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91.
Hanjiang Dong Zhengping Zhang Man-Ho Lee D. W. Mueller Richard F. Reidy 《Journal of Sol-Gel Science and Technology》2007,41(1):11-17
Sol-gel polymerization of methyltrimethoxysilane (MTMS) in ethanol using a two-step acid/base catalyzed procedure (B2) is
followed by 29Si NMR spectroscopy. Analysis of the structural evolution of the B2 system shows that esterification of monomeric and end
silicon species is rate-limited while that of linear and cyclic species is able to reach pseudoequilibrium in the second basic
step. Condensation reactivity is reduced with increasing network connectivity, however, to a much less degree under B2 conditions
than MTMS polymerization under acidic conditions. Steric effects as well as many other factors are attributed to this trend.
The concentration of cyclic and polycyclic species of the B2 system is nearly 3 times lower compared to the acid-catalyzed
system. The empirical degree of condensation at the gel point is determined to be 0.88. The effects of cyclization and phase
separation on MTMS gelation are discussed for both B2 and acid-catalyzed systems. Based on these results it is believed that
MTMS-based gels form for B2 and not acid-catalyzed conditions due to reduced cyclization, rapid hydrolysis and condensation,
effective use of functional groups, and effective contribution of branched and polycyclic species as crosslinking points to
connect polymeric chains in the B2 system. 相似文献
92.
Wang J Struckmeier U Yang B Cool TA Osswald P Kohse-Höinghaus K Kasper T Hansen N Westmoreland PR 《The journal of physical chemistry. A》2008,112(39):9255-9265
This work provides experimental evidence on how the molecular compositions of fuel-rich low-pressure premixed flames are influenced as the oxygenates dimethyl ether (DME) or ethanol are incrementally blended into the propene fuel. Ten different flames with a carbon-to-oxygen ratio of 0.5, ranging from 100% propene (phi = 1.5) to 100% oxygenated fuel (phi = 2.0), are analyzed with flame-sampling molecular-beam mass spectrometry employing electron- or photoionization. Absolute mole fraction profiles for flame species with masses ranging from m/z = 2 (H2) to m/z = 80 (C6H8) are analyzed with particular emphasis on the formation of harmful emissions. Fuel-specific destruction pathways, likely to be initiated by hydrogen abstraction, appear to lead to benzene from propene combustion and to formaldehyde and acetaldehyde through DME and ethanol combustion, respectively. While the concentration of acetaldehyde increases 10-fold as propene is substituted by ethanol, it decreases as propene is replaced with DME. In contrast, the formaldehyde concentration rises only slightly with ethanol replacement but increases markedly with addition of DME. Allyl and propargyl radicals, the dominant precursors for benzene formation, are likely to be produced directly from propene decomposition or via allene and propyne. Benzene formation through propargyl radicals formed via unsaturated C2 intermediates in the decomposition of DME and ethanol is negligibly small. As a consequence, DME and ethanol addition lead to similar reductions of the benzene concentration. 相似文献
93.
Ruthenium‐Catalyzed Reductive Methylation of Imines Using Carbon Dioxide and Molecular Hydrogen
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Dr. Kassem Beydoun Ghazi Ghattas Katharina Thenert Prof. Dr. Jürgen Klankermayer Prof. Dr. Walter Leitner 《Angewandte Chemie (International ed. in English)》2014,53(41):11010-11014
The use of the well‐defined [Ru(triphos)(tmm)] catalyst, CO2 as C1 source, and H2 as reducing agent enabled the reductive methylation of isolated imines, as well as the direct coupling of amines with aldehydes and the subsequent reductive methylation of the in situ formed imines. The method, which afforded the corresponding N‐methyl amines in very good to excellent yields, was also used for the preparation of the antifungal agent butenafine in one step with no apparent waste, thus increasing the atom efficiency of its synthesis. 相似文献
94.
Valentin Chabert Lucille Babel Michael P. Füeg Maksym Karamash Edwin S. Madivoli Nelly Herault Joana M. Dantas Carlos A. Salgueiro Bernd Giese Katharina M. Fromm 《Angewandte Chemie (International ed. in English)》2020,59(30):12331-12336
Anaerobic microorganisms of the Geobacter genus are effective electron sources for the synthesis of nanoparticles, for bioremediation of polluted water, and for the production of electricity in fuel cells. In multistep reactions, electrons are transferred via iron/heme cofactors of c‐type cytochromes from the inner cell membrane to extracellular metal ions, which are bound to outer membrane cytochromes. We measured electron production and electron flux rates to 5×105 e s?1 per G. sulfurreducens. Remarkably, these rates are independent of the oxidants, and follow zero order kinetics. It turned out that the microorganisms regulate electron flux rates by increasing their Fe2+/Fe3+ ratios in the multiheme cytochromes whenever the activity of the extracellular metal oxidants is diminished. By this mechanism the respiration remains constant even when oxidizing conditions are changing. This homeostasis is a vital condition for living systems, and makes G. sulfurreducens a versatile electron source. 相似文献
95.
96.
97.
EDOT‐diketopyrrolopyrrole copolymers for high bulk hole mobility and near infrared absorption
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Christian J. Mueller Chetan R. Singh Mukundan Thelakkat 《Journal of Polymer Science.Polymer Physics》2016,54(6):639-648
To obtain novel low‐bandgap materials with tailored hole‐transport properties and extended absorption, electron rich 3,4‐ethylenedioxythiophene is introduced as a comonomer in diketopyrrolo[3,4‐c]pyrrole copolymers with different aryl flanking units. The polymers are characterized by absorption and photoluminescence spectroscopy, dynamic scanning calorimetry, cyclic voltammetry, and X‐ray diffraction. The charge transport properties of these new materials are studied carefully using an organic field effect transistor geometry where the charge carriers are transported over a narrow channel at the semiconductor/dielectric interface. These results are compared to bulk charge carrier mobilities using space‐charge limited current (SCLC) measurements, in which the charge carrier is transported through the complete film thickness of several hundred nanometers. Finally, charge carrier mobilities are correlated with the electronic structure of the compounds. We find that in particular the thiophene‐flanked copolymer PDPP[T]2‐EDOT is a very promising candidate for organic photovoltaics, showing an absorption response in the near infrared region with an optical bandgap of 1.15 eV and a very high bulk hole mobility of 2.9 × 10?4 cm2 V?1 s?1 as measured by SCLC. This value is two orders of magnitudes higher than SCLC mobilities reported for other polydiketopyrrolopyrroles and is in the range of the well‐known hole transporting polymer poly(3‐hexylthiophene). © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 639–648 相似文献
98.
99.
V. Mathieu A. H. Mueller D. N. Triantafyllopoulos 《The European Physical Journal C - Particles and Fields》2014,74(5):1-15
We give a detailed derivation of the Boltzmann equation, and in particular its collision integral, in classical field theory. We first carry this out in a scalar theory with both cubic and quartic interactions and subsequently in a Yang–Mills theory. Our method does not rely on a doubling of the fields, rather it is based on a diagrammatic approach representing the classical solution to the problem. 相似文献
100.
Kurosaki Hiromu Mueller Rebecca J. Lambert Susan B. Rao Govind R. 《Journal of Radioanalytical and Nuclear Chemistry》2017,311(1):323-329
Journal of Radioanalytical and Nuclear Chemistry - An alternate method of preparing actinide alpha counting sources was developed in place of electrodeposition or lanthanide fluoride... 相似文献