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21.
Garcia-Lopez JJ Zapotoczny S Timmerman P van Veggel FC Vancso GJ Crego-Calama M Reinhoudt DN 《Chemical communications (Cambridge, England)》2003,(3):352-353
The growth of individual nanometer-sized (3.4 +/- 1.4 nm) hydrogen bonded assemblies 1(2) x (DEB)6 on gold monolayers was achieved through an exchange reaction between single isolated calix[4]arene dimelamine 2 (1.1 +/- 0.2 nm) embedded in hexanethiol monolayers and double rosette hydrogen bonded assembly 1(3) x (DEB)6 in solution. The growth process was monitored by tapping mode atomic force microscopy (TM-AFM). 相似文献
22.
Marc J. van Drooge Gabriëlle M. Donné-op den Kelder Hendrik Timmerman 《Journal of computer-aided molecular design》1991,5(4):357-370
Summary The active conformation of several histamine H1-antagonists is investigated. As a template molecule we used the antagonist cyproheptadine, which consists of a piperidylene ring connected to a tricyclic system. The piperidylene moiety is shown to be flexible. The global minimum is a chair conformation but, additionally, a second chair and various boat conformations have to be considered, as their energies are less than 5 kcal/mol above the energy of the global minimum. Two semi-rigid histamine H1-antagonists, phenindamine and triprolidine, were fitted onto the various conformations of cyproheptadine in order to derive the pharmacologically active conformation of cyproheptadine. At the same time, the active conformation of both phenindamine and triprolidine was derived. It is demonstrated that, within the receptor-bound conformation of cyproheptadine, the piperidylene ring most probably exists in a boat form. 相似文献
23.
P. Bryanston-Cross M. Burnett B. Timmerman W. K. Lee P. Dunkley 《Optics & Laser Technology》2000,32(7-8):641-654
A review of several current optical diagnostics used for flow visualization is presented and the limitations and strengths of each technique are described. A new type of intelligent diagnostic optic designed for making three-dimensional measurement of velocity in a gas turbine combustor is proposed. The diagnostic uses an in-line tomographic approach combined with correlation theory to spatially locate structure within the flow. A discussion is then made as to why some optical diagnostics have been more successful than others in their general application. The potential advantages of evolving new technology and the implications for future instrumentation are also discussed. 相似文献
24.
Vinkers HM de Jonge MR Daeyaert ED Heeres J Koymans LM van Lenthe JH Lewi PJ Timmerman H Janssen PA 《Journal of computer-aided molecular design》2003,17(9):567-581
We have developed a computational approach in which an inhibitor's strength is determined from its interaction energy with a limited set of amino acid residues of the inhibited protein. We applied this method to HIV protease. The method uses a consensus structure built from X-ray crystallographic data. All inhibitors are docked into the consensus structure. Given that not every ligand-protein interaction causes inhibition, we implemented a genetic algorithm to determine the relevant set of residues. The algorithm optimizes the q2 between the sum of interaction energies and the observed inhibition constants. The best possible predictive model resulting has a q2 of 0.63. External validation by examining the predictivity for compounds not used in derivation of the model leads to a prediction accuracy between 0.9 and 1.5 log10 unit. Out of 198 residues in the whole protein, the best internally predictive model defines a subset of 20 residues and the best externally predictive model one of 9 residues. These residues are distributed over the subsites of the enzyme. This approach provides insight in which interactions are important for inhibiting HIV protease and it allows for quantitative prediction of inhibitor strength. 相似文献
25.
Arduini M Crego-Calama M Timmerman P Reinhoudt DN 《The Journal of organic chemistry》2003,68(3):1097-1106
This paper reports the formation of novel hydrogen-bonded assemblies 1(3).CA obtained upon mixing cyanuric acid (CA) with melamine derivatives 1, in which two of the three possible H-bonding arrays have been blocked. The four components are held together by 9 hydrogen bonds and form a rigid planar structure in which a central CA (three ADA motifs: A = acceptor, D = donor) is hydrogen bonded to three peripheral melamine derivatives (DAD motif). Furthermore, the synthesis and assembly studies are described of hydrogen-bonded assemblies 2-4.CA, comprised of three melamine derivatives that are covalently connected, and CA. The overall thermodynamic stability of assemblies 2-4.CA is superior to 1(3).CA (I(Tm) = 9 vs 3.6). The presence of the 2.CA complex in chloroform was confirmed by (1)H NMR spectroscopy and MALDI-TOF mass spectrometry. Substitution of the trimelamines with chiral or fluorescent groups (R(3)) enabled the study of the assemblies by CD and fluorescence spectroscopy. Titration experiments revealed strongly enhanced stabilities even in the presence of polar solvents, such as THF and CH(3)OH. Depending on the polarity of the solvent, stacking between the planar assembly units was observed. 相似文献
26.
Prins LJ Hulst R Timmerman P Reinhoudt DN 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(10):2288-2301
Chiral centers present either in the dimelamine components of calix[4]arene 1 or in the cyanurate components CA quantitatively induce one handedness (P or M) in the corresponding hydrogen-bonded assemblies 1(3).(CA)(6) (de>98 %). The high degree of chiral induction results from the presence of six chiral centers in close proximity (C(alpha)) to the core of the assembly. A much lower level of chiral induction is observed for assemblies with chiral centers that are more remote (C(beta)). All diastereomerically pure assemblies 1(3).(CA)(6) exhibit very high CD activities (deltavarepsilon(max) approximately 100 L mol(-1) cm(-1)), in sharp contrast to the low CD activities (deltavarepsilon(max)相似文献
27.
Meloen RH Puijk WC Langeveld JP Langedijk JP Timmerman P 《Current protein & peptide science》2003,4(4):253-260
Due to the advantageous properties of synthetic molecules compared to biological ones biological molecules in diagnostic tests are replaced increasingly by synthetic ones, usually synthetic peptides or related molecules. The replacement of biological antigens by synthetic peptides is most advanced at present, as well as the use of site-specific antibodies induced with synthetic peptides. Moreover recent results indicate that synthetic molecules may also replace antibodies. Ultimately this will lead to diagnostic assays built of synthetic molecules only. 相似文献
28.
The resistance of microfilters in a flow of micellar solutions indicates that the surfactant which is adsorbed in the pores
forms a mobile admicelle. The flow in these admicelles can be stopped by Marangoni forces if there is a concentration gradient
of surfactant across the filter. On the basis of thermodynamic concepts and experimental data it is argued that the resistance
of the filters could be affected by shear-induced surfactant adsorption. To minimize the entropy production in the flow through
a narrow pore the micellar solution separates into parallel fluxes of liquid through the lumen of the pore and of mobile surfactant
in the flowing admicelle.
Received: 14 July 1999 Accepted: 24 November 1999 相似文献
29.
30.
In a molecular beam the effects of vibrational pumping of SF6 (ν3 = 948 cm?1) are studied, using a line-tunable cw CO2 laser. Intracavity spontaneous Raman scattering is used for analysis. For excitation in the collision regime (xE/D ≤ 1), a thermal redistribution of the ν3 excitation over all vibrational modes is found, together with an average absorption up to six photons per molecule. The infrared absorption profile shows a red-shift of 6 cm?1. For excitation in the relatively rare collision regime (xE/D ? 4), a structured non-thermal ν1 Raman spectrum is observed, especially in the case of seeded molecular beams (10% in He). The observed hot-band peaks can be explained in terms of single-photon absorptions and collision-induced near-resonant V-V energy transfer, leading to single, double and triple excitations of the ν3 mode. The value of Trot in the beam is found to influence sensitively the non-resonant energy-transfer rate [e.g. hν3(948 cm?1)+ΔErot → h(ν4 + ν6)(962 cm?1) relative to the near-resonant transfer rate (hν3 + hν3 → 2hν3 + 3.5 cm?1)]. 相似文献