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991.
An analytical method for the determination of US EPA priority pollutant 16 polycyclic aromatic hydrocarbons (PAHs) in edible oil was developed by an isotope dilution gas chromatography–mass spectrometry (GC–MS). Extraction was performed with ultrasonication mode using acetonitrile as solvent, and subsequent clean-up was applied using narrow gel permeation chromatographic column. Three deuterated PAHs surrogate standards were used as internal standards for quantification and analytical quality control. The limits of quantification (LOQs) were globally below 0.5 ng/g, the recoveries were in the range of 81–96%, and the relative standard deviations (RSDs) were lower than 20%. Further trueness assessment of the method was also verified through participation in international cocoa butter proficiency test (T0638) organised by the FAPAS with excellent results in 2008. The results obtained with the described method were satisfying (z ≤ 2). The method has been applied to determine PAH in real edible oil samples. 相似文献
992.
993.
Pamornrat Kueseng Chongdee Thammakhet Panote Thavarungkul Proespichaya Kanatharana 《Microchemical Journal》2010,96(2):317-323
A new cost-effective sorbent, multiwalled carbon nanotubes/poly (vinyl alcohol) cryogel composite (MWCNTs/PVA), was prepared under frozen conditions for the extraction and preconcentration of trace polycyclic aromatic hydrocarbons (PAHs) in water samples. This was followed by high performance liquid chromatography (HPLC) with fluorescence detection. The proposed method provided a high enrichment factor with an extremely high extraction efficiency (89–98%) of three spiked levels of three standard PAHs with relative standard deviations of less than 8%. The low detection limits of the method were 5, 8 and 5 ng L− 1 for benzo(a)anthracene, benzo(b)fluoranthene and benzo(a)pyrene, respectively. This method was successfully applied for the determination of the three PAHs in real water samples where they were found in the range of 7 to 22 ng L− 1. The major advantages of MWCNTs/PVA over the commercial C18 is that it can be operated at a higher loading flow rate without sorbent clogging and requires a shorter time for completion without any loss of extraction efficiency. 相似文献
994.
Siegbert Rummel Michael Herrmann Manfred Wahren Safar M. Yunusov Margarita A. Ilatovskaya Yuri B. Isaev 《Isotopes in environmental and health studies》2013,49(3):391-392
Potassium graphite intercalation compounds are able to activate C–H bonds of hydrocarbons at room temperature. In this paper, the hydrogen–deuterium exchange of CHD3 in the presence of C8K, C24K and C36K is described. 相似文献
995.
The weakest bound potential method was proposed to estimate the ionization potential (IP) of polyhalogenated methanes, that is, the model IP = aχve + bPEIfi + c was developed, in which χve is molecular electronegativity calculated by valence electrons equilibration method, and polarizability effect index (PEI)fi is the influence of polarizability effect. The result indicates that the model is reasonable and effective to predict the IP for polyhalogenated methanes. Besides, the quantum chemistry method, the MOPAC AM1 method, and the density functional theory (B3LYP) method were employed to calculate the IP values of the same polyhalogenated methanes, and those results were less than that of the weakest bound potential method. Furthermore, the experimental values of 67 polyhalogenated hydrocarbons were correlated with the parameters χve and PEIfi. The regression results show a good correlation (R = 0.988), and the average absolute error between the experimental values and the calculated values is only 0.10 eV. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
996.
997.
Summary A molecular-statistical calculation of the retention volumes at zero sample size on graphitized thermal carbon black is carried out for quasi-rigid molecules of fluorene, indene, 1-methylindene, 2-methylindene and three dimethylindenes. A reasonable agreement is observed between the calculated and the available experimental gas chromatographic data. The potential barrier to internal rotation and the torsional angle in styrene molecules are estimated by comparing theoretically calculated and measured retention volumes. 相似文献
998.
K. Günther D. Schlosser H. -P. Schmauder U. Rausch 《Applied biochemistry and biotechnology》1994,48(1):11-14
Contaminated groundwater from industrial areas in former East Germany was biologically treated using lab-scale solid-state
reactors. The ability of bacterial strains of the autochroneous microflora to utilize representative pollutants was tested. 相似文献
999.
B. A. Dolgoplosk V. A. Vakovlev E. I. Tinyakova S. B. Gol'shtein G. N. Bondarenko 《Russian Chemical Bulletin》1996,45(6):1316-1320
The conversions of cyclohexene and 1,3- and 1,4-cyclohexadiencs treated with neodymium metal under the conditions of mechanochemical activation at 20 °C have been studied. A complicated cycle of conversions, including isomerization, disproportionation, and polymerization, occurs under the reaction conditions. A mechanism for the conversion of the hydrocarbons involving organornetallic intermediates is proposed.The conversion of hexane under the conditions used for the reactions with cyclohexene and cyclohexadienes varies only slightly, which makes it possible to use hexane as the internal standard.Deceased.Translated fromlzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1386–1390, June, 1996. 相似文献
1000.
A general theory which points out the relations between Hückel-electron energy, the number of Kekulé structures and the HOMO-LUMO separation is presented. Some normalized topological invariants are derived from the concept of the spectral density function. A reasonably simple (three parameters) model spectral density function leads to universal relations between topological invariants that, although valid for any alternant molecule, were tested numerically for polycyclic benzenoid hydrocarbons. Some general conclusions concerning a distribution of the adjacency matrix eigenvalues are drawn. 相似文献