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81.
Gary E. Martin Bruce D. Hilton Kirill A. Blinov Antony J. Williams 《Journal of heterocyclic chemistry》2008,45(4):1109-1113
Recent reports have demonstrated the unsymmetrical indirect covariance combination of discretely acquired 2D NMR experiments into spectra that provide an alternative means of accessing the information content of these spectra. The method can be thought of as being analogous to the Fourier transform conversion of time domain data into the more readily interpreted frequency domain. Hyphenated 2D‐NMR spectra such as GHSQC‐TOCSY, when available, provide an investigator with the means of sorting proton‐proton homonuclear connectivity networks as a function of the 13C chemical shift of the carbon directly bound to the proton from which propagation begins. Long‐range heteronuclear chemical shift correlation experiments establish proton‐carbon correlations via heteronuclear coupling pathways, most commonly across three bonds (3JCH), but in more general terms across two (2JCH) to four bonds (4JCH). In many instances 3JCH correlations dominate GHMBC spectra. We demonstrate in this report the improved visualization of 2JCH and 4JCH correlations through the unsymmetrical indirect covariance processing of GHSQC‐TOCSY and GHMBC 2D spectra. 相似文献
82.
Kirill A. Kolmakov 《Journal of heterocyclic chemistry》2008,45(4):1215-1220
In acetic acid medium, 2‐chloro‐4,6‐dimorpholin‐4‐yl‐[1,3,5]triazine undergoes amination by bifunctional heterocyclic compounds containing both amino and thioamide groups. The reactions are high‐yielding and selective; the thioamide functions are unaffected under the requisite conditions. The reactions do not proceed in satisfactory yields in other solvents and, thus, require acetic acid. The resulting thioamides, consisting of multiple biologically relevant residues, are easily alkylated at the sulfur (thiolthione) centers to furnish new thioethers in subsequent steps. 相似文献
83.
Zaikina JV Kovnir KA Haarmann F Schnelle W Burkhardt U Borrmann H Schwarz U Grin Y Shevelkov AV 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(18):5414-5422
A new representative of a very rare clathrate III family, Si130P42Te21, has been synthesized from the elements. It crystallizes in the tetragonal space group P4(2)/mnm (no. 136) with the unit cell parameters a=19.2632(3) angstroms, c=10.0706(2) angstroms. Single crystal X-ray diffraction and solid state 31P NMR revealed a non-random distribution of phosphorus atoms over the framework positions. The crystal structure features a peculiar packing of large polyhedra Te@(Si/P)(n) never observed before for cationic clathrates. Despite the structural complexity, the composition of the novel clathrate Is in accordance with the Zintl rule, which was confirmed by a combination of optical metallography, scanning electron microscopy (SEM) and wavelength dispersive X-ray spectroscopy (WDXS), as well as by diamagnetic and semiconducting behavior of the synthesized phase. Clathrate Si130P42Te21 exhibits the highest reported thermal stability for this class of materials, it decomposes at 1510 K. This opens new perspectives for the creation of clathrate-based materials for high-temperature applications. 相似文献
84.
Ng SH Tran N Bramnik KG Hibst H Novák P 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(35):11141-11148
Li(4)V(3)O(8) materials have been prepared by chemical lithiation by Li(2)S of spherical Li(1.1)V(3)O(8) precursor materials obtained by a spray-drying technique. The over-lithiated vanadates were characterised physically by using scanning electron microscopy (SEM) and X-ray diffraction (XRD), and electrochemically using galvanostatic charge-discharge and cyclic voltammetry measurements in both the half-cell (vs. Li metal) and full-cell (vs. graphite) systems. The Li(4)V(3)O(8) materials are stable in air for up to 5 h, with almost no capacity drop for the samples stored under air. However, prolonged exposure to air will severely change the composition of the Li(4)V(3)O(8) materials, resulting in both Li(1.1)V(3)O(8) and Li(2)CO(3). The electrochemical performance of these over-lithiated vanadates was found to be very sensitive to the conductive additive (carbon black) content in the cathode. When sufficient carbon black is added, the Li(4)V(3)O(8) cathode exhibits good cycling behaviour and excellent rate capabilities, matching those of the Li(1.1)V(3)O(8) precursor material, that is, retaining an average charge capacity of 205 mAh g(-1) at 2800 mA g(-1) (8C rate; 1C rate means full charge or discharge of a battery in one hour), when cycled in the potential range of 2.0-4.0 V versus Li metal. When applied in a non-optimised full cell system (vs. graphite), the Li(4)V(3)O(8) cathode showed promising cycling behaviour, retaining a charge capacity (Li(+) extraction) above 130 mAh g(-1) beyond 50 cycles, when cycled in the voltage range of 1.6-4.0 V, at a specific current of 117 mA g(-1) (C/3 rate). 相似文献
85.
Altobello S Nikitin K Stolarczyk JK Lestini E Fitzmaurice D 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(4):1107-1116
This paper reports a novel methodology for the conformational analysis of [2]rotaxanes. It combines NMR spectroscopic (COSY, NOESY and the recently reported paramagnetic line-broadening and suppression technique) and electrochemical techniques to enable a quantitative analysis of the co-conformations of interlocked molecules and the conformations of their components. This methodology was used to study a model [2]rotaxane in solution. This [2]rotaxane consists of an axle that incorporates an electron-poor, doubly positively charged viologen that threads an electron-rich crown ether. It has been shown that the axle of the [2]rotaxane in its dicationic state adopts a folded conformation in solution and the crown ether is localised at the viologen moiety. Following a one-electron reduction of viologen, the paramagnetic radical cation of the [2]rotaxane retains its folded conformation in solution. The data also demonstrate that in the radical cation the crown ether remains localised at the viologen, despite its reduced affinity for the singly reduced viologen. The combined quantitative NMR spectroscopic and electrochemical characterisation of the electromechanical function of the model [2]rotaxane in solution provides an important reference point for the study of switching in structurally related bistable [2]rotaxanes, which is the subject of the second part of this work. 相似文献
86.
Wong E Okhonin V Berezovski MV Nozaki T Waldmann H Alexandrov K Krylov SN 《Journal of the American Chemical Society》2008,130(36):11862-11863
Many regulatory enzymes are considered attractive therapeutic targets, and their inhibitors are potential drug candidates. Screening combinatorial libraries for enzyme inhibitors is pivotal to identifying hit compounds for the development of drugs targeting regulatory enzymes. Here, we introduce the first inhibitor screening method that consumes only nanoliters of the reactant solutions and is applicable to regulatory enzymes. The method is termed inject-mix-react-separate-and-quantitate (IMReSQ) and includes five steps. First, nanoliter volumes of substrate, candidate inhibitor, and enzyme solutions are injected by pressure into a capillary as separate plugs. Second, the plugs are mixed inside this capillary microreactor by transverse diffusion of laminar flow profiles. Third, the reaction mixture is incubated to form the enzymatic product. Fourth, the product is separated from the substrate inside the capillary by electrophoresis. Fifth, the amounts of the product and substrate are quantitated. In this proof-of-principle work, we applied IMReSQ to study inhibition of recently cloned protein farnesyltransferase from parasite Entamoeba histolytica. This enzyme is a potential therapeutic target for antiparasitic drugs. We identified three previously unknown inhibitors of this enzyme and proved that IMReSQ could be used for quantitatively ranking the potencies of inhibitors. 相似文献
87.
This article proposes a systematic, quantitative treatment of the problem of associating a scalar Flory-Huggins-like chi parameter directly with the interaction potentials in a binary mixture of point particles. This work fulfills the need for a general, quantitative way to compare chi values in explicitly simulated ensembles of lattice and off-lattice polymer models with field theoretic calculations. Emphasis is placed on constructing particle models where chi is relatively well defined. In general, chi is defined through pair correlation functions, whose thermal fluctuations are coupled to local average composition and composition gradients. This implies that chi is composition dependent even in the simplest particle models. At the same time, by quantifying this effect, it is found that composition-independent chi may be defined to within a few percent for cases where the range of the potential is large relative to the interparticle distance. An explicit formula for chi in terms of interaction potentials is given. 相似文献
88.
89.
Krivdin LB Chernyshev KA Rosentsveig GN Ushakova IV Rosentsveig IB Levkovskaya GG 《Magnetic resonance in chemistry : MRC》2007,45(11):980-984
Configurational assignment of seven synthesized N-arylsulfonylimines of alpha-polychloroaldehydes has been carried out by means of experimental measurements and high-level ab initio calculations of their (13)C--(13)C, (13)C--(1)H and (15)N--(1)H spin-spin coupling constants. The title compounds were shown to exist in solution solely in the form of E isomers, in line with thermodynamic reasoning. 相似文献
90.