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91.
Environmental (in)dependence of a hybrid zone: Insights from molecular markers and ecological niche modeling in a hybrid zone of Origanum (Lamiaceae) on the island of Crete 下载免费PDF全文
The role of environment and the relative significance of endogenous versus exogenous selection in shaping hybrid zones have been crucial issues in the studies of hybridization. Recent advances in ecological niche modeling (ENM) offer new methodological tools, especially in combination with the genotyping of individuals in the hybrid zone. Here, we study the hybrid zone between the widely known spices Origanum onites and Origanum vulgare ssp. hirtum in Crete. We analyze the genetic structure of both parental taxa and their hybrid Origanum × intercendens using AFLP markers on 15 sympatric and 12 allopatric populations and employ ecological niche modeling and niche similarity tests to study their niche patterns. We complement these analyses with seed viability measurements. Our study revealed that the hybridizing taxa O. onites and O. vulgare ssp. hirtum and the resulting genotypic classes showed geographical and environmental niche similarities based on the predictions of ENMs and the subsequent similarity tests. The occurrence of the hybrid zone is not directly dependent on environmental factors which favor the fitness of the hybrid compared to the parental taxa, but rather on aspects such as historical factors and management practices, which may contribute to the localization and maintenance of the contact zone between parental species. Our results suggest that if a minimum required niche differentiation between genotypic classes is not achieved, environmental dependence might not have a prominent role on the outcome of the hybridization. 相似文献
92.
93.
Invasion of native habitats by alien or generalist species is recognized worldwide as one of the major causes behind species
decline and extinction. One mechanism determining community invasibility, i.e. the susceptibility of a community to invasion,
which has been supported by recent experimental studies, is species richness and functional diversity acting as barriers to
invasion. We used Scandinavian semi-natural grasslands, exceptionally species-rich at small spatial scales, to examine this
mechanism, using three grassland generalists and one alien species as experimental invaders. Removal of two putative functional
groups, legumes and dominant non-legume forbs, had no effect on invasibility except a marginally insignificant effect of non-legume
forb removal. The amount of removed biomass and original plot species richness had no effect on invasibility. Actually, invasibility
was high already in the unmanipulated community, leading us to further examine the relationship between invasion and propagule
pressure, i.e. the inflow of seeds into the community. Results from an additional experiment suggested that these species-rich
grasslands are effectively open to invasion and that diversity may be immigration driven. Thus, species richness is no barrier
to invasion. The high species diversity is probably in itself a result of the community being highly invasible, and species
have accumulated at small scales during centuries of grassland management. 相似文献
94.
Claudia M. Jacobi Flávio F. do Carmo Regina C. Vincent João R. Stehmann 《Biodiversity and Conservation》2007,16(7):2185-2200
Mountain areas are recognized centres of endemism and diversity on account of their isolation and altitudinal diversity. In
tropical regions, mountain tops usually stand as islands of xeric vegetation among mesophytic assemblages. Unlike the vegetation
growing on other rock outcrops lithologies, such as inselbergs (granite/gneiss) or campos rupestres (quartz/arenite), ironstone outcrop plant communities still lack systematic studies in Brazil. These outcrops (locally known
as canga) share most of the characteristics of other rock outcrops, such as isolation and edapho-climatic harshness, but differ in
that they are the object of opencast mining, and thus subjected to irrecoverable degradation. In addition, they are expected
to harbour metal-tolerant and hyperaccumulator plant species. A botanical survey of two ironstone outcrop locations in the
most important mining region of southeastern Brazil, the Iron Quadrangle, revealed a high within-site (138 and 160 species
per site), and between-site diversity (only 27% of common species), totaling 64 families and 234 species among basal families
and eudicots (154 species), monocots (68 species), and ferns (12 species). Canga crusts are rich in dicots, several of which play an important role in community structuring, together with the more usual
monocot aggregations. Distinct plant communities are found associated to different microhabitats within the iron crust, depending
primarily on the amount of soil and moisture retention in the different microtopographies. The environmental uniqueness, high
diversity, lack of studies and rapid destruction of these ecosystems pose an immediate challenge for their conservation. 相似文献
95.
Gabriel S. Lopes Camila Righetto Cassano Laila Santim Mureb Flavia Regina Miranda Ariovaldo P. Cruz-Neto Gastón Andrés Fernandez Giné 《Austral ecology》2023,48(7):1344-1360
Changes in ambient temperature and solar radiation may affect sloths' metabolic rate and body temperature, with consequent changes in activities, postures and microhabitat selection. Although the separate effect of temperature and solar radiation on sloth's behaviour have been previously studied, the combined effect of these climatic factors on behavioural aspects of sloths has never been systematically evaluated in field conditions. Here we evaluated the influence of hourly ambient temperature variation on maned sloth (Bradypus torquatus) activities, postures and tree crown positions, under sunny and cloudy conditions; and tested if any of the animal posture and position increase their exposure to human detection. We performed 350 h of visual observation on eight maned sloths, equipped with radio-backpacks, in northern Bahia, Brazil, recording their activities, and their resting postures and positions on tree crowns. We also recorded the time taken to visualize the sloths on 58 days to analyse if sloths' detection is affected by posture and position. Higher ambient temperature, within a range of 21–33°C, increased the sloths' activity levels in cloudy conditions but reduced their activity in sunny conditions. Increasing ambient temperature also reduced the frequency of huddled posture and increased the frequency of extended posture and permanence in the inner tree crown. Lastly, the postures and positions did not influence sloths' detectability. Thus, the direction of the temperature–activity relationship depends on climatic conditions (sunny/cloudy), and individuals rely on resting postures and positions to thermoregulate. The warmer and drier future climate, expected to occur in the northern Atlantic Forest, may impose change in the diurnal activity levels and postural pattern for this threatened species, leading maned sloths to reduce its activity on sunny and warmer days and adopting an extended posture. 相似文献
96.
Guilherme Augusto Peres Silva Salvador Alejandro Gezan Melissa Pisaroglo de Carvalho Lígia Regina Lima Gouvêa Cecília Khusala Verardi André Luis Bombonato de Oliveira Paulo de Souza Gonçalves 《Tree Genetics & Genomes》2014,10(6):1511-1518
Rubber tree breeding programs are mainly driven by selection of individuals with high yield and quality of rubber. Data from 51 open-pollinated progenies tested on six sites in Brazil were analyzed over several traits to estimate the following: genetic parameters such as narrow-sense heritability and additive genetic variance in single- and multi-site analyses, type B correlations to determine the relevance of genotype-by-environment interactions and its effects on alternative selection strategies, additive genetic repeatability correlation for rubber yield based on three consecutive yearly measurements, and type A correlations to evaluate trait-to-trait genetic associations for all measured traits. Average rubber yield (RYm) showed an estimated narrow-sense heritability of 0.31, with an estimated type B correlation of 0.84, indicating low levels of genotype-by-environment interaction. The trait survival and number of latex vessel rings (RG) showed larger genotype-by-environment interaction and the lowest heritabilites. High to moderate type B correlation was found for most traits, with a value of 0.85 between diameter (or girth) and RYm; therefore, it is possible to achieve interesting rubber yield genetic gains (over 3 years of measurements) from indirect selection based on diameter at age 2. 相似文献
97.
Regulation of hyphal morphogenesis and the DNA damage response by the Aspergillus nidulans ATM homolog AtmA 下载免费PDF全文
Ataxia telangiectasia (A-T) is an inherited disorder characterized by progressive loss of motor function and susceptibility to cancer. The most prominent clinical feature observed in A-T patients is the degeneration of Purkinje motor neurons. Numerous studies have emphasized the role of the affected gene product, ATM, in the regulation of the DNA damage response. However, in Purkinje cells, the bulk of ATM localizes to the cytoplasm and may play a role in vesicle trafficking. The nature of this function, and its involvement in the pathology underlying A-T, remain unknown. Here we characterize the homolog of ATM (AtmA) in the filamentous fungus Aspergillus nidulans. In addition to its expected role in the DNA damage response, we find that AtmA is also required for polarized hyphal growth. We demonstrate that an atmA mutant fails to generate a stable axis of hyphal polarity. Notably, cytoplasmic microtubules display aberrant cortical interactions at the hyphal tip. Our results suggest that AtmA regulates the function and/or localization of landmark proteins required for the formation of a polarity axis. We propose that a similar function may contribute to the establishment of neuronal polarity. 相似文献
98.
Regina Fluhrer Harald Steiner Christian Haass 《The Journal of biological chemistry》2009,284(21):13975-13979
Intramembrane-cleaving proteases are required for reverse signaling and
membrane protein degradation. A major class of these proteases is represented
by the GXGD-type aspartyl proteases. GXGD describes a novel
signature sequence that distinguishes these proteases from conventional
aspartyl proteases. Members of the family of the GXGD-type aspartyl
proteases are the Alzheimer disease-related γ-secretase, the signal
peptide peptidases and their homologs, and the bacterial type IV prepilin
peptidases. We will describe the major biochemical and functional properties
of the signal peptide peptidases and their relatives. We then compare these
properties with those of γ-secretase and discuss common mechanisms but
also point out a number of substantial differences.During the last years, a number of intramembrane-cleaving proteases termed
I-CLiPs3 have been
identified (1). I-CLiPs are
generally involved in regulated intramembrane proteolysis
(2). Upon shedding of a large
part of the ectodomain of membrane proteins, the remaining membrane-retained
stub is cleaved by specialized proteases within the hydrophobic lipid
membrane. Generally, this cleavage can have two predominant biological
functions: first, signaling via the liberated ICD within the
substrate-expressing cell (reverse signaling)
(2); and second, degradation of
membrane-retained stubs, which are not required for any further biological
function (3). I-CLiPs of three
protease classes, metalloproteases, serine proteases, and aspartyl proteases,
have been discovered so far (see accompanying minireview by Wolfe
(44)).Intramembrane-cleaving aspartyl proteases are represented by the class of
the GXGD-type proteases
(4). These are unconventional
aspartyl proteases that, like the conventional aspartyl proteases, utilize two
critical aspartyl residues for peptide bond cleavage. However, in contrast to
the conventional proteases, the critical aspartyl residues are located within
two TMDs (Fig. 1A).
Moreover, these aspartyl residues are embedded in active-site motifs that are
completely different from those of conventional aspartyl proteases. The class
of GXGD-type aspartyl proteases is currently represented by three
different protease families, the most prominent of which is the PS family,
providing the catalytically active subunit of γ-secretase
(Fig. 1A)
(4). PS/γ-secretase is
the I-CLiP that liberates amyloid β-peptide, the major component of
senile plaques in Alzheimer disease patients
(5). In addition, the bacterial
type IV prepilin peptidases also belong to the class of the GXGD-type
proteases (6). Besides these
two protease families, two additional subfamilies of related proteases that
also belong to the GXGD-type aspartyl protease family have been
identified. These include SPP as well as the SPP homologs, the
SPP-like (SPPL) proteases
(Fig. 1A)
(7,
8).Open in a separate windowFIGURE 1.A, schematic representation of SPPL2a/b, a member of the SPP/SPPL
family, and PS, the catalytic core of theγ-secretase. Note the opposite
topology of the active sites (indicated by arrows) of the two
proteases and their substrates, APP for PS and TNFα for SPPL2a/b.
B, proteolytic processing of APP and TNFα. Shedding releases
the extracellular part of APP (APPs) and TNFα
(TNFα soluble). In the case of APP, a C-terminal
fragment (APP CTF), and in case of TNFα, an N-terminal fragment
(TNFα NTF) are produced. These membrane-bound
fragments are substrate to intramembrane cleavage by PS or SPPL2a/b,
respectively, releasing small peptides to the extracellular space
(Aβ and TNFα C-domain, respectively) and
to the cytosol (APP intracellular domain (AICD) and
TNFα ICD), respectively). TNFα
FL, full-length TNFα.We will first describe the biochemical, functional, and structural
properties of SPP family members. By comparison of these properties, we will
then identify common mechanisms of intramembrane proteolysis by
GXGD-type proteases but also point out some fundamental
differences. 相似文献
99.
Effects of Restoration on Plant Species Richness and Composition in Scandinavian Semi-Natural Grasslands 总被引:4,自引:0,他引:4
Plant species richness in rural landscapes of northern Europe has been positively influenced by traditional management for millennia. Owing to abandonment of these practices, the number of species‐rich semi‐natural grasslands has decreased, and remaining habitats suffer from deterioration, fragmentation, and plant species decline. To prevent further extinctions, restoration efforts have increased during the last decades, by reintroducing grazing in former semi‐natural grasslands. To assess the ecological factors that might influence the outcome of such restorations, we made a survey of semi‐natural grasslands in Sweden that have been restored during the last decade. We investigated how plant species richness, species density, species composition, and abundance of 10 species that are indicators of grazing are affected by (1) the size of the restored site, (2) the time between abandonment of grazing and restoration, (3) the time elapsed since restoration, and (4) the abundance of trees and shrubs at the restored site. Only two factors, abundance of trees and shrubs and time since restoration, were positively associated with total species richness and species density per meter square at restored sites. Variation in species composition among restored sites was not related to any of the investigated factors. Species composition was relatively similar among sites, except in mesic/wet grasslands. The investigated factors had small effects on the abundance of the grazing‐indicator species. Only Campanula rotundifolia responded to restoration with increasing abundance and may thus be a suitable indicator of improved habitat quality. In conclusion, positive effects on species richness may appear relatively soon after restoration, but rare, short‐lived species are still absent. Therefore, remnant populations in surrounding areas may be important in fully recreating former species richness and composition. 相似文献
100.
The human c-erbB-2 oncogene is homologous to the ratneu oncogene, both encoding transmembrane growth factor receptors. Overexpression and point mutations in the transmembrane domain of the encoded proteins in both cases have been implicated in cell transformation and carcinogenesis. In the case of theneu protein, it has been proposed that these effects are mediated by conformational preferences for anα-helix in the transmembrane domain, which facilitates receptor dimerization, an important step in the signal transduction process. To examine whether this is the case for c-erbB-2 as well, we have used conformational energy analysis to determine the preferred three-dimensional structures for the transmembrane domain of the c-erbB-2 protein from residues 650 to 668 with Val (nontransforming) and Glu (transforming) at position 659. The global minimum energy conformation for the Val-659 peptide from the normal, nontransforming protein was found to contain several bends, whereas the global minimum energy conformation for Glu-659 peptide from the mutant, transforming protein was found to beα-helical. Thus, the difference in conformational preferences for these transmembrane domains may explain the difference in transforming ability of these proteins. The presence of higher-energyα-helical conformations for the transmembrane domain from the normal Val-659 protein may provide an explanation for the presence of a transforming effect from overexpression of c-erbB-2. In addition, docking of the oncogenic sequences in theirα-helical and bend conformations shows that the all-α-helical dimer is clearly favored energetically over the bend dimer. 相似文献