全文获取类型
收费全文 | 24723篇 |
免费 | 3678篇 |
国内免费 | 5048篇 |
专业分类
测绘学 | 3171篇 |
大气科学 | 4065篇 |
地球物理 | 6210篇 |
地质学 | 10110篇 |
海洋学 | 3156篇 |
天文学 | 1090篇 |
综合类 | 1754篇 |
自然地理 | 3893篇 |
出版年
2024年 | 93篇 |
2023年 | 279篇 |
2022年 | 699篇 |
2021年 | 886篇 |
2020年 | 1025篇 |
2019年 | 1290篇 |
2018年 | 873篇 |
2017年 | 1169篇 |
2016年 | 1145篇 |
2015年 | 1219篇 |
2014年 | 1560篇 |
2013年 | 1841篇 |
2012年 | 1564篇 |
2011年 | 1672篇 |
2010年 | 1294篇 |
2009年 | 1694篇 |
2008年 | 1675篇 |
2007年 | 1745篇 |
2006年 | 1690篇 |
2005年 | 1322篇 |
2004年 | 1235篇 |
2003年 | 1046篇 |
2002年 | 798篇 |
2001年 | 715篇 |
2000年 | 642篇 |
1999年 | 600篇 |
1998年 | 599篇 |
1997年 | 519篇 |
1996年 | 424篇 |
1995年 | 380篇 |
1994年 | 316篇 |
1993年 | 308篇 |
1992年 | 215篇 |
1991年 | 170篇 |
1990年 | 130篇 |
1989年 | 126篇 |
1988年 | 100篇 |
1987年 | 57篇 |
1986年 | 53篇 |
1985年 | 51篇 |
1984年 | 29篇 |
1983年 | 13篇 |
1982年 | 23篇 |
1981年 | 19篇 |
1980年 | 21篇 |
1978年 | 13篇 |
1977年 | 19篇 |
1976年 | 25篇 |
1973年 | 17篇 |
1971年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 224 毫秒
951.
中国省际人口迁移的多边效应机制分析 总被引:12,自引:6,他引:6
区际人口迁移不仅与迁出地和目的地的要素特征以及距离有关,而且还受到周边迁移流的影响.基于网络自相关理论,利用"六普"省际人口迁移数据和相关统计资料,在重力模型的基础上考虑迁移流之间可能存在的几种空间依赖形式,构建中国省际迁移流的空间OD模型,初步揭示区域经济社会等因素及其空间溢出效应对省际人口迁移的影响,并就区域要素变化对整个省际人口迁移系统产生的"连锁反应"进行了模拟.结果表明:① 中国省际迁移流之间存在显著的网络自相关效应.目的地和迁出地的自相关效应皆为正,导致迁入和迁出流的空间效仿行为;迁出地和目的地周边则出现负的自相关效应,导致迁移流的空间竞争行为;② 区域经济社会等因素通过网络空间关系对周边地区产生的多边溢出效应导致迁移流在空间上集聚.其中,距离衰减效应位居各要素之首,其溢出效应进一步加剧距离的摩擦作用;对目的地而言,区域工资水平和迁移存量超过GDP的影响并产生正的溢出效应,促进周边地区吸引更多的外来人口;对迁出地而言,人口规模和迁移存量产生正的溢出效应,推动周边地区人口外迁;③ 区域要素变化潜在地对整个省际人口迁移系统产生一系列"连锁反应",震荡中心及其周边区域的迁移流波动较大.江苏省GDP增长5%的模拟结果表明,江苏迁往全国其他省份的人口数量都有不同程度地减少,而其他省份入迁人口均有所增加.相对而言,江苏周边省份的迁入或迁出流受到的波动较大,偏远省份波及较小,这是传统的重力模型所无法解释的. 相似文献
952.
953.
临沂市城市建设发展迅速,城市面貌日新月异,但高楼密集、交通拥挤等问题也逐渐显现出来,城市建设需要更多的空间,开发利用城市地下空间已是首要解决的问题。临沂市位于沂沭断裂带与临沂单斜、平邑-方城盆地多个地质单元的交会处,断裂构造发育,地震活动强烈,地质条件复杂,城市地下空间开发的影响因素众多,该文从水文及水文地质条件、工程地质条件、环境地质条件、人类工程活动等方面对临沂城市地下空间资源地质环境适宜性进行了分析研究,提出了其主要制约因素为极其发育的活动性断裂的看法,凡是活动性断裂对地下空间开发有影响的区域,均为地下空间资源开发制约区。评价结论对于提高城市发展格局、提高城市空间利用率、指导城市空间开发利用规划具有一定的参考意义。 相似文献
954.
955.
Mohammad M. M. Alsahli Ahmed M. AlHasem 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2016,116(1):56-70
Assessing coastal vulnerability to sea level rise (SLR) at local and regional scales is a fundamental step for designing successful long-term coastal management plans. This study was thus designed to assess Kuwait coastal vulnerability to SLR at four scenarios (.5, 1, 1.5 and 2 m). Potential inundated areas and the number of people at risk were estimated based on these SLR scenarios. A coastal vulnerability index (CVI) map of Kuwait was then computed based on the lowest scenario using eight parameters: elevation, coastal slope, geomorphology, distance to 20-m isobath, population, land use, cultural heritage and transportation. The geographic distribution of inundated areas at an SLR of .5 m revealed that the northern islands of Kuwait and coastal areas along Kuwait Bay would be highly impacted, whereas the coastal area near Shuaibah Port was the most influenced among the southern coasts. Most of the coastal area exhibited a moderate vulnerability to SLR, especially the northern islands. This study presented an initial vulnerability assessment for Kuwait coasts to SLR, which can be extended with more variables. The integrated remote sensing and geographic information system methodology demonstrated in this study can be applied in similar studies elsewhere. 相似文献
956.
Wen-Chao Huang Hong-Wen Yu 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2016,10(4):269-279
In this study, the failure mechanisms for Chiuliao 1st Levee and Gueishan Levee in Taiwan were re-examined comprehensively considering the uncertainty of different parameters. Results have shown that for Chiuliao 1st Levee, the slope sliding failure has a higher coefficient of variation (COV). For Gueishan Levee, retaining wall sliding and overturning failure have higher values of COV instead. It can also be found that the scouring depths affect the stability of the levee significantly, therefore, a protecting system for the backfill material may be necessary to increase the stability of the levee effectively. 相似文献
957.
Tom R. Robinson Tim R. H. Davies Thomas M. Wilson Caroline Orchiston Nicolas Barth 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2016,10(2):146-163
Coseismic landsliding presents a major hazard to infrastructure in mountains during large earthquakes. This is particularly true for road networks, as historically coseismic landsliding has resulted in road losses larger than those due to ground shaking. Assessing the exposure of current and planned highway links to coseismic landsliding for future earthquake scenarios is therefore vital for disaster risk reduction. This study presents a method to evaluate the exposure of critical infrastructure to landsliding from scenario earthquakes from an underlying quantitative landslide hazard assessment. The method is applied to a proposed new highway link in South Island, New Zealand, for a scenario Alpine Fault earthquake and compared to the current network. Exposure (the likelihood of a network being affected by one or more landslides) is evaluated from a regional-scale coseismic landslide hazard model and assessed on a relative basis from 0 to 1. The results show that the proposed Haast-Hollyford Highway (HHH) would be highly exposed to coseismic landsliding with at least 30–40?km likely to be badly affected (the Simonin Pass route being the worse affected of the two routes). In the current South Island State Highway network, the HHH would be the link most exposed to landsliding and would increase the total network exposure by 50–70% despite increasing the total road length by just 3%. The present work is intended to provide an effective method to assess coseismic landslide hazard of infrastructure in mountains with seismic hazard, and potentially identify mitigation options and critical network segments. 相似文献
958.
Gregory B. Baecher 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2016,10(2):92-108
The character and importance of uncertainty in dam safety risk analysis drives how risk assessments are used in practice. The current interpretation of uncertainty is that, in addition to the aleatory risk which arises from presumed uncertainty in the world, it comprises the epistemic aspects of irresolution in a model or forecast, specifically model and parameter uncertainty. This is true in part but it is not all there is to uncertainty in risk analysis. The physics of hazards and of failure may be poorly understood, which goes beyond uncertainty in its conventional sense. There may be alternative scenarios of future conditions, for example non-stationarity in the environment, which cannot easily be forecast. There may also be deep uncertainties of the type associated with climate change. These are situations in which analysts do not know or do not agree on the system characterisation relating actions to consequences or on the probability distributions for key parameters. All of these facets are part of the uncertainty in risk analysis with which we must deal. 相似文献
959.
Keyan Yu Philippe Rosset 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2016,10(2):164-178
In Canada, Montreal is the second city with the highest seismic risk. This is due to its relatively high seismic hazard, old infrastructures and high population density. The region is characterised by moderate seismic activity with no recent record of a major earthquake. The lack of historical strong ground motion records for the region contributes to large uncertainties in the estimation of hazards. Among the sources of uncertainty, the attenuation function is the main contributor and its effect on estimates of risks is investigated. Epistemic uncertainty was considered by obtaining damage estimates for three attenuation functions that were developed for Eastern North America. The results indicate that loss estimates are highly sensitive to the choice of the attenuation function and suggest that epistemic uncertainty should be considered both for the definition of the hazard function and in loss estimation methodologies. Seismic loss estimates are performed for a 2% in 50 years seismic threat, which corresponds to the design level earthquake in the national building code of Canada, using HAZUS-MH4 for the Montreal region over 522 census tracts. The study estimated that for the average scenario roughly 5% of the building stock would be damaged with direct economic losses evaluated at 1.4 billion dollars for such a scenario. The maximum number of casualties would result in approximately 500 people being injured or dead at a calculated time of occurrence of 2?pm. 相似文献
960.
Applying disk-based discontinuous deformation analysis (DDA) to simulate Donghekou landslide triggered by the Wenchuan earthquake 总被引:1,自引:0,他引:1
S. Amir Reza Beyabanaki Amvrossios C. Bagtzoglou Lanbo Liu 《Geomechanics and Geoengineering》2016,11(3):177-188
In this paper, for the first time, disk-based discontinuous deformation analysis (DDA) is applied to simulate a real landslide triggered by an earthquake. For this purpose, the kinematic behaviour of the Donghekou landslide triggered by the Wenchuan earthquake is simulated and the results obtained using disk-based DDA are compared with actual data. The comparisons show that there is a good agreement between the results obtained using disk-based DDA and observed data. The simulation results provided an understanding of the failure behaviour and temporal evolution of the landslide. This study shows that disk-based DDA is a practical numerical tool that can be used to simulate the post-failure behaviour of landslides triggered by an earthquake. 相似文献