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排序方式: 共有1061条查询结果,搜索用时 46 毫秒
961.
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963.
Venera Ferrito Anna Maria Pappalardo Adriana Canapa Marco Barucca Ignacio Doadrio Ettore Olmo Concetta Tigano 《Marine Biology》2013,160(12):3193-3208
We studied the genetic structure of the Mediterranean killifish Aphanius fasciatus. Analysis of the sequence variation in a 372-bp portion of the mitochondrial control region in 623 fish from 27 sampling sites along the species’ distributional range (Tyrrhenian coast, Sardinia, Sicily, Adriatic coast, Malta, Tunisia, and Greece) yielded 120 distinct haplotypes. Most of the haplotypes are unique, and only 15 % are shared among different populations. The high F ST value (=0.80) suggests a strong population genetic structuring. The phylogenetic analysis based on Bayesian inference, maximum likelihood and maximum parsimony, and the median-joining network show a sharp separation of the Southeastern Sicilian populations (belonging to the Hyblean region) and of the fluvial Tunisian population of Rio Melah from the others. The Adriatic, the Eastern Sicilian, and the Greek populations are well differentiated, while the group of populations from the Central-Western Mediterranean does not show a clear pattern of differentiation. Our findings indicate that the current genetic structuring of A. fasciatus reflects historical geographical patterns occurring within the Mediterranean basin from the Late Miocene to the Pleistocene. The presence of divergent evolutionary entities in the Hyblean region and the Tunisian Rio Melah supports their inclusion as target areas for the conservation of A. fasciatus. 相似文献
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965.
Floral nectar is offered by plants to animals as a reward for pollination. While nectar is typically a clear liquid containing sugar and trace amounts of amino acids, colored nectar has evolved in several plant families. Here we explore the functional significance of the phenolic compounds that impart a dark brown color to the nectar of the South African succulent shrub Aloe vryheidensis. Flowers of this aloe are visited for their nectar by a suite of short-billed birds that are occasional nectarivores, including bulbuls, white-eyes, rock thrushes, and chats. Dark-capped Bulbuls were more likely to probe model flowers containing dark nectar than those containing clear nectar, suggesting a potential signaling function for dark nectar. However, the main effect of the phenolics appears to be to repel "unwanted" nectarivores that find their bitter taste unpalatable. Nectar-feeding honey bees and sunbirds are morphologically mismatched for pollinating A. vryheidensis flowers and strongly reject its nectar. However, the frugivorous and insectivorous birds that effectively pollinate this aloe are seemingly unaffected by the nectar's bitter taste. Thus the dark phenolic component of the nectar appears to function as a floral filter by attracting some animals visually and deterring others by its taste. 相似文献
966.
Elisabet Forsgren Anna Karlsson Charlotta Kvarnemo 《Behavioral ecology and sociobiology》1996,39(2):91-96
In some fish species with paternal care, females prefer to spawn with males whose nests already contain eggs. Several hypotheses
have been put forward to explain this behaviour, such as reduced risk of predation or cannibalism (the dilution effect), increased
parental investment, and mate copying. This experimental study focuses on female mate choice in the sand goby, Pomatoschistus minutus. Females were found to choose males with eggs in their nests. In addition, hatching success increased with clutch size, mainly
because males with larger clutches showed less filial cannibalism. Increased egg survival in large clutches may thus be explained
by a combination of the dilution effect and higher parental investment. In another experiment, females did not seem to copy
the observed mate choice of other females. In conclusion, female preference for males with eggs in their nests is adaptive,
and can be explained by direct benefits, as more surviving offspring are produced.
Received: 23 December 1995/Accepted after revision: 11 May 1996 相似文献
967.
Abstract: Changes in historical disturbance regimes have been shown to facilitate non-native plant invasions, but reinstatement of disturbance can be successful only if native colonizers are able to outcompete colonizing invasives. Reintroduction of flooding in the southwestern United States is being promoted as a means of reestablishing Populus deltoides subsp. wislizenii , but flooding can also promote establishment of an introduced, invasive species, Tamarix ramosissima . We investigated competition between Populus and Tamarix at the seedling stage to aid in characterizing the process by which Tamarix may invade and to determine the potential ability of Populus to establish itself with competitive pressure from Tamarix . We planted seedlings of Tamarix and Populus in five ratios at three densities for a total of 15 treatments. The growth response of each species was measured in terms of height, above-ground biomass, and tissue concentrations of nitrogen and phosphorous. These measurements across treatments were modeled as three-dimensional response surfaces. For both species, Populus density was more important than Tamarix density for determining growth response. Both species were negatively affected by increasing numbers of Populus seedlings. Due to the larger size of the native Populus , we predict that its superior competitive ability can lead to its dominance when conditions allow native establishment. Our results suggest that even in the presence of an invader that positively responds to disturbance, reestablishment of historical flooding regimes and post-flood hydrology can restore this ecosystem by promoting its dominant plant species. 相似文献
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969.
Many Canadian communities are facing resource depletion and high unemployment as a result of a model of economic development which has consistently promoted large capital-intensive, resource-based companies. A new model of sustainable community development is required which incorporates ecological, economic and social concerns. One aspect of sustainable community development is the use and promotion of locally-based and controlled financing mechanisms, including community loan funds, community bonds, and peer lending circles providing micro-credit. Widely successful across the USA and Canada, these 'alternative' financing mechanisms use local control and a proximity to local ecosystems to foster small businesses which are less resource-intensive and create long-term jobs within communities. Improving these financing tools through broader government facilitation of them as innovative public policy instruments, and the incorporation of specific ecological lending and investment screens, could dramatically further the development of healthy communities. 相似文献
970.
Altered menstrual cycles in women with a high dietary intake of persistent organochlorine compounds 总被引:1,自引:0,他引:1
Dietary exposure to persistent organochlorine compounds (POCs) has been found to affect the menstrual cycle in both animals and humans. In Sweden, the major exposure route for POCs is the consumption of fatty fish from the Baltic Sea. Thus, women who eat relatively large amounts of this fish constitute a suitable study group when investigating a possible association between dietary exposure to POC and menstrual cycle disruption. Questionnaires were sent to the exposed women, as well as to a socioeconomically similar cohort of controls, and information was collected on their menstrual cycles. Since the exposed women tended to smoke more than the controls, all results were adjusted for smoking habits. A cohort comparison found that the exposed women on average had 0.46 (95% confidence interval: 0.03, 0.89) days shorter menstrual cycles than controls. However, within the exposed cohort no effects were found of the proxy variables early life exposure and high consumption of Baltic Sea fatty fish. The results give some support to previous results from studies on women with similar exposure, but are not conclusive with respect to whether there is a causal association between POC exposure and menstrual cycle disruption. 相似文献