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91.
The influence of the root holoparasitic angiosperm Orobanche minor Sm. on the biomass, photosynthesis, carbohydrate and nitrogen content of Trifolium repens L. was determined for plants grown at two CO2 concentrations (350 and 550 μmol mol−1 ). Infected plants accumulated less biomass than their uninfected counterparts, although early in the association there was a transient stimulation of growth. Infection also influenced biomass allocation both between tissues (infected plants had lower root:shoot ratios) and within tissues:infected roots were considerably thicker before the point of parasite attachment and thinner below. Higher concentrations of starch were also found in roots above the point of attachment, particularly for plants grown in elevated CO2 . Elevated CO2 stimulated the growth of T. repens only during the early stages of development. There was a significant interaction between infection and CO2 on growth, with infected plants showing a greater response, such that elevated CO2 partly alleviated the effects of the parasite on host growth. Elevated CO2 did not affect total O. minor biomass per host, the number of individual parasites supported by each host, or their time of attachment to the host root system. Photosynthesis was stimulated by elevated CO2 but was unaffected by O. minor . There was no evidence of down-regulation of photosynthesis in T. repens grown at elevated CO2 in either infected or uninfected plants. The data are discussed with regard to the influence of elevated CO2 on other parasitic angiosperm-host associations and factors which control plant responses to elevated CO2 . 相似文献
92.
93.
MONDAL M. F.; BREWSTER J. L.; MORRIS G. E. L.; BUTLER HEATHER A. 《Annals of botany》1986,58(2):197-206
Bulb development was followed in four onion cultivars growingin controlled environments under 17 h days in factorial combinationsof photon-flux densities (PFD) of 111 and 333 µmol m2s1 with red: far-red spectral ratios (R : FR) of 2.88and 1.41. A PFD of 111with R : FR of 0.86 was used in a secondexperiment. The lower the R : FR or the higher the PFD the higherthe mean bulbing ratio and the ratio of bulb plus sheath toleaf blade dry weight and the earlier the bulb swelling. LowerR : FR accelerated scale initiation as did the higher PFD underR : FR 2.88 but not under R : FR 1.41. In high PFD bulb swellingoccurred before scale initiation because many sheaths of bladedleaves thickened, but in low PFD and low R : FR bulb swellingand scale initiation were concurrent. In the low PFD a low R: FR increased soluble carbohydrate concentrations in sheathsand scales compared to high R : FR. In high PFD, soluble carbohydrateconcentrations did not vary with R : FR and were higher thanunder low PFD. Onion, Allium cepa L., bulb, photon flux density, red: far-red ratio, light spectral quality, soluble carbohydrate 相似文献
94.
BRIAN D. E. CHATTERTON HEATHER L. WHITEHEAD 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1987,20(1):67-74
A sample containing inarticulate acrotretid brachiopods, from the Silurian Clarita Formation of Oklahoma, was studied to determine the occurrence, nature and frequency of boring in the shells, and the possible identity of the boring organism. Specimens of Artiotreta parva Ireland, 1961 are abundant and specimens of Opsiconidion n. sp. and Acrotretella siluriana Ireland, 1961 are rare in the samples studied. All of the borings discovered are in A. parva except for one, which is in a specimen of O. n. sp. The boreholes are considered to be of predatory origin, and are similar in morphology to borings made by Recent gastropods. The small countersunk boreholes are equally frequent on pedicle and brachial valves, but preferentially located in particular regions of each valve. Boring frequency is high. The identity of the boring organism has not been determined, but is considered to be a soft bodied predator or an archaeo-gastropod. 相似文献
95.
SHERWIN HEATHER W.; PAMMENTER N. W.; FEBRUARY ED; VANDER WILLIGEN CLARE; FARRANT JILL M. 《Annals of botany》1998,81(4):567-575
Myrothamnus flabellifoliusWelw. is a desiccation-tolerant (resurrection)plant with a woody stem. Xylem vessels are narrow (14 µmmean diameter) and perforation plates are reticulate. This leadsto specific and leaf specific hydraulic conductivities thatare amongst the lowest recorded for angiosperms (ks0.87 kg m-1MPa-1s-1;kl3.28x10-5kg m-1MPa-1s-1, stem diameter 3 mm). Hydraulic conductivitiesdecrease with increasing pressure gradient. Transpiration ratesin well watered plants were moderate to low, generating xylemwater potentials of -1 to -2 MPa. Acoustic emissions indicatedextensive cavitation events that were initiated at xylem waterpotentials of -2 to -3 MPa. The desiccation-tolerant natureof the tissue permits this species to survive this interruptionof the water supply. On rewatering the roots pressures thatwere developed were low (2.4 kPa). However capillary forceswere demonstrated to be adequate to account for the refillingof xylem vessels and re-establishment of hydraulic continuityeven when water was under a tension of -8 kPa. During dehydrationand rehydration cycles stems showed considerable shrinking andswelling. Unusual knob-like structures of unknown chemical compositionwere observed on the outer surface of xylem vessels. These maybe related to the ability of the stem to withstand the mechanicalstresses associated with this shrinkage and swelling.Copyright1998 Annals of Botany Company cavitation, desiccation, hydraulic conductivity, refilling, resurrection plant, root pressure, xylem anatomy,Myrothamnus flabellifolius 相似文献
96.
MONDAL M. F.; BREWSTER J. L.; MORRIS G. E. L.; BUTLER HEATHER A. 《Annals of botany》1986,58(2):187-195
Early and later maturing cultivars of both spring- and autumn-sownonions were sown on two dates at 25, 100 and400 plants m2.High levels of nutrients and irrigation were applied. Both high plant density and early sowing advanced the date atwhich bulb scales, rather than leaf blades, were initiated atthe shoot apex and so advanced the date of maturity by up to46 d. The later maturing spring-sown cultivar showed greaterresponses to density and sowing date than the earlier maturingspring-sown cultivar which in turn was more responsive thanthe autumn-sown cultivars. For each cultivar, maturity date increased linearly with decreasesin the percentage radiation intercepted by the leaf canopy. Onion, Allium cepa L., bulbing, competition, spacing 相似文献
97.
1. The effects of sunflower, Helianthus annuus , and groundcherry, Physalis pubescens , eaten by the tobacco budworm ( Heliothis virescens ), on predation by paper wasps ( Polistes arizonensis ) were examined.
2. Polistes arizonensis foragers took more caterpillars from H. annuus plants than P. pubescens in paired-choice tests.
3. They took longer to locate prey and apparently gave up searching faster on artificial plants mimicking P. pubescens than on artificial plants mimicking H. annuus .
4. In paired-choice tests for chemical effects, wasps chose more caterpillars within H. annuus odour than in P. pubescens odour.
5. They also chose more H. annuus -reared larvae than P. pubescens -reared larvae when they were presented without plants. Handling time was not affected. 相似文献
2. Polistes arizonensis foragers took more caterpillars from H. annuus plants than P. pubescens in paired-choice tests.
3. They took longer to locate prey and apparently gave up searching faster on artificial plants mimicking P. pubescens than on artificial plants mimicking H. annuus .
4. In paired-choice tests for chemical effects, wasps chose more caterpillars within H. annuus odour than in P. pubescens odour.
5. They also chose more H. annuus -reared larvae than P. pubescens -reared larvae when they were presented without plants. Handling time was not affected. 相似文献
98.
99.
MONDAL M. F.; BREWSTER J. L.; MORRIS G. E. L.; BUTLER HEATHER A. 《Annals of botany》1986,58(2):207-219
Field experiments were done to investigate why onion crops witha high leaf area index (LAI) initiate bulb scales and maturesooner than those with a low LAI. When small plants were growneither mixed with large plants or in pure stands, those in themixed stands initiated bulb scales earlier than those in purestands. The timing of bulb development therefore depended onthe size of neighbouring plants and the LAI of the stand andwas not simply determined by the size or age of individual plants.Shading plots with neutral filters which caused no spectralchanges slightly accelerated bulb development compared to unshadedplots but shading by a canopy of climbing pea and bean leaveshad a larger effect. Lack of irrigation advanced bulb maturitybut in the highly irrigated treatments plots of high plant densitystill initiated bulb scales and matured before those of lowdensity. Quantitative relationships between the change in R : FR andeither LAI or total radiation interception were determined foronion leaf canopies. It is suggested that the decrease in thered to far-red spectral ratio (R : FR) as LAI increases maybe the cause of the earlier bulb scale initiation and maturitythat occurs as LAI increases. Onion, Allium cepa (L.), spacing, competition, leaf area index, red: far red, irrigation, nitrogen, shading, bulbing 相似文献
100.