全文获取类型
收费全文 | 493篇 |
免费 | 56篇 |
出版年
2021年 | 4篇 |
2020年 | 1篇 |
2019年 | 6篇 |
2018年 | 14篇 |
2017年 | 8篇 |
2016年 | 14篇 |
2015年 | 16篇 |
2014年 | 30篇 |
2013年 | 40篇 |
2012年 | 41篇 |
2011年 | 42篇 |
2010年 | 29篇 |
2009年 | 25篇 |
2008年 | 37篇 |
2007年 | 23篇 |
2006年 | 20篇 |
2005年 | 14篇 |
2004年 | 28篇 |
2003年 | 19篇 |
2002年 | 13篇 |
2001年 | 3篇 |
2000年 | 9篇 |
1999年 | 8篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 2篇 |
1995年 | 7篇 |
1994年 | 4篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 10篇 |
1989年 | 13篇 |
1988年 | 3篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 6篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有549条查询结果,搜索用时 15 毫秒
1.
Phosphorylation is a potent mechanism regulating the activity of many intracellular enzymes. We have discovered that the product of the human urokinase plasminogen activator gene, pro-uPA, is phosphorylated in serine in at least two human cell lines. Phosphorylation occurs within the cell during biosynthesis, and phosphorylated intracellular pro-uPA is secreted into the medium. Of the secreted pro-uPA molecules, 20-50% are phosphorylated in serine, thus representing a meaningful fraction of the total biosynthetic pro-uPA. Although the sites of phosphorylation have not yet been determined, at least two such sites must exist; in fact plasmin cleavage of phosphorylated single chain pro-uPA yields a two chain uPA in which both chains are phosphorylated. A specific function for pro-uPA phosphorylation has not yet been identified; however, it is tempting to speculate that, as in many other cases, phosphorylation may affect the activity of the enzyme, its response to inhibitors or the conversion of pro-uPA zymogen to active two-chain uPA. This would represent an additional way of regulating extracellular proteolysis, an important pathway involved in both intra- and extravascular phenomena like fibrinolysis, cell migration and invasiveness. 相似文献
2.
3.
Enrica L. Santarcangelo Giulia Paoletti Iacopo Chiavacci Carlo Palombo Giancarlo Carli Maurizio Varanini 《PloS one》2013,8(10)
In healthy subjects with high hypnotisability (highs) under hypnosis, subjectively effective suggestions for analgesia abolish the increases in blood pressure associated with cold pressor test (cpt) by reducing the peripheral vascular resistance. The aim of the present study was to investigate the effects of the suggestions of analgesia on the responses to cpt in healthy highs (n = 22) and in low hypnotisable participants (lows, n = 22) out of hypnosis. Cpt was administered without (CPT) and with suggestions for analgesia (CPT+AN). Psychophysical (pain intensity, pain threshold, cpt duration (time of immersion) and pain tolerance, defined as the difference between cpt duration and pain threshold), respiratory (amplitude and frequency) and autonomic variables (tonic skin conductance, mean RR interval (RR = 1/heart rate), blood pressure, skin blood flow) were studied. The suggestions for analgesia increased cpt duration and RR in both groups, but decreased pain intensity and enhanced pain threshold only in highs; in both groups they did not modulate systolic blood pressure, tonic skin conductance and skin blood flow; thus, increased parasympathetic activity appears responsible for the heart rate reduction induced by suggestions in both groups. In conclusion, our findings show that suggestions modulate pain experience differentially in highs and lows, and are partially effective also in lows. We hypothesize that the mechanisms responsible for the efficacy of suggestions in healthy lows may be involved also in their efficacy in chronic pain patients with low hypnotisability. 相似文献
4.
Ran Zuo Aline de Oliveira Enrica Bullita Maria Ines Torino Kaylie A. Padgett-Pagliai Christopher L. Gardner Natalie A. Harrison Danilo da Silva Marcelo L. Merli Claudio F. Gonzalez Graciela L. Lorca 《Environmental microbiology》2019,21(12):4822-4835
Liberibacter asiaticus is the prevalent causative pathogen of Huanglongbing or citrus greening disease, which has resulted in a devastating crisis in the citrus industry. A thorough understanding of this pathogen's physiology and mechanisms to control cell survival is critical in the identification of therapeutic targets. YbeY is a highly conserved bacterial RNase that has been implicated in multiple roles. In this study, we evaluated the biochemical characteristics of the L. asiaticus YbeY (CLIBASIA_01560) and assessed its potential as a target for antimicrobials. YbeYLas was characterized as an endoribonuclease with activity on 3′ and 5′ termini of 16S and 23S rRNAs, and the capacity to suppress the E. coli ΔybeY phenotype. We predicted the YbeYLas protein:ligand interface and subsequently identified a flavone compound, luteolin, as a selective inhibitor. Site-directed mutagenesis was subsequently used to identify key residues involved in the catalytic activity of YbeYLas. Further evaluation of naturally occurring flavonoids in citrus trees indicated that both flavones and flavonols had potent inhibitory effects on YbeYLas. Luteolin was subsequently examined for efficacy against L. asiaticus in Huanglongbing-infected citrus trees, where a significant reduction in L. asiaticus gene expression was observed. 相似文献
5.
6.
Chiara Ciaccio Francisco Oca?a-Calahorro Enrica Droghetti Grazia R. Tundo Emanuel Sanz-Luque Fabio Polticelli Paolo Visca Giulietta Smulevich Paolo Ascenzi Massimo Coletta 《PloS one》2015,10(5)
The single-cell green alga Chlamydomonas reinhardtii harbors twelve truncated hemoglobins (Cr-TrHbs). Cr-TrHb1-1 and Cr-TrHb1-8 have been postulated to be parts of the nitrogen assimilation pathway, and of a NO-dependent signaling pathway, respectively. Here, spectroscopic and reactivity properties of Cr-TrHb1-1, Cr-TrHb1-2, and Cr-TrHb1-4, all belonging to clsss 1 (previously known as group N or group I), are reported. The ferric form of Cr-TrHb1-1, Cr-TrHb1-2, and Cr-TrHb1-4 displays a stable 6cLS heme-Fe atom, whereas the hexa-coordination of the ferrous derivative appears less strongly stabilized. Accordingly, kinetics of azide binding to ferric Cr-TrHb1-1, Cr-TrHb1-2, and Cr-TrHb1-4 are independent of the ligand concentration. Conversely, kinetics of CO or NO2− binding to ferrous Cr-TrHb1-1, Cr-TrHb1-2, and Cr-TrHb1-4 are ligand-dependent at low CO or NO2− concentrations, tending to level off at high ligand concentrations, suggesting the presence of a rate-limiting step. In agreement with the different heme-Fe environments, the pH-dependent kinetics for CO and NO2−binding to ferrous Cr-TrHb1-1, Cr-TrHb1-2, and Cr-TrHb1-4 are characterized by different ligand-linked protonation events. This raises the question of whether the simultaneous presence in C. reinhardtii of multiple TrHb1s may be related to different regulatory roles. 相似文献
7.
Long Tree-Ring Chronologies Provide Evidence of Recent Tree Growth Decrease in a Central African Tropical Forest 总被引:1,自引:0,他引:1
Giovanna Battipaglia Enrica Zalloni Simona Castaldi Fabio Marzaioli Roberto Cazzolla- Gatti Bruno Lasserre Roberto Tognetti Marco Marchetti Riccardo Valentini 《PloS one》2015,10(3)
It is still unclear whether the exponential rise of atmospheric CO2 concentration has produced a fertilization effect on tropical forests, thus incrementing their growth rate, in the last two centuries. As many factors affect tree growth patterns, short -term studies might be influenced by the confounding effect of several interacting environmental variables on plant growth. Long-term analyses of tree growth can elucidate long-term trends of plant growth response to dominant drivers. The study of annual rings, applied to long tree-ring chronologies in tropical forest trees enables such analysis. Long-term tree-ring chronologies of three widespread African species were measured in Central Africa to analyze the growth of trees over the last two centuries. Growth trends were correlated to changes in global atmospheric CO2 concentration and local variations in the main climatic drivers, temperature and rainfall. Our results provided no evidence for a fertilization effect of CO2 on tree growth. On the contrary, an overall growth decline was observed for all three species in the last century, which appears to be significantly correlated to the increase in local temperature. These findings provide additional support to the global observations of a slowing down of C sequestration in the trunks of forest trees in recent decades. Data indicate that the CO2 increase alone has not been sufficient to obtain a tree growth increase in tropical trees. The effect of other changing environmental factors, like temperature, may have overridden the fertilization effect of CO2. 相似文献
8.
9.
Enrica Roccotiello Gabriele Casazza Loris Galli Laura Cornara Alessandro Moncalvo Luigi Minuto 《Plant Systematics and Evolution》2009,279(1-4):41-49
Daphne gnidium is a circum-Mediterranean evergreen shrub. Flower and pollen features related to pollination mechanism were analyzed, and the seasonal presence of insects visiting the plant was monitored. The morphology and functionality of flowers are compatible with entomophily, as are pollen viability, which is maintained for a few hours only after anthesis, and the very short stigmatic receptivity. The reproductive fitness of the species is low and the ripening process often fails (35% collapsed embryos). While male organ functionality is fairly regular, the female organ often shows developmental arrest. The complex or transient evolutionary traits displayed by D. gnidium are comparable to those of Thymelaea hirsuta and other members of the Thymelaeaceae. 相似文献
10.
Claudio Gardana Enrica Canzi Paolo Simonetti 《The Journal of nutritional biochemistry》2009,20(12):940-947
The intestinal microbial transformation of daidzein into equol is subject to a wide inter-individual variability. The aim of this study was to investigate in vitro this transformation and to evaluate possible correlations between individual diet and equol production. The transformation of daidzein was investigated in anaerobic batch cultures inoculated with mixed fecal bacteria from 90 volunteers. The daidzein metabolism was monitored by liquid chromatography-mass spectrometry, and a chiral column was used to distinguish equol and dihydrodaidzein enantiomers. The obtained results show that daidzein was unchanged (≈27%) or degraded to equol (≈28%), O-desmethylangolensin (≈12%) or dihydrodaidzein (≈31%). Furthermore, some subjects (≈2%) are able to produce both equol and O-desmethylangolensin. Bacteria represent sub-dominant populations (105–109 cell/g wet faeces) in “slow” equol producers, while higher counts of equol-producing microorganisms (1010–1011 cell/g wet faeces) were found in “quick” equol producers. The in vitro test to evaluate equol-producing status is quick and not invasive, and the obtained results are comparable with those reported in vivo. Indeed, the only enantiomer present in the batch cultures containing equol was the S-form. No significant correlations between equol production, BMI, age and sex were found. It seems that the equol-producer group consumed less fibre, vegetables and cereals, and more lipids from animal sources. 相似文献