全文获取类型
收费全文 | 30598篇 |
免费 | 347篇 |
国内免费 | 262篇 |
专业分类
安全科学 | 1041篇 |
废物处理 | 1470篇 |
环保管理 | 4091篇 |
综合类 | 4603篇 |
基础理论 | 7978篇 |
环境理论 | 10篇 |
污染及防治 | 7553篇 |
评价与监测 | 2193篇 |
社会与环境 | 2078篇 |
灾害及防治 | 190篇 |
出版年
2023年 | 144篇 |
2022年 | 266篇 |
2021年 | 328篇 |
2020年 | 203篇 |
2019年 | 253篇 |
2018年 | 450篇 |
2017年 | 474篇 |
2016年 | 735篇 |
2015年 | 555篇 |
2014年 | 867篇 |
2013年 | 2556篇 |
2012年 | 1039篇 |
2011年 | 1404篇 |
2010年 | 1140篇 |
2009年 | 1185篇 |
2008年 | 1459篇 |
2007年 | 1370篇 |
2006年 | 1240篇 |
2005年 | 1112篇 |
2004年 | 1065篇 |
2003年 | 1015篇 |
2002年 | 970篇 |
2001年 | 1108篇 |
2000年 | 784篇 |
1999年 | 491篇 |
1998年 | 377篇 |
1997年 | 392篇 |
1996年 | 414篇 |
1995年 | 475篇 |
1994年 | 404篇 |
1993年 | 350篇 |
1992年 | 388篇 |
1991年 | 370篇 |
1990年 | 334篇 |
1989年 | 330篇 |
1988年 | 298篇 |
1987年 | 247篇 |
1986年 | 253篇 |
1985年 | 254篇 |
1984年 | 270篇 |
1983年 | 258篇 |
1982年 | 279篇 |
1981年 | 227篇 |
1980年 | 173篇 |
1979年 | 185篇 |
1978年 | 167篇 |
1977年 | 137篇 |
1975年 | 140篇 |
1973年 | 168篇 |
1972年 | 143篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
A dynamic programming code was formulated for the purpose of assigning sampling frequencies throughout a regulatory water quality monitoring network in order to optimize the statistical performance of the network while operating within a fixed budgetary constraint. The statistical objective is to achieve the greatest possible station to station uniformity in confidence interval widths about annual geometric means of the measured water quality variables and to keep the average confidence width reasonably small. The objective function is the sum (over several selected variables and all stations) of the normalized positive deviations of the predicted confidence interval widths from preselected design confidence interval widths. The code was designed to account for the effects of deterministic seasonal variation and serial correlation of the water quality observations by incorporating the results of the time series analysis of historical quality data. The economic constraint ensures that the annual operating cost of the system, including direct costs of travel and laboratory analysis, will not exceed the allowable budget. As an example situation, the dynamic programming code was used to assign sampling frequencies to the nine stations in Illinois from which historical quality data had been obtained and analyzed. Using five design quality constituents and representative travel and laboratory costs, an “optimal” design was produced. The optimal design achieved a 10% improvement in uniformity (standard deviation) of confidence interval widths when compared to a more traditional design based on the same budget and using identical sampling frequencies at every station. 相似文献
92.
The results of recent IAEA intercomparison programs are reviewed. 相似文献
93.
V. A. OVCHARENKO 《Natural resources forum》1980,4(3):277-290
Natural gas may provide a major contribution to the world energy supply during the next few decades. The developing countries command about 50 per cent of the world proved natural gas reserves, with gas accounting for only 6 per cent of commercial primary energy production. The challenging task of expanding gas production and utilization in the developing countries, especially through effective use of gas associated with petroleum deposits and transportation of gas in liquefied form (LNG), will require long-term technical co-operation policy commitments with regard to investment, manpower and the transfer of technology. The article is intended to analyse the basic factors involved in these problems. Au cours des prochaines décennies, le gaz naturel peut constituer un apport considérable à l'approvisionnement énergétique mondial. Les pays en développement détiennent approximativement 50 pour cent des réserves mondiales prouvées de gaz naturel, le gaz représentant seulement 6 pour cent de la production d'énergie primaire commerciale. Le défi lancé par la production et l'utilisation croissantes de gaz dans les pays en développement, particulièrement par l'utilisation efficace du gaz lié aux gisements de pétrole et le transport du gaz liquéfié (GNL), requiert des engagements à long terme en matière de politique de coopération technique dans le domaine des investissements, de la main-d'oeuvre et du transfert de technologie. Cet article a pour but d'analyser les facteurs fondamentaux à prendre en considération lorsqu'on traite de ces problèmes. El gas natural podría representar una gran contribucíon a la oferta mundial de energía dentro de las próximas décadas. Los países en desarrollo poseen cerca del 50 porciento de la reserva provada mundial de gas y solamente el 6 porciento de la producción primaria de energía comercial proviene del gas. La tarea de expandir la producción y utilización de gas en los países en desarrollo, especialmente ia utilización efectiva en forma líquida (LNG) de gas asociado al petróleo, requiere de compromisos de cooperación técnica a largo plazo en lo referente a inversiones, recursos humanos y transferencia de tecnología. Este artículo intenta analizar los factores básicos pertinentes a dicha tarea. 相似文献
94.
This paper describes the help given by the social services department of a shipping company to bereaved families following a shipping disaster. In the absence of clear, factual and prompt information from an authoritative source, there is a tendency for bereaved individuals to deny their loss and thereby delay the process of mourning and eventual recovery. Appropriate intervention and support can help to overcome this tendency as was seen in the Madasa case. 相似文献
95.
Results of a recent intercomparison on the determination of trace elements in simulated air filter samples are reported. A large scatter of results is obtained for some elements and systematic differences between laboratories are observed. The performance of different methods, in particular neutron activation analysis and atomic absorption spectrophotometry, used by the various laboratories is discussed (air filter analysis; intercomparison; trace elements; control charts). 相似文献
96.
J A Heidman 《Journal - Water Pollution Control Federation》1975,47(6):1493-1498
97.
98.
There is a growing recognition that knowledge of indigenous communities, based on accumulated observations and experience over time, is significant for sustainable environmental management in collaboration with modern scientific knowledge. A number of innovative policy initiatives are currently being implemented in New Zealand to enable indigenous Maori tribes and sub-tribes to rehabilitate and manage their local fisheries in accordance with customary values and practices. These policies are an important milestone from an historical perspective as they are meant to recognise and empower the role of Maori as Treaty partners. The fisheries management regime in New Zealand now provides for Maori representation at the local level within a co-management framework that enables local Maori communities to exercise their customary rights. These institutional arrangements have been crafted to facilitate Maori input, based on customary values and practices, to complement modern Western management practices for sustainable harvesting of marine resources. Nevertheless, the degree to which these initiatives constitute an adequate response to Maori Treaty aspirations is debatable. A major constraint in this respect is that the government is compelled to recognise the needs of other, economically and politically more dominant, non-Maori user-groups in allocating and managing access to fishery resources and the marine environment. 相似文献
99.
Laboratory column experiments run for up to 13 days compared air sparging of groundwater contaminated by dissolved petroleum hydrocarbons in sterile and non-sterile aquifer sediments as well as uncontaminated sediments and groundwater. Loss of dissolved BTEX compounds in the contaminated columns was very rapid, occurring through volatilisation. The majority of the dissolved total organic carbon (TOC) persisted for much longer periods however. A direct comparison between losses from sterile and non-sterile columns suggested a negligible contribution of biodegradation to the removal of TOC. This was difficult to confirm through examination of O2 utilisation because oxidation of a small amount of reduced sulphur in the aquifer materials was the dominant sink for O2. Despite this, it was possible to conclude that less than 22% of the removal of TOC was through biodegradation during the first three days of air sparging. 相似文献
100.
MICHAEL A. SCHUETT 《Environmental management》1997,21(2):239-246
/ This study intended to explore the perceptions of mountain bikingmanagement through a mail survey of state park directors in all 50 states.With a 100% response rate, it was found that 47 states permit mountainbiking in their state parks, however, few state parks have formalized plansto manage this outdoor activity. The management policies that do exist arenot followed on a statewide basis but vary within each state and at eachstate park. Many states have worked cooperatively with local mountain bikingclubs to develop and maintain mountain bike trails, promote rider education,and provide volunteer patrols on trails. The issue of user conflict surfacedwith almost three-fourths of the managers responding that conflict existedbetween mountain bikers and other trail users. This preliminary study shouldprompt further research with on-site managers focusing on the use ofmanagement plans for mountain biking, cooperation between managers and usergroups, and user conflict. It is recommended that an Internet-basedinformation clearinghouse or discussion group be made available to landmanagers by a national bicycling organization.KEY WORDS: Mountain biking; State parks; State park directors;Recreation resource management 相似文献