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排序方式: 共有221条查询结果,搜索用时 62 毫秒
81.
William H. Stickel Lucille F. Stickel Russell A. Dyrland Donald L. Hughes 《Environmental monitoring and assessment》1984,4(2):113-118
Formalin preservation, freezing, spoiling followed by freezing, and phenoxyethanol were compared in terms of concentrations of DDT, DDD, DDE, endrin, and heptachlor epoxide measured in brain, liver and carcass of birds fed dietary dosages of pesticides and in spiked egg homogenate. Phenoxyethanol proved to be an unsatisfactory preservative; the amount of extractable lipid was excessive, and measurements of concentrations in replicates were erratic. Concentrations of residues in formalin-preserved and frozen samples did not differ significantly in any tissue. Percentage lipid in brains and eggs, however, were significantly lower in formalin-preserved samples. Samples of muscle and liver that had been spoiled before freezing yielded less DDD, and muscle samples yielded more DDT than formalin-preserved samples. We conclude that formalin preservation is a satisfactory method for preservation of field samples and that the warming and spoiling of samples that may occur unavoidably in the field will not result in misleading analytical results. 相似文献
82.
Multiple mating by females with different males (polyandry) is difficult to explain in many taxa because it carries significant
costs to females, yet benefits are often hard to identify. Polyandry is a derived trait in social insects, the evolutionary
origins of which remain unclear. One of several leading hypotheses for its evolution is that it improves division of labour
by increasing intra-colonial genetic diversity. Division of labour is a key player in the ecological success of social insects,
and in many successful species of ants is based on morphologically distinct castes of workers, each with their own task specialisations.
Atta leaf-cutting ants exhibit one of the most extreme and complicated forms of morphologically specialised worker castes and
have been reported to be polyandrous but with relatively low mating frequencies (~2.5 on average). Here, we show for the first
time that there is a significant genetic influence on worker size in Atta colombica leaf-cutting ants. We also provide the first estimate of the mating frequency of Atta cephalotes (four matings) and, by analysing much higher within-colony sample sizes, find that Atta are more polyandrous than previously thought (approximately six to seven matings). The results show that high polyandry and
a genetic influence on worker caste are present in both genera of leaf-cutting ants and add weight to the hypothesis that
division of labour is a potential driver of the evolution of polyandry in this clade of ants. 相似文献
83.
84.
Francisco Leitão Vânia Baptista Maria Alexandra Teodósio Samantha Jane Hughes Vasco Vieira Luís Chícharo 《Regional Environmental Change》2016,16(1):163-176
Evaluating the effects of fishing and environmental factors on fish populations are fundamental tenets of fisheries science. In this study, we assess associations between environmental variables (sea surface temperature; North Atlantic Oscillation index; upwelling; wind magnitude; westerly winds; northerly winds; river discharge) and fishing variables (fishing effort) in Diplodus sagus catch rates accounting for regional analyses (northwest coast; southwest coast and Algarve—Algarve south coast). Different time series models for data fitting (multi-model approach) were used. The models were lagged, according to species fishing recruitment age based on the hypothesis that fisheries catches depend on larvae recruitment and survivorship. D. sargus catch rates across areas were unrelated to fishing effort but correlated to environmental variables, with seasonal events explaining much of the variability in trends. On the northwestern coast, the catch rates were mainly set by sea surface temperature (SST) and wind magnitude; however, southwestern coast catch rates were set by NAO winter. On the south coast, only one statistical model (SST, upwelling and westerly winds) associated spring conditions with D. sargus catch rates. The multi-model approach revealed autumn, winter and spring seasonal effects to be related with northwest, southwest and Algarve coastal catch rates, respectively, indicating a possible coastal longitudinal gradient related with given periods of spawning and larval availability. The metadata analysis yielded different results from the regional analyses. In summary, marine resource management should take regional environment characteristics and variability into account when determining sustainable catch rates in given areas for species with high habitat site fidelity. 相似文献
85.
Andrew O. Hughes Jon M. Olley Jacky C. Croke Ian T. Webster 《Journal of environmental radioactivity》2009,100(10):858-865
Fallout 137Cs has been widely used to determine floodplain sedimentation rates in temperate environments, particularly in the northern hemisphere. Its application in low fallout, tropical environments in the southern hemisphere has been limited. In this study we assess the utility of 137Cs for determining rates of floodplain sedimentation in a dry-tropical catchment in central Queensland, Australia. Floodplain and reference site cores were analysed in two centimetre increments, depth profiles were produced and total 137Cs inventories calculated from the detailed profile data. Information on the rates of 137Cs migration through local soils was obtained from the reference site soil cores. This data was used in an advection–diffusion model to account of 137Cs mobility in floodplain sediment cores. This allowed sedimentation rates to be determined without the first year of detection for 137Cs being known and without having to assume that 137Cs remains immobile following deposition. Caesium-137 depth profiles in this environment are demonstrated to be an effective way of determining floodplain sedimentation rates. The total 137Cs inventory approach was found to be less successful, with only one of the three sites analysed being in unequivocal agreement with the depth profile results. The input of sediment from catchment sources that have little, or no, 137Cs attached results in true depositional sites having total inventories that are not significantly different from those of undisturbed reference sites. 相似文献
86.
Melissa Hughes Stephen Nowicki William A. Searcy Susan Peters 《Behavioral ecology and sociobiology》1998,42(6):437-446
One hypothesis for the function of song repertoires is that males learn multiple song types so that they may share songs
with neighbors, allowing them to match during territorial interactions. In at least one song sparrow population, in Washington,
territorial males share a high proportion of song types with their neighbors and use these shared songs in matching. We recorded
song sparrows in Pennsylvania and quantified sharing of whole songs and song segments. We found that song sharing is an order
of magnitude less common in the Pennsylvania population. We found sharing of song segments to be significantly more common
than the sharing of whole songs in three of the five fields we examined, while we found no significant differences between
whole and partial song sharing in the remaining two fields. Finally, we found no evidence that sharing is greater between
birds in the same field compared to birds in different fields. Taken with the data from Washington song sparrows, these results
provide evidence for intraspecific geographic variation in the organization of song repertoires, and suggest that song sharing
has not been a strong selective force in the evolution of song repertoires in song sparrows as a species. Furthermore, Washington
and Pennsylvania song sparrows differ in how they learn song, in that Washington birds copy whole songs, while Pennsylvania
birds appear to copy and recombine song segments, as has been found in laboratory studies of song learning. Thus both song
learning and the function of song repertoires differ between populations of song sparrows. Such intraspecific geographic variation
offers a unique opportunity to explore the ecological and historical factors which have influenced the evolution of song.
Received: 30 June 1997 / Accepted after revision: 8 March 1998 相似文献
87.
88.
We report the use of DNA probes to determine carrier status in three young women from a large kindred with Norrie disease. One of the women requested prenatal diagnosis during pregnancy. In this pedigree, Norrie disease was not characterized by a deletion at DXS7. 相似文献
89.
The thalli ofHalimeda tuna (Ellis & Solander) grow horizontally from rocky surfaces and present an upper and lower surface which can be colonized by epiphytes. Thalli ofH. tuna were collected twice a month from March 1985 to March 1986 at Tossa de Mar (northeast Spain). Thirty five species of hydroid were recorded living onH. tuna thalli; of these, the 15 most abundant species were classified into three groups on the basis of their horizontal zonation on the thalli: those most abundant on the proximal, medial or distal articles. Those hydroids common on the proximal (oldest) articles were relatively large and were present throughout the year, those common on the medial articles were smaller and often occurred in dense monospecific patches, while those common on the distal (youngest) articles were present for only short periods and were the most opportunistic hydroids found onH. tuna. We hypothesize that this zonation reflects interspecific niche-selection, enabling successful competition for space with other hydroids, algae and bryozonas. Three hydroid species were more abundant on the upper surfaces of the algae than on the lower, probably because of gravitationally enhanced settlement of planula larvae coupled with (unusually) limited hydrorhizal growth on the underside. Three opportunistic species were more common on the lower surfaces of the thalli, possibly reflecting the greater availability of substratum in the shade, where epiphytic algae were less abundant. Many hydroids declined in abundance in summer because of the death of old thalli, the growth of new thalli and of apical articles on existing thalli, and possibly because of interspecific competition with epiphytic algae. The death of old thalli and the growth of new thalli reduced the abundance of epiphytic algae; this may have facilitated the increase in abundance of hydroids recorded in the autumn. 相似文献
90.
Adam D. Hughes Maeve S. Kelly David K. A. Barnes Ana I. Catarino Kenneth D. Black 《Marine Biology》2006,148(4):789-798
Fatty acid analyses are emerging as a powerful technique to probe trophic interactions between organisms. In this paper, the
application of both this procedure and gonad index (GI) determination on two populations (intertidal and subtidal) of the
echinoid Psammechinus miliaris is reported. The investigation spanned the 3-month spawning period of Scottish west coast populations. In both populations
a progressive decrease in the GI was found, coupled with an increasing maturity stage (from mature to spent). Sexual maturation
and decrease in GI was synchronous between the two populations. In conjunction, there were distinct changes in gonad biochemistry.
Differences in the fatty acid composition of the gonad reflected the changes in sexual maturation. Mature males and females
had significant differences in the fatty acid composition of their gonads, whereas post-spawned individuals showed no gender
differences. Male urchins had higher levels of polyunsaturated fatty acids (PUFAs) compared to females, and there was a dramatic
reduction in the fatty acids 22:6(n−3) and 20:5(n−3) with increasing maturity stage. Using multivariate statistical techniques, these changes in the fatty acid composition
of the sea urchin gonad were linked to habitat related diet differences combined with gender differences. These changes in
the fatty acid signatures clearly reflect the dual function of the gonad as both a nutrient store and a reproductive organ. 相似文献