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21.
GORDON B. CURRY 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1981,14(1):9-20
Extremely variable pedicle morphology is described in a large sample of the Recent articulate brachiopod Terebratulina septentrionalis (Couthouy) from off the coast of Nova Scotia. The majority of these specimens were attached to the shells of living or dead scaphopods by a dense network of pedicle rootlets. Other brachiopods had been lying on the sea-floor anchored solely by the weight of sediment enmeshed within the bush-like network of pedicle rootlets. Some brachiopod larvae had settled on the exposed pedicle rootlets of adults, presumably because of the scarcity of other suitable substrate. Such a mode of life is thought 'to indicate that these brachiopods could survive a further reduction in the available substrate and it is suggested that, should such conditions persist, changes in hard-part morphology would enable descendants of the species to adopt a predominantly free-lying mode of life. Likely morphological adaptions are suggested, based on examples from the fossil record. This evolutionary trend, from attached to free-lying and perhaps vice versa, has occurred many times in the history of the Phylum Brachiopoda, and it is suggested that the mode of life of this T. septentrionalis population provides an important insight into at least one of the possible evolutionary pathways which bring about such transformations. 相似文献
22.
GORDON PRITCHARD 《Ecological Entomology》1980,5(2):165-173
Abstract.
- 1 A population of Tipula sacra was studied intensively from 1969 to 1974 in a series of abandoned beaver ponds. Beavers recolonized the ponds from 1974 to 1976 and again in 1978.
- 2 The basic life-cycle is of 2 years duration, but cohort-splitting occurs in the autumn as a result of some larvae growing faster and completing the life-cycle in 1 year.
- 3 Some periods are more favourable for growth than others and the size of the fast-growing cohort varies from year to year. This insight allows some anomalies in the estimates of population size to be explained and life budgets have been produced for three year-classes.
- 4 The short-fall in realization of egg potential is massive, apparently due to heavy female mortality by predation and the prevention of oviposition by inclement weather.
- 5 Mortality rate is relatively low and constant from stage II larvae until pupation, but increases to adult emergence. There is a correlation between larval density and mortality rate.
- 6 Certain aspects of the life-history (e.g. high fecundity, variability in growth rate) appear to fit the species to life in a temporally unstable habitat.
23.
Analysis of growth during light-induced hook opening in cress 总被引:1,自引:1,他引:0
Abstract. Growth in various regions of the hypocotyls of dark-grown cress seedlings before and after exposure lo continuous white light has been analysed by time-lapse photography. In the dark, growth in the hook was minimal, the upward growth of the seedling being sustained by extension of the shank, especially the uppermost zones. Following irradiation, the hook and the remainder of the hypocotyl showed dissimilar growth responses. Previously growing regions of the shank were inhibited while zones within the hook, especially the apical end of the inner (concave) side, showed marked growth stimulation. These changes in growth rates commenced within 1 h from exposure to the light stimulus and thus considerably preceded any observable changes in hook angle. 相似文献
24.
The present study investigates the effects of triacontanol (CH3(CH2)28CH2OH),on plant growth (root and stem), peroxidase activity (apicalmeristem tissue), and auxin destruction (apical meristem tissue)in Little Marvel dwarf (LM) and Alaskapeas (AP). Triacontanol inhibited root growth in LM comparedto untreated controls. However, root growth in AP tissue wasenhanced by 1.0 mg I1 triacontanol and inhibited by allother treatments, in comparison to untreated controls. Wateruptake in triacontanol-treated AP plants was greater than inuntreated controls, with the converse being the case for LM.Triacontanol treatment caused an increase in peroxidase activityin both LM and AP plants compared to untreated controls. Interms of (114C)IAA destruction, GA3 + 0.01 mg 11triacontanol caused appreciable auxin breakdown (40%) in LMtissue, with GA3 + 0.1 mg 11 triacontanol giving a 43%decrease compared to untreated controls. In AP tissue, 10 µMGA3 increased auxin destruction by 188% whereas 0.1 mg I1triacontanol caused a 20% decrease compared to untreated controls.The effects of triacontanol on root and stem growth, peroxidaseactivity, and auxin destruction appear to be cultivar-specific,with respect to LM and AP varieties of peas. 相似文献
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IAN J. GORDON MALCOLM EDMUNDS JOHN A. EDGAR JAMES LAWRENCE DAVID A. S. SMITH 《Biological journal of the Linnean Society. Linnean Society of London》2010,100(1):180-194
On two occasions, on opposite sides of the African continent (Cape Coast, Ghana, and Dar es Salaam, Tanzania), high adult population densities in the polymorphic butterfly Hypolimnas misippus (a presumed mimic of Danaus chrysippus) were followed by linkage disequilibrium in combinations of fore‐ and hindwing colour patterns. On both occasions, disequilibrium was caused by significant changes in morph frequencies favouring rarer and more mimetic forms. Recaptures were too few for analysis at Dar, although the changes there took place within a single generation and must have been the result of differential survival. Recapture rate data and survival rate estimates at Cape Coast support the hypothesis that selective predation was responsible, as does the observation of synchronous linkage disequilibrium at Dar in the model D. chrysippus, indicating parasitic mimicry. There was clear selection for the perfection of mimicry for forewings at Dar and for hindwings at Cape Coast. Disequilibrium is also reported for two other sites, Legon (Ghana) and Boksburg (South Africa) and, in all four sites, it was associated with an increase in the most mimetic forms. New chemical evidence is presented to support the contention that D. chrysippus is a defended model. Although all the evidence leads to the conclusion that H. misippus is a Batesian mimic of D. chrysippus, many questions remain, particularly with regard to the identity of predators, the episodic nature of selective predation events, and their apparent lack of lasting and significant impact on overall gene frequencies. We conclude that H. misippus presents both challenges and opportunities for studies on mimicry, and we suggest that linkage disequilibrium can be a useful generic indicator for Gestalt predation on polymorphic prey. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 180–194. 相似文献
28.
ANDREW J. GORDON 《American anthropologist》2006,108(3):561-562
Urban Place: Reconnecting with the Natural World. Peggy F. Barlett, ed. Cambridge, MA: MIT Press, 2005. 330 pp. 相似文献
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