全文获取类型
收费全文 | 1052篇 |
免费 | 183篇 |
国内免费 | 247篇 |
专业分类
测绘学 | 89篇 |
大气科学 | 85篇 |
地球物理 | 283篇 |
地质学 | 629篇 |
海洋学 | 94篇 |
天文学 | 8篇 |
综合类 | 122篇 |
自然地理 | 172篇 |
出版年
2024年 | 8篇 |
2023年 | 22篇 |
2022年 | 44篇 |
2021年 | 40篇 |
2020年 | 52篇 |
2019年 | 60篇 |
2018年 | 44篇 |
2017年 | 39篇 |
2016年 | 55篇 |
2015年 | 48篇 |
2014年 | 62篇 |
2013年 | 68篇 |
2012年 | 60篇 |
2011年 | 54篇 |
2010年 | 69篇 |
2009年 | 77篇 |
2008年 | 52篇 |
2007年 | 66篇 |
2006年 | 65篇 |
2005年 | 38篇 |
2004年 | 53篇 |
2003年 | 42篇 |
2002年 | 58篇 |
2001年 | 54篇 |
2000年 | 33篇 |
1999年 | 43篇 |
1998年 | 24篇 |
1997年 | 18篇 |
1996年 | 21篇 |
1995年 | 24篇 |
1994年 | 20篇 |
1993年 | 8篇 |
1992年 | 12篇 |
1991年 | 9篇 |
1990年 | 6篇 |
1989年 | 9篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1976年 | 1篇 |
排序方式: 共有1482条查询结果,搜索用时 24 毫秒
291.
Postrevolutionary land encroachments in Cairo: Rhizomatic urban space making and the line of flight from illegality 下载免费PDF全文
Jamie Furniss 《Singapore journal of tropical geography》2016,37(3):310-329
After the January 2011 revolution, new and unpermitted constructions on previously empty land went up across Cairo at striking speed. This paper explores a case of such land encroachments carried out by waste collectors in the neighbourhood of Manshiet Nasser in Cairo, Egypt. It begins with theoretical debates about the production of urban space, arguing that the de Certeauian paradigm, in which urban marginals poach or hijack others' spaces evanescently, fails to account for the way such encroachments produce permanent new spaces rhizomatically alongside the pre‐existing order. The paper then turns to a close examination of the events in Manshiet Nasser. Although in a broad view the actors are marginals living in the ‘informal’ city, the conditions enabling the encroachments were such that only the wealthiest and most powerful members of the ‘community’ benefitted. In a context of generalized ‘illegality’, the squatters rely on practical norms and de facto recognitions to obtain some degree of tenure security. Since these efforts rely on and play off legal norms even as the squatters violate them, the paper argues that property rights in this context should be understood not in classificatory terms based on the legal/illegal binary, but rather through a trajectory of ‘becoming‐legal’: a ‘line of flight’ that approaches legality asymptotically. 相似文献
292.
Concerns about police militarization have become an important public policy issue since the aggressive police response to the 2014 protests in Ferguson, Missouri, where police officers used military-style equipment to confront protestors. This event was a stark visual reminder that many U.S. police departments have used federal programs to acquire surplus military equipment, including weapons, armored vehicles, and body armor. We explore the geographies and histories of one the most important programs, called 1033, which supplies police with military equipment under the rationale of prosecuting the War on Drugs. We show that the legal blurring of the police and the military has been ongoing for decades at the national scale but this has resulted in an uneven landscape of police militarization at the county scale. We also investigate one of the most common global arguments for why police become militarized, which is the presence of Special Weapons and Tactics-style paramilitary teams, finding little support for that claim. More geographic inquiry is needed to understand the trajectories, causes, and consequences of police militarization. 相似文献
293.
294.
Underwater Explosion Treatment of Marine Soft Foundation 总被引:11,自引:0,他引:11
Zheng Zhemin Yang Zhengsheng Jin Liu
Professor Academician of Chinese Academy of Sciences Director of Mechanics Institute of Chinese Academy of Sciences Beijing
Professor Mechanics Institute of Chinese Academy of Sciences Beijing Senior Engineer Lianyungang Harbor Construction Command Post Lianyungang Province of Jiangsu 《中国海洋工程》1991,(2)
The consolidation of soft foundation is a problem that commonly appears in harbor construction engineering on muddy coast. Introduced in this paper is the experimental study on underwater explosion treatment of soft foundation, including the regulations of explosion hollow development and medium movement, the law of similarity of densification and settlement of filled stone mass by shock wave pressure and explosion energy and their construction technologies, etc. A number of projects have been completed by applying this new technique, and the technique itself has been proved practicable. 相似文献
295.
The physical impact of offshore dredging on the reclamation area at the Changhwa coast, Taiwan, is investigated using a three-dimensional movable-bed model test. A distorted modeling law consisting of maintaining similarity of the equilibrium beach profile between the model and prototype is proposed. The geometric distortion was verified through a series of preliminary experiments conducted in a wave flume. Experimental results show that the distorted modeling is able to reproduce the beach-face slope in nature. An appropriate long-term morphological time-scale was determined based on a comparison of model longshore littoral transport rates and equivalent prototype values. Seabed topographical changes before and after offshore dredging are evaluated in model tests. A suitable countermeasure to prevent beach erosion from wave attack along the reclamation area is suggested from the experimental results. 相似文献
296.
The scaling law linking the strength of the meridional overturning to the surface meridional temperature gradient is re-examined in two ocean general circulation models at coarse resolution in an idealised single-hemisphere setting. Two sets of results are presented, where the surface meridional temperature gradient is decreased either by increasing the northernmost temperature and keeping the equator temperature fixed, or by decreasing the equator temperature and keeping the northernmost temperature fixed. The maximum of the meridional overturning first increases and then decreases when the northernmost temperature is gradually increased, whereas the maximum overturning decreases monotonically when the equator temperature is decreased. No scaling law can be derived when the northernmost temperature is increased, whereas a 2/3 power law is found when the temperature is decreased at the equator. The behaviour of the overturning is strongly influenced by the vigour and, particularly, the spatial patterns of convection, which vary substantially between the two sets and which control the horizontal and vertical density gradients at high latitudes. 相似文献
297.
自然海况下波浪特性的初步研究 总被引:2,自引:0,他引:2
赵栋梁 《中国海洋大学学报(自然科学版)》2002,32(6):853-858
通过分析大量的外海浮标观测资料 ,发现波龄和无因次波高之间存在非常好的相关性 ,自然海况下的波浪场满足 3/ 5指数律 ,其波龄可达到几十 ,远远超过风浪波龄的上限 1 .4,说明波浪组成波之间波 -波共振非线性相互作用是波浪内部结构的主要调节机制 ,使波高和周期之间具有很好的相关性。 相似文献
298.
骑田岭矿集区以复杂的深部地质结构和多期、多类型的成岩成矿作用为特色,是南岭中段最为重要的有色、稀有金属资源基地之一。区域成矿类型主要包括中-低温成矿作用和中-高温成矿作用2个系列;多金属矿产的赋矿围岩具有显著的“成矿专属性”,控矿构造则表现为褶皱与多向断层联合控矿的特征;空间分布上,区域成岩成矿作用主要受深断裂控制;从成岩成矿谱系来看,该区完整记录了从印支晚期—燕山晚期的多期成岩成矿作用,两者之间时间和化学成分关系十分复杂,且晚期岩相普遍具有更高的演化程度。总体来看,该区发育印支晚期造山后伸展背景下的与壳源岩浆作用有关的锡多金属矿→燕山中晚期壳幔相互作用有关的钨锡钼铋铅锌矿(西)+燕山中-晚期壳源岩浆作用有关的钨钼铋铅锌矿(东)→燕山晚期壳源与岩浆有关的锡、稀有、萤石矿的演化系列。骑田岭矿集区可能存在深及地幔的通道,且区内的小岩体从浅部至深部由岩枝过渡为隐伏大岩基。区内骑田岭岩体主要由南向北侵位于左旋构造形成的近“S”型膨大空间,在北侧前锋部位、超覆区和S型内凹部位,有利于大规模矿化的发育。从不同尺度的“全位成矿和缺位找矿”来看,骑田岭矿集区有望在类型(斑岩型、石英脉型、云英岩型)、层位(泥盆系—石炭系—二叠系)、元素组合(Li、REE、Sn)等取得突破。因此,基于骑田岭矿集区成矿规律和深部结构的总结,文章提出了2个重点远景区:① 芙蓉外围钨锡铅银找矿远景区;② 廖家湾-清河东钨锡铅银找矿远景区为进一步找矿勘察提供了理论依据。 相似文献
299.
为识别及分析浚县地震台地磁秒采样观测数据中的高频干扰成分,采用别尔采夫滤波剔除其日波及半日波,然后通过时频分析得到高频干扰时段。通过查询工作日志及进行毕奥萨伐尔定律分析,认为浚县地震台地磁秒采样数据所受高频干扰除磁暴外,主要来自电焊施工和雷电,同时发现2种干扰类型有不同的典型干扰形态。 相似文献
300.