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281.
Ariel Novoplansky 《Oecologia》1991,88(1):138-140
Summary
Portulaca oleracea seedlings avoid growing in the direction of neighbouring plants even when they are very small or remote. The present study was designed to determine the relative effect on the development of Portulaca seedlings of light availability (i.e. the resource level) as compared with spectral composition (i.e. the signal of future competition for the resource). The plants were subjected to various intensities of photosynthetic light and red/far-red (R/FR) ratios from opposite directions. The seedlings became recumbent preferentially towards the direction with the lower FR light, even when this meant growing towards plastic that absorbed 20 times more photosynthetic light. A preference for the direction with higher photosynthetic light over lower FR was also found, though only under extreme light differences. The response of the seedlings was not absolute: the orientation chosen depended on the light received from other alternative directions. 相似文献
282.
283.
Naturally growing plants are able to plastically respond to myriad environmental challenges and opportunities. When confronted
with multiple stresses, plants are expected to be able to prioritize their responses according to immediacy and predicted
acuteness of these stresses. Here, we studied the interactive effects of competition and nutrient deprivation on growth responses
of damaged Trifolium purpureum plants to salivary cues of a mammalian grazer. Salivary cues elicited marked growth responses in damaged but otherwise well-nourished
and competition-free T. purpureum plants; however, this positive effect was annulled under Stipa capensis competition and was reversed under nutrient deficiency. The results suggest that the magnitude and direction of the effects
of salivary cues on plant growth depend on an intricate prioritization of plant responses to prevailing and expected challenges
and that T. purpureum plants perceive competition as a more acute stress than grazing. While herbivore saliva enables plants to reliably differentiate
between herbivory and physical damage, the limited correlation between prevailing and future herbivory might reduce the informative
value of salivary cues, rendering their effects weaker than those of prevalent competition and nutrient deficiency, whose
continued detrimental effects are usually highly predictive. The results stress the importance of further studying the interactive
effects of the acuteness and reliability of prevailing and anticipated stresses, and the informational content and adaptive
value of environmental cues under various environmental circumstances. 相似文献
284.
Summary The hygrochastic apparatus in Anastatica hierochuntica was investigated from the standpoint of morphology of the skeleton and fruit and its contribution to the regulation of seed dispersal in accordance with the water conditions.Water absorption by the dry skeletons upon shoot immersion under laboratory conditions is a rapid process requiring only a few minutes. It is followed by a slow opening of the curled branches of the skeleton. Maximal opening is attained by the saturated skeletons in approximately 2h. Absorption of water and subsequent opening occur also when only the main root of the skeleton is immersed in water. The process was duplicated also by intact skeletons irrigated in situ. Skeletons closure in response to evaporation is initially slow, noticable curling of the branches obtained only after 60% of the water is lost from the saturated skeletons. Opening of the skeleton exposes most of the fruits to the force of falling raindrops. The fact that no spontaneous opening of fruits occurred under most laboratory procedures of skeleton immersion suggests that in nature two successive processes occur: the skeletons must first uncurl-hygrochasticly so that raindrops can impinge forcefully on the appendages of the fruit valves and thus cause seed release by ombrohydrochory. Under adequate rainfall, the first fruits to open are those at the outer infructescences; heavier rainfall will release seeds from the upper fruits of the inner infructescences, and later, from fruits at their bases. The force that binds the valves of the fruits to the septa is variable, its strength correlated with different structure of the fruist at different positions on the skeleton. This ensures a rate of seed release commensurate with the rainfall, and secures at least a minimum of water for the first seeds. The heterogeneity of skeleton populations insofar as age of the plants is concerned, further ensures that seed dispersal in a given area will be proportional to the amount of rainfall. 相似文献
285.
The properties of laccase isolated from Schinus molle, including its MW, amino acid and carbohydrate composition, are described. The enzyme is distinct from Rhus laccase both in Km and in carbohydrate composition. 相似文献
286.