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101.
Adrian Ares Constance A. Harrington Thomas A. Terry Joseph M. Kraft 《Trees - Structure and Function》2008,22(5):603-609
The stable carbon (C) composition of tree rings expressed as δ13C, is a measure of intrinsic water-use efficiency and can indicate the occurrence of past water shortages for tree growth.
We examined δ13C in 3- to 5-year-old rings of Douglas-fir (Pseudotsuga menziesii (Mirb) Franco) trees to elucidate if decreased water supply or uptake was a critical factor in the observed growth reduction
of trees competing with understory herb and shrub vegetation compared to those growing without competition. We hypothesized
that there would be no differences in δ13C of earlywood in trees growing in plots with competing vegetation and those in plots receiving complete vegetation control
during 5 years because earlywood formed early in the growing season when soil water was ample. We also hypothesized that δ13C in latewood which was formed during the later half of the growing season when precipitation was low, would be greater (less
negative) in trees in plots without vegetation control. We then separated early and latewood from rings for three consecutive
years and analyzed their δ13C composition. No significant differences in earlywood δ13C in years 3–5 were observed for trees in the two vegetation control treatments. δ13C of untreated latewood separated from wood cores was greater in 4- and 5-year-old rings of trees growing with competing vegetation
compared to trees growing without vegetation competition (i.e., −25.5 vs. −26.3‰ for year 4, and −26.1 vs. −26.8‰ for year
5). Results suggest that water shortages occurred in Douglas-fir trees on this coastal Washington site in the latewood-forming
portion of the growing season of years 4 and 5 in the no-vegetation control treatment. We also compared δ13C from untreated wood, crude cellulose extracted with the Diglyme–HCl method, and holocellulose extracted with toluene–ethanol
to see if the extraction method would increase the sensitivity of the analysis. δ13C values from the two extraction methods were highly correlated with those from untreated samples (r
2 = 0.97, 0.98, respectively). Therefore, using untreated wood would be as effective as using crude cellulose or holocellulose
to investigate δ13C patterns in young Douglas-fir. 相似文献
102.
Walter Oberhuber Werner Kofler Klaus Pfeifer Andrea Seeber Andreas Gruber Gerhard Wieser 《Trees - Structure and Function》2008,22(1):31-40
Although growth limitation of trees at Alpine and high-latitude timberlines by prevailing summer temperature is well established,
the loss of thermal response of radial tree growth during last decades has repeatedly been addressed. We examined long-term
variability of climate–growth relationships in ring width chronologies of Stone pine (Pinus cembra L.) by means of moving response functions (MRF). The study area is situated in the timberline ecotone (ca. 2,000–2,200 m
a.s.l.) on Mt. Patscherkofel (Tyrol, Austria). Five site chronologies were developed within the ecotone with constant sample
depth (≥19 trees) throughout most of the time period analysed. MRF calculated for the period 1866–1999 and 1901–1999 for ca.
200- and ca. 100-year-old stands, respectively, revealed that mean July temperature is the major and long-term stable driving
force of Pinus cembra radial growth within the timberline ecotone. However, since the mid-1980s, radial growth in timberline and tree line chronologies
strikingly diverges from the July temperature trend. This is probably a result of extreme climate events (e.g. low winter
precipitation, late frost) and/or increasing drought stress on cambial activity. The latter assumption is supported by a <10%
increase in annual increments of ca. 50-year-old trees at the timberline and at the tree line in 2003 compared with 2002,
when extraordinary hot and dry conditions prevailed during summer. Furthermore, especially during the second half of the twentieth
century, influence of climate variables on radial growth show abrupt fluctuations, which might also be a consequence of climate
warming on tree physiology. 相似文献
103.
Qilian juniper (Sabina przewalskii kom.) is one of the dominant tree species on Qinghai-Tibetan Plateau and has been used in dendroclimatological studies. Here
we designed a test to examine whether or not the climate–growth responses in tree rings of Qilian Juniper vary with the change
in tree's age. A total number of 135 increment cores were sampled from Qilian Juniper trees at five sites, in which 112 cores
were selected and grouped into five 100-year age classes for analysis of age-dependent climate–growth relationships. Chronology
statistics, response functions and ANOVA F-test were used to test the consistency of five age-class mean chronologies (AGCs). The results showed that mean sensitivity
(MS) and standard deviation (SD) did not change significantly with age. Response function analysis indicated that (a) climate
accounts for a high amount of variance in tree-ring widths; (b) tree-ring growth has significant positive correlation with
mean monthly air temperature of previous October and November, and with total monthly precipitation of current January and
June, while has significant negative correlation with mean monthly air temperature of current May; and (c) AGC-2, AGC-3 and
AGC-4 have stronger response to climate change than AGC-1 and AGC-5. The ANOVA F-test showed that generally there are significant differences between the first age class and other four age classes, but
among the four classes in which trees are older than 200 years, the differences are usually insignificant. Overall the long-lived
Qilian Juniper is still an ideal tree species for dendroclimatic reconstruction. 相似文献
104.
Pollen productivity estimates of key European plant taxa for quantitative reconstruction of past vegetation: a review 总被引:2,自引:2,他引:0
Anna Broström Anne Birgitte Nielsen Marie-José Gaillard Kari Hjelle Florence Mazier Heather Binney Jane Bunting Ralph Fyfe Viveca Meltsov Anneli Poska Satu Räsänen Welmoed Soepboer Henrik von Stedingk Henna Suutari Shinya Sugita 《Vegetation History and Archaeobotany》2008,17(5):461-478
Information on the spatial distribution of past vegetation on local, regional and global scales is increasingly used within
climate modelling, nature conservancy and archaeology. It is possible to obtain such information from fossil pollen records
in lakes and bogs using the landscape reconstruction algorithm (LRA) and its two models, REVEALS and LOVE. These models assume
that reliable pollen productivity estimates (PPEs) are available for the plant taxa involved in the quantitative reconstructions
of past vegetation, and that PPEs are constant through time. This paper presents and discusses the PPEs for 15 tree and 18
herb taxa obtained in nine study areas of Europe. Observed differences in PPEs between regions may be explained by methodological
issues and environmental variables, of which climate and related factors such as reproduction strategies and growth forms
appear to be the most important. An evaluation of the PPEs at hand so far suggests that they can be used in modelling applications
and quantitative reconstructions of past vegetation, provided that consideration of past environmental variability within
the region is used to inform selection of PPEs, and bearing in mind that PPEs might have changed through time as a response
to climate change. Application of a range of possible PPEs will allow a better evaluation of the results. 相似文献
105.
The prediction of RNA secondary structure including pseudoknots remains a challenge due to the intractable computation of
the sequence conformation from nucleotide interactions under free energy models. Optimal algorithms often assume a restricted
class for the predicted RNA structures and yet still require a high-degree polynomial time complexity, which is too expensive
to use. Heuristic methods may yield time-efficient algorithms but they do not guarantee optimality of the predicted structure.
This paper introduces a new and efficient algorithm for the prediction of RNA structure with pseudoknots for which the structure
is not restricted. Novel prediction techniques are developed based on graph tree decomposition. In particular, based on a
simplified energy model, stem overlapping relationships are defined with a graph, in which a specialized maximum independent
set corresponds to the desired optimal structure. Such a graph is tree decomposable; dynamic programming over a tree decomposition
of the graph leads to an efficient optimal algorithm. The final structure predictions are then based on re-ranking a list
of suboptimal structures under a more comprehensive free energy model. The new algorithm is evaluated on a large number of
RNA sequence sets taken from diverse resources. It demonstrates overall sensitivity and specificity that outperforms or is
comparable with those of previous optimal and heuristic algorithms yet it requires significantly less time than the compared
optimal algorithms.
The preliminary version of this paper appeared in the proceedings of the 6th Workshop on Algorithms for Bioinformatics (WABI
2006). 相似文献
106.
How does forest landscape structure explain tree species richness in a Mediterranean context? 总被引:1,自引:0,他引:1
Although the strong relationship between vegetation and climatic factors is widely accepted, other landscape composition and
configuration characteristics could be significantly related with vegetation diversity patterns at different scales. Variation
partitioning was conducted in order to analyse to what degree forest landscape structure, compared to other spatial and environmental
factors, explained forest tree species richness in 278 UTM 10 × 10 km cells in the Mediterranean region of Catalonia (NE Spain).
Tree species richness variation was decomposed through linear regression into three groups of explanatory variables: forest
landscape (composition and configuration), environmental (topography and climate) and spatial variables. Additionally, the
forest landscape characteristics which significantly contributed to explain richness variation were identified through a multiple
regression model. About 60% of tree species richness variation was explained by the whole set of variables, while their joint
effects explained nearly 28%. Forest landscape variables were those with a greater pure explanatory power for tree species
richness (about 15% of total variation), much larger than the pure effect of environmental or spatial variables (about 2%
each). Forest canopy cover, forest area and land cover diversity were the most significant composition variables in the regression
model. Landscape configuration metrics had a minor effect on forest tree species richness, with the exception of some shape
complexity indices, as indicators of land use intensity and edge effects. Our results highlight the importance of considering
the forest landscape structure in order to understand the distribution of vegetation diversity in strongly human-modified
regions like the Mediterranean. 相似文献
107.
Gianluca Piovesan Franco Biondi Mauro Bernabei Alfredo Di Filippo Bartolomeo Schirone 《Acta Oecologica》2005,27(3):197-210
A network of 24 beech (Fagus sylvatica L.) tree-ring chronologies has been developed for the Italian peninsula. Principal component and cluster analyses were used to identify geographical and altitudinal patterns of tree growth. Correlations and response functions were then applied to the main modes of tree-ring variability to uncover climatic signals. In a landscape occupied by humans for millennia, this approach provided a detailed quantitative ecological characterization of forest types. Altitude was significantly correlated with dendrochronological parameters. The Alps and northern Apennines could be distinguished from the central-southern Apennines. In central Italy, we recognized three different vegetation belts occupied by beech forests, from low- to high-elevation sites. Summer drought impacted beech growth with different intensity at different elevations, depending on the onset and duration of the growing season. Moreover, low-elevation beech forests showed a distinct late spring climate signal, which was opposite to that of high-elevation sites. The coherent geographical and ecological patterns of tree-ring variability suggest that dendrochronological networks help define bioclimatic zones and forest types. 相似文献
108.
109.
Molecular Characterization of Tree Peony Germplasm Using Sequence-Related Amplified Polymorphism Markers 总被引:4,自引:0,他引:4
This study examined 63 tree peony specimens, consisting of 3 wild species and 63 cultivars, using sequence-related amplified
polymorphism (SRAP) markers for the purpose of detecting genomic polymorphisms. Bulk DNA samples from each specimen were evaluated
with 23 SRAP primer pairs. Among the 296 different amplicons, 262 were polymorphic. The maximum parsimony, neighbor-joining,
and unweighted pair-group method using arithmetic average trees were largely in congruence. In the three trees, the wild species
Paeonia ludlowii and P. delavayi formed separate clusters with strong bootstrap support, and P. ostii was closely related to all cultivars. The cultivars were divided into groups with various corresponding bootstrap values.
The genetic similarity among the genotypes ranged from 0.02 to 0.73. These results demonstrate that SRAP markers are effective
in detecting genomic polymorphisms in the tree peony and should be useful for linkage map construction and molecular marker
assisted selection breeding.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
110.
Inventories of trees and lianas were performed at a 13-year interval (1979–1992) in an evergreen forest in north-east Gabon. The number of trees decreased while their basal area and species richness increased. In contrast, both the richness and density of lianas decreased. Lianas with active climbing mechanisms were the main types to disappear. 相似文献