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排序方式: 共有589条查询结果,搜索用时 250 毫秒
511.
Michael Greenberg Joanna Burger Charles Powers Thomas Leschine Karen Lowrie Barry Friedlander Elaine Faustman William Griffith David Kosson 《补救:环境净化治理成本、技术与工艺杂志》2002,13(1):39-58
This article discusses a process for finding insights that will allow federal agencies and environmental professionals to more effectively manage contaminated sites. The process is built around what Etzioni (1968) called mixed‐scanning, that is, perpetually doing both comprehensive and detailed analyses and periodically re‐scanning for new circumstances that change the decision‐making environment. The article offers a checklist of 127 items, which is one part of the multiple‐stage scanning process. The checklist includes questions about technology; public, worker, and ecological health; economic cost and benefits; social impacts; and legal issues. While developed for a DOE high‐level radioactive waste application, the decision‐making framework and specific questions can be used for other large‐scale remediation and management projects. © 2002 Wiley Periodicals, Inc. 相似文献
512.
Karen L. Bushaw‐Newton David D. Hart James E. Pizzuto James R. Thomson Jennifer Egan Jeffrey T. Ashley Thomas E. Johnson Richard J. Horwitz Melissa Keeley Joy Lawrence Don Charles Catherine Gatenby Daniel A. Kreeger Tim Nightengale Roger L. Thomas David J. Velinsky 《Journal of the American Water Resources Association》2002,38(6):1581-1599
ABSTRACT: Dam removal has been proposed as an effective method of river restoration, but few integrative studies have examined ecological responses to the removal of dams. In 1999, we initiated an interdisciplinary study to determine ecological responses to the removal of a 2 m high dam on lower Manatawny Creek in southeastern Pennsylvania. We used an integrative monitoring program to assess the physical, chemical, and biological responses to dam removal. Following removal in 2000, increased sediment transport has led to major changes in channel form in the former impoundment and downstream reaches. Water quality did not change markedly following removal, probably because of the impoundment's short hydraulic residence time (less than two hours at base flow) and infrequent temperature stratification. When the impoundment was converted to a free flowing reach, the composition of the benthic macroinvertebrate and fish assemblages in this portion of Manatawny Creek shifted dramatically from lentic to lotic taxa. Some fish species inhabiting the free flowing reach downstream from the dam were negatively affected by large scale sediment transport and habitat alteration following dam removal, but this appears to be a short term response. Based on our observations and experiences in this study, we provide a list of issues to evaluate when considering future dam removals. 相似文献
513.
Chromosome analysis in a boy aged 10 months, with psychomotor retardation, revealed the fragile X-chromosome in lymphocytes and skin fibroblasts cultured in low folate medium (TC 199). Amniocentesis and chromosomal analysis had been carried out during pregnancy because of advanced maternal age. Review of the slides from amniotic fluid cells grown routinely in low folate medium showed the marker X in 10.6 per cent of the metaphases. Possible explanations for the appearance of the marker X in amniotic cell culture are discussed. 相似文献
514.
The prenatal diagnosis of thrombocytopenia absent radius syndrome in both dizygotic twins utilizing ultrasound, radiography and fetoscopy is described. 相似文献
515.
Karen?B.?London Robert?L.?JeanneEmail author 《Behavioral ecology and sociobiology》2003,54(6):539-546
In social insects the level of defensive effort generally increases with colony size, but the effects of the size of the defending adult population and the size of the brood population being defended have not been separated. We used pre-emergence-stage colonies of the swarm-founding wasp, Polybia occidentalis, to distinguish the effects of these two parameters on the intensity of colony defense. We elicited defensive behavior by using both mechanical (taps) and chemical (alarm-pheromone-containing venom) stimuli, and scored the responses as the number of attacks on a standard target. The intensity of defense increased linearly throughout the colony's first 25 days of development, despite the decrease in absolute numbers of adults during the same period. That is, the per capita attack rate increased strongly during this period, leading us to conclude that the intensity of defense is a function of the colony's investment in brood and not of the number of defending adults. We provide evidence that the increase is attributable neither to sensitization due to frequent disturbance, nor to the aging of the adult wasps. We further show that defensive effort on a per capita basis decreased with increasing size across colonies, whether colony size was measured as number of adults or as investment in brood. This pattern suggests that the cost-benefit relationship of defending the colony changes with colony size.Communicated by R.F.A. Moritz 相似文献
516.
Beverly A. Dale Tracy B. Perry Karen A. Holbrook Emily F. Hamilton Vyta Senikas 《黑龙江环境通报》1986,6(1):37-44
This paper describes a method for biochemical analysis of proteins from fetal skin biopsy samples. The method has wide potential application for diagnosis of disorders with a known protein abnormality detectable by protein staining or a specific antibody. Analysis requires a single 1 mm biopsy, is rapid (2 days) and extremely sensitive. In the present study, fetal skin biopsies from normal fetuses and a fetus at risk for lamellar ichthyosis were obtained. The epidermis or hairs with attached follicular cells were dissected from the remaining skin. Proteins were extracted and separated by SDS-polyacrylamide gel electrophoresis. Proteins from duplicate gels were transferred to nitrocellulose and immunostained for the acidic and basic keratins and for the keratin filament associated protein, filaggrin, using monoclonal antibodies. All samples contained keratins typical of fetal epidermis at 20 weeks gestation. Presence of filaggrin is variable at this age and depends on the presence of keratinized cells of hair canals. No keratin abnormalities in the fetus at risk for lamellar ichthyosis were detected, however, in one presumably normal biopsy, an abnormally low proportion of the 67 kd keratin and the presence of follicular keratins were evident. These results demonstrate that biochemical analysis of fetal biopsies is possible, thus increasing the diagnostic potential of the fetal biopsy procedure for disorders in which a known protein or antigen is altered in utero. 相似文献
517.
Dr Wayne S. Stanley G. Shashidhar Pai Edgar O. Horger III Yan Yongshan Karen S. McNeal 《黑龙江环境通报》1988,8(8):565-569
Premature centromere separation (PCS) was detected in amniocytes after an amniocentesis was done because of markedly elevated maternal serum alpha-fetoprotein values in a healthy primiparous young woman. PCS has been associated with the Roberts-SC phocomelia syndrome (RS). By 23 weeks' gestation, ultrasonic evaluations did not reveal abnormal fetal development. The pregnancy continued and a male infant was born with mild manifestations of RS. PCS was confirmed in cord blood lymphocytes. This case illustrates that PCS, when detected in amniotic fluid cell cultures, requires a thorough evaluation. 相似文献
518.
Parasite faunas,testosterone and secondary sexual traits in male red-winged blackbirds 总被引:3,自引:0,他引:3
Patrick J. Weatherhead Karen J. Metz Gordon F. Bennett Rebecca E. Irwin 《Behavioral ecology and sociobiology》1993,33(1):13-23
Summary We examined associations among parasite infections, secondary sexual traits and testosterone in male red-winged blackbirds sampled at the start of the breeding season. Parasites quantified included ectoparasitic lice and mites and endoparasitic blood protozoans, nematodes, trematodes and cestodes. Secondary sexual traits that we quantified included body size, epaulet size and color, song repertoire size and song switching rate, and behavioral responses to male and female models. Overall we found few significant associations between parasites and secondary sexual traits, between secondary sexual traits and testosterone, or between parasites and testosterone. In addition, most parasite taxa appeared to infect birds independently, although the low prevalence (<50%) of many of the parasites meant that our sample sizes were too small to detect weak associations. Our most promising results were obtained for ectoparasitic mites, which tended to occur on birds uninfected with other parasites, on birds with longer epaulets, and on birds with higher levels of testosterone. Epaulet length and testosterone are both probable correlates of dominance in this species. Further research will be required to determine whether there is a causal link between the immunosuppressive effects of testosterone and the mite infections, and between testosterone, epaulet length and male mating success.
Correspondence to: P. Weatherhead 相似文献
519.
Before populations of green turtles (Chelonia mydas) were severely reduced by human overexploitation, the seagrass Thalassia testudinum was intensively grazed by green turtles in the Caribbean. To explore how nutrient composition of T. testudinum pastures responds to intense grazing pressure, we simulated green turtle grazing in 15 plots (each 3 m × 3 m) for 16 months
in the central Bahamas. Comparisons of clipped plots with 15 adjacent control (unclipped) plots revealed that simulated grazing
resulted in significantly higher energy, nitrogen, phosphorus, lignin, cutin, and condensed tannin content in blades in clipped
plots, but sediment organic content was not affected. By continually re-cropping blades in grazing plots, turtles ingest young,
actively growing blade tissue with higher energy, nitrogen, and phosphorus concentrations. Our 16-month clipping trial did
not generate the expected decline in nutrient content in T. testudinum blades under intensive grazing. However, significant decreases in nitrogen and organic matter reserves in rhizomes, with
declines apparent after 16 and 11 months, respectively, indicate that nutrient content of blades and/or blade productivity
may decline under continued clipping. 相似文献
520.
To determine whether life history differences can occur in salt marsh fishes that occupy different habitats within the same
marsh, we compared reproductive allocation in female mummichog (Fundulus heteroclitus) inhabiting creeks and ponds of a coastal salt marsh in southern New Jersey, USA during the spring and summer of 2001 and
2002. Females were collected in phase with the lunar spawning cycle from four sites of each habitat type, and assessed for
gonad-to-body-mass ratio and growth increment. Annual reproductive allocation, expressed as a percent of somatic mass, was
estimated for each site and year from the gonadosomatic indices of individuals collected during each spawning period. Mummichogs
from creeks showed little change in annual reproductive allocation from 2001 to 2002, whereas those inhabiting ponds showed
a significant increase between these years. Seasonal reproductive patterns indicated that pond females cease spawning at least
one lunar cycle earlier than creek fish. While ponds experienced considerably higher maximum summer temperatures than creeks
as well as near-anoxic pre-dawn conditions, neither of these variables explained a significant amount of variation in annual
reproductive allocation. In contrast, annual reproductive allocation of mummichogs in a pond correlated with its flood frequency
in both years of study. Our results suggest that while the length of the spawning season differs in mummichogs inhabiting
marsh creeks and ponds, annual reproductive allocation depends more upon the hydrodynamic conditions of the particular waterbody
than its habitat type per se. 相似文献