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951.
952.
David N. Cole 《Environmental management》1992,16(2):255-264
A standard campsite model is proposed and then manipulated to examine the influence of individual variables on amount of vegetation
loss. Amount of impact is influenced by amount of use, vegetation fragility, vegetation density, and the degree to which activities
are concentrated spatially on the site. Degree of concentration also influences the importance of the other explanatory variables.
Amount of use and vegetation fragility are equally important determinants of impact and are most influential where activity
concentration is low. The curvilinear relationship between amount of use and amount of impact can be explained by the tendency
for activities to become increasingly concentrated as amount of use increases. This relationship should not vary with regional
or environmental characteristics except where these influence degree of activity concentration. 相似文献
953.
954.
Francis J. Singer 《Environmental management》1981,5(3):263-270
Populations of introduced European wild boar, feral pigs, and combinations of both types (all Susscrola L.) inhabit thirteen areas in the National Park Service system. All parks have relatively stable populations, with the exception of Great Smoky Mountains National Park, which reported a rapidly expanding wild boar population. Suspected and documented impacts were apparently related to pig densities and sensitivity of the ecosystem; the three largest units with dense wild pig populations reported the most damage. Overall, wild pigs are a relatively minor problem for the Park Service; however, problems are severe in at least three parks, and there is potential for invasion of wild boars into several additional parks in the Appalachian Mountains. More specific information is needed on numbers of wild pigs and their impacts in the various parks. 相似文献
955.
Ecological land classification: A survey approach 总被引:10,自引:0,他引:10
A landscape approach to ecological land mapping, as illustrated in this article, proceeds by pattern recognition based on ecological theory. The unit areas delineated are hypotheses that arise from a knowledge of what is ecologically important in the land. Units formed by the mapper are likely to be inefficient or irrelevant for ecological purposes unless he possesses a sound rationale as to the interactions and controlling influences of the structural components of ecosystems. Here is the central problem with what have been called objective multivariate approaches to mapping based on grid units and the sometimes arbitrary attributes thereof; they tend to conceal the importance of ecological theory and the necessity for theory-based supervision of pattern recognition. Multivariate techniques are best used iteratively to verify and refine map units initially recognized and delineated by theoretical considerations. These ideas are illustrated by an example of a reconnaissance survey in the Northwest Territories of Canada. 相似文献
956.
957.
Riparian livestock exclosure research in the western United States: a critique and some recommendations 总被引:1,自引:1,他引:0
Sarr DA 《Environmental management》2002,30(4):516-526
Over the last three decades, livestock exclosure research has emerged as a preferred method to evaluate the ecology of riparian
ecosystems and their susceptibility to livestock impacts. This research has addressed the effects of livestock exclusion on
many characteristics of riparian ecosystems, including vegetation, aquatic and terrestrial animals, and geomorphology. This
paper reviews, critiques, and provides recommendations for the improvement of riparian livestock exclosure research. Exclosure-based
research has left considerable scientific uncertainty due to popularization of relatively few studies, weak study designs,
a poor understanding of the scales and mechanisms of ecosystem recovery, and selective, agenda-laden literature reviews advocating
for or against public lands livestock grazing. Exclosures are often too small (<50 ha) and improperly placed to accurately
measure the responses of aquatic organisms or geomorphic processes to livestock removal. Depending upon the site conditions
when and where livestock exclosures are established, postexclusion dynamics may vary considerably. Systems can recover quickly
and predictably with livestock removal (the “rubber band” model), fail to recover due to changes in system structure or function
(the “Humpty Dumpty” model), or recover slowly and remain more sensitive to livestock impacts than they were before grazing
was initiated (the “broken leg” model). Several initial ideas for strengthening the scientific basis for livestock exclosure
research are presented: (1) incorporation of meta-analyses and critical reviews. (2) use of restoration ecology as a unifying
conceptual framework; (3) development of long-term research programs; (4) improved exclosure placement/design; and (5) a stronger
commitment to collection of pretreatment data. 相似文献
958.
Quantifying natural resource injuries and ecological service reductions: challenges and opportunities 总被引:1,自引:0,他引:1
The natural resource damage assessment (NRDA) provisions of the Comprehensive Environmental Response, Compensation, and Liability
Act (CERCLA) and the Oil Pollution Act (OPA) are complex and have been difficult to implement. The complexity and difficulty
in implementation arise both from the assessment procedures specified in agency NRDA guidance and from the limited ability
of ecologists to quantify impacts of hazardous substances on natural resources. This paper explores the scientific aspects
of NRDA implementation, and discusses conceptual and methodological relationships between NRDA and the much broader field
of ecological risk assessment (ERA). We discuss three critical components of the NRDA assessment approach: measuring natural
resource injuries and reductions in resource services; evaluating causality; and establishing baseline conditions. We identify
(1) specific approaches drawn from ERA practice that could improve each of these components, and (2) research needs and institutional
changes that may improve the ability of the NRDA process to achieve its stated objectives. We recommend the acceleration of
the ongoing dialogue among NRDA practitioners from the Trustee and PRP communities as a first step toward resolving the procedural
and technical deficiencies of the NRDA process. 相似文献
959.
L. Van Rensburg T.L. Morgenthal H. van Hamburg M.D. Michael 《The Environmentalist》2003,23(4):285-295
The aim of this paper is to compare the rehabilitation result between two ash disposal sites with regard to its vegetation establishment and soil nutrient status. The study areas were situated in close proximity, in the Mpumalanga coalfield, South Africa. Although both areas received a similar amelioration treatment and were seeded with similar seed mixture the vegetation composition were significantly different. Both areas were poor in essential nutrients, this probably being one of the most limiting factors for vegetation establishment. No serious phytotoxic conditions, as is frequently experience with coal ash, could be identified. A regular monitoring and low level maintenance program is therefore proposed to improve the sustainability of the vegetation. The study proposed that results form such evaluations be used to identify performance standards for rehabilitated derelict land. 相似文献
960.