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   772篇
  免费   147篇
  国内免费   123篇
安全科学   102篇
废物处理   26篇
环保管理   131篇
综合类   408篇
基础理论   122篇
污染及防治   122篇
评价与监测   15篇
社会与环境   98篇
灾害及防治   18篇
  2024年   2篇
  2023年   21篇
  2022年   43篇
  2021年   30篇
  2020年   38篇
  2019年   31篇
  2018年   27篇
  2017年   59篇
  2016年   41篇
  2015年   42篇
  2014年   34篇
  2013年   72篇
  2012年   57篇
  2011年   53篇
  2010年   46篇
  2009年   53篇
  2008年   46篇
  2007年   50篇
  2006年   57篇
  2005年   42篇
  2004年   26篇
  2003年   31篇
  2002年   19篇
  2001年   21篇
  2000年   16篇
  1999年   13篇
  1998年   9篇
  1997年   14篇
  1996年   6篇
  1995年   4篇
  1994年   1篇
  1993年   4篇
  1991年   4篇
  1990年   1篇
  1989年   3篇
  1988年   4篇
  1987年   1篇
  1985年   1篇
  1984年   1篇
  1983年   1篇
  1982年   1篇
  1981年   3篇
  1979年   1篇
  1978年   3篇
  1977年   2篇
  1976年   1篇
  1975年   1篇
  1974年   2篇
  1973年   1篇
  1971年   3篇
排序方式: 共有1042条查询结果,搜索用时 15 毫秒
1.
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   
2.
低温液氮与泡沫混合液直接接触产生氮气泡沫是一种新型的掺混形式,利用液氮高汽化比的特点,搭建液氮泡沫可视化实验装置,进行氮气-水两相流及液氮泡沫流动特性的研究。结果表明,液氮相变产生大量氮气,其与泡沫液混合产生泡沫,温度有所回升,最终趋于泡沫混合液温度;管路沿程压降较小;液氮射流破碎及流动过程可分为6个区域:低温液氮区、向上循环翻滚区、滞留区、泡沫与泡沫混合液混合区、致密泡沫区、泡沫混合液区。流体向下游流动过程中持续发泡;为防止管路结冰,需合理控制泡沫混合液与液氮流量。  相似文献   
3.
Drawing from signaling theory, we propose a work passion transfer model where leaders' passion is transmitted to employees through the former's leadership style and is contingent on employees' perceived importance of performance to self-esteem (IPSE). Data from 201 supervisor–employee dyads from the health-care industry show that leaders' harmonious passion led to employees' harmonious passion through charismatic leadership, whereas contingent reward leadership accounted for the transfer of obsessive passion; IPSE did not play a moderating role for either form of passion. Results from a supplementary study further reveal that the link between leadership and employee passion operated through employees' perception of leader passion and that employees' IPSE accentuated for the relationship between perceived leader obsessive passion and employees' obsessive passion. This study advances research in work passion, leadership, and signaling theory and provides important implications for managerial practice.  相似文献   
4.
为研究松散煤体低温氧化及通风供氧下的渗流传热规律,研发了渗流传热试验装置。试验装置由气体加湿系统、气体加热系统、煤样反应系统、数据采集系统和安全保护系统组成;本装置可实现自动加湿、控温、自动采集数据及处理数据。为解决装置使用和运行中的安全问题,设计了断电保护、有害气体检测等措施,保障试验装置的安全、可靠。  相似文献   
5.
• Fe(III) accepted the most electrons from organics, followed by NO3, SO42‒, and O2. • The electrons accepted by SO42‒ could be stored in the solid AVS, FeS2-S, and S0. • The autotrophic denitrification driven by solid S had two-phase characteristics. • A conceptual model involving electron acceptance, storage, and donation was built. • S cycle transferred electrons between organics and NO3 with an efficiency of 15%. A constructed wetland microcosm was employed to investigate the sulfur cycle-mediated electron transfer between carbon and nitrate. Sulfate accepted electrons from organics at the average rate of 0.84 mol/(m3·d) through sulfate reduction, which accounted for 20.0% of the electron input rate. The remainder of the electrons derived from organics were accepted by dissolved oxygen (2.6%), nitrate (26.8%), and iron(III) (39.9%). The sulfide produced from sulfate reduction was transformed into acid-volatile sulfide, pyrite, and elemental sulfur, which were deposited in the substratum, storing electrons in the microcosm at the average rate of 0.52 mol/(m3·d). In the presence of nitrate, the acid-volatile and elemental sulfur were oxidized to sulfate, donating electrons at the average rate of 0.14 mol/(m3·d) and driving autotrophic denitrification at the average rate of 0.30 g N/(m3·d). The overall electron transfer efficiency of the sulfur cycle for autotrophic denitrification was 15.3%. A mass balance assessment indicated that approximately 50% of the input sulfur was discharged from the microcosm, and the remainder was removed through deposition (49%) and plant uptake (1%). Dominant sulfate-reducing (i.e., Desulfovirga, Desulforhopalus, Desulfatitalea, and Desulfatirhabdium) and sulfur-oxidizing bacteria (i.e., Thiohalobacter, Thiobacillus, Sulfuritalea, and Sulfurisoma), which jointly fulfilled a sustainable sulfur cycle, were identified. These results improved understanding of electron transfers among carbon, nitrogen, and sulfur cycles in constructed wetlands, and are of engineering significance.  相似文献   
6.
为研究地铁网络化运营枢纽车站火灾烟气扩散特征和防排烟技术,根据工程资料和标准规范对典型多线换乘车站进行1∶10火灾实验模型设计,并依据设计方案完成车站模型主体结构和通风排烟系统的搭建,同时在各个防烟分区设计安装温度、流速、烟气浓度和热辐射测量装置,可实现对“T”形、“十”形和“L”形换乘等不同换乘形式车站的火灾场景模拟和危险参数测量。研究结果表明:该模型装置能够开展一系列针对不同换乘形式和通风模式的火灾实验,对于全面揭示大型换乘车站火灾烟气运动规律、验证并优化火灾防排烟设计方法、支撑复杂结构枢纽车站火灾烟气控制技术具有重要意义。  相似文献   
7.
Modern work is frequently characterized by jobs where adaptive performance (AP) is crucial for employees to succeed in light of new or altered task demands. This recognition has fueled growing interest in AP as a dimension of workplace performance. To this point, however, research on AP has evolved from disparate perspectives and methods, resulting in fragmentation and a less than coherent knowledge base. This paper presents a comprehensive review of research studies regarding the nomological network of individual AP. In doing so, we synthesize the current knowledge base surrounding correlates of AP, elucidate current ambiguities, and suggest directions for future research efforts. We conclude that although the extant AP literature has amassed a critical body of studies linking various predictors to successful AP outcomes, much remains unknown, most critically regarding the implications of different methods of assessing AP, the effects of different types of changes in the task environment, the process of AP, and the steps organizations can take to foster AP among their employees. We hope that our synthesis and analysis paves the way for efforts to address these important questions. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   
8.
为适时、有效地控制炼化过程系统风险,以模糊Petri网(FPN)为基础,针对炼化系统动态退化性和系统中保护层对风险转移的干预性,建立考虑保护层响应的炼化过程系统风险动态转移模型。描述基于FPN的保护层作用动态机制,分析炼化系统在保护层干预下,从非正常干扰触发开始至炼化系统退化过程的风险变化趋势。最后通过正己烷缓冲罐案例分析验证模型。结果表明:正己烷缓冲罐在开始运行的30 000 h内,系统风险等级呈阶段性变化,在工作的前16 800 h,风险为Ⅰ级;第16 800~27 600 h,风险为Ⅱ级;第27 600~30 000 h,风险为Ⅲ级。  相似文献   
9.
变更平衡表为国土资源管理部门历年实地调查、汇总所得,精度高,目前的研究中对其深入的应用较少,基于变更平衡表的应用方法研究可为区域土地利用演变信息提取与预测提供帮助。推导了由连续年份的年度变更平衡表求多年周期的平衡表的方法,提出了基于土地利用综合动态度分析土地利用有序程度的思路,探讨了利用连续年份的变更平衡表预测任意年份土地利用结构的方法,并基于传统方法进行了改进,提出了利用矩阵开方法求预测概率矩阵。应用苏州市一定时期的连续年份的年度变更平衡表对上述方法进行了验证,结果表明:提出的信息提取方法有效,预测结果可信;在分析期内(1998~2008年),苏州市耕地大量减少的去向是各类建设用地增加的来源,区域土地利用有序程度较高;预测显示至2020年土地利用结构变化仍将维持农用地、耕地不断减少和建设用地总量不断增加的趋势,但转化的速率将有所放缓;对变更平衡表的深入应用有一定的借鉴意义。  相似文献   
10.
长江源多年冻土区土壤水热传输过程机理与模拟,是广泛关系到高原生态环境保护恢复和区域水文过程的关键科学问题。因此,以GEOtop模型为研究平台,以长江源不同植被盖度下(裸地、30%、65%和92%)高寒草甸的观测数据为基础,检验模型对土壤水热迁移过程的描述与模拟精度。总体而言,GEOtop模型需要率定的参数较少,从而减少模型模拟的不确定性,提高了模拟精度。对不同植被盖度下土壤温度、水分和实际蒸散发模拟的NSE 系数基本达到08,表明模型能准确模拟高寒生态系统土壤的水热传输过程,可以作为长江源区土壤水热过程的有效模拟工具  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