全文获取类型
收费全文 | 20036篇 |
免费 | 2202篇 |
国内免费 | 2762篇 |
出版年
2024年 | 73篇 |
2023年 | 346篇 |
2022年 | 680篇 |
2021年 | 988篇 |
2020年 | 705篇 |
2019年 | 1017篇 |
2018年 | 902篇 |
2017年 | 750篇 |
2016年 | 928篇 |
2015年 | 1268篇 |
2014年 | 1528篇 |
2013年 | 1618篇 |
2012年 | 1898篇 |
2011年 | 1738篇 |
2010年 | 1111篇 |
2009年 | 993篇 |
2008年 | 1167篇 |
2007年 | 1007篇 |
2006年 | 925篇 |
2005年 | 771篇 |
2004年 | 658篇 |
2003年 | 590篇 |
2002年 | 517篇 |
2001年 | 358篇 |
2000年 | 314篇 |
1999年 | 268篇 |
1998年 | 184篇 |
1997年 | 134篇 |
1996年 | 122篇 |
1995年 | 85篇 |
1994年 | 95篇 |
1993年 | 62篇 |
1992年 | 91篇 |
1991年 | 100篇 |
1990年 | 93篇 |
1989年 | 79篇 |
1988年 | 49篇 |
1987年 | 55篇 |
1986年 | 64篇 |
1985年 | 49篇 |
1984年 | 57篇 |
1983年 | 58篇 |
1982年 | 36篇 |
1981年 | 25篇 |
1979年 | 43篇 |
1977年 | 27篇 |
1976年 | 32篇 |
1975年 | 26篇 |
1974年 | 29篇 |
1973年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
John G. Neuhoff Katherine L. Long Rebecca C. Worthington 《Evolution and human behavior》2012,33(4):318-322
Listeners consistently perceive approaching sounds to be closer than they actually are and perceptually underestimate the time to arrival of looming sound sources. In a natural environment, this underestimation results in more time than expected to evade or engage the source and affords a “margin of safety” that may provide a selective advantage. However, a key component in the proposed evolutionary origins of the perceptual bias is the appropriate timing of anticipatory motor behaviors. Here we show that listeners with poorer physical fitness respond sooner to looming sounds and with a larger margin of safety than listeners with better physical fitness. The anticipatory perceptual bias for looming sounds is negatively correlated with physical strength and positively correlated with recovery heart rate (a measure of aerobic fitness). The results suggest that the auditory perception of looming sounds may be modulated by the response capacity of the motor system. 相似文献
5.
Combining experimental evolution with whole‐genome resequencing is a promising new strategy for investigating the dynamics of evolutionary change. Published studies that have resequenced laboratory‐selected populations of sexual organisms have typically focused on populations sampled at the end of an evolution experiment. These studies have attempted to associate particular alleles with phenotypic change and attempted to distinguish between different theoretical models of adaptation. However, neither the population used to initiate the experiment nor multiple time points sampled during the evolutionary trajectory are generally available for examination. In this issue of Molecular Ecology, Orozco‐terWengel et al. (2012) take a significant step forward by estimating genome‐wide allele frequencies at the start, 15 generations into and at the end of a 37‐generation Drosophila experimental evolution study. The authors identify regions of the genome that have responded to laboratory selection and describe the temporal dynamics of allele frequency change. They identify two common trajectories for putatively adaptive alleles: alleles either gradually increase in frequency throughout the entire 37 generations or alleles plateau at a new frequency by generation 15. The identification of complex trajectories of alleles under selection contributes to a growing body of literature suggesting that simple models of adaptation, whereby beneficial alleles arise and increase in frequency unimpeded until they become fixed, may not adequately describe short‐term response to selection. 相似文献
6.
Correlation between bilayer destabilization and activity enhancement by diacylglycerols in reconstituted Ca-ATPase vesicles 总被引:1,自引:0,他引:1
Using the reconstituted Ca-ATPase vesicles as a model system, we demonstrated that the presence of 1,2-dioleoyl-sn-glycerol (diolein) in the membrane introduces a pronounced enhancement in the Ca-transport function of Ca-ATPase, while the 1,2-dipalmitoyl-sn-glycerol (dipalmitin) does not. We also found by both 31P NMR and freeze-fraction electron microscopy that diolein destabilized lipid bilayers to a greater extent than did dipalmitin. We conclude that the tendency of diacylglycerols to destabilize the phospholipid bilayer is related to their capacity to enhance the activity of the membrane calcium pump. 相似文献
7.
8.
9.
Yang Su-Rong Sun Huan-Xin Hu Zhen-Zhen Wang Si-Heng Sun Hui Xue Yin-Jia Ye Chen-Bo 《Sleep and biological rhythms》2017,15(1):57-65
Sleep and Biological Rhythms - Chronic sleep deprivation (SD) is an overwhelming problem in young students. Firstly, we investigated whether different levels of pre-training SD had effects on... 相似文献
10.
<正>Nanozymes, nanomaterials with enzyme-like characteristics,are emerging as novel artificial enzymes (Gao et al., 2007;Manea et al., 2004; Yan, 2018). They are superior to natural enzymes in many ways, such as higher stability, lower cost in preparation, and better robustness toward harsh environments (Wei and Wang, 2013). Various nanomaterials (e.g., 相似文献