全文获取类型
收费全文 | 18183篇 |
免费 | 189篇 |
国内免费 | 164篇 |
专业分类
安全科学 | 532篇 |
废物处理 | 750篇 |
环保管理 | 2545篇 |
综合类 | 2453篇 |
基础理论 | 4836篇 |
环境理论 | 4篇 |
污染及防治 | 5262篇 |
评价与监测 | 1177篇 |
社会与环境 | 850篇 |
灾害及防治 | 127篇 |
出版年
2022年 | 128篇 |
2021年 | 157篇 |
2020年 | 100篇 |
2019年 | 146篇 |
2018年 | 255篇 |
2017年 | 253篇 |
2016年 | 414篇 |
2015年 | 345篇 |
2014年 | 512篇 |
2013年 | 1547篇 |
2012年 | 601篇 |
2011年 | 780篇 |
2010年 | 613篇 |
2009年 | 718篇 |
2008年 | 838篇 |
2007年 | 881篇 |
2006年 | 765篇 |
2005年 | 644篇 |
2004年 | 658篇 |
2003年 | 619篇 |
2002年 | 615篇 |
2001年 | 755篇 |
2000年 | 558篇 |
1999年 | 311篇 |
1998年 | 237篇 |
1997年 | 224篇 |
1996年 | 269篇 |
1995年 | 266篇 |
1994年 | 255篇 |
1993年 | 231篇 |
1992年 | 206篇 |
1991年 | 185篇 |
1990年 | 207篇 |
1989年 | 189篇 |
1988年 | 181篇 |
1987年 | 171篇 |
1986年 | 149篇 |
1985年 | 147篇 |
1984年 | 176篇 |
1983年 | 174篇 |
1982年 | 169篇 |
1981年 | 169篇 |
1980年 | 136篇 |
1979年 | 159篇 |
1978年 | 108篇 |
1977年 | 100篇 |
1976年 | 88篇 |
1975年 | 94篇 |
1973年 | 92篇 |
1972年 | 99篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
912.
913.
E T. Foster T. C. Chen J. P. Newton E. O. Isu 《Journal of the American Water Resources Association》1972,8(5):863-870
ABSTRACT. Theoretical and practical results are summarized for a study to determine optimal water resource allocation in a proposed water conservancy district. The area of this district, which covers several river basins, contains a large number of existing and proposed facilities such as reservoirs and diversions. The operation of all of these facilities was to be determined along with the sizing of the proposed facilities in order to optimize given objective functions. Related efforts in optimal river basin utilization were surveyed, and linear programming was selected as an expedient optimization technique. The problem is formulated by identifying time stages which together constitute a repetitive cycle such as a year. With these stages, it is possible to associate operational and capacity variables with network components, which are branches and nodes. Objective functions are assembled for the component variables. Constraint equations are written in terms of the variables to reflect network nodal continuity, capacity restrictions, and adjudications such as water rights. A numerical example is considered in which the existing and proposed facilities are aggregated to produce a small, tractable number of facilities. This paper examines the example results and suggests future improvements for models of this type. 相似文献
914.
CHESTER C. KISIEL 《Journal of the American Water Resources Association》1971,7(5):1093-1094
A. I. Johnson, President-elect of AWRA, was elected President of the International Commission on Subsurface Water at the International Union of Geodesy and Geophysics meeting in Moscow in August. Mr. Johnson, who was a member of the U.S. delegation to the meeting, also presented a paper at the meeting on "Ground Water and the International Association of Scientific Hydrology, 1967-1970," and served as Rapporteur for the Symposium on Pollution of Ground Water.
HISTORICAL NOTE-In defiance of laws, international treaties, and the rights of other communities to live and prosper, the city of Detroit has for many years sent a constant torrent of human and industrial filth into the Detroit River and Lake Erie. Time and time again reports from engineers, commissions and governmental forces, all sounding the danger cry, have been received by the Detroit fathers, and have been tabled, prospects are evident… that 20 years from now will see Detroit still making a wallowing trough of the Great Lakes. 相似文献
HISTORICAL NOTE-In defiance of laws, international treaties, and the rights of other communities to live and prosper, the city of Detroit has for many years sent a constant torrent of human and industrial filth into the Detroit River and Lake Erie. Time and time again reports from engineers, commissions and governmental forces, all sounding the danger cry, have been received by the Detroit fathers, and have been tabled, prospects are evident… that 20 years from now will see Detroit still making a wallowing trough of the Great Lakes. 相似文献
915.
C. B. Cluff K. J. DeCook W. G. Matlock 《Journal of the American Water Resources Association》1971,7(4):726-739
ABSTRACT .Many growing municipalities near irrigated agriculture are advocating a transfer of water now utilized for irrigation to municipal use. Alternatives are presented whereby this water can be transferred to municipal use in exchange for treated sewage effluent. The irrigation water would in effect be cycled through the municipal system prior to use on the farms. A case study of the Tucson region illustrates the relevant legal, economic and technical aspects. Effluent could be delivered to irrigators in Avra Valley at a cost less than that now paid for water pumped from declining water tables. In return the City of Tucson could import ground water now being used for irrigation through an existing pipeline which presently cannot be used because of a court injunction obtained by the irrigators. It appears that such an exchange agreement could be made without modification of existing statutory law. Similar exchange arrangements may prove to be feasible in other regions containing irrigated agriculture. Increased efficiency of water use can be achieved avoiding external effects which commonly arise in a direct transfer and are difficult to evaluate. High quality water is allocated to municipal use whereas nutrient-rich sewage effluent is transferred to irrigation. 相似文献
916.
C. Michael York 《Journal of the American Water Resources Association》1971,7(5):920-924
ABSTRACT. Elected officials, technical specialists and the public are talking more about “citizen input” into the decision process, and how the people view a given issue or kind of public service. However, problem definition and valid instruments are needed before we can meaningfully predict or understand public attitude relating to a particular issue or concept. The fluoridation of community water supplies was chosen for the present methodological demonstration. This issue achieves a high level of controversy among many public segments [Crain, Katz and Rosenthal, 1969; Davis, 1959; McNeal, 1957]. By 1950, there was widespread endorsement for a national program relating to controlled water fluoridation. Yet, public acceptance of this particular technological advance has not been very high. 相似文献
917.
ABSTRACT. In 1970, the Canadian Federal Government passed the Canada Water Act which provides for a co-operative federal-provincial approach to water resource management. The purpose of this paper is to outline our definition of comprehensive planning and the approach being taken under the new legislation. Two basic premises underly the definition. They are that resource management consists of an array of problems and that the prime function of planning is to provide information for decision making. The definition of comprehensive planning is embodied in a general statement and a set of principles. The principles define the approach that should be taken to provide adequate information for decision making in today's complex environment. A brief resume of the jurisdictions for water management in Canada leads to a discussion of a joint federal-provincial comprehensive study of the Qu'Appelle River Basin in Southern Saskatchewan. The basin and the study are described briefly. This is followed by an outline of the economic and social considerations which are being incorporated into the comprehensive planning study for the basin. 相似文献
918.
Kenneth C. Jurgens 《Journal of the American Water Resources Association》1971,7(2):260-264
.Fish and wildlife enhancement through water resources development implies fish and wildlife will be enhanced or benefit directly from such development. As a matter of practicality, the opposite may be the case in that wildlife lands of prime value and stream fisheries are often lost or severely altered as a result of reservoir construction or stream channelization. Additionally, estuarine fish and wildlife can also suffer from water resources development due to reductions in volume of fresh waters reaching the estuaries and adjacent marshes. In some instances waterfowl habitat can be created by reservoir construction and with good planning waterfowl habitat and use may be enhanced. To offset losses of thousands of acres of wildlife habitat when a river system is to be totally harnessed, planners could set aside sufficiently large natural areas dedicated for use by wildlife. This, however, would be replacement rather than enhancement. Reservoir fisheries can be enhanced with good planning to include timber clearing, shoreline clearing, boat road clearing, variable level drawoff devices and tailrace escapement channels. To sum up, it is possible for some species offish and wildlife to be enhanced through water resources development but only at the expense of others, and then only through careful and integrated planning. 相似文献
919.
Four satellites have been used in meteorology. They are TIROS, ESSA, Nimbus, and Applications Technology Satellite (ATS). The first three operate in the orbital altitudes of about 1000 to 1200 km while the fourth, ATS, is at geosynchronous altitude of 36,000 km. Cloud cover is being observed operationally from low orbit and experimentally from synchronous altitude. Wind velocity has been inferred from the frequent cloud cover pictures taken by ATS and satellite-balloon systems are being developed which will locate and track constant-density level balloons for determining wind flow. Spectrometers and radiometers operating in the electromagnetic spectral region from the ultraviolet to the microwave region are being developed to quantitatively measure temperature, water vapor, density, and wind profiles. These will furnish data for the development and testing of atmospheric models for numerical prediction. In addition, experiments are being developed to measure ozone and other constituents of the air, solar energy, surface conditions, heat balance and other atmospheric attributes which affect the structure and dynamics of the atmosphere. 相似文献
920.
T. L. Dobbs C. E. Olson W. G. Wedemeyer G. H. Pfeiffer 《Journal of the American Water Resources Association》1973,9(1):129-139
ABSTRACT. A State loan program was analyzed for its effects on groundwater development in Wyoming. The analysis focused on the effects of low-interest State financing on the economic feasibility of investments in center-pivot sprinkler irrigation systems. The feasibility analysis indicated that investments in sprinkler systems for production of cash crops are highly profitable, and would frequently be carried out whether or not the State loan program were available. Investments in sprinklers for production of forage crops are perhaps frequently made attractive by the loan program. Thus, while the program appears to have accelerated the pace of private water resource development in Wyoming, it has also subsidized some investments that would have been carried out regardless of the program's existence. Further analysis indicated that sprinkler investments carried out with State financing contribute substantially to firm growth when cast crops are grown, but have less marked, and sometimes negative, effects on growth when forage crops are produced. Some positive effects of the loan program on southeast Wyoming's regional economy were noted, though a complete empirical analysis of regional impacts was beyond the scope of the study. 相似文献