全文获取类型
收费全文 | 327篇 |
免费 | 8篇 |
国内免费 | 5篇 |
专业分类
化学 | 202篇 |
力学 | 3篇 |
数学 | 28篇 |
物理学 | 107篇 |
出版年
2022年 | 3篇 |
2021年 | 3篇 |
2020年 | 3篇 |
2019年 | 2篇 |
2018年 | 4篇 |
2016年 | 7篇 |
2015年 | 4篇 |
2014年 | 3篇 |
2013年 | 14篇 |
2012年 | 15篇 |
2011年 | 15篇 |
2010年 | 7篇 |
2009年 | 7篇 |
2008年 | 15篇 |
2007年 | 8篇 |
2006年 | 17篇 |
2005年 | 17篇 |
2004年 | 10篇 |
2003年 | 7篇 |
2002年 | 22篇 |
2001年 | 14篇 |
2000年 | 16篇 |
1999年 | 11篇 |
1998年 | 5篇 |
1997年 | 3篇 |
1996年 | 6篇 |
1995年 | 7篇 |
1994年 | 4篇 |
1993年 | 6篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 5篇 |
1981年 | 3篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1974年 | 5篇 |
1973年 | 8篇 |
1971年 | 3篇 |
1970年 | 2篇 |
1968年 | 2篇 |
1939年 | 2篇 |
1865年 | 2篇 |
排序方式: 共有340条查询结果,搜索用时 15 毫秒
51.
T.J. Brady 《Physics letters. [Part B]》1973,45(1):4-6
The 180° nucleon-deutron elastic cross section exhibits a peak as a function of nucleon energy which has been interpreted as due to a virtual state of the trinucleon. This interpretation is examined within the context of the Amado model. 相似文献
52.
The configurations of 6-methoxyaurone prepared by the condensation of 6-methoxy- coumaran-3-one and benzaldehyde and of its photoisomer are assigned on the basis of chemical and NMR evidence. 相似文献
53.
N.?F.?Brady J.?M.?Montgomery G.?Tsoi T.?Gebre S.?T.?Weir Y.?K.?Vohra D.?J.?HiltonEmail author 《The European Physical Journal B - Condensed Matter and Complex Systems》2013,86(7):334
We have used X-ray diffraction to study the structural phase of CeCoIn5 in external pressure. Using high-pressure X-ray diffraction, we find that the crystalline phase is stable in the P4/mmm phase for pressures ≤51.2 GPa. From our measured equation of state, we find a bulk modulus given by B 0 = 72.8 ± 2.9 GPa and a first pressure derivative of B ′ = 5.1 ± 0.3. Measurement of the electrical resistivity of CeCoIn5 to pressures as high as 34.4 GPa shows the existence of a peak in resistivity at p ? = 8.2 ± 0.2 GPa. 相似文献
54.
Mohamed I. Hassan Benjamin R. Lundgren Michael Chaumun Dennis M. Whitfield Brady Clark Ian C. Schoenhofen Christopher N. Boddy 《Angewandte Chemie (International ed. in English)》2016,55(39):12018-12021
Legionaminic acid, Leg5,7Ac2, a nonulosonic acid like 5‐acetamido neuraminic acid (Neu5Ac, sialic acid), is found in cell surface glycoconjugates of bacteria including the pathogens Campylobacter jejuni, Acinetobacter baumanii and Legionella pneumophila. The presence of Leg5,7Ac2 has been correlated with virulence in humans by mechanisms that likely involve subversion of the host's immune system or interactions with host cell surfaces due to its similarity to Neu5Ac. Investigation into its role in bacterial physiology and pathogenicity is limited as there are no effective sources of it. Herein, we construct a de novo Leg5,7Ac2 biosynthetic pathway by combining multiple metabolic modules from three different microbial sources (Saccharomyces cerevisiae, C. jejuni, and L. pneumophila). Over‐expression of this de novo pathway in Escherichia coli that has been engineered to lack two native catabolic pathways, enables significant quantities of Leg5,7Ac2 (≈120 mg L?1 of culture broth) to be produced. Pure Leg5,7Ac2 could be isolated and converted into CMP‐activated sugar for biochemical applications and a phenyl thioglycoside for chemical synthesis applications. This first total biosynthesis provides an essential source of Leg5,7Ac2 enabling study of its role in prokaryotic and eukaryotic glycobiology. 相似文献
55.
Effects of Visible‐Light Irradiation of Protoporphyrin IX on the Self‐Assembly of Tubulin Heterodimers 下载免费PDF全文
Alicia Vall‐Sagarra Dr. Brady McMicken Prof. Santi Nonell Dr. Lorenzo Brancaleon 《Chemphyschem》2016,17(20):3269-3282
The formation and the effects of laser irradiation of the complex formed by protoporphyrin IX (PPIX) and tubulin was investigated. We have used tubulin as a model protein to investigate whether docked photoactive ligands can affect the structure and function of polypeptides upon exposure to visible light. We observed that laser irradiation in the Soret band prompts bleaching of the PPIX, which is accompanied by a sharp decrease in the intensity and average fluorescence lifetime of the protein (dominated by the four tryptophan residues of the tubulin monomer). The kinetics indicate non‐trivial effects and suggest that the photosensitization of the PPIX bound to tubulin prompts structural alterations of the protein. These modifications were also observed through changes in the energy transfer between Trp residues and PPIX. The results suggest that laser irradiation produces localized partial unfolding of tubulin and that the changes prompt modification of the formation of microtubules in vitro. Measurements of singlet oxygen formation were inconclusive in determining whether the changes are prompted by reactive oxygen species or other excited state mechanisms. 相似文献
56.
Dempsey CE Mason PE Brady JW Neilson GW 《Journal of the American Chemical Society》2007,129(51):15895-15902
Guanidinium (Gdm+) chloride is a powerful protein denaturant, whereas the sulfate dianion (SO42-) is a strong stabilizer of folded protein states; Gdm2SO4 is effectively neutral in its effects on protein stability. While the "neutralizing" effects of protein-stabilizing solutes on the activity of denaturants can be broadly interpreted in terms of additive effects of the solutes, recent experimental and simulation studies support a role for hetero-ion interactions in the effect of sulfate on Gdm+ denaturation [Mason, P. E.; et al. J. Phys. Chem. B 2005, 109, 24185-24196]. Here we describe an experimental strategy for testing this mechanism that involves spectroscopic analysis of the separate effects of alkali metal sulfates (Na2SO4, Rb2SO4), GdmCl, and Gdm2SO4 on the folded populations of several peptides chosen to dissect specific noncovalent contributions to the conformational stability of proteins [alanine-based helical peptides stabilized by hydrogen bonds, tryptophan zipper (trpzip) peptides stabilized largely by cross-strand indole-indole interactions]. While the trpzip peptides are highly sensitive to GdmCl denaturation, they are unaffected by NaCl, Na2SO4, or Gdm2SO4, indicating that the reversal of the denaturant activity of Gdm+ by sulfate in this case is not due to competing stabilizing (sulfate) and destabilizing (Gdm+) interactions. Gdm2SO4 was found to retain considerable denaturant activity against alanine-based alpha-helical peptides. The differences in the effects of Gdm2SO4 on the two peptide types can be understood in terms of the different mechanisms of Gdm+ denaturation of trpzip peptides and helical peptides, respectively, and the specific nature of Gdm+ and SO42- ionic "clustering" that differentially affects the ability of Gdm+ to make the molecular interactions with the peptides that underlie its denaturant activity. 相似文献
57.
William M. Dawson Freddie J. O. Martin Guto G. Rhys Kathryn L. Shelley R. Leo Brady Derek N. Woolfson 《Chemical science》2021,12(20):6923
The rational design of linear peptides that assemble controllably and predictably in water is challenging. Short sequences must encode unique target structures and avoid alternative states. However, the non-covalent forces that stabilize and discriminate between states are weak. Nonetheless, for α-helical coiled-coil assemblies considerable progress has been made in rational de novo design. In these, sequence repeats of nominally hydrophobic (h) and polar (p) residues, hpphppp, direct the assembly of amphipathic helices into dimeric to tetrameric bundles. Expanding this pattern to hpphhph can produce larger α-helical barrels. Here, we show that pentameric to nonameric barrels are accessed by varying the residue at one of the h sites. In peptides with four L/I–K–E–I–A–x–Z repeats, decreasing the size of Z from threonine to serine to alanine to glycine gives progressively larger oligomers. X-ray crystal structures of the resulting α-helical barrels rationalize this: side chains at Z point directly into the helical interfaces, and smaller residues allow closer helix contacts and larger assemblies.Systematic de novo design of peptides that form α-helical barrels with functionalisable central channels with a range of internal diameters. 相似文献
58.
A new general synthesis of substituted coumarins is described. The in situ cycloaddition of chloroketenes with α-methoxymethylenecyclohexanones yields (4 + 2) cycloaddition products, 3,4-dihydro-2-pyranones. The chlorine atom is reductively removed and methanol is spontaneously eliminated to yield the 5,6,7,8-tetra-hydrocoumarins. Dehydrogenation of these compounds results in good yields of the substituted coumarins. 相似文献
59.
Improved synthesis of C4α- and C4β-methyl analogues of 2-aminobicyclo[3.1.0]hexane-2,6-dicarboxylate
An efficient and divergent synthesis of C4α- and C4β-methyl-substituted analogues of 2-aminobicyclo[3.1.0]hexane 2,6-dicarboxylate, which are important tools in the study of metabotropic glutamate receptor function, has been achieved. By taking advantage of an unanticipated facial selectivity of the bicyclo[3.1.0]hexane ring system, either the C4α- or C4β-methyl substituent was introduced in a highly stereoselective and high-yielding manner. 相似文献
60.
Feng Z Chakraborty D Dewell SB Reddy BV Brady SF 《Journal of the American Chemical Society》2012,134(6):2981-2987
In a recent study of polyketide biosynthetic gene clusters cloned directly from soil, we isolated two antibiotics, fasamycins A and B, which showed activity against methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecalis. To identify the target of the fasamycins, mutants with elevated fasamycin A minimum inhibitory concentrations were selected from a wild-type culture of E. faecalis OG1RF. Next-generation sequencing of these mutants, in conjunction with in vitro biochemical assays, showed that the fasamycins inhibit FabF of type II fatty acid biosynthesis (FASII). Candidate gene overexpression studies also showed that fasamycin resistance is conferred by fabF overexpression. On the basis of comparisons with known FASII inhibitors and in silico docking studies, the chloro-gem-dimethyl-anthracenone substructure seen in the fasamycins is predicted to represent a naturally occurring FabF-specific antibiotic pharmacophore. Optimization of this pharmacophore should yield FabF-specific antibiotics with increased potencies and differing spectra of activity. This study demonstrates that culture-independent antibiotic discovery methods have the potential to provide access to novel metabolites with modes of action that differ from those of antibiotics currently in clinical use. 相似文献