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241.
Formation of μ-peroxodicobalt(III) complexes has been studied in solutions containing tris(2-aminoethyl)aminecobalt(II) and additional monodentate ligands X. Depending n the nature and the concentration of X and on pH, singly bridged [(tren)XCoOOCoX(tren)]4+ and/or doubly bridged [(tren)Co(C2OH)Co(tren)]3+ are formed. The UV/VIS spectra of these complexes are discussed on the basis of a theoretical model which stresses the importance of the dihedral angle of the CoOOCo-group. [(tren)(CN)CoOOCo(CN)(tren)](ClO4)2 has been synthesized and its structure determined by single crystal X-ray diffraction. The CoOOCo-group of the cation is planar. Solutions of the complex as well as the solid show two CT bands in the 300–400 nm region. 相似文献
242.
On Reactions of oxygenated Cobalt(II) Chelates. VI. Preparation of diastereoisomeric tetrakis(ethylenediamine)-μ-peroxo-μl-hydroxo-dicobalt(III) Perchlorates Oxygenation of Co(en)22+ leads to a mixture of two isomeric forms of [(en)2Co(O2, OH)-Co(en)2] (ClO4)3 · H2O from which the less soluble meso form can be readily crystallized. Further crystallization from the mother liquor yields the racemate ΔΔ/ΔΔ. The pure racemate may be obtained by either of the following methods: (a) By ligand exchange starting from mono bridged [(NH3)5CoO2Co(NH3)5] (NO3)4 or from doubly bridged [(SCN) (NH3)3Co(O2, OH)Co(NH3)3(SCN)] SCN · 2H2O. (b) By reaction of cis-[Co(en)2(OH2)2]3+ with H2O2. Reaction (b) proceeds via an intermediate cis-[Co(en)2(OOH) (OH2)] (ClO4)2 · H2O which at higher pH reacts with [Co(en)2(OH) (OH2)]2+ to yield the desired doubly bridged ΔΔ/ΔΔ tetrakis(ethylenediamine)-μ-peroxo-μ-hydroxodikobalt(III)-perchlorate. 相似文献
243.
Paulsson B Athanassiadis I Rydberg P Törnqvist M 《Rapid communications in mass spectrometry : RCM》2003,17(16):1859-1865
Acrylamide (AA) is a reactive compound widely used as an industrial chemical. It is also, as recently shown, present in heated foodstuffs. AA is known to cause tumors in rodents and is classified as probably carcinogenic to humans. The metabolite glycidamide (GA) is assumed to be the predominant genotoxic agent in AA exposure. Therefore, knowledge about in vivo doses of GA is essential for cancer risk assessment of exposure to AA. The in vivo dose of GA could be inferred from the level of the adduct formed by GA with N-terminal valine (GA-Val) in hemoglobin (Hb), detached as a pentafluorophenylthiohydantoin (PFPTH) and measured by gas chromatography/tandem mass spectrometric (GC/MS/MS) analysis. However, due to the highly polar character of the GA-Val-PFPTH derivative, it was found necessary to modify the method through further derivatization. This paper presents an evaluation of acetonization for derivatization of the adjacent bond;OH and bond;NH(2) groups in the adduct formed from GA. Good reproducibility was obtained. Also, acetonization improves the response and thus increases the sensitivity of the GC/MS/MS analysis of the PFPTH derivative of GA-Val. The sensitivity obtained is sufficient for studies of background adduct levels of GA in animals and in humans. Acetonization as a method for derivatization is robust and simple. 相似文献
244.
S Guttmann J Pless R L Huguenin E Sandrin H Bossert K Zehnder 《Helvetica chimica acta》1969,52(7):1789-1795
A total synthesis of salmon calcitonin is described. The C-terminal nonapeptide amide 24–32 was coupled with the heptapeptide 17–23. The resulting hexadecapeptide amide 17–32 was reacted with the heptapeptide 10–16 to give the tricosapeptide 10–32. This was condensed with the N-terminal nonapeptide 1–9, yielding the protected dotriacontapeptide amide 1–32. After removal of the protective groups and purification by gel-filtration the free peptide obtained exhibited the physical, chemical and biological properties of the natural hormone. Its hypocalcaemic activity (ca. 3500 MRC U/mg) is 20–30 times higher than that of porcine or human calcitonin. 相似文献
245.
Johannes Zehnder Riccardo Cadalbert Dr. Laurent Terradot Prof. Matthias Ernst Dr. Anja Böckmann Prof. Peter Güntert Prof. Beat H. Meier Dr. Thomas Wiegand 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(28):7745-7755
Paramagnetic metal ions can be inserted into ATP-fueled motor proteins by exchanging the diamagnetic Mg2+ cofactor with Mn2+ or Co2+. Then, paramagnetic relaxation enhancement (PRE) or pseudo-contact shifts (PCSs) can be measured to report on the localization of the metal ion within the protein. We determine the metal position in the oligomeric bacterial DnaB helicase from Helicobacter pylori complexed with the transition-state ATP-analogue ADP:AlF4− and single-stranded DNA using solid-state NMR and a structure-calculation protocol employing CYANA. We discuss and compare the use of Mn2+ and Co2+ in localizing the ATP cofactor in large oligomeric protein assemblies. 31P PCSs induced in the Co2+-containing sample are then used to localize the DNA phosphate groups on the Co2+ PCS tensor surface enabling structural insights into DNA binding to the DnaB helicase. 相似文献
246.
Huub H. M. Rijnaarts Willem Norde Johannes Lyklema Alexander J. B. Zehnder 《Colloids and surfaces. B, Biointerfaces》1999,14(1-4):179-195
The deposition of eight bacterial strains on Teflon and glass in aqueous media with ionic strengths varying between 0.0001 and 1 M was measured and interpreted. Two types of interactions were considered: (1) those described by the DLVO theory, which comprise van der Waals attraction and electrostatic repulsion (bacteria and surfaces are both negatively charged); and (2) steric interactions between the outer cell surface macromolecules and the substrata. As a trend, at low ionic strength (<0.001 M), deposition is inhibited by DLVO-type electrostatic repulsion, but at high ionic strength (≥0.1 M) it is dominated by steric interactions. The ionic strength at which the transition from the DLVO-controlled to the sterically controlled deposition occurs, is determined by the extension of the macromolecules into the surrounding medium, which varied between 5 and 100 nm among the bacterial strains studied. The steric interactions either promote deposition by bridging or inhibit it by steric repulsion. Between Teflon and hydrophobic bacteria, bridging is generally observed. The surface of one bacterial strain contains amphiphilic macromolecules that form bridges with Teflon but induce steric repulsion on glass. The presence of highly polar anionic polysaccharide coatings on the cell impedes attachment on both glass and Teflon. For practice, the general conclusion is that the deposition of most bacteria is: (1) strongly inhibited by DLVO-type electrostatic repulsion in aqueous environments of low ionic strength such as rain water, streams and lakes; (2) controlled by DLVO and/or steric interactions in systems as domestic waste waters and saliva; and (3) determined by steric interactions only in more saline environments as milk, urine, blood and sea water. 相似文献
247.
A combined experimental and computational study is carried out to characterize a nickel-alumina interface in terms of the two parameter (σ̂, Γ0) computational cohesive zone (CCZ) model of Tvergaard and Hutchinson. Experiments were performed using a sandwich specimen consisting of a thin nickel foil bonded between two pre-cracked alumina plates. The specimen was loaded in tension with the nickel foil bridging the cracks in the ceramic. Numerical simulations of the experiments were used to extract the parameters for the CCZ model.Effects of various parameters of the CCZ model are investigated and it is found that the most dominant parameter is the interface strength, σ̂. Effects of the residual thermal stresses are also investigated and it is shown that these stresses can enhance the specimen fracture toughness by almost 16%. The parameters for the nickel-alumina interface are found to be σ̂ = 148 MPa and Γ0 = 11 J m−2. It is observed that for the foil thicknesses tested, the work of rupture does not vary linearly with the thickness as predicted by many theoretical models. We found that interfaces which are neither too strong nor too weak contribute most to the overall fracture toughness of such a composite. Although the macroscopic loading at the nickel-alumina interface is shear, the failure is primarily tensile due to the thinning that occurs in the metal as it is stretched. 相似文献
248.
Rajeev Prabhakar Margareta R. A. Blomberg Per E. M. Siegbahn 《Theoretical chemistry accounts》2000,104(6):461-470
A concerted mechanism for proton exchange between water and the amino acid side chains of cysteine, serine, arginine and
glutamic acid has been investigated with hybrid density functional theory. The models used include, besides the amino acid
side chain, a number of water molecules ranging from one to five in some cases. The modeling of the amino acids without their
backbones is shown to be an excellent approximation. Long-range polarization effects were incorporated through a dielectric
cavity method allowing a better comparison to existing measurements for free amino acids in water. The barriers converge rather
fast with the number of water molecules for all the present amino acids and the converged values are in reasonable agreement
with experiments with discrepancies in the range 2–6 kcal/mol. The dielectric effects were found to be small for all systems
except cysteine, where there is a lowering of the barrier by 3–5 kcal/mol. The transition states for these concerted pathways
form rings in which the separated charges can be stabilized.
Received: 25 October 1999 / Accepted: 5 April 2000 / Published online: 21 June 2000 相似文献
249.
Johanna Steen Margareta RamströmSophia Hober Jenny Ottosson 《Journal of chromatography. A》2009,1216(20):4457-4464
A completely automated procedure for the purification and desalting of proteins with a polyhistidine purification tag prior to mass spectrometry analysis is presented. The system is ideal for rapid quality control and optimization studies and it provides researchers with a straightforward, reliable tool for studies of recombinant proteins. Forty-eight samples can be prepared within 4.5 h and only small cultivation and buffer volumes are needed. In this proof of concept, 19,000–35,000 Da recombinant proteins from both crude and clarified cell lysates were successfully prepared for subsequent analysis by electrospray ionization and matrix-assisted laser desorption/ionization mass spectrometry as well as by gel electrophoresis. 相似文献
250.
We extend to the context of \(L^p\) spaces and \(C_0\)-semigroups of operators our previous results from Heilmann and Ra?a (Positivity 21:897–910, 2017. https://doi.org/10.1007/s11117-016-0441-1), concerning the eigenstructure and iterates of uniquely ergodic Kantorovich modifications of linking operators. 相似文献