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排序方式: 共有186条查询结果,搜索用时 15 毫秒
181.
182.
Aromatic hydroxylation catalyzed by toluene 4-monooxygenase in organic solvent/aqueous buffer mixtures 总被引:3,自引:0,他引:3
Toluene 4-monooxygenase is a four-protein component diiron enzyme complex. The enzyme catalyzes the hydroxylation of toluene
to give p-cresol with ∼96% regioselectivity. The performance of the enzyme in two-phase reaction systems consisting of toluene, hexane,
or perfluorohexane and an aqueous buffer was tested. In each of the cosolvent systems, containing up to 93% (v/v) of solvent,
the enzyme was active and exhibited regioselectivity indistinguishable from the aqueous reaction. Using the perfluorohexane/buffer
system, a number of polycyclic aromatic hydrocarbons were oxidized that were not readily oxidized in aqueous buffer. An instability
of the hydroxylase component and a substantial uncoupling of NADH utilization and product formation were observed in reactions
that were continued for longer than ∼3 min. More stable enzyme complexes will be needed for broad applicability of this hydroxylating
system in nonaqueous media. 相似文献
183.
Shekhar KC Roshan K. Dhungana Namrata Khanal Prof. Ramesh Giri 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(21):8124-8128
We report a Ni-catalyzed regioselective α-carbonylalkylarylation of vinylarenes with α-halocarbonyl compounds and arylzinc reagents. The reaction works with primary, secondary, and tertiary α-halocarbonyl molecules, and electronically varied arylzinc reagents. The reaction generates γ,γ-diarylcarbonyl derivatives with α-secondary, tertiary, and quaternary carbon centers. The products can be readily converted to aryltetralones, including a precursor to Zoloft, an antidepressant drug. 相似文献
184.
The black hole information problem provides important clues for trying to piece together a quantum theory of gravity. Discussions on this topic have generally assumed that in a consistent theory of gravity and quantum mechanics, quantum theory is unmodified. In this review, we discuss the black hole information problem in the context of generalisations of quantum theory. In this preliminary exploration, we examine black holes in the setting of generalised probabilistic theories, in which quantum theory and classical probability theory are special cases. We are able to calculate the time it takes information to escape a black hole, assuming that information is preserved. In quantum mechanics, information should escape pure state black holes after half the Hawking photons have been emitted, but we find that this get’s modified in generalisations of quantum mechanics. Likewise the black-hole mirror result of Hayden and Preskill, that information from entangled black holes can escape quickly, also get’s modified. We find that although information exits the black hole as predicted by quantum theory, it is fairly generic that it fails to appear outside the black hole at this point—something impossible in quantum theory due to the no-hiding theorem. The information is neither inside the black hole, nor outside it, but is delocalised. 相似文献
185.
Supramolecular Tetrad Featuring Covalently Linked Bis(porphyrin)–Phthalocyanine Coordinated to Fullerene: Construction and Photochemical Studies 下载免费PDF全文
Chandra B. KC Gary N. Lim Prof. Dr. Paul A. Karr Prof. Francis D'Souza 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(25):7725-7735
A multimodular donor–acceptor tetrad featuring a bis(zinc porphyrin)–(zinc phthalocyanine) ((ZnP–ZnP)–ZnPc) triad and bis‐pyridine‐functionalized fullerene was assembled by a “two‐point” binding strategy, and investigated as a charge‐separating photosynthetic antenna‐reaction center mimic. The spectral and computational studies suggested that the mode of binding of the bis‐pyridine‐functionalized fullerene involves either one of the zinc porphyrin and zinc phthalocyanine (Pc) entities of the triad or both zinc porphyrin entities leaving ZnPc unbound. The binding constant evaluated by constructing a Benesi–Hildebrand plot by using the optical data was found to be 1.17×105 M ?1, whereas a plot of “mole‐ratio” method revealed a 1:1 stoichiometry for the supramolecular tetrad. The mode of binding was further supported by differential pulse voltammetry studies, in which redox modulation of both zinc porphyrin and zinc phthalocyanine entities was observed. The geometry of the tetrad was deduced by B3LYP/6‐31G* optimization, whereas the energy levels for different photochemical events was established by using data from the optical absorption and emission, and electrochemical studies. Excitation of the zinc porphyrin entity of the triad and tetrad revealed ultrafast singlet–singlet energy transfer to the appended zinc phthalocyanine. The estimated rate of energy transfer (kENT) in the case of the triad was found to be 7.5×1011 s?1 in toluene and 6.3×1011 s?1 in o‐dichlorobenzene, respectively. As was predicted from the energy levels, photoinduced electron transfer from the energy‐transfer product, that is, singlet‐excited zinc phthalocyanine to fullerene was verified from the femtosecond‐transient spectral studies, both in o‐dichlorobenzene and toluene. Transient bands corresponding to ZnPc ? + in the 850 nm range and C60 ? ? in the 1020 nm range were clearly observed. The rate of charge separation, kCS, and rate of charge recombination, kCR, for the (ZnP–ZnP)–ZnPc ? +:Py2C60 ? ? radical ion pair (from the time profile of 849 nm peak) were found to be 2.20×1011 and 6.10×108 s?1 in toluene, and 6.82×1011 and 1.20×109 s?1 in o‐dichlorobenzene, respectively. These results revealed efficient energy transfer followed by charge separation in the newly assembled supramolecular tetrad. 相似文献
186.
Ron S. Dickson Alan P. Oppenheim Geoff N. Pain 《Journal of organometallic chemistry》1982,224(4):377-386
Treatment of the μ(η1)-alkyne complex (η-C5H5)2Rh2(CO)2(CF3C2CF3) with trimethylamine-N-oxide results in mono-decarbonylation to give the μ(η2)- alkyne complex (η-C5H5)2Rh2(μ-CO)(CF3C2CF3). Coordinative addition of a variety of ligands L to the monocarbonyl complex has been achieved at room temperature, and stable adducts (η-C5H5)2Rh2(CO)L(CF3C2CF3) (L CO, CNBut, PPh3, PMePh2, P(OMe)3, AsPh3, PF3 and PF2(NEt2)) have been fully characterized by infrared and NMR spectroscopy. In each complex, there is a μ(η1)-attachment of the hexafluorobut-2-yne and a trans-arrangement of CO and L. The spectroscopic data establish that there is rapid scrambling of CO and L when L CNBut. An unstable adduct is formed when (η-C5H5)2Rh2(μ-CO)(CF3C2CF3) is dissolved in pyridine. 相似文献