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排序方式: 共有325条查询结果,搜索用时 15 毫秒
251.
Martin Wozniak Stefan Sander Dr. Beatrice Cula Dr. Mike Ahrens Prof. Dr. Thomas Braun 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(33):e202200626
S−F-bond activation of sulfur tetrafluoride at [Rh(Cl)(tBuxanPOP)] ( 1 ; tBuxanPOP=9,9-dimethyl-4,5-bis-(di-tert-butylphosphino)-xanthene) led to the formation of the cationic complex [Rh(F)(Cl)(SF2)(tBuxanPOP)][SF5] ( 2 a ) together with trans-[Rh(Cl)(F)2(tBuxanPOP)] ( 3 ) and cis-[Rh(Cl)2(F)(tBuxanPOP)] ( 4 ) which both could also be obtained by the reaction of SF5Cl with 1 . In contrast to that, the conversion of SF4 at the methyl complex [Rh(Me)(tBuxanPOP)] ( 5 ) gave the isolable and room-temperature stable cationic λ4-trifluorosulfanyl complex [Rh(Me)(SF3)(tBuxanPOP)][SF5] ( 6 ). Treatment of 6 with the Lewis acids BF3 or AsF5 produced the dicationic difluorosulfanyl complex [Rh(Me)(SF2)(tBuxanPOP)][BF4]2 ( 8 a ) or [Rh(Me)(SF2)(tBuxanPOP)][AsF6]2 ( 8 b ), respectively. Refluorination of 8 a was possible with the use of dimethylamine giving [Rh(Me)(SF3)(tBuxanPOP)][BF4] ( 9 ). A reaction of 6 with trichloroisocyanuric acid (TClCA) gave the fluorido complex [Rh(F)(Cl)(SF2)(tBuxanPOP)][Cl] ( 2 b ) together with chloromethane and SF5Cl. 相似文献
252.
Patrick Federmann Dr. Robert Müller Fabian Beckmann Caroline Lau Dr. Beatrice Cula Prof. Dr. Martin Kaupp Prof. Dr. Christian Limberg 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(25):e202200404
Frustrated Lewis pairs (FLPs) composed of acidic alane and basic phosphane functions, separated by a xanthene linker, can be prepared through the corresponding Me3Sn derivative and methyl aluminum compounds with elimination of Me4Sn. This way MeClAl-, Cl2Al- and (C6F5)2Al- moieties could be introduced and the resulting FLPs are stabilized by a further equivalent of the alane precursors. In contact with the FLPs CO2 is bound via the C atom at the phosphane functions and the two O atoms at the Al centers. The residues at the latter determine the binding strength. Hence, in case of MeClAl CO2 capture occurs at higher pressure and under ambient conditions CO2 is released again, while for Cl2Al and (C6F5)2Al CO2 binding becomes irreversible. The results of DFT calculations rationalize these findings by the high thermodynamic stabilization in case of more electronegative residues, which concomitantly lead to higher barriers, and in case of (C6F5)2Al further stabilization is achieved through a low reorganization energy. 相似文献
253.
Han Y Tuccio B Lauricella R Rockenbauer A Zweier JL Villamena FA 《The Journal of organic chemistry》2008,73(7):2533-2541
Spin trapping using electron paramagnetic resonance (EPR) spectroscopy is commonly employed for the identification of transient radicals in chemical and biological systems. A spirolactonyl-nitrone with rigid H-bond acceptor, 7-oxa-1-azaspiro[4.4]non-1-en-6-one 1-oxide, CPCOMPO, has been synthesized and characterized, and its spin-trapping properties were investigated. The rate of formation of CPCOMPO-O2H was determined using competition kinetics between the superoxide/hydroperoxyl radical (O2*-/HO2*) trapping by CPCOMPO and the spontaneous dismutation of this radical in aqueous media. The rate constant of 60 M-1.s-1 is the highest rate constant thus far observed at neutral pH for any nitrones using the kinetic method employed. Decay kinetics were also experimentally investigated for CPCOMPO-O2H. The effect of rigid H-bond acceptor on the stability of the CPCOMPO-O2H were computationally rationalized and compared to that of EMPO-O2H, which has flexible H-bond acceptor, and results show the need of a "loose" H-bond acceptor for improved adduct stability. 相似文献
254.
255.
Flower snarks and Goldberg snarks are two infinite families of cyclically 5–edge–connected cubic graphs with girth at least
five and chromatic index four. For any odd integer k, k > 3, there is a Flower snark, say J
k
, of order 4k and a Goldberg snark, say B
k
, of order 8k. We determine the automorphism groups of J
k
and B
k
for every k and prove that they are isomorphic to the dihedral group D
4k
of order 4k.
Research performed within the activity of INdAM–GNSAGA with the financial support of the Italian Ministry MIUR, project “Strutture
Geometriche, Combinatoria e loro Applicazioni”. 相似文献
256.
Beln Rubial Beatrice S. L. Collins Raphael Bigler Stefan Aichhorn Adam Noble Varinder K. Aggarwal 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(5):1380-1384
The one‐pot sequential coupling of benzylamines, boronic esters, and aryl iodides has been investigated. In the presence of an N‐activator, the boronate complex formed from an ortho‐lithiated benzylamine and a boronic ester undergoes stereospecific 1,2‐metalate rearrangement/anti‐SN2′ elimination to form a dearomatized tertiary boronic ester. Treatment with an aryl iodide under palladium catalysis leads to rearomatizing γ‐selective allylic Suzuki–Miyaura cross‐coupling to generate 1,1‐diarylalkanes. When enantioenriched α‐substituted benzylamines are employed, the corresponding 1,1‐diarylalkanes are formed with high stereospecificity. 相似文献
257.
Beatrice Karg Swantje Mohr Klaus Weisz 《Angewandte Chemie (International ed. in English)》2019,58(32):11068-11071
The oligomer d(GCGTG3TCAG3TG3TG3ACGC) with short complementary flanking sequences at the 5′‐ and 3′‐ends was shown to fold into three different DNA G‐quadruplex species. In contrast, a corresponding oligomer that lacks base complementarity between the two overhang sequences folds into a single parallel G‐quadruplex. The three coexisting quadruplex structures were unambiguously identified and structurally characterized through detailed spectral comparisons with well‐defined G‐quadruplexes formed upon the deliberate incorporation of syn‐favoring 8‐bromoguanosine analogues into specific positions of the G‐core. Two (3+1) hybrid structures coexist with the parallel fold and feature a novel lateral–propeller–propeller loop architecture that has not yet been confirmed experimentally. Both hybrid quadruplexes adopt the same topology and only differ in their pattern of anti→syn transitions and tetrad stackings. 相似文献
258.
259.
Kara M. Stamm Justin T. Fermann Thomas Whelan Rachel R. Broudy Beatrice Botch William J. Vining 《The Chemical Educator》1999,4(1):19-22
This paper reviews a project conducted as part of a general chemistry course. The primary goal of the assignment was to involve our students in the process of teaching chemistry. Our work is part of STEMTEC, the Science, Technology, Engineering, and Mathematics Teacher Education Collaborative, which has been developed to improve the preparation of preservice teachers, stimulate the interest of undergraduate science and mathematics majors in the teaching profession, and increase the educational effectiveness of science and mathematics courses. The assigned project required students to create an interactive computer module that could be used to educate other students about concepts taught in general chemistry. The paper includes examples of these modules and evaluates this method of instruction. The software programs designed by the students are available for download from the Internet (). 相似文献
260.