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41.
Liyu Xia Sarah L. Master Maria K. Eckstein Beth Baribault Ronald E. Dahl Linda Wilbrecht Anne Gabrielle Eva Collins 《PLoS computational biology》2021,17(7)
In the real world, many relationships between events are uncertain and probabilistic. Uncertainty is also likely to be a more common feature of daily experience for youth because they have less experience to draw from than adults. Some studies suggest probabilistic learning may be inefficient in youths compared to adults, while others suggest it may be more efficient in youths in mid adolescence. Here we used a probabilistic reinforcement learning task to test how youth age 8-17 (N = 187) and adults age 18-30 (N = 110) learn about stable probabilistic contingencies. Performance increased with age through early-twenties, then stabilized. Using hierarchical Bayesian methods to fit computational reinforcement learning models, we show that all participants’ performance was better explained by models in which negative outcomes had minimal to no impact on learning. The performance increase over age was driven by 1) an increase in learning rate (i.e. decrease in integration time scale); 2) a decrease in noisy/exploratory choices. In mid-adolescence age 13-15, salivary testosterone and learning rate were positively related. We discuss our findings in the context of other studies and hypotheses about adolescent brain development. 相似文献
42.
A. Maier M. W. Gee C. Reeps H.-H. Eckstein W. A. Wall 《Biomechanics and modeling in mechanobiology》2010,9(5):511-521
As a degenerative and inflammatory desease of elderly patients, about 80% of abdominal aortic aneurysms (AAA) show considerable
wall calcification. Effect of calcifications on computational wall stress analyses of AAAs has been rarely treated in literature
so far. Calcifications are heterogeneously distributed, non-fibrous, stiff plaques which are most commonly found near the
luminal surface in between the intima and the media layer of the vessel wall. In this study, we therefore investigate the
influence of calcifications as separate AAA constituents on finite element simulation results. Thus, three AAAs are reconstructed
with regard to intraluminal thrombus (ILT), calcifications and vessel wall. Each patient-specific AAA is simulated twice,
once including all three AAA constituents and once neglecting calcifications as it is still common in literature. Parameters
for constitutive modeling of calcifications are thereby taken from experiments performed by the authors, showing that calcifications
exhibit an almost linear stress–strain behavior with a Young’s modulus E ≥ 40 MPa. Simulation results show that calcifications exhibit significant load-bearing effects and reduce stress in adjacent
vessel wall. Average stress within the vessel wall is reduced by 9.7 to 59.2%. For two out of three AAAs, peak wall stress
decreases when taking calcifications into consideration (8.9 and 28.9%). For one AAA, simulated peak wall stress increases
by 5.5% due to stress peaks near calcification borders. However, such stress singularities due to sudden stiffness jumps are
physiologically doubtful. It can further be observed that large calcifications are mostly situated in concavely shaped regions
of the AAA wall. We deduce that AAA shape is influenced by existent calcifications, thus crucial errors occur if they are
neglected in computational wall stress analyses. A general increase in rupture risk for calcified AAAs is doubted. 相似文献
43.
Studying global change through investigation of the plastic responses of xylem anatomy in tree rings 总被引:1,自引:0,他引:1
Patrick Fonti Georg von Arx Ignacio García-González Britta Eilmann Ute Sass-Klaassen Holger Gärtner Dieter Eckstein 《The New phytologist》2010,185(1):42-53
Variability in xylem anatomy is of interest to plant scientists because of the role water transport plays in plant performance and survival. Insights into plant adjustments to changing environmental conditions have mainly been obtained through structural and functional comparative studies between taxa or within taxa on contrasting sites or along environmental gradients. Yet, a gap exists regarding the study of hydraulic adjustments in response to environmental changes over the lifetimes of plants. In trees, dated tree-ring series are often exploited to reconstruct dynamics in ecological conditions, and recent work in which wood-anatomical variables have been used in dendrochronology has produced promising results. Environmental signals identified in water-conducting cells carry novel information reflecting changes in regional conditions and are mostly related to short, sub-annual intervals. Although the idea of investigating environmental signals through wood anatomical time series goes back to the 1960s, it is only recently that low-cost computerized image-analysis systems have enabled increased scientific output in this field. We believe that the study of tree-ring anatomy is emerging as a promising approach in tree biology and climate change research, particularly if complemented by physiological and ecological studies. This contribution presents the rationale, the potential, and the methodological challenges of this innovative approach. 相似文献
44.
A prevailing theory proposes that the brain''s two visual pathways, the ventral and dorsal, lead to differing visual processing and world representations for conscious perception than those for action. Others have claimed that perception and action share much of their visual processing. But which of these two neural architectures is favored by evolution? Successful visual search is life-critical and here we investigate the evolution and optimality of neural mechanisms mediating perception and eye movement actions for visual search in natural images. We implement an approximation to the ideal Bayesian searcher with two separate processing streams, one controlling the eye movements and the other stream determining the perceptual search decisions. We virtually evolved the neural mechanisms of the searchers'' two separate pathways built from linear combinations of primary visual cortex receptive fields (V1) by making the simulated individuals'' probability of survival depend on the perceptual accuracy finding targets in cluttered backgrounds. We find that for a variety of targets, backgrounds, and dependence of target detectability on retinal eccentricity, the mechanisms of the searchers'' two processing streams converge to similar representations showing that mismatches in the mechanisms for perception and eye movements lead to suboptimal search. Three exceptions which resulted in partial or no convergence were a case of an organism for which the targets are equally detectable across the retina, an organism with sufficient time to foveate all possible target locations, and a strict two-pathway model with no interconnections and differential pre-filtering based on parvocellular and magnocellular lateral geniculate cell properties. Thus, similar neural mechanisms for perception and eye movement actions during search are optimal and should be expected from the effects of natural selection on an organism with limited time to search for food that is not equi-detectable across its retina and interconnected perception and action neural pathways. 相似文献
45.
The pinning method: From pinning to data preparation 总被引:2,自引:0,他引:2
The pinning method is one of the various approaches to trace the intra-annual cambium dynamics of trees along a highly resolved time axis. After a brief retrospect on preceding developmental steps, the pinning of trees and the measurement of the radial increments, formed within distinct intervals, as well as the transformation of the data necessary for subsequent statistical analyses are illustrated. Finally, some drawbacks of the pinning method are discussed. 相似文献
46.
Vicky Roslinsky Peter E. Eckstein Victor Raboy Brian G. Rossnagel Graham J. Scoles 《Molecular breeding : new strategies in plant improvement》2007,20(4):323-330
Phytate is the primary form of phosphorus found in mature cereal grain. This form of phosphorus is not available to monogastric
animals due to a lack of the enzyme phytase in their digestive tract. Several barley low
phytic
acid (lpa) mutants have been identified that contain substantial decreases in seed phytate accompanied by concomitant increases in
inorganic phosphorus. Seed homozygous for low phytic acid
1-1 (lpa1-1) or low phytic acid
2-1 (lpa2-1) has a 50% and 70% decrease in seed phytate respectively. These mutations were previously mapped to chromosomes 2HL and 7HL
respectively. The RFLP marker ABC153 located in the same region of 2H was converted to a sequence-characterized-amplified-region
(SCAR) marker. Segregation analysis of the CDC McGwire × Lp422 doubled haploid population confirmed linkage between the SCAR
marker and the lpa1-1 locus with 15% recombination. A third low phytic acid mutant, M635, has a 75% decrease in phytate. This mutation was located
to chromosome 1HL by linkage with an inter-simple sequence repeat (ISSR) based marker (LP75) identified through bulked-segregant
analysis, and has been designated lpa3-1. Based on analysis of recombination between marker LP75 and low phytic acid in an additional mutant line M955 (95% phytate
decrease), lpa3-1 and the mutation in M955 are in the same region on chromosome 1HL, and may be allelic. 相似文献
47.
Populations of the introduced Heracleum mantegazzianum consist of dense central stands, which gradually give way to open stands towards the margins. To analyse whether open stands
are due to unsuitable conditions or represent the invading front for further spread, we studied life-cycle, population dynamics,
stand structure and soil conditions of open and dense stands over two transition periods. Populations decreased during the
first interval but increased after the extremely dry and warm summer of 2003 during the second interval. Open stands had shorter
generation times, lower height, smaller proportions of small individuals and were less in equilibrium with the environment
than dense stands. In open stands, growth to higher stages was most important, while in dense stands delayed development (self-loops)
had a strong effect on population growth; stasis and fecundity contributed most to the difference in λ between stand types.
By petiole extension H. mantegazzianum may raise its leaves just above the resident vegetation. Therefore, younger stages develop faster in open stands, whereas
strong competition by conspecific adults leads to longer generation times and a higher proportion of small individuals in
dense stands. Disturbance due to extreme climatic conditions in summer 2003 equalised population dynamics of both stand types.
Life-cycle variation between stand types makes it difficult to infer simple management rules. However, our data suggest that
small and/or open stands of H. mantegazzianum may eventually serve as initials for further spread after land-use changes, whereas dense stands are stable and may represent
sources of propagules. 相似文献
48.
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