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941.
Dominique Despeyroux Richard B. Cole Jean-Claude Tabet 《Journal of mass spectrometry : JMS》1992,27(3):300-308
The comparative behaviour of the endo- and exo-norborneols and diastereomeric derivatives (acetates and benzoates) towards the NH3/NH4+ system was investigated. It appears that the proton affinity (PA) of the substrate relative to Pa(NH3) strongly influences competition between the protonation and nucleophilic substitution processes yielding the MH+ and [M + NH4 ? H2O]+ ions, respectively. Tandem mass spectrometry was used to compare collision-activated dissociation spectra of [M + NH4 ? H2O]+ with those of analogous endo- and exo-norbornylamines protonated in the source. This demonstrates that an SNimechanism occurs specifically for the isomeric norborneols; in contrast, for acetates and benzoates, stereospecific SNi and SN2 pathways take place for exo and endo derivatives, respectively. This particular behaviour is explained by considering the steric effect induced by the endo-H at C(6). In addition, the competitive decompositions of [M + NH4 – H2O]+ into NH4+ and [C7H11]+ daughter ions are consistent with the formation of a proton-bound complex intermediate. The observed stereochemical effects for these dauther ions are rationalized by means of arguments based on the estimated heats of formation of the transition states, which is lower for the exo-norbonyl protonated amine, consistent with anchimeric assistance, rather than a stepwise pathway which is proposed for the endoisomer. 相似文献
942.
Shayesteh A Appadoo DR Gordon IE Bernath PF 《Journal of the American Chemical Society》2004,126(44):14356-14357
Gaseous ZnH2 and ZnD2 have been discovered in an emission source that combines an electrical discharge with a high-temperature furnace. High-resolution infrared emission spectra of ZnH2 and ZnD2 have been recorded with a Fourier transform spectrometer, and the antisymmetric stretching fundamental bands of 64ZnH2 and 64ZnD2 were detected near 1889.4 and 1371.6 cm-1, respectively. Rotational analysis of the bands yielded r0 bond distances of 1.535 271(1) and 1.531 836(9) A for linear 64ZnH2 and 64ZnD2, respectively. 相似文献
943.
Study of acylation of 3-acetyl-8-acetoxyindolizine by miscellaneous acid chlorides in the presence of aluminium chloride shows that this reaction is either limited to a transesterification (in the case of benzoyl chloride) or leads to introduction of an acyl group in position 1 with simultaneous liberation of the phenol function in position 8. When acylation takes place, acetyl chloride resulting from the cleavage of the acetoxy group competes with the acid chloride used in the reaction. Predominant acylation by the latter is observed when the reaction is performed with ethoxalyl chloride or with non branched aliphatic acid chlorides; by contrast solely acetylation takes place when pivaloyl or phenylacetyl chloride is used. These results are tentatively explained by a process related to the Fries rearrangement. The hypothesis of intramolecular transfer of an acyl group from the ester function in position 8 can be discarded by the observed results. 相似文献
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947.
Luca Mauri Alessia Colombo Claudia Dragonetti Dominique Roberto Francesco Fagnani 《Molecules (Basel, Switzerland)》2021,26(24)
Three decades ago, dye-sensitized solar cells (DSSCs) emerged as a method for harnessing the energy of the sun and for converting it into electricity. Since then, a lot of work has been devoted to create better global photovoltaic efficiencies and long term stability. Among photosensitizers for DSSCs, thiocyanate-free ruthenium(II) complexes have gained increasing interest due to their better stability compared to conventional thiocyanate-based complexes, such as benchmark dyes N719 and Z907. In this mini-review, two classes of thiocyanate-free Ru(II) complexes are presented: (a) bis-bipyridyl compounds bearing an ancillary cyclometalating bidentate ligand; (b) bipyridyl compounds bearing non-cyclometalating ancillary ligands. The coverage, mainly from 2014 up to now, is not exhaustive, but illustrates the most recent design strategies and photovoltaic properties of these two families of ruthenium(II) dyes. 相似文献
948.
Dominique Durand Taco Nicolai Patrice Lefevre Frederic Prochazka Hery Randrianantoandro 《Macromolecular Symposia》1997,122(1):179-184
Static and dynamic properties of a polyurethane system at different stages of the gelation process have been investigated. Shear modulus data were collected over a wide frequency range covering both the α-relaxation and the internal modes relaxations. The evolution of the relaxation spectra in relation with the structural transformation occurring during the growth process is analysed within the percolation model. 相似文献
949.
An efficient and versatile synthesis of aminophosphine phosphinite (AMPP) ligands derived from ephedrine, with possible stereogenic P(III)-center(s) is described, using the borane complex methodology. The reaction of oxazaphospholidine borane with an organolithium reagent, leads to the formation of the ring-opened product, which is trapped by a chlorophosphine (borane), to afford the corresponding aminophosphine phosphinite boranes in good yields. Treatment of the borane complexes with dabco, gives the corresponding aminophosphine phosphinite ligands in 70–90% yield. These ligands are used for the preparation of Rh catalysts applied to the asymmetric hydrogenation of methyl α-acetamidocinnamate yielding the phenylalanine derivative with (R) 22% to (S) 99% e.e. These results show the importance of the structural modification at the P-stereogenic center(s), which could either amplify or cancel out the asymmetric induction resulting from the ephedrine backbone, for enantioselective catalysis. 相似文献
950.
Catherine Wieser-Jeunesse Dominique Matt Andr De Cian 《Angewandte Chemie (International ed. in English)》1998,37(20):2861-2864
A hemispherical diphosphane based on a calixarene allows encapsulation of reactive M–R fragments (M=transition metal; R=H, alkyl, CO) inside the calixarene cavity. The ruthenium complex 1 has an unprecedented sandwich structure that contains a CO ligand confined between two phosphane-substituted phenyl rings. The separation between the CO segment and the two aromatic rings is only 2.75 Å! 相似文献