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131.
L. A. GIGUÈRE 《Freshwater Biology》1986,16(4):557-560
SUMMARY. 1. Crop evacuation rates were estimated for the first time in Chaoborus larvae, using natural prey.
2. Fourth instar C. americanus Matheson digested copepods (Diaptomus leptopus S.A. Forbes) 48.7% faster than daphnids (Daphnia rosea Leydig) of similar size; meal size did not significantly affect the instantaneous rate of digestion (IRD) within each prey type. Prey specific IRD has not been reported before for zooplankton.
3. Prey specific differences in IRD require the use of natural prey when digestion experiments are to be used to estimate natural rates of food consumption of animals. 相似文献
2. Fourth instar C. americanus Matheson digested copepods (Diaptomus leptopus S.A. Forbes) 48.7% faster than daphnids (Daphnia rosea Leydig) of similar size; meal size did not significantly affect the instantaneous rate of digestion (IRD) within each prey type. Prey specific IRD has not been reported before for zooplankton.
3. Prey specific differences in IRD require the use of natural prey when digestion experiments are to be used to estimate natural rates of food consumption of animals. 相似文献
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Spatial patterns in vessel diameter, vessel density and xylem conducting efficiency within a crown were examined in closed-canopy
trees of silver birch (Betula pendula). The variation in anatomical and hydraulic characteristics of branches was considered from three perspectives: vertically
within a crown (lower, middle and upper crown), radially along main branches (proximal, middle and distal part), and with
respect to branch orders (first-, second- and third-order branches). Hydraulically weighted mean diameter of vessels (D
h) and theoretical specific conductivity of the xylem (k
t) exhibited no vertical trend within the tree crown, whereas leaf-specific conductivity of the xylem (LSCt) decreased acropetally. Variation in LSCt was governed by sapwood area to leaf area ratio (Huber value) rather than by changes in xylem anatomy. The acropetal increase
in soil-to-leaf conductance (G
T) within the birch canopy is attributable to longer path length within the lower-crown branches and higher hydraulic resistance
of the shade leaves. D
h, k
t and LSCt decreased, while vessel density (VD) and relative area of vessel lumina (VA) increased distally along main branches. A strong
negative relationship between vessel diameter and VD implies a trade-off between hydraulic efficiency and mechanical stability
of xylem. D
h and VD combined explained 85.4% of the total variation of k
t in the regression model applied to the whole data set. Xylem in fast-growing branches (primary branches) had greater area
of vessel lumina per unit cross-sectional area of sapwood, resulting in a positive relationship between branch radial growth
rate and k
t. D
h, k
t and LSCt decreased, whereas VD increased with increasing branch order. This pattern promotes the hydraulic dominance of primary branches
over the secondary branches and their dominance over tertiary branches. In this way crown architecture contributes to preferential
water flow along the main axes, potentially providing better water supply for the branch apical bud and foliage located in
the outer, better-insolated part of the crown. 相似文献
137.
138.
Christopher RE McEvoy Paul D van Helden Robin M Warren Nicolaas C Gey van Pittius 《BMC evolutionary biology》2009,9(1):237-21
Background
PPE38 (Rv 2352c) is a member of the large PPE gene family of Mycobacterium tuberculosis and related mycobacteria. The function of PPE proteins is unknown but evidence suggests that many are cell-surface associated and recognised by the host immune system. Previous studies targeting other PPE gene members suggest that some display high levels of polymorphism and it is thought that this might represent a means of providing antigenic variation. We have analysed the genetic variability of the PPE38 genomic region on a cohort of M. tuberculosis clinical isolates representing all of the major phylogenetic lineages, along with the ancestral M. tuberculosis complex (MTBC) member M. canettii, and supplemented this with analysis of publicly available whole genome sequences representing additional M. tuberculosis clinical isolates, other MTBC members and non tuberculous mycobacteria (NTM). Where possible we have extended this analysis to include the adjacent plcABC and PPE39/40 genomic regions. 相似文献139.
Shaw AJ Cox CJ Buck WR Devos N Buchanan AM Cave L Seppelt R Shaw B Larraín J Andrus R Greilhuber J Temsch EM 《American journal of botany》2010,97(9):1511-1531
? Premise of the study: The Sphagnopsida, an early-diverging lineage of mosses (phylum Bryophyta), are morphologically and ecologically unique and have profound impacts on global climate. The Sphagnopsida are currently classified in two genera, Sphagnum (peat mosses) with some 350-500 species and Ambuchanania with one species. An analysis of phylogenetic relationships among species and genera in the Sphagnopsida were conducted to resolve major lineages and relationships among species within the Sphagnopsida. ? Methods: Phylogenetic analyses of nucleotide sequences from the nuclear, plastid, and mitochondrial genomes (11 704 nucleotides total) were conducted and analyzed using maximum likelihood and Bayesian inference employing seven different substitution models of varying complexity. ? Key results: Phylogenetic analyses resolved three lineages within the Sphagnopsida: (1) Sphagnum sericeum, (2) S. inretortum plus Ambuchanania leucobryoides, and (3) all remaining species of Sphagnum. Sister group relationships among these three clades could not be resolved, but the phylogenetic results indicate that the highly divergent morphology of A. leucobryoides is derived within the Sphagnopsida rather than plesiomorphic. A new classification is proposed for class Sphagnopsida, with one order (Sphagnales), three families, and four genera. ? Conclusions: The Sphagnopsida are an old lineage within the phylum Bryophyta, but the extant species of Sphagnum represent a relatively recent radiation. It is likely that additional species critical to understanding the evolution of peat mosses await discovery, especially in the southern hemisphere. 相似文献
140.
CengizTURE ElifSALKURT 《植物学报(英文版)》2005,47(6):660-667
Airborne pollen grains in the atmosphere of Bozuyuk were investigated over a 2 yr period from 2000 to 2001 using a Durham sampler. A total number of pollen grains of 5 170 pollen grains belonging to 32 taxa were identified and recorded along with some unidentified pollen grains. Of all the pollen grains, 78.66% were arboreal, 19.20% were non-arboreal, and 2.12% were unidentified. The majority of pollen grains investigated were Pinus, Platanus, Quercus, Cupressaceae, Poaceae, Fagus, Salix, Rosaceae, Urticaceae, Asteraceae, and Chenopodiaceae. The maximum number of pollen grains was recorded in May. 相似文献