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排序方式: 共有143条查询结果,搜索用时 15 毫秒
51.
Molecular approaches towards mixed metal oxides and their behaviour in mixed oxide support Au catalysts for CO oxidation 总被引:1,自引:0,他引:1
Geserick J Fröschl T Hüsing N Kucerova G Makosch M Diemant T Eckle S Behm RJ 《Dalton transactions (Cambridge, England : 2003)》2011,40(13):3269-3286
We herein report a water-based sol-gel approach towards porous mixed Si/Ti oxides using co-precipitated glycol-modified precursors. By adjusting synthesis parameters such as the pH value and the Si/Ti ratio of the precursor, the morphology as well as the Si/Ti-composition of the resulting mixed oxide particles can be varied in a wide range. The behaviour of the mixed oxides as substrates for Au catalysts and the performance of the resulting catalysts in the CO oxidation reaction was investigated and compared to catalysts supported on mesoporous anatase and rutile synthesized analogously. For comparable Au particle sizes and Au loadings, the composition of the mixed oxide support was found to significantly affect the reactivity and reaction behaviour, with mixed oxide supported Au catalysts synthesized at pH=5 or 10 and with a Si/Ti-ratio of 1:19 and 1:34 exhibiting the maximum activity. In contrast to the enhanced activity, the mixed oxide supports do not lead to a significant improvement in deactivation behaviour and catalyst stability. 相似文献
52.
Hamed RB Henry L Gomez-Castellanos JR Mecinović J Ducho C Sorensen JL Claridge TD Schofield CJ 《Journal of the American Chemical Society》2012,134(1):471-479
The biocatalytic versatility of wildtype and engineered carboxymethylproline synthases (CMPSs) is demonstrated by the preparation of functionalized 5-carboxymethylproline derivatives methylated at C-2, C-3, C-4, or C-5 of the proline ring from appropriately substituted amino acid aldehydes and malonyl-coenzyme A. Notably, compounds with a quaternary center (at C-2 or C-5) were prepared in a stereoselective fashion by engineered CMPSs. The substituted-5-carboxymethyl-prolines were converted into the corresponding bicyclic β-lactams using a carbapenam synthetase. The results demonstrate the utility of the crotonase superfamily enzymes for stereoselective biocatalysis, the amenability of carbapenem biosynthesis pathways to engineering for the production of new bicyclic β-lactam derivatives, and the potential of engineered biocatalysts for the production of quaternary centers. 相似文献
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54.
Christoph Schoo Sebastian Bestgen Alexander Egeberg Jasmin Seibert Sergey N. Konchenko Claus Feldmann Peter W. Roesky 《Angewandte Chemie (International ed. in English)》2019,58(13):4386-4389
Zintl phases of arsenic and molecular compounds containing Zintl‐type polyarsenide ions are of fundamental interest in basic and applied sciences. Unfortunately, the most obvious and reactive arsenic source for the preparation of defined molecular polyarsenide compounds, yellow arsenic As4, is very inconvenient to prepare and neither storable in pure form nor easy to handle. Herein, we present the synthesis and reactivity of elemental As0 nanoparticles (As0Nano, d=7.2±1.8 nm), which were successfully utilized as a reactive arsenic source in reductive f‐element chemistry. Starting from [Cp*2Sm] (Cp*=η5‐C5Me5), the samarium polyarsenide complexes [(Cp*2Sm)2(μ‐η2:η2‐As2)] and [(Cp*2Sm)4As8] were obtained from As0nano, thereby generating the largest molecular polyarsenide of the f‐elements and circumventing the use of As4 in preparative chemistry. 相似文献
55.
The catalytic hydrogenation of CO2 includes the dissociation of hydrogen and further reaction with CO2 and intermediates. We investigate how the amount of hydrogen in the bulk of the catalyst affects the hydrogenation reaction taking place at the surface. For this, we developed an experimental setup described herein, based on a magnetic suspension balance and an infrared spectrometer, and measured pressure-composition isotherms of the Pd−H system under conditions relevant for CO2 reduction. The addition of CO2 has no influence on the measured hydrogen absorption isotherms. The pressure dependence of the CO formation rate changes suddenly upon formation of the β-PdH phase. This effect is attributed to a smaller surface coverage of hydrogen due to repulsive electronic interactions affecting both bulk and surface hydrogen. 相似文献
56.
Kalpani K. Somarathne Jordan A. J. McCone Amira Brackovic Jos Luis Pinedo Rivera J. Robin Fulton Euan Russell Jessica J. Field Christopher L. Orme Hedley L. Stirrat Jasmin Riesterer Paul H. Teesdale‐Spittle John H. Miller Joanne E. Harvey 《化学:亚洲杂志》2019,14(8):1230-1237
The fungal metabolite TAN‐2483B has a 2,6‐trans‐relationship across the pyran ring of its furo[3,4‐b]pyran‐5‐one core, which has thwarted previous attempts at its synthesis. We have now developed a chiral pool approach to this core and prepared side‐chain analogues of TAN‐2483B. The synthesis relies on ring expansion of a reactive furan ring‐fused dibromocyclopropane and alkynylation of the resulting pyran. The furan ring is constructed by palladium‐catalysed carbonylative lactonisation. Various side‐chains are appended through Wittig‐type chemistry. The prepared analogues showed micromolar activity towards cancer cell lines HL‐60, 1A9 and MCF‐7 and certain human disease‐relevant kinases, including Bruton's tyrosine kinase (Btk). 相似文献
57.
David Schmidt Matthias Stolte Jasmin Süß Andreas Liess Vladimir Stepanenko Frank Würthner 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(38):13519-13523
Strongly emissive solid‐state materials are mandatory components for many emerging optoelectronic technologies, but fluorescence is often quenched in the solid state owing to strong intermolecular interactions. The design of new organic pigments, which retain their optical properties despite their high tendency to crystallize, could overcome such limitations. Herein, we show a new material with monomer‐like absorption and emission profiles as well as fluorescence quantum yields over 90 % in its crystalline solid state. The material was synthesized by attaching two bulky tris(4‐tert‐butylphenyl)phenoxy substituents at the perylene bisimide bay positions. These substituents direct a packing arrangement with full enwrapping of the chromophore and unidirectional chromophore alignment within the crystal lattice to afford optical properties that resemble those of their natural pigment counterparts, in which chromophores are rigidly embedded in protein environments. 相似文献
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59.
Kerstin Mayer Jasmin V. Dums Christian B. Benda Wilhelm Klein Thomas F. Fssler 《Angewandte Chemie (International ed. in English)》2020,59(17):6800-6805
Polymeric [Bi]? in KBi?NH3 has planar zigzag chains with two‐connected Bi atoms and metallic properties, whereas KBi, which has helical chains of Bi atoms, is semiconducting. The isomerization of the Bi chain is induced by solvate molecules. In the novel layered solvate structure uncharged [KBi] layers are separated by intercalated NH3 molecules. These layers are a structural excerpt of the iso(valence)electronic CaSi, whose metallic properties arise from the planarity of the zigzag chain of Si atoms. Computational studies support this view, they show an anisotropic metallic behavior along the Bi chain. Electron delocalization is also found in the new cyclic anion [Bi6]4? isolated in K2[K(18‐crown‐6)]2[Bi6]?9 NH3. Although [Bi6]4? should exhibit one localized double bond, electron delocalization is observed in analogy to the lighter homologues [P6]4? and [As6]4?. Both compounds were characterized by single‐crystal X‐ray structure determination. 相似文献
60.
Cation–π Interactions Contribute to Substrate Recognition in γ‐Butyrobetaine Hydroxylase Catalysis
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Jos J. A. G. Kamps Amjad Khan Dr. Hwanho Choi Robert K. Lesniak Dr. Jürgen Brem Dr. Anna M. Rydzik Dr. Michael A. McDonough Prof. Christopher J. Schofield Prof. Timothy D. W. Claridge Dr. Jasmin Mecinović 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(4):1270-1276
γ‐Butyrobetaine hydroxylase (BBOX) is a non‐heme FeII‐ and 2‐oxoglutarate‐dependent oxygenase that catalyzes the stereoselective hydroxylation of an unactivated C?H bond of γ‐butyrobetaine (γBB) in the final step of carnitine biosynthesis. BBOX contains an aromatic cage for the recognition of the positively charged trimethylammonium group of the γBB substrate. Enzyme binding and kinetic analyses on substrate analogues with P and As substituting for N in the trimethylammonium group show that the analogues are good BBOX substrates, which follow the efficiency trend N+>P+>As+. The results reveal that an uncharged carbon analogue of γBB is not a BBOX substrate, thus highlighting the importance of the energetically favorable cation–π interactions in productive substrate recognition. 相似文献