全文获取类型
收费全文 | 1037篇 |
免费 | 104篇 |
国内免费 | 148篇 |
专业分类
测绘学 | 45篇 |
大气科学 | 56篇 |
地球物理 | 129篇 |
地质学 | 578篇 |
海洋学 | 88篇 |
天文学 | 3篇 |
综合类 | 51篇 |
自然地理 | 339篇 |
出版年
2023年 | 12篇 |
2022年 | 38篇 |
2021年 | 32篇 |
2020年 | 43篇 |
2019年 | 56篇 |
2018年 | 36篇 |
2017年 | 51篇 |
2016年 | 52篇 |
2015年 | 51篇 |
2014年 | 68篇 |
2013年 | 85篇 |
2012年 | 51篇 |
2011年 | 63篇 |
2010年 | 53篇 |
2009年 | 54篇 |
2008年 | 63篇 |
2007年 | 53篇 |
2006年 | 64篇 |
2005年 | 38篇 |
2004年 | 33篇 |
2003年 | 28篇 |
2002年 | 28篇 |
2001年 | 28篇 |
2000年 | 30篇 |
1999年 | 32篇 |
1998年 | 21篇 |
1997年 | 23篇 |
1996年 | 14篇 |
1995年 | 9篇 |
1994年 | 15篇 |
1993年 | 16篇 |
1992年 | 7篇 |
1991年 | 7篇 |
1990年 | 8篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 6篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1980年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1289条查询结果,搜索用时 15 毫秒
61.
62.
敖荣军 《地理与地理信息科学》2007,23(1):59-63
由于劳动力的异质性,不同技能劳动力之间的合作和互补可以获得递增收益。客观存在的技能互补性导致技能劳动力迁入与迁入地技能劳动力需求之间的正反馈关系,从而引发了劳动力区际流动与人力资本地区集中之间的累积循环。该文基于Giannetti提出的技能互补性假说,从一个新的角度对劳动力区际流动的动因进行理论与实证分析,并揭示该假说的区域经济学含义。 相似文献
63.
土地节约与集约利用评价研究——以湖南省为例 总被引:1,自引:0,他引:1
土地节约与集约利用是发展循环经济和建设节约型社会的必然要求。首先明确提出土地节约和集约利用评价方法与指标选取原则,完善节约和集约用地的评价指标结构层,特别是农用地和农村宅基地等土地利用类型的评价指标,建立区域和土地利用分区的节约与集约利用土地评价指标体系,以湖南省为例,运用层次分析法,得出湖南省土地节约与集约利用水平的动态变化发展趋势以及农用地集约利用的效益,最后利用加权求和的综合方法,计算出湖南省农用地集约利用水平的综合评价值。 相似文献
64.
Elana Wilson 《Area》2007,39(3):323-330
In this article, I trace the efforts of a development team working to promote a Canadian approach to natural resources management in the Russian North. These development workers used two communication strategies related to time and history to render Canadian knowledge mobile and applicable to a new location: (1) imagining today's Russian North as equivalent to the Canadian northern past and (2) reframing and idealising the Canadian past and present to make the governance export less discursively 'messy' for an outside audience. The relative failure of these communicative strategies points to the need for richer dialogue in efforts to move knowledge cross-culturally. 相似文献
65.
G. Toyos D. Oramas Dorta C. Oppenheimer M. T. Pareschi R. Sulpizio G. Zanchetta 《地球表面变化过程与地形》2007,32(10):1491-1502
Based on the debris flow events that occurred in May 1998 in the area of Sarno, Southern Italy, this paper presents an approach to simulate debris flow maximum run‐out. On the basis of the flow source areas and an average thickness of 1·2 m of the scarps, we estimated debris flow volumes of the order of 104 and 105 m3. Flow mobility ratios (ΔH/L) derived from the x, y, z coordinates of the lower‐most limit of the source areas (i.e. apex of the alluvial fan) and the distal limit of the flows ranged between 0·27 and 0·09. We performed regression analyses that showed a good correlation between the estimated flow volumes and mobility ratios. This paper presents a methodology for predicting maximum run‐out of future debris flow events, based on the developed empirical relationship. We implemented the equation that resulted from the calibration as a set of GIS macros written in Visual Basic for Applications (VBA) and running within ArcGIS. We carried out sensitivity analyses and observed that hazard mapping with this methodology should attempt to delineate hazard zones with a minimum horizontal resolution of 0·4 km. The developed procedure enables the rapid delineation of debris flow maximum extent within reasonable levels of uncertainty, it incorporates sensitivities and it facilitates hazard assessments via graphic user interfaces and with modest computing resources. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
66.
地下水有机污染的水文地球化学标志物探讨——以河南油田为例 总被引:4,自引:3,他引:4
经过野外现场调查和取样分析及室内研究得知南阳油田地下水已遭受不同程度的有机物污染,且污染范围可能进一步向油田南部扩散。根据近似地下水流线方向上地下水中总油质量浓度和Fe,Mn等无机组分的变化势态,结合含水介质化学分析结果,发现硫酸盐、Fe和Mn可作为地下水有机污染和地球化学标志物。在含水介质中Fe和Mn质量浓度较高的地方,地下水有机污染物降解速度快,含水介质中Fe和Mn的氧化物和氢氧化物的还原作用导致了含水层介质中Fe和Mn的缺乏和地下水中溶解Fe和Mn的积聚;在含水介质中Fe和Mn质量浓度低的地方,地下水中的有机物质量浓度并没有降低,相应地地下水中溶解Fe和Mn的质量浓度也很低。同时,由于有机污染物的存在使地下水中硫酸盐被还原,导致城下水中硫酸盐质量浓度偏低,且地下水中Fe对有机物污染的敏感性比Mn强。 相似文献
67.
Iain Docherty 《Area》2001,33(3):321-328
This paper presents an analysis of Transport 2010, the government's ten-year plan for transport. It develops discussions held by members of the RGS-IBG's Transport Geography Research Group (TGRG) in September 2000. It is argued that the plan marks something of a return to previous policies designed to accommodate increasing mobility. 相似文献
68.
210Pb and 137Cs dating methods in lakes: A retrospective study 总被引:1,自引:0,他引:1
210Pb has been used for more than two decades to provide the geochronology of annually deposited sediments and to construct pollution histories. Evidence from some lakes suggests that this radionuclide may be adequately mobile to compromise dating reliability. This study provides one test of that possibility by comparing recent measurements of 210Pb and trace metals to ones carried out more than 20 yrs in the past. 137Cs dating is used to confirm sediment accumulation rates in the recent cores. In the three Connecticut, USA, lakes studied, sediment accumulation rates changed abruptly to higher values between 40-50 yrs ago (increasing by factors of 2.2, 2.9, and 3.0). In all three lakes, rates calculated from 210Pb distributions both above and below this horizon agreed, within measurement uncertainty, in recent and older cores. Furthermore, when the older data were corrected for 20 yrs of burial, the changes in slope in 210Pb distributions occurred at the same depth in each pair of cores. The depth of sharp peaks in concentrations of trace metals also matched. In general, this evidence supports the idea that sediments in these lakes have simply been buried, without significant diagenetic remobilization of 210Pb and trace metals . Nevertheless, some important differences were also observed. For two of the three lakes, there was a significant difference in average sediment accumulation rate during the past 33 yrs as calculated from 137Cs and 210Pb in the recent cores. Most potential causes for this difference can be ruled out, and it appears that one of the two nuclides is remobilized compared to the other. There were also significant differences in the total inventories of both 210Pb and trace metals (both up to 2 ×) between recent and older cores in some cases. This may be due to dissimilar sediment focusing, since it is not known for certain whether the new cores were collected at exactly the same sites as in the past. 相似文献
69.
Residential Mobility and Urban Restructuring under Market Transition: A Study of Guangzhou,China 总被引:1,自引:0,他引:1
Residential mobility can be conceptualized as an outcome of a choice process exercised under complex institutional and personal constraints. China's rather unique pattern of housing market segmentation under market transition impinges directly on residential location and relocation. Drawing upon data from a sample survey, this paper analyzes the pattern of residential moves resulting from commodity housing construction in a major Chinese city, Guangzhou. Most moves are of short distance, although the general direction is towards the urban periphery. Danweis and the municipal housing bureau, rather than the market per se, are the primary driving forces behind suburbanization in China today. 相似文献
70.