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481.
M. Rute G. da Costa M. João M. Curto Stephen G. Davies Fátima C. Teixeira James E. Thomson 《Tetrahedron》2018,74(40):5965-5973
(Aryl aldehyde)- and (aryl ketone)-chromium tricarbonyl complexes ortho-substituted with the chiral auxiliary O-methyl-N-(α-methylbenzyl)hydroxylamine undergo diastereoselective addition of Grignard reagents and Super-Hydride®, respectively, to give the corresponding secondary alcohols in high diastereoisomeric purity. These compounds may be easily decomplexed and deprotected to give the corresponding enantiopure amino alcohols. 相似文献
482.
P. Bruère R. Gille L. P. Hammett A. J. Deyrup L. Rosenthaler G. Calcagni M. Sturnajolo J. L. Meyer B. Englund P. S. Roller J. N. Bronsted K. Linderstrøm-Lang A. Perret A. M. Krawczynski G. Batchelder V. W. Meloche S. Snyder J. Fialkow M. Stschigol B. B. Owen L. Wolf A. Thiel G. Coch G. Marsh T. Karantassis L. Capatos J. M. A. van Liempt Fr. L. Hahn R. Klockmann R. Schulz J. M. Olsen F. Reimers C. J. Schollenberger R. T. Thomson S. Saito J. Trtilek F. J. Garrick A. J. Berry L. Belladen G. Piazza F. Burriel F. Sierra H. Wycis G. W. Bennett Z. Ernst K. Hickman C. R. Sanford J. Lindner G. Bruhns 《Analytical and bioanalytical chemistry》1934,96(3-4):118-127
483.
Robert C. Worrest Krystyna U. Wolniakowski James D. Scott Deborah L. Brooker Bruce E. Thomson Henry Van Dyke 《Photochemistry and photobiology》1981,33(2):223-227
Abstract Human activities may cause a 16% reduction of stratospheric ozone. The concomitant increase in solar UV-B radiation reaching the surface of the earth could detrimentally affect the phytoplankton that form the base of the food web in oceanic and estuarine ecosystems. In the current study acute exposure of seven species of marine phytoplankton to UV–B radiation depressed the radiocarbon estimate of primary production. A model of a marine ecosystem was constructed based on the differential sensitivities of the seven species of phytoplankton. Increasing the UV–B exposure within the model from 100 EffDNA J/m2 /day to 150 EffDNA J/m2 /day significantly altered the community composition of the ecosystem. In nature, alteration of the phytoplanktonic community structure could result in a significant impact upon successional patterns and primary producer–consumer trophodynamics. 相似文献
484.
The use of AM1, MNDO, and MNDOC semiempirical MO methods for calculation of heats of formation and ionization potentials of a series of 38 radicals are described. AM1 and MNDO calculations are reported using both half-electron (HE) and Unrestricted Hartree Fock (UHF) wavefunctions. Results show the MNDOC method to give lowest overall errors, being slightly better than the HE-AM1 method. In all cases, the AM1 method shows considerable improvement over MNDO. 相似文献
485.
The results of ab initio “supermolecule” calculations of the charge transfer between formamide and the enol forms of methylglyoxal, ethylglyoxal, dimethylglyoxal, and propenylglyoxal are compared for several different conformations of the constituent molecules. The enols were found to be poorer electron acceptors than their respective keto isomers. 相似文献
486.
Photolysis of -butyl azide in N2 matrices at 12 K gives the imine 3a; matrix IR spectra for imines 4a and 5a are also reported. 相似文献
487.
Polymer mediated self-assembly of magnetic nanoparticles 总被引:2,自引:0,他引:2
Sun S Anders S Hamann HF Thiele JU Baglin JE Thomson T Fullerton EE Murray CB Terris BD 《Journal of the American Chemical Society》2002,124(12):2884-2885
We present a simple polymer-mediated process of assembling magnetic FePt nanoparticles on a solid substrate. Alternatively absorbing the PEI molecule and FePt nanoparticles on a HO-terminated solid surface leads to a smooth FePt nanoparticle assembly with controlled assembly thickness and dimension. Magnetic measurements show that the thermally annealed FePt nanoparticle assembly as thin as three nanoparticle layers is ferromagnetic. The magnetization direction of this thin FePt nanoparticle assembly is readily controlled with the laser-assisted magnetic writing. The reported process can be applied to various substrates, nanoparticles, and functional macromolecules and will be useful for future magnetic nanodevice fabrication. 相似文献
488.
The CD. spectra of carotenoids with an asymmetric centre at C(3) have the following unusual features: (1) All-trans and di-cis compounds with two end-rings, at least one of which possesses an asymmetric C-atom, have very similar CD. spectra, whereas the corresponding mono-cis compounds give mirror-image CD. spectra; (2) In carotenoids or apocarotenoids with only one end-ring all-trans and mono-cis compounds have the same CD. spectra; (3) The CD. spectra of such carotenoids are strongly temperature dependent either increasing in magnitude or completely changing in sign upon cooling. These properties have been rationalized with the aid of a model with takes the total chromophore of the carotenoid as being intrinsically chiral with symmetry C2. It seems that the chirality arises not only from the presence of the hydroxyl group of an asymmetric carbon atom, C(3), which occupies an equatorial position thereby locking the conformation of the end-ring, but also from the steric hindrance across the formal single bond C(6), C(7), linking the end-ring to the chain and thus creating a chiral π-system. (The twist about the C(6), C(7)-bond acquires a handedness because of the predominance of one conformational form of the end-ring. In this way, the double bonds of the end-ring become twisted out of the plane of the chain with one hand predominating. Thus the whole conjugated system becomes chiral). The reversal of sign between the trans (and di-cis) and mono-cis compounds is due to a tilt of the 2-fold symmetry axis and thereby a change of chirality. The temperature dependence stems from the varying population of forms of different twist of the end-group relative to the chain. Compounds with 7, 8-triple bonds also show distinct CD. spectra and a sign change between all-trans and mono-cis isomers in addition to temperature dependence. The latter property demonstrates that some steric hindrance between the end-ring and the main chain is present in these compounds. Some suggestions for the origins of the sign patterns and band intensities of the CD. and absorption spectra are included. 相似文献
489.
Christopher A. Reynolds Colin Thomson 《International journal of quantum chemistry》1987,32(1):123-131
Various isomers of CH3(H2O) (where n = 1–3) have been studied using self-consistent field gradient techniques. The calculations have largely employed a split valence (4-21G) basis set, although the effects of polarization functions and electron correlation have been considered for a model system. A mechanism for the formation of CH3OH from CH3(H2O), involving linear hydration chains, is proposed, and the relevance of the results to the various proposed pathways for the decomposition of nitrosamine metabolites is discussed. 相似文献
490.
Barry Thomson Zhiyu Wang Anthony Paine Gilles Lajoie Alfred Rudin 《Journal of polymer science. Part A, Polymer chemistry》1995,33(14):2297-2304
A “surfactant-free” emulsion polymerization of methyl methacrylate was conducted at 80°C with ammonium persulfate initiator. The water-soluble MMA-based oligomers re-maining were isolated and analyzed both as-produced and after hydrolysis. NMR analysis revealed that the mole ratio of MMA repeat units to sulfate end groups in the former is 6.5. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and gel permeation chromatography both showed that the mean number of MMA repeat units comprising the extracted material is 8–9. The hydrolysis procedure rids the oligomers of their terminal groups and converts some of the methyl ester groups to acid, greatly sim-plifying the mass spectrum. This appears to be the first direct measurement of “surfactants” produced in situ from monomer and persulfate initiator. © 1995 John Wiley & Sons, Inc. 相似文献