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61.
62.
《Electroanalysis》2005,17(22):2090-2094
A copper solid amalgam electrode was prepared and used for the voltammetric determination of atrazine in natural water samples by square wave voltammetry. This electrode is a convenient substitute for the hanging mercury electrode since it is selective, sensitive, reliable and inexpensive and presents low toxicity characteristic. The detection limit of atrazine obtained in pure water (laboratory samples) was shown to be lower than the maximum limit of residue established for natural water by the Brazilian Environmental Agency. The relative standard deviation for 10 different measurements was found to be only 3.98% in solutions containing 8.16×10?6 mol L?1 of atrazine. In polluted stream water samples, the recovery measurements were approximately 70.00%, sustaining the applicability of the proposed methodology to the analysis of atrazine in such matrices. 相似文献
63.
Breher F Rüegger H Mlakar M Rudolph M Deblon S Schönberg H Boulmaâz S Thomaier J Grützmacher H 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(3):641-653
The formation of adducts of the square-planar 16-electron complexes trans-[M(tropp(ph))(2)](+) and cis-[M(tropp(ph))(2)](+) (M=Rh, Ir; tropp(Ph)=5-diphenylphosphanyldibenzo[a,d]cycloheptene) with acetonitrile (acn) and Cl(-), and the redox chemistry of these complexes was investigated by various physical methods (NMR and UV-visible spectroscopy, square-wave voltammetry), in order to obtain some fundamental thermodynamic and kinetic data for these systems. A trans/cis isomerization cannot be detected for [M(tropp(ph))(2)](+) in non-coordinating solvents. However, both isomers are connected through equilibria of the type trans-[M(tropp(ph))(2)](+)+L<==>[ML(tropp(ph))(2)](n)<==>cis-[M(tropp(ph))(2)](+)+L, involving five-coordinate intermediates [ML(tropp(ph))(2)](n) (L=acn, n=+1; L=Cl(-), n=0). Values for K(d) (K(f)), that is, the dissociation (formation) equilibrium constant, and k(d) (k(f)), that is, the dissociation (formation) rate constant, were obtained. The formation reactions are fast, especially with the trans isomers (k(f)>1x10(5) m(-1) s(-1)). The reaction with the sterically more hindered cis isomers is at least one order of magnitude slower. The stability of the five-coordinate complexes [ML(tropp(ph))(2)](n) increases with Ir>Rh and Cl(-)>acn. The dissociation reaction has a pronounced influence on the square-wave (SW) voltammograms of trans/cis-[Ir(tropp(ph))(2)](+). With the help of the thermodynamic and kinetic data independently determined by other physical means, these reactions could be simulated and allowed the setting up of a reaction sequence. Examination of the data obtained showed that the trans/cis isomerization is a process with a low activation barrier for the four-coordinate 17-electron complexes [M(tropp(ph))(2)](0) and especially that a disproportionation reaction 2 trans/cis-[M(tropp(ph))(2)](0)-->[M(tropp(ph))(2)](+)+[M(tropp(ph))(2)](-) may be sufficiently fast to mask the true reactivity of the paramagnetic species, which are probably less reactive than their diamagnetic equilibrium partners. 相似文献
64.
镓(Ⅲ)-茜素氨羧络合剂在碳糊电极上的阳极吸附伏安法研究及应用 总被引:1,自引:0,他引:1
研究了镓(Ⅲ)-茜素氨羧络合剂(ALC)在碳糊电极上的阳极吸附伏安行为,并以此建立了一种高灵敏度、高选择性测定镓的吸附伏安法.在0.12 mol/L HAc-NaAc-0.24 mol/L邻苯二甲酸氢钾底液(pH 4.5)中,-0.10 V (vs.SCE) 富集90 s (或180 s),以250 mV/s扫速线性扫描至0.90 V, Ga3+-ALC在碳糊电极上产生灵敏的与ALC的峰电位相差近230 mV的吸附氧化峰,其二次导数峰电流与镓浓度在5.0×10-10~8.0×10-7 mol/L范围内呈线性关系;富集240 s检出限达3.0×10-10 mol/L(S/N=3).探讨了电极反应机理.该法用于粮食样品中镓的测定,结果满意. 相似文献
65.
Qijin Chi Wolfgang Göpel Tautgirdas Ruzgas Lo Gorton Peter Heiduschka 《Electroanalysis》1997,9(5):357-365
The electrochemical properties of carbon paste electrodes (CPEs), including unmodified and modified with protein and polycations, were investigated by impedance spectroscopy (IS) using ferricyanide and ferrocene monocarboxylic acid (FcMA) as redox probes. Various electrochemical pretreatments were applied to the unmodified CPE. The heterogeneous charge transfer rate constant of ferro/ferricyanide couple is enhanced by 2 to 10 times compared with that obtained at untreated electrodes. It was found that for ferricyanide the more suitable pretreatments are successive cyclic voltammetric scans, cathodization and a square wave-like stepping rather than high-potential anodization. However, the pretreatment only exhibits a slight effect on the kinetics of FcMA. At the CPEs containing modifier, the electron transfer rate of the redox couple depends more on the pH of electrolyte solution if ferro/ferricyanide is used. The results can be explained by the differently charged states of the CPEs that were caused by the protonation or deprotonation of the modifiers in various pH solutions and demonstrate the importance of the electrostatic interaction on the kinetics of the highly polar species such as ferricyanide. The different adsorptive behavior of ferricyanide and FcMA is also discussed. 相似文献
66.
《Electroanalysis》2005,17(20):1861-1864
Electrochemical study of barley grain lipid‐transfer protein (LTP) revealed that it may belong to the metal‐binding protein class. Using differential pulse polarography the presence of Cu(II) and Zn(II) ions in the native LTP structure was proved, as well as its affinity for binding Ni(II) ion. Application of a more sensitive electroanalytical technique, such as anodic stripping voltammetry with analyte preconcentration, revealed the presence of Pb(II) and Cd(II) ions and also enabled the following Hg(II) ion binding. Possible biological role of LTP in plant stress response and its contribution to barley phytoextraction potential are discussed. 相似文献
67.
Díaz MC Illescas BM Martín N Viruela R Viruela PM Ortí E Brede O Zilbermann I Guldi DM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(8):2067-2077
A new class of pi-extended TTF-type electron donors (11 a-c) has been synthesized by Wittig-Horner olefination of bianthrone (9) with 1,3-dithiole phosphonate esters (10 a-c). In cyclic voltammetry experiments, donors 11 a-c reveal a single, electrochemically irreversible oxidation-yielding the corresponding dicationic products-at relatively low oxidation potentials (approximately 0.7-0.8 V). Theoretical calculations, performed at the DFT level (B3 P86/6-31 G*), predict a highly-folded C(2h) structure for 11 a. In the ground state, the molecule adopts a double saddle-like conformation to compensate the steric hindrance. The calculations suggest that the intramolecular charge transfer associated with the HOMO-->LUMO transition is responsible for an absorption band observed above 400 nm. While the radical cation 11 a*+ retains the folded C(2h) structure predicted for the neutral molecule as the most stable conformation, the dication 11 a(2+) has a fully aromatic D(2) structure, formed by an orthogonal 9,9'-bianthryl central unit to which two singly-charged dithiole rings are attached. The drastic conformational changes that compounds 11 undergo upon oxidation account for their electrochemical properties. By means of pulse radiolysis measurements, radical-induced one-electron oxidation of 11 a-c was shown to lead to the radical cation species (11 a-c*+), which were found to disproportionate with generation of the respective dication species (11 a-c(2+)) and the neutral molecules (11 a-c). 相似文献
68.
69.
《Electroanalysis》2006,18(18):1786-1792
Electrochemical detection of quercetin has been carried out on glassy carbon electrodes modified with carbon nanotubes and Nafion (GC/Nafion‐CNT). GC/Nafion‐CNT electrodes did not show passivation effect that occurs on the unmodified electrodes and displayed better stability and reproducibility. Quercetin oxidation was most favorable in acidic conditions and current gradually decreased as the solution pH increased. No oxidation was observed when two ? OH groups in a catechol moiety were fully deprotonated. These electrodes enabled selective determination of quercetin in the presence of interfering species such as ascorbic acid, uric acid, glucose, and catechol in large excess. Quantification of quercetin in a yellow onion has been made and favorably compared with reported values. Good selectivity and high sensitivity obtained by Osteryoung sSquare‐wave voltammetry can open new possibilities of direct quercetin determination in vegetables with a minimal sample treatment. 相似文献
70.
《Electroanalysis》2006,18(21):2115-2120
A new type of voltammetric sensor, Langmuir–Blodgett film of p‐tert‐butylthiacalix[4]arene modified glassy carbon electrode, was advanced and used for determining copper at trace levels by differential pulse stripping voltammetry. Calibration plot was found to be linear in the range of 2×10?8 M to 5×10?6 M; the detection limit was 2×10?9 M. Possible recognition mechanism was also discussed. From determination of Copper in real samples (river, lake and tap water) it can be concluded that the method is rapid, sensitive in determining of copper and can be used in the analysis of natural water samples. 相似文献