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31.
To explore tertiary contact formation in alpha-synuclein, a natively unfolded protein implicated in Parkinson's disease, we have measured the rates of reaction between a powerful electron donor, the tryptophan (W) triplet excited state, and an acceptor, 3-nitro-tyrosine (Y(NO2)) in six different variants, probing loop sizes between 15 and 132 residues. Electron transfer rates decrease with loop size with the fastest contact time of 140 ns for the N-terminal pair and the slowest of 1.2 mus for the N- to C-terminal pair. Diffusion coefficients ranging from approximately 2 x 10-6 to approximately 10-5 cm2 s-1 were extracted from simultaneous fits of the W to Y(NO2) electron (triplet excited state) and energy transfer (singlet excited state) kinetics. 相似文献
32.
Fazil O. Gülaar Franois Mermound F. Johann Winkler Armand Vuchs 《Helvetica chimica acta》1984,67(2):488-501
Ammonia chemical ionization (CI) mass spectra of various open-chain, cyclic and unsaturated C5- to C10-alcohols were obtained at source temperatures ranging from 60° to 250°C. The reactivity of the ammonia adduct ion MNH and its fragmentation channels are characteristic for substrate structure. Although strongly temperature-dependent, the spectra give nevertheless information on the OH-group environment as well as on the C-skeleton at any source temperature. Primary, secondary and tertiary alcohols as well as allylic and simple olefinic alcohols can be distinguished by their spectra, which show ammonium adduct ions [MNH4]+, adduct dehydrogenation ions [MNH4-H2], ammonium substitution ions [MNH4-H2O]+ and [M-OH]+-ions as the main characteristic peaks. Moreover, konfigurational assignments of stereoisomeric alcohols are possible for larger substrate-size and source-temperature ranges than with isobutane CI mass spectrometry. Homologous M NH-ions show molecular-size control of fragmentation and linear MNH-ions are less stable than branched isomers due to incomplete energy randomization. 相似文献
33.
In Arbuzov-type reactions CFnCl3?nSCl reacts with ROPCl2 (R = CH3, C2H5) to give CFnCl3?nSP(O)Cl2 (n = 3,2,1,0). The corresponding reaction with CF3SeX (X = Cl, Br) produces CF3SeP(O)Cl2 in good yields only in the presence of catalysts such as SbCl5 or BCl3. Reactions between P4 and the sulfenylchlorides produce (CFnCl3?nS)xPCl3?n (n = 3,2,1 and x = 1,2). On heating CFn′ Cl3?n′ SP(O)Cl2 (n′ = 2,1,0) decompose to P(O)Cl3 and SCFn′ Cl2?n′. During this process fluorination of P(O)Cl3 to P(O)F3 by SCF2 is observed. A Cl/Br exchange between CFnCl3?nSP(O)Cl2 (n = 3,2) and PBr3 was proved 19F? and 31P-NMR-spectroscopically.Chemical and physical properties of the newly synthesized compounds will be discussed. 相似文献
34.
Miller JE Grădinaru C Crane BR Di Bilio AJ Wehbi WA Un S Winkler JR Gray HB 《Journal of the American Chemical Society》2003,125(47):14220-14221
Near-UV irradiation of structurally characterized [Re(I)(CO)3(1,10-phenanthroline)(Q107H)](W48F/Y72F/H83Q/Y108W)AzM(II) [Az = Pseudomonas aeruginosa azurin, M = Cu, Zn]/[Co(NH3)5Cl]Cl2 produces a tryptophan radical (W108*) with unprecedented kinetic stability. After rapid formation (k = 2.8 x 106 s-1), the radical persists for more than 5 h at room temperature in the folded ReAzM(II) structure. The absorption spectrum of ReAz(W108*)M(II) exhibits maxima at 512 and 536 nm. Oxidation of K4[Mo(CN)8] by ReAz(W108*)Zn(II) places the W108*/W108 reduction potential in the protein above 0.8 V vs NHE. 相似文献
35.
[reaction: see text] The stereoselective aldol reaction of 3-silyloxyfurans with aldehydes in the presence of a Lewis acid is described. N-Bromosuccinimide (NBS)-mediated cyclization of the aldol product leads to the formation of the 2,7-dioxa-bicyclo[2.2.1]heptan-3-one ring system, which represents the formal product of hetero Diels-Alder reaction of the furan with the aldehyde. 相似文献
36.
Charles J. Colbourn Dean G. Hoffman Kevin T. Phelps Vojtěch Rödl Peter M. Winkler 《Combinatorica》1991,11(3):207-218
We prove that the number oft-wise balanced designs of ordern is asymptotically
, provided that blocks of sizet are permitted. In the process, we prove that the number oft-profiles (multisets of block sizes) is bounded below by
and above by
for constants c2>c1>0. 相似文献
37.
Rhodium-Katalysierte Isomerisierungen von 2-Methylidenglutarsäureestern zu Methylglutaconsäureestern
The Rhodium(III)-catalyzed thermal isomerization of 2-methylidenglutaric acid esters affords predominantly mixtures of cis/trans-2-methylglutaconic acid esters ( 2, 3 ) which upon slow distillation isomerize completely into the cis-esters ( 2 ). Saponification of 2 yields trans-2-methylglutaconic acid ( 5 ). Attempts to prepare the acid chloride of 5 produces 6-chloro-5-methylpyrone-2 ( 9 ) or 6-chloro-3-methylpyrone-2 ( 10 ) which react with anilines to N-substituted derivatives of trans-4-methylglutaconic acid amides ( 11 ). The thermal isomerizations of the respective esters are discussed in terms of 1,5-hydrogen shifts in their ester enol structures. 相似文献
38.
J. Winkler 《Fresenius' Journal of Analytical Chemistry》1968,235(1):18-29
Zusammenfassung Zur Messung der magnetooptischen Rotationsdispersion wird ein registrierendes Spektralpolarimeter verwendet, dessen Probenraum so groß ausgelegt ist, daß sich darin die zusätzlich notwendige Magneteinheit unterbringen läßt. Bei Untersuchungen an verdünnten Lösungen hat sich zur Kompensation der Magnetorotation des Lösungsmittels ein Doppelmagnet mit entgegengesetzten Magnetfeldeinrichtungen bewährt. Neben einer leicht durchführbaren Korrektur für unterschiedliche Dichten von Lösungsmittel und Lösung muß bei der Auswertung der gemessenen Spektren ein systematischer Fehler berücksichtigt werden, der durch Reflexionen innerhalb der Küvetten entsteht, und der Cotton-Effekte vortäuschen kann.
Wir danken der Stiftung Volkswagenwerk für die großzügige finanzielle Unterstützung dieser Arbeit. 相似文献
Summary For measuring the magnetic optical rotation a recording spectropolarimeter is used, the sample compartment of which is large enough to store the necessary magnet unit. When examining dilute solutions a double magnet having contrary magnetic field directions has proven to be effective to compensate for the magnetic rotation of the solvent. Besides a simple correction for the different densities of the solvent and the solution a systematic error has to be taken into consideration, which results from a reflection in the sample cell and may erroneously be taken for Cotton effects.
Wir danken der Stiftung Volkswagenwerk für die großzügige finanzielle Unterstützung dieser Arbeit. 相似文献
39.
M. Voss W. Weiss B. Buchholz R. Winkler 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1986,1(2):151-156
By optical interference and VUV spectroscopy the doublet system of SbI 5p 26s was investigated, so that now the hyperfinestructure of all 8 levels of 5p 26s (A- andB-splitting constants) are known. From the analysis we receive a spin-orbit parameter ζ5p =3,538(57) cm?1 and from the hyperfine-analysis single electron splitting constantsa 5p 01 =52.4(4.6),a 5p 10 =?1.6(7.3),a 5p 12 =72.3(2.3),a 6s 10 =91.7(4.1),b 5p 02 =?49.6(1.1) andb 5p 11 =30.4(3.2) (all values in mK). For all calculations in the fs- and hfs-analysis the 5p 26s 2 D 3/2 has to be excluded (see discussion). With the figures given above the quadrupole moment121 Q(5p 26s)=?0.44(3) barn was obtained. It is in good agreement with the121 Q(5p 3). For the core-polarization by the 5p electron in the innerfieldns-shells (n=1, 2, 3, 4, 5) and the unpaired 6s electron a field of +500(300) kG was obtained. 相似文献
40.
Abstract Methyl-substituted psoralens (4'-(hydroxymethyl)-4,5',8-trimethylpsoralen and 4,5',8-trimethylpsoralen) are found to yield an ene product as well as the expected [2+2] cycloaddition product from photochemical reaction with simple olefins. As determined by absorbance, liquid chromatography-mass spectrometry and nuclear magnetic resonance, both products are formed at the pyrone side of the respective psoralen. The product distribution is dependent on olefin concentration as well as the nature of the olefin. In deoxygenated solutions, cyclic olefins form as much as 50% ene product, while unsubstituted straight-chain olefins form as little as 3%. In oxygenated solutions, the product distribution is strongly affected by singlet oxygen. 相似文献