其熔体包裹体研究 总被引:1,自引:1,他引:0
腾冲火山群位于我国云南省西部和缅甸的交界处,由黑空山、大空山、小空山、打鹰山、马鞍山等一系列火山组成,是我国著名的第四纪火山群,从喷发活动时间上可分为老期火山和新期火山.前人研究证实,打鹰山、马鞍山和黑空山为新期火山,它们在全新世都有过喷发活动.这些新期火山岩的主要斑晶矿物为辉石、橄榄石和长石,主要的斑晶矿物中都含有熔体包裹体,它们形态多样,分布不规则,且部分显示后期有变化.探针分析表明,新期火山岩矿物中熔体包裹体成分的变化范围大于其基质玻璃成分的变化范围,它们的化学成分分布范围涵盖了玄武粗安岩、粗面安山岩、粗面岩和流纹岩等岩石类型,与腾冲火山区晚更新世以来火山岩的成分分布范围基本一致.根据对新期火山岩斑晶和微晶矿物中熔体包裹体及基质玻璃成分的测试研究,其中挥发分Cl的含量在包裹体和基质中变化不大,但F、SO3在熔体包裹体中的含量高于基质,总体上腾冲新期火山喷发时岩浆的脱气率较低,喷发时并未向空中喷出大量气体,推测对当时的气候环境影响不大,但未来喷发的灾害效应不容忽视. 相似文献
182.
The Huimin (惠民) depression is a third-level tectonic element of the Bohai (渤海) Bay basin in eastern China. The central uplift belt is the most important oil and gas accumulation zone in the depression, but the lack of adequate geological studies in the area has greatly hindered exploration and development. In this article, using seismic data, fracture mechanics, and a combination of data on fault growth indices and fault throws, we present an analysis of tectonic activity in the central uplift belt and adja... 相似文献
183.
184.
Breakage models and particle analyses have been widely used as tools for describing and interpreting various deposits and
providing parameters for assessing the particle-size distribution of the deposits. Debris flows can be seen as a two-phase
rheological fluid with a clay-fluid composition, and debris-flow deposits comprise mud, silt, sand, and boulders, with grain
sizes ranging from less than one μm to more than several meters. As a consequence, according to fractal theory, the particles
in debris-flow deposits have self-similarity in geometrical shape and scale invariance in size. In this paper, the fractal
dimensions of particles in various debris-flow deposits are calculated and corresponding fractal features are determined based
on fractal-statistical theory. The aims of the study are: to provide a quantitative grain parameter that reflects both the
grain composition and grain-size distribution in debris-flow deposits; to compare the fractal dimensions of grains in different
types of debris-flow deposits and the degree of self-organization of debris flows; as well as to discuss the geological implications
of fractal dimensions and fractal features of particles in debris-flow deposits. 相似文献
185.
186.
Guifang Yang Xujiao Zhang Mingzhong Tian Yamin Ping Anze Chen Zhiliang Ge Zhiyun Ni Zhen Yang 《Environmental Earth Sciences》2011,64(3):671-683
The Zhangjiajie Sandstone Peak Forest Geopark (Zhangjiajie World Geopark) of northwest Hunan, China hosts a well-preserved
sequence of fluvial terraces and karst caves. In this contribution, a comparative study of fluvial terraces with karst caves
along the middle-lower Suoxi River in Zhangjiajie World Geopark is presented to improve the understanding of the development
of striking sandstone landscape in the upper Suoxi River. By integrating geomorphological, sedimentological, and geochronological
techniques, the possible correlation between fluvial terraces and karst caves, as well as their climatic and tectonic implications
is investigated. The available electron spin resonance and thermo-luminescence numerical ages coupled with morphostratigraphic
analysis indicate that aggradation of fluvial terrace levels occurred at ca. 347 ± 34 ka (T4), 104.45 ± 8.88 to 117.62 ± 9.99 ka (T3), 60.95 ± 5.18 ka (T2), and Holocene (T1), followed by the stream incision. Fluvial terrace levels (T4 to T1) correlate morphologically with the karst cave levels (L1 to L4), yet the proposed chronology for the fluvial terrace levels is a bit later than the chronological data obtained from karst
caves. In northwest Hunan, where a unique sandstone peak forest landscape was extensively developed, the fluvial terrace sequences
as well as the cave systems are the important archives for studying the evolution of the sandstone landscape. The beginning
of the sandstone landscape development must be earlier than the aggradation of the fluvial terrace T4, allowing this unique landscape to occur in the Middle Pleistocene. 相似文献
187.
气候变化对阿拉善荒漠植被的影响研究 总被引:15,自引:10,他引:5
利用1982—2003年NASA GIMMS归一化植被指数(NDVI)数据集和阿拉善左旗、右旗和额济纳旗气温和降水资料,对阿拉善地区NDVI变化和气候变化特征及其相互关系进行了分析。结果表明:①1982—2003年东部地区(左旗植被指数略有增加,而中部(右旗)和西部地区(额济纳旗)则呈下降趋势。季节变化东、中、西部表现不同。左旗和额济纳旗多年平均NDVI的月变化和右旗相反。②东部地区升温率最大,其次是西部和中部地区。降水表现为东部和西部地区(额济纳旗)稍有增加,而中部地区(右旗)呈缓慢减少趋势。季节变化东、中、西部表现不同。多年平均气温和降水量的月变化趋势东、中、西部一致,呈单峰型曲线。③东部地区和中部地区,降水量与植被指数存在明显的年相关、隔季和当季相关,而西部地区额济纳旗没有明显的相关性。阿拉善地区NDVI同温度的相关性不好。 相似文献
188.
189.
There occurred several eruptions from Changbaishan Tianchi volcano in Holocene, and at least three of them were believed to be true according to the formal studies. The products of three eruptions were yellow comenditic pumice of - 5000a B.P. (Eruption Ⅰ ), gray comenditic pumice and pyroclastic flow of - 1000a B.P. ( Eruption II, i.e. the millennium explosive eruption), black trachy pumice and welded tuff of - 300a B.P. ( Eruption Ⅲ ) respectively. There were a large number of melt inclusions found in phenocrysts, which differ in size and color. The Leitz 1350 heating stage experiments for melt inclusions in host feldspars from three Holocene eruptions of Changbaishan Tianchi volcano imply that there were little differences between the homogenization temperatures of melt inclusions from Eruptions Ⅰ and Ⅲ, whereas it was rather complicated for Eruption H, i.e. there might be two kinds of melt with different homogenization temperature periods, which gave the evidence for the assumption that the explosive millennium eruption of Tianchi volcano was triggered by injection and mixing of two different magmas. The experimental results also indicate that ( 1 ) small melt inclusion is easy to be homogenized, while the large one, especially the one with lots of daughter crystals, is rather difficult to be homogenized; (2) homogenization temperature closely correlates with the size of melt inclusion within host crystal, with the temperature point switching from high heating rate to low heating rate, and correlates with whether it is the first time to obtain homogenization as well; and (3) a melt inclusion can get different homogenization temperatures when it is repeatedly heated. Even more, the next homogenization temperature is usually higher than the former one, which testifies the phenomenon that hydrogen migration occurs during repeated heating. 相似文献
190.
Introduction D’’ layer plays an important role in geodynamic process. And seismological research indicates that D’’ layer has large scale seismic anisotropy, however, most research concentrated on areas such as Northern Pacific, Central Pacific, Caribbean, Central America, Alaska etc. (Wookey et al, 2005; Garnero and Lay, 2003; Matzel et al, 1996; 相似文献