全文获取类型
收费全文 | 120篇 |
免费 | 29篇 |
出版年
2022年 | 2篇 |
2021年 | 3篇 |
2019年 | 4篇 |
2018年 | 3篇 |
2017年 | 1篇 |
2016年 | 5篇 |
2015年 | 6篇 |
2014年 | 7篇 |
2013年 | 3篇 |
2012年 | 3篇 |
2011年 | 3篇 |
2010年 | 4篇 |
2009年 | 2篇 |
2008年 | 3篇 |
2007年 | 2篇 |
2006年 | 1篇 |
2005年 | 1篇 |
2004年 | 2篇 |
2003年 | 4篇 |
2002年 | 4篇 |
2001年 | 4篇 |
2000年 | 8篇 |
1999年 | 9篇 |
1998年 | 6篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1994年 | 3篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 8篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1978年 | 1篇 |
1976年 | 2篇 |
1973年 | 2篇 |
1970年 | 2篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1930年 | 1篇 |
1929年 | 1篇 |
1928年 | 1篇 |
1923年 | 1篇 |
1921年 | 1篇 |
排序方式: 共有149条查询结果,搜索用时 31 毫秒
81.
Apoconalbumin binds Mn(II) at two sites with association constants of K1 = 7 (+/- 1) X 10(4) and K2 = 0.4 (+/- 0.25) X 10(4) M-1. The binding is tighter in the presence of excess bicarbonate resulting in K1 = 1.8 (+/- 0.2) X 10(5) and K2 = 3 (+/- 2) X 10(4) M-1. The electron paramagnetic resonance spectrum (at both 9 and 35 GHz) of Mn(II) bound at the tight site reveals a rhombic distortion (lambda = E/D approximately equal to 0.25-0.31) in the protein ligand environment of the mental ion. An evaluation of the 1/pT1p, paramagnetic contribution to the longitudinal relaxation rate of solvent protons with Mn(II)-, Mn(III)-, and Fe(III)-derivatives of conalbumin revealed that the mental ion in each site of conalbumin is accessible to one water molecule. For Mn(II)-conalbumin and Mn(III)-conalbumin species, inner coordination sphere protons are rapidly exchanging with the bulk solvent, while slow exchange conditions prevail for Fe(III)-conalbumin. 相似文献
82.
Kumaran Kandasamy Sujatha S Mohan Rajesh Raju Shivakumar Keerthikumar Ghantasala S Sameer Kumar Abhilash K Venugopal Deepthi Telikicherla Daniel J Navarro Suresh Mathivanan Christian Pecquet Sashi Kanth Gollapudi Sudhir Gopal Tattikota Shyam Mohan Hariprasad Padhukasahasram Yashwanth Subbannayya Renu Goel Harrys KC Jacob Jun Zhong Raja Sekhar Vishalakshi Nanjappa Lavanya Balakrishnan Roopashree Subbaiah YL Ramachandra Abdul B Rahiman Keshava TS Prasad Jian-Xin Lin Jon CD Houtman Stephen Desiderio Jean-Christophe Renauld Stefan N Constantinescu Osamu Ohara Toshio Hirano Masato Kubo Sujay Singh Purvesh Khatri Sorin Draghici Gary D Bader Chris Sander Warren J Leonard Akhilesh Pandey 《Genome biology》2010,11(1):1-9
83.
Alejandra Garces Krishnamohan Atmakuri Michael R. Chase Joshua S. Woodworth Bryan Krastins Alissa C. Rothchild Talia L. Ramsdell Mary F. Lopez Samuel M. Behar David A. Sarracino Sarah M. Fortune 《PLoS pathogens》2010,6(6)
Mycobacterium tuberculosis (Mtb) requires the ESX1 specialized protein secretion system for virulence, for triggering cytosolic immune surveillance pathways, and for priming an optimal CD8+ T cell response. This suggests that ESX1 might act primarily by destabilizing the phagosomal membrane that surrounds the bacterium. However, identifying the primary function of the ESX1 system has been difficult because deletion of any substrate inhibits the secretion of all known substrates, thereby abolishing all ESX1 activity. Here we demonstrate that the ESX1 substrate EspA forms a disulfide bonded homodimer after secretion. By disrupting EspA disulfide bond formation, we have dissociated virulence from other known ESX1-mediated activities. Inhibition of EspA disulfide bond formation does not inhibit ESX1 secretion, ESX1-dependent stimulation of the cytosolic pattern receptors in the infected macrophage or the ability of Mtb to prime an adaptive immune response to ESX1 substrates. However, blocking EspA disulfide bond formation severely attenuates the ability of Mtb to survive and cause disease in mice. Strikingly, we show that inhibition of EspA disulfide bond formation also significantly compromises the stability of the mycobacterial cell wall, as does deletion of the ESX1 locus or individual components of the ESX1 system. Thus, we demonstrate that EspA is a major determinant of ESX1-mediated virulence independent of its function in ESX1 secretion. We propose that ESX1 and EspA play central roles in the virulence of Mtb in vivo because they alter the integrity of the mycobacterial cell wall. 相似文献
84.
M?ssbauer spectra from frozen solutions of ovotransferrin were recorded in a variety of applied external magnetic fields and at various temperatures in a small applied field. The results were fitted to a simple model for the electronic structure at the iron site. This model requires admixtures of the free ion 6S and 4P states, indicating a weak cubic crystal field. Possible implications of this model regarding the binding site are discussed. 相似文献
85.
The binding of Ga(III) to the proteolytically derived N-terminal half-molecule of human transferrin (HTF/2N) was studied by proton nuclear magnetic resonance spectroscopy. The pH-dependent titration curves of the histidinyl C(2) proton chemical shifts were altered upon formation of the GaIIIHTF/2N(C2O4) ternary complex. Two high-pK'a histidines failed to titrate when the metal and synergistic anion formed a complex with the protein. These results implicated two histidinyl residues as direct ligands to the metal. The rates of hydrogen-deuterium exchange for the C(2) protons of certain histidinyl residues were substantially decreased by metal ion binding. The two ligand histidines were protected from exchange, and a third, low-pK'a, histidinyl residue was protected. We propose that this third histidinyl residue is involved in anion binding and may serve as the base in the putative proton-relay scheme proposed for complex formation. 相似文献
86.
87.
88.
89.
Bradley K. Woodworth Charles M. Francis Philip D. Taylor 《Journal of avian biology》2014,45(4):387-395
Inland dispersal of migrating land birds away from the coast, often opposite to the direction of migration, occurs frequently. Many of these movements may involve migrants seeking improved stopover conditions farther inland, but direct study of inland flights and of the ecological factors influencing their occurrence is limited. We used an automated telemetry array and ground‐tracking to assess flight behaviours, survival, and habitat use of young red‐eyed vireos Vireo olivaceus during fall migration at a coastal island and an inland stopover site in southwest Nova Scotia. We recorded inland flights for 41% (11/27) of individuals that departed the island. At least 25% of 16 individuals tagged at the inland site also relocated within the landscape prior to continuing migration, but due to the higher proportion of ambiguous flights at the inland site (44%) compared to the island (15%), we could not be sure if actual proportions of relocations differed between sites. Mortality on the island (at least 10 of 39 individuals) was significantly higher than at the inland site (0 of 16 individuals). At mainland sites near the coast where we found 6 of 11 individuals after they relocated away from the island, mortality remained high (2/6). Lack of deciduous canopy cover may have contributed to the high mortality on the island, but coastal mainland sites had a relatively high amount of deciduous canopy cover, similar to at the inland site where there was no mortality. Although coastal stopover sites may be important for migrating songbirds, especially before or after making a large water crossing, our results show that mortality can be much higher, and habitat poorer, at the coast compared to farther inland. Therefore, relocating inland may be an adaptive strategy for individuals that initially settle at the coast and that need to rest and refuel before they continue migration. 相似文献
90.
Saman Bowatte Paul CD Newton Shona Brock Phil Theobald Dongwen Luo 《The ISME journal》2015,9(1):265-267
Nitrous oxide (N2O) emissions from grazed pastures are a product of microbial transformations of nitrogen and the prevailing view is that these only occur in the soil. Here we show this is not the case. We have found ammonia-oxidising bacteria (AOB) are present on plant leaves where they produce N2O just as in soil. AOB (Nitrosospira sp. predominantly) on the pasture grass Lolium perenne converted 0.02–0.42% (mean 0.12%) of the oxidised ammonia to N2O. As we have found AOB to be ubiquitous on grasses sampled from urine patches, we propose a ‘plant'' source of N2O may be a feature of grazed grassland.In terms of climate forcing, nitrous oxide (N2O) is the third most important greenhouse gas (Blunden and Arndt, 2013). Agriculture is the largest source of anthropogenic N2O (Reay et al., 2012) with about 20% of agricultural emissions coming from grassland grazed by animals (Oenema et al., 2005).Grazed grassland is a major source of N2O because grazers harvest nitrogen (N) from plants across a wide area but recycle it back onto the pasture, largely as urine, in patches of very high N concentration. The N in urine patches is often in excess of what can be used by plants resulting in losses through leaching as nitrate, as N2O and through volatilisation as ammonia (NH3) creating a high NH3 environment in the soil and plant canopy; an important point that we will return to later. The established wisdom is that N2O is generated exclusively by soil-based microbes such as ammonia-oxidising bacteria (AOB). This soil biology is represented in models designed to simulate N2O emissions and the soil is a target for mitigation strategies such as the use of nitrification inhibitors.We have previously shown that pasture plants can emit N2O largely through acting as a conduit for emissions generated in the soil, which are themselves controlled to some degree by the plant (Bowatte et al., 2014). In this case the origin of the emission is still the soil microbes. However, AOB have been found on the leaves of plants, for example, Norway spruce (Papen et al., 2002; Teuber et al., 2007) and weeds in rice paddies (Bowatte et al., 2006), prompting us to ask whether AOB might be present on the leaves of pasture species and contribute to N2O emissions as they do in soil.We looked for AOB on plants in situations where NH3 concentrations were likely to be high, choosing plants from urine patches in grazed pastures and plants from pastures surrounding a urea fertiliser manufacturing plant. DNA was extracted from the leaves (including both the surface and apoplast) and the presence of AOB tested using PCR. AOB were present in all the species we examined—the grasses Lolium perenne, Dactylis glomerata, Anthoxanthum odoratum, Poa pratensis, Bromus wildenowii and legumes Trifolium repens and T. subterraneum.To measure whether leaf AOB produce N2O, we used intact plants of ryegrass (L. perenne) lifted as cores from a paddock that had been recently grazed by adult sheep. The cores were installed in a chamber system designed to allow sampling of above- and belowground environments separately (Bowatte et al., 2014). N2O emissions were measured from untreated (control) plants and from plants where NH3 was added to the aboveground chamber and leaves were either untreated or sterilised by wiping twice with paper towels soaked in 1% hypoclorite (Sturz et al., 1997) and then with sterile water. We tested for the presence and abundance of AOB on the leaves by extracting DNA and using PCR and real-time PCR targeting the ammonia monoxygenase A (amoA) gene, which is characteristic of AOB. AOB identity was established using cloning and DNA sequencing. Further details of these experiments can be found in the Supplementary Information.The addition of NH3 to untreated plants significantly stimulated N2O emissions (P<0.001) compared with the controls; by contrast, the plants with sterilised leaves produced significantly less N2O than controls (P<0.001) even with NH3 added (Figure 1) providing strong evidence for emissions being associated with bacteria on the leaves. Control plants did emit N2O suggesting there was either sufficient NH3 available for bacterially generated emissions and/or other plant-based mechanisms were involved (Bowatte et al., 2014).Open in a separate windowFigure 1Effect of an elevated NH3 atmosphere and surface sterilisation of leaves on leaf N2O emissions measured over 1-h periods on three occasions during the day. Values are means (s.e.m.), where n=7.The major AOB species identified was Nitrosospira strain III7 that has been previously shown to produce N2O (Jiang and Bakken, 1999). We measured 109 AOB cells per m2 ryegrass leaf, assuming a specific leaf area of 250 cm2 g−1 leaf.The rate of production of N2O (0.1–0.17 mg N2O-N per m2 leaf area per hour) can be translated to a field situation using the leaf area index (LAI)—1 m2 leaf per m2 ground would be an LAI of 1. LAI in a pasture can vary from <1 to >6 depending on the management (for example, Orr et al., 1988). At LAI of 1, the AOB leaf emission rate would equate to a N2O emission rate of about 0.1–0.3 mg N2O-N per m2 ground per hour. By comparison, the emission rates measured after dairy cattle urine (650 kg N ha−1) was applied to freely and poorly drained soil were 0.024–1.55 and 0.048–3.33 mg N2O-N per m2 ground per hour, respectively (Li and Kelliher, 2005).The fraction of the NH3 that was converted to N2O by the leaf AOB was 0.02–0.42% (mean 0.12%). The mean value is close to that measured for Nitrosospira strains including strain III7 isolated from acidic, loamy and sandy soils where values ranged from 0.07 to 0.10% (Jiang and Bakken, 1999). This is good evidence that the AOB on leaves have the capacity to produce N2O at the same rate as AOB in soils. We do not suggest that leaf AOB will produce as much N2O as soil microbes; however, because leaf AOB have access to a source of substrate—volatilised NH3—that is unavailable to soil microbes and may constitute 26% (Laubach et al., 2013) to 40% (Carran et al., 1982) of the N deposited in the urine, N2O emissions from these aboveground AOB are additional to soil emissions. Further research is required to identify the situations in which leaf AOB contribute to total emissions and to quantify this contribution. 相似文献