全文获取类型
收费全文 | 167篇 |
免费 | 13篇 |
国内免费 | 11篇 |
专业分类
测绘学 | 1篇 |
地球物理 | 4篇 |
地质学 | 50篇 |
海洋学 | 16篇 |
综合类 | 4篇 |
自然地理 | 116篇 |
出版年
2023年 | 2篇 |
2021年 | 2篇 |
2019年 | 2篇 |
2018年 | 1篇 |
2017年 | 2篇 |
2016年 | 4篇 |
2015年 | 3篇 |
2014年 | 6篇 |
2013年 | 3篇 |
2012年 | 4篇 |
2011年 | 6篇 |
2010年 | 11篇 |
2009年 | 15篇 |
2008年 | 17篇 |
2007年 | 10篇 |
2006年 | 10篇 |
2005年 | 7篇 |
2004年 | 12篇 |
2003年 | 7篇 |
2002年 | 8篇 |
2001年 | 8篇 |
2000年 | 5篇 |
1999年 | 1篇 |
1998年 | 5篇 |
1997年 | 6篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 4篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 2篇 |
排序方式: 共有191条查询结果,搜索用时 15 毫秒
181.
This study presents an analysis of the spatial-temporal distribution of 230 archaeological sites in Guizhou Province, Southwest China for three selected time periods from the Paleolithic Age to the Shang-Zhou Dynasties. The relationship between archaeological sites distribution and environmental changes is also discussed based on paleo-environmental proxies of δ18O and δ13C recorded in stalagmites from Southwest China. The results show that: in the Paleolithic Age(260–10 ka BP), archaeological sites were concentrated in the central, northwestern and southwestern parts of Guizhou, where the high-altitudinal karst landforms with many natural caves suitable for human habitation are developed. In the Neolithic Age(10–3.6 ka BP), most of human settlements were concentrated in the central, northwestern and southwestern parts, while, a fewer sites were found on river terraces in the southern and eastern parts, and the intermontane basins in the central and western Guizhou. During the Shang-Zhou Dynasties(3.6–2.2 ka BP), the sites were mainly distributed in the intermontane basins and on river terraces, which were suitable for primitive aerial farming. The analysis of paleo-environmental proxies of δ18O and δ13C since 260 ka BP suggested that climate fluctuations had little impact on human settlements in this study area. The distinct physical environment, especially the spatial patterns of karst landforms and arable land played an important role in the archaeological sites distribution of Guizhou. 相似文献
182.
The temporal-spatial distribution features of prehistoric cultures since the Holocene in Zhejiang region were comparatively analyzed based on GIS spatial analysis. Results show that the prehistoric cultures expanded gradually in this region before 4000 cal. a BP. The notable expansions occurred twice, one in the Majiabang-Hemudu cultural period, the other in the Liangzhu cultural period. Meanwhile, the prehistoric cultures were disseminated from west to east coast along river valleys. After 4000 cal. a BP, as represented by the Maqiao Culture, the distributed area of each prehistoric culture contracted. This is obviously due to the termination of spreading trends to east coast, which was simultaneously accompanied by two different modes of production and economic transitions in the north and south Zhejiang region respectively. The distribution of prehistoric cultures was closely related with Holocene sea-level fluctuations, especially on the banks of Hangzhou Bay, where the distribution changes of prehistoric cultural sites were greatly affected by sea-level changes, with the closest relationships between them. After 7000 cal. a BP, the process of lowered sea-level and regression-epeirogenesis provided wider terrestrial living spaces for prehistoric inhabitants. Based on the comparative analyses of the changes of prehistoric cultures and the environmental evolution information recorded in the Qianmutian subalpine peat of Mt. Tianmu and muddy area on the inner shelf of the East China Sea, it is indicated that the changes of prehistoric cultures were synchronized with environmental changes in Zhejiang region. Before 4000 cal. a BP, the eastward expansion of prehistoric cultures in Zhejiang occurred under the background of the Holocene Optimum, and was the expansion and extension under the joint influences of agricultural civilization and maritime civilization. However, after 4000 cal. a BP, the geographical contraction of prehistoric cultures in Zhejiang occurred under the back-ground of dry-cold climate trend and deterioration of coastal marine environment. It is evidenced from the above fact that the development, expansion and contraction of prehistoric cultures are positively correlated to environmental change. The change of the climatic environment is just the underlying reason for these changes and transitions of production modes and economic forms. Therefore, the climatic environment is the dominant factor of prehistoric culture vicissitudes in Zhejiang region, which has exerted great influence on distribution, dissemination, expansion and transmutation of the culture. 相似文献
183.
主要通过对骆驼墩遗址地层样品的粒度和重砂矿物的鉴定、样品中锆石形态的对比研究,铷锶值的测定与分析,了解该区域全新世以来的沉积环境及其气候变化,探索气候变化与人类文明和文化发展的关系。对骆驼墩遗址文化层下的自然淤积层的粒度分析和锆石形态研究发现该区域在人类出现之前可能经历过浅水泻湖环境; 结合重矿物及铷锶研究发现,该区域在全新世早期降水量较大,气候较为湿热,之后气候逐渐变得温暖湿润,为人类文明的出现和文化的发展提供了一个优越的气候条件; 通过对地层中文化层样品的重矿物鉴定及百分含量分析、ZTR稳定系数及Rb/Sr分析发现,全新世的气候是不断变化的。尤其在马家浜文化时期、良渚文化时期和广富林文化时期气候经历过温湿与干凉的交替变化过程。同时良渚文化时期的中晚期稳定系数出现了该地层的最高值,说明当时气候较为湿热,降水量偏多,这与良渚文化的消失与洪水有关的结论相一致。 相似文献
184.
根据生物、湖泊及冰川地层记录,分析了青藏高原末次冰消期的气候演化特点,并将其与格陵兰、欧洲气候演化序列进行了对比分析.结果表明,末次冰消期的气候演化大致可分为两个阶段:前一阶段为暖期,但波动频繁;格陵兰、欧洲在经历了H1事件后,迅速转暖,Bolling期比Allerod期气候更为适宜;而青藏高原渐趋回暖,夏季风降水逐渐增加,存在由冰融水与降水增加所形成的高湖面,气候温湿,进入一次湖泊扩涨期;大部分记录指示Allerod期比Bolling期气候更为适宜.后一阶段为冷期,格陵兰、欧洲气候恶化并显示出有回返冰期的气候特点;青藏高原气候严酷、荒漠扩展、冰流推进、湖面下降.气候演化的这种异同性表明:格陵兰、欧洲与青藏高原气候系统彼此存在联系,特别是在冷期;而在暖期,气候演化表现出各自的特点.气候演化格局所呈现的可比性,可能是通过冷期的一致而体现的. 相似文献
185.
186.
187.
海平面变化对太湖流域排涝的影响 总被引:1,自引:1,他引:0
太湖流域位于长江三角洲地区,其排涝过程受长江口海平面变化及潮位变化的控制。本文采用一维河网非恒定流理论,建立了太湖流域河网水文模型,并对1991年太湖流域洪涝过程进行的模拟。在此基础上,假定当太湖流域发生1991年特大暴雨过程时,海平面上升0.5m和长江口发生了百年一遇高潮位,太湖最高水位可分别达到5.01m和4.99m,整个梅雨期排涝量分别比1991年少排14.9×108m3和13.1×108m3,加剧了该地区洪涝灾害的严峻程度。 相似文献
188.
张家界砂岩峰林景观成因机制 总被引:7,自引:0,他引:7
通过实地考察,室内遥感影像分析,得出如下结论:张家界石英砂岩峰林地貌岩层产状平缓,地壳水平上升,流水沿构造破裂面的节理侵蚀及重力崩塌作用造就了石英砂岩峰林地貌的基本形态。地貌形态的物质基础是特定的岩性。石英砂岩峰林地貌主要由方山、台地、峰墙、峰丛、峰林、石门、天生桥及峡谷、嶂谷等构成。其岩石胶结良好,刚性强,节理发育。物理风化很强烈,风化物和土壤十分疏松,内聚力小,抗蚀能力弱。存在着水土流失的潜在地质条件。另外,石英砂岩峰林地貌本身的地貌特点,水文气象要素都促使其山体风化、崩塌,景观消亡。为了保证景区的可持续发展,环境保护意义重大。 相似文献
189.
南京地区下蜀黄土磁性地层年代与古环境变化 总被引:2,自引:0,他引:2
通过对南京江北泰山新村下蜀土剖面所采的144个样品和南京江南燕子矶下蜀土剖面所采的467个样品所进行的古地磁测年、磁化率测量和粒度测定,建立了南京地区下蜀黄土地层220kaB.P.以来较精细的时间标尺;在此工作基础上,将南京下蜀黄土堆积所记录的环境信息同北方经典黄土、深海沉积氧同位素记录进行了对比,发现燕子矶剖面磁化率曲线能够与深海沉积氧同位素曲线1—7阶段进行良好的对比,两者之间的细节变化具有一致性,其中S0表现为高值,可与氧同位素曲线阶段1对比,为一高温期;L1可以划分为两层黄土(L1LL1、L1LL2)和一层弱发育的古土壤(L1SS1),L1LL1和L1LL2可与阶段2和4对比,L1SS1可与阶段3对比;S1古土壤层由3个古土壤亚层(S1SS1、S1SS2、S1SS3)和2个弱成土亚层(S1LL1、S1LL2)叠置而成,磁化率曲线具有明显的三峰夹两谷形式,正好可与氧同位素阶段5对比,表明这一时期的古气候特点是在湿热的背景下有两次干冷波动,其中S1SS1、S1SS2、S1SS3分别对应于5a、5c、5e,S1LL1、S1LL2对应于5b、5d;L2黄土磁化率曲线整体呈谷形,但中下部有一次峰,下部磁化率偏高,与阶段6的曲线特征相吻合;S2古土壤层未见底,目前获得的磁化率曲线特征可与7a和7b对比。以上研究结果确立了江南风尘堆积的古气候全球变化意义。 相似文献
190.
1 Introduction Global warming and the global-warming-related global environmental problems are receiving increasing attention from scientists, the public and governments of countries. In the coming century anthropological activities may result in further … 相似文献