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   130篇
  免费   3篇
  国内免费   2篇
测绘学   4篇
大气科学   18篇
地球物理   30篇
地质学   46篇
海洋学   6篇
天文学   26篇
自然地理   5篇
  2021年   5篇
  2019年   2篇
  2018年   5篇
  2016年   3篇
  2015年   5篇
  2014年   2篇
  2013年   7篇
  2011年   4篇
  2010年   4篇
  2009年   5篇
  2008年   6篇
  2007年   5篇
  2006年   3篇
  2005年   2篇
  2004年   3篇
  2003年   5篇
  2002年   6篇
  2001年   3篇
  2000年   1篇
  1999年   2篇
  1998年   4篇
  1997年   2篇
  1996年   2篇
  1995年   5篇
  1994年   1篇
  1992年   3篇
  1991年   1篇
  1990年   2篇
  1989年   1篇
  1988年   4篇
  1987年   1篇
  1986年   2篇
  1985年   1篇
  1984年   1篇
  1981年   6篇
  1980年   4篇
  1979年   1篇
  1977年   1篇
  1976年   1篇
  1975年   1篇
  1972年   1篇
  1970年   1篇
  1964年   1篇
  1960年   1篇
  1957年   1篇
  1955年   1篇
  1949年   1篇
  1927年   1篇
  1914年   1篇
  1913年   1篇
排序方式: 共有135条查询结果,搜索用时 15 毫秒
71.
Changes in labour productivity feed through directly to national income. An external shock, like climate change, which may substantially reduce the productivity of workers is therefore a macroeconomic concern. The biophysical impact of higher temperatures on human performance is well documented. Less well understood are the wider effects of higher temperatures on the aggregate productivity of modern, diversified economies, where economic output is produced in contexts ranging from outdoor agriculture to work in air-conditioned buildings. Working conditions are at least to some extent the result of societal choices, which means that the labour productivity effects of heat can be alleviated through careful adaptation. A range of technical, regulatory/infrastructural and behavioural options are available to individuals, businesses and governments. The importance of local contexts prevents a general ranking of the available measures, but many appear cost-effective. Promising options include the optimization of working hours and passive cooling mechanisms. Climate-smart urban planning and adjustments to building design are most suitable to respond to high base temperature, while air conditioning can respond flexibly to short temperature peaks if there is sufficient cheap, reliable and clean electricity.

Key policy insights

  • The effect of heat stress on labour productivity is a key economic impact of climate change, which could affect national output and workers’ income.

  • Effective adaptation options exist, such as shifting working hours and cool roofs, but they require policy intervention and forward planning.

  • Strategic interventions, such as climate-smart municipal design, are as important as reactive or project-level adaptations.

  • Adaptation solutions to heat stress are highly context specific and need to be assessed accordingly. For example, shifting working hours could be an effective way of reducing the effect of peak temperatures, but only if there is sufficient flexibility in working patterns.

  相似文献   
72.
When fugitive methane migrates upward along boreholes of oil and gas wells, it may migrate into shallow ground water or pass through overlying soil to the atmosphere. Prior to this study, there was little information on the fate of fugitive methane that migrates into ground water. In a field study near Lloydminster, Alberta, Canada, we found hydrogeochemical evidence that fugitive methane from an oil well migrated into a shallow aquifer but has been attenuated by dissimilatory bacterial sulfate reduction at low temperature ( approximately 5 degrees C) under anaerobic conditions. Evidence includes spatial and temporal trends in concentrations of methane and sulfate in ground water and associated trends in concentrations of bicarbonate and sulfide. Within 10 m of the oil well, sulfate concentrations were low, and sulfate was enriched in both 34S and 18O. Sulfate concentrations had a strong positive correlation with delta13C values of bicarbonate, and sulfide was depleted in 34S compared to sulfate. These data indicate that bacterial sulfate reduction occurred near the production well. Near the oil well, elevated concentrations of bicarbonate were observed, and the bicarbonate was depleted in 13C. Modeling indicates that the main source of this excess 13C-depleted bicarbonate is oxidized methane. In concert with the sulfate concentration and isotope data, these results support an interpretation that in situ bacterial oxidation of methane has occurred, linked to bacterial sulfate reduction. Bacterial sulfate reduction may play a major role in bioattenuation of fugitive natural gas in ground water in western Canada.  相似文献   
73.
Fluid-flow measuring devices intended for full scale use were designed and tested. One device consisted of a rake supporting different types of pitot tubes. This will be used to obtain a velocity profile of the boundary layer of a test ship. The other device was a five-hole pitot tube that was used in a wake survey. The pressure transport medium (i.e. the medium that carried the pressure signal from the pitot tube to the pressure transducer) was air instead of water. This proved to be successful, as the results indicate.  相似文献   
74.
Beckers  Jacques M.  Leon  Ed  Mason  Jim  Wilkins  Larry 《Solar physics》1997,176(1):23-36
Since 1993 it is known that there is a good correlation between the scintillation in the solar irradiance and solar image quality (Seykora, 1993). This effect is now being used in a number of experiments to evaluate solar image quality and to measure site seeing. In this paper we explore further the calibration of this scintillation (I) in terms of the Fried parameter (r0) taking into account variations in the refractive index structure constant C N 2 with height (h), zenith distance () dependence and the effects of wind velocities. A variant in the scintillometer setup is proposed which decreases sharply the dependance on C N 2 , , and the wind velocities. It uses an array of scintillometers. The same array can be used to measure theC N 2 profile with height. Some preliminary results of the calibration of current NSO site survey measurements are presented.  相似文献   
75.
76.
1.IntroductionThispaperexploresanensembleforecaststrategyforthelarge--scaletropicalpredictionproblem.Thisisgeneralizedfromarecentstudyontheuseofempiricalorthogonalfunction(EOF)--basedperturbationsforhurricanetrackensembleforecasts,(ZhangandKrishnamur...  相似文献   
77.
Residual displacement, as a significant measure of structural inelasticity, is effectively used in post-earthquake seismic assessment of structures. This demand can be considered for seismic evaluation of structures under multiple earthquakes. This study introduces a simple and novel index to predict the residual displacement of mainshock-damaged structures against subsequent aftershock. The proposed index is defined as a ratio between residual displacement of damaged structures against aftershock and peak inelastic displacement of intact structures under mainshock. In this study, constantstrength spectra based on the index are developed considering the effects of important structural characteristics and also significant seismic parameters. Moreover, analytical equations are presented to predict the proposed index for bi-linear single-degree-of-freedom(SDOF) systems considering both the effects of positive and negative polarities of aftershock. Furthermore, an equation is suggested to estimate the peak inelastic displacement of intact systems under mainshock, which is required to compute the index.  相似文献   
78.
A small‐diameter nuclear magnetic resonance (NMR) logging tool has been developed and field tested at various sites in the United States and Australia. A novel design approach has produced relatively inexpensive, small‐diameter probes that can be run in open or PVC‐cased boreholes as small as 2 inches in diameter. The complete system, including surface electronics and various downhole probes, has been successfully tested in small‐diameter monitoring wells in a range of hydrogeological settings. A variant of the probe that can be deployed by a direct‐push machine has also been developed and tested in the field. The new NMR logging tool provides reliable, direct, and high‐resolution information that is of importance for groundwater studies. Specifically, the technology provides direct measurement of total water content (total porosity in the saturated zone or moisture content in the unsaturated zone), and estimates of relative pore‐size distribution (bound vs. mobile water content) and hydraulic conductivity. The NMR measurements show good agreement with ancillary data from lithologic logs, geophysical logs, and hydrogeologic measurements, and provide valuable information for groundwater investigations.  相似文献   
79.
A simplified empirical equation is developed for widespread prediction of dynamic catchment response time. This model allows for time-to-peak prediction to evolve from static, lumped models, thereby providing a single value for any storm within a given catchment, using a single set of input parameters, that can be applied to a dynamic model, thus accounting for the variability between storm sizes and catchment moisture conditions. These dynamic prediction methods are translated to North America for the first time. This allows the concepts and prediction methods for catchment response time prediction previously established for the United Kingdom (UK), to be translated to a simple empirical equation for use in North America, through the use of selected study areas in Canada and the United States. This reconfigured model is statistically successful in both the UK and North America and allows for a straightforward implementation of dynamic time-to-peak prediction. Further, the reconfigured model introduces the use of a runoff coefficient (Rc) to encompass historical catchment wetness, increasing the ease of incorporating antecedent moisture condition into predictions.  相似文献   
80.
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