全文获取类型
收费全文 | 1808篇 |
免费 | 209篇 |
国内免费 | 195篇 |
专业分类
测绘学 | 51篇 |
大气科学 | 240篇 |
地球物理 | 419篇 |
地质学 | 732篇 |
海洋学 | 345篇 |
天文学 | 10篇 |
综合类 | 73篇 |
自然地理 | 342篇 |
出版年
2024年 | 7篇 |
2023年 | 27篇 |
2022年 | 46篇 |
2021年 | 47篇 |
2020年 | 63篇 |
2019年 | 66篇 |
2018年 | 28篇 |
2017年 | 96篇 |
2016年 | 73篇 |
2015年 | 90篇 |
2014年 | 113篇 |
2013年 | 108篇 |
2012年 | 63篇 |
2011年 | 102篇 |
2010年 | 75篇 |
2009年 | 143篇 |
2008年 | 127篇 |
2007年 | 111篇 |
2006年 | 109篇 |
2005年 | 99篇 |
2004年 | 70篇 |
2003年 | 53篇 |
2002年 | 69篇 |
2001年 | 41篇 |
2000年 | 57篇 |
1999年 | 54篇 |
1998年 | 45篇 |
1997年 | 36篇 |
1996年 | 36篇 |
1995年 | 40篇 |
1994年 | 18篇 |
1993年 | 24篇 |
1992年 | 21篇 |
1991年 | 13篇 |
1990年 | 10篇 |
1989年 | 10篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1980年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有2212条查询结果,搜索用时 562 毫秒
931.
Nebkha development and its relationship to environmental change in the Alaxa Plateau,China 总被引:2,自引:0,他引:2
Xunming Wang Honglang Xiao Jinchang Li Mingrui Qiang Zhizu Su 《Environmental Geology》2008,56(2):359-365
Extensive nebkha areas develop mainly under the control of aeolian processes, and their sediments record information on regional
environmental changes during different periods. Such areas have developed on the dry riverbeds and deserted arable lands of
China’s Alaxa Plateau, Taklimakan, and Kumutage deserts. In this paper, we studied nebkhas that had developed in the Heicheng–Juyan
region to determine their CaCO3 contents, particle size distributions, and creation dates. Extensive human activities have occurred in this region since
at least in the late Tang Dynasty (618–907 ad). Although historical records show that most of the region’s rivers dried up around 1372, surface water persisted in some
areas until the early Qing Dynasty (1644–1911 ad). After the 1600s, extensive nebkhas began to develop due to drying of the region’s rivers. The early stages of nebkha development
were controlled by both the sediment supply and the regional wind regime, whereas late stages were controlled primarily by
variations in wind activity. In the Alaxa Plateau, it took about 100 years for arable lands and riverbeds to evolve into gobi
deserts, and during this time, several phases occurred with different levels of wind activity. The land degradation processes
in this region are mainly controlled by surface water resources, and the impact of human activities such as reclamation on
land degradation appear to have been overestimated in previous studies. 相似文献
932.
The main purpose of this article is to evaluate the extent to which the Cohesion Policy of the EU contributes to its climate change mitigation effort. While climate change mitigation and the EU Cohesion Policy have been both thoroughly studied theoretically, the novelty of the present article lies in an analysis of their mutual relationship. Also, a unique feature of this research is an analysis of the contribution of the Cohesion Policy to climate change mitigation over a period of 20 years, including a comparison of the three last programming periods (2000–2006, 2007–2013 and 2014–2020). The results of this research suggest that, while the beginning of the new millennium saw the Cohesion Policy neglecting the issue of climate change mitigation, the current programming period (2014–2020) placed it among its key priorities. This conclusion is supported by a comprehensive set of data on five selected indicators. This article also displays the results against the perspective of the overall climate change mitigation objectives of the EU.
POLICY RELEVANCE
The present article shows how a policy, which used to be considered rather distant from climate change, progressively adopted climate change mitigation as one of its principal objectives. As such, it provides a practical guidance on the integration of climate change mitigation in other policy areas, which may be applied not only in a supranational organisation but also on a national, regional or local level. 相似文献
933.
利用2008-2017年5~8月天山南侧喀什地区气象台站观测记录、人工防雹作业点记录、灾害调查等资料,喀什探空站08时、20时探空资料,喀什雷达探测资料及其基数据反演产品,对冰雹的年分布、月分布及日变化特征进行了分析,归纳出冰雹云的雷达回波特征及移动路径,依据百分位数方法确定了以0℃层高度、-20℃层高度、冻结层厚度、全总指数、杰弗逊指数、K指数、沙氏指数为代表的冰雹预报指标,以及以回波顶高及其与当日0℃层高度差、40~50 dBZ回波高度及其与当日0℃层高度差、组合反射率、垂直积分液态水含量为代表的雷达特征预警指标。 相似文献
934.
935.
《Marine Policy》2016
The management of waterways, including marine parks, typically centres on assessment of biophysical phenomena, whilst social dimensions are relatively neglected. The diverse ways people interact with and relate to aquatic environments are consequently overlooked in planning and management. This misses opportunities as people's decisions and actions have direct and indirect impacts on how natural systems function. Effective management requires appreciation of how people interact with these environments in order to tailor, and build public support for, management plans and ensure compliance. This qualitative study, using 30 semi-structured interviews, explores people's values towards Moreton Bay Marine Park and its tributary rivers in south east Queensland, Australia. The values offer a powerful means to understand the different ways people relate to these waters. The study found that these waterway environments provide people with a diversity of rich and meaningful experiences, and that individuals hold several values each; they are not discrete. Some types of value frequently occur together. These clusters of values suggest new ways of working with the public to achieve management goals of protecting and improving waterway environments. 相似文献
936.
Characterization of sub‐daily thermal regime in alpine rivers: quantification of alterations induced by hydropeaking
下载免费PDF全文
![点击此处可从《水文研究》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The thermal regime of rivers is threatened by anthropogenic stresses at a large variety of timescales. We focus on sub‐daily thermal alterations induced by the release of hypolimnetic water for hydropower production (thermopeaking). We analyse the thermal signal focusing on the following characteristics that are potentially affected by hypolimnetic releases: (i) sub‐daily thermal rate of change and (ii) oscillation frequencies contained in the thermal signal. Through a proper scaling, we derive two dimensionless at‐a‐station indicators to compare alterations among stations with different locations and physiographic characteristics of the basins. Then we analyse the data from two different thermal datasets (Italy/Switzerland) for a total of 48 stations with 10 min time resolution of temperature data. The stations are grouped according to the absence of upstream hydropeaking releases (29 stations, reference group) and the existence of upstream hydropeaking, hence potentially impacted by thermopeaking (19 stations, altered group). Using a simple statistical approach, based on a non‐parametric definition of outliers, we identify the range of variability of the two indicators for the reference, unaltered group. This range measures the ‘natural’ sub‐daily thermal variability of the proposed indicators. Finally, we investigate the seasonality effects on the two proposed indicators and it results, that sub‐daily alterations mostly occur during summer. The two indicators represent a novel tool for the assessment of river thermal regime alterations and can be easily included in existing methodologies to assess river quality. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
937.
《Geoforum》2015
The themes of immigration and mobility have not been adequately examined by environmental justice (EJ) scholars. This study addresses that gap by clarifying factors shaping Hispanic people’s residential decision-making and their associated exposures to cancer risks from Hazardous Air Pollutants (HAPs) in Greater Houston, Texas. In-depth semi-structured interviews were conducted with 29 Hispanic householders who had previously completed a structured survey, which was representative of Greater Houston’s population. Our research design enabled data collection from immigrant and United States (US)-born Hispanics living at high and low risk to HAPs. By using a comparative qualitative analysis approach to examine divergent experiences of Hispanic subgroups, we advance from the monolithic treatment of the US Hispanic population reflected in the extant EJ literature. Our findings reveal that key determinants of high HAP risks included economic constraint on residential locational options for both US-born and immigrant Hispanics, and attraction to sociocultural benefits in co-ethnic enclaves among immigrants in particular. In contrast, protective factors differed entirely between US-born and immigrant Hispanics. For US-born participants, the experience of upward-and-outward sociospatial mobility – coupled with detachment from the Hispanic community – generated lower HAP risks, while the experience of living in social isolation within a less-than-ideal rental unit was protective for immigrants. The pernicious, multiscalar nature of environmental injustice experienced by Greater Houston’s Hispanic immigrants is encapsulated by the fact that their pursuit of affordable and comfortable residential settings at the household level contributes to the reproduction of their collectively disproportionate HAP exposures. 相似文献
938.
Issues concerning what measures should be adopted to achieve a sustainable world with less carbon dioxide emission and in what magnitude should we reduce our emission have been on agenda in both international negotiations and countries’ policy making aimed at coping with potential global climate change. These issues cannot be easily addressed unless comprehensive understanding about the countries’ status quo as well as historical relationship between economic development and carbon dioxide emission are gained. In this paper, we examine the historical relationship between economic development and carbon dioxide emission; the ex ante restrictions on function forms and the poorly handled robustness issues rife in economics literature are synthetically addressed. Evidence from recent four decades indicates that per capita carbon dioxide emission first significantly and monotonously increase at low income level and flattens after per capita income reaches at about 22,000 $ (2005 constant price). We perform various robustness checks by employing different data sources, different model specifications and different econometric estimates. The captured development–emission relationship is robust. Our empirical results indicate factors such as urbanization, population density, trade, energy mix and economic environment impact the absolute level of carbon dioxide emission not the overall income elasticity structure of carbon dioxide emission. 相似文献
939.
A. Das Gupta 《Physics and Chemistry of the Earth》2008,33(5):298-303
Consideration of environmental flows in river basin management poses great challenges. Environmental flows are interpreted as the natural or regulated releases of water needed in a river to maintain specified valued features of the river ecosystems. This has never been considered explicitly in water resources management of a river basin. An attempt is, therefore, made here to reflect the perception and implications of environmental flows in water resources management. Assessment approaches are reviewed in the context of flow characteristics of a river system and recommendations are put forward on what is to be done to adopt this new concept in practice. 相似文献
940.
Ling Gao Ying Wang Yang Xu Shi Lu Zhou Ting Ting Zhuang Zheng Ying Wu Jian Hua Zhu 《洁净——土壤、空气、水》2008,36(3):270-278
A new effort to control the pollution caused by smoking by use of zeolite sieving the N‐nitrosamines in smoke is depicted and assessed in this paper, which is a first preliminary approach to demonstrate the performance characteristics of zeolite for the reduction of the concentration of N‐nitrosamines in the cigarette smoke. Smoking causes global pollution and is difficult to control because smoke is a complex system containing thousands of components. A new strategy is presented here for the reduction of the harmful effects of smoking through dispersion of zeolite into the tobacco rod of cigarettes to eliminate the N‐nitrosamines once they form in the smoke, and both in vitro and in vivo tests were employed to check the efficiency of this strategy. The impact of zeolite on the combustion of tobacco and the total toxicity of smoke are evaluated for the first time. Lower mutagenic activity and higher CHO cell livability were found for the test cigarette containing zeolite in comparison with the control, and no significant damage was detected in 30‐day animal experiments when exposed to the cigarette smoke. This confirms the feasibility of the new strategy and promotes the potential application of zeolite for protecting public health. 相似文献