全文获取类型
收费全文 | 33197篇 |
免费 | 5389篇 |
国内免费 | 30402篇 |
专业分类
安全科学 | 3087篇 |
废物处理 | 1631篇 |
环保管理 | 2785篇 |
综合类 | 40290篇 |
基础理论 | 5716篇 |
环境理论 | 4篇 |
污染及防治 | 10724篇 |
评价与监测 | 2301篇 |
社会与环境 | 1111篇 |
灾害及防治 | 1339篇 |
出版年
2024年 | 59篇 |
2023年 | 452篇 |
2022年 | 1276篇 |
2021年 | 1131篇 |
2020年 | 1582篇 |
2019年 | 2581篇 |
2018年 | 2861篇 |
2017年 | 3066篇 |
2016年 | 2811篇 |
2015年 | 3353篇 |
2014年 | 4099篇 |
2013年 | 4966篇 |
2012年 | 4406篇 |
2011年 | 4146篇 |
2010年 | 3543篇 |
2009年 | 3546篇 |
2008年 | 3342篇 |
2007年 | 3173篇 |
2006年 | 2614篇 |
2005年 | 1906篇 |
2004年 | 1562篇 |
2003年 | 1398篇 |
2002年 | 1219篇 |
2001年 | 1140篇 |
2000年 | 1278篇 |
1999年 | 1209篇 |
1998年 | 957篇 |
1997年 | 868篇 |
1996年 | 845篇 |
1995年 | 720篇 |
1994年 | 558篇 |
1993年 | 438篇 |
1992年 | 422篇 |
1991年 | 340篇 |
1990年 | 271篇 |
1989年 | 230篇 |
1988年 | 164篇 |
1987年 | 89篇 |
1986年 | 77篇 |
1985年 | 56篇 |
1984年 | 57篇 |
1983年 | 46篇 |
1982年 | 47篇 |
1981年 | 38篇 |
1978年 | 8篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1972年 | 8篇 |
1971年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Chengyuan Gong Yi Yu Kaiqiang Wang Zhengkai Tu 《International Journal of Green Energy》2020,17(10):591-601
ABSTRACT In this study, a three-dimension (3D) computational model was proposed to investigate the flow and heat transfer characteristics of the intake grilles of two different fuel cell vehicles. The models of the intake grilles were constructed according to the actual sizes of two vehicles, namely, Roewe 950 and Toyota Mirai, considering the heat dissipation unit to simplify the heat transfer model of the vehicle. The results showed that relative to Roewe 950, Mirai intake air flow rate was approximately 10% higher, the heat transfer capacity was approximately 7% higher, and the intake grille area was larger. The coolant outlet temperature of Mirai was lower than that of Roewe 950, which was beneficial for the long term and stable operation of a fuel cell. This comparative study provided guidance for the intake grille and radiator design of fuel cell vehicles. The only difference between fuel cell vehicles on the market and conventional vehicles was that in the former, the internal combustion engine was replaced with a fuel cell stack, which had insufficient heat transfer capacity because of the reducing temperature difference. Increasing the intake grille area and the heat exchange capacity of the radiator were the key issues for the development of fuel cell vehicles. In this study, an optimal window opening angle of the radiator fin of 23° provided a maximal heat transfer coefficient. 相似文献
12.
Tang Zhi Li Yilian Yang Zhe Liu Danqing Tang Min Yang Sen Tang Ye 《Environmental science and pollution research international》2019,26(20):20277-20285
Environmental Science and Pollution Research - The sorption/desorption behaviors of benzene, toluene, ethylbenzene, and xylene (BTEX) on soil organic matter (SOM) have a significant influence on... 相似文献
13.
Luo Xiaofang Dessie Wubliker Wang Meifeng Duns Gregory J. Rong Nianhang Feng Luya Zeng Jianqing Qin Zuodong Tan Yimin 《Journal of Material Cycles and Waste Management》2021,23(2):548-556
Journal of Material Cycles and Waste Management - The traditional Chinese medicinal plant Magnolia officinalis has a wide range of applications; including more than 200 kinds of patented Chinese... 相似文献
14.
15.
16.
此文提出了内螺纹变截面铜管分段拉仲一次成形新工艺,并就工艺因素对该管拉伸成形的影响进行了试验研究,从而为合理制订成形工艺提供了依据。 相似文献
17.
王新茹 《防灾科技学院学报》2007,9(1):111-113
布鲁纳在20世纪60年代以结构主义理论为基础领导了美国的课程改革运动.虽然此次课程改革以失败而告终,但是发现式学习方法及其教学方法的提出却受到了广泛的关注.布鲁纳也曾就发现式学习进行了专门的论述.本文从发现式学习法的特点、作用出发来探求我国目前正在进行的第八轮新课程改革,试图为我国新课程改革中学习、教学方法的改革提供一个新的视角. 相似文献
18.
Wang Degang Huang Xiaoting 《中国人口.资源与环境(英文版)》2006,4(1):45-53
At present, internal rural tourism is at the stage of upgrading and renewing, and ecotourism has been considered to be the main direction. This paper discussed the concepts and criteria of rural tourism and ecotourism, analyzed a typical case of Nongke Village of Chengdu City-being considered to be the first rural tourism site in China, went deep into the problems of the contents and criteria of the development of rural ecotourism, and tried to probe into the principles of the development of rural ecotourism both theoretically and practically so as to understand the rules of the development of rural ecotourism . 相似文献
19.
本文从柑桔冻害和热害的危害因子和指标等级划分的研究和选取入手,着重探讨了长江三峡地区(湖北境内)两害显著的时空变化特征、差异与关联性及对柑桔生产的影响;揭示了80年代以来冬暖春热的重大气候变化是使两害向“两极分化”的根本原因;讨论了三峡水利工程对两害时空格局的可能调整及减灾原理;最后提出了可能的对策。 相似文献
20.
Processes involved in uptake and release of nitrogen dioxide from soil and building stones into the atmosphere 总被引:1,自引:0,他引:1
Atmospheric NO2 was taken up by samples of various soils and building stones. The NO2 uptake rate constants were highest in soil samples taken during the summer months. However, the NO2 uptake rate constants of the soils and building stones were not significantly correlated with any of the following variables: moisture, pH, ammonium, nitrite, or nitrate. NO2 uptake by soil and stone was not abolished by autoclaving indicating a chemical uptake process. NO2 uptake by acidic and air-dry soils and stones resulted in nearly stoichiometric reduction of NO2 to NO. This reduction was enhanced by the addition of ferrous iron and was further enhanced by incubation under 1 ppmv SO2. The results suggest that NO2 reduction may be coupled to oxidation of ferrous to ferric iron which may be reduced again by atmospheric SO2 thus regenerating the ferrous iron content of the soil or stone. Conversion of NO2 to NO was not observed in neutral or/and moist soils and stones. NO2 was also taken up by purified and sterilized quartz sand moistend with water. This uptake was enhanced by addition of humic material but not by addition of bacteria which both had been extracted from genuine soil. Under most conditions, only uptake but no release of NO2 was observed. However, NO2 was released in air-dry soils that were heated to 45–65°C, or in ammonium-fertilized soil or stone that was drying up at room temperature. Under the latter conditions mimicking field practice, the NO2 release reached rates that were similar to the NO release rates. 相似文献