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951.
Wojciech Nogala Ewa Rozniecka Izabella Zawisza Jerzy Rogalski Marcin Opallo 《Electrochemistry communications》2006,8(12):1850-1854
Voltametrically stable 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS2−) modified electrode was obtained by sol–gel processing of methyltrimethoxysilane based sol with dissolved ABTS2− together with dispersed graphite particles. Next, extracellular laccase from Cerrena unicolor was encapsulated within a thin hydrophilic tetramethoxysilane film on the top the electrode. The obtained ABTS2− modified carbon ceramic electrode exhibits stable voltammetry corresponding to the surface confined oxidation reduction process. The biocatalytic activity of this electrode is similar to that observed when ABTS2− is present in solution. 相似文献
952.
Sikorska E Khmelinskii IV Kubicki M Prukała W Nowacka G Siemiarczuk A Koput J Ferreira LF Sikorski M 《The journal of physical chemistry. A》2005,109(9):1785-1794
Hydrogen bonds were shown to play an important role in the lumichrome photophysics and photochemistry both in solutions and in the solid state. In solutions, lumichrome can form hydrogen-bonded complexes with a variety of molecules, such as acetic acid or methanol, as supported by spectral and equilibrium studies. Photoexcitation of some hydrogen-bonded complexes, having appropriate configuration, as in the case of acetic acid, may lead to excited-state proton transfer, resulting in formation of the isoalloxazinic structure, detectable by its characteristic emission, distinct from that of the intrinsically alloxazinic lumichrome. Theoretical calculations confirmed the role of the hydrogen-bonded complexes, yielding several stable eight-membered cyclic structures of such complexes characterized by spectral changes similar to those observed experimentally. Hydrogen bonds play an essential role in the formation of the lumichrome crystal structure, as follows from the X-ray diffraction results. Interestingly, the crystals studied included molecules of methanol used as solvent in crystal growth. The emission studies of polycrystalline samples, similar to the processes occurring in solutions, point to the importance of hydrogen-bonding interactions in crystal packing allowed by the symmetry of the hydrogen-bonded dimers. 相似文献
953.
Małgorzata Pazderska-Szabłowicz Adam Karpiński Ewa Kita 《Transition Metal Chemistry》2006,31(8):1075-1080
Two new chromium(III) complexes with picolinamide (pica) and oxalates, [Cr(C2O4)2(N,N′-pica)]2− and [Cr(C2O4)2(N,O-pica)]−, were obtained and the kinetics of their aquation in HClO4 solutions were studied. The aquation leads to pica liberation and proceeds in two stages: (i) the chelate-ring opening at
the Cr–amide bond and (ii) the Cr–N-pyridine bond breaking, which gives free pica and cis-[Cr(C2O4)2(H2O2)2]−. In the case of N,N′-bonded pica the kinetics of both stages was determined and in the case of the N,O-bonded pica only the second stage was
investigated. The following rate laws were established: (k
obs)1 = k
0 + k
1
Q
1[H+] and (k
obs)2 = k
2
Q
2[H+], where k
0 and k
1 are the rate constants of the chelate-ring opening in the unprotonated and protonated starting complex, and k
2 is the rate constant of the pica liberation from the protonated intermediate. Kinetic parameters are calculated and the aquation
mechanism is discussed. 相似文献
954.
Summary The carbonyl ligands in the Rh1 complexes Rh(L-L)(CO)2 [L-L=anthranilate (AA) orN-phenylanthranilate(FA) ions] are replaced by P(OPh)3 to form the mono-or disubstituted products, Rh(L-L)(CO)[P(OPh)3] and Rh(L-L)[P(OPh)3]2 respectively depending on the [P(OPh)3]/[Rh] molar ratio, at room temperature and in air. Under argon at [P(OPh)3]/[Rh]4 theortho-metallated Rh1 complex Rh[P(OPh)3]3[P(OC6H4)-OPh)2] is formed. The new route forortho-metallated Rh1 complex synthesis is described.The Rh(AA)(CO)2 complex was used as a catalyst precursor in hydroformylation of olefins. 相似文献
955.
956.
Different methods for the determination of several metals in soils by flame atomic absorption spectrometry (FAAS) were investigated. Different procedures for total dissolution of soil: I – HF+HClO4, H3BO3, HCl digestion (conventional heating), II – HF+HClO4, H3BO3 digestion followed by fusion with LiBO2 (conventional heating) and III – HF+HCl+HNO3, H3BO3 digestion (microwave heating), as well as a leaching procedure with HNO3+HClO4, HCl were tested and compared. For quality assessment, the certified reference material S-1 soil was used. For most of the investigated metals, the best accuracy and precision were achieved when the procedure I or III were used. The developed procedure was applied to the analysis of soil samples from crude oil refinery and dump of petroleum origin wastes regions. 相似文献
957.
Reactions of hydrogen sulfates of quino‐ and diquino‐annelated 1,4‐dithiins 11 and 2 with DMF/hydroxylamine‐O‐sulfonic acid/Fe++ ion system took place at the α‐quinolinyl positions and led to N,N‐dimethylcarbamoyl and N‐methyl‐N‐formylaminomethyl derivatives 6 , 8 , 12 and 7 , 9 , 13 , respectively. The 1H and 13C NMR spectra of N‐methyl‐N‐formylaminomethyl derivatives 7 , 9 , 13 showed the presence of rotational isomers E and Z regarding to the N‐methyl‐N‐formylaminomethyl substituent. The spectra of 6 , 7 , 8 , 12 and 13 were completely assigned with the use of 1D and 2D NMR techniques. In the case of rotational isomers 7a and 7b , the crucial correlations came from the NOE interaction between the methylene and methyl protons from CH2N(CH3)CHO groups and benzene‐rings protons. Synthesis of 2,3‐dihydro‐1,4‐dithiino[6,5‐e]quinoline 4‐oxide 14 was presented as well. 相似文献
958.
Oxidation of 2-(2-hydroxyethyl)pyridine (pyeol) to 2-pyridylacetaldehyde (pyeal) by CrVI has been studied in the 0.5–2.0M HClO4 range at I=2.2M and in super acidic media within the 3–7M HClO4 range. In all cases the reaction has been examined under pseudo-first order conditions keeping the alcohol and H+
aq in excess. CrIII-complexes formed during reduction of CrVI by pyeol at different molar ratios of the reactants, were isolated chromatographically and identified as [Cr(H2O)6]3+ and [Cr(pyeac)(H2O)4]2+ ions (pyeac=2-pyridylacetic acid). Free 2-pyridylacetaldehyde (pyeal) was separated and determined as its 2,4-dinitro-phenylhydrazone derivative. A dependence of the rate constants on [pyeol] and [H+] has been established at I=1.2M and I=2.2M. The apparent activation parameters at [H+]=1 and 2M have been determined. A rate law of the form d[CrVI]/dt= (k
1[H
+]+k
2[H
+]2)[pyeol][CrVI] is proposed. A linear dependence of log k
obs on H0 in the super acidic media is obeyed. A rate decrease is observed if oxygen instead of argon is in the reaction cell. The reaction mechanism has been discussed. 相似文献
959.
Oxidation of 3-pyridinemethanol (3-pyol), 4-pyridinemethanol (4-pyol), 3-pyridinecarboxaldehyde (3-pyal) and 4-pyridinecarboxaldehyde (4-pyal) by CrVI was studied under pseudo-first-order conditions in the presence of a large excess of reductant and at various Haq
+ concentrations; [CrVI] = 8 × 10–4 M, [reductant] = 0.025–0.20 M, [HClO4] = 1.0 and 2.0 M (I = 1.2 and 2.1 M) or 0.5–2.0 (I = 2.1 M). A linear dependence of the pseudo-first-order rate constant (k
obs) on [reductant] and a parabolic function of k
obs
versus [H+] lead to the rate law: –d[CrVI]/dt = (a + b[H+]2)[reductant][CrVI], where a and b describe the reaction paths via HCrO4
– and H3CrO4
+ species respectively, and are composite values including rate constants and equilibrium constants. The apparent activation parameters were determined from second-order rate constants at 1.0 and 2.0 M HClO4, at three temperatures within the 293–323 K range. The presence of chromium species with intermediate oxidation states – CrV, CrIV and CrII, was deduced based on e.s.r. measurements and the kinetic effects of MnII or O2 (Ar), respectively. The alcohols were oxidized to the aldehydes, and carboxylic acids and the aldehydes to the carboxylic acids. Chromium(III) was in the form of the [Cr(H2O)6]3+ complex. 相似文献
960.
Ewa Pasgreta Ralph Puchta Michael Galle Nico van Eikema Hommes Achim Zahl Rudi van Eldik 《Journal of inclusion phenomena and macrocyclic chemistry》2007,58(1-2):81-88
Kinetic studies on Li+ exchange between the cryptands C222 and C221, and γ-butyrolactone as solvent were performed as a function of ligand-to-metal
ratio, temperature and pressure using 7Li NMR. The thermal rate and activation parameters are: C222: k
298 = (3.3 ± 0.8)×104 M−1 s−1, ΔH
# = 35 ± 1 kJ mol−1 and ΔS
# = −41 ± 3 J K−1 mol−1; C221: k
298 = 105 ± 32 M−1 s−1, ΔH
# = 48 ± 1 kJ mol−1 and ΔS
# = −45 ± 2 J K−1 mol−1. Temperature and pressure dependence measurements were performed in the presence of an excess of Li+. The influence of pressure on the exchange rate is insignificant for both ligands, such that the value of activation volume
is around zero within the experimental error limits. The activation parameters obtained in this study indicate that the exchange
of Li+ between solvated and chelated Li+ ions follows an associative interchange mechanism.
Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .
For Part I see: R. Puchta, M. Galle, N.J.R. van Hommes, E. Pasgreta and R. van Eldik: Inorg. Chem.
43, 8227 (2004). 相似文献