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101.
Monika K. Baraniak Prof. Roger A. Lalancette Prof. Frieder Jäkle 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(60):13799-13810
The Lewis acidic character of borinic-acid-functionalized polymers suggests broad potential applications in supramolecular materials, chemo- and biosensors, as well as supported catalysts. Two highly electron-deficient borinic acid copolymers ( 3 a and 3 b ) with variable steric hindrance at the boron center were prepared by reaction of aryldibromoboranes ArBBr2 ( 2 , Ar=2,4-Cl2Ph, 3,5-Cl2Ph) with a 10 % stannylated polystyrene random copolymer, followed by conversion to the desired PS-B(Ar)OH functionalities. The supramolecular assembly of these polymers through Lewis acid–Lewis base interactions and reversible covalent B−O−B bond formation was investigated. Exposure of a polymer solution of 3 a to pyridine triggered spontaneous gelation, whereas 3 b only gelled upon addition of molecular sieves to favor formation of boroxane crosslinks. The crosslinking process was readily reversed by addition of small amounts of water or wet solvent. The dynamic processes were studied in detail by variable-temperature (VT) NMR by using molecular model compounds. The polymers and their corresponding model compounds were also examined as catalysts in the amide bond formation reaction between phenylacetic acid and benzylamine. The 3,5-dichlorophenyl borinic acid derivatives proved to be the more effective catalysts. Mechanistic studies suggested that the borane Lewis acid-catalyzed coupling involves initial acid-induced protodeboronation to release the dichlorophenyl boronic acid as the active catalyst. 相似文献
102.
We give an elementary self-contained proof to Botha’s theorem on the factorization of a singular transformation into idempotent mappings. 相似文献
103.
Andrew W. Baggett Fang Guo Bo Li Shih‐Yuan Liu Frieder Jkle 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(38):11343-11347
The regioregular synthesis of the first azaborine oligomers and a corresponding conjugated polymer was accomplished by Suzuki–Miyaura coupling methods. An almost perfectly coplanar syn arrangement of the heterocycles was deduced from an X‐ray crystal structure of the dimer, which also suggested that N H⋅⋅⋅π interactions play an important role. Computational studies further supported these experimental observations and indicated that the electronic structure of the longer azaborine oligomers and polymer resembles that of poly(cyclohexadiene) more than poly(p‐phenylene). A comparison of the absorption and emission properties of the polymer with those of the oligomers revealed dramatic bathochromic shifts upon chain elongation, thus suggesting highly effective extension of conjugation. 相似文献
104.
The properties of template-directed nucleation are studied in the transition region where full nucleation control is lost and additional nucleation beyond the prepatterned structure is observed. To get deeper insight into the microscopic mechanisms, Monte Carlo simulations were performed. In this context, the previously used continuous algorithm [F. Kalischewski, J. Zhu, and A. Heuer, Phys. Rev. B 77, 155401, (2008)] was replaced by a discrete one to reduce simulation time and to allow more detailed calculations. The applied method is based on the assumption that the molecules on the surface occupy the sites of a simple fcc lattice. It is shown that a careful mapping of the continuous Monte Carlo technique onto the discrete algorithm leads to a good reproduction of the former results by means of the latter method. Furthermore, the new method facilitates the calculation of the spatial distribution of nuclei on the surface. This provides a detailed comparison with experimental data. 相似文献
105.
Noya Loew Ulla Wollenberger Frieder W. Scheller Martin Katterle 《Bioelectrochemistry (Amsterdam, Netherlands)》2009,76(1-2):28
In this contribution the substitution of the central protoporphyrin IX iron complex of horseradish peroxidase by the respective osmium porphyrin complex is described. The direct electrochemical reduction of the Os containing horseradish peroxidase (OsHRP) was achieved at ITO and modified glassy carbon electrodes and in combination with spectroscopy revealed the three redox couples OsIIIHRP/OsIVHRP, OsIVHRP/OsVHRP and OsVHRP/OsVIHRP. The midpoint potentials differ dependent on the electrode material used with E1/2 (OsIII/IV) of − 0.4 V (ITO) and − 0.25 V (GC), E1/2 (OsIV/V) of − 0.16 V (ITO) and + 0.10 V (GC), and E1/2 (OsV/VI)of + 0.18 V (ITO), respectively. Moreover, with immobilised OsHRP the direct electrocatalytic reduction of hydrogen peroxide and tert-butyl hydroperoxide was observed. In comparison to electrodes modified with native HRP the sensitivity of the OsHRP-electrode for tert-butyl hydroperoxide is higher. 相似文献
106.
Vassileva ND van den Ende D Mugele F Mellema J 《Langmuir : the ACS journal of surfaces and colloids》2006,22(11):4959-4967
We consider single two-dimensional aggregates, containing glass particles, placed at a water/air interface. We have investigated the critical shear rate for break-up of aggregates with different sizes in a simple shear flow. All aggregates break-up nearly at the same shear rate (1.8 +/- 0.2 s(-)(1)) independent of their size. The evolution of the aggregate structure before break-up was also investigated. With increasing shear rate, the aggregates adopt a more circular shape, and the particles order in a more dense, hexagonal structure. A simple theoretical model was developed to explain the experimentally observed break-up. In the model, the aggregate is considered as a solid circular disk that will break near its diameter. The capillary and drag force on the two parts of the aggregate were calculated, and from this force balance, the critical shear rate was found. The model shows a weak size dependence of the critical shear rate for the considered aggregates. This is consistent with the experimental observations. 相似文献
107.
[Structure: see text] A series of organoboron quinolates with emission colors ranging from blue to red have been prepared. In comparison to the respective AlQ3 derivatives a distinct blue-shift of the emission is observed. Theoretical calculations serve to provide insight into the nature of the frontier orbitals and the effect of the substituents in the 5-position of the quinolate ligands on the relative HOMO and LUMO energy levels. An efficient new blue emitting material with a pinacolborane substituent has been identified. 相似文献
108.
A chiral 2-naphthylferrocenylcopper heteroaggregate (2) was prepared in high yield by reaction of (Sp-2-naphthylferrocenyl)trimethyltin with (C6F5Cu)4 and fully characterized by multinuclear NMR, single crystal X-ray diffraction, and elemental analysis. The reactivity of 2 toward boron halides was examined. Rearrangement reactions resulted in formation of 1,2-, 1,3-, and 1,1′-disubstituted naphthylferrocenylboranes. 相似文献
109.
110.