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   17545篇
  免费   218篇
  国内免费   140篇
安全科学   515篇
废物处理   662篇
环保管理   2367篇
综合类   3272篇
基础理论   4296篇
环境理论   13篇
污染及防治   4473篇
评价与监测   1120篇
社会与环境   1054篇
灾害及防治   131篇
  2022年   164篇
  2021年   174篇
  2020年   131篇
  2019年   159篇
  2018年   227篇
  2017年   281篇
  2016年   399篇
  2015年   341篇
  2014年   467篇
  2013年   1513篇
  2012年   584篇
  2011年   737篇
  2010年   581篇
  2009年   642篇
  2008年   734篇
  2007年   740篇
  2006年   713篇
  2005年   561篇
  2004年   539篇
  2003年   544篇
  2002年   492篇
  2001年   572篇
  2000年   436篇
  1999年   260篇
  1998年   210篇
  1997年   203篇
  1996年   219篇
  1995年   231篇
  1994年   222篇
  1993年   214篇
  1992年   222篇
  1991年   209篇
  1990年   208篇
  1989年   177篇
  1988年   153篇
  1987年   133篇
  1986年   159篇
  1985年   162篇
  1984年   164篇
  1983年   165篇
  1982年   159篇
  1981年   163篇
  1980年   151篇
  1979年   145篇
  1978年   109篇
  1977年   123篇
  1974年   109篇
  1973年   92篇
  1972年   107篇
  1971年   88篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
Heat and mechanical protection properties of 6 fabric combinations commonly used in firefighters’ protective clothing were assessed before and after different heat treatment. It was shown that after heat exposure, the values obtained were generally lower than in the original state. The mechanical properties of the materials were more affected by heat than by heat protective properties. In 2 cases, degradation started before a visible change in the material could be observed, which might be potentially dangerous for the end user who will not realize the alteration of the material.  相似文献   
112.
Quantifying the risk of accidental ignition of flammable mixtures is extremely important in industry and aviation safety. The concept of a minimum ignition energy (MIE), obtained using a capacitive spark discharge ignition source, has traditionally formed the basis for determining the hazard posed by fuels. While extensive tabulations of historical MIE data exist, there has been little work done on ignition of realistic industrial and aviation fuels, such as gasoline or kerosene. In the current work, spark ignition tests are performed in a gaseous kerosene–air mixture with a liquid fuel temperature of 60 °C and a fixed spark gap of 3.3 mm. The required ignition energy was examined, and a range of spark energies over which there is a probability of ignition is identified and compared with previous test results in Jet A (aviation kerosene). The kerosene results are also compared with ignition test results obtained in previous work for traditional hydrogen-based surrogate mixtures used in safety testing as well as two hexane–air mixtures. Additionally, the statistical nature of spark ignition is discussed.  相似文献   
113.
Natech accidents at industrial plants are an emerging risk with possibly serious consequences. For the mitigation of natech risk, authorities need to identify natech prone areas in a systematic manner. In order to facilitate probabilistic natech risk mapping, a unified methodology was developed that is based on the estimation of on-site natural hazard parameters, determination of damage probabilities of plant units, and assessment of probability and severity of possibly triggered natech events. The methodology was implemented as an on-line, extensible risk assessment and mapping software framework called RAPID-N, which allows rapid local and regional natech risk assessment and mapping with minimal data input. RAPID-N features an innovative data estimation framework to complete missing input data, such as on-site natural hazard parameters and plant unit characteristics. The framework is also used for damage assessment and natech consequence analysis, and allows easy modification of input parameters, dynamic generation of consequence models according to data availability, and extension of models by adding new equations or substituting existing ones with alternatives. Results are presented as summary reports and interactive risk maps, which can be used for land-use and emergency planning purposes by using scenario hazards, or for rapid natech consequence assessment following actual disasters. As proof of concept, the framework provides a custom implementation of the U.S. EPA's RMP Guidance for Offsite Consequence Analysis methodology to perform natech consequence analysis and includes comprehensive data for earthquakes. It is readily extendible to other natural hazards and more comprehensive risk assessment methods.  相似文献   
114.
115.
Plastic was tested to select biofilm support media that would enhance nitrification in the presence of heterotrophs. Eight different types (acrylonitrile butadiene styrene, nylon, polycarbonate, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinyl chloride and tufnol) were immersed in an aerobic fed-batch reactor receiving domestic settled wastewater. Nitrification rates did not correlate with biomass concentrations, nor surface roughness of the plastics as measured by atomic force microscopy (AFM). The maximum nitrification rate of 1.5 g/m2 d?1 was obtained from biofilms growing on PTFE which had the lowest surface adhesion force (8 nN). Nitrification rates for the biofilms were inversely correlated with the attraction forces as measured by AFM.  相似文献   
116.
闽江河口潮汐沼泽湿地CO_2排放通量特征   总被引:6,自引:7,他引:6  
以闽江河口区面积最大的鳝鱼滩湿地分布的3种植物沼泽湿地:土著种咸草(Cyperus malaccensis Lam.var.brevifolius Bocklr.)沼泽湿地、芦苇(Phragmites australis)沼泽湿地及外来入侵种互花米草(Spartina alterniflora Loisel.)沼泽湿地...  相似文献   
117.
Among the difficulties found in the implementation of ISO 14001 systems, resistance to change can always be found. It is mainly a consequence of the hurry to change, loss of focus, concentration of decision making at the level of top management, arbitrary imposition of objectives and results, faulty communication, and the absence of motivational and financial incentive for change.Therefore, the main objective of this paper is to present best practices with respect to the management of organizational change due to the implementation of ISO 14001 norms in two industrial companies in the Midwest region of the State of São Paulo – Brazil.  相似文献   
118.
Carotenoids may provide numerous health benefits and are also responsible for the integumentary coloration of many bird species. Despite their importance, many aspects of their metabolism are still poorly known, and even basic issues such as the anatomical sites of conversion remain controversial. Recent studies suggest that the transformation of carotenoid pigments takes place directly in the follicles during feather growth, even though the liver has been previously recognised as a storing organ for these pigments with a certain potential for conversion. In this context, we analysed the carotenoid profile of plasma, liver, skin and feathers of male Common Crossbills (Loxia curvirostra). Interestingly, the derivative feather pigment 3-hydroxy-echinenone was detected in the liver and in the bloodstream (i.e. the necessary vehicle to transport metabolites to colourful peripheral tissues). Our results demonstrate for the first time with empirical data that the liver may act as the main site for the synthesis of integumentary carotenoids. This finding contradicts previous assumptions and raises the question of possible inter-specific differences in the site of carotenoid conversion in birds.  相似文献   
119.
在活动流场模型的基础上建立了新的溶质运移控制方程,研究了流场分形特征参数的计算方法;采用4组染色示踪试验资料,分析了活动流场模型模拟土壤水流运动和溶质运移宏观非均匀特征的适用性.模拟分析表明,活动流场模型能较准确地捕捉到土壤中的优先流特别是不稳定流的宏观运动特征;土壤存在大孔隙结构的情况下,水流和溶质将更快的迁移到深层土壤,活动流场模型模拟计算的入渗深度偏小,但大于连续性模型的模拟计算结果;当土壤中的大孔隙结构较少时,活动流场模型模拟预测的土壤含水率分布和溶质浓度分布与实测结果比较一致.  相似文献   
120.
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