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21.
Alejandro De Falco Mirta L. Fascio Melisa E. Lamanna Maria A. Corcuera Iaki Mondragon Gerardo H. Rubiolo Norma B. DAccorso Silvia Goyanes 《Physica B: Condensed Matter》2009,404(18):2780-2783
In this work we studied the functionalization of commercially available multiwalled carbon nanotubes (MWCNT) (Nanocyl 3100) with polystyrene by the method so called “grafting from”. The nanotubes were used as received and oxidized in air at 400 °C. The functionalization was started using thionyl chloride under reflux, followed by a reaction with ethylene glycol which allowed the inclusion of hydroxyl groups. The reaction of those with 2-chloropropionyl chloride led to the generation of the polymerization initiator. Last, the radical polymerization of the functionalized nanotubes, using styrene as the monomer, led to new materials which were studied with thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM) and ultraviolet–visible (UV–vis) spectroscopy. 相似文献
22.
Supercritical fluid chromatography with photodiode array detection for pesticide analysis in papaya and avocado samples 下载免费PDF全文
Norma S. Pano‐Farias Silvia G. Ceballos‐Magaña Jorge Gonzalez José M. Jurado Roberto Muñiz‐Valencia 《Journal of separation science》2015,38(7):1240-1247
To improve the analysis of pesticides in complex food matrices with economic importance, alternative chromatographic techniques, such as supercritical fluid chromatography, can be used. Supercritical fluid chromatography has barely been applied for pesticide analysis in food matrices. In this paper, an analytical method using supercritical fluid chromatography coupled to a photodiode array detection has been established for the first time for the quantification of pesticides in papaya and avocado. The extraction of methyl parathion, atrazine, ametryn, carbofuran, and carbaryl was performed through the quick, easy, cheap, effective, rugged, and safe methodology. The method was validated using papaya and avocado samples. For papaya, the correlation coefficient values were higher than 0.99; limits of detection and quantification ranged from 130–380 and 220–640 μg/kg, respectively; recovery values ranged from 72.8–94.6%; precision was lower than 3%. For avocado, limit of detection values were ?450 μg/kg; precision was lower than 11%; recoveries ranged from 50.0–94.2%. Method feasibility was tested for lime, banana, mango, and melon samples. Our results demonstrate that the proposed method is applicable to methyl parathion, atrazine, ametryn, and carbaryl, toxics pesticides used worldwide. The methodology presented in this work could be applicable to other fruits. 相似文献
23.
Mendes G Soares AR Sigiliano L Machado F Kaiser C Romeiro N Gestinari L Santos N Romanos MT 《Molecules (Basel, Switzerland)》2011,16(10):8437-8450
In this paper, we evaluated the antiviral activity against HMPV replication of crude extract of the marine algae Stypopodium zonale and of two meroditerpenoids obtained from it, atomaric acid and epitaondiol, and a methyl ester derivative of atomaric acid. Their selectivity indexes were 20.78, >56.81, 49.26 and 12.82, respectively. Compared to ribavirin, the substances showed a relatively low cytotoxicity on LLC-MK2 cells, with a significant antiviral activity, inhibiting at least 90% of viral replication in vitro, which demonstrates the potential of these marine natural products to combat infections caused by HMPV in vitro. 相似文献
24.
Norma Elias 《Integral Equations and Operator Theory》1988,11(3):310-331
In [2], Axler, Conway and McDonald, discuss the essential spectrum of Toeplitz operator, with continuous symbol, on the unweighted Bergman space. This paper extends their results to the weighted Bergman space, where the weight and its logarithm are assumed to be locally integrable.This paper represents part of the author's Ph.D. thesis, written at Indiana University under the direction of Professor John B. Conway. 相似文献
25.
Macías-Ruvalcaba NA Okumura N Evans DH 《The journal of physical chemistry. B》2006,110(43):22043-22047
The electrochemical reduction of 3,5-di-tert-butyl-1,2-benzoquinone, 1, has been studied in acetonitrile with added 2,2,2-trifluoroethanol, 2. At low concentrations of 2 the reaction proceeds by the following pathway: reduction of the quinone (Q) to its anion radical (Q*-) followed by complexation of the anion radical with 2 (HA) and the further reduction of the hydrogen-bonded complex (Q*- (HA)) to form HQ- and A-. The latter reaction is a concerted proton and electron- transfer reaction (CPET). At higher concentrations of 2, the pathway changes. The first steps remain the same, but now Q*- (HA) is reduced to HQ- via a disproportionation reaction with Q*- along with proton transfer from HA to Q*- to form HQ* which is reduced to HQ-. The only mechanism that could be found which would account for all of the data involves proton transfer to Q*- occurring within a higher complex, Q*-(HA)3. 相似文献
26.
The inner reorganization energy of the cation radical of 1,4-bis(dimethylamino)benzene, 1, has been determined to be 0.72 +/- 0.02 eV by means of gas-phase photoelectron spectroscopy (PES). PES studies of 9,10-bis(dimethylamino)anthracene, 2, and 3,6-bis(dimethylamino)durene, 3, demonstrate that their reorganization energies are smaller than that of 1. The effect of lowering the inner reorganization energy on the rate constant for an electrochemical electron-transfer reaction is to increase the electron-transfer rate constant, k(s). However, voltammetric studies of the two-electron oxidation of 2 and 3 indicate that the values of k(s) for each step are smaller than those for 1, in contradistinction to the measured differences in reorganization energies. The voltammetric studies of 2 and 3 were reinterpreted according to a mechanism in which each step of oxidation was written as a two-step process, electron transfer with a small inner reorganization energy plus a chemical step of structural change. The agreement of simulations according to this mechanism with the experimental data was excellent. The new reaction scheme eliminated some suspicious features previously obtained with an analysis where electron transfer and structural change were considered to be concerted. In particular, all electron-transfer coefficients (alpha) were close to one-half, whereas the earlier treatment produced values of alpha much larger or smaller than one-half. 相似文献
27.
The electrochemical reduction of the title compounds, 2a and 3a, and 7,7,8,8-tetracyanoquinodimethane, 1a, was studied in acetonitrile. The reduction of 1a shows normal ordering of potentials, i.e., the potential for insertion of the first electron, E degrees1, is more positive than the potential for the second step of reduction, E degrees2. Thus, E degrees1 - E degrees2 > 0. By contrast, 2a and 3a show inversion of potentials where introduction of the second electron occurs with greater ease than the first (E degrees1 - E degrees2 < 0). The extent of inversion has been determined by simulation of the cyclic voltammograms obtained at 298 and 257 K. Electron paramagnetic resonance measurements at room temperature of solutions containing equimolar mixtures of the neutral and dianion allow determination of the concentration of anion radicals from which the disproportionation equilibrium constant and E degrees1 - E degrees2 can be calculated. The results were in good agreement with the voltammetric determinations. Calculations were conducted to characterize the structural changes accompanying reduction to the anion radical and dianion forms. Fast scan experiments at low temperatures (up to 10 000 V/s at 257 K; 500 V/s at 233 K) were conducted in an attempt to detect intermediates in the reduction, but none was found. Thus, it is not possible to state whether structural change and electron transfer are concerted or occur in discrete steps. 相似文献
28.
Rodríguez-Laguna Norma Reyes-García Luis Ignacio Pacheco-Gómez Raúl Flores Raúl Rojas-Hernández Alberto Gómez-Balderas Rodolfo 《Journal of Thermal Analysis and Calorimetry》2019,136(4):1701-1709
Journal of Thermal Analysis and Calorimetry - In this work, a thermodynamic study of the Zn(II)/L systems (L??=?acetate, AcO? or indomethacin anion, Indo? or... 相似文献
29.
Electronic Structure Modulation in an Exceptionally Stable Non‐Heme Nitrosyl Iron(II) Spin‐Crossover Complex 下载免费PDF全文
Lucía Piñeiro‐López Dr. Norma Ortega‐Villar Prof. Dr. M. Carmen Muñoz Dr. Gábor Molnár Dr. Jordi Cirera Prof. Dr. Rafael Moreno‐Esparza Prof. Dr. Víctor M. Ugalde‐Saldívar Dr. Azzedine Bousseksou Prof. Dr. Eliseo Ruiz Prof. Dr. José A. Real 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(36):12741-12751
The highly stable nitrosyl iron(II) mononuclear complex [Fe(bztpen)(NO)](PF6)2 (bztpen=N‐benzyl‐N,N′,N′‐tris(2‐pyridylmethyl)ethylenediamine) displays an S=1/2?S=3/2 spin crossover (SCO) behavior (T1/2=370 K, ΔH=12.48 kJ mol?1, ΔS=33 J K?1 mol?1) stemming from strong magnetic coupling between the NO radical (S=1/2) and thermally interconverted (S=0?S=2) ferrous spin states. The crystal structure of this robust complex has been investigated in the temperature range 120–420 K affording a detailed picture of how the electronic distribution of the t2g–eg orbitals modulates the structure of the {FeNO}7 bond, providing valuable magneto–structural and spectroscopic correlations and DFT analysis. 相似文献
30.
Macías-Ruvalcaba NA Evans DH 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(16):4386-4395
In electron-transfer reactions accompanied by structural changes, the structural change can be concerted with electron transfer or can occur in a separate reaction either preceding or following the electron-transfer step. In this paper we discuss ways of distinguishing concerted reactions from the latter two-step type. Included are recent examples in which no intermediates have been detected in the reactions, thus precluding the direct assignment to the two-step category. In these cases, other means are used to build support for the two-step mechanism with respect to the concerted process. These include an example of structural change preceding electron transfer, a demonstration that the current models of concerted reactions cannot fit the voltammetric data, and a case in which an independent measure of the inner reorganization energy was used to show that the reaction could not be a concerted electron transfer and structural change. 相似文献