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排序方式: 共有1693条查询结果,搜索用时 15 毫秒
101.
Damien Berthier Alain Trachsel Charles Fehr Lahoussine Ouali Andreas Herrmann 《Helvetica chimica acta》2005,88(12):3089-3108
Amphiphilic polystyrene‐ and polymethacrylate‐based β‐acyloxy ketones were investigated as potential delivery systems for the controlled release of damascones by retro‐1,4‐addition in applications of functional perfumery. A series of random copolymers being composed of the hydrophobic damascone‐release unit and a second hydrophilic monomer were obtained by radical polymerization in organic solution by using 2,2′‐azobis[2‐methylpropanenitrile] (AIBN) as the radical source (Schemes 2 and 3). A first evaluation of the polymer conjugates in acidic or alkaline buffered aqueous solution, and in the presence of a surfactant, showed that polymethacrylates and polystyrenes having a carboxylic acid function as hydrophilic group are particularly interesting for the targeted applications (Table 2). The release of δ‐damascone ( 1 ) from polymers with poly(methacrylic acid) and poly(vinylbenzoic acid) comonomers in different stoichiometric ratios was thus followed over several days at pH 4, 7, and 9 by comparison of fluorescence probing, solvent extraction, and particle‐size measurements (Tables 3 and 4). In acidic media, the polymers were found to be stable, and almost no δ‐damascone ( 1 ) was released. In neutral or alkaline solution, where the carboxylic acid functions are deprotonated, the concentration of 1 increased over time. In the case of the polymethacrylates, the fluorescence probing experiments showed an increasing hydrophilicity of the polymer backbone with increasing fragrance release, whereas in the case of the polystyrene support, the hydrophilicity of the environment remained constant. These results suggest that the nature of the polymer backbone may have a stronger influence on the fragrance release than the ratio of hydrophilic and hydrophobic monomers in the polymer chain. 相似文献
102.
J. N. Kavanagh F. J. Currell D. J. Timson M. H. Holzscheiter N. Bassler R. Herrmann K. M. Prise G. Schettino 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2010,60(1):209-214
Radiotherapy employs ionizing radiation to induce lethal DNA lesions in
cancer cells while minimizing damage to healthy tissues. Due to their
pattern of energy deposition, better therapeutic outcomes can, in theory, be
achieved with ions compared to photons. Antiprotons have been proposed to
offer a further enhancement due to their annihilation at the end of the
path. The work presented here aimed to establish and validate an
experimental procedure for the quantification of plasmid and genomic DNA
damage resulting from antiproton exposure. Immunocytochemistry was used to
assess DNA damage in directly and indirectly exposed human fibroblasts
irradiated in both plateau and Bragg peak regions of a 126 MeV antiproton
beam at CERN. Cells were stained post irradiation with an anti-γ-H2AX antibody. Quantification of the
γ-H2AX foci-dose relationship is consistent with a linear increase in the Bragg peak region. A qualitative analysis of the
foci
detected in the Bragg peak and plateau
region indicates significant differences highlighting the different severity
of DNA lesions produced along the particle path. Irradiation of desalted
plasmid DNA with 5 Gy antiprotons at the Bragg peak resulted in a significant
portion of linear plasmid in the resultant solution. 相似文献
103.
K. Suzuki P. Bühler L. Fabbietti N. Herrmann P. Kienle M. Kis Y. Leifels J. Marton E. Widmann T. Yamazaki J. Zmeskal 《Hyperfine Interactions》2009,193(1-3):189-194
We search for the most fundamental kaonic nuclear state, K ??? pp by employing the reaction p?+?p→K ?+??+?X at 3.0 GeV incident beam energy. The experiment makes use of the SIS-18 synchrotron and the ~4π acceptance FOPI apparatus in the cave-B at the GSI, Darmstadt, Germany and aims to collect full kinematics information of the reaction. We look for a signature of the X (?≡?K ??? pp) in both missing mass spectrum by measuring K ?+?, and invariant mass spectrum by measuring decay particles; X?→?Λ?+?p. The experiment is planned to take place in 2009. 相似文献
104.
Simal F Delfosse S Demonceau A Noels AF Denk K Kohl FJ Weskamp T Herrmann WA 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(13):3047-3052
Air-stable and readily available ruthenium benzylidene complexes of the general type [RuCl2(=CHPh)(L)(L')] (L, L' = PCy3 and/or N-heterocyclic carbene) constitute a new class of catalyst precursors for atom-transfer radical polymerization (ATRP) of methyl methacrylate and styrene, and provide an unprecedented example for the involvement of ruthenium alkylidenes in radical reactions. They promote the polymerization of various monomers with good to excellent yields, and in a controlled way with methyl methacrylate and styrene. Variations of their basic structural motif provide insights into the essential parameters responsible for catalytic activity. The ligands L (PCy3 and/or N-heterocyclic carbene) turned out to play a particularly important role in determining the rate of the polymerizations. A similarly pronounced influence is exerted by the substituents on the N-heterocyclic carbene. Our results indicate that the catalysts decompose quickly under ATRP conditions, and polymerizations are mediated by both [RuCl2(=CHPh)(L)(L')] complexes and ruthenium species bereft of the benzylidene moiety, through a pathway in which both tricyclohexylphosphane and/or N-heterocyclic carbene ligands remain bound to the metal center. Polymerization of n-butyl acrylate and vinyl acetate is not controlled and most probably takes place through a redox-initiated free-radical process. 相似文献
105.
Zbigniew GrobelnyAndrzej Stolarzewicz Barbara Morejko-Bu?Adalbert Maercker 《Journal of organometallic chemistry》2002,660(1):6-13
The linear ether bond was exclusively cleaved in benzyl glycidyl ether and triphenylmethyl glycidyl ether under the influence of K−, K+(15-crown-5)2 (1), whereas the strongly strained three-membered oxacyclic ring remained undisturbed. Potassium glycidoxide and benzylpotassium were found as the primary reaction products of benzyl glycidyl ether with 1. Subsequently, benzylpotassium reacted with benzyl glycidyl ether giving the next potassium glycidoxide molecule and bibenzyl. Benzyl phenyl ether was used as a model compound to explain the mechanism of bibenzyl formation. The reaction of triphenylmethyl glycidyl ether with 1 resulted in potassium glycidoxide and stable triphenylmethylpotassium. After treating with a quenching agent a new glycidyl ether or glycidyl ester was obtained from potassium glycidoxide. These results were found when the reaction occurred at the excess of glycidyl ether. In another case, i.e. at the excess of 1 further reactions took place with the participation of potassium anions and various new compounds were observed in the reaction mixture after benzylation or methylation. Thus, the method of substrates delivery influences the course of studied processes in a decisive way. 相似文献
106.
107.
The compaction of granular packings or soils is a collective process which for higher densities becomes increasingly slower
reaching glassy behaviour. We present a study of this problem from various points of view, in particular we will represent
the evolving force network that percolates through the system by an inverse fiber rupture model.
Received 15 March 2002 and Received in final form 29 July 2002 相似文献
108.
Nicodemi M Coniglio A Herrmann HJ 《Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics》1999,59(6):6830-6837
This paper presents the study of density fluctuations in a model for vibrated granular media. Their microscopic origin is shown to be linked to the microscopic disorder in grains packing. Varying vibrations amplitude and duration, several regimes are found for density relaxation. Its power spectrum is well described by power laws. 相似文献
109.
D. Hildebrandt H. Grote A. Herrmann M. Laux P. Pech H.-D. Reiner H. Wolff 《等离子体物理论文集》1988,28(1):85-95
It is shown that the efflux of impurities injected into the core plasma can be detected by collector probes in the scrape-off plasma. The time evolution, orientation and radial dependences of these effluxes allow to conclude on the impurity confinement in the core plasma and the scrape-off plasma. Moreover, recycling effects can also be measured. 相似文献
110.
L. Monz R. Hohmann H.-J. Kluge S. Kunze J. Lantzsch E.W. Otten G. Passler P. Senne J. Stenner K. Stratmann K. Swendt K. Zimmer G. Herrmann N. Trautmann K. Walter 《Spectrochimica Acta Part B: Atomic Spectroscopy》1993,48(14):1655-1671
Environmental assessment in the wake of a nuclear accident requires the rapid determination of the radiotoxic isotopes 89Sr and 90Sr. Useful measurements must be able to detect 108 atoms in the presence of about 1018 atoms of the stable, naturally occurring isotopes. This paper describes a new approach to this problem using resonance ionization spectroscopy in collinear geometry, combined with classical mass separation. After collection and chemical separation, the strontium from a sample is surface-ionized and the ions are accelerated to an energy of about 30 keV. Initially, a magnetic mass separator provides an isotopic selectivity of about 106. The ions are then neutralized by charge exchange and the resulting fast strontium atoms are selectively excited into high-lying atomic Rydberg states by narrow-band cw laser light in collinear geometry. The Rydberg atoms are then field-ionized and detected. Thus far, a total isotopic selectivity of S > 1010 and an overall efficiency of ξ = 5 × 10−6 have been achieved. The desired detection limit of 108 atoms 90Sr has been demonstrated with synthetic samples. 相似文献