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421.
Biochemical genetic variation provided evidence for the mode of reproduction of brooded young in the sea anemone Epiactis prolifera Verrill, 1869. Individuals of E. prolifera are female when small but hermaphroditic when large (i.e., gynodioecious); juveniles are brooded externally on the column. Brooding individuals collected from 6 intertidal sites (5 in central California and 1 in Washington State, USA) in the spring and summer of 1980 were assayed for gene-enzyme variation by starch-gel electrophoresis. Three of 12 enzyme loci were polymorphic; phosphoglucose isomerase appeared to be encoded by two, closely linked loci. Genotypic frequencies deviated markedly from expected random mating proportions. Only three heterozygotes were found; two were heterozygous at all three polymorphic loci, and the other was polymorphic at the two PGI loci. All 158 juveniles from 25 brooding individuals were assayed (2–19 juveniles per parent). Juveniles on homozygous adults were always identical to their parent. However, brooded young of heterozygous individuals were not identical to their parent. but showed 1:2:1 phenotypic segregation ratios consistent with reproduction by self-fertilization. This genetic evidence together with findings of marked heterozygote deficiencies and genetic identity of homozygous adults and their brooded young supports the conclusion that E. prolifera usually reproduces by self-fertilization, and cross-fertilization is rate. 相似文献
422.
Dennis R. Jaasma Mahesh Gundappa Mark R. Champion Robert C. Mccrillis 《Environmental monitoring and assessment》1993,24(3):189-204
The carbon monoxide (CO) and particulate matter (PM) emissions of woodburning stoves have been measured under field conditions. Both conventional airtight stoves and newly installed airtight stoves certified by the U.S. Environmental Protection Agency to be low emitters of PM were monitored. The certified stoves were of two types, catalytic and noncatalytic. Compared to the conventional stoves, PM emission rates (g/hr) were reduced approximately 70% by both types of certified stoves. The CO emission rates were reduced 71% and 53% by catalytic and noncatalytic stoves respectively. These rate reductions occur because the certified stoves burn cleaner (less pollutant formation per kg of wood burned) and the average burn rate of certified stoves in field use is less than the average burn rate of conventional stoves. 相似文献
423.
Russell R. Dynes Dennis Wenger 《Journal of the American Water Resources Association》1971,7(4):644-651
ABSTRACT The study explores the perception of community problems, including flooding and pollution, among leaders in four different communities, ranging in size from 10,000 to 20,000. Water-related problems were considered in the context of other community problems which were defined by these leaders. Among these leaders, water-related problems were characterized by low salience and by low consensus. In seeking solutions, these leaders see water problems as being less likely to be solved at the local community level and to necessitate extra-community assistance. They also see water-related problems as requiring a relatively low level of community coordination and as being primarily the responsibility of the public sector. Local governmental leaders were seen as being more important in problem solving in water-related problems than they were in other community problems. 相似文献
424.
Péter László Pap Gábor Árpád Czirják Csongor István Vágási Zoltán Barta Dennis Hasselquist 《Die Naturwissenschaften》2010,97(10):891-901
Difference between sexes in parasitism is a common phenomenon among birds, which may be related to differences between males and females in their investment into immune functions or as a consequence of differential exposure to parasites. Because life-history strategies change sex specifically during the annual cycle, immunological responses of the host aiming to reduce the impact of parasites may be sexually dimorphic. Despite the great complexity of the immune system, studies on immunoecology generally characterise the immune status through a few variables, often overlooking potentially important seasonal and gender effects. However, because of the differences in physiological and defence mechanisms among different arms of the immune system, we expect divergent responses of immune components to environmental seasonality. In male and female house sparrows (Passer domesticus), we measured the major components of the immune system (innate, acquired, cellular and humoral) during four important life-history stages across the year: (1) mating, (2) breeding, (3) moulting and (4) during the winter capture and also following introduction to captivity in aviary. Different individuals were sampled from the same population during the four life cycle stages. We found that three out of eight immune variables showed a significant life cycle stage × sex interaction. The difference in immune response between the sexes was significant in five immune variables during the mating stage, when females had consistently stronger immune function than males, while variables varied generally non-significantly with sex during the remaining three life cycle stages. Our results show that the immune system is highly variable between life cycle stages and sexes, highlighting the potential fine tuning of the immune system to specific physiological states and environmental conditions. 相似文献
425.
Dennis Sprenger Rolanda Lange Nico K. Michiels Nils Anthes 《Behavioral ecology and sociobiology》2009,63(6):953-958
Intraspecific variation in mating behavior is widespread among simultaneous hermaphrodites but its underlying sources remain
largely unexplored. In the sea slug Chelidonura sandrana, most matings are reciprocal. However, despite non-conditional sperm exchange and potential polygamy-mediated benefits, 30%
of matings end after unilateral insemination. To resolve this apparent inconsistency, we here investigated the effect of body
size on the frequency of reciprocal matings by testing the following two hypotheses. First, sex-allocation theory predicts
that the likelihood of reciprocity depends on the size difference between mating partners. Second, if both sex functions temporally
differ in reaching maturity, reciprocal matings should be more frequent with increasing absolute body size of the smaller
partner. The likelihood of reciprocity increased with body size of the smaller partner. Moreover, smaller individuals acted
more often as males among unilateral matings. These findings suggest that the ability to donate sperm develops prior to female
functionality in C. sandrana. 相似文献
426.
SCRAM: A scoring and ranking system for persistent, bioaccumulative, and toxic substances for the North American Great Lakes 总被引:1,自引:0,他引:1
Erin M. Snyder Shane A. Snyder John P. Giesy Shari A. Blonde Gary K. Hurlburt Cheryl L. Summer Rachel R. Mitchell Dennis M. Bush 《Environmental science and pollution research international》2000,7(1):51-51
Hundreds of chemical contaminants have been identified in the Great Lakes System of North America. Depending on the agency or organization, various subset lists of these contaminants have been identified as chemicals of potential concern. However, there is no agreement on the method that should be used to make management decisions. Except for consensus on approximately 40 chemicals that most North American agencies agree can cause deleterious effects if released into the environment, no agreement has been reached regarding the priority that contaminants should receive for further action. That leaves hundreds of chemicals that have been, are being, or potentially could be released into the environment that have not been evaluated yet. A profile for potential chemicals of concern is generally thought to include persistence in the environment, potential to bioaccumulate, and ability to cause toxic effects at environmentally relevant concentrations. Except for the International Joint Commission’s definition of persistence (> 8 weeks residence time in air, water, soil or sediment), there is little concurrence about what defines these characteristics. For instance, the State of Michigan currently has no established definitions or profiles of persistent, bioaccumulative, toxic substances. Furthermore, there is no standard process to rank chemicals relative to these characteristics. The Chemical Scoring and Ranking Assessment Model (SCRAM) has been developed to provide a process to rank-order chemicals based on these characteristics. The SCRAM system was developed primarily for use in the Great Lakes region of North America and particularly in Michigan, but it is not site-specific. Use of this system may assist in pollution prevention activities and other future chemical control efforts, allowing attention to be focused first on those chemicals likely to present the greatest hazard. 相似文献
427.
Teri L. Copeland Ann M. Holbrow Joanne M. Otani Kevin T. Connor Dennis J. Paustenbach 《Journal of the Air & Waste Management Association (1995)》2013,63(12):1399-1413
Many state and federal agencies have prepared risk assessment guidelines, which describe methods for quantifying health risks associated with exposure to vapors and particulates emitted from point and area sources (e.g., California Air Pollution Control Officers Association [CAPCOA] under the Air Toxics “Hot Spots” Act [Assembly Bill 2588] and the U.S. Environmental Protection Agency [EPA] under the Clean Air Act). In general, these guidelines recommend or require the use of upper bound “point” estimates for numerous exposure parameters. This methodology yields a single risk estimate, which is intended not to underestimate the true risk and may significantly overstate it. This paper describes a risk assessment of a facility’s airborne emissions using a probabilistic approach, which presents a range and distribution of risk estimates rather than a single point estimate. The health risks to residents living near a food processing facility, as estimated using techniques recommended by California AB2588, are compared to the results of a probabilistic analysis. Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) were identified as the emitted chemicals of concern. The point estimate method recommended by CAPCOA resulted in estimates that were greater than the 99.99th percentile risk predicted by the probabilistic analysis. As shown in other assessments of persistent airborne chemicals, secondary or indirect exposure pathways (i.e., ingestion of beef, ingestion of cow’s milk, and ingestion of mother’s milk) rather than inhalation, were the greatest contributors to risk. In this analysis, the probability distributions for the cancer potency factor and ingestion of cow’s milk had the largest impact on the results of the 33 exposure factors considered. 相似文献
428.
Vlad Isakov Todd Sax Akula Venkatram David Pankratz James Heumann Dennis Fitz 《Journal of the Air & Waste Management Association (1995)》2013,63(4):473-482
Abstract This paper evaluates the application of dispersion models to estimate near-field pollutant concentrations in two case studies. The Industrial Source Complex Short-Term Model (ISCST3) was evaluated with hexavalent chromium measurements collected within 100 m of two facilities in Barrio Logan, San Diego, CA. ISCST3 provided reasonable estimates for higher pollutant concentrations but underestimated lower concentrations. To understand the observed distribution of concentrations in Barrio Logan, a recently conducted tracer experiment was analyzed. The tracer, sulfur hexafluoride, was released at ambient temperature from an urban facility at the University of California at Riverside, and concentrations were measured within 20 m of the source. Modeling results indicated that Industrial Source Complex–Plume Rise Model Enhancement and American Meteorological Society/U.S. Environmental Protection Agency Regulatory Model–Plume Rise Model Enhancement overestimated high concentrations and underestimated low concentrations. A diagnostic study with a simple Gaussian dispersion model that incorporated site-specific meteorology was used to evaluate model results. This study found that incorporating lateral meandering for nonbuoyant urban plumes in Gaussian dispersion models could improve concentration estimates even when downwash is not considered. Incorporating a meandering component in ISCST3 resulted in improvements in estimating hexavalent chromium concentrations in Barrio Logan. Credible near-source concentration estimates depend on accurate characterization of emissions, onsite micrometeorology, and a method to account for lateral meandering in the near field. 相似文献
429.
Dennis C. Drehmel 《Journal of the Air & Waste Management Association (1995)》2013,63(11):1090-1092
Of the advanced electrostatic collection concepts studied, those employing water droplets or filters have demonstrated enhanced performance and should be considered for future applications. Electrostatic collection with water drops shows high removal efficiencies for 0.5 µm particles which are difficult to capture. Electrostatic collection with filters shows the potential for operation at either lower pressure drops or higher filtration rates. 相似文献
430.
Dennis Palmini Daniel Rossi 《Journal of the Air & Waste Management Association (1995)》2013,63(10):1081-1088
Selection of acceptable sites for industrial facilities, especially hazardous waste management facilities, can be made using a relatively new technique referred to as “fuzzy set analysis.” The methodology presented is applicable to multiple alternative decision making, when criteria are of unequal importance, and is based on the concept of establishing a subjective value for each alternative according to each criterion, and then raising the subjective value to a power commensurate with the relative importance of the criterion. This exponential weight is calculated on the basis of a preferential analysis of criteria comparisons. Apart from the ranking of the alternatives, fuzzy set analysis provides a quantitative representation of the community opinion of the order of importance of the criteria, regardless of the sites being considered. Based on the importance factors averaged from a cross section of the community, public concern could also be ranked. 相似文献