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   530篇
  免费   30篇
  国内免费   30篇
测绘学   9篇
大气科学   280篇
地球物理   50篇
地质学   51篇
海洋学   11篇
天文学   14篇
综合类   7篇
自然地理   168篇
  2024年   1篇
  2023年   10篇
  2022年   34篇
  2021年   27篇
  2020年   21篇
  2019年   36篇
  2018年   36篇
  2017年   24篇
  2016年   38篇
  2015年   19篇
  2014年   29篇
  2013年   105篇
  2012年   25篇
  2011年   20篇
  2010年   7篇
  2009年   17篇
  2008年   16篇
  2007年   15篇
  2006年   14篇
  2005年   6篇
  2004年   12篇
  2003年   9篇
  2002年   11篇
  2001年   14篇
  2000年   5篇
  1999年   1篇
  1998年   9篇
  1997年   4篇
  1996年   5篇
  1995年   7篇
  1994年   1篇
  1993年   2篇
  1992年   3篇
  1990年   1篇
  1989年   2篇
  1988年   1篇
  1987年   1篇
  1985年   2篇
排序方式: 共有590条查询结果,搜索用时 15 毫秒
91.
资源型区域碳排放影响因素分析——以山西省为例   总被引:1,自引:0,他引:1  
碳排放问题是应对气候变化的主要问题,更是困扰资源型区域改革与可持续发展的关键性问题。以山西省为例,采用LMDI分解方法,将碳排放分解为5种影响因素,对山西省碳排放趋势和变化、影响因素做了深入探讨。结果表明:1)山西省未来碳排放增速减缓,排放量将持续增加,生态环境压力进一步加大;2)能源结构效应为负向影响,虽效应值较小,但潜力巨大。而人口规模正向效应值缓慢变大需要关注;3)在产业结构效应方面,工业、交通运输仓储邮政业及批发零售住宿餐饮业部门产业效应为正效应,且有逐年增大的趋势。表明第二产业和第三产业内部结构不合理,产业结构优化有待提高。  相似文献   
92.
Analysis of carbon emission mechanism based on regional perspectives is an important research method capable of achieving energy savings and emission reductions. Xinjiang, an important Chinese energy production base, is currently going through a period of strategic opportunities for rapid development. Ensuring stable socio-economic development while achieving energy savings and meeting emission reductions targets, is the key issue currently facing the region. This paper is based on the input-output theory, and conducts a structural decomposition analysis on the factors affecting energy-related carbon emissions in Xinjiang from 1997 to 2007; this analysis employs a hybrid input-output analysis framework of “energy - economy - carbon emissions”. (1) Xinjiang’s carbon emissions from energy consumption increased from 20.70 million tons in 1997 to 40.34 million tons in 2007; carbon emissions growth was mainly concentrated in the production and processing of energy resources, the mining of mineral resources, and the processing industry. (2) The analysis of the direct effects of the influencing factors on carbon emissions showed that the change in per capita GDP, the final demand structure, the population scale, and the production structure were the important factors causing an increase in carbon emissions, while the decrease in carbon emission intensity during this period was the important influencing factor in stopping the growth of carbon emissions. This showed that while the sizes of Xinjiang’s economy and population were growing, the economic structure had not been effectively optimized and the production technology had not been efficiently improved, resulting in a rapid growth of carbon emissions from energy consumption. (3) The analysis of the indirect effects of the influencing factors of carbon emission showed that the inter-provincial export, fixed capital formation, and the consumption by urban residents had significant influence on the changes in carbon emissions from energy consumption in Xinjiang. (4) The growth of investments in fixed assets of carbon intensive industry sectors, in addition to the growth of inter-provincial exports of energy resource products, makes the transfer effect of inter-provincial “embodied carbon” very significant.  相似文献   
93.
Based on the estimation of greenhouse gases (GHG) emissions and carbon sequestration of the total conversion of marshlands (TMC), marshlands conversion to paddy fields (MCPFs) and marshlands conversion to uplands (MCULs), this study revealed the contribution to the global warming mitigation (CGWM) of paddy fields versus uplands converted from marshlands in the Sanjiang Plain (excluding the Muling‐Xingkai Plain on south of Wanda Mountain), Heilongjiang Province, northeast China. The results showed that the total area of MCPFs and MCULs was 504.23 × 103 ha between 1982 and 2005. The CGWM per unit area was 45.53 t CO2eq/ha for MCPFs and that was 23.95 t CO2eq/ha for MCULs, with an obvious 47.40% reduction. The MCPFs and MCULs ecosystems acted as the carbon sink all of the year. As far as CGWM per unit area is concerned, MCPFs mitigated the greenhouse effect which was greater than MCULs. And it was effective that the implementation of the uplands transformed into paddy fields in Northeast China with regard to marshlands protection and croplands (including paddy fields and uplands) reclamation.  相似文献   
94.
Household consumption represents an important proportion of all energy consumption,and it is an important source of CO2 emission. But household consumption and carbon emissions are often overlooked in climate change policies and measures. Through literature review, the research status of household consumption and carbon emissions were reviewed. On this basis, the main aspects and directions of the research are summarized and the main research of household carbon emissions should focus on three aspects in the future: ①The impact of income, consumption levels and other factors on household carbon emission; ②The relationship between direct and indirect carbon emissions of household carbon emission; ③The structure and source of household carbon emission. In future research, there are four issues which need in-depth study: ①Index and models study of household carbon emissions;②Impact of demographic change on household carbon emissions; ③The path of how to achieve sustainable and green urban lifestyle;④The relevant policy research of household carbon emissions.  相似文献   
95.
This paper presents a field study conducted in northwest Turkey and characterizes the NH3 concentration and emission measured in summer season from three chicken farms. The influence of environmental conditions on NH3 concentration and emission was also investigated in this study. Ammonia concentration, temperature, relative humidity and airflow rate were continuously recorded for four sequential days. The environmental conditions were measured using a multifunction temperature and humidity‐meter with a hot wire probe. Portable multiple gas detectors with electro‐chemical sensors were used to measure NH3 concentration. The NH3 emission rates for houses were calculated by multiplying simultaneously measured NH3 concentrations and air flow rates. The average daily mean (ADM) house concentrations of house 1 (H1), house 2 (H2), and house 3 (H3) were measured as 4.43, 3.71, and 6.20 ppm, respectively. NH3 concentration was inversely proportional to temperature (r = ?0.279), relative humidity (r = ?0.063) and airflow rate (r = ?0.554) for all monitored houses. The ADM house NH3 emission was 135 g/(h house) for H1, 255 g/(h house) for H2, and 117 g/(h house) for H3. The combined average emission rate in this study (0.26 g/(d bird)) was lower than the emission rate measured in chicken farms in the USA. However, our results were comparable to rates calculated in European studies because house design, ventilation system and bird diet applied in Turkish chicken farms are very similar to those employed in European countries. The NH3 emissions were significantly correlated to NH3 concentrations (r = 0.45, p ≤ 0.001) and airflow rates (r = 0.97, p ≤ 0.001). A clear diurnal pattern was obtained for NH3 concentrations rather than NH3 emissions at the end of the study.  相似文献   
96.
Using the global chemistry and transport model MOZART,the simulated distributions of tropospheric hydroxyl free radicals(OH) over China and its sensitivities to global emissions of carbon monoxide(CO),nitrogen oxide(NO x),and methane(CH 4) were investigated in this study.Due to various distributions of OH sources and sinks,the concentrations of tropospheric OH in east China are much greater than in west China.The contribution of NO + perhydroxyl radical(HO 2) reaction to OH production in east China is more pronounced than that in west China,and because of the higher reaction activity of non-methane volatile organic compounds(NMVOCs),the contributions to OH loss by NMVOCs exceed those of CO and take the dominant position in summer.The results of the sensitivity runs show a significant increase of tropospheric OH in east China from 1990 to 2000,and the trend continues.The positive effect of double emissions of NO x on OH is partly offset by the contrary effect of increased CO and CH 4 emissions:the double emissions of NO x will cause an increase of OH of 18.1%-30.1%,while the increases of CO and CH 4 will cause a decrease of OH of 12.2%-20.8% and 0.3%-3.0%,respectively.In turn,the lifetimes of CH 4,CO,and NO x will increase by 0.3%-3.1% with regard to double emissions of CH 4,13.9%-26.3% to double emissions of CO and decrease by 15.3%-23.2% to double emissions of NO x.  相似文献   
97.
A coupled chemical/dynamical model (SOCOL-SOlar Climate Ozone Links) is applied to study the impacts of future enhanced CO and NOx emissions over eastern China on regional chemistry and climate. The result shows that the increase of CO and NOx emissions has significant effects on regional chemistry, including NOx, CO, O3, and OH concentrations. During winter, the CO concentration is uniformly increased in the northern hemisphere by about 10 ppbv. During summer, the increase of CO has a regional distribution. The change in O3, concentrations near eastern China has both strong seasonal and spatial variations. During winter, the surface O3, concentrations decrease by about 2 ppbv, while during summer they increase by about 2 ppbv in eastern China. The changes of CO, NOx, and O3, induce important impacts on OH concentrations. The changes in chemistry, especially O3, induce important effects on regional climate. The analysis suggests that during winter, the surface temperature decreases and air pressure increases in central-eastern China. The changes of temperature and pressure produce decreases in vertical velocity. We should mention that the model resolution is coarse, and the calculated concentrations are generally underestimated when they are compared to measured results. However, because this model is a coupled dynamical/chemical model, it can provide some useful insights regarding the climate impacts due to changes in air pollutant emissions.  相似文献   
98.
以科学发展观为指导,积极应对气候变化   总被引:1,自引:1,他引:0  
气候变化已经对全球生态、环境、经济和社会可持续发展以及外交和国家安全产生极大影响,引起各国政府、公众和学术界的极大关注。气候变化关系人类的生存和发展,应对气候变化实现可持续发展具有重要性和紧迫性。我们要以科学发展观为指导,把握好共同但有区别的责任,积极应对气候变化。  相似文献   
99.
种植不同作物对农田N2O和CH4排放的影响及其驱动因子   总被引:3,自引:0,他引:3  
以种植玉米(Zea mays)、大豆(Glycine max)和水稻(Oryza sativa)的农田生态系统为研究对象,于2003年6~10月系统观测了N2O和CH4的排放、土壤温度和湿度以及相关的生物学因子。玉米和水稻分别施化肥氮300 kg.hm-2,大豆未施氮肥。研究结果表明,作物类型对农田N2O和CH4排放具有显著的影响。土壤-玉米系统、土壤-大豆系统和土壤-水稻系统的N2O季节性平均排放通量分别为620.5±57.6、338.0±7.5和238.8±13.6μg.m-2.h-1(N2O)。种植作物促进了农田生态系统的N2O排放,玉米地土壤和裸地土壤的N2O平均排放通量分别为364.2±11.7和163.7±10.5μg.m-2.h-1(N2O)。土壤-玉米系统、土壤-水稻系统、玉米地土壤和裸地土壤N2O排放受土壤温度的影响,与土壤湿度无显著统计相关,但受土壤温度和水分的综合影响。土壤-大豆系统N2O排放随作物绿叶干重的增加而指数增加,与土壤温度和水分条件无统计相关,由大豆作物自身氮代谢所产生的N2O-N季节总量约为6.2 kg.hm-2(N)。土壤-水稻系统CH4平均排放通量为1.7±0.1 mg.m-2.h-1(CH4),烤田抑制了稻田CH4的排放。烤田前影响稻田CH4排放的主要因素是水稻生物量,烤田后的浅水灌溉及湿润灌溉阶段的CH4排放与土壤温度和水稻生物量无关。本研究未观测到旱作农田有吸收CH4的现象。  相似文献   
100.
基于最新的GTAP8 (Global Trade Analysis Project)数据库,使用投入产出法,分析了2004年到2007年全球贸易变化下南北集团贸易隐含碳变化及对全球碳排放的影响。结果显示,随着发展中国家进出口规模扩张,全球贸易隐含碳流向的重心逐渐向发展中国家转移。2004年到2007年,发达国家高端设备制造业和服务业出口以及发展中国家资源、能源密集型行业及中低端制造业出口的趋势加强,该过程的生产转移导致全球碳排放增长4.15亿t,占研究时段全球贸易隐含碳增量的63%。未来发展中国家的出口隐含碳比重还将进一步提高。贸易变化带来的南北集团隐含碳流动变化对全球应对气候变化行动的影响日益突出,发达国家对此负有重要责任。  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