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101.
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Robert Rotzoll Philipp Vana 《Journal of polymer science. Part A, Polymer chemistry》2008,46(23):7656-7666
Reversible addition‐fragmentation chain transfer (RAFT) polymerization was used to produce poly(methyl acrylate) (pMA) loops grafted onto silica nanoparticles using doubly anchored bifunctional RAFT agents 1,4‐bis(3′‐trimethoxysilylpropyltrithiocarbonylmethyl)benzene (Z‐group approach) and 1,6‐bis(o,p‐2′‐trimethoxysilylethylbenzyltrithiocarbonyl)hexane (R‐group approach) as mediators. In both cases, molecular weights of the resulting surface‐confined polymer loops increased with monomer conversion, whereas the grafting density was significantly higher in the case of the R‐group supported RAFT polymerization due to mechanistic differences of the RAFT process at the surface. This result was evident from thermogravimetric analysis and supported by scanning electron microscopy. Polymer loops with molecular weights up to 53,000 g mol?1 were accessible with polydispersities of about 2.0 without and 1.5 with the addition of free RAFT agent. UV signals of the detached pMA loops measured via size exclusion chromatography were shifted to higher molecular weights compared with the corresponding RI signals, indicating branching reactions caused by the close proximity of growing radicals and polymer at the surface of the silica nanoparticles. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7656–7666, 2008 相似文献
104.
Diana Dhler Philipp Michael Steve Neumann Wolfgang H. Binder 《Chemie in Unserer Zeit》2016,50(2):90-101
Even though the field of self‐healing is rarely known so far – self healing materials are already present at our market. Nevertheless just due to modern scientific concepts we are now able to understand the basic mechanistic steps in a more detailed way. Further progress on this field will open access to materials with a wide range of adjustable properties. Therefore, applications of such self healing materials are not limited – assuming the market‐price is competitive and the elongated lifetime delivers an appropriate advantage. Already demonstrated for concrete and clear coatings for cars, the investigations done so far have generated materials with improved properties and prolonged durability. 相似文献
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Chemical reactions inside cells occur in compartment volumes in the range of atto- to femtoliters. Physiological concentrations realized in such small volumes imply low copy numbers of interacting molecules with the consequence of considerable fluctuations in the concentrations. In contrast, rate equation models are based on the implicit assumption of infinitely large numbers of interacting molecules, or equivalently, that reactions occur in infinite volumes at constant macroscopic concentrations. In this article we compute the finite-volume corrections (or equivalently the finite copy number corrections) to the solutions of the rate equations for chemical reaction networks composed of arbitrarily large numbers of enzyme-catalyzed reactions which are confined inside a small subcellular compartment. This is achieved by applying a mesoscopic version of the quasisteady-state assumption to the exact Fokker-Planck equation associated with the Poisson representation of the chemical master equation. The procedure yields impressively simple and compact expressions for the finite-volume corrections. We prove that the predictions of the rate equations will always underestimate the actual steady-state substrate concentrations for an enzyme-reaction network confined in a small volume. In particular we show that the finite-volume corrections increase with decreasing subcellular volume, decreasing Michaelis-Menten constants, and increasing enzyme saturation. The magnitude of the corrections depends sensitively on the topology of the network. The predictions of the theory are shown to be in excellent agreement with stochastic simulations for two types of networks typically associated with protein methylation and metabolism. 相似文献
107.
Philipp AA Wissenbach DK Weber AA Zapp J Maurer HH 《Journal of mass spectrometry : JMS》2010,45(11):1344-1357
Mitragyna speciosa (Kratom in Thai), a Thai medical plant, is misused as herbal drug of abuse. Besides the most abundant alkaloids mitragynine (MG) and paynantheine (PAY), several other alkaloids were isolated from Kratom leaves, among them the third abundant alkaloid is speciogynine (SG), a diastereomer of MG. The aim of this present study was to identify the phase I and II metabolites of SG in rat urine after the administration of a rather high dose of the pure alkaloid and then to confirm these findings using human urine samples after Kratom use. The applied liquid chromatography coupled to low- and high-resolution mass spectrometry (LC-HRMS-MS) provided detailed information on the structure in the MS(n) mode particularly with high resolution. For the analysis of the human samples, the LC separation had to be improved markedly allowing the separation of SG and its metabolites from its diastereomer MG and its metabolites. In analogy to MG, besides SG, nine phase I and eight phase II metabolites could be identified in rat urine, but only three phase I and five phase II metabolites in human urine. These differences may be caused by the lower SG dose applied by the user of Kratom preparations. SG and its metabolites could be differentiated in the human samples from the diastereomeric MG and its metabolites comparing the different retention times determined after application of the single alkaloids to rats. In addition, some differences in MS(2) and/or MS(3) spectra of the corresponding diastereomers were observed. 相似文献
108.
Rosemarie Philipp Olaf Hanebeck Sebastian Hein Wolfram Bremser Tin Win Irene Nehls 《Accreditation and quality assurance》2010,15(3):141-146
The Federal Institute for Materials Research and Testing (BAM), Germany, has issued a series of large volume ethanol in water
certified reference materials (CRMs), primarily developed for the calibration of evidential breath alcohol analyzers in Germany.
The certified parameter is the ethanol mass concentration at 20 °C. When used in a wet bath simulator, the solutions deliver
gas samples that meet the requirements set by the Organization of Legal Metrology for calibration of breathalyzers. The materials
were prepared gravimetrically by spiking of ethanol into water in single 5 L units. A complete uncertainty budget for the
preparation process has been established. The purity of the commercial ethanol stock solution was identified to be the main
source of uncertainty. For stability and homogeneity measurements and for the verification of the gravimetric mass concentration
of the CRMs, a robust high-precision gas chromatography, with flame-ionization detection method for ethanol determination
in aqueous samples was developed and validated. The good performance of this method has been demonstrated in several international
comparisons organized by the Consultative Committee for Amount of Substance—Metrology in Chemistry at the International Bureau
of Weights and Measures. 相似文献
109.
Philipp Wachter Christian Schreiner Hans-Georg Schweiger Heiner Jakob Gores 《The Journal of chemical thermodynamics》2010,42(7):900-903
The determination of phase transition points of nine different ionic liquids (ILs) was performed by thermal analysis with simultaneous recording of conductivity. Conductivity of electrolyte solutions and ILs drastically changes during phase transitions and thus is an additional and very sensitive indicator for measuring phase transition points. Evaluation of temperature–time functions and conductivity–time functions with our computer-coupled automated equipment enabled the determination of melting temperatures with high accuracy and reliability. This claim is based on large samples, low temperature change rates and by regularly repeated measurements, i.e. at least seven measurements per IL. The melting temperatures of 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate, 1-butyl-1-methylpyrrolidinium tris(penta-fluoroethyl)trifluorophosphate, and 1-methyl-3-propylimidazolium iodide were, to our knowledge, determined for the first time. The melting temperatures of the other 1-butyl-1-methylpyrrolidinium-, 1-ethyl-3-methylimidazolium-, 1-hexyl-3-methylimidazolium-, and trimethylsulfonium-based ILs showed either a very good accordance with values published in literature or were distinctly higher. 相似文献
110.
Charmonia spectral functions at finite temperature are studied using QCD sum rules in combination with the maximum entropy method. This approach enables us to directly obtain the spectral function from the sum rules, without having to introduce any specific assumption about its functional form. As a result, it is found that while J/ψ and η(c) manifest themselves as significant peaks in the spectral function below the deconfinement temperature T(c), they quickly dissolve into the continuum and almost completely disappear at temperatures between 1.0T(c) and 1.1T(c). 相似文献