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991.
Andrei V. Afonin Igor A. Ushakov Dmitry V. Pavlov Elena Yu. Schmidt Marina Yu. Dvorko 《Magnetic resonance in chemistry : MRC》2013,51(6):339-349
Comparative analysis of the 1Н and 13С NMR data for a series of the E and Z‐1‐styrylpyrroles, E and Z‐1‐(1‐propenyl)pyrroles, 1‐vinylpyrroles and styrene suggests that the conjugation between the unsaturated fragments in the former compounds is reduced. This is the result of the mutual influence of the donor p–π and π–π conjugation having opposite directions. According to the NMR data combined with the density functional theory calculations, the Z isomer of 1‐styrylpyrrole has essentially a nonplanar structure because of the steric hindrance. However, the E isomer of 1‐styrylpyrrole is also an out‐of‐plane structure despite the absence of a sterical barrier for the planar one. Deviation of the E isomer from the planar structure seems to be caused by an electronic hindrance produced by a mutual influence of the p–π and π–π conjugation. The structure of the E isomer of the 2‐substituted 1‐styrylpyrroles is similar to that of the 2‐substituted 1‐vinylpyrroles. The steric effects in the Z isomer of the 2‐substituted 1‐styrylpyrroles result in the large increase of the dihedral angle between planes of the pyrrole ring and double bond. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
992.
Marc Comí Gerard Lligadas Juan C. Ronda Marina Galià Virginia Cádiz 《Journal of polymer science. Part A, Polymer chemistry》2013,51(22):4894-4903
The benzoxazines of three naturally occurring phenylpropanoid phenols: ferulic, coumaric, and phloretic acids, and their esters are described. Benzoxazines with conjugated unsaturated chains exhibit unusual poor thermal stability and degrade partially at the polymerization temperature making necessary the use of a catalyst (BF3.Et2O) to low the polymerization temperature and prevent degradation. Polybenzoxazines are prepared thermally and characterized by DSC and TGA techniques. The resulting materials have superior Tgs when compared with those prepared from an unsubstituted monofuctional benzoxazine due to the additional crosslinking through the ester and carboxylic moieties. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4894–4903 相似文献
993.
Maryluz Moreno Gerard Lligadas Juan C. Ronda Marina Galià Virginia Cádiz 《Journal of polymer science. Part A, Polymer chemistry》2013,51(8):1808-1815
Phosphorus‐containing thermosetting resins derived from high oleic sunflower oil were prepared through phospha‐Michael addition of a difunctional secondary phosphine oxide, the 1,3‐bis(phenylphosphino)propane dioxide on the α,β‐unsaturated ketone derived from high oleic acid (ETR). The aim of this approach was to introduce phosphorus and to crosslink the material in one single step. Materials with increasing aromatic content were also prepared by addition 4,4′‐diaminodiphenylmethane and co‐crosslinking through aza‐Michael addition. The kinetics of the phospha and aza‐Michael additions was investigated using the enone derivative of methyl oleate (EO) in presence of BF3·Et2O as catalyst and in absence of catalyst at different temperatures. Competitive experiments showed that phospha‐Michael addition proceeds faster than the aza‐Michael addition. The new triglyceride‐based thermosets containing up to 4.2% of P, were characterized and their thermal and flame retardant properties evaluated. Limiting oxygen index values increase from 21.5 for the phosphorus free material up to 38.0 for the final material with 4.2% P content. These results demonstrate that the flame retardant properties of vegetable oil‐based thermosets can be significantly improved by adding covalently bonded phosphorus to the polymer. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013 相似文献
994.
Robert Andreu Marina Galià Virginia Cádiz Gerard Lligadas Jose A. Reina Juan C. Ronda 《Journal of polymer science. Part A, Polymer chemistry》2013,51(23):5075-5084
3‐Phenyl‐3,4‐dihydro‐2H‐1,3‐benzoxazine ( m 1 ) underwent cationic ring opening polymerization using BF3·OEt2 in alcoholic solution under mild conditions. The polymerization of m 1 proceeds through an intermediate hemiaminal ether leading mainly to the formation of polybenzoxazines with diphenylmethane bridges, and not only the classical Mannich‐type ones. During the first stages of the reaction, low‐molecular weight soluble oligomers containing benzoxazine rings are formed. At longer polymerization times, the propagation proceeds conventionally through the phenolic active sites. This polymerization mechanism is extensible to other substituted 3‐phenyl‐3,4‐dihydro‐2H‐1,3‐benzoxazines but fails in the case of 3‐alkyl‐3,4‐dihydro‐2H‐1,3‐benzoxazines or when the phenyl group in Position 3 have a substituent in the p‐position. Spectroscopic studies and kinetic experiments using model reactions and deuterium labeled benzoxazines, allow proposing a plausible different polymerization mechanism. These soluble benzoxazine‐containing polymers can be conveniently processed and impregnated on appropriate substrates before underwent crosslinking producing materials with comparable properties to those of conventional bis‐benzoxazines. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 5075–5084 相似文献
995.
Maddalena Bronzato Prof. Paolo Calvini Prof. Carlo Federici Prof. Sara Bogialli Prof. Gabriella Favaro Prof. Moreno Meneghetti Prof. Miriam Mba Prof. Marina Brustolon Prof. Alfonso Zoleo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(29):9569-9577
In this work, we present a wide‐range spectrochemical analysis of the degradation products from naturally aged paper. The samples obtained from wash waters used during the de‐acidification treatment of leaves from a 16th‐century‐printed book were analysed through NMR, IR, Raman UV/Vis, EPR and X‐ray fluorescence (XRF) spectroscopy and HPLC‐MS and inductively coupled plasma (ICP) analysis. By these methods we also studied some of the previous samples treated by acidification (sample AP) and catalytic hydrogenation (sample HP). Crossing all the data, we obtained precise indications about the main functional groups occurring on the degraded, water‐soluble cellulose oligomers. These results point out that the chromophores responsible for browning are conjugated carbonyl and carboxyl compounds. As a whole, we show that the analysis of wash waters, used in the usual conservation treatments of paper de‐acidification, gives much valuable information about both the conservation state of the book and the degradation reactions occurring on the leaves, due to the huge amount of cellulose by‐products contained in the samples. We propose therefore this procedure as a new very convenient general method to obtain precious and normally unavailable information on the cellulose degradation by‐products from naturally aged paper. 相似文献
996.
Vassiliki Theodorou Marina GogouMaria Philippidou Valentine RagoussisGeorgios Paraskevopoulos Konstantinos Skobridis 《Tetrahedron》2011,67(31):5630-5634
α,β-Unsaturated acids, through their acid chlorides, react with tritylamine in the presence of triethylamine under mild conditions, to afford in high yield and high regioselectivity the corresponding β,γ-unsaturated tritylamides. Detritylation with TFA generates quantitatively β,γ-unsaturated primary amides. An investigation of this deconjugative isomerization was performed. 相似文献
997.
Cyclohexane (cC6H12) plays an important role in the combustion of practical liquid fuels, as a major component of naphthenic compounds. Therefore, the pyrolysis of cyclohexane was investigated by measuring the formation of H‐atoms. The thermal decomposition of 1‐hexene (1‐C6H12) was also studied, because of the assumption that 1‐hexene is the sole initial product of cyclohexane decomposition. For cyclohexane, the measurements were performed over a temperature range of 1320–1550 K, at pressures ranging from 1.8 to 2.2 bar; 1‐hexene experiments were done at temperatures between 1250 and 1380 K and pressures between 1.5 and 2.5 bar. For each experiment, the time‐dependent formation of H‐atoms was measured behind reflected shock waves by using the method of atomic resonance absorption spectrometry. For the dissociation of 1‐hexene to n‐propyl (C3H7) and allyl (C3H5) radicals, the following Arrhenius expression was derived: kR2(T) = 2.3 × 1016 exp(?36,672 K/T) s?1. For cyclohexane, overall rate coefficients (kov) were deduced for the global reaction cC6H12 → products + H from the H‐atom time profiles; the following temperature dependency was obtained: kov(T) = 4.7 × 1016 exp(?44,481 K/T) s?1. For both sets of rate coefficient values, an uncertainty of ±30% is estimated. Especially concerning the isomerization cC6H12 → 1‐C6H12, our experimental results are in excellent agreement with the rate coefficient values given by Tsang (Tsang, W. Int J Chem Kinet 1978, 10, 1119–1138). A reaction model was assembled that is able to reproduce the H‐atom profiles measured for both sets of experiments. According to this model, H‐atoms are mostly stemming from the thermal decomposition of allyl radicals (C3H5), which arise from the decomposition of 1‐hexene. Furthermore, it will be shown that the recombination of allyl radicals with H‐atoms to propene (C3H6) also represents a very important subsequent reaction. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 43: 107–119, 2011 相似文献
998.
Ilaria D'auria Mina Mazzeo Daniela Pappalardo Marina Lamberti Claudio Pellecchia 《Journal of polymer science. Part A, Polymer chemistry》2011,49(2):403-413
Phosphido‐diphosphine Group 3 metal complexes 1–4 [(o‐C6H4PR2)2P‐M(CH2SiMe3)2; R = Ph, 1 : M = Y, 2 : M = Sc; R = iPr, 3 : M = Y, 4 : M = Sc] are very efficient catalysts for the ring‐opening polymerization (ROP) of cyclic esters such as ε‐caprolactone (ε‐CL), L ‐lactide, and δ‐valerolactone under mild polymerization conditions. In the ROP of ε‐CL, complexes 1–4 promote quantitative conversion of high amount of monomer (up to 3000 equiv) with very high turnover frequencies (TOF) (~4 × 104 molCL/molI h) showing a catalytic activity among the highest reported in the literature. The immortal and living ROP of ε‐CL and L ‐lactide is feasible by combining complexes 1–4 with 5 equiv of 2‐propanol. Polymers with controlled molecular parameters (Mn, end groups) and low polydispersities (Mw/Mn = 1.05–1.09) are formed as a result of fast alkoxide/alcohol exchange. In the ROP of δ‐valerolactone, complexes 1–4 showed the same activity observed for lactide (L ‐ and D ,L ‐lactide) producing high molecular weight polymers with narrow distribution of molar masses. Complexes 1–4 also promote the ROP of rac‐β butyrolactone affording atactic low molecular weight poly(hydroxybutyrate) bearing unsaturated end groups probably generated by elimination reactions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
999.
Enrique Del Rio Gerard Lligadas Juan Carlos Ronda Marina Galià Virginia Cádiz 《Journal of polymer science. Part A, Polymer chemistry》2011,49(14):3069-3079
2‐Nonyl‐2‐oxazoline and 2‐(9‐decenyl)‐2‐oxazoline have been copolymerized in different proportions by cationic ring‐opening polymerization to obtain a series of random linear copolymers with tailored molecular weight and double bond functionality in the side chains. Thiol‐ene addition of 2‐mercaptoethanol has been used to produce a set of polyoxazoline–polyols under mild conditions and with quantitative double bond transformation. The polyols obtained in this way were reacted with methylene‐bis(phenylisocyanate) to yield a series of amorphous and semicrystalline polyurethane networks. The thermal stability and the thermomechanical properties of these thermosets have been studied and related with the structure of the parent polyols. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011 相似文献
1000.