收费全文 | 89236篇 |
免费 | 1267篇 |
国内免费 | 1660篇 |
安全科学 | 3810篇 |
废物处理 | 3244篇 |
环保管理 | 13724篇 |
综合类 | 21800篇 |
基础理论 | 26095篇 |
环境理论 | 71篇 |
污染及防治 | 13991篇 |
评价与监测 | 5336篇 |
社会与环境 | 3519篇 |
灾害及防治 | 573篇 |
2022年 | 850篇 |
2021年 | 838篇 |
2020年 | 678篇 |
2019年 | 882篇 |
2018年 | 1130篇 |
2017年 | 1179篇 |
2016年 | 2184篇 |
2015年 | 1867篇 |
2014年 | 2678篇 |
2013年 | 9368篇 |
2012年 | 2207篇 |
2011年 | 2340篇 |
2010年 | 3303篇 |
2009年 | 3432篇 |
2008年 | 1876篇 |
2007年 | 1686篇 |
2006年 | 2162篇 |
2005年 | 2196篇 |
2004年 | 2440篇 |
2003年 | 2321篇 |
2002年 | 1860篇 |
2001年 | 2157篇 |
2000年 | 1943篇 |
1999年 | 1520篇 |
1998年 | 1403篇 |
1997年 | 1382篇 |
1996年 | 1505篇 |
1995年 | 1603篇 |
1994年 | 1472篇 |
1993年 | 1330篇 |
1992年 | 1324篇 |
1991年 | 1282篇 |
1990年 | 1232篇 |
1989年 | 1205篇 |
1988年 | 1038篇 |
1987年 | 968篇 |
1986年 | 987篇 |
1985年 | 1058篇 |
1984年 | 1147篇 |
1983年 | 1161篇 |
1982年 | 1172篇 |
1981年 | 1090篇 |
1980年 | 936篇 |
1979年 | 913篇 |
1978年 | 815篇 |
1977年 | 711篇 |
1976年 | 636篇 |
1975年 | 603篇 |
1973年 | 624篇 |
1972年 | 629篇 |
Both China’s national subsidy policies for plug-in electric vehicles (PEVs) purchasers and passenger cars corporate average fuel consumption and new vehicle credit regulation (dual-credit policy) favor long-range 300+ km battery electric vehicles (BEVs) and 80+ km plug-in hybrid electric vehicles (PHEVs). However, these electric vehicles tend to have lower energy efficiency and higher purchase and operation costs. Vehicle with larger batteries can also be less equitable because the subsidies are often provided to more expensive vehicles and wealthier owners. This study takes advantage of a novel dataset of daily driving data from 39,854 conventional gasoline vehicles in Beijing and 4999 PHEVs in Shanghai to determine the optimal range of BEVs and PHEVs within their respective cities. We simulate a model to explore ranges with which PEVs emit less GHGs than that of a baseline hybrid and conventional gasoline vehicle while ensuring that all daily travel demands are met. Our findings indicate that in both cities, the optimal ranges to balance cost and travel demand for BEVs are 350 km or less and for PHEVs are 60 km or less in Beijing and 80 km or less in Shanghai. We also find that to minimize carbon dioxide (CO2) emissions, the ranges are even lower 10 km in Beijing and 30 km in Shanghai. Our study suggests that instead of encouraging long-range PEVs, governments should subsidize PEV models with shorter ranges. Parallel efforts should also be made to both increase renewable energy over fossil fuels and expand charging facilities. Although individual mobility demand varies, the government could reduce occasional long-distance driving by subsidizing alternative transportation choices. Providing week-long driving trials to consumers before their purchases may help decrease the demand of very long range PEVs by alleviating the range anxiety through a learning process.
相似文献The combination of concentrated solar power–chemical looping air separation (CSP-CLAS) with an oxy-fuel combustion process for carbon dioxide (CO2) capture is a novel system to generate electricity from solar power and biomass while being able to store solar power efficiently. In this study, the computer program Advanced System for Process Engineering Plus (ASPEN Plus) was used to develop models to assess the process performance of such a process with manganese (Mn)-based oxygen carriers on alumina (Al2O3) support for a location in the region of Seville in Spain, using real solar beam irradiance and electricity demand data. It was shown that the utilisation of olive tree prunings (Olea europaea) as the fuel—an agricultural residue produced locally—results in negative CO2 emissions (a net removal of CO2 from the atmosphere). Furthermore, it was found that the process with an annual average electricity output of 18 MW would utilise 2.43% of Andalusia’s olive tree prunings, thereby capturing 260.5 k-tonnes of CO2, annually. Drawbacks of the system are its relatively high complexity, a significant energy penalty in the CLAS process associated with the steam requirements for the loop-seal fluidisation, and the gas storage requirements. Nevertheless, the utilisation of agricultural residues is highly promising, and given the large quantities produced globally (~?4 billion tonnes/year), it is suggested that other novel processes tailored to these fuels should be investigated, under consideration of a future price on CO2 emissions, integration potential with a likely electricity grid system, and based on the local conditions and real data.
相似文献This study explored the national hydrogen refueling infrastructure requirement along major United States (US) interstate highway corridors to support the deployment of fuel cell electric trucks (FCETs) for the national long-haul trucking fleet. Given the long-haul trucking shipment demand in 2025 projected by the Freight Analysis Framework, locations and capacities of hydrogen stations were identified for inter-zone freight flows, and the total daily refueling demand was estimated for intra-zone flows for each FAF zone. Based on the infrastructure deployment results, we conducted an economic feasibility analysis of FCETs by evaluating the total ownership cost. We found that when the FCET penetration is relatively high (e.g., 10% penetration), FCETs become more competitive in terms of fuel cost and idling cost and could be economic viable if the incremental vehicle cost is reduced to meet the near-term FCET technology cost targets and the liquefaction cost is reduced to an optimal case. We also observed that the station cost depends on regional factors, particularly regional demand, which is used to determine station capacity. Thus, one possible strategy for station roll-out is to have early investment in target regions where station costs are expected to be relatively low such as the Pacific and West South Central regions.
相似文献