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排序方式: 共有125条查询结果,搜索用时 31 毫秒
21.
In this work new polymer/carrier composites are described which serve as novel materials in flow-through reactors for polymer-supported organic solution-phase synthesis. Monolithic polymer/carrier columns are prepared by a new precipitation polymerization process inside the void pore volume of megaporous glass carrier materials. Chemical functionalization of the internal polymer phase with chlorosulfonic acid or trimethylamine generates small, interconnected ion-exchange resin beads with a diameter of 1-3 microm which can be used for a large variety of organic syntheses. These monolithic rods are incorporated into an appropriate casing and can conveniently be operated in the flow-through mode. Important successful applications are polymer-assisted solution-phase reductions, oxidations and Horner-Emmons olefinations. Additionally, the use of these monolithic columns as catalytic microreactors and their performance in selected reactions are described. 相似文献
22.
The mobilities of lithium, PF6- and solvents in the electrolyte LiPF6-(ethylene carbonate-dimethyl carbonate-diethyl carbonate) were measured using the pulsed gradient spin-echo NMR. They were compared to those of the same electrolyte filling a macroporous poly(vinylidene fluoride) membrane. The conductivity decrease resulting in the incorporation of this macroporous membrane and the cationic transport number were analyzed in terms of (i) solvent/polymer and solvent/salt interactions, (ii) ionic dissociation, and (iii) tortuosity. 相似文献
23.
Miguel E. Alonso Reinaldo Compagnone Wladimir Chitty 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-2):9-10
Abstract Recent studies on the fragmentation of some organic disulfides upon electron impact in a mass spectrometer have shown two main decomposition routes besides simple bond disconnection: skeletal rearrangements1–3 and proton transfer4. Transposition of the molecular components takes place via loss of one or two sulfur atoms while the carbon skeleton is preserved. Such molecular rearrangements are particularly noticeable in small molecules like dimethyl disulfide. Larger systems show a different fragmentation pattern in which proton transfer to give alkyl hydro-disulfides becomes predominant. The transfer of protons has been shown to proceed by way of intramolecular 1,2 and 1,3 hydrogen shifts from α and β carbons respectively by means of selective deuterium labbeling of diethyl disulfide.4 相似文献
24.
Wladimir Lewicki 《Monatshefte für Mathematik》1903,14(1):283-292
Ohne Zusammenfassung 相似文献
25.
Wladimir Skinder 《Analytical and bioanalytical chemistry》1912,51(10-11):670-671
26.
Wladimir de Azevedo Pribitkin 《Proceedings of the American Mathematical Society》2008,136(9):3089-3094
Under what conditions do the (possibly complex) coefficients of a general Dirichlet series exhibit oscillatory behavior? In this work we invoke Laguerre's Rule of Signs and Landau's Theorem to provide a rather simple answer to this question. Furthermore, we explain how our result easily applies to a multitude of functions.
27.
Ohne Zusammenfassung 相似文献
28.
Abel S Waks M Marchi M Urbach W 《Langmuir : the ACS journal of surfaces and colloids》2006,22(22):9112-9120
We used constant pressure (P=0.1 MPa) and temperature (T=298 K) molecular dynamics simulations to study the structures and dynamics of small size reverse micelles (RMs) with poly(ethylene glycol) alkyl ether (CmEn) surfactants. The water-to-surfactant molar ratio was 3, with decane as the apolar solvent. We focused on the effect of the two possible imposed conformations (trans vs gauche) for the surfactant headgroups on RMs structures and water dynamics. For this purpose, we built up two RMs, which only differ by their surfactant headgroup conformations. The results obtained for the two RMs were compared to what is known in the literature. Here, we show that the surfactant headgroup conformation affects mainly the water-related properties such as the water core size, the area per surfactant headgroup, the headgroup hydration, and the water core translational diffusion. The properties computed for the RM with the surfactant in trans conformation fit better with the experimental data than the gauche conformation. We further show that the surfactant hydrophilic headgroup plays a crucial role in the micellar structures, favors the entrapment of the micellar water, and reduces strongly their diffusion compared to the bulk water. 相似文献
29.
Kirschning A Solodenko W Mennecke K 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(23):5972-5990
The concepts article describes enabling techniques (solid-phase assisted synthesis, new reactor design, microwave irradiation and new solvents) in organic chemistry and emphasizes the combination of several of them for creating new synthetic technology platforms. Particular focus is put on the combination of immobilized catalysts as well as biocatalysts with continuous flow processes. In this context, the PASSflow continuous flow technique fulfils both chemical as well as chemical engineering requirements. It combines reactor design with optimized, monolithic solid phases as well as reversible immobilization techniques for performing small as well as large scale synthesis with heterogenized catalysts under continuous flow conditions. 相似文献
30.
In this communication, we provide theoretical evidence that the folded structure of a simple peptide, alanine zwitterionic octapeptide, or A8, unstable in solution, becomes stable in a reverse micelle (RM) of appropriate size. Our molecular dynamics simulations were carried out for realistic models of sodium 2-ethylhexylsulfosuccinate RM in isooctane, simulated for an extended period of time. For the RM of the smaller size, we find that a helical structure is stable for the whole length of the simulation. On the contrary, the peptide very quickly takes an extended structure in larger micelles. 相似文献