全文获取类型
收费全文 | 5562篇 |
免费 | 413篇 |
国内免费 | 1篇 |
出版年
2023年 | 17篇 |
2022年 | 45篇 |
2021年 | 88篇 |
2020年 | 44篇 |
2019年 | 55篇 |
2018年 | 62篇 |
2017年 | 73篇 |
2016年 | 114篇 |
2015年 | 206篇 |
2014年 | 223篇 |
2013年 | 261篇 |
2012年 | 381篇 |
2011年 | 394篇 |
2010年 | 239篇 |
2009年 | 208篇 |
2008年 | 319篇 |
2007年 | 295篇 |
2006年 | 273篇 |
2005年 | 310篇 |
2004年 | 264篇 |
2003年 | 288篇 |
2002年 | 276篇 |
2001年 | 81篇 |
2000年 | 62篇 |
1999年 | 92篇 |
1998年 | 91篇 |
1997年 | 67篇 |
1996年 | 54篇 |
1995年 | 50篇 |
1994年 | 56篇 |
1993年 | 57篇 |
1992年 | 77篇 |
1991年 | 53篇 |
1990年 | 49篇 |
1989年 | 40篇 |
1988年 | 52篇 |
1987年 | 44篇 |
1986年 | 30篇 |
1985年 | 46篇 |
1984年 | 52篇 |
1983年 | 28篇 |
1982年 | 36篇 |
1981年 | 45篇 |
1980年 | 35篇 |
1979年 | 26篇 |
1978年 | 31篇 |
1977年 | 26篇 |
1976年 | 20篇 |
1974年 | 23篇 |
1961年 | 11篇 |
排序方式: 共有5976条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
5.
The elongation rate, the gradient of the local elongation rate and the surface pH of maize roots were measured over 12 h. A data bank was constituted by storing these values. By sorting these results on the basis of different elongation rates, different classes of root were obtained. Two classes were chosen: the low-growth roots and the high-growth roots. The mean growth of these two root classes was stable with time and differed significantly from one another. The surface pH of the elongation zone was the same for the roots of these two classes, but the roots selected for their higher growth rate had a larger acid efflux in this zone. 相似文献
6.
In many ecological situations, resources are difficult to find but become more apparent to nearby searchers after one of their numbers discovers and begins to exploit them. If the discoverer cannot monopolize the resources, then others may benefit from joining the discoverer and sharing their discovery. Existing theories for this type of conspecific attraction have often used very simple rules for how the decision to join a discovered resource patch should be influenced by the number of individuals already exploiting that patch. We use a mechanistic, spatially explicit model to demonstrate that individuals should not necessarily simply join patches more often as the number of individuals exploiting the patch increases, because those patches are likely to be exhausted soon or joining them will intensify future local competition. Furthermore, we show that this decision should be sensitive to the nature of the resource patches, with individuals being more responsive to discoveries in general and more tolerant of larger numbers of existing exploiters on a patch when patches are resource-rich and challenging to locate alone. As such, we argue that this greater focus on underlying joining mechanisms suggests that conspecific attraction is a more sophisticated and flexible tactic than currently appreciated. 相似文献
7.
Yedael Y. Waldman Tamir Tuller Tomer Shlomi Roded Sharan Eytan Ruppin 《Nucleic acids research》2010,38(9):2964-2974
Various studies in unicellular and multicellular organisms have shown that codon bias plays a significant role in translation efficiency (TE) by co-adaptation to the tRNA pool. Yet, in humans and other mammals the role of codon bias is still an open question, with contradictory results from different studies. Here we address this question, performing a large-scale tissue-specific analysis of TE in humans, using the tRNA Adaptation Index (tAI) as a direct measure for TE. We find tAI to significantly correlate with expression levels both in tissue-specific and in global expression measures, testifying to the TE of human tissues. Interestingly, we find significantly higher correlations in adult tissues as opposed to fetal tissues, suggesting that the tRNA pool is more adjusted to the adult period. Optimization based analysis suggests that the tRNA pool—codon bias co-adaptation is globally (and not tissue-specific) driven. Additionally, we find that tAI correlates with several measures related to the protein functionally importance, including gene essentiality. Using inferred tissue-specific tRNA pools lead to similar results and shows that tissue-specific genes are more adapted to their tRNA pool than other genes and that related sets of functional gene groups are translated efficiently in each tissue. Similar results are obtained for other mammals. Taken together, these results demonstrate the role of codon bias in TE in humans, and pave the way for future studies of tissue-specific TE in multicellular organisms. 相似文献
8.
Antoine Wystrach Sebastian Schwarz Patrick Schultheiss Guy Beugnon Ken Cheng 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2011,197(2):167-179
The Australian desert ant Melophorus bagoti often follows stereotypical routes through a cluttered landscape containing both distant panoramic views and obstacles (plants)
to navigate around. We created an artificial obstacle course for the ants between a feeder and their nest. Landmarks comprised
natural objects in the landscape such as logs, branches, and tussocks. Many ants travelled stereotypical routes home through
the obstacle course in training, threading repeatedly the same gaps in the landmarks. Manipulations altering the relations
between the landmarks and the surrounding panorama, however, affected the routes in two major ways. Both interchanging the
positions of landmarks (transpositions) and displacing the entire landmark set along with the starting position of the ants
(translations) (1) reduced the stereotypicality of the route, and (2) increased turns and meanders during travel. The ants
might have used the entire panorama in view-based travel, or the distal panorama might prime the identification and use of
landmarks en route. Despite the large data set, both options (not mutually exclusive) remain viable. 相似文献
9.
A. A. Gheyas R. D. Houston J. C. Mota-Velasco D. R. Guy A. E. Tinch C. S. Haley J. A. Woolliams 《Animal genetics》2010,41(5):531-536
In a previous study, three significant quantitative trait loci (QTL) associated with resistance to Infectious Pancreatic Necrosis (IPN) disease were identified by analysing challenge data from one sub-population of Landcatch Atlantic salmon (Salmo salar) smolt. While these QTL were shown to affect the resistance in seawater, their effect in freshwater was unknown. This study investigates the effect of these QTL on IPN resistance in salmon fry in freshwater. Twenty families with intermediate levels of IPN mortality were analysed from a freshwater challenge trial undertaken on a different sup-population of LNS salmon to that studied previously. Only the QTL from linkage group 21 (LG21) appeared to have a significant and large effect on resistance in freshwater; the same QTL was found to have the largest effect in seawater in the previous study. Variance component analysis showed a high heritability for the QTL: 0.45 ± 0.07 on the liability scale and 0.25 ± 0.05 on the observed scale. In a family where both parents were segregating for the QTL, there was a 0% vs. 100% mortality in homozygous offspring for resistant and susceptible QTL alleles. The finding that the same QTL has major effect in both freshwater and seawater has important practical implications, as this will allow the improvement of resistance in both phases through marker assisted selection by targeting this QTL. Moreover, the segregation of the LG21 QTL in a different sub-population gives further evidence of its association with IPN-resistance. 相似文献
10.