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971.
Martínez Vidal JL Moreno Frías M Garrido Frenich A Olea-Serrano F Olea N 《Rapid communications in mass spectrometry : RCM》2000,14(11):939-946
Endosufan, alpha and beta, and three conversion products, sulphate, ether and lactone, were simultaneously determined in human serum by means of an analytical procedure which combines extraction with organic solvents, clean-up with H(2)SO(4) and by liquid column chromatography, and detection by gas chromatography (GC) using electron capture detection (ECD) and tandem mass spectrometry (MS/MS). The procedure was validated and the values of some merit figures, such as linear range, detection and quantitation limits, accuracy, precision and recovery, obtained with the GC/ECD and the GC/MS/MS methods, were compared. The lower limits of detection in GC/ECD and GC/MS/MS were 0.03 and 0.05 microg I(-1), respectively. The recovery of the pesticides at the 20 microg I(-1) concentration level was 60-65%, with the exception of endosufan alpha. Recovery studies at higher levels (100 and 200 microg I(-1)) were independent of pesticide concentration in serum samples. The application of the proposed analytical methodology to the determination of endosulfans and their metabolites in real samples was tested by analyzing serum samples from a population living in agricultural areas of Almeria (Spain). The results show the advantage of MS/MS over the ECD detector in the analysis of serum samples where matrix interferences can be confused with target pesticides. 相似文献
972.
The absorbance of the microcolloidal zirconium/alizarin red S/polyvinylpyrrolidone complex is measured at 525 nm in acetate buffered medium at pH 4.75. The molar absorptivity is 3.8 × 104 l mol?1 cm?1, which is much greater than that of the classical method. Sulphate and fluoride do not interfere. 相似文献
973.
The lithiation of 2,7-dihydrodinaphthoheteroepines (5) with 2.2 equiv of lithium naphthalenide in THF at −78 °C gives dianionic intermediates 8, which by reaction with different electrophiles [H2O, D2O, tBuCHO, Me2CO, Et2CO, (CH2)4CO, (CH2)5CO] at the same temperature, followed by hydrolysis, leads to unsymmetrically 2,2′-disubstituted binaphthyls 6. When the lithiation is performed with an excess of lithium in the presence of a catalytic amount of 4,4′-di-tert-butylbiphenyl (DTBB, 10 mol %), a double reductive cleavage takes place to give dianionic intermediate 9, which by reaction with different electrophiles [H2O, Me2CO, Et2CO, (CH2)4CO, (CH2)5CO], followed by hydrolysis with water, yields symmetrically 2,2′-disubstituted binaphthyls 7. In the case of starting from (R)-5a, the reductive opening by treatment with 2.2 equiv of lithium naphthalenide followed by reaction with H2O or (CH2)5CO as electrophiles and final hydrolysis, leads to enantiomerically pure compounds (R)-6aa and (R)-6af, respectively. 相似文献
974.
Optimisation of headspace solid-phase microextraction for the analysis of volatile phenols in wine 总被引:1,自引:0,他引:1
Castro Mejías R Natera Marín R García Moreno Mde V García Barroso C 《Journal of chromatography. A》2003,995(1-2):11-20
Headspace solid-phase microextraction has been applied to the analysis of volatile phenols in wine. Silica fibre coated with Carbowax-divinylbenzene was found to be more efficient at extracting these compounds than other fibres such as those coated with polydimethylsiloxane, polyacrylate, carboxen-polydimethylsiloxane, and polydimethylsiloxane-divinylbenzene. Different parameters such as extraction time, temperature of the sample during the extraction, ionic strength and sample volume were optimised using a two-level factorial design expanded further to a central composite design, in order to evaluate several possibly influential and/or interacting factors. The headspace (HS)-SPME procedure developed shows adequate detection and quantitation limits, and linear ranges for correctly analysing these compounds in wine. The recoveries obtained were close to 100%, with repeatability values lower than 16%. The method was applied to a variety of white and red wines. 相似文献
975.
Haematoporphyrin derivative (Photofrin II) photosensitization of isolated mitochondria: inhibition of ADP/ATP translocator 总被引:3,自引:0,他引:3
A Atlante S Passarella E Quagliariello G Moreno C Salet 《Journal of photochemistry and photobiology. B, Biology》1989,4(1):35-46
To gain further insight into the mechanism by which irradiation of mitochondria in the presence of haematoporphyrin derivative (Photofrin II) (PF II) causes impairment of mitochondrial oxidative phosphorylation, the rate of ADP/ATP exchange via the ADP/ATP translocator was measured fluorometrically is isolated rat liver mitochondria. In accord with noncompetitive inhibition, PF II photosensitization decreases the maximum rate of exchange Vmax (20.8 and 9.6 nmol ATP effluxed min-1 x mg protein in the control and after 2 min irradiation, respectively) without changing the ADP affinity for the carrier (Km = 5 microM in both cases). Comparison of the rate of oxygen uptake by mitochondria stimulated by either ADP or by the uncoupler carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone (FCCP) confirms that the adenine nucleotide carrier is a major target of photodynamic action which causes oxidative phosphorylation impairment. 相似文献
976.
del Nogal Sánchez M Pérez Pavón JL Fernández Laespada ME García Pinto C Moreno Cordero B 《Analytical and bioanalytical chemistry》2005,382(2):372-380
One of the main limitations to the use of direct coupling of headspace mass spectrometry (HS-MS) for the quantitative determination of analytes in a sample is related to factors affecting the signal intensity. The importance of strategies aimed at compensating this problem is considerable in the case of classification, and is indeed critical as regards the problems involved in quantification. This paper reports the effects of the different factors affecting HS-MS signal intensity in the quantification of the pollution of beach sands by hydrocarbons—the matrix effect, signal instability over time and nature of the different pollutants present in the polluted sands—and proposes possible solutions. Signal instability was solved by using a multiplicative calibration transfer algorithm. A three-factor Box–Behnken experimental design was used to study the matrix effect, mainly as regards the moisture of the samples, and the results are discussed. 相似文献
977.
R. Valiente F. Rodríguez J. A. Aramburu M. Moreno M. T. Barriuso C. Sousa C. de Graaf 《International journal of quantum chemistry》2002,86(2):239-244
The variations experienced by the energy Eu(π) of the eu(π)→b1g (~x2–y2) charge‐transfer transition of (C2H5NH3)2CdCl4:Cu2+ upon pressure in the 0‐ to 40‐kbar range have been measured at room temperature by means of a sapphire anvil cell. These data reveal that Eu(π) undergoes a red shift of 1400 cm?1 on passing from ambient pressure to 40 kbars. To understand this puzzling result theoretical calculations of ?Eu(π)/?Req and ?Eu(π)/?Rax have been performed where Req and Rax mean the equatorial and axial Cu2+–Cl? distances of the elongated CuCl64? complex, respectively. All results indicate that ?Eu(π)/?Req and ?Eu(π)/?Rax for Req=228 pm and Rax=297 pm are indeed negative. Moreover ab initio complete active space self‐consistent field (CASSCF/CASPT2) and density functional calculations lead to ?Eu(π)/?Rax values, which are about 10 times smaller than those of ?Eu(π)/?Req. From the ensemble of experimental and theoretical results, it is concluded that a pressure of 40 kbars gives rise to a decrement of ≈25 pm of the axial distance and at the same time to an increase of ≈7 pm of the equatorial one. It is stressed that the present study on a diluted Jahn–Teller impurity lies far beyond the current possibilities of X‐ray absorption structure techniques. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001 相似文献
978.
R. Castro M. V. G. Moreno R. Natera F. García-Rowe M. J. Hernández C. G. Barroso 《Chromatographia》2002,56(1-2):57-61
Summary Ion-exclusion chromatography (IEC) and capillary electrophoresis (CE) have been compared for determination of organic acids
in samples of Sherry wine vinegar. The accuracy of each technique was evaluated by use of the standard addition method. There
were no differences between the techniques at a significance level of 5%, except for determination of malic acid by CE. Both
analytical methods were used to analyse sixteen samples of Sherry wine vinegar supplied by different producers. The regression
coefficients (r
2) for analysis by IEC and CE exceeded 0.94 for all acids. Results from both methods were in good agreement and the methods
are sufficiently selective and sensitive to be applied directly to sherry wine vinegars. 相似文献
979.
The reaction of (NBu(4))(2)[Pt(C triple bond CPh)(4)] with Cd(ClO(4))(2).6H(2)O in a 1:1 molar ratio yields a white solid [PtCd(C triple bond CPh)(4)](n) 1 (75% yield) together with yellow crystals of a very unusual decanuclear platinum-cadmium cluster [Pt(4)Cd(6)(C triple bond CPh)(4)(mu-C triple bond CPh)(12)(mu(3)-OH)(4)] 2 in low yield. Slow diffusion of acetonic solutions of the starting materials under aerobic conditions only produces crystals of 2 which have been shown by an X-ray analysis to be composed of a big hexanuclear cation [Cd(6)(mu(3)-OH)(4)](8+) and four [Pt(C triple bond CPh)(4)](2-) anions, held together by Pt.Cd and pi.Cd acetylide interactions. On the other hand, treatment of the insoluble product 1 with 1 equiv of NBu(4)X yields tetranuclear mixed-metal soluble complexes (NBu(4))(2)[[Pt(mu-C triple bond CPh)(4)](2)(CdX)(2)] (X = Cl A, Br 3, CN 4), which contain two platinate fragments connected by two CdX units through Pt.Cd and mainly Cd.C(alpha) interactions. All complexes are strongly emissive in the solid state at room temperature. 相似文献
980.
Jalón FA Manzano BR Caballero A Carrión MC Santos L Espino G Moreno M 《Journal of the American Chemical Society》2005,127(44):15364-15365
The use of the phosphine PPh2py instead of PPh3 in complexes of the type [Cp*RuH(P)2] enormously alters the kinetic control of the proton-transfer reactions over this compound and its chemical behavior. The reaction at low temperature of [Cp*RuH(PPh2py)2], 2, with HBF4 gives as products the classical dihydride trans-[Cp*RuH2(PPh2py)2](BF4), 3 (1 equiv of HBF4) or the dihydrogen-bonded complex [Cp*RuHH(PPh2pyH)(PPh2py)](BF4)2, 4 (2 equiv of HBF4). These complexes exhibit very accessible intramolecular processes of proton transfer, and finally, a slow release of H2 takes place at room temperature. Derivatives 2 and 3 are active catalysts for the deuterium labeling of H2 using methanol-d4 as an isotopic source. This demonstrates that the release of hydrogen is reversible, that the heterolytic activation of H2 is an easy process, and that acid species participate in the intramolecular proton-transfer processes. These observations are supported by reaction-coordinate calculations at the DFT/B3LYP level that show the existence of a low-energy reaction path that easily transforms the classical trans dihydride complex into the nonclassical cis dihydrogen compound in a reversible way, through the involvement of hydrogen- and dihydrogen-bonded intermediates and the essential participation of the pyridine centers. The different energy minima of this reaction profile are very accessible through low-energy transition states, all of which have been located. 相似文献