全文获取类型
收费全文 | 372篇 |
免费 | 33篇 |
专业分类
405篇 |
出版年
2023年 | 2篇 |
2022年 | 3篇 |
2021年 | 7篇 |
2020年 | 3篇 |
2019年 | 7篇 |
2018年 | 7篇 |
2017年 | 6篇 |
2016年 | 11篇 |
2015年 | 17篇 |
2014年 | 20篇 |
2013年 | 22篇 |
2012年 | 20篇 |
2011年 | 22篇 |
2010年 | 19篇 |
2009年 | 12篇 |
2008年 | 13篇 |
2007年 | 20篇 |
2006年 | 15篇 |
2005年 | 13篇 |
2004年 | 22篇 |
2003年 | 12篇 |
2002年 | 9篇 |
2001年 | 12篇 |
2000年 | 9篇 |
1999年 | 14篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 7篇 |
1991年 | 14篇 |
1990年 | 6篇 |
1989年 | 3篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 10篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1968年 | 1篇 |
1967年 | 1篇 |
1966年 | 2篇 |
排序方式: 共有405条查询结果,搜索用时 12 毫秒
1.
The amides of Leu5-enkephalin, Met5-enkephalin, and three analogues, D-Ala2,Leu5-enkephalin, (AcO)Tyr1,Met5-enkephalin, and (AcO)Tyr1,D-Ala2,Met5-enkephalin, have been studied by means of 1H NMR spectroscopy in two different solvent systems: Me2SO-d6 and CDCl3. In the latter solvent the peptides were dissolved as complexes with 18-crown-6-ether, a coronand that binds strongly to the NH3+ groups. The crown ether complexation and the apolar solvent were used to simulate the anionic subsite of the receptor and the hydrophobic environment of the receptor cavity, respectively. The very unusual amide proton chemical shifts and their temperature coefficients suggest the presence of folded conformations in CDCl3 for all peptides, consistent with several models of opioid receptors and with the crystal structure of Leu5-enkephalin. The differences among the proposed cyclic conformations of the five peptides may be correlated, in part, with their different biological activity. All peptides in Me2SO-d6 are characterized by complex mixtures of extended fully solvated conformations. 相似文献
2.
A conformational study of the opioid peptide dermorphin by one-dimensional and two-dimensional nuclear magnetic resonance spectroscopy
下载免费PDF全文
![点击此处可从《Biophysical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dermorphin, a natural peptide opioid containing a D-Ala2 residue, has been studied in dimethyl sulfoxide (DMSO) solution by means of several one-dimensional and two-dimensional 1H nuclear magnetic resonance (NMR) methods at various fields from 80 to 600 MHz. The combined use of conventional NMR parameters and of nuclear Overhauser effect effects points to an essentially extended structure. This conformation may be, in part, the result of strong interaction of the amide groups with DMSO molecules. 相似文献
3.
T Santantonio E Albore G Angarano G Pastore 《Bollettino della Società italiana di biologia sperimentale》1983,59(7):983-989
Soluble (free) and insoluble (IgG-bound) hepatitis B e antigen (HBeAg) activities in 1,33 M ammonium sulfate solution was evaluated serially in sera from 12 patients with acute type B hepatitis followed up to 60 days. In three cases preclinical sera were available. In patients who showed clinical and biochemical resolution of hepatitis within 60 days, HBeAg free was the prevalent form of circulating HBeAg during the incubation period of disease, then gradually shifting to the IgG-bound form at the onset of jaundice. Finally HBeAg-bound was no longer demonstrable, followed by detection of anti-HBe antibody. On the contrary, in all patients with unresolved hepatitis both HBeAg-free and HBeAg-bound were detected with prevalence of HBeAg-free ratio. These data suggest a striking correlation between synthesis of HBeAg and HBV replication and may indicate that HBeAg-free and IgG-bound ratio reflects the stage and prognosis of acute HBV infection. 相似文献
4.
Summary Two strains of osmophilic yeast which were isolated from honey-comb, produced good yields of erythritol as a main product. These strains were identified as Trichosporonoides sp., 150-5 and 331-1.From the fermentation studies with these strains using glucose and sucrose as substrate, strain 331-1 produced more erythritol as the sole polyhydric product,with trace quantities of glycerol, than strain 150-5. 相似文献
5.
Anthony John Pastore Alvaro Montoya Manasi Kamat Kari B. Basso James S. Italia Abhishek Chatterjee Maria Drosou Dimitrios A. Pantazis Alexander Angerhofer 《Protein science : a publication of the Protein Society》2023,32(1):e4537
Oxalate decarboxylase from Bacillus subtilis is a binuclear Mn-dependent acid stress response enzyme that converts the mono-anion of oxalic acid into formate and carbon dioxide in a redox neutral unimolecular disproportionation reaction. A π-stacked tryptophan dimer, W96 and W274, at the interface between two monomer subunits facilitates long-range electron transfer between the two Mn ions and plays an important role in the catalytic mechanism. Substitution of W96 with the unnatural amino acid 5-hydroxytryptophan leads to a persistent EPR signal which can be traced back to the neutral radical of 5-hydroxytryptophan with its hydroxyl proton removed. 5-Hydroxytryptophan acts as a hole sink preventing the formation of Mn(III) at the N-terminal active site and strongly suppresses enzymatic activity. The lower boundary of the standard reduction potential for the active site Mn(II)/Mn(III) couple can therefore be estimated as 740 mV against the normal hydrogen electrode at pH 4, the pH of maximum catalytic efficiency. Our results support the catalytic importance of long-range electron transfer in oxalate decarboxylase while at the same time highlighting the utility of unnatural amino acid incorporation and specifically the use of 5-hydroxytryptophan as an energetic sink for hole hopping to probe electron transfer in redox proteins. 相似文献
6.
7.
G Esposito A M Lesk H Molinari A Motta N Niccolai A Pastore 《Journal of molecular biology》1992,224(3):659-670
Soluble spin labels, which "bleach" the surface proton resonances of a protein to n.m.r. measurements, can provide useful information about protein conformation and dynamics. The use of the soluble nitroxide, TEMPOL, has been explored to show the correlation of the paramagnetic perturbations of protein two-dimensional n.m.r. data with proton exposure to the free radical in hen egg-white lysozyme. The results demonstrate that the nitroxide approaches the protein randomly, and that the extent of the observed paramagnetic effects reflects the native folding pattern of the protein. A correlation of spectral simplification with the known tertiary structure establishes the feasibility of new strategies for topological mapping of surface and buried protons of the protein. Application to the elucidation of protein structure and to the study of dynamical processes is discussed. 相似文献
8.
The 32 amino acid hormone salmon calcitonin was studied at pH 3.7 and 7.4 by two-dimensional NMR in sodium dodecyl sulfate (SDS) micelles at 310 K. The spectrum was fully assigned, and the secondary structure was obtained from nuclear Overhauser enhancement spectroscopy (NOESY), 3JHN alpha coupling constants, and slowly exchanging amide data. Three-dimensional structures consistent with NMR data were generated by using distance geometry calculations. A set of 260 interproton distances, derived from NOESY, and hydrogen-bond constraints, obtained from analysis of the amide exchange, were used. From the initial random conformations, 13 distance geometry structures with minimal violations were selected for further refinement with restrained energy minimization. In SDS, at both pHs, the main conformational feature of the hormone is an alpha-helix from Thr6 through Tyr22, thus including the amphipathic 8-22 segment and two residues of the Cys1-Cys7 N-terminal loop. The C-terminal decapeptide forms a loop folded back toward the helix. The biological significance of this conformation is discussed. 相似文献
9.
When calculating three-dimensional structures from NMR data, alternative solutions with very large RMS deviation can be obtained. Sometimes local or global inversions of the protein folding can be observed. We call these different solutions topological mirror images, as they keep the correct amino acid chirality. They are observed when the number of restraints is insufficient and represent different solutions from the same scalar information. Therefore they are common in small peptides where the NMR data are often limited and the secondary structure is not very well defined. They can also be observed in large molecules in regions of higher flexibility. In our experience the observation of topological mirror images is independent of the efficiency of sampling of the algorithm used. We present four examples of proteins with different size and folding. We also discuss ways to distinguish among the different solutions. 相似文献
10.
Mahendra Rai Dnyaneshwar Rathod Gauravi Agarkar Mudasir Dar Marian Brestic Glaucia Maria Pastore Mario Roberto Marostica Junior 《Symbiosis (Philadelphia, Pa.)》2014,62(2):63-79
Agricultural productivity suffers a heavy loss due to plant pathogens, insect pests and various abiotic stresses. Agriculture being the world’s largest economic sector, it is the need of time to find and establish the ideal strategy for sustainable agriculture and improvement in crop growth. Endophytes are microorganisms that asymptomatically grow within the plant tissues without causing any disease to the host. Endophytic fungi live in symbiotic association with plants and play an important role in plant growth promotion, higher seed yield and plants resistant to various biotic, abiotic stresses and diseases. Many are able to produce antimicrobial compounds, plant growth hormones and various agrochemical bioactive metabolites. These mycoendophytes hold enormous potential for the development of eco-friendly and economically viable agricultural products. In this review we focused on the endophytic fungi recovered from different medicinal plants, their active principles involved in plant growth enhancement and the applications of fungal endophytes in agriculture. Moreover, we also discussed about endophytic fungi and their pragmatic approach towards sustainable food and agriculture. 相似文献