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331.
The take of Nearctic songbirds for the caged-bird trade is an important cultural and economic activity in Mexico, but its sustainability has been questioned. We relied on the theta-logistic population model to explore options for setting allowable levels of take for 11 species of passerines that were subject to legal take in Mexico in 2010. Because estimates of population size necessary for making-periodic adjustments to levels of take are not routinely available, we examined the conditions under which a constant level of take might contribute to population depletion (i.e., a population below its level of maximum net productivity). The chance of depleting a population is highest when levels of take are based on population sizes that happen to be much lower or higher than the level of maximum net productivity, when environmental variation is relatively high and serially correlated, and when the interval between estimation of population size is relatively long (> or = 5 years). To estimate demographic rates of songbirds involved in the Mexican trade we relied on published information and allometric relationships to develop probability distributions for key rates, and then sampled from those distributions to characterize the uncertainty in potential levels of take. Estimates of the intrinsic rate of growth (r) were highly variable, but median estimates were consistent with those expected for relatively short-lived, highly fecund species. Allowing for the possibility of nonlinear density dependence generally resulted in allowable levels of take that were lower than would have been the case under an assumption of linearity. Levels of take authorized by the Mexican government in 2010 for the 11 species we examined were small in comparison to relatively conservative allowable levels of take (i.e., those intended to achieve 50% of maximum sustainable yield). However, the actual levels of take in Mexico are unknown and almost certainly exceed the authorized take. Also, the take of Nearctic songbirds in other Latin American and Caribbean countries ultimately must be considered in assessing population-level impacts. 相似文献
332.
When animals die in traps in a mark-recapture study, straightforward likelihood inferences are possible in a class of models.
The class includes M0, Mt, and Mb as reported by White et al. (Los Alamos National Laboratory, LA-8787-NERP, pp 235, 1982), those that do not involve heterogeneity.
We include three Markov chain “persistence” models and show that they provide good fits in a trapping study of deer mice in
the Cascade-Siskiyou National Monument of Southern Oregon where trapping mortality was high.
相似文献
Fred L. RamseyEmail: |
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Prioritizing Pacific Salmon Stocks for Conservation 总被引:3,自引:1,他引:2
Fred W. Allendorf David Bayles Daniel L. Bottom Kenneth P. Currens Christopher A. Frissell David Hankin James A. Lichatowich Willa Nehlsen Patrick C. Trotter & Thomas H. Williams 《Conservation biology》1997,11(1):140-152
Over 300 native stocks of Pacific salmon, steelhead, and coastal cutthroat trout (Oncorhynchus spp.) are at risk of extinction in the Pacific Northwest. With only limited resources available for conservation and recovery, prioritization of these stocks may become necessary if meaningful measures are to be implemented. We propose criteria by which prioritization may be guided. First, we rank stocks for risk of extinction, either by population viability analysis or by a set of surrogate measures. Then we rank stocks for biological consequences of extinction, using sets of questions designed to establish the genetic and evolutionary consequences and the ecological consequences if a stock were to become extinct. Together, these rankings allow stocks to be prioritized for a range of possible actions, with those stocks at highest risk and bearing the greatest biological consequences of extinction receiving attention first. Application of the prioritization process to 20 Pacific anadromous salmonid stocks worked as intended, although data limitations are considerable. The process is most likely to work successfully when applied to many stocks on which data exist, when several experts carry out the prioritization, and when the results are peer reviewed. 相似文献
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Fluorescent illumination has become common, but its alleged effects on behavior are still controversial. This experiment was designed to determine whether warm white, cool white, and full-spectrum fluorescent spectra at approximately equal illuminances differentially affect performance on simple verbal and quantitative tasks, salary recommendations, rated attractiveness and friendliness of others, judged room attractiveness, estimated room size, and self-reported pleasure and arousal. The results showed no significant differences among the three lighting types on any of the dependent measures. A subsequent power analysis indicated that if differences actually do exist, they are quite small. Cool white or warm white lamps are recommended because they are much less expensive than full-spectrum lamps. 相似文献
337.
Micheline Devaurs Gerald F. Gifford 《Journal of the American Water Resources Association》1986,22(1):19-27
ABSTRACT: The objective of this study was to investigate the use of Green and Ampt infiltration equation parameters (determined by least squares fitting of field infiltration data or predicted from soil texture properties) to characterize infiltration on spatially varying rangeland sites. It was found that a least squares regression approach reduces the physically based parameters in the Green and Ampt to empirical coefficients since negative coefficients are obtained, particularly on plots with low infiltration rates. Green and Ampt parameters predicted from soil texture data describe infiltration rates less than 3 cm/hr. The applicability of these Green and Ampt parameters appears limited to sites with lower infiltration rates. Results indicate that soil texture predictive triangles, developed to describe infiltration on agricultural soils, need revision to adequately describe infiltration patterns on rangelands. 相似文献
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Fred Curtis 《The Environmentalist》1985,5(2):129-135
Summary This paper describes the demand and supply information requirements to determine whether a curriculum for a new program, Natural Resources Planning and Management (NRPM), should be developed by Athabasca University (AU). Demand considerations assist in determining forecasted job opportunities and student needs. Supply considerations, including the type and location of existing natural resource programs and their student enrollment levels, assist in determining the enrollment level, the type of degree program, and that the student profile of AU's NRPM graduates will be high, particularly in western Canada. AU has, therefore, been advised to offer an undergraduate bachelor's degree in NRPM. This paper also serves as a model, for organizing demand and supply information for any new university or college program.Fred Curtis, is Professor and Co-ordinator of Regional Systems Engineering, at the University of Regina, Regina, Saskatchewan, Canada. His teaching and research areas include environmental and behavioural systems engineering. His recent publications focus on environmental impact assessment procedures, environmental mediation, natural resources planning and management, energy conservation and land use planning and distance education. 相似文献