首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   2345篇
  免费   410篇
  国内免费   537篇
测绘学   30篇
大气科学   189篇
地球物理   352篇
地质学   1526篇
海洋学   598篇
天文学   43篇
综合类   136篇
自然地理   418篇
  2024年   10篇
  2023年   46篇
  2022年   86篇
  2021年   146篇
  2020年   104篇
  2019年   115篇
  2018年   89篇
  2017年   114篇
  2016年   112篇
  2015年   116篇
  2014年   127篇
  2013年   192篇
  2012年   128篇
  2011年   151篇
  2010年   115篇
  2009年   157篇
  2008年   156篇
  2007年   119篇
  2006年   126篇
  2005年   121篇
  2004年   98篇
  2003年   96篇
  2002年   94篇
  2001年   100篇
  2000年   103篇
  1999年   73篇
  1998年   79篇
  1997年   73篇
  1996年   54篇
  1995年   37篇
  1994年   42篇
  1993年   29篇
  1992年   15篇
  1991年   11篇
  1990年   11篇
  1989年   5篇
  1988年   6篇
  1987年   6篇
  1986年   3篇
  1985年   4篇
  1984年   8篇
  1983年   6篇
  1982年   2篇
  1981年   7篇
排序方式: 共有3292条查询结果,搜索用时 15 毫秒
991.
Many Mediterranean areas have recently witnessed a proliferation of new urban and tourist-related features following low-density residential patterns that contrast with the traditional high-density urban typologies of Mediterranean cities. The aim of this research is to investigate the links between residential tourism and water consumption through swimming pools, which constitute one key element of the new urban landscapes in the coast of Alicante (southeastern Spain). We have digitized pools in nine municipalities of coastal Alicante and calculated the average depth and estimated water losses due to evaporation. Results show that swimming pools are widely available in tourist residential enclaves but that they tend to display different characteristics according to factors such as the history of the urbanization process and relative wealth of the different areas. We have detected a clear contrast between the large individual pools of the richer northern municipalities and the smaller individual pools and community pools in the newly developed but less well-off urban enclaves of the southern coast.  相似文献   
992.
旅游食物消费是旅游消费的首要内容。随着旅游学科研究的不断深入,旅游食物消费近年来逐渐成为学界关注的热点。目前,国内对旅游食物消费的研究仅限于对饮食文化资源的开发和旅游食物卫生等方面,处于描述性研究的初级阶段。国际上旅游食物消费研究起步较早,内容也较为全面,除对旅游食物安全风险、食物旅游产品开发和市场营销进行广泛探讨外,更在游客食物消费行为、旅游食物消费综合效应等领域取得了系统成果。本文利用文献分析方法,在综合分析和梳理国内外食物消费研究文献基础上,归纳总结了旅游食物消费发展阶段和特征,并重点从游客食物消费行为模式、旅游食物资源开发、旅游地美食节庆与营销、旅游食物安全与风险、旅游食物消费与旅游地发展、旅游食物消费环境影响与可持续发展等6个方面对旅游食物消费的研究内容和进展进行了分析,最后提出了中国现阶段旅游食物消费研究应关注的重点领域和方向。  相似文献   
993.
Fei ZHENG  Jin-Yi YU 《大气科学进展》2017,34(12):1395-1403
The tropical Pacific has begun to experience a new type of El Nio, which has occurred particularly frequently during the last decade, referred to as the central Pacific(CP) El Nio. Various coupled models with different degrees of complexity have been used to make real-time El Nio predictions, but high uncertainty still exists in their forecasts. It remains unknown as to how much of this uncertainty is specifically related to the new CP-type El Nio and how much is common to both this type and the conventional Eastern Pacific(EP)-type El Nio. In this study, the deterministic performance of an El Nio–Southern Oscillation(ENSO) ensemble prediction system is examined for the two types of El Nio. Ensemble hindcasts are run for the nine EP El Nio events and twelve CP El Nio events that have occurred since 1950. The results show that(1) the skill scores for the EP events are significantly better than those for the CP events, at all lead times;(2) the systematic forecast biases come mostly from the prediction of the CP events; and(3) the systematic error is characterized by an overly warm eastern Pacific during the spring season, indicating a stronger spring prediction barrier for the CP El Nio. Further improvements to coupled atmosphere–ocean models in terms of CP El Nio prediction should be recognized as a key and high-priority task for the climate prediction community.  相似文献   
994.
Cellular automata (CA) models are commonly used to model vegetation dynamics, with the genetic algorithm (GA) being one method of calibration. This article investigates different GA settings, as well as the combination of a GA with a local optimiser to improve the calibration effort. The case study is a pattern-calibrated CA to model vegetation regrowth in central Victoria, Australia. We tested 16 GA models, varying population size, mutation rate, and level of allowable mutation. We also investigated the effect of applying a local optimiser, the Nelder?Mead Downhill Simplex (NMDS) at GA convergence. We found that using a decreasing mutation rate can reduce computational cost while avoiding premature GA convergence, while increasing population size does not make the GA more efficient. The hybrid GA-NMDS can also reduce computational cost compared to a GA alone, while also improving the calibration metric. We conclude that careful consideration of GA settings, including population size and mutation rate, and in particular the addition of a local optimiser, can positively impact the efficiency and success of the GA algorithm, which can in turn lead to improved simulations using a well-calibrated CA model.  相似文献   
995.
Remote sensing digital image analysis has been applied to monitor land clearing and degradation processes on a plateau covered by tiger bush near Niamey in South West Niger, where signs of severe landscape degradation due to fuelwood supply have been observed in the last decades. A MODIS NDVI dataset (2000–2015) and five LANDSAT images (1986–2012) were used to identify spatial and temporal dynamics and to emphasize areas of greater degradation. The study indicates that the land clearing found by previous investigations in the second part of the 20th century is still ongoing, with a decreasing trend of MODIS NDVI values recorded in the period 2000–2015. This trend appeared to be linked to an increase in bare soil areas that was demonstrated by analysis of LANDSAT SAVI images. The investigation also indicated that rates of degradation are stronger in more deteriorated areas like those located nearer Niamey; degradation patterns also tend to increase from the inner areas to the edges of the plateau. These results attest to the urgency to develop effective environmental preservation policies and find alternative solutions for domestic energy supply.  相似文献   
996.
极点对称模态分解下西安高温天气的趋势特征   总被引:1,自引:0,他引:1  
基于1960-2016年西安均一化气象资料,采用极点对称模态分解法,对西安市的高温天气变化特征进行分析,探讨赤道东太平洋海温异常(El Ni?o)、西太平洋副热带高压变化(WPSH),与西安极端高温变化的关系。结果表明:① 采用非均一化数据,会低估西安暖夜、夏季、热夜、热浪日数变化趋势,高估冬季供暖能耗下降幅度、夏季制冷能耗上升幅度,对暖昼、高温日数影响相对较小。② 在年代变化上,暖昼、热浪、高温日数和制冷度日等四个指标,反映西安白天高温变化特征,呈现一致的四阶段“下降—上升—下降—上升”的变化过程;表征夜间高温变化的暖夜和热夜日数,以1993年为节点,呈现两阶段“阶梯状”的上升趋势。③ 在影响因素上,赤道太平洋中西部海温异常与西安高温关系更为密切。当Ni?o 4区海温异常偏高时,西安暖昼、夏季、炎热天气制冷耗能明显增加,寒冷天气供暖能耗显著降低;同时,当WPSH强度越大,控制面积越大、西伸脊点偏西时,西安暖夜、夏季、热夜日数明显增加、寒冷天气供暖能耗明显下降。  相似文献   
997.
One-third of all food produced in the world is lost or wasted, which has negative consequences for societies and the environment. Thus, curbing food waste is critical to securing human well-being and protecting the environment. This study examines the drivers of household food waste decisions by investigating the activation and deactivation of moral norms and introducing the concept of the ‘good provider’ in an augmented norm-activation model (NAM). A survey of 643 consumers in Australia and Singapore explores the ‘good provider’ norm as a driver of food waste behaviours in both cultures. For Australians, ‘good provider’ norms suppress intentions to avoid food waste, most likely to provide for the immediate family, which can be a motive that overrides moral concern about food waste in an individualistic culture. For Singaporeans, ‘good provider’ norms do not suppress food waste intentions, possibly due to the value placed on thrift by a long-term-oriented culture. The paper significantly extends the previous research on norms, culture and sustainable consumption and provides policy and practical implications for curbing food waste in different cultural contexts.  相似文献   
998.
Strategic issue framing is widely regarded as an effective communication strategy to alter public opinion and citizens’ policy support. However, it is unclear to what extent strategic framing can increase support for ambitious demand-side actions and policies that make the cost of mitigation perceptible in citizens’ everyday lives. Taking an exploratory approach, we conducted qualitative interviews and a comparative framing experiment with 9,750 survey respondents from China, Germany, and the United States. We analyzed strategic issue framing effects in two areas known to be key for increasing the sustainability of consumption: meat/fish consumption, and fossil-fuel car usage. Employing both classical linear regressions and advanced Bayesian sparse estimations, we show that in all three countries widespread arguments in favor of reduced meat/fish consumption and car use are unlikely to substantially alter citizens’ concern, willingness to pay, behavioral intentions and policy support for demand-side action. Our findings suggest that in the absence of a broader behavioral change campaign, strategic issue framing alone is unlikely to be effective in changing entrenched attitudes and behaviors. On its own, it is also unlikely to substantially increase public support for demand-side policies to reduce consumption. More careful research is needed to help policymakers understand the role and limits of different strategic framing techniques.  相似文献   
999.
Reducing emissions of greenhouse gases is facilitated by changes in several consumption activities, such as food choices. This paper examines factors explaining red meat consumption in Norway, especially the role of climate concerns. The paper adds to our knowledge as most existing analyses of (red) meat consumption focus on health and animal welfare issues. Moreover, it expands our understanding by drawing on perspectives from both institutional and social psychological theory, including variables emphasizing the social dynamics behind consumption decisions. The study is based on data from a survey of 2000 people aged 18 years or older conducted in 2018. The data are analyzed using structural equation modelling. We find that there is a strong pro-meat culture in Norway, currently rather weakly influenced by climate concerns – specifically, personal norms and social pressures focused on reducing climate impacts. Instead, habits, beliefs about the qualities of red meat (being tasteful, nutritious, healthy) and social norms supporting red meat consumption are the three most important factors explaining the variation observed. Gender and income also influence red meat consumption, but less than found in other studies. The paper discusses policy implications of these findings, including for taxation, point-of-sale information and communicative processes to support changes in the perceptions of what could be a new “normal” diet.  相似文献   
1000.
This study reveals a significant positive connection between autumn non-tropical-cyclone heavy rainfall on Hainan Island and the intensity of Eastern Pacific (EP) El Ni?o events. That is, the amount of rainfall in super EP El Ni?o years is more than that in normal EP El Ni?o years. Comparing EP El Ni?o years of different intensities, the cooler sea surface temperature in the northwestern Pacific during super EP El Ni?o years stimulates a negative surface latent heat flux (LHF) anomaly and abnormal anticyclonic circulation at 850 hPa. Under these conditions, an abnormal zonal vertical circulation develops in the northern South China Sea once a positive LHF anomaly and abnormal cyclonic circulation (ACC) at 850 hPa occur in the Beibu Gulf. The abnormal zonal vertical circulation further strengthens the ascending motion over Hainan Island, as the critical factor that leads to excessive rainfall. Further analysis shows that the positive LHF anomaly, which can be attributed to the increased latent heat transfer which resulted from the increased surface wind speed, is an important trigger for the ACC. However, the ACC is also the supplier of favorable moisture conditions because it intensifies vapor convergence over Hainan Island and meridionally transports moisture from the South China Sea to northeastern Hainan Island, thereby generating heavy rainfall. This paper emphasizes that the impact of El Ni?o events, especially super El Ni?o events, on rainfall over Hainan Island cannot be ignored, even if the traditional view is that frequent rainfall occurs mainly in La Ni?a years.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号