全文获取类型
收费全文 | 571篇 |
免费 | 44篇 |
国内免费 | 1篇 |
专业分类
616篇 |
出版年
2023年 | 4篇 |
2022年 | 9篇 |
2021年 | 13篇 |
2020年 | 3篇 |
2019年 | 8篇 |
2018年 | 12篇 |
2017年 | 12篇 |
2016年 | 20篇 |
2015年 | 32篇 |
2014年 | 29篇 |
2013年 | 43篇 |
2012年 | 59篇 |
2011年 | 47篇 |
2010年 | 32篇 |
2009年 | 25篇 |
2008年 | 30篇 |
2007年 | 27篇 |
2006年 | 20篇 |
2005年 | 33篇 |
2004年 | 19篇 |
2003年 | 30篇 |
2002年 | 19篇 |
2001年 | 8篇 |
2000年 | 5篇 |
1999年 | 8篇 |
1998年 | 5篇 |
1997年 | 9篇 |
1996年 | 1篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 5篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1988年 | 1篇 |
1987年 | 4篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 1篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1979年 | 5篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有616条查询结果,搜索用时 15 毫秒
1.
Embryo survival and alevin emergence pattern of brown trout were studied in simulated redds with different homogeneous gravel sizes and different concentrations of peat material. Optimal survival (95%) occurred in 18 mm gravel and survival decreased with decreasing gravel size. High concentrations (40%) of peat material resulted in low survival (65%). The proportion of premature emerging alevins increased in finer gravels and at high peat concentrations. Premature alevins had a large yolk sac and are probably very vulnerable to predators. 相似文献
2.
Abstract The effect of culture filtrate containing cholera toxin (CT) on rat intestinal permeability was studied using fluorescein isothiocyanate-labelled dextran 3000 (FITC-D3, M r , 3000) as probe molecule. CT was given either perorally, via a gastric tube 90 min before, or locally in conjunction with the permeability measurement in the distal ileum. Compaired to the control animals, either mode of administration resulted in increased permeation of FITC-D3 from the intestine to portal blood. The effect of the local treatment was apparent after 5–10 min and prevailed during the 60-min measurement period. The results indicate that CT not only affects net water transport at the intestinal mucosa but also the passage of larger molecules across the intestinal wall. 相似文献
3.
Maninder K. Sohi Tommy Wan Brian J. Sutton Tony Atkinson Max A. Atkinson Jonathan P. Murphy Stephen P. Bottomley Michael G. Gore 《Proteins》1995,23(4):610-612
Protein L is a multi domain cell wall constituent of certain strains of Peptostreptococcus magnus which binds to the variable domain of immunoglobulin κ-light chains. A single immunoglobulin-binding domain of Mr = 9000 from this protein has been isolated and crystallized. The crystals are of space group P42212, with cell dimensions a = b = 66.9 Å, c = 68.3 Å, and diffract to at least 2.2 Å resolution. The asymmetric unit of the crystal contains two molecules of the protein L domain, related by a noncrystallographic 2-fold axis, as revealed by a self-rotation function calculated with native diffraction data. © 1995 Wiley-Liss, Inc. 相似文献
4.
Shengyi Wu Tommy Blanchard Emily Meschke Richard N. Aslin Benjamin Y. Hayden Celeste Kidd 《Biology letters》2022,18(7)
Normative learning theories dictate that we should preferentially attend to informative sources, but only up to the point that our limited learning systems can process their content. Humans, including infants, show this predicted strategic deployment of attention. Here, we demonstrate that rhesus monkeys, much like humans, attend to events of moderate surprisingness over both more and less surprising events. They do this in the absence of any specific goal or contingent reward, indicating that the behavioural pattern is spontaneous. We suggest this U-shaped attentional preference represents an evolutionarily preserved strategy for guiding intelligent organisms toward material that is maximally useful for learning. 相似文献
5.
In the early stages of infection, gaining control of the cellular protein synthesis machinery including its ribosomes is the ultimate combat objective for a virus. To successfully replicate, viruses unequivocally need to usurp and redeploy this machinery for translation of their own mRNA. In response, the host triggers global shutdown of translation while paradoxically allowing swift synthesis of antiviral proteins as a strategy to limit collateral damage. This fundamental conflict at the level of translational control defines the outcome of infection. As part of this special issue on molecular mechanisms of early virus–host cell interactions, we review the current state of knowledge regarding translational control during viral infection with specific emphasis on protein kinase RNA-activated and mammalian target of rapamycin-mediated mechanisms. We also describe recent technological advances that will allow unprecedented insight into how viruses and host cells battle for ribosomes. 相似文献
6.
Linking molecular evolution to biological function is a long‐standing challenge in evolutionary biology. Some of the best examples of this involve opsins, the genes that encode the molecular basis of light reception. In this issue of Molecular Ecology, three studies examine opsin gene sequence, expression and repertoire to determine how natural selection has shaped the visual system. First, Escobar‐Camacho et al. ( 2017 ) use opsin repertoire and expression in three Amazonian cichlid species to show that a shift in sensitivity towards longer wavelengths is coincident with the long‐wavelength‐dominated Amazon basin. Second, Stieb et al. ( 2017 ) explore opsin sequence and expression in reef‐dwelling damselfish and find that UV‐ and long‐wavelength vision are both important, but likely for different ecological functions. Lastly, Suvorov et al. ( 2017 ) study an expansive opsin repertoire in the insect order Odonata and find evidence that copy number expansion is consistent with the permanent heterozygote model of gene duplication. Together these studies emphasize the utility of opsin genes for studying both the local adaptation of sensory systems and, more generally, gene family evolution. 相似文献
7.
Separating water‐potential induced swelling and shrinking from measured radial stem variations reveals a cambial growth and osmotic concentration signal
下载免费PDF全文
![点击此处可从《Plant, cell & environment》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Tommy Chan Teemu Hölttä Frank Berninger Harri Mäkinen Pekka Nöjd Maurizio Mencuccini Eero Nikinmaa 《Plant, cell & environment》2016,39(2):233-244
The quantification of cambial growth over short time periods has been hampered by problems to discern between growth and the swelling and shrinking of a tree stem. This paper presents a model, which separates cambial growth and reversible water‐potential induced diurnal changes from simultaneously measured whole stem and xylem radial variations, from field‐measured Scots pine trees in Finland. The modelled growth, which includes osmotic concentration changes, was compared with (direct) dendrometer measurements and microcore samples. In addition, the relationship of modelled growth and dendrometer measurements to environmental factors was analysed. The results showed that the water‐potential induced changes of tree radius were successfully separated from stem growth. Daily growth predicted by the model exhibited a high correlation with the modelled daily changes of osmotic concentration in phloem, and a temperature dependency in early summer. Late‐summer growth saw higher dependency on water availability and temperature. Evaluation of the model against dendrometer measurements showed that the latter masked a true environmental signal in stem growth due to water‐potential induced changes. The model provides better understanding of radial growth physiology and offers potential to examine growth dynamics and changes due to osmotic concentration, and how the environment affects growth. 相似文献
8.
Flix Manuel Medina Tommy Melo Paulo Oliveira Manuel Nogales Pedro Geraldes 《African Journal of Ecology》2021,59(1):88-98
Studies on feral cat diet offer important ecological information and are the first step towards determining their impact upon endangered species. However, in comparing seasonal changes in diet with seasonal prey availability, the scarce amount of research into oceanic islands worldwide must be considered when deciding if a specific population is actually affected by cat predation. Cat diet was analysed on Santa Luzia (Cabo Verde Islands) since this invasive predator is considered one of the main threats to native endangered species that require conservation measures. These previous studies were carried out in different seasons, providing contrasting results, skinks being more preyed upon in the rainy season and mice in the driest periods. To check these different results, we focussed on how cat diet varied seasonally in response to changes in prey abundance. Saurians were the most important prey group, followed by mice, invertebrates and birds. No seasonal differences were, however, observed in the different prey groups consumed, saurians being the main prey in both seasons. All cases reflected their respective abundances. Results corroborate the generalist and opportunistic trophic ecology of feral cats, providing important information to assess their impact on prey populations and design future eradication programmes. 相似文献
9.
Jian-Jun Jia Roni M Lahr Michael T Solgaard Bruno J Moraes Roberta Pointet An-Dao Yang Giovanna Celucci Tyson E Graber Huy-Dung Hoang Marius
R Niklaus Izabella A Pena Anne K Hollensen Ewan M Smith Malik Chaker-Margot Leonie Anton Christopher Dajadian Mark Livingstone Jaclyn Hearnden Xu-Dong Wang Yonghao Yu Timm Maier Christian K Damgaard Andrea J Berman Tommy Alain Bruno D Fonseca 《Nucleic acids research》2021,49(6):3461
10.
Sanhao Ji Yong Ju Hua Fu Yufen Zhao Tommy Johansson Jacek Stawinski 《Nucleosides, nucleotides & nucleic acids》2013,32(7):771-784
2-,3-,4-Pyridylphosphonates and their phosphonothioate congeners were analyzed by electrospray ionization multistage tandem mass spectrometry (ESI-MSn). It was found that the fragmentation pathways of these compounds were not influenced to any detectable extent by the stereochemistry at the phosphorus centers but were sensitive to the position of a nitrogen atom in the pyridine ring of these compounds. Possible mechanisms for fragmentations of the investigated compounds are discussed in detail. 相似文献