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61.
Using dimethyl peroxide as a thermal source of methoxy radicals overthe temperature range of 110–160°C, and the combination of methoxy radicals and nitrogen dioxide as a reference reaction: a value was determined of the rate constant for the reaction of methoxy radicals with oxygen: is independent of nitrogen dioxide or oxygen concentration and added inert gas (carbon tetrafluoride). No heterogeneous effects were detected. The value of k4 is given by the expression In terms of atmospheric chemistry, this corresponds to a value of 105.6 M?1·sec?1 at 298 K. Extrapolation to temperatures where the combustion of organic compounds has been studied (813 K) produces a value of 107.7 M?1·sec?1 for k4. Under these conditions, reaction (4) competes with hydrogen abstraction or disproportionation reactions of the methoxy radical and its decomposition (3): In particular k3 is in the falloff region under these conditions. It is concluded that reaction (4) takes place as the result of a bimolecular collision process rather than via the formation of a cyclic complex. 相似文献
62.
Hoogesteger FJ van Walree CA Jenneskens LW Roest MR Verhoeven JW Schuddeboom W Piet JJ Warman JM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2000,6(16):2948-2959
The photophysical properties of a bicyclohexylidene (1DA) and a bicyclohexyl (2DA) substituted with an anilino electron donor and a dicyanoethylene electron acceptor have been studied. Quenching of local donor emission is observed for these compounds as well as quenching of the "pseudo-local" acceptor emission. Transient absorption spectra show dialkylanilino-type radical-cation and dicyanoethylene-type radical-anion absorptions. These results show that intramolecular charge separation takes place in 1DA and 2DA. This was corroborated by time-resolved microwave conductivity measurements from which large excited-state dipole moments were found for both 1DA and 2DA. Time-resolved fluorescence spectroscopy revealed that in the charge-separated state in cyclohexane for 2DA, molecular folding takes place on a nanosecond timescale. For 1DA in cyclohexane, either charge separation takes place in a (fully) folded conformation or very rapid (subnanosecond timescale) folding takes place subsequent to charge separation. In addition to this difference in conformational behavior, the presence of the exocyclic double bond between the cyclohexyl-type rings results in efficient quenching of the anilino donor triplet state and acceleration of the charge recombination rate by a factor of 20. 相似文献
63.
64.
Frédéric Batt 《Tetrahedron letters》2008,49(3):566-568
Depending on the double bond position, tosyl deprotection was observed during olefin dihydroxylation using osmium tetroxide, leading to triols. 相似文献
65.
A design of polarization-maintaining retro-reflectors(PMRRs) for folded-path applications is proposed and analyzed.The prism-based scheme enables the output light,which is parallel to the input,to have an identical state of polarization.The principle of the design is theoretically verified,and the related error is analyzed due to possible manufacturing imperfection.The maximum spatial angle error is ±2.75°.The effect on the extinction ratio and insertion loss is also discussed,which further proves the design’s feasibility in practical applications. 相似文献
66.
Mark SS Bergkvist M Yang X Teixeira LM Bhatnagar P Angert ER Batt CA 《Langmuir : the ACS journal of surfaces and colloids》2006,22(8):3763-3774
Two-dimensional (2-D) surface layer (S-layer) protein lattices isolated from the gram-positive bacterium Deinococcus radiodurans and the acidothermophilic archaeon Sulfolobus acidocaldarius were investigated and compared for their ability to biotemplate the formation of self-assembled, ordered arrays of inorganic nanoparticles (NPs). The NPs employed for these studies included citrate-capped gold NPs and various species of CdSe/ZnS core/shell quantum dots (QDs). The QD nanocrystals were functionalized with different types of thiol ligands (negative- or positive-charged/short- or long-chain length) in order to render them hydrophilic and thus water-soluble. Transmission electron microscopy, Fourier transform analyses, and pair correlation function calculations revealed that ordered nanostructured arrays with a range of spacings (approximately 7-22 nm) and different geometrical arrangements could be fabricated through the use of the two types of S-layers. These results demonstrate that it is possible to exploit the physicochemical/structural diversity of prokaryotic S-layer scaffolds to vary the morphological patterning of nanoscale metallic and semiconductor NP arrays. 相似文献
67.
68.
本文证明了n+k多体系(k≥4)的全部可能的封闭网均可以通过若干相应的子n+3相多体系的拼合运算得出,从而为具体构造n+k相多体系(k≥4)的全部合理的封闭网,提供了基本方法。 相似文献
69.
The rate of decomposition of tert-amyl nitrite (t-AmONO) has been studied in the absence (120°–155°C) and presence (160°–190°C) of nitric oxide. In the absence of nitric oxide for low concentrations of tert-amyl nitrite (~10?4M) and small extents of reaction (~1%), the first-order homogeneous rates of acetone formation are a direct measure of reaction (1) since k3a ? k2(NO): The rate of acetone formation is unaffected by the addition of large amounts of carbon tetrafluoride or isobutane (~1 atm) but is completely suppressed by large amounts of nitric oxide (1 atm 120°–155°C). The rate of reaction (1) is given by k1 = 1016.3±0.1 10?40.3±0.1/θ sec?1. Since (E1 + RT) and ΔH°1 are identical, both may be equated with D(t-AmO – NO) = 40.9 ± 0.1 kcal/mol and E2 = 0 ± 0.1 kcal/mol. The thermochemistry leads to the result that ΔH°f (t-AmO) = ?26.6 ± 1 kcal/mol. From ΔS°1 and A1, k2 is calculated to be 1010.5±0.2 M?1·sec?1. Although the addition of nitric oxide completely suppresses acetone formation at lower temperatures, it reappears at higher temperatures. This is a result of reaction (3a) now competing with reaction (2), thus allowing k3a to be determined. The rate constant for reaction (3a) is given by k3a = 1014.7 ± 0.2 10?14.3 ± 1/θ sec?1. There are two possible routes for the decomposition of the tert-amyloxyl radical: The dominating process is (3a). From the result at 160°C that k3a/k3b = 80, we arrive at the result k3b = 1015.0–18.7/θ sec?1. In addition to the products accounted for by the radical split (1), methyl-2-but-1-ene and methyl-2-but-2-ene are produced as a result of the six-centre elimination of nitrous acid (5): The ratio k5a/k5b was 0.35. Unlike tert-butyl where the rates of the two paths were comparable [(l) and (5)], here the total rate of the elimination process was only 0.5% that of the radical split (1). The reason for this is not clear. 相似文献
70.