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31.
The bis(oxazoline) ligand, 2,2-bis[4(R)-phenyl-1,3-oxazolon-2-yl]propane (bpop), was introduced to the η6-benzenemthenium(II) moiety on treatment with [Ru(η6-C6H6)Cl2]2 to give [Ru(η6-C6H6)(bpop)Cl]+. Aquo and amine complexes [Ru(η6-C6H6)(bpop)(L)]2+ (L = H2O (1), NH2R; R = H (2) , Me (3) , and n-Bu (4) ) were prepared by treating the chloride complex with AgBF4 in the presence of L. X-ray structure determinations of 1 and 3 were carried out. Both complexes possessed a three-leg piano stool structure with the N or O donors located at the three comers of a pseudo octahedron. The aquo complex 1 exhibited a dynamic NMR feature in which two magnetically nonequivalent oxazoline parts observed at lower temperatures were interchanged with each other at higher temperatures. This observation was ascribed to the formation of a C2-symmetric 16-electron intermediate via Ru-OH2 cleavage, which is slower in acetone than in dichloromethane owing to more effective solvation by acetone around hydrogens of the coordinated water molecule. The two diastereotopic N-hydrogens of 4 underwent deuterium exchange with CD3OD with greatly different rates from each other owing to different energy of NHO (D) (CD3) interaction. Carboxylate and sulfonate ions (A−) formed second sphere complexes with 4 by means of NHA− hydrogen bonding, as evidenced by continuous shift of NH2 resonances with increasing amounts of the anions added. 相似文献
32.
Alberts IL Nadassy K Wodak SJ 《Protein science : a publication of the Protein Society》1998,7(8):1700-1716
The geometrical properties of zinc binding sites in a dataset of high quality protein crystal structures deposited in the Protein Data Bank have been examined to identify important differences between zinc sites that are directly involved in catalysis and those that play a structural role. Coordination angles in the zinc primary coordination sphere are compared with ideal values for each coordination geometry, and zinc coordination distances are compared with those in small zinc complexes from the Cambridge Structural Database as a guide of expected trends. We find that distances and angles in the primary coordination sphere are in general close to the expected (or ideal) values. Deviations occur primarily for oxygen coordinating atoms and are found to be mainly due to H-bonding of the oxygen coordinating ligand to protein residues, bidentate binding arrangements, and multi-zinc sites. We find that H-bonding of oxygen containing residues (or water) to zinc bound histidines is almost universal in our dataset and defines the elec-His-Zn motif. Analysis of the stereochemistry shows that carboxyl elec-His-Zn motifs are geometrically rigid, while water elec-His-Zn motifs show the most geometrical variation. As catalytic motifs have a higher proportion of carboxyl elec atoms than structural motifs, they provide a more rigid framework for zinc binding. This is understood biologically, as a small distortion in the zinc position in an enzyme can have serious consequences on the enzymatic reaction. We also analyze the sequence pattern of the zinc ligands and residues that provide elecs, and identify conserved hydrophobic residues in the endopeptidases that also appear to contribute to stabilizing the catalytic zinc site. A zinc binding template in protein crystal structures is derived from these observations. 相似文献
33.
A growth‐rate composition formula for the growth of E. coli on co‐utilized carbon substrates
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When bacteria are cultured in medium with multiple carbon substrates, they frequently consume these substrates simultaneously. Building on recent advances in the understanding of metabolic coordination exhibited by Escherichia coli cells through cAMP‐Crp signaling, we show that this signaling system responds to the total carbon‐uptake flux when substrates are co‐utilized and derive a mathematical formula that accurately predicts the resulting growth rate, based only on the growth rates on individual substrates. 相似文献
34.
Steven M. Berry Madelyn H. Baker Nicole J. Reardon 《Journal of inorganic biochemistry》2010,104(10):1071-4131
Recent evidence has shown that the properties of metal binding sites can be tuned by more than the ligands in the primary coordination sphere. We investigated the incorporation of four phenylalanine residues into the secondary coordination sphere of the small soluble blue copper protein azurin. The locations for placement of these residues in azurin were based on the structure of the highly hydrophobic blue copper protein rusticyanin, which is known to have a significantly higher reduction potential than azurin. Using site-directed mutagenesis, these residues in close proximity to the copper binding site were mutated to large hydrophobic phenylalanine residues individually and in combination. We also added the Met121Leu mutation on top of the Phe mutations to construct a total of 13 variants. We found little change in the UV-visible absorption and EPR data for these proteins, however modest increases in reduction potential were observed with increases by as much as 30 mV per Phe residue. Furthermore, we observed the increases in potential to be additive. 相似文献
35.
Effects of physical connection and genetic identity of neighbouring ramets on root-placement patterns in two clonal species 总被引:5,自引:0,他引:5
Root-placement patterns were examined in the clonal species Glechoma hederacea and Fragaria vesca when grown with different types of neighbours. Three different patterns were predicted as consequences of different types of interactions between roots: the avoidance pattern if root growth decreases in the presence of neighbouring roots; the intrusive pattern if root growth increases towards neighbouring roots; and the unresponsive pattern if root growth is unaffected by neighbouring roots. Experiments were conducted in which physical connection between ramets, and the genetic identity of neighbouring ramets, were manipulated. The patterns of distribution of entire root systems and elongation rates of individual roots were measured. Root systems and individual roots of G. hederacea avoided contact with roots of neighbouring ramets, irrespective of connection to the neighbour and its genetic or specific identity. In contrast, F. vesca roots grew equally towards and away from intraspecific ramet neighbours and their elongation was stimulated by contact with roots of G. hederacea ramets. These results demonstrate that root-placement patterns of plants grown with different types of neighbours vary between species, and suggest that factors additional to resource depletion could be involved in their development. 相似文献
36.
Patricia S. Santiago Leonardo M. MoreiraErika V. de Almeida Marcel Tabak 《Biochimica et Biophysica Acta (BBA)/General Subjects》2007
The effects of two ionic surfactants on the oligomeric structure of the giant extracellular hemoglobin of Glossoscolex paulistus (HbGp) in the oxy - form have been studied through the use of several spectroscopic techniques such as electronic optical absorption, fluorescence emission, light scattering, and circular dichroism. The use of anionic sodium dodecyl sulphate (SDS) and cationic cethyltrimethyl ammonium chloride (CTAC) has allowed to differentiate the effects of opposite headgroup charges on the oligomeric structure dissociation and hemoglobin autoxidation. At pH 7.0, both surfactants induce the protein dissociation and a significant oxidation. Spectral changes occur at very low CTAC concentrations suggesting a significant electrostatic contribution to the protein–surfactant interaction. At low protein concentration, 0.08 mg/ml, some light scattering within a narrow CTAC concentration range occurs due to protein–surfactant precipitation. Light scattering experiments showed the dissociation of the oligomeric structure by SDS and CTAC, and the effect of precipitation induced by CTAC. At higher protein concentrations, 3.0 mg/ml, a precipitation was observed due to the intense charge neutralization upon formation of ion pair in the protein–surfactant precipitate. The spectral changes are spread over a much wider SDS concentration range, implying a smaller electrostatic contribution to the protein–surfactant interactions. The observed effects are consistent with the acid isoelectric point (pI) of this class of hemoglobins, which favors the intense interaction of HbGp with the cationic surfactant due to the existence of excess acid anionic residues at the protein surface. Protein secondary structure changes are significant for CTAC at low concentrations while they occur at significantly higher concentrations for SDS. In summary, the cationic surfactant seems to interact more strongly with the protein producing more dramatic spectral changes as compared to the anionic one. This is opposite as observed for several other hemoproteins. The surfactants at low concentrations produce the oligomeric dissociation, which facilitates the iron oxidation, an important factor modulating further oligomeric protein dissociation. 相似文献
37.
A new series of chiral carboxylate-bridged complexes of Mn(II), Co(II), and Ni(II) has been synthesized by reaction of M(II) salts with (S)-2-hydroxy-2-methyl-butanedioic acid ((S)-citramalic acid) under solvothermal conditions. The Mn(II) compound 1 is obtained as a crystalline powder, whereas the Co(II) and Ni(II) compounds (2 and 3 respectively) are obtained as single crystals. All the compounds crystallize in orthorhombic chiral space group P212121. Compounds 2 and 3 are isostructural, and their structure consists in helicoïdal chains of M(II) centres linked by carboxylate bridges. The magnetic data indicate a rather weak coupling interaction between paramagnetic centres. The Mn(II) compound 1 exhibits antiferromagnetic ordering at TN = 2.64 K. The Co(II) and Ni(II) compounds show ferromagnetic interactions within the chains. For 3, the chains couple antiferromagnetically, which leads to a metamagnetic behaviour with TN = 1.69 K. 相似文献
38.
The polymer {[Co(ox)(Htr)2] · 2H2O}n (ox = oxalate dianion; Htr = 1,2,4-triazole) (1) has been synthesized and characterized by FT-IR spectroscopy, thermal analysis, variable-temperature magnetic measurements and X-ray diffraction methods. The physical analysis allows us to propose a one-dimensional structure in which [Co(Htr)2]2+ units are bridged by bis-bidentate oxalato ligands. Magnetic measurements at variable temperature show an overall antiferromagnetic behavior of the compound. Isolated chains of this polymer have been obtained by sonication of 1 in water and deposition on mica or on mica treated with poly-l-lysine. Circular molecules and nano-fibres have been isolated on Highly Oriented Pyrolitic Graphite (HOPG) by casting deposition of sonicated solutions of 1 in ethanol. The direct reaction on HOPG surface between CoII, H2ox and Htr has proved a useful route to isolate one-dimensional systems on surfaces. The development of new strategies to characterize these types of polymers on surfaces opens the possibility to perform nano-scale studies on their properties and their potential use as nano-materials. 相似文献
39.
Yu Xie Hao-Han Wu Yong Cui Long Pan Rong Fan Yang-Chao Tian Liu-Si Sheng 《Inorganica chimica acta》2007,360(5):1669-1677
Three homochiral metal-organic coordination networks [Co2(l-Trp)2(Py)6] · Py · (ClO4)2 (1), [Ni(l-Trp)(Py)3] · H2O · ClO4 (2) and [Co2(l-Trp)(INT)2(H2O)2(ClO4)] (3), all containing natural amino acid l-HTrp (l-typtophan), were hydrothermally synthesized and structurally characterized. The compounds 1 and 2 crystallize in the orthorhombic space group C2221, with a = 10.731(2) Å, b = 19.709(4) Å, c = 27.365(6) Å and Z = 4 for 1 and a = 10.710(10) Å, b = 20.088(18) Å, c = 27.63(3) Å and Z = 8 for 2, respectively. The compound 3 has the monoclinic space group P21, with a = 8.1934(14) Å, b = 13.209(2) Å, c = 12.464(2) Å, β = 104.107(3)° and Z = 2. Both 1 and 2 consist of 1D helical chains. Compound 3 is composed of 2D networks, which further assemble into a 3D supramolecular structure via weak interlayer interactions. The optically pure amino acid l-HTrp plays an important role leading to homochiral structures reported here. 相似文献
40.
To elucidate the specific mode and site of binding between metal ions and prion protein (PrPc), we synthesized the pentapeptide Ac184-188NH2 (AcIKQHTNH2), corresponding to helical region II of the protein, and its analogous acetylated at the lysine side chain. The acid-base properties of both peptides and their interaction with Cd2+ were studied in aqueous solution by NMR and potentiometry. Speciation data were compared with those achieved for Cd2+/4-methylimidazole, taken as the reference system. Both NMR and potentiometric data indicate that Cd2+ is coordinated by the histidine residue. The involvement of the side chain amine of lysine in the metal coordination is excluded by NMR data, whereas a role for either the carbonyl or the amide group of threonine is suggested. 相似文献