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11.
Addition–elimination reactions involving a nucleophile and a remote leaving group [SH
N(AE)tele] are well-known under basic conditions, especially amongst electron-poor six-membered heterocycles, but are less commonly
encountered for five-membered heterocycles and are rare under acidic conditions. Concentrated HCl converts 1-hydroxy-1H-pyrazolo[3,4-c] isoquinoline and 1-hydroxy-1H-pyrazolo[3,4-c]quinoline into 3-chloro-1H-pyrazolo[3,4-c]isoquinoline and 3-chloro-1H-pyrazolo[3,4-c]quinoline, respectively. However, apparently neither the isomeric 1-hydroxy-1H-pyrazolo[4,3-c](iso)-quinolines nor the parent 1-hydroxypyrazole undergo this reaction. Additionally, all these systems are refractory under
basic conditions. We present a plausible mechanism for the reaction, involving the 3-addition of Cl- to the diprotonated heterocycle, followed by the elimination of water. Calculations of the initial transition states and
intermediates, using optimisation at B3LYP/6-311+G(d,p), including thermochemistry [HF/6-31+G(d)], and single-point Poisson–Boltzmann
self-consistent reaction field determination of the free energy of solvation (Jaguar Poisson–Boltzmann self-consistent reaction
field), support this mechanism and reproduce the observed order of reactivity, the addition step being 2–4 kcal less favourable
for the isomeric 1-hydroxy-1H-pyrazolo[4,3-c](iso)quinolines and provide a rationalisation for the role of strong acid.
Received: 27 June 2002 / Accepted: 6 September 2002 /
Published online: 14 February 2003 相似文献
12.
Inmaculada Fernandez Robert Greatrex Norman N. Greenwood 《Journal of solid state chemistry》1980,34(1):121-128
99Ru Mössbauer spectra have been recorded at 4.2 K for the quaternary oxides Ba3Ru2MO9 (M = Mg, Ca, Sr; Co, Ni, Cu, Zn; and Cd), all of which crystallize with the hexagonal barium titanate structure. The Ca, Sr, and Cd compounds give sharp symmetrical singlets with chemical isomer shifts typical of ruthenium in the +5 oxidation state. The absence of magnetic hyperfine splitting is consistent with the published interpretation of magnetic susceptibility data in terms of binuclear intracluster spin pairing which leads to an S = 0 ground state. In contrast, magnetic hyperfine splitting is seen for the Mg, Zn, Co, Ni, and Cu compounds; this can be interpreted only in terms of long-range magnetic order and the absence of such an S = 0 ground state at 4.2 K. This differs from the published interpretation of the magnetic susceptibility data for Ba3Ru2MgO9 in the low-temperature region. The magnetic flux densities at the ruthenium nuclei in the magnetically ordered compounds (32.5–51.6 T) are lower than those normally associated with ruthenium(V), and the spectra cannot be curve fitted satisfactorily with single hyperfine patterns having the natural linewidth. Possible reasons for these observations are discussed. 相似文献
13.
Bernard W. TaylorIII Arthur J. Keown Allen G. Greenwood 《The Journal of the Operational Research Society》1983,34(5):379-390
The decision-making process involved in the procurement of military weapon systems, although quite critical and complex, still encompasses the basic characteristics of a capital budgeting problem. Given a number of expenditure items and a limited budget, it is desired to procure those weapon systems that will achieve the goals and objectives of the government and/or military in the most efficient manner. Since these objectives are typically numerous and diverse, traditional decision-making techniques are not applicable. As such, integer goal programming is suggested as a technique to be employed to determine the number of military aircraft to be procured, given conflicting expenditure, budget and effectiveness goals. This method is demonstrated via a case example in which the solution results are presented. 相似文献
14.
Greenwood RF 《Talanta》1970,17(10):999-1003
An apparatus for the determination of the melting point of a partially frozen liquid is described. Thermal equilibrium is rapidly attained, largely because of the presence of glass balls in the experimental flask, and the method of agitation. The use of a thermistor and a recording potentiometer allows charting of the temperature changes with time. The melting point can be calculated from points on the trace. The apparatus has been used to study melting point depressions for solutions of hydrocarbons and phenols in benzene, nitrobenzene, water and dioxan. 相似文献
15.
J. D. Baker R. J. Gehrke R. C. Greenwood D. H. Meikrantz 《Journal of Radioanalytical and Nuclear Chemistry》1982,74(1-2):117-124
A microprocessor-controlled radiochemical separation system, which has been developed at the INEL, has been further advanced
to separate individual rare-earth elements from mixed fission products in times of a few minutes. The system was composed
of an automated chemistry system fed by two ∼300μg252Cf sources coupled directly by a He-jet to transport the fission products. Chemical separations were performed using two high
performance liquid chromatography columns coupled in series. The first column separated the rare-earth group by extraction
chromatography using dihexyldiethylcarbamoylmethylphosphonate (DHDECMP) adsorbed on Vydac C8 resin. The second column isolated the individual rare-earth elements by cation exchange chromatography using Aminex A-9 resin
with α-hydroxyisobutyric acid (α-HIBA) as the eluent. Significant results, which have been obtained to date with this advanced
system, are the identification of several new neutron-rich rare-earth isotopes including155Pm (T=48±4 s) and163Gd (T=68±3 s). In addition a half-life of 41±4 s is reported for160Eu.
Work supported by the U.S. Department of Energy under DOE Contract No. De-ACO7-76IDO-1570. 相似文献
16.
Terence C. Gibb Robert Greatrex Norman N. Greenwood Kenneth G. Snowdon 《Journal of solid state chemistry》1975,14(2):193-202
The magnetic and structural properties of the solid solution SrFexRu1?xO3?y (0 ? x ? 0.5) have been studied using 57Fe and 99Ru Mössbauer spectroscopy and other techniques. These phases, which are here reported for the first time, have a distorted perovskite structure. The iron substitutes exclusively as Fe3+ and thereby causes oxygen deficiency, but has little effect on the magnetic behaviour of the Ru4+ until x > 0.2, whereupon the metallic band system begins to revert to a localized electron structure. The properties of a sample with x = 0.3 are complex and intermediate in character. For x > 0.3 the oxygen deficiency is reduced by substantial oxidation to Ru5+ until at x = 0.5 the system corresponds to Sr2Fe3+Ru5+O6. 相似文献
17.
Priscilla E. Greenwood Gerard Hooghiemstra 《Probability Theory and Related Fields》1991,89(2):201-210
Summary Between the operations which produce partial maxima and partial sums of a sequenceY
1,Y
2, ..., lies the inductive operation:X
n
=X
n-1(X
n-1+Y
n
),n1, for 0<<1. If theY
n
are independent random variables with common distributionF, we show that the limiting behavior of normed sequences formed from {X
n
,n1}, is, for 0<<1, parallel to the extreme value case =0. ForFD() we give a full proof of the convergence, whereas forFD()D(), we only succeeded in proving tightness of the involved sequence. The processX
n
is interesting for some applied probability models. 相似文献
18.
The title compounds have been synthesized, characterized by spectroscopic and analytical methods, and the complete structure of (IV) determined by single-crystal X-ray methods. Compound (IV) is monoclinic:a=13.891(3),b=4.935(2),c=12.499(2)Å,=112.10(1) deg,P21/n,Z=4. The structure was determined by the heavy-atom method, and refined by full-matrix least squares onF toR=4.6%, with 1283 reflexions for whichI3 (I). The structure (IV) was confirmed, and the molecule was shown to be planar to within 0.01 Å. 相似文献
19.
Vogensen SB Greenwood JR Varming AR Brehm L Pickering DS Nielsen B Liljefors T Clausen RP Johansen TN Krogsgaard-Larsen P 《Organic & biomolecular chemistry》2004,2(2):206-213
(RS)-3-Hydroxy-4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridine-5-carboxylic acid (5-HPCA)(), which is a conformationally constrained cyclised analogue of AMPA has previously been described as causing glutamate receptor mediated excitations of spontaneously firing cat spinal interneurons in a similar fashion to AMPA. We have now prepared the enantiomers of through chiral chromatographic resolution of (RS)-3-(carboxymethoxy)-4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridine-5-carboxylic acid () followed by a stereoconservative hydrolysis resulting in the enantiomers of with high enantiomeric excess (% ee [greater-than-or-equal] 99). The absolute configurations indicated by an X-ray analysis of (-)- monohydrate were confirmed by comparing observed and ab initio calculated electronic circular dichroism spectra and by stereoconservative synthesis of (S)- from (S)-AMPA, the pharmacologically active form of AMPA. The pharmacological effects at native and cloned (GluR1-4) AMPA receptors were shown to reside exclusively with (R)-(+)-, in striking contrast to the usual stereoselectivity trend among AMPA receptor agonists. The reasons for this anomalous behaviour became clear upon docking both enantiomers of to the agonist binding site of GluR2. 相似文献
20.