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801.
Darii E Saravanamuthu G Afonso C Alves S Gut I Tabet JC 《Rapid communications in mass spectrometry : RCM》2011,25(12):1725-1734
Electrospray ionization mass spectrometry (ESI-MS) has become an analytical technique widely used for the investigation of non-covalent protein-protein and protein-ligand complexes due to the soft desolvation conditions that preserve the stoichiometry of the interacting partners. Dissociation studies of solvated or desolvated complexes (in the source and in the collision cell, respectively) allow access to information on protein conformation and localization of the metal ions involved in protein structure stabilization and biological activity. The complex of bovine trypsin and small soybean Bowman-Birk inhibitor (sBBI) was studied by ESI-MS to determine changes occurring within the complex during its transfer from droplets to the gas phase independently of the ion polarity. Under collision-induced dissociation (CID) conditions, unexpected binding of the Ca(2+) ion (cofactor of native trypsin) to the inhibitor molecule was observed within the desolvated sBBI/trypsin/Ca(2+) complex (with a 1:1:1 stoichiometry). This formal gas-phase migration of the calcium ion from trypsin to the inhibitor may be related to conformational rearrangements in the solvent-free and likely collapsed complex. However, under conditions leading to the increase in complex charge state, the appearance of the cationized trypsin molecule was detected during complex dissociation, thus reflecting different pathways of the evolution of complex conformation. 相似文献
802.
Svetlana I. Bakholdina Anna M. Stenkova Evgenia P. Bystritskaya Evgeniy V. Sidorin Natalya Yu. Kim Ekaterina S. Menchinskaya Tatiana Yu. Gorpenchenko Dmitry L. Aminin Nikita A. Shved Tamara F. Soloveva 《Molecules (Basel, Switzerland)》2021,26(13)
The effect of cultivation temperatures (37, 26, and 18 °C) on the conformational quality of Yersinia pseudotuberculosis phospholipase A1 (PldA) in inclusion bodies (IBs) was studied using green fluorescent protein (GFP) as a folding reporter. GFP was fused to the C-terminus of PldA to form the PldA-GFP chimeric protein. It was found that the maximum level of fluorescence and expression of the chimeric protein is observed in cells grown at 18 °C, while at 37 °C no formation of fluorescently active forms of PldA-GFP occurs. The size, stability in denaturant solutions, and enzymatic and biological activity of PldA-GFP IBs expressed at 18 °C, as well as the secondary structure and arrangement of protein molecules inside the IBs, were studied. Solubilization of the chimeric protein from IBs in urea and SDS is accompanied by its denaturation. The obtained data show the structural heterogeneity of PldA-GFP IBs. It can be assumed that compactly packed, properly folded, proteolytic resistant, and structurally less organized, susceptible to proteolysis polypeptides can coexist in PldA-GFP IBs. The use of GFP as a fusion partner improves the conformational quality of PldA, but negatively affects its enzymatic activity. The PldA-GFP IBs are not toxic to eukaryotic cells and have the property to penetrate neuroblastoma cells. Data presented in the work show that the GFP-marker can be useful not only as target protein folding indicator, but also as a tool for studying the molecular organization of IBs, their morphology, and localization in E. coli, as well as for visualization of IBs interactions with eukaryotic cells. 相似文献
803.
Alexander L. Pomadchik Alexander S. Belov Ekaterina G. Lebed Irina G. Belaya Anna V. Vologzhanina Yan Z. Voloshin 《Molecules (Basel, Switzerland)》2021,26(13)
Kinetics and thermodynamics of the template synthesis and of the acidic decomposition of the methylboron-capped iron(II) tris-1,2-dioximates—the clathrochelate derivatives of six (nioxime)- and eight (octoxime)-membered alicyclic ligand synthons—were compared. In the case of a macrobicyclic iron(II) tris-nioximate, the plausible pathway of its formation contains a rate-determining stage and includes a reversible formation of an almost trigonal-antiprismatic (TAP) protonated tris-complex, followed by its monodeprotonation and addition of CH3B(OH)2. Thus, the formed TAP intermediate undergoes a multistep rate-determining stage of double cyclization with the elimination of two water molecules accompanied by a structural rearrangement, thus giving an almost trigonal-prismatic (TP) iron(FII) semiclathrochelate. It easily undergoes a cross-linking with CH3B(OH)2, resulting in the elimination of H+ ion and in the formation of a macrobicyclic structure. In contrast, the analogous scheme for its macrobicyclic tris-octoximate analog was found to contain up to three initial stages affecting the overall synthesis reaction rate. The rates of acidic decomposition of the above clathrochelates were found to be also affected by the nature of their ribbed substituents. Therefore, the single crystal XRD experiments were performed in order to explain these results. The difference in the kinetic schemes of a formation of the boron-capped iron(II) tris-nioximates and tris-octoximates is explained by necessity of the substantial changes in a geometry of the latter ligand synthon, caused by its coordination to the iron(II) ion, due to both the higher distortion of the FeN6-coordination polyhedra, and the intramolecular sterical clashes in the molecules of the macrobicyclic iron(II) tris-octoximates. 相似文献
804.
Christian Helgert Thomas Pertsch Carsten Rockstuhl Ekaterina Pshenay-Severin Christoph Menzel Ernst-Bernhard Kley Arkadi Chipouline Christoph Etrich Uwe Huebner Andreas Tuennermann Falk Lederer 《中国光学与应用光学文摘》2010,(1)
In this contribution we review our latest achievements of combined experimental and theoretical studies to tailor the properties of optical metamaterials(MMs) at will. We give three examples of metamaterial designs that have been realized by means of electron-beam lithography and whose spectroscopic characteristics have been comprehensively investigated. In every case, our experiments are complemented by rigorous numerical simulations. Particular emphasis is put on the significance of such tailored effectiv... 相似文献
805.
We investigate the local structures of oxynitride La-Si-(Al)-O-N glasses by 29Si and 27Al magic-angle spinning (MAS) solid state Nuclear Magnetic Resonance (NMR). The glasses studied span an unprecedented range of compositions, up to >50 at.% lanthanum and nitrogen out of the cations and anions, respectively, and achievable through a recently introduced glass preparation route. Transmission as well as scanning electron microscopy verified homogeneous samples over length-scales down to 20 nm. As the nitrogen content of the glasses increased, 29Si NMR evidenced a progressive formation of Si-N bonds, with SiO2N2 tetrahedra dominating in the nitrogen-rich glass networks. In the oxygen-rich end of the series, aluminum is predominantly present in tetrahedral coordination as AlO4, whereas the glasses with highest nitrogen contents have a major fraction of AlO3N structural units. Trends in isotropic 29Si and 27Al chemical shifts and 27Al quadrupolar couplings are compared with results of La-Si-Al-O glasses and are discussed in relation to the glass compositions and their proposed structures. 相似文献
806.
Ekaterina V. Bakhmutova Heinrich Nth Rosalinda Contreras Bernd Wrackmeyer 《无机化学与普通化学杂志》2001,627(8):1846-1854
Pseudo‐ephedrine derived 2‐imino‐1,3‐thiazolidine 1 reacts with tris(diethylamino)phosphane by stepwise replacement of the diethylamino group to give the mono‐, bis‐ and tris(imino)phosphanes 2 , 3 and 4 , respectively, of which 4 could be isolated in pure state. The analogous reaction with diethylamino‐diphenylphosphane affords the imino‐diphenylphosphane 5 . The iminophosphanes react with sulfur or selenium to give the corresponding phosphorus(V) compounds. In contrast, the reaction of the iminophosphanes with oxygen is very slow; anhydrous trimethylamine N‐oxide reacts in the melt with the phosphanes to give the oxides 4(O) and 5(O) . The molecular structures of 4(O) (in mixture with 4 ), 4(Se) , 5(S) and 5(Se) were determined by X‐ray analysis. In all cases the ring‐sulfur and the phosphorus atoms are in cis‐positions at the C=N bonds. The analogous solution structures were determined by 1H, 13C, 15N, 31P and 77Se NMR spectroscopy. In the case of the compounds 5 , 5(O) , 5(S) and 5(Se) the isotope‐induced chemical shifts 1δ14/15N(31P) were determined, using INEPT‐HEED experiments. 相似文献
807.
Victor A. Kasaikin Julia A. Zakharova Ekaterina A. Litmanovich Elena M. Ivleva Alexander B. Zezin Victor A. Kabanov 《Macromolecular Symposia》2003,195(1):269-274
Formation and structure of water-soluble complexes of poly(acrylic acid) (PA) and poly(diallyldimethylammonium chloride) (PDADMAC) with oppositely charged surfactants have been studied by elastic and quasi-elastic laser light-scattering and high-speed sedimentation technique. It was experimentally shown that generation of intracomplex micellar phase is the necessary condition for formation of such complexes. Minimum aggregation number of the surfactant ions in the complex micelle was found to be determined by the chemical nature of the polymer. 相似文献
808.
Tatiana M. Birshtein Anna A. Mercurieva Ekaterina B. Zhulina 《Macromolecular theory and simulations》2001,10(7):719-728
An analog of the Alexander‐De Gennes box model is used for the theoretical investigation of an external deformation of polymer brushes in a mixture of two solvents. The basic solvent A and the admixture B are assumed to be highly incompatible (Flory‐Huggins parameter χAB = 3.5). The thermodynamics of a polymer in the solvents A and B is described by parameters χA and χB, χA > χB. The brush behavior under deformation is investigated with regard to solvent composition and polymer‐solvent interactions. It is shown that in a pre‐binodal range of the solvent composition ΦB < ΦB0 in the bulk (here ΦB0 is a binodal value) there is such a value of ΦB = Φ B* that deformation does not affect solvent composition inside the brush. This invariant quantity Φ B*, being a function of only thermodynamic parameters, is independent of the brush characteristics, such as grafting density. It is shown that two types of the first‐order phase transitions can arise in the system considered: a compositional phase transition induced by a change in the solvent composition in the bulk, and a deformational phase transition caused by an external deformation of the brush. The value of Φ B* defines a borderline concentration of the admixture in the bulk; the brush behavior in the ranges 00 ⪇ ΦB ⪇ Φ B* and Φ B* ⪇ ΦB < ΦB0 are different. If no compositional phase transition occurs in the system, the deformational phase transition should arise under stretching at Φ B* ⪇ ΦB. If the compositional phase transition exists, it is realized in the range ΦB < Φ B* and causes the deformational phase transition in this concentration range, not only under stretching, but also under compression. Microphase segregation inside the brush is demonstrated for both phase transitions despite overestimation of the brush homogeneity in the box model. 相似文献
809.
Dr. Vyacheslav Sushev Dr. Yulia Panova Dr. Alexandra Khristolyubova Dr. Natalia Zolotareva Matvey Grishin Dr. Roman Rumyantcev Ekaterina Kozlova Prof. Dr. Georgy Fukin Prof. Dr. Alexander Kornev 《欧洲无机化学杂志》2023,26(23):e202300252
A number of two-deck dicationic 3a,6a-diaza-1,4-diphosphapentalenes (DDP)2X2 (X=halogen or complex ion) have been characterized. Interdeck distances P(1)⋅⋅⋅P(3) and P(2)⋅⋅⋅P(4) in crystal structures, as a rule, significantly exceed the sum of covalent radii, however they are still within the sum of van der Waals radii. The 31P NMR data indicate that phosphorus atoms are equivalent in solution even at low temperatures (233 K). Based on DFT calculations, the formation of two equivalent P−P covalent bonds (<2.4 Å) is energetically unfavorable, despite the absence of steric barriers. The total energy of the model dication as a function of the P⋅⋅⋅P separation has a minimum at the P−P distance of 2.85 Å. This distance corresponds to the highest aromaticity index in the interdeck space (NICS(1.0)=−20.72). The energy of interdeck interactions is estimated at 10–15 kcal/mol. 相似文献