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51.
A solid spin-labeled material was obtained starting from 2-chloro-3,5-dinitro-N-(4-(2,2,6,6-tetramethyl-piperidine-1-oxyl)-benzamide) and aminopropyl-silica gel. Stability tests showed that even after several months the spin-labeled material had the same properties as immediately after synthesis. EPR properties of the TEMPO-derivatized silica were studied as a function of solvent polarity and temperature. Rotational correlation times were calculated from EPR spectra and correlated with solvent characteristics and temperature. Polar solvents induce a fast motion of the spin-label, clearly seen in the EPR spectra by the apparition of the well-known TEMPO radical triplet. The solid spin-labeled (dry) sample showed a high interspin interaction, which can be disrupted not only by different (liquid) solvents, but also by absorption of different solids, like cyclodextrins, dendrimers or polyethyleneglycols. Also, changes induced by the temperature were studied in the case of toluene wet sample. From 150 to 370 K, the spectrum is changing from a slow motion spectrum type to a fast motion regime. The preparative procedures to obtain the spin-labeled silica as well as some of its parameters are described. 相似文献
52.
53.
Balaban MC Eichhöfer A Buth G Hauschild R Szmytkowski J Kalt H Balaban TS 《The journal of physical chemistry. B》2008,112(17):5512-5521
The title dicyano compound was synthesized via cyanation and it self-assembles in nonpolar solvents giving red-shifted and broad absorption maxima just as the bacteriochlorophylls which are encountered in the light-harvesting organelles of early photosynthetic bacteria. In the crystal, stacks are formed through a hierarchic combination of pi-stacking and a CN-Zn electrostatic interaction. Push-pull 15-N,N-dialkylamino-5-cyano congeners could be obtained in high yields using a solvent- and catalyst-free direct amination of meso-bromoporphyrins. Importantly, the fluorescence of the self-assembled species due to the very orderly manner in which the chromophores are arranged is not entirely quenched and has a surprisingly long lifetime of over 1 ns. This lends hope of using the trapped energy in biomimetic hybrid solar cells. 相似文献
54.
Santiago PS Neto Dde S Barbosa LR Itri R Tabak M 《Journal of colloid and interface science》2007,316(2):730-740
Small angle X-ray scattering (SAXS) and electron paramagnetic resonance (EPR) have been used to investigate the interaction of the water-soluble meso-tetrakis (4-sulfonatophenyl) porphyrin (TPPS(4)) with cationic cethyltrimethylammonium chloride (CTAC) micelles. To evaluate if the porphyrin protonation state affects its interaction with the micelle, both SAXS and EPR measurements were performed at pH 4.0 and 9.0. The best-fit SAXS curves were obtained assuming for CTAC micelle a prolate ellipsoidal shape in the absence and upon incorporation of 2-10 mM TPPS(4). SAXS results show that the presence of porphyrin impacts on micellar hydrophobic core, leading to a micellar reassembling into smaller micelles. Lineshapes of EPR spectra of 5- and 16-doxyl stearic acids (5- and 16-DSA, respectively) bound to 100 mM CTAC micelles exhibited slight changes as a function of porphyrin concentration. Spectral simulations revealed an increase of mobility restriction for both spin probes, especially at higher porphyrin concentration, where a small reduction of environment polarity was also observed for 16-DSA. The spin labels monitored only slight differences between pH 4.0 and 9.0, in agreement with the SAXS results. 相似文献
55.
Caetano W Haddad PS Itri R Severino D Vieira VC Baptista MS Schröder AP Marques CM 《Langmuir : the ACS journal of surfaces and colloids》2007,23(3):1307-1314
We study the photodecomposition of phospholipid bilayers in aqueous solutions of methylene blue. Observation of giant unilamellar vesicles under an optical microscope reveals a consistent pattern of membrane disruption as a function of methylene blue concentration and photon density for different substrates supporting the vesicles. 相似文献
56.
Ana M. S. Maia Marta Costa Redouane Borsali Rosangela B. Garcia 《Macromolecular Symposia》2005,229(1):217-227
Summary: In this paper the chemical structure of an acrylamide-N,N-dihexylacrylamide copolymer was established by IR and NMR. Static and dynamic light scattering in formamide were used in order to evaluate the polymer structural parameters, such as weight-average molecular weight (Mw), second virial coefficient (A2), radius of gyration (RG), the form factor P(q) and the hydrodynamic radius (RH). Additionally to the classical characterization, those results indicated the presence of aggregation, showing that formamide is not a very good solvent, as stated in earlier investigations. The rheological behavior in aqueous solutions was evaluated as a function of the salt concentration. The solutions presented an important viscosity increase in the presence of NaCl and did not show any sensitivity to the presence of CaCl2. This result is in favor of the oil recovery especially in high salinity reservoirs. 相似文献
57.
Christian Gancet Rosangela Pirri Jean Marc Dalens Bernard Boutevin Bernard Guyot Cdric Loubat Jean Le Petit Anne Marie Farnet Simone Tagger 《Macromolecular Symposia》1999,144(1):211-217
The biodegradability of polyacrylic acid derivatives may be improved through introduction of some fragility points within the main carbon chains. These weakness points can be either hydrolizable bonds or oxidizable sites. Enzymatic hydrolysis and oxydative biomimetic degradation tests have been set up in order to quickly evaluate new polymeric structures, before their possible evaluation through microbial degradation by Candida tropicalis. 相似文献
58.
Chiara Dall’Asta Mattia Mangia Franz Berthiller Alexandra Molinelli Michael Sulyok Rainer Schuhmacher Rudolf Krska Gianni Galaverna Arnaldo Dossena Rosangela Marchelli 《Analytical and bioanalytical chemistry》2009,395(5):1335-1345
In this paper, the results obtained by five independent methods for the quantification of fumonisins B1, B2, and B3 in raw maize are reported. Five naturally contaminated maize samples and a reference material were analyzed in three different
laboratories. Although each method was validated and common calibrants were used, a poor agreement about fumonisin contamination
levels was obtained. In order to investigate the interactions among analyte and matrix leading to this lack of consistency,
the occurrence of fumonisin derivatives was checked. Significant amounts of hidden fumonisins were detected for all the considered
samples. Furthermore, the application of an in vitro digestion protocol to raw maize allowed for a higher recovery of native
fumonisins, suggesting that the interaction occurring among analytes and matrix macromolecules is associative rather than
covalent. Depending on the analytical method as well as the maize sample, only 37–68% of the total fumonisin concentrations
were found to be extractable from the samples. These results are particularly impressive and significant in the case of the
certified reference material, underlying the actual difficulties in ascertaining the trueness of a method for fumonisin determination,
opening thus an important issue for risk assessment. 相似文献
59.
Linke-Schaetzel M Anson CE Powell AK Buth G Palomares E Durrant JD Balaban TS Lehn JM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(7):1931-1940
A series of butterfly-type molecular constructs has been prepared in good yield by using a double Stille coupling synthetic protocol. They are composed of a terpyridine (terpy) scaffold and two wings composed of appended porphyrins that are capable of switching from an extended W geometry to a compact U geometry upon cation coordination of the terpy unit. The porphyrin moieties exist in the constructs either as free bases or they can be sequentially metallated, thus giving rise to wings of different "colours". Stationary and time-resolved emission studies of the HZn, ZnAu and Zn2Au constructs show that the electronic properties are strongly dependent on the geometry. In the extended W conformation an energy-transfer process is seen from the free base to the Zn-metallated porphyrin. In the U conformation in Zn2Au the donor luminescence resulting from the singlet excited state of the Zn wing is strongly, quenched not only due to the heavy atom effect but also due to a fast electron-transfer process to the ground state of the Au wing. Furthermore, the binding of (alpha,omega)-diamine substrates to the Zn(II)-porphyrin sites can also influence the conformation of the system. For the Zn2Zn construct, single-crystal diffraction experiments with synchrotron radiation allowed the structure to be solved by direct methods and fully refined; it shows the expected U conformation. The central Zn atom is six-coordinate, whereby the zinc atom is coordinated by the eta3-terpy ligand as well by monodentate and semi-chelating acetate anions. The structure is made rigid by hydrogen bonds involving the aqua ligands on the outer Zn centres and acetate oxygen atoms. The present system thus represents a double-trigger-modulated optomechanical switching device with selective substrate binding for either metal atoms or tailored ligands. Both energy- and electron-transfer processes can be controlled opening a means of improving the on/off ratio in future constructs. 相似文献
60.
Ayla Balaban Gündüzalp Hande Fecriye Özbay 《Russian Journal of Inorganic Chemistry》2012,57(2):257-260
Schiff base; N,N′-bis-(2-hydroxy-1-naphthaldimine)-1,3-diaminopropanol (napdapOH) reacts with metal chlorides to form dinuclear
complexes of the type [M2L2] · nCl2 where M = Ni, Cu, Fe and n = 0, 1. Schiff base complexes were characterized by using FT-IR, LC-MS, magnetic moments and conductance measurements. Coordination
was found to be through the phenolic oxygen atoms and azomethine nitrogen atoms. The electronic properties of the compounds
were investigated theoretically by performing semiempirical molecular orbital theory PM3 method in Hyperchem 7 (Release).
The antibacterial activities of the compounds were investigated against Escherichia coli ATCC 11230, Bacillus subtilis RSKK 244, Bacillus megaterium RSKK 5117, Salmonella enteritidis ATCC 13076, Staphylococcus aureus ATCC 25923 by using microdilution method. 相似文献