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31.
Hua JiangJean-Michel Léger Christel DolainPhilippe Guionneau Ivan Huc 《Tetrahedron》2003,59(42):8365-8374
Oligoamides of 8-amino-4-isobutoxy-2-quinolinecarboxylic acid were designed and synthesized, and their helical structures were characterized in the solid state by single crystal X-ray diffraction, and in solution by 1H NMR. The monomer methyl 4-isobutoxy-8-nitro-2-quinolinecarboxylate is easily prepared in three steps from 2-nitroaninile and dimethyl acetylene dicarboxylate. Successive hydrogenations of nitro groups, saponifications of esters and couplings of amines and acids via the acid chlorides gave a dimer, tetramer, hexamer, octamer, and decamer in a convergent fashion. The oligomers were shown to adopt a bent conformation stabilized by intramolecular hydrogen bonds between amide hydrogens and adjacent quinoline nitrogens. In the solid, the dimer adopts a planar crescent shape and the octamer a helical conformation. All NMR data are consistent with similar conformations in solution. The helices are apparently remarkably stable. Some of them remain helical even at 120°C in deuterated DMSO. The structural studies confirm the predictions made by computer and demonstrate the high potency of the design principles. 相似文献
32.
Monika Kuemmel Cédric Boissière Lionel Nicole Christel Laberty-Robert Clément Sanchez David Grosso 《Journal of Sol-Gel Science and Technology》2008,48(1-2):102-112
TiO2, Al2O3, and ZrO2 patterns composed of ordered nano motifs of various morphologies (i.e. perforations (craters), rings, canyons, wires, dots, or channels) with typical lateral dimensions of less than 40 nm and thickness below 15 nm are presented. Simple chemical solution deposition (CSD) of molecular inorganic precursors and commercial block copolymers was used to create patterns on several substrate surfaces (bare, hydrophobized or gold covered silicon wafers and ITO). Self-assembly during evaporation and subsequent stabilization at 500 °C leads to the various nanostructures. Compared to other techniques for surface nano patterning, the present method has the advantage of being cheap, reproducible and easy to scale up and does not require specialized equipment. The type, dimension, and organization of these motifs were assessed by AFM, FE-SEM, spectroscopic ellipsometry, and GI-SAXS and are shown to depend on the conditions of preparation. Usage as model surfaces for modelling of wetting properties and as nanoelectrode arrays were investigated. 相似文献
33.
Probabilities for the spin-forbidden transitions from the b1Σ+ and a1Δ states to the X3Σ? ground state of NH have been evaluated by a first-order perturbation expansion into S-eigenfunctions Nine 3Π and 1Π, five 1Σ+ and three 3Σ? states have been calculated by the MRD CI method at the experimental equilibrium distance of the X3Σ? state (1.0362 Å) which cover a vertical spectral region of = 100000 cm?1. The expansion terms of the perturbation sum are spin-orbit coupling coefficients obtained by using the Breit-Pauli one- and two-electron spin-orbit operator. The radiative lifetime of b1Σ+ has been determined in the Franck-Condon approximation to be 72 ms from ab initio data and 97 ms if experimental excitation energies for the low-lying valence states are employed. Recent experiments give a somewhat shorter lifetime for the corresponding 0-0 transition of 53 ms. The lifetime is governed by the transition to the 3Σ?±1 level of the non-rotating molecule, borrowing its intensity mainly from the A3Π → X3Σ? dipole transition. The second possible transition to the Ω = 0 level of the ground state is found to be weak. A similar relation of μ1/μ0 is expected for all the hydrogen containing isovalent molecules such as PH and AsH. The radiative lifetime of the a1Δ state has been calculated to be = 1.7 s. Recent matrix experiments predict a gas-phase lifetime of at least 3 s. Further experimental and theoretical investigations are in progress to clarify this unusual finding that the experimentally determined lifetime is longer than that calculated theoretically. 相似文献
34.
35.
Miljenko Perić Mirjana Mladenović Jasenka Fejzo Christel M. Marian Pablo J. Bruna 《Chemical physics letters》1982,88(6):547-552
The results of an ab initio study of the vibronic and rotational structure in the 2Π state of HNO+ are presented. It is shown that the absorption spectrum at 7200 Å observed by Herzberg could be caused by the transition from the ground to the first excited electronic state of HNO+ 相似文献
36.
37.
R. C. Potter Christel Schneider M. Ryska D. O. Hummel 《Angewandte Chemie (International ed. in English)》1968,7(11):845-856
Previously it was generally assumed that high energy radiation could only initiate radical polymerization in solutions of monomers. However, examples of radiation-induced polymerization have recently become known that proceed via an ionic mechanism. Thus, solutions of a monomer can be polymerized ionically, preferably in the presence of a solid, at low temperatures. Suprisingly, this may also be accomplished with ultra-pure, mainly anhydrous systems, even at room temperature. The nature of the ions has not yet been fully elucidated. 相似文献
38.
Antignac JP Marchand P Gade C Matayron G Qannari el M Le Bizec B Andre F 《Analytical and bioanalytical chemistry》2006,384(1):271-279
Polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) are widely recognized by the scientific community as persistent organic
pollutants due to their toxicity and adverse effects on wildlife and human health. The actual regulation dedicated to the
monitoring of dioxins in food is based on the measurement of 17 congener concentrations. The final result is reported as a
toxic equivalent value that takes into account the relative toxicity of each congener. This procedure can minimize the qualitative
information available from the abundances of each PCDD/PCDF congener: the characteristic contamination profile of the sample.
Multivariate statistical techniques, such as principal component analysis (PCA) or linear discriminant analysis (LDA), represent
an interesting way to investigate this qualitative information. Nevertheless, they have only been applied to the analysis
of contamination data from food products and biological matrices infrequently. The objective of the present study was to analyze
a large data set from dioxin analyses performed on various food products of animal origin. The results demonstrate the existence
of differences in congener-specific patterns between the analyzed samples. Variability was first demonstrated in terms of
the food type (fish, meat, milk, fatty products). Then a variability was observed that was related to the specific animal
species for meat and milk samples (bovine, ovine, porcine, caprine and poultry). Some practical applications of these results
are discussed. The origin(s) of the observed differences, as well as their significance, now remain to be investigated, both
in terms of environmental factors and transfer through living organisms. A better knowledge of the relation between a contamination
profile and its specific source and/or food product should be of great interest to scientists working in the fields of contaminant
analysis, toxicology and metabolism, as well as to regulatory bodies and risk assessors in charge of final decisions regarding
the eventual hazards associated with theses substances. 相似文献
39.
40.
Zhu Wu Jrn Nitsch Julia Schuster Alexandra Friedrich Katharina Edkins Marcel Loebnitz Fabian Dinkelbach Vladimir Stepanenko Frank Würthner Christel M. Marian Lei Ji Todd B. Marder 《Angewandte Chemie (International ed. in English)》2020,59(39):17137-17144
Achieving highly efficient phosphorescence in purely organic luminophors at room temperature remains a major challenge due to slow intersystem crossing (ISC) rates in combination with effective non‐radiative processes in those systems. Most room temperature phosphorescent (RTP) organic materials have O‐ or N‐lone pairs leading to low lying (n, π*) and (π, π*) excited states which accelerate kisc through El‐Sayed's rule. Herein, we report the first persistent RTP with lifetimes up to 0.5 s from simple triarylboranes which have no lone pairs. RTP is only observed in the crystalline state and in highly doped PMMA films which are indicative of aggregation induced emission (AIE). Detailed crystal structure analysis suggested that intermolecular interactions are important for efficient RTP. Furthermore, photophysical studies of the isolated molecules in a frozen glass, in combination with DFT/MRCI calculations, show that (σ, B p)→(π, B p) transitions accelerate the ISC process. This work provides a new approach for the design of RTP materials without (n, π*) transitions. 相似文献