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Allocation of resources to growth and defense against herbivores crucially affects plant competitiveness and survival, resulting
in a specific distribution of assimilates and defense compounds within plant individuals. Additionally, plants rarely experience
stable environmental conditions, and adaptations to abiotic and biotic stresses may involve shifts in resistance to herbivores.
We studied the allocation of phytochemicals in Brassica oleracea (Brussels sprouts) due to leaf age, drought stress and herbivore damage and assessed effects on two lepidopteran herbivores
differing in diet breadth: the generalist Spodoptera littoralis and the specialist Pieris brassicae. Glucosinolates as secondary defense compounds and total nitrogen and carbon were quantified and linked to plant palatability,
i.e., herbivore feeding preference. Herbivore responses were highly species-specific and partially related to changes in phytochemicals.
Spodoptera littoralis preferred middle-aged leaves with intermediate levels of glucosinolates and nitrogen over young, glucosinolate and nitrogen
rich leaves, as well as over old leaves, poor in glucosinolates and nitrogen. In contrast, P. brassicae preferred young leaves. Both species preferred severely drought-stressed plants to the well-watered control, although analyzed
glucosinolate concentrations did not differ. Both S. littoralis and P. brassicae feeding induced an increase of indole glucosinolate levels, which may explain a reduced consumption of damaged plants detected
for S. littoralis but not for P. brassicae. By revealing distinct, sometimes contrasting responses of two insect herbivores to within-plant and stress-mediated intraspecific
variation in phytochemistry of B. oleracea, this study emphasizes the need to consider specific herbivore responses to understand and predict the interactions between
herbivores and variable plants. 相似文献
75.
In contrast to the modern cephalopods, the nautiloids use primarily the chemosensory sense to explore their environment. So far there have been few studies on sexual-selection processes in solitary-living nautiloid cephalopods, but it can be posited that conspecifics are also discovered by odour. In order to determine whether a special area of the rectum, the rectal gland, plays a role in the intraspecific communication processes of Nautilus pompilius, Y-maze experiments were performed. We tested the reaction of juvenile, early-adolescent male and female, and adult male N. pompilius to homogenates of the rectum of male and female conspecifics. As negative controls, homogenates of gills or mantle, or seawater were used. To check the set-up of the experiment, carrion was presented as a positive attractant. We demonstrated that the adult (mature) males significantly preferred the rectum homogenate containing the stimulus of females, whereas the homogenates from males and/or females had no influence on the behaviour of immature animals of both sexes. Our behavioural studies provide evidence that sexually mature male N. pompilius are attracted to females by excretions of the rectum.Communicated by O. Kinne, Oldendorf/Luhe 相似文献
76.
Heinz-Ulrich?ReyerEmail author Bettina?Niederer Attila?Hettyey 《Behavioral ecology and sociobiology》2003,54(3):274-284
In many species, males and females mate with multiple partners, which gives rise to sperm competition and multiple paternity. The experiments on water frogs presented here demonstrate that such sperm competition can affect the structure and dynamics of mixed-species communities. The hybrid frog Rana esculenta (LR) mates with one of its parental species, usually R. lessonae (LL), although in some areas R. ridibunda (RR), to regain the premeiotically eliminated parental genome ("hybridogenesis"). Mixed LL/LR-populations are stable although hybrid numbers should continuously increase at the expense of parental animals, because of differences in female fecundity and other factors. This would finally lead to the extinction of the sexual host, followed by that of the sexual parasite, unless the reproductive superiority of R. esculenta is reduced by other factors, such as lower hybrid male fertility. Eggs from LL- and LR-females were fertilised in vitro by single- and multi-male sperm suspensions of LL-, LR- and RR-males. In all experiments, the proportion of offspring sired by R. esculenta sperm was significantly lower than that sired by R. lessonae or R. ridibunda sperm. Gonad mass, sperm morphology, sperm swimming velocity, and sperm survival did not explain these differences in fertilisation success; nor did gamete recognition and compatibility. Sperm density was the only trait that paralleled fertilisation success, but it offers no explanation either, because densities were equalised for the in-vitro fertilisations. In natural LL/LR populations, the significantly smaller amount, poorer competitive ability and lower long-term survival of R. esculenta compared to R. lessonae sperm will reduce the initial reproductive superiority of hybrids and contribute to the stabilisation of mixed water-frog populations. Differences in fertilisation ability are also likely to be relevant for the structure and dynamics of several other systems with encounters between eggs and sperm from different genotypes, ecotypes, ploidy levels and/or species. 相似文献