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951.
C. Paal E. Weidenkaff E. Fischer U. Suzuki W. Traube A. Biltz St. W. Collins J. Litzendorff M. Busch G. Lunge E. Berl L. H. Ingham H. E. Patten A. Robinson E. Pozzi-Escot R. Bensemann J. Meisenheimer F. Heim F. Raschig G. Maderna G. Cofetti K. Farnsteiner W. Stüber G. Mehrtens A. Ganghofer und O. Köpke 《Fresenius' Journal of Analytical Chemistry》1911,50(7):454-463
Ohne Zusammenfassung 相似文献
952.
Low-temperature nuclear spin-lattice relaxation in glasses - homogeneous and inhomogeneous averaging
A phenomenological model is presented which is able to explain both temperature and magnetic field dependences of nuclear spin-lattice relaxation rates T1?1 observed recently in glasses at low temperatures. The model assumes randomly distributed defect centres, typical of glasses, producing internal fluctuating fields. The only restrictive assumption is a power law for the distance dependence of the responsible interaction. In accordance with experiment, homogeneous and inhomogeneous relaxation, corresponding to exponential and non-exponential relaxation behaviour, is predicted in the cases of rapid and slow spin diffusion, respectively. Describing the fluctuating interactions by a BPP-type spectral density and assuming an Arrhenius law for the correlation time, explicit expressions for T-1? are obtained. It is shown that by comparison of homogeneous and inhomogeneous relaxation data information on the type of interaction and the density of defect centres can be obtained. 相似文献
953.
Agne??KaporEmail author Dieter?Zobel Marianna?Strümpel Ljilja?Torovi? Mirjana?Popsavin 《Journal of chemical crystallography》2005,35(9):687-695
Methyl E(Z)-4,7 anhydro-5-benzamido-6,8-di-O-benzoyl-2,3,5-trideoxy-d-allo-oct-2-enoate have been synthesized like intermediates and isolated as single crystals during the synthesis of pyrazole-related C nucleosides as synthetic product with cytotoxic activity.1 Crystal structures of E(Z) isomers were determined by X-ray analysis. E isomer crystallizes in the triclinic crystal system, space group P1, a = 5.319(1) Å, b = 10.758(2) Å, c = 12.229(2) Å, α = 72.38(2)∘, β = 89.97(2)∘, γ = 87.07(2)∘, Dx = 1.320 Mgm−3 and Z isomer in the orthorhombic crystal system, space group P212121, a = 5.1297(13) Å, b = 19.667(5) Å, c = 25.871(6) Å, Dx = 1.348 Mgm−3. The molecular structure was solved by direct method on the basis of 2609 and 2727 unique reflections recorded at the temperature 293 K (E-isomer) and 173 K (Z-isomer) up to the final R-factor 0.0378 and 0.0435, respectively. C–H⋅sO contact networks were analyzed and the correlation established between the existence of the weak C–H⋅sO hydrogen bonds and the melting point of the single crystals. 相似文献
954.
Pouységu L Marguerit M Gagnepain J Lyvinec G Eatherton AJ Quideau S 《Organic letters》2008,10(22):5211-5214
The first total synthesis of the natural nondimerizing o-quinol (+)-wasabidienone B1 was achieved from commercially available 1,3,5-trimethoxybenzene. The key dearomatizing transformation was efficiently accomplished via a hydroxylative phenol dearomatization reaction using the stabilized lambda(5)-iodane reagent IBX (SIBX). (+)-Wasabidienone B1 was then converted into its congener (-)-wasabidienone B0 via an improved thermally induced ring-contracting isomerization reaction. 相似文献
955.
Lohier JF Foucoin F Jaffrès PA Garcia JI Sopková-de Oliveira Santos J Perrio S Metzner P 《Organic letters》2008,10(6):1271-1274
A straightforward and high-yielding access to various [2.2]paracyclophanes possessing a sulfur-based functional group is reported, the key step being a SEAr reaction mediated by a sulfonium salt. The versatility of the methodology was exemplified by an original application in sulfenate salt chemistry, from which a remarkable chirality transfer was observed. 相似文献
956.
We have investigated the influence of the ratio between the volume of the hydrophilic head ( V A) and the volume of the hydrophobic part ( V B) of the surfactant on the mesopore ordering. To understand the difference of behavior we have performed a complete study dealing with fluorinated [R m (F)(EO) n ] and hydrogenated [R m (H)(EO) n ] surfactants. Their mixtures have also been taken into account. Here only the phase diagrams and the structural parameters of the liquid crystal phases of the mixed systems are reported. We have shown that the mutual or partial miscibility of the fluorinated and the hydrogenated surfactants depends on the number of oxyethylene units of each surfactant. To follow, various systems were used for the preparation of silica mesoporous materials via a cooperative templating mechanism (CTM). Results clearly reveal that V A/ V B ratios in the range between 0.95 and 1.78 lead to the formation of well-ordered mesostructures. Wormhole-like structures are obtained for higher or lower values. Moreover, results show that from the V A/ V B point of view, polyoxyethylene fluoroalkyl ether surfactants behave like their hydrogenated analogues. 相似文献
957.
Jalal Ghilane Olivier Fontaine Pascal Martin Jean-Christophe Lacroix Hyacinthe Randriamahazaka 《Electrochemistry communications》2008,10(8):1205-1209
The electrochemical reduction of noble metal electrodes in the presence of redox ionic liquid, 1-ferrocenylethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [FcEMIM][TFSI], was investigated by cyclic voltammetry. Our experiments suggest the formation of metal with negative oxidation states, in the cases of platinum and gold electrodes [Mn−, FcEMIM+]. By analogy with the previous work, the formation of these phases is concomitant with the insertion of the supporting electrolyte; which correspond in our experimental condition to the redox cation of the ionic liquid. As an exciting result, the electrochemical investigations of the reduced electrode in electrolytic solution, containing solvent and supporting electrolyte, evidence the presence of the ferrocene groups at the electrode surface. Moreover, the reduced electrode exhibits the presence of the ferrocene even after, contact with air, after ultrasound, and after physical polishing, highlighting the large stability of this organo-metallic phases formed in this media. The AFM investigations demonstrate the morphological change of the platinum surface after the reduction process. Finally, our works bring a formal electrochemical proof of the presence of the ionic liquid cation inside the electrode material after the cathodic treatment in this media. 相似文献
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