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141.
142.
143.
The effect of fluctuations and anisotropy on the transition from the normal to the superconducting state are studied. Neglecting magnetic fluctuations, which is justified as long as the Ginzburg-Landau parameter 1, the critical behavior belongs to thexy-universality class including superfluid helium. Since (t)=0
t
2/3, wheret=1-T/T
c
, upon approachingT
c
further, the intrinsic fluctuating magnetic field might change the nature of the transition. Concentrating on thexy-regime, we derive with the aid of the helicity modulus a universal relation betweenT
c
and the amplitudes of the phase correlation length and penetration depth. We also extend the universal critical point amplitude relations to the case of superconductors with uniaxial mass anisotropy. Our analysis of recent specific heat and excess dc conductivity measurement suggest that for both static and dynamic properties three-dimensional critical behavior has been observed. The -like specific heat singularity points to criticalxy-behavior. Further evidence is provided in terms of the universal amplitude relations, providing estimates for the amplitudes of the correlation lengths for the magnitude and phase of the order parameter and the London penetration depth. We find remarkable agreement with experiment and the correlation volume is comparable to that in superfluid helium. 相似文献
144.
145.
Preparation, Characterization and Reaction Behaviour of Sodium and Potassium Hydridosilylamides R2(H)Si—N(M)R′ (M = Na, K) — Crystal Structure of [(Me3C)2(H)Si—N(K)SiMe3]2 · THF The alkali metal hydridosilylamides R2(H)Si—N(M)R′ 1a‐Na — 1d—Na and 1a‐K — 1d‐K ( a : R = Me, R′ = CMe3; b : R = Me, R′ = SiMe3; c : R = Me, R′ = Si(H)Me2; d : R = CMe3, R′= SiMe3) have been prepared by reaction of the corresponding hydridosilylamines 1a — 1d with alkali metal M (M = Na, K) in presence of styrene or with alkali metal hydrides MH (M = Na, K). With NaNH2 in toluene Me2(H)Si—NHCMe3 ( 1a ) reacted not under metalation but under nucleophilic substitution of the H(Si) atom to give Me2(NaNH)Si—NHCMe3 ( 5 ). In the reaction of Me2(H)Si—NHSiMe3 ( 1b ) with NaNH2 intoluene a mixture of Me2(NaNH)Si—NHSiMe3 and Me2(H)Si—N(Na)SiMe3 ( 1b‐Na ) was obtained. The hydridosilylamides have been characterized spectroscopically. The spectroscopic data of these amides and of the corresponding lithium derivatives are discussed. The 29Si‐NMR‐chemical shifts and the 29Si—1H coupling constants of homologous alkali metal hydridosilylamides R2(H)Si—N(M)R′ (M = Li, Na, K) are depending on the alkali metal. With increasing of the ionic character of the M—N bond M = K > Na > Li the 29Si‐NMR‐signals are shifted upfield and the 29Si—1H coupling constants except for compounds (Me3C)(H)Si—N(M)SiMe3 are decreased. The reaction behaviour of the amides 1a‐Na — 1c‐Na and 1a‐K — 1c‐K was investigated toward chlorotrimethylsilane in tetrahydrofuran (THF) and in n‐pentane. In THF the amides produced just like the analogous lithium amides the corresponding N‐silylation products Me2(H)Si—N(SiMe3)R′ ( 2a — 2c ) in high yields. The reaction of the sodium amides with chlorotrimethylsilane in nonpolar solvent n‐pentane produced from 1a‐Na the cyclodisilazane [Me2Si—NCMe3]2 ( 8a ), from 1b‐Na and 1‐Na mixtures of cyclodisilazane [Me2Si—NR′]2 ( 8b , 8c ) and N‐silylation product 2b , 2c . In contrast to 1b‐Na and 1c‐Na and to the analogous lithium amides the reaction of 1b‐K and 1c‐K with chlorotrimethylsilane afforded the N‐silylation products Me2(H)Si—N(SiMe3)R′ ( 2b , 2c ) in high yields. The amide [(Me3C)2(H)Si—N(K)SiMe3]2·THF ( 9 ) crystallizes in the space group C2/c with Z = 4. The central part of the molecule is a planar four‐membered K2N2 ring. One potassium atom is coordinated by two nitrogen atoms and the other one by two nitrogen atoms and one oxygen atom. Furthermore K···H(Si) and K···CH3 contacts exist in 9 . The K—N distances in the K2N2 ring differ marginally. 相似文献
146.
147.
S. Schneider C.-J. Prenzel G. Brehm L. Gottschalk K.-H. Zhao † H. Scheer 《Photochemistry and photobiology》1995,62(5):847-854
Abstract— Resonance-enhanced coherent anti-Stokes Raman spectra (CARS) are reported for monomers and for trimers with and without linker proteins of allophycocyanin isolated from Mastigocladus laminosus. The CARS spectrum of the monomer is independent of the presence of linker proteins and is very similar to that of phycocyanin monomers indicating that the equivalent chromophores exhibit like structures in both biliproteins. Large differences are, however, observed between the spectra of phycocyanin trimers and those of allophycocyanin trimers with or without linker proteins (Lc 8,9 ). The observed differences between monomer and trimer spectra are consistent with a change of the α-chromophore-protein arrangement upon aggregation without linker. If linker proteins are present in the trimer, then additional geometry changes of the β-chromophores are induced; these could relate to a transition from the 15Z- anti to 15Z- syn conformation. 相似文献
148.
Bis(cyclopentadienyl)methane-bridged Dinuclear Complexes, V[1]. – Heteronuclear Co/Rh-, Co/Ir-, Rh/Ir-, and Ti/Ir Complexes with the Bis(cyclopentadienyl)methane Dianion as Bridging Ligand* The lithium and sodium salts of the [C5H5CH2C5H4]- anion, 1 and 2 , react with [Co(CO)4I], [Rh(CO)2Cl]2, and [Ir(CO)3Cl]n to give predominantly the mononuclear complexes [(C5H5-CH2C5H4)M(CO)2] ( 3, 5, 7 ) together with small amounts of the dinuclear compounds [CH2(C5H4)2][M(CO)2]2 ( 4, 6, 8 ). The 1H- and 13C-NMR spectra of 3, 5 , and 7 prove that the CH2C5H5 substituent is linked to the π-bonded ring in two isomeric forms. Metalation of 5 and 7 with nBuLi affords the lithiated derivatives 9 and 10 from which on reaction with [Co(CO)4I], [Rh(CO)2Cl]2, and [C5H5TiCl3] the heteronuclear complexes [CH2(C5H4)2][M(CO)2][M′(CO)2] ( 11–13 ) and [CH2(C5H4)2]-[Ir(CO)2][C5H5TiCl2] ( 17 ) are obtained. Photolysis of 11 and 12 leads almost quantitatively to the formation of the CO-bridged compounds [CH2(C5H4)2][M(CO)(μ-CO)M′(CO)] ( 14, 15 ). According to an X-ray crystal structure analysis the Co/Rh complex 14 is isostructural to [CH2(C5H4)2][Rh2(CO)2(μ-CO)] ( 16 ). 相似文献
149.
Len F. Lee Francis M. Schleppnik Ronald W. Schneider Dwane H. Campbell 《Journal of heterocyclic chemistry》1990,27(2):243-245
Reaction of ethyl 4,4,4-trifluoroacetoacetate with methylhydrazine produced not only the previously reported 5-hydroxy-3-(trifluoromethyl)pyrazole 1 but also its unknown isomer the 3-hydroxy-5-(trifluoromethyl)pyrazole 4 . The structure assignments are established based on 13C nmr spectra. Compound 1 was converted to 5-chloro-3-(trifluoromethyl)pyrazolecarboxylic acid 3 in two steps. 相似文献
150.
A. Schneider und H. Beisken 《Fresenius' Journal of Analytical Chemistry》1954,141(5):326-336
Zusammenfassung Kleine Bleimengen (0,2–0,005 mg Pb in 50 bzw. 20 ml Lösung) lassen sich konduktometrisch mit H2S-Wasser als Maßflüssigkeit zuverlässig bestimmen. Die Sicherheit der Titration wird besonders von folgenden, experimentell geprüften Faktoren beeinflußt: Verhältnis von Gas- und Flüssigkeitsvolumen im Vorratsgefäß der H2S-Lösung, Temperaturkonstanz der Maß- und Analysenlösung, Verhältnis der Normalität von Maßlösung und Bleilösung, pH-Wert sowie Art und Behandlung des destillierten Wassers. Der Einfluß dieser und aller anderen, die Genauigkeit der Methode bedingenden Faktoren wird an Hand experimenteller Daten erörtert. Bei Berücksichtigung aller Fehlerquellen können Pb-Mengen über 0,02 mg mit einem Fehler von ± 2%, Mengen von 0,005 mg noch mit etwa ± 10% bestimmt werden. 相似文献