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21.
We investigated the influence of fertilization on the abundance of species with different clonal growth characteristics using the data from a 20-year fertilization experiment from the Laelatu wooded meadow, in Estonia. The experiment comprised four different fertilization treatments and created a gradient of nitrogen availability. The vegetation composition was recorded every year by measuring the proportions of aboveground biomass for all species. For each species, four parameters of vegetative propagation were measured: speed of ramet vegetative mobility (annual increment of rhizome length), frequency of rhizome branching, placement of branches, and ramet life span. The weighted average of each parameter was calculated for each plot both at the beginning and at the end of the experiment using the relative abundances of the species in the plot as weights. The community changes resulting from the fertilization are reflected in the significant changes of the average values of all studied clonal growth parameters. Increased levels of phosphorus and potassium led to a community with an increased average vegetative mobility and rhizome branching. Both of these traits, however, declined with the increasing availability of nitrogen. The proportion of species with long-living ramets in the community decreased with the increase in the productivity irrespective of the fertilizer used. There was a strong positive correlation between the average ramet life span of the community and the number of species on the plot. We concluded that fertilization increased the ramet turnover rate in this meadow community and reduced species richness. Thus, our results contradict the prediction of a higher ramet turnover rate in species-rich compared to the species-poor grasslands. 相似文献
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23.
The role of disturbed photoperiod on the developing surface layers of ripening Scots pine (Pinus sylvestris L.) seeds was studied from August 14 to October 30. The embryo sizes of both the light-treated and the control seeds were
examined by the X-ray method prior to germination tests. The anatomical details of resin-embedded seeds were examined by fluorescence
and light microscopy. The timing of the ripening process of the surface structures was described and documented. The greatest
anatomical changes in the ripening seeds occurred in the sarcotesta and in the nucellar layers. Maturation of the surface
structures was essentially slower than could have been interpreted by the size of the embryo and responded clearly to the
disturbance of photoperiod. Accumulation of phenolic substances and degeneration of cells, particularly at the chalazal region,
advanced faster in the light-treated than in the control seeds up to mid-September. The ripening effect of the altered photoperiod
diminished, however, after mid-September. This was also confirmed by the brown colour of the seed coat getting darker only
in the control seeds at the end of the test period. Consequently, fully ripe structures were first found about a fortnight
earlier in the control than in the light-treated seeds. The coincidental advancement of the anatomical potential examined
by the X-ray method supported the role of the surface structures on the anatomical maturity of pine seeds and the timing of
cone collecting.
Received: 26 January 1998 / Accepted: 30 March 1998 相似文献
24.
Stina?EdelfeldtEmail author Anneli?Lundkvist Johannes?Forkman Theo?Verwijst 《Bioenergy Research》2015,8(2):796-806
To assess the effects of different planting systems on early performance (survival, shoot emergence time, number of shoots, maximum shoot height and biomass shoot production) of willow, cuttings of varying lengths were planted horizontally at different depths and compared with vertically planted cuttings. Cutting lengths of (i) 25–200 cm and (ii) 7–21 cm were studied in a field experiment and in a box experiment, respectively. Shorter cuttings planted deeper had a lower survival rate and emerged a few days later compared to longer cuttings planted shallower. The performance was considerably higher at the apical part of the cuttings, regardless of cutting length. Longer cuttings planted shallow had a higher performance. Vertically planted cuttings produced more biomass and shoots per length unit than horizontally planted cuttings. We conclude that planting systems based on the use of longer horizontally planted cuttings would probably lead to an uneven establishment and gaps in the stand caused by apical dominance. Also, to achieve the same performance, the need of planting material would be considerably higher compared to systems with vertically planted cuttings. To obtain a fast and more even early establishment of willows, we recommend the use of vertically planted cuttings with a length of at least 20 cm. If cuttings are planted horizontally, they should not be planted deeper than 5 cm. 相似文献
25.
Rhonda R. Snook Anneli Hoikkala 《Evolution; international journal of organic evolution》2014,68(11):3095-3108
An outstanding goal in speciation research is to trace the mode and tempo of the evolution of barriers to gene flow. Such research benefits from studying incipient speciation, in which speciation between populations has not yet occurred, but where multiple potential mechanisms of reproductive isolation (RI: i.e., premating, postmating‐prezygotic (PMPZ), and postzygotic barriers) may act. We used such a system to investigate these barriers among allopatric populations of Drosophila montana. In all heteropopulation crosses we found premating (sexual) isolation, which was either symmetric or asymmetric depending on the population pair compared. Postmating isolation was particularly strong in crosses involving males from one of the study populations, and while sperm were successfully transferred, stored, and motile, we experimentally demonstrated that the majority of eggs produced were unfertilized. Thus, we identified the nature of a PMPZ incompatibility. There was no evidence of intrinsic postzygotic effects. Measures of absolute and relative strengths of pre‐ and postmating barriers showed that populations differed in the mode and magnitude of RI barriers. Our results indicate that incipient RI among populations can be driven by different contributions of both premating and PMPZ barriers occurring between different population pairs and without the evolution of postzygotic barriers. 相似文献
26.
Tove Alm Louise Yderland Johan Nilvebrant Anneli Halldin Sophia Hober Professor 《Biotechnology journal》2010,5(6):605-617
A novel protein domain with dual affinity has been created by randomization and selection. The small alkali-stabilized albumin-binding domain (ABD*), used as scaffold to construct the library, has affinity to human serum albumin (HSA) and is constituted of 46 amino acids of which 11 were randomized. To achieve a dual binder, the binding site of the inherent HSA affinity was untouched and the randomization was made on the opposite side of the molecule. Despite its small size and randomization of almost a quarter of its amino acids, a bifunctional molecule, ABDz1, with ability to bind to both HSA and the Z2 domain/protein A was successfully selected using phage display. Moreover, the newly selected variant showed improved affinity for HSA compared to the parental molecule. This novel protein domain has been characterized regarding secondary structure and affinity to the two different ligands. The possibility for affinity purification on two different matrices has been investigated using the two ligands, the HSA matrix and the protein A-based, MabSelect SuRe matrix, and the new protein domain was purified to homogeneity. Furthermore, gene fusions between the new domain and three different target proteins with different characteristics were made. To take advantage of both affinities, a purification strategy referred to as orthogonal affinity purification using two different matrices was created. Successful purification of all three versions was efficiently carried out using this strategy. 相似文献
27.
28.
Mirol PM Schäfer MA Orsini L Routtu J Schlötterer C Hoikkala A Butlin RK 《Molecular ecology》2007,16(5):1085-1097
The Drosophila virilis species group offers valuable opportunities for studying the roles of chromosomal re-arrangements and mating signals in speciation. The 13 species are divided into two subgroups, the montana and virilis 'phylads'. There is greater differentiation among species within the montana phylad in both karyotype and acoustic signals than exists among members of the virilis phylad. Drosophila montana is a divergent species which is included in the montana phylad. Here, we analyse the phylogeography of D. montana to provide a framework for understanding divergence of acoustic signals among populations. We analysed mitochondrial sequences corresponding to the cytochrome oxidase I and cytochrome oxidase II genes, as well as 16 microsatellite loci, from 108 lines of D. montana covering most of the species' range. The species shows a clear genetic differentiation between North American and Scandinavian populations. Microsatellite allele frequencies and mitochondrial DNA haplotypes gave significant FST values between populations from Canada, USA and Finland. A Bayesian analysis of population structure based on the microsatellite frequencies showed four genetically distinct groups, corresponding to these three populations plus a small sample from Japan. A network based on mitochondrial haplotypes showed two Finnish clades of very different shape and variability, and another clade with all sequences from North America and Japan. All D. montana populations showed evidence of demographic expansion but the patterns inferred by coalescent analysis differed between populations. The divergence times between Scandinavian and North American clades were estimated to range from 450,000 to 900,000 years with populations in Canada and the USA possibly representing descendants of different refugial populations. Long-term separation of D. montana populations could have provided the opportunity for differentiation observed in male signal traits, especially carrier frequency of the song, but relaxation of sexual selection during population expansion may have been necessary. 相似文献
29.
P Veltsos E Gregson B Morrissey J Slate A Hoikkala R K Butlin M G Ritchie 《Heredity》2015,115(6):565-572
We investigated the genetic architecture of courtship song and cuticular hydrocarbon
traits in two phygenetically distinct populations of Drosophila montana. To
study natural variation in these two important traits, we analysed within-population
crosses among individuals sampled from the wild. Hence, the genetic variation
analysed should represent that available for natural and sexual selection to act
upon. In contrast to previous between-population crosses in this species, no major
quantitative trait loci (QTLs) were detected, perhaps because the between-population
QTLs were due to fixed differences between the populations. Partitioning the trait
variation to chromosomes suggested a broadly polygenic genetic architecture of
within-population variation, although some chromosomes explained more variation in
one population compared with the other. Studies of natural variation provide an
important contrast to crosses between species or divergent lines, but our analysis
highlights recent concerns that segregating variation within populations for
important quantitative ecological traits may largely consist of small effect alleles,
difficult to detect with studies of moderate power. 相似文献
30.