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21.
M. C. Linton P. H. Crowley J. T. Williams P. M. Dillon H. Aral K. L. Strohmeier C. Wood 《Evolutionary ecology》1991,5(2):93-104
Summary We generated a computer model to analyse the effects of shadow competition for sit-and-wait predators, particularly antlion larvae. The model used a simple foraging assessment rule to determine the quality of an antlion's location, and antlions relocated randomly in their habitat when a location proved to be of low quality. Shadow competition, or competition for food caused when one sit-and-wait predator intercepts moving prey before a second sit-and-wait predator is encountered, was incorporated into the model by restricting antlions to a bounded arena, and having prey for the antlions enter from the arena periphery. Antlions responded to shadow competition by relocating their pits to peripheral areas of their habitat. This peripheral accumulation of pits was most pronounced when antlion densities were high, and when prey availabilities were intermediate. An experimental test with the antlionMyrmeleon immaculatus supported the importance of shadow competition as a cause of observed pit distributions. Only the treatment which incorporated shadowing had pit distributions near the periphery, while the pit distributions in the control treatments did not differ from randomly generated distributions. We conclude that shadowing can influence sit-and-wait predator distributions when the prey distributions and movement patterns generate the conditions necessary for shadowing. But when prey availability is unpredictable, making assessment of patches difficult, or when prey do not originate in the periphery of the habitat, other factors, such as temperature or moisture, could be more important. 相似文献
22.
本文运用石蜡切片法、整体透明法研究了草地早熟禾的假受精现象。结果表明,草地早熟禾在两极核清晰可见时,卵细胞就已自发分裂成原胚,此现象占观察总数88%;但是,其极核必需经过受精过程才能发育为胚乳。 相似文献
23.
Steeve Bourassa Jacques Brodeur & Yves Carrière 《Entomologia Experimentalis et Applicata》2007,124(2):221-228
Overseeding non‐endophytic turfgrass lawns with endophytic turfgrass is considered promising for the development of integrated pest management programs in urban landscapes. In this context, a better understanding of the variability in the preference–performance response of insect herbivores exposed to endophytic grasses could be useful to develop efficient practices. Specifically, while endophytic varieties that are strongly toxic and avoided could provide good control of mobile pests, varieties that are toxic but not avoided could be more suitable for the control of sedentary pests. In this laboratory study, we investigated how the infection of 10 grass varieties by Neotyphodium endophytes affected the feeding performance and preference of newly hatched nymphs of the hairy chinch bug, Blissus leucopterus hirtus Montandon (Heteroptera: Lygaeidae), a common turfgrass pest in north‐eastern USA. We found that endophytes generally induced a strong relationship between feeding performance and preference in this herbivore. However, two endophytic varieties did not conform to this relationship, with one variety being highly toxic but not avoided and the other less toxic but highly avoided. These results provide a solid basis to further explore the impacts of endophytic grasses on the dispersal and survival of insect pests in mixed stands of endophytic and non‐endophytic plants. 相似文献
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Leaf blight symptom caused by Gibberella moniliformis was observed in the seedlings of Kentucky bluegrass (cv. Perfection) in Jinju, Korea, in January 2013. The symptoms first appeared as brown to yellow lesions on leaves, which later became white and bleached. The pathogen was isolated from turfgrass leaves and identified as G. moniliformis by using the internal transcribed spacer (ITS)1 and ITS4 sequences of rRNA. G. moniliformis was confirmed by a pathogenicity test, and the causal agent was reisolated from infected turfgrass. 相似文献
25.
G. Barcaccia A. Mazzucato A. Belardinelli M. Pezzotti S. Lucretti M. Falcinelli 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1997,95(4):516-524
Moving gene(s) responsible for the apomictic trait into crop plants that naturally reproduce through a sexual process would
open up new areas in plant breeding and agricultural systems. Kentucky bluegrass (Poa pratensis L.) is one of the most important forage and turf grasses in temperate climates. It reproduces through facultative aposporous
parthenogenesis, but the reproductive behaviour ranges naturally from nearly obligate apomixis to complete sexuality. In addition
to apomictic reproduction, sexual hybridization may take place. Selfing may also occur, and occasionally reduced egg cells
may develop through parthenogenesis generating (poly)haploids. The inheritance of parental genomes was assessed in Kentucky
bluegrass progenies by employing RAPD markers in combination with flow cytometry (FCM). Nine progenies from different crosses
carried out between completely sexual and highly apomictic genotypes were evaluated in order to probe the reproductive behaviour
of the mother plants and to distinguish the different classes of aberrant plants. Not only were maternals and balanced BII hybrids recorded, but so were (poly)triploid BIII hybrids, selfs, and (poly)haploids. The application of these techniques demonstrated that FCM analysis accurately distinguishes
the n, 2n, and 3n ploidy levels of progenies, and that RAPD markers unequivocally recognize progenies of apomictic and hybrid
origin. The occurrence of aneusomaty was documented in one of the selected sexual genotypes, whose crossed progeny plants
manifested two distinct classes of ploidy. The nomenclature BI was adopted to refer to hybrids with a hypodiploid nuclear condition. On the whole, the FCM analysis confirmed most of the
RAPD data. The combined evaluation of DNA markers and DNA contents proved to be an efficient screening tool for scoring maternal
plants, assessing the genetic origin of aberrant plants, and quantifying the inheritance of parental genomes in Kentucky bluegrass.
Hybrid populations from sexual×apomictic matings that segregate for the mode of reproduction represent a valuable basis for
attempting to identify molecular markers linked to the apomixis gene(s).
Received: 11 November 1996/Accepted: 22 November 1996 相似文献
26.
KINCHEL C. DOERNER WES BRADEN JENNIFER CORK TOM CUNNINGHAM AMANDA RICE BONNIE J. FURMAN DOUG McELROY 《The Journal of wildlife management》2005,69(1):345-355
Abstract: White-tailed deer (Odocoileus virginianus) in Kentucky represent an example of successful wildlife restoration. Eliminated from all but a few remnant areas by the early part of the twentieth century, the species is once again widely distributed and abundant as a result of intensive restocking efforts since the 1940s. Seven DNA microsatellite markers were used to survey the extent and pattern of genetic variation in 322 deer from multiple localities throughout the commonwealth. Six genetically homogeneous regions and 1 heterogeneous region were identified across Kentucky. High levels of allelic diversity were detected with no apparent reduction in heterozygosity, disproportionate loss of rare alleles, or shift in modal allele frequency class as might be expected if the severe historical population size reduction generated a concomitant genetic bottleneck. These results are consistent with predictions of founder-flush models: that rapid population growth may minimize the loss of genetic variability associated with a population bottleneck. Nevertheless, comparisons of our data to that derived from other imperiled taxa suggest that species demographics can also play an important role in determining the genetic consequences of population size reduction and subsequent recovery. Our data also illuminate the critical role of deer from Land Between the Lakes (LBL) as the initial source population from which all extant Kentucky deer are descended. While generally supporting current regional management perspectives, our results argue for recognition of the LBL herd as a distinct management island of genetic and historical value. 相似文献
27.
Prescribed fire has become a common tool of natural area managers for removal of non‐indigenous invasive species and maintenance of barrens plant communities. Certain non‐native species, such as tall fescue (Festuca arundinacea), tolerate fire and may require additional removal treatments. We studied changes in soil N and C dynamics after prescribed fire and herbicide application in remnant barrens in west central Kentucky. The effects of a single spring burn post‐emergence herbicide, combined fire and herbicide treatments, and an unburned no‐herbicide control were compared on five replicate blocks. In fire‐plus‐herbicide plots, fescue averaged 8% at the end of the growing season compared with 46% fescue cover in control plots. The extent of bare soil increased from near 0 in control to 11% in burned plots and 25% in fire‐plus‐herbicide plots. Over the course of the growing season, fire had little effect on soil N pools or processes. Fire caused a decline in soil CO2 flux in parallel to decreased soil moisture. When applied alone, herbicide increased plant‐available soil N slightly but had no effect on soil respiration, moisture, or temperature. Fire‐plus‐herbicide significantly increased plant‐available soil N and net N transformation rates; soil respiration declined by 33%. Removal of non‐native plants modified the chemical, physical, and biological soil conditions that control availability of plant nutrients and influence plant species performance and community composition. 相似文献
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