全文获取类型
收费全文 | 8726篇 |
免费 | 1378篇 |
国内免费 | 1610篇 |
专业分类
测绘学 | 641篇 |
大气科学 | 935篇 |
地球物理 | 2233篇 |
地质学 | 4387篇 |
海洋学 | 1168篇 |
天文学 | 23篇 |
综合类 | 603篇 |
自然地理 | 1724篇 |
出版年
2024年 | 36篇 |
2023年 | 133篇 |
2022年 | 287篇 |
2021年 | 361篇 |
2020年 | 363篇 |
2019年 | 413篇 |
2018年 | 342篇 |
2017年 | 388篇 |
2016年 | 414篇 |
2015年 | 386篇 |
2014年 | 607篇 |
2013年 | 594篇 |
2012年 | 522篇 |
2011年 | 583篇 |
2010年 | 541篇 |
2009年 | 568篇 |
2008年 | 578篇 |
2007年 | 619篇 |
2006年 | 607篇 |
2005年 | 498篇 |
2004年 | 413篇 |
2003年 | 374篇 |
2002年 | 371篇 |
2001年 | 286篇 |
2000年 | 246篇 |
1999年 | 187篇 |
1998年 | 196篇 |
1997年 | 142篇 |
1996年 | 134篇 |
1995年 | 105篇 |
1994年 | 92篇 |
1993年 | 78篇 |
1992年 | 87篇 |
1991年 | 34篇 |
1990年 | 28篇 |
1989年 | 21篇 |
1988年 | 14篇 |
1987年 | 8篇 |
1986年 | 12篇 |
1985年 | 7篇 |
1984年 | 11篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 1篇 |
1980年 | 3篇 |
1978年 | 8篇 |
1977年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
911.
The potential impacts of progressing climate change are alarming. Some adverse consequences are now unavoidable and adaptation measures are increasingly needful. This poses enormous challenges for emerging megacities in the Global South, which barely manage in current weather conditions. This paper introduces Fuzzy Cognitive Mapping as a new tool for structured, semi-quantitative assessments of climate change impacts and adaptation measures.Fuzzy Cognitive Mapping is used to evaluate differences in sensitivities to heatwaves and rainstorms across socio-economic groups and for the ranking of useful adaptation options, based on 188 individual interviews to the impacts of extreme weather events in Hyderabad, India. The results of this multi-stakeholder assessment indicate that rainstorms affect low-income residents more than heatwaves, while the opposite is true for medium-income respondents. The latter are also less seriously affected by extreme weather in general. Profession, though, not income determines the kind of impact that people feel most affected by. Individual characteristics like age and gender do not significantly explain differences in the data, but religion does. This is because, in Hyderabad, Muslims live in the older, less serviced and more affected parts of the city. However, semi-quantitative scenario analyses suggest that, under future climate change, many parts of the city will become increasingly exposed to the effects of extreme weather. Planned investments in urban infrastructure will be seriously challenged by climate change and preventive adaptation measures are urgently needed to at least maintain the current level of quality of life. Investments in the health infrastructure appear to be most effective in reducing the impact of heatwaves and investments in the traffic infrastructure most effective in reducing the impact of rainstorms. However, looking at heat and rain events together—which is realistic as they are both projected to increase and often occur in the same year—reveals that investments in water infrastructure and management have greatest potential to reduce impacts across all localities and on all social groups, particularly the lower-income classes. This is because first-order impacts caused by inadequate water infrastructure often give rise to second- or third-order impacts. Addressing the root cause is the most effective way to break cause-and-effect chains and prevent proliferation of negative consequences. Similar studies are suggested in other cities in order to support adaptation mainstreaming in complex urban environments. Fuzzy Cognitive Mapping proved a useful, semi-quantitative tool for climate change impact and adaptation assessments. 相似文献
912.
In many coastal nations, community-based arrangements for marine resource management (CBRM) are promoted by government, advocated for by non-government actors, and are seen by both as one of the most promising options to achieve sustainable use and secure inshore fisheries and aquatic resources. Although there is an abundant literature on what makes CBRM effective, is it less clear how CBRM is introduced or develops as an idea in a community, and the process of how the idea leads to the adoption of a new resource management approach with supporting institutions. Here we aim to address this gap by applying an explicit process-based approach drawing on innovation history methodology by mapping and analysing the initiation and emergence of CBRM in five fishing-dependent communities in Solomon Islands. We use insights from the literatures on diffusion of innovation and transformability to define phases of the process and help guide the inductive analysis of qualitative data. We show the CBRM institutionalisation processes were non-linear, required specific strategies to move from one phase to the next, and key elements facilitated or hindered movement. Building active support for CBRM within communities depended on the types of events that happened at the beginning of the process and actions taken to sustain this. Matching CBRM to known resource management ideas or other social problems in the community, developing legitimate institutions and decision-making processes, strong continual interactions between key actors and the rest of the community (not necessarily NGO actors), and community members witnessing benefits of CBRM, all contributed to the emergence and diffusion of CBRM in the communities, and helped to overcome barriers to transformative change. 相似文献
913.
本文首先采用基于多准则决策的层次分析评价法,根据自然灾害风险理论,将洪涝风险影响因子分为危险性和脆弱性两类,子准则层包括平均降雨量、汇流累积量、坡度、海拔和土地覆盖度、道路级别、地表产流能力7个因子,构建了道路洪涝灾害风险评价模型。然后以福建省武夷山地区为研究区,利用地形数据、气象数据及遥感影像提取土地覆盖类型数据,通过道路洪涝灾害风险评价模型,绘制了道路风险分区图。结果表明,中、高风险积水道路占比较高,主要集中在东部、西部和中南部地区。本文对道路洪涝灾害风险所进行的评价,可服务于洪涝灾害风险预警和应急救援规划。 相似文献
914.
915.
916.
通过分析研究某农药化工企业密集区地下水水质及污染状况,按照国家有关标准,采用单指标评价法和内梅罗指数法对地下水的质量进行评价。评价结果显示:该区域地下水水质普遍较差,大部分为Ⅳ类及Ⅴ类水质,已不适于饮用。然后对该区域地下水污染进行评价,结果显示地下水有机和无机污染严重,并形成了以某农药化工企业为污染源并沿岩溶地下水流向的一个卤代烃类有机物污染羽,这表明造成该研究区岩溶地下水污染的主要污染源为某农药化工企业。最后根据评价结果,提出相应的控制地下水污染的建议和措施,为该地区制定地下水开发利用规划提供科学依据。 相似文献
917.
石棉县后沟是一条典型的自然泥石流和矿渣泥石流并存的泥石流沟。本文以石棉后沟为例,结合早期自然泥石流、矿产开采以来矿渣泥石流、以及2013年7 4复合型泥石流,总结了自然泥石流和矿渣泥石流的复合效应,包括泥石流物源补给的多元效应、泥石流发展演化的逆转效应、泥石流起动发生的复杂效应、泥石流动力沿程的放大效应、泥石流致灾破坏的链式效应。对照泥石流对已建防治工程的破坏,提出了自然泥石流和矿渣泥石流复合型泥石流沟防治对策,建议充分利用起动位置和物源集中补给位置的差异,加强对中上游及支沟自然泥石流起动和运动的拦挡防治,最大限度减小自然泥石流对下游矿渣防护工程的基底侵蚀和冲击破坏,从而保障综合防治工程的有效性。 相似文献
918.
919.
龙门山地区强震荷载导致大量已建边坡支挡结构严重受损,如何对震区受损挡土墙进行震害评估成为亟待解决的技术难点。本文首先通过对研究区挡土墙的震害分析,总结出其主要破坏模式包括滑移破坏、沉降破坏、倾覆破坏、墙身破坏以及越顶破坏5类。然后根据全面性、重要性以及科学性原则对影响震害评价的因子进行定性分析和分类,并结合挡墙的破坏模式,综合分析得到挡土墙安全评估的敏感性因子和一般因子。将震害范围60%作为挡墙评价的敏感性因子,而一般因子分为两级共10个指标,包括:滑移距离,沉降深度,倾斜角度,裂缝数量,裂缝长度比,开裂深度比,开裂宽度,错动距离,垮塌范围,覆盖范围。最后,采用灰色关联分析与模糊数学理论相结合的方法构建挡土墙震害评估体系,从而变事后处理为事先预防,为灾后恢复重建服务。 相似文献
920.
煤矿塌陷区复垦土壤环境质量评价 总被引:1,自引:0,他引:1
通过对煤矿塌陷区复垦土壤采样测试,研究土壤中重金属铜、锌、镉、汞、砷、铅、铬的含量对土壤环境的影响。研究结果表明:按单因子污染指数法和内梅罗综合污染指数法,结合国家土壤环境质量标准对复垦土壤的质量进行评价:研究区内土壤环境质量良好,基本上可以达到国家土壤环境质量二级标准,安全清洁级别;参照《无公害食品蔬菜产地环境条件标准》、《绿色食品产地环境质量标准》和《有机农业生产基地环境质量标准》,对复垦土壤的农用环境进行评价:研究区内土壤全部达到绿色食品产地环境质量标准,如果选择合理的修复方法,对部分有轻微污染的土壤进行,则可以达到有机农业生产基地环境质量标准;以潜在生态危害指数RI分析,复垦区内土壤重金属潜在生态危害指数相对较低,复垦区农业生产具有良好的发展前景。 相似文献