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1.
JEFFREY M. BLACK 《Ibis》1995,137(S1):S153-S160
Since 1960, about 2150 Hawaiian Geese or Nene Branta sandvicensis were reintroduced in Hawaii to supplement the remaining wild population of about 30 birds. These geese were released mostly in high mountain sanctuaries. These sites became unsuitable during prolonged drought and the few surviving birds were those which had moved away from the release sites. The geese that survived had moved to, or were released near, agricultural pasture land. About 600 Nene are currently living in the wild; numbers are declining on the island of Hawaii, stable on Maui and increasing on Kauai. Management priorities include enhancement of grasslands, predator control and maximizing genetic diversity. To enable the species to recover, management will probably have to be large scale, intensive and prolonged. Further released captive-bred or translocated Nene should have access to enhanced habitats after predators have been controlled. 相似文献
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Prior to illumination, the embryonic axis of sunflower seedlingsmakes a contribution to the cotyledons which enables them togreen more rapidly when subsequently irradiated with white light.The contributions made to this stimulation by the hypocotylhook, hypocotyl, and roots have been investigated. Greeningin sunflower cotyledons reaches an optimum rate when they are6 d old. The developing embryonic axis not only promotes theattainment of this optimum rate but also aids in the maintenanceof this optimum rate as the cotyledons continue to age. Thisstimulatory effect appears to arise primarily from the rootsand can be duplicated by the exogenous application of benzyladenine. In contrast to previous reports we find that the hypocotyl hookplays no role in the control of greening when present duringillumination. 相似文献
4.
Experiments were carried out to investigate the influence ofatmospheric saturation deficit on the stomatal conductancesof millet and groundnut plants grown in undisturbed soil incontrolled environment glasshouses. Environmental conditionsduring growth were maintained close to those experienced inthe semi-arid tropics. The results demonstrated that the stomatal conductances of well-wateredplants of both species were affected strongly by changes insaturation deficit. The response was stronger at higher irradianceswhen variations in saturation deficit between 1.5 and 3.0 kPacaused 34-fold changes in leaf conductance. However,the stomatal response was greatly reduced or absent in unirrigatedplants in which stomatal conductances were reduced. Reduction of the transpiring leaf area by covering some of theleaves increased the leaf conductances of the remaining leavesand partially restored the stomatal response to saturation deficitin unirrigated plants. Leaf conductance was sensitive to thetranspiring area per plant and declined as the transpiring areaincreased. However, the reduction in mean leaf conductance wasinsufficient to prevent an increase in canopy conductance owingto the increased transpiring area: The results are compared to earlier field data for millet, andthe possible origin of the stomatal response is discussed. 相似文献
5.
Hydroponic sunflower plants were used in a quantitative studyof the relationship between total plant and leaf resistancesto transpirational water movement and transpiration rate. Theresults demonstrate that both resistances are flux-dependentand decline 56-fold during a comparable increase in transpiration.The resistance of excised leaves including the petiole was approximatelyhalf the total plant resistance. Subsequent analyses of the water potential gradients and transpirationalfluxes in whole plants permitted calculation of the magnitudeof the partial resistances imposed by roots, stem, petiole,and leaf. The root and leaf resistances were approximately 50%and 30% of the total resistance respectively. Stem and petiolarresistances were relatively small and both influenced watermovement to the upper leaves similarly. The values obtainedare compared with previous published results obtained usingdiverse experimental techniques. 相似文献
6.
The Onset of Germination Ability in Developing Wheat 总被引:1,自引:0,他引:1
GOSLING PETER G.; BUTLER RICHARD A.; BLACK MICHAEL; CHAPMAN JOHN M. 《Journal of experimental botany》1981,32(3):621-627
The ability of primary wheat grains (cv. Sappo) to germinatewas determined at different times from anthesis. Fresh, prematurelyharvested grains germinated best at low temperatures (<10°C). The temperature range over which appreciable germinationtook place broadened and the maximum percentage germinationachieved increased with lengthening time between anthesis andharvest. Chilling and exogenous applications of GA3 each affectedthe rate of germination and the maximum percentage germinationof grains in their own ways. The results are discussed in relationto the identification of dormancy in wheat grains. 相似文献
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Determining uptake of 'non-labile' soil
cadmium by Thlaspi caerulescens using
isotopic dilution techniques 总被引:3,自引:0,他引:3
JULIAN J. HUTCHINSON SCOTT D. YOUNG STEVE P. MCGRATH HELEN M. WEST COLIN R. BLACK & ALAN J. M. BAKER 《The New phytologist》2000,146(3):453-460
We assessed the ability of several populations of the metal-hyperaccumulator species, Thlaspi caerulescens , to mobilize non-labile cadmium in soils historically contaminated by Pb/Zn mine spoil or sewage sludge. Radio- labile Cd was determined chemically as an ' E -value', [Cd E ], and biologically as an ' L -value', [Cd L ]. For comparison, chloride-extractable Cd, [Cdchlor ], was also determined using 1 M CaCl2 as a single-step soil extractant. Values of [Cd L ] were measured for six populations of T. caerulescens that varied substantially in their ability to assimilate soil Cd, and a non-accumulator species with a similar growth habit, Lepidium heterophyllum . Seeds were sown in soil spiked with 109 Cd and grown for 9–12 wk in a controlled environment room. Values of [Cd L ] were determined from the specific activity of 109 Cd and concentration of Cd in the plant leaves. For the six soils studied, [Cd E ] ranged from 4.9 to 49% of total soil Cd [CdT ]. Values of [Cd L ] were, in general, in close agreement with both [Cd E ] and [Cdchlor ] and substantially less than [CdT ]. However, [Cd L ] showed no correlation with the concentration of Cd in plant tissue, [Cdshoot ]. This suggests that, in the soils studied, T. caerulescens did not mobilize non-labile soil Cd by producing root exudates or altering rhizosphere pH. The results imply that there may be significant restrictions to metal bioavailability, even to hyperaccumulator species, in heavily contaminated soils in which a large proportion of the metal may be present in 'non-labile' forms. 相似文献
9.
Effects of Low Concentration of Ozone, Singly, and in Combination with Sulphur Dioxide on Net Photosynthesis Rates of Vicia faba L. 总被引:3,自引:0,他引:3
Net photosynthesis rates (PN) of Viciafaba plants were measuredin chambers containing either clean air or air containing between50 and 300 parts 109 ozone (O3) with or without 40 parts10 9 SO2. Exposure to O3 concentrations greater than 50 parts 109 for periods of 4 h resulted in reductions in PN with greaterreductions at higher concentrations. After exposure ceased,recovery of pre-exposure PN depended on O3 concentration. Exposureto less than 90. 100 parts 10 9 was followed by completerecovery after 20 h whereas 200-300 parts 10 9 resultedin visible injury and irreversible depression of PN. The additionof 40 parts 10 9 SO2 to O3 significantly decreased Psbut the effect of SO2 declined with increasing O3. The additionof SO2 had no significant affect on recovery patterns. It is postulated that Vicia faba plants are able to toleratethe absorption of O, up to a threshold above which progressivedecreases in PN occur due to effects on photosynthetic processes.The slow and sometimes incompletely reversible effects of O3on PN indicate cellular differences in the injury mechanismand repair capacity compared with the action of SO2 alone. Lowconcentrations of O3 with SO2 result in additive injury to PNsuggesting independent action of the pollutants, but the reductionin SO2 action with increasing O3 indicates a limit for potentialphysiological injury More the onset of visible injury. 相似文献
10.