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991.
Steven M. Boker Jeffrey F. Cohn Barry-John Theobald Iain Matthews Timothy R. Brick Jeffrey R. Spies 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2009,364(1535):3485-3495
When people speak with one another, they tend to adapt their head movements and facial expressions in response to each others'' head movements and facial expressions. We present an experiment in which confederates'' head movements and facial expressions were motion tracked during videoconference conversations, an avatar face was reconstructed in real time, and naive participants spoke with the avatar face. No naive participant guessed that the computer generated face was not video. Confederates'' facial expressions, vocal inflections and head movements were attenuated at 1 min intervals in a fully crossed experimental design. Attenuated head movements led to increased head nods and lateral head turns, and attenuated facial expressions led to increased head nodding in both naive participants and confederates. Together, these results are consistent with a hypothesis that the dynamics of head movements in dyadicconversation include a shared equilibrium. Although both conversational partners were blind to the manipulation, when apparent head movement of one conversant was attenuated, both partners responded by increasing the velocity of their head movements. 相似文献
992.
F. Pelletier D. Garant A.P. Hendry 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2009,364(1523):1483-1489
Evolutionary ecologists and population biologists have recently considered that ecological and evolutionary changes are intimately linked and can occur on the same time-scale. Recent theoretical developments have shown how the feedback between ecological and evolutionary dynamics can be linked, and there are now empirical demonstrations showing that ecological change can lead to rapid evolutionary change. We also have evidence that microevolutionary change can leave an ecological signature. We are at a stage where the integration of ecology and evolution is a necessary step towards major advances in our understanding of the processes that shape and maintain biodiversity. This special feature about ‘eco-evolutionary dynamics’ brings together biologists from empirical and theoretical backgrounds to bridge the gap between ecology and evolution and provide a series of contributions aimed at quantifying the interactions between these fundamental processes. 相似文献
993.
Blaine D. Griffen John M. Drake 《Proceedings. Biological sciences / The Royal Society》2009,276(1677):4363-4371
Ecological theory suggests that several demographic factors influence metapopulation extinction risk, including synchrony in population size between subpopulations, metapopulation size and the magnitude of fluctuations in population size. Theoretically, each of these is influenced by the rate of migration between subpopulations. Here we report on an experiment where we manipulated migration rate within metapopulations of the freshwater zooplankton Daphnia magna to examine how migration influenced each of these demographic variables, and subsequent effects on metapopulation extinction. In addition, our experimental procedures introduced unplanned but controlled differences between metapopulations in light intensity, enabling us to examine the relative influences of environmental and demographic factors. We found that increasing migration rate increased subpopulation synchrony. We failed to detect effects of migration on population size and fluctuations in population size at the metapopulation or subpopulation level, however. In contrast, light intensity did not influence synchrony, but was positively correlated with population size and negatively correlated with population fluctuation. Finally, synchrony did not influence time to extinction, while population size and the magnitude of fluctuations did. We conclude that environmental factors had a greater influence on extinction risk than demographic factors, and that metapopulation size and fluctuation were more important to extinction risk than metapopulation synchrony. 相似文献
994.
Hisashi Ohtsuki Martin A. Nowak 《Proceedings. Biological sciences / The Royal Society》2009,276(1674):3783-3790
Life is based on replication and evolution. But replication cannot be taken for granted. We must ask what there was prior to replication and evolution. How does evolution begin? We have proposed prelife as a generative system that produces information and diversity in the absence of replication. We model prelife as a binary soup of active monomers that form random polymers. ‘Prevolutionary’ dynamics can have mutation and selection prior to replication. Some sequences might have catalytic activity, thereby enhancing the rates of certain prelife reactions. We study the selection criteria for these prelife catalysts. Their catalytic efficiency must be above certain critical values. We find a maintenance threshold and an initiation threshold. The former is a linear function of sequence length, and the latter is an exponential function of sequence length. Therefore, it is extremely hard to select for prelife catalysts that have long sequences. We compare prelife catalysis with a simple model for replication. Assuming fast template-based elongation reactions, we can show that replicators have selection thresholds that are independent of their sequence length. Our calculation demonstrates the efficiency of replication and provides an explanation of why replication was selected over other forms of prelife catalysis. 相似文献
995.
外来物种入侵后的多物种竞争共存的集合种群模型 总被引:3,自引:0,他引:3
基于多物种竞争共存模型,提出外来物种与本地物种竞争共存途径的两种假想:外来物种通过插队竞争与本地物种实现共存;外来物种通过等位竞争与本地物种实现共存.并提出根据外来物种在两种竞争共存模式下占据生境斑块比例的稳定值大小来判断外来物种和本地物种的竞争共存途径.根据两种假想,分别建立了外来物种插队竞争共存模型和等位竞争共存模型.通过应用数学软件Mathematica 4.0对两个模型进行了模拟,得出以下结论:在外来物种与本地物种竞争共存状态下,如果外来物种通过插队竞争与本地物种实现共存,当本地物种竞争力差异较大时,外来物种极易对本地稀少物种构成危害.虽然外来物种不会直接造成本地稀少物种的灭绝,但是会使本地稀少物种的生境斑块急剧减少,增加本地稀少物种灭绝的可能性,而当本地物种竞争力差异较小时,外来物种对本地所有物种的影响都较小.如果外来物种通过等位竞争与本地物种实现共存,无论本地物种竞争力差异大小与否,外来物种只是影响到与其生态位相同的本地物种,影响程度取决于外来物种侵入时所占据生境斑块的比例大小. 相似文献
996.
The stability of brain networks with randomly connected excitatory and inhibitory neural populations is investigated using
a simplified physiological model of brain electrical activity. Neural populations are randomly assigned to be excitatory or
inhibitory and the stability of a brain network is determined by the spectrum of the network’s matrix of connection strengths.
The probability that a network is stable is determined from its spectral density which is numerically determined and is approximated
by a spectral distribution recently derived by Rajan and Abbott. The probability that a brain network is stable is maximum
when the total connection strength into a population is approximately zero and is shown to depend on the arrangement of the
excitatory and inhibitory connections and the parameters of the network. The maximum excitatory and inhibitory input into
a structure allowed by stability occurs when the net input equals zero and, in contrast to networks with randomly distributed
excitatory and inhibitory connections, substantially increases as the number of connections increases. Networks with the largest
excitatory and inhibitory input allowed by stability have multiple marginally stable modes, are highly responsive and adaptable
to external stimuli, have the same total input into each structure with minimal variance in the excitatory and inhibitory
connection strengths, and have a wide range of flexible, adaptable, and complex behavior. 相似文献
997.
A 50 m-long radiocarbon dated core was studied through sediment and pollen analysis to reconstruct the Holocene mangrove and
environmental changes at a coastal site Pakhiralaya in the Sundarban Biosphere Reserve in the western Ganga–Brahmaputra Delta,
India. This biosphere reserve harbours a diverse mangrove ecosystem and supports a large number of people living in the area.
Pollen and stratigraphic data indicate the existence of a brackish water estuarine mangrove swamp forest in this area during
the last 9880 cal yr b.p. The development of the mangrove forest is not shown continuously in the Holocene record. Rapid transgression of the sea
(9240 cal yr b.p.) halted the development of the mangrove. After about 8420 cal yr b.p. mangrove recolonised the area and persisted until 7560 cal yr b.p. as a result of a balance between the sedimentation and sea level fluctuation. The mangrove disappeared again from the site
until 4800 cal yr b.p. because of a high sedimentation rate and possible delta progradation with loss of habitats. The reappearance of mangrove
at the study site occurred with a return of a brackish water estuarine environment and the site then gradually became supra
tidal during the mid-late Holocene. The continuity of the mangrove development and dynamics was interrupted by the fluctuating
sea levels. Climatic fluctuations were viewed as an indirect factor influencing the mangrove ecosystem. 相似文献
998.
Researchers can have unintentional, yet significant effects on their study systems. We tested for the effects of an intensive
tree census on seedling dynamics in a 50-ha permanent forest plot on Barro Colorado Island, Panama. At the community level,
and for different shade-tolerance guilds, we found no significant differences in seedling recruitment or survival inside compared
to controls outside the plot. However, among growth forms, canopy trees and lianas exhibited significantly lower seedling
survival inside the plot. Results suggest that intense researcher activity impacts short-term vegetation dynamics, but effects
do not accumulate over time. 相似文献
999.
The patch mosaic of an old-growth warm-temperate forest: patch-level descriptions of 40-year gap-forming processes and community structures 总被引:1,自引:0,他引:1
Tohru Manabe Kenichiro Shimatani Satoko Kawarasaki Shin-Ichi Aikawa Shin-Ichi Yamamoto 《Ecological Research》2009,24(3):575-586
Old-growth forests consist of various types of small patches that reflect their own gap-forming process, which includes changes
in environmental conditions occurring over several decades. We reconstructed the gap-forming processes that had occurred during
a 40-year period for eight representative patches of an old-growth evergreen broad-leaved forest in Japan, and examined the
current community structure. The selected patches were based on (1) changes in canopy heights estimated from aerial photographs
taken in four different years, (2) long-term ecological research (LTER) monitoring records, and (3) a recent field survey,
so that they sufficiently covered characteristic gap-forming processes such as a new gap, an old gap and consistently closed
canopy. Height and diameter at breast height (DBH) were measured on all living trees taller than 1.3 m. In their height distributions,
currently almost closed patches that were open in 1966 show a rotated sigmoid, whereas their DBH distributions are an inverse
J-shape. In contrast, patches that have been consistently under a closed canopy exhibit gentle inverse J-shapes for both distributions.
For species composition, there are no clear contrasts associated with the past gap-forming processes except for the existence
of fast-growing deciduous species in large currently open patches. Our results suggested that the variation in several decades
of gap-forming processes played a central role in the high patch diversity and the complex patch mosaic of the forest. Diverse
gap-forming processes created micro-environmental heterogeneity both vertically and horizontally, and contributed to the maintenance
of the species-rich, warm-temperate old-growth forest. 相似文献
1000.