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   27329篇
  免费   6239篇
  国内免费   780篇
安全科学   2907篇
废物处理   405篇
环保管理   5938篇
综合类   15089篇
基础理论   2874篇
环境理论   12篇
污染及防治   1942篇
评价与监测   1928篇
社会与环境   2083篇
灾害及防治   1170篇
  2023年   338篇
  2022年   587篇
  2021年   706篇
  2020年   776篇
  2019年   614篇
  2018年   568篇
  2017年   847篇
  2016年   981篇
  2015年   1150篇
  2014年   1212篇
  2013年   1684篇
  2012年   1949篇
  2011年   2137篇
  2010年   1537篇
  2009年   1569篇
  2008年   1240篇
  2007年   1931篇
  2006年   1903篇
  2005年   1512篇
  2004年   1289篇
  2003年   1391篇
  2002年   1145篇
  2001年   958篇
  2000年   900篇
  1999年   840篇
  1998年   617篇
  1997年   528篇
  1996年   456篇
  1995年   415篇
  1994年   390篇
  1993年   339篇
  1992年   254篇
  1991年   198篇
  1990年   146篇
  1989年   122篇
  1988年   107篇
  1987年   83篇
  1986年   57篇
  1985年   59篇
  1984年   60篇
  1983年   71篇
  1982年   66篇
  1981年   79篇
  1980年   84篇
  1979年   78篇
  1978年   53篇
  1977年   51篇
  1973年   46篇
  1972年   40篇
  1971年   61篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
This paper presents a computer simulation of reflected and scattered laser radiation for calculating the angle of laser shields performed with the Laser Shield Solver computer program. The authors describe a method of calculating the shield angle for laser shields which protect workers against reflected and scattered laser radiation and which are made from different materials. The main assumptions of the program, which calculates and simulates reflected laser radiation from any material and which can be used for designing shield angles, are presented. Calculations are compared with measurements of reflected laser radiation. The results for one type of laser and different materials which interacted with a laser beam showed that the Laser Shield Solver was an appropriate tool for designing laser shields and its simulations of reflected laser radiation distribution have practical use.  相似文献   
2.
The study aimed to find out the influence of sweating on footwear insulation with a thermal foot model. Simultaneously, the influence of applied weight (35 kg), sock, and steel toe cap were studied. Water to 3 sweat glands was supplied with a pump at the rate of 10 g/hr in total. Four models of boots with steel toe caps were tested. The same models were manufactured also without steel toe. Sweating reduced footwear insulation 19–25% (30–37% in toes). During static conditions, only a minimal amount of sweat evaporated from boots. Weight affected sole insulation: Reduction depended on compressibility of sole material. The influence of steel toe varied with insulation. The method of thermal foot model appears to be a practical tool for footwear evaluation.  相似文献   
3.
《Environmental Forensics》2013,14(3-4):219-225
Naturally weathered oil residues from an arid dumpsite in Al-Alamein, Egypt were analyzed for monoaromatic and triaromatic steranes to demonstrate the utility of biomarker compounds in assessing the chemical composition changes during the degradation of the released oil residues in a terrestrial environment. The characterizations of individual aromatic compounds were based on gas chromatography/mass spectrometry (GC/MS) analyses. The results showed that triaromatic sterane distributions were similar in the oil residues of varying weathering degradation extents and correlated with a fresh crude oil sample of the Western Desert-sourced oil. Molecular ratios of triaromatic sterane compounds (ratios of C 28 20R /C 28 20S , C 27 20R /C 28 20R , and C 28 20S /[C 26 20R + C 27 20S ]) were proved to be suitable for source identification. Major changes in chemical compositions during weathering of the oil residues were the depletion of short chain mono- and tri-aromatic steranes in samples that had undergone extensive degradation. The results of triaromatic sterane distribution are in good agreement with weathering classification based on the analyses of saturate and aromatic hydrocarbons and the ratios of n -alkanes, PAHs and saturate biomarker compounds.  相似文献   
4.
《Environmental Forensics》2013,14(3-4):331-340
Prince William Sound (PWS), Alaska has an extensive history of human and industrial activity that has produced a complex organic geochemistry record in subtidal sediments of embayments throughout the sound. In addition to contributions from recent oil spills and a regional background of natural petroleum hydrocarbons originating from active hydrocarbon systems in the northern Gulf of Alaska (GOA), pyrogenic and petrogenic PAH were, and continue to be introduced to subtidal sediments at numerous sites of past and present human activities. These sites include villages, fish hatcheries, fish camps and recreational campsites in addition to abandoned settlements, canneries, sawmills, and mines. A holistic approach is used to fingerprint and quantify hydrocarbon contributions from multiple sources in a sediment sample. It involves acquiring a comprehensive understanding of the history of the area to identify potential sources, collection of representative samples, and accurate quantitative analyses of the source and sediment samples for a suite of diagnostic PAH analytes and chemical biomarker compounds. Unlike the deepwater sediments of the sound and GOA, the TOC tool, described elsewhere, does not work as well in some restricted embayments due to their high contents of recent organic matter (ROM). The current study employs a constrained least-squares algorithm to allocate hydrocarbon sources contributing to subtidal sediments collected from PWS embayments in 1991, 1999 and 2000. Results show that sources contributing to the natural petrogenic background are present in the embayments, pyrogenic hydrocarbons including combustion products of diesel are important where human activity was high, and petroleum produced from the Monterey Formation (CA) is present locally. Oil and asphalt shipped from California were widely used for fuel and construction prior to development of the Cook Inlet and North Slope fields. In certain locations that were oiled in 1989, low levels of highly degraded Alaska North Slope crude oil residues attributable to the Exxon Valdez spill remain.  相似文献   
5.
Participatory irrigation management (PIM) was adopted in Thailand in 2004 to encourage the sustainable use of water in the agricultural sector. The research presented in this paper sought to understand the relationships between public participation, learning, and the implementation of more sustainable water practices through PIM in Thailand. Data was collected through document reviews, observation, informal meetings, and a total of 55 semi‐structured face‐to‐face interviews of local irrigators from two case study regions around the Krasiew Reservoir. Results showed that participating in PIM activities facilitated both instrumental (e.g., water supply and demand data, benefits of on‐time water delivery) and communicative (e.g., reasons for past PIM failure, expectations of fellow farmers) learning among PIM participants. Findings also revealed that social action is fostered through the recognition of human dignity and compassionate communication that instils a sense of ownership and solidarity among irrigators. Sustainable water practices among local farmers were spurred further through learning that the reservoir is a finite water source.  相似文献   
6.
长庆油田学一联合站油田采出水经三级处理后,出水水质达到低渗透、特低渗透油田回注指标,但不久水质变浑浊,并伴有大量的红棕色沉淀物生成。取样分析,红棕色沉淀物为氢氧化铁,水中pH值为6.0~6.5,铁含量在50~100mg/L。文章针对含铁量过高为主的高矿化度油田采出水可能带来的危害进行分析,并提出解决方法。  相似文献   
7.
针对油田采出废水的特点,以粘胶基活性炭纤维为原料,经二次炭化和二次活化方式处理制得ACF样品。以ACF为过滤材料,对延长某采油厂经过沉降、分离处理后的采油废水进行动态吸附实验,实验结果表明:经水蒸汽二次活化得到的ACF样品对选用的油田废水处理效果最佳,其悬浮物颗粒粒径中值0.496μm(<1.0μm)、悬浮物含量为0.77mg/L(<1.0mg/L)。  相似文献   
8.
针对川西北某轻烃厂循环冷却水水质的特点,拟采用无磷药剂配方将循环水浓缩倍数从3.0提高到5.0,并新增软水处理系统作为循环水补水,从而达到优化水质、节水减排的目的。针对浓缩倍数提高引起得的水质稳定难题提出相应的技术方案,最终达到改善水质,保护水环境,节水减排的效果。  相似文献   
9.
The European Union Water Framework Directive (WFD) has provided the European Member States with a range of interacting governance challenges. This article studies three of these (the need for new administrative arrangements, public participation, and the enforced strict time frame). It questions how these interacting governance challenges were addressed in implementing the WFD in the Netherlands – a particularly interesting country since the European Commission assesses its implementation process in relatively positive terms, while an in-depth study reported on in this article tells a contrasting story. Based on this study, the article concludes that especially the interaction effects between the governance challenges may help us to better understand the outcome of the WFD-implementation process, and to provide more suitable advice as to how to improve the implementation process in future rounds.  相似文献   
10.
Abstract

Earlier papers indicated that the first incident of green discoloration in oysters (Crassostrea gigas) and the mass mortality observed in 1986 along the Taiwan Erhjin Chi coastal area were caused by the higher contents of total copper and copper species (mainly bioavailable and free ion) in sea water. the copper in sea water would be sorbed by suspended matter and transferred to sediments, and the copper in the sediments would also be desorbed to sea water. Processes of copper adsorption and desorption are the major factors influencing the contents of total copper and copper species in sea water and sediments. in this study, the Erhjin Chi sediments were mixed with sea water by a shaker technique. When the mixture was shaken for one hour, analogous to tidal mixing in estuaries, only copper desorption from sediments was observed. If the shaking time is increased for more than 3 hours, the copper released from the sediments was resorbed to the remaining solid phases. the higher the contents of mud (91.71%) and total copper (701 mg kg?1) in sediments, the higher the copper desorption rate (1.86 ppm hr?1) and copper adsorption rate (0.50 ppm hr?1) were observed. in sediments containing lower mud (0.80%) and lower copper (43.5 mg kg?1), the copper desorption and adsorption rates were 0.83 ppm hr?1 and 0.22 ppm hr?1, respectively. the interactions among the total copper and copper species in sea water and sediments, chemical and ecological parameters, and copper bioaccumulation in oysters in the Erhjin Chi estuarine and coastal area are also discussed.  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