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排序方式: 共有204条查询结果,搜索用时 15 毫秒
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FRANCIS L. K. HSU 《American anthropologist》1974,76(2):351-354
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In the Cory's Shearwater Calonectris diomedis boreadis breeding on Selvagem Grande (30̀ 09'N, 15̀52'W), mate fidelity averaged 71.4%. Two-thirds of the changes were the result of the absence of the former mate and one-third only, carried out in its presence, were true divorces. The rate of divorce and the rate of replacement of an absent former mate had increased since the beginning of the 1980s. Among young and inexperienced birds, the rate of divorce decreased with the increase of age and experience before becoming stable. Breeding failure during the previous year increased the probability of divorce. Temporary non-breeding increased both the rate of divorce and the rate of replacement of an absent former mate. 相似文献
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EMILY J. BARLOW FRANCIS DAUNT SARAH WANLESS DAVID ÁLVAREZ JANE M. REID STEPHEN CAVERS 《Ibis》2011,153(4):768-778
Quantifying population genetic structure is fundamental to testing hypotheses regarding gene flow, population divergence and dynamics across large spatial scales. In species with highly mobile life‐history stages, where it is unclear whether such movements translate into effective dispersal among discrete philopatric breeding populations, this approach can be particularly effective. We used seven nuclear microsatellite loci and mitochondrial DNA (ND2) markers to quantify population genetic structure and variation across 20 populations (447 individuals) of one such species, the European Shag, spanning a large geographical range. Despite high breeding philopatry, rare cross‐sea movements and recognized subspecies, population genetic structure was weak across both microsatellites and mitochondrial markers. Furthermore, although isolation‐by‐distance was detected, microsatellite variation provided no evidence that open sea formed a complete barrier to effective dispersal. These data suggest that occasional long‐distance, cross‐sea movements translate into gene flow across a large spatial scale. Historical factors may also have shaped contemporary genetic structure: cluster analyses of microsatellite data identified three groups, comprising colonies at southern, mid‐ and northern latitudes, and similar structure was observed at mitochondrial loci. Only one private mitochondrial haplotype was found among subspecies, suggesting that this current taxonomic subdivision may not be mirrored by genetic isolation. 相似文献
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VIRGILIO HERMOSO FRANCIS PANTUS JON OLLEY SIMON LINKE JAMES MUGODO PATRICK LEA 《Freshwater Biology》2012,57(1):1-9
1. Owing to intensive human use, freshwaters are among the most seriously threatened and modified environments on the planet. Their poor condition and the risk to services that humans need from these ecosystems make their rehabilitation a priority. However, many previous studies have reported the poor performance of many rehabilitation activities. 2. Here, we analyse reasons for this poor performance, focussing on the planning of rehabilitation activities, and propose a new approach. We argue that the failure to include driving factors at a scale adequate to capture the ecological processes involved, together with an insufficient incorporation of socio‐economic aspects, is a key factor leading the poor performance of many rehabilitation activities. 3. We propose a new approach, ‘systematic rehabilitation planning’, that brings together advances made in conservation planning (cost‐effectiveness analysis) and ecosystem science (understanding the complexity of ecosystem processes). This enables planning to be done at the catchment scale, and the trade‐offs between various rehabilitation actions to be integrated and prioritised. 4. Finally, it is important, given the constraints imposed by a lack of knowledge, that the planning process is part of an adaptive cycle where it can benefit from and consolidate the experience gained during the implementation and monitoring stages. 相似文献
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The changes in germinability and phospholipid content of naturallyand artificially aged tomato seeds, variety Kingley Cross, werecompared. Subsequent low temperature pre-sowing treatment (LTPST)was unable to prevent decreases in the germination capacityof aged samples, but significantly improved germination rates.However, in contrast to previous studies on artificial ageingusing the variety Moneymaker, losses of total phospholipid werenot always well correlated with decreased germinability. Totalphospholipid levels in naturally aged seeds were largely unaffectedby pre-sowing treatment, but the proportion of phosphatidylcholinewas greatly increased. These results strongly suggest that lossesof phospholipid are coincidental rather than causative eventsin the loss of seed viability during ageing, and that the patternof changes depends on the type of ageing experienced by theseeds. Controlled deterioration, seed ageing, tomato seeds, seed treatment, phospholipids 相似文献
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