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111.
SERGEY SHABALA JIAYIN PANG MEIXUE ZHOU LANA SHABALA TRACEY A. CUIN PETER NICK & LARS H. WEGNER 《Plant, cell & environment》2009,32(2):194-207
Nutrient acquisition in the mature root zone is under systemic control by the shoot and the root tip. In maize, exposure of the shoot to light induces short-term (within 1–2 min) effects on net K+ and H+ transport at the root surface. H+ efflux decreased (from −18 to −12 nmol m−2 s−1 ) and K+ uptake (∼2 nmol m−2 s−1 ) reverted to efflux (∼−3 nmol m−2 s−1 ). Xylem probing revealed that the trans-root (electrical) potential drop between xylem vessels and an external electrode responded within seconds to a stepwise increase in light intensity; xylem pressure started to decrease after a ∼3 min delay, favouring electrical as opposed to hydraulic signalling. Cutting of maize and barley roots at the base reduced H+ efflux and stopped K+ influx in low-salt medium; xylem pressure rapidly increased to atmospheric levels. With 100 m m NaCl added to the bath, the pressure jump upon cutting was more dramatic, but fluxes remained unaffected, providing further evidence against hydraulic regulation of ion uptake. Following excision of the apical part of barley roots, influx changed to large efflux (−50 nmol m−2 s−1 ). Kinetin (2–4 µ m ), a synthetic cytokinin, reversed this effect. Regulation of ion transport by root-tip-synthesized cytokinins is discussed. 相似文献
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LARS WERDELIN FLS MARGARET E. LEWIS FLS 《Zoological Journal of the Linnean Society》2001,132(2):147-258
This paper consists of a taxonomic and systematic revision of the extinct felid genus Dinofelis (Felidae, Ma-chairodontinae) and an analysis of its ecomorphology and evolution. Dinofelis has a broad distribution, with material from all northern continents and Africa, the latter of which was the apparent centre of evolution of the genus. We describe new material of Dinofelis from a number of sites in eastern Africa and reconsider all previously described material. We name two new species and identify several other distinct species-level taxa but refrain from naming these due to a paucity of well-preserved material. At the same time, we synonymize the two named Asian species, D. cristata and D. abeli , of which the former has priority. There are few characters useful in systematic analysis, but we can suggest at least one migration from eastern to southern Africa. Ecomorphological analysis of both craniodental and postcranial characters suggests that Dinofelis in many respects converged on modern pantherine cats in morphology and behaviour, a trend culminating in the South African D. barlowi and the Asian D. cristata , which are the most pantherine-like of all machairodont felids. This trend is reversed in the evolution of the youngest species, D. piveteaui , which is also the most machairodont in its ecomorphology. The timing of the extinction of Dinofelis is difficult to determine. Outside Africa material is scarce at all times, while in Africa the apparent extinction of Dinofelis at about 1.4 Mya coincides with the end of the good, semi-continuous fossil record present in eastern Africa from about 4 Mya onwards. Dating of Kanam East (with D. piveteaui) to the Jaramillo Subchron (1.070-0.990 Mya) suggests possible survival considerably later. Thus, the extinction datum for Dinofelis cannot at present be firmly established. 相似文献
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LARS WERDELIN F.L.S. 《Zoological Journal of the Linnean Society》1988,93(2):93-105
Samples of the Miocene hyaenid Ictitherium from China and Pikermi, Greece, are analysed statistically. Ictitherium viverrinum Roth & Wagner, 1854 and Ictitherium gaudryi Zdansky, 1924, are found to be conspecific. Ictitherium sinense Zdansky, 1924 is also reduced to synonymy with Ictitherium viverrinum. Ictitherium kurteni sp. nov. differs from 1. viverrinum particularly in its large Cs and large and broad P3 . 相似文献
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LARS VILHELMSEN 《Biological journal of the Linnean Society. Linnean Society of London》2004,82(2):139-160
The phylogenetic relationships of the fossil orussid taxa Mesorussus taimyrensis and Minyorussus luzzi are examined by analysing them together with a large data set compiled previously for the extant Orussidae. The fossils are placed in an unresolved trichotomy with the extant Orussidae. The phylogeny is used for evaluating the hypothesis that the ancestors of the family had reduced body size; the results of this analysis are inconclusive. The biogeographical history of the Orussidae is explored. The common ancestor of the family was probably widespread, the initial splitting events taking place prior to or coinciding with the separation of Laurasia from Gondwana. Later putative vicariance events can be correlated with the gradual breakup of Gondwana. However, the biogeographical history of the Orussidae is dominated by speciation within regions and dispersal. The minimum age of the common ancestor of the Orussidae is >180 Myr when estimated from the biogeographical pattern, >95 Myr when estimated from the phylogenetic position of the fossils; the earlier date is considered to be the most likely. © 2004 The Linnean Society of London , Biological Journal of the Linnean Society , 2004, 82 , 139–160. 相似文献
116.
Trends in floral scent chemistry in pollination syndromes: floral scent composition in hummingbird-pollinated taxa 总被引:2,自引:0,他引:2
JETTE T. KNUDSEN LARS TOLLSTEN INGA GROTH GUNNAR BERGSTRÖM ROBERT A. RAGUSO 《Botanical journal of the Linnean Society. Linnean Society of London》2004,146(2):191-199
We studied an assemblage of 17 species of bird-pollinated Ecuadorian plants (from 14 angiosperm families), including taxa pollinated by short-billed (trochiline) and sickle-billed (hermit) hummingbirds. Hummingbirds are widely supposed to ignore fragrance while visiting flowers. We collected floral headspace odours in order to test the general prediction that specialist hummingbird-pollinated flowers are scentless. In nine out of 17 of these species we failed to detect any odours using gas chromatography-mass spectrometry (GC-MS), whereas the remaining eight species produced trace levels of volatile compounds. Most of these odour compounds were of terpenoid or lipoxygenase derivation and are commonly emitted by vegetative as well as floral plant tissues. Further studies will be required to determine whether these weak odours attract alternative pollinators, repel enemies or represent vestiges of a scented ancestry. © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 146 , 191–199. 相似文献
117.
Nitrate leaching from three afforestation chronosequences on former arable land in Denmark 总被引:1,自引:0,他引:1
KARIN HANSEN LARS ROSENQVIST† LARS VESTERDAL PER GUNDERSEN 《Global Change Biology》2007,13(6):1250-1264
In regions dominated by agricultural activities, nitrogen (N) is recognized as a major pollutant in aquatic environments. In north‐western Europe, afforestation of agricultural land is part of a strategy to improve water quality. In Denmark, former arable land has been afforested during the past 40–50 years. This study evaluated the effect of afforestation of former arable land on nitrate leaching, based on three afforestation chronosequences. Precipitation, canopy throughfall and soil water were collected and soil moisture was monitored at two Danish locations, Vestskoven (nutrient‐rich, medium deposition) and Gejlvang (nutrient‐poor, high deposition). Afforestation was performed using Norway spruce [Picea abies (Karst.) L.] and common oak (Quercus robur L.) at Vestskoven and Norway spruce at Gejlvang. The results suggest that afforestation of former arable land initially leads to lower nitrate leaching than that occurring under the former agricultural land use, and largely below the standard of 50 mg NO−3 L−1 for groundwater to be utilized as drinking water. Nitrate concentrations became almost negligible in forest stands of 5–20 years of age. However, after canopy closure (>20 years) nitrate concentrations below the root zone and nitrate leaching tended to increase. This was attributed to increased N deposition with increasing canopy development and decreased N demand once the most N‐rich biomass compartments had been built up. Nitrate leaching started to increase at a throughfall deposition level of about 10 kg N ha−1 yr−1. Compared with nutrient‐poor sandy soils, nutrient‐rich clayey soils appeared more vulnerable to disturbance of the N cycle and to increased N deposition, leading to N saturation and enhanced nitrate leaching. In approximately the first 35 years after afforestation, nitrate leaching below the root zone was generally higher below oak than below Norway spruce. 相似文献
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