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排序方式: 共有1087条查询结果,搜索用时 15 毫秒
1.
Dr. Jordan Donat Mr. Patrick Dubourdeaux Dr. Martin Clémancey Dr. Julia Rendon Clara Gervasoni Mr. Morgan Barbier Jessica Barilone Dr. Jacques Pécaut Prof. Dr. Serge Gambarelli Prof. Dr. Pascale Maldivi Prof. Dr. Jean-Marc Latour 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(70):e202201875
Nitrene transfer reactions have emerged as one of the most powerful and versatile ways to insert an amine function to various kinds of hydrocarbon substrates. However, the mechanisms of nitrene generation have not been studied in depth albeit their formation is taken for granted in most cases without definitive evidence of their occurrence. In the present work, we compare the generation of tosylimido iron species and NTs transfer from FeII and FeIII precursors where the metal is embedded in a tetracarbene macrocycle. Catalytic nitrene transfer to reference substrates (thioanisole, styrene, ethylbenzene and cyclohexane) revealed that the same active species was at play, irrespective of the ferrous versus ferric nature of the precursor. Through combination of spectroscopic (UV-visible, Mössbauer), ESI-MS and DFT studies, an FeIV tosylimido species was identified as the catalytically active species and was characterized spectroscopically and computationally. Whereas its formation from the FeII precursor was expected by a two-electron oxidative addition, its formation from an FeIII precursor was unprecedented. Thanks to a combination of spectroscopic (UV-visible, EPR, Hyscore and Mössbauer), ESI-MS and DFT studies, we found that, when starting from the FeIII precursor, an FeIII tosyliodinane adduct was formed and decomposed into an FeV tosylimido species which generated the catalytically active FeIV tosylimide through a comproportionation process with the FeIII precursor. 相似文献
2.
Marius Lupu Adnana Zaulet Prof. Dr. Francesc Teixidor Prof. Dr. Eliseo Ruiz Prof. Dr. Clara Viñas 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(18):6888-6897
The metallacarborane [3,3′‐Co(1,2‐closo‐C2B9H11)2]? has been synthesized. This species allows the formation of redox couples in which both partners are negatively charged. The E1/2 potential can be tuned by adjusting the nature and number of substituents on B and C. The octaiodinated species [3,3′‐Co(1,2‐closo‐C2B9H7I4)2]? is the most favorable, as it is isolatable and stable in air. A DFT study on stability and redox potentials of complexes has been performed. 相似文献
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Shock waves and the relevant Rankine-Hugoniot conditions may be inadequate even in simple cases. As an example, the electromagnetic field generated by a point charge, whose velocity jumps from0 to a constant value, not only jumps across a spherical surface expanding at light speed, but also includes a-distribution term. This suggests that the concept of higher order shock waves be introduced, the associated compatibility conditions being also deduced.
Sommario Il concetto di onda d'urto può rivelarsi inadeguato per descrivere situazioni anche semplici. A titolo di esempio, si determina esplicitamente l'espressione del campo elettromagnetico generato da una carica puntiforme la cui velocità passa istantaneamente da0 a un valore costante. Il campo elettromagnetico non solo è discontinuo attraverso una superficie sferica che si espande alla velocità della luce, ma include anche un termine che coinvolge la distribuzione. Ciò suggerisce di definire le onde d'urto di ordine superiore, per le quali si determinano le corrispondenti condizioni di compatibilità.相似文献
7.
Brunsveld L Watzke A Durek T Alexandrov K Goody RS Waldmann H 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(9):2756-2772
Prenylated proteins with non-native functionalities are generally very difficult to obtain by recombinant or enzymatic means. The semisynthesis of preparative amounts of prenylated Rab guanosine triphosphatases (GTPases) from recombinant proteins and synthetic prenylated peptides depends largely on the availability of functionalised prenylated peptides corresponding to the proteins' native structure or modifications thereof. Here, we describe and compare solution-phase and solid-phase strategies for the generation of peptides corresponding to the prenylated C terminus of Rab7 GTPase. The solid-phase with utilisation of a hydrazide linker emerges as the more favourable approach. It allows a fast and practical synthesis of pure peptides and gives a high degree of flexibility in their modification. To facilitate the analysis of semisynthetic proteins, the synthesised peptides were equipped with a fluorescent group. Using the described approach, we introduced fluorophores at several different positions of the Rab7 C terminus. The position of the incorporated fluorescent groups in the peptides did not influence the protein-ligation reaction, as the generated peptides could be ligated onto thioester-tagged Rab7. However, it was found that the positioning of the fluorescent group had an influence on the functionality of the Rab7 proteins; analysis of the interaction of the semisynthetic Rab7 proteins with REP (Rab escort protein) and GDI (guanosine diphosphate dissociation inhibitor) molecules revealed that modification of the peptide side chains or of the C-terminal isoprenoid did not significantly interfere with complex formation. However, functionalisation of the C terminus was found to have an adverse effect on complex formation and stability, possibly reflecting low structural flexibility of the Rab GDI/REP molecules in the vicinity of the lipid-binding site. 相似文献
8.
Tutusaus O Viñas C Núñez R Teixidor F Demonceau A Delfosse S Noels AF Mata I Molins E 《Journal of the American Chemical Society》2003,125(39):11830-11831
exo-Cluster dicarbollides substitution has allowed tuning of the E degrees (Ru(II)/Ru(III)) potential to obtain the best-performing Kharasch catalyst. We postulate that this is possible through the to-and-fro electron movement between the boron cluster and the sulfonium moieties. 相似文献
9.
Huttenloch O Laxman E Waldmann H 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(20):4767-4780
The development of a method for the optimization of chiral ligands for the steric steering of enantioselective Cu-catalyzed conjugate additions of Znalkyls to enones is described. The method is based on combinatorial principles and solid-phase techniques. It includes the combinatorial synthesis of chiral bispidine-derived ligands embodying a phosphoramidite group on the solid phase and their investigation in immobilized form in the conjugate addition of ZnEt2 to cyclohexenone as test reaction. The best identified ligands were also synthesized separately and investigated in its soluble form. The results obtained for the polymer-bound ligands correctly mirrored the performance of the soluble ligands. The library embodied members giving ee values varying between 3 and 67%. The "positional scanning" approach proved to be invalid for the study of the ligand system, indicating that this approach in general should be applied with care. Taken together, the method allowed for rapid and efficient optimization of the ligands and led to the development of the first enantioselective, Cu-catalyzed conjugate addition reaction with a polymer-bound ligand. 相似文献
10.
High nuclearity paramagnetic, spin-coupled transition metal clusters and grids are fascinating chemists and physicists partly because of their structural beauty, and the challenge of creating them, but also because of their novel physical properties. Magnetic interactions between the spin centers are a primary focus. This review will examine a selection of Mn(II) polynuclear grids and clusters, with nuclearities in the range Mn4 to Mn9. Theoretical treatments of the magnetic properties are discussed, and approaches to solving the exchange problem for ‘large’ spin systems related to computational difficulties. A freely available software package (MAGMUN4.1) is presented as a means of dealing simply with spin-coupled clusters in general, and symmetry reduction methods are discussed briefly as a means of dealing with ‘large’ spin systems. 相似文献