全文获取类型
收费全文 | 809篇 |
免费 | 59篇 |
国内免费 | 59篇 |
专业分类
安全科学 | 70篇 |
废物处理 | 14篇 |
环保管理 | 239篇 |
综合类 | 321篇 |
基础理论 | 122篇 |
环境理论 | 2篇 |
污染及防治 | 27篇 |
评价与监测 | 13篇 |
社会与环境 | 93篇 |
灾害及防治 | 26篇 |
出版年
2023年 | 4篇 |
2022年 | 9篇 |
2021年 | 21篇 |
2020年 | 15篇 |
2019年 | 25篇 |
2018年 | 23篇 |
2017年 | 39篇 |
2016年 | 38篇 |
2015年 | 33篇 |
2014年 | 31篇 |
2013年 | 54篇 |
2012年 | 59篇 |
2011年 | 49篇 |
2010年 | 38篇 |
2009年 | 38篇 |
2008年 | 32篇 |
2007年 | 44篇 |
2006年 | 38篇 |
2005年 | 27篇 |
2004年 | 25篇 |
2003年 | 36篇 |
2002年 | 31篇 |
2001年 | 21篇 |
2000年 | 26篇 |
1999年 | 24篇 |
1998年 | 11篇 |
1997年 | 15篇 |
1996年 | 6篇 |
1995年 | 8篇 |
1994年 | 13篇 |
1993年 | 7篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1988年 | 2篇 |
1987年 | 7篇 |
1986年 | 2篇 |
1983年 | 6篇 |
1982年 | 2篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1979年 | 8篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1975年 | 4篇 |
1974年 | 1篇 |
1973年 | 3篇 |
1972年 | 3篇 |
1971年 | 7篇 |
排序方式: 共有927条查询结果,搜索用时 296 毫秒
641.
Mohamed Nasr Allam 《Journal of the American Water Resources Association》1987,23(2):207-219
ABSTRACT: An allocation model for irrigation water cost, based on the Use of Facilities method, is presented. The model is developed for large-scale irrigation systems which may include multipurpose reservoirs, irrigation control works, pump stations and irrigation canals of various orders. The model accounts for the water conveyance losses as well as the water gains in the irrigation canals, and their effects on irrigation cost. It is applied to the irrigation distribution system of the Nile Valley in Egypt, which contains the High Aswan Dam, 16 irrigation structures, 12 pump stations, and numerous irrigation canals. The irrigation water cost at 29 areas representing the Nile Valley is determined. 相似文献
642.
Donald A. Downing 《Journal of the American Water Resources Association》1975,11(2):345-355
ABSTRACT. The article proposes the use of certain water and sewer extension pricing and investment policies. Such policies would complement an urban growth policy designed to guide the location and timing of growth in urbanizing areas. Proposed pricing policies are based upon marginal cost principles. The types of pricing policies discussed include benefit assessments, connection fees, and user charges. Proposed investment policies deal with the division of financing responsiblities between the public and private sectors. Discussion of each proposal explains the economic influence of the proposed policies upon key decision makers in the land development process. The application of proposed pricing and investment policies in the case study communities is mixed. In Knoxville, Tennessee, where pricing and investment policies reflect the proposed policies, no urban growth policy exists. In Lexington, Kentucky, mixed pricing and investment policies do not complement what is a relatively good urban growth policy. In Greensboro, North Carolina, reasonably effective pricing and investment policies complement other policies which provide some guidance to the urban growth pattern. It is hoped that the article will increase the recognition of utility pricing and investment policies as one means of implementing urban growth policy. 相似文献
643.
Jackie Sellers Ronald M. North 《Journal of the American Water Resources Association》1979,15(1):189-197
ABSTRACT: In this article a managerial approach to developing and implementing National Water Resources policy is suggested. Proper consideration can be given to national economic development (NED), environmental quality (EQ) and conservation and still result in an implementable policy at the operational level if proper incentives are built into the process with proper attention to alternate non-Federal cost sharing rates. Not only can these multiple objectives be entertained but the Administration and Congress will have a management tool that should ensure a certain probability of success. 相似文献
644.
Janusz R. Rydzewski Saeed Nairizi 《Journal of the American Water Resources Association》1979,15(2):316-325
ABSTRACT: The deliberate underwatering of a larger land area, as practiced in Southern Asia, has provided impetus for a systematic investigation into the effects of designing projects for crop water deficits on Benefit-Cost performance. The study began with the derivation, from published experimental results, of functions relating ultimate crop yield to the magnitude and timing of water deficits, i.e., of the productivity of irrigation water. To obtain the net benefit of the project, the relation between the harvested area and output and the on-farm production costs was then suggested. The cost of supplying the irrigation water to the proposed area and of distributing and applying it to the field was determined, thus completing the Benefit-Cost equation. A computer simulation model was then established to search for the irrigation project design capacity and area to maximize the net present value in the Benefit-Cost analysis for the development proposed. 相似文献
645.
G. R. Soltani 《Journal of the American Water Resources Association》1977,13(1):137-142
ABSTRACT: The possibility of increasing the water supply for irrigation through adoption of more efficient water-application techniques as an alternative to new irrigation projects was studied in an irrigated region of Iran. Excessive water application at the farm level ranks high among the causes of water shortages in the selected region. An empirical analysis of the effect of water-saving technology on the farm operator's net return was made choosing two farms in the region as a case study. The problems facing these farms are common to most farms throughout the country. The results of the budgeting analysis of the selected farms indicated that an improvement in irrigation technique can result in the expansion of water supply and higher marginal value product for water. Comparing the costs of irrigation systems with the net returns resulting from the higher efficiency showed that such an investment is economically feasible. 相似文献
646.
Clayton W. Ogg Ralph Heimlich Harry Pionke 《Journal of the American Water Resources Association》1980,16(6):967-970
ABSTRACT: Several problems that make it difficult to deal with water pollution from cropland are identified. The most immediate need is for a rational framework for determining where conservation programs can make an impact on eutrophication problems in reservoirs draining rural watersheds. This includes estimating the level of control that would be required for each local farm situation and the economic impacts for the planning area. A modeling approach is suggested for a planning area in Southeastern Pennsylvania. 相似文献
647.
A model describing parents’ preferences to relieve their own and their children's acute illnesses is estimated using stated-preference data. Estimated marginal rates of substitution (MRS) between child and parent illness are about two, indicating that parents value children's illness attributes twice as highly as their own. The MRS is larger for younger children, falls toward unity as the child approaches adulthood, and appears to reflect parental altruism rather than parent–child differences in initial health or illness costs. Intra-family allocations may compensate for chronic health impairments. Parents’ willingness to pay to avoid own or child illness increases with income, declines with fertility, increases at a decreasing rate with duration and number of symptoms, and depends on perceived discomfort and activity restrictions. Current methods of assessing morbidity benefits of environmental regulations may understate substantially the value of children's health, particularly in African-American families. 相似文献
648.
刘红梅 《湖南环境生物职业技术学院学报》2007,13(4):42-44
提升农业职业教育水平和提高农业职业院校办学效益,要本着收益原则与承受能力原则相结合、公平原则与效率原则相结合、确实原则与透明度原则相结合.在对农业高等职业教育成本补偿的现状进行了较为充分的分析研究后,建议通过合理确定学费补偿标准、增加国家财政负担份额、利用贷款制、发展教育储蓄、实行订单式培养、积极拓展经费来源等途径来完善农业高等职业教育成本补偿. 相似文献
649.
Ø. Holand R. B. Weladji K. H. Røed H. Gjøstein J. Kumpula J.-M. Gaillard M. E. Smith M. Nieminen 《Behavioral ecology and sociobiology》2006,59(5):682-688
The manipulation of the sex ratio and age structure in many managed ungulate populations calls for a better understanding
of their potential consequences on females’ condition and behavior during rut. During 1996–2002, we manipulated the male age
structure and male percentage (nine treatments during 7 years) within an experimental herd of semidomestic reindeer (Rangifer tarandus) and investigated their influence on both the body mass change and the behavior of females during rut. On average, the females
lost body mass (−0.95±SE 0.18 kg) during rut, which we contend to reflect somatic costs. The females’ losses increased as
the percentage of male decreased, but this was certainly ascribed to one treatment with high male percentage (27.7%) as compared
to the others (ranging from 3.9 to 12.2%). Female losses were highest for treatments including both young and adult males
as compared to only adult or only young males, and higher for treatments including only young compared to only adult males.
This is supported by (1) the higher female harassment frequency when females are exposed to only young or a mixture of young
and adult males as compared to only adults, (2) the higher female harassment frequency by young males as compared to adults
in the mixed treatments, and (3) the reduced females’ feeding activity in treatments including both young and adult males.
We conclude that the male age structure during rut will influence the females’ behavior and mass change and may have implications
for females’ life history and for population dynamics. 相似文献
650.
Measuring the welfare cost of climate change policies is a real challenge, raising difficult issues of micro- and macro-economics: cost-benefit analysis on the one hand, foreign trade and international specialization on the second hand. At the domestic level the possible existence of distortions, in particular in the fiscal system, may either increase or alleviate the welfare cost of a climate change policy, as illustrated by the debate on double dividend. Effects on the prices in international markets and distorted competition between countries committed to abate (Annex B) and uncommitted countries affect both the sharing of the burden, in particular through the change in the terms of trade, and the allocation of activities with the frequently waved threat of delocalization. Based on a companion theoretical analysis, the present paper aims at putting order in the welfare analysis of climate change policy and to present and compare various estimations, issuing from macro- or computable general equilibrium models. Beside the global welfare cost, the paper focuses on the marginal abatement cost and its relation to the carbon price.Most present conceptual and applied analysis is based on the case of a single domestic household-consumer. Taking into account several consumers raises new challenges, concerning equity but even more fundamentally the mere definition of fiscal distortion, which have not yet been really addressed. 相似文献