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101.
Unique Stereocontrol in Carborane Chemistry: Skeletal Alkylcarbonation (SAC) versus Exoskeletal Alkylmethylation (EAM) Reactions 下载免费PDF全文
Dr. Mario Bakardjiev Dr. Josef Holub Dr. Jan Macháček Dr. Drahomír Hnyk Prof. Dr. Bohumil Štíbr Dr. Zdeňka Růžičková Prof. Dr. Aleš Růžička 《Angewandte Chemie (International ed. in English)》2015,54(16):4937-4940
Reactions between the arachno‐6,9‐C2B8H14 ( 1 ) dicarbaborane and acyl chlorides, RCOCl ( 2 ), are subject to stereocontrol that completely changes the nature of the reaction products. While most chlorides produce the 8‐R‐nido‐7,8,9‐C3B8H11 ( 3 ) tricarbollides (by skeletal alkylcarbonation=SAC), bulky RCOCls ( 2 ; where R=1‐adamantyl, 2 a ; 1‐mesityl, 2 b ; 9‐anthranyl, 2 c ; 1‐naphthyl, 2 d ) in 1,2‐dichloroethane (DCE) in the presence of triethylamine at 40–60 °C gave a series of entirely different 1‐R‐2‐CH3‐closo‐1,6‐C2B8H8 ( 4 ) dicarbaboranes upon acidification with conc. H2SO4 (by exosleletal alkylmehylation=EAM). Both types of reactions seem to proceed via a common [8‐R‐nido‐7,8,9‐C3B8H10]? ( 3? ) anion which in the EAM case is unstable because of steric crowd and undergoes rearrangement via the isomeric [R‐nido‐7,8,10‐C3B8H10]? tricarbollide structures which, on protonation, undergo reductive extraction of one CH vertex to generate the 2‐CH3 substituent in structure 4 . 相似文献
102.
Danecek P Kapitán J Baumruk V Bednárová L Kopecký V Bour P 《The Journal of chemical physics》2007,126(22):224513
The difference spectroscopy of the Raman optical activity (ROA) provides extended information about molecular structure. However, interpretation of the spectra is based on complex and often inaccurate simulations. Previously, the authors attempted to make the calculations more robust by including the solvent and exploring the role of molecular flexibility for alanine and proline zwitterions. In the current study, they analyze the IR, Raman, and ROA spectra of these molecules with the emphasis on the force field modeling. Vibrational harmonic frequencies obtained with 25 ab initio methods are compared to experimental band positions. The role of anharmonic terms in the potential and intensity tensors is also systematically explored using the vibrational self-consistent field, vibrational configuration interaction (VCI), and degeneracy-corrected perturbation calculations. The harmonic approach appeared satisfactory for most of the lower-wavelength (200-1800 cm(-1)) vibrations. Modern generalized gradient approximation and hybrid density functionals, such as the common B3LYP method, provided a very good statistical agreement with the experiment. Although the inclusion of the anharmonic corrections still did not lead to complete agreement between the simulations and the experiment, occasional enhancements were achieved across the entire region of wave numbers. Not only the transitional frequencies of the C-H stretching modes were significantly improved but also Raman and ROA spectral profiles including N-H and C-H lower-frequency bending modes were more realistic after application of the VCI correction. A limited Boltzmann averaging for the lowest-frequency modes that could not be included directly in the anharmonic calculus provided a realistic inhomogeneous band broadening. The anharmonic parts of the intensity tensors (second dipole and polarizability derivatives) were found less important for the entire spectral profiles than the force field anharmonicities (third and fourth energy derivatives), except for a few weak combination bands which were dominated by the anharmonic tensor contributions. 相似文献
103.
Valík M Cejka J Havlík M Král V Dolenský B 《Chemical communications (Cambridge, England)》2007,(37):3835-3837
The first members of a new cavitand family, represented by calix-shaped tris Tr?ger's base diastereoisomers, are prepared via step-by-step synthesis as well as one-pot mixed troegeration. 相似文献
104.
Jan ejka Bohumil Kratochvíl Ivana Císaov Alexandr Jegorov 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(8):o428-o430
Simvastatin, or (1S,3R,7S,8S,8aR)‐8‐{2‐[(2R,4R)‐4‐hydroxy‐6‐oxo‐3,4,5,6‐tetrahydro‐2H‐pyran‐2‐yl]ethyl}‐3,7‐dimethyl‐1,2,3,7,8,8a‐hexahydronaphthalen‐1‐yl 2,2‐dimethylbutanoate, C25H38O5, is almost isostructural with lovastatin, and the general conformational features are closely related to those of other reported crystal structures of statins. The only hydrogen bond present facilitates the formation of infinite chains of molecules along the b axis. 相似文献
105.
Jií Kvapil Josef Kvapil Bohumil Perner Betislav Mnek 《Crystal Research and Technology》1975,10(10):1051-1056
Absorption spectra of molybdenum doped YAG crystals annealed in hydrogen, vacuum, oxygen and argon and exposed to an UV irradiation are given. Yellow or brown colour of the crystals is attributed to the O− centre formation connected with the reduction of molybdenum ions to a lower valency state. Most intensive yellow colour was shown by crystals, the argon annealing of which was followed by a treatment in oxygen at rather low temperature (∼1000 °C) and by UV irradiation. Two types of O− centres are suggested Blue colour of the samples annealed in argon is attributed to e− centres. 相似文献
106.
Prepilková Veronika Poništ Juraj Schwarz Marián Bednárová Dagmara 《Journal of Analytical Chemistry》2022,77(7):830-843
Journal of Analytical Chemistry - Microplastics (MPs) currently cause an environmental risk due to their transport to all components of the environment. The review article aims to evaluate and... 相似文献
107.
Lenka Zají?ková Ond?ej Jašek Bohumil David Nadě?da Pizúrová Lukáš Lazar 《Applied Surface Science》2009,255(10):5421-5424
The MW plasma torch (2.45 GHz) in the mixture of CH4/H2/Ar (42/430/1540 sccm) with added Fe(CO)5vapors was used for the synthesis of iron oxide nanoparticles and carbon nanotubes. The particles with well-defined facets consisting of Fe3O4 and -Fe2O3 and self-assembled into long chains were produced at the power of 360 W. At higher power of 440-460 W the deposit contained significant amount of multi-walled carbon nanotubes covered by iron oxide nanoparticles. The diameter of CNTs was 8-20 nm. The particles had Fe3O4 and/or -Fe2O3 cores of spherical shape covered by a thin layer of carbon. 相似文献
108.
109.
Stíbr B Bakardjiev M Holub J Růzicka A Padelková Z Stepnicka P 《Inorganic chemistry》2011,50(7):3097-3102
A systematic method for the incorporation of the {(η(6)-Me(n)C(6)H(6-n))Fe} fragment into the dicarbollide cage was developed based on reactions between [(η(6)-Me(n)C(6)H(6-n))(2)Fe][PF(6)](2) salts (1) and Tl(2)[nido-7,8-C(2)B(9)H(11)]. These reactions proceed with elimination of one arene ligand to generate a complete series of the neutral [1-(η(6)-Me(n)C(6)H(6-n))-closo-1,2,3-FeC(2)B(9)H(11)] (2) complexes with n = 1-6 in yields ranging 15-70% depending on the arene. The structures of mesitylene and pentamethylbenzene complexes were established by X-ray diffraction analyses. All compounds were characterized by (11)B and (1)H NMR measurements, mass spectra, melting points and elemental analyses. Correlations between selected (1)H and (11)B NMR parameters and the Fe(II/III) redox potentials and the number of arene methyls for complexes 2 are linear. These facts establish direct evidence for a strictly additive character of electron donation by the methyl substituents to the arene ring and further to the Fe center and the second (dicarbollide) ligand.Correlations between the number of arene methyls (n) and selected (1)H and (11)B NMR parameters or the Fe(II/III) redox potentials for complexes [1-(η(6)-MenC(6)H(6-n))-closo-1,2,3-FeC(2)B(9)H(11)] are of strictly linear character. 相似文献
110.
Holub J Štíbr B Bakardjiev M Růžička A Padělková Z 《Dalton transactions (Cambridge, England : 2003)》2011,40(25):6623-6625
The heating of selected [1-(η(6)-arene)-closo-1,2,3-FeC(2)B(9)H(11)] complexes resulted in the thermal rearrangement and isolation of the corresponding 1,2,4-, 1,2,7-, and 1,2,8-cage isomers. Demonstrated here is a similar rearrangement and the NMR behaviour for isostructural [1-(η(5)-cyclopentadienyl)-closo-1,2,3-CoC(2)B(9)H(11)] compounds. 相似文献