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991.
Characterisation of fatty acids in biological oil samples using comprehensive multidimensional gas chromatography 总被引:1,自引:0,他引:1
Comprehensive multidimensional gas chromatography can adequately resolve very complex mixtures of analytes such as the fatty acid mixtures which are contained in, e.g., fish and vegetable oils. Well-ordered patterns are obtained in the two-dimensional separation plane which can be used to tentatively identify peaks when no standard is available. The technique which can also be used for quantification, i.e., quantitative ratio analysis, should be especially useful for fingerprinting purposes. Unravelling the composition of complex mixtures such as fish oils appears to be highly rewarding. 相似文献
992.
[reaction: see text] Photochemically generated nitrate radicals (NO(3)(*)) cleave the stereoisomeric N,N-dimethyl-substituted uracil cyclobutane dimers 1a-d into the monomeric uracil derivative 2 as the major reaction pathway. A preferred splitting of the syn dimers 1a,b was observed. The reaction is expected to proceed through initial one-electron oxidation with formation of an intermediate cyclobutane radical cation 11. In addition to cycloreversion, competing reaction steps of 11, which lead to the observed byproducts, are suggested. 相似文献
993.
Various types of sodium cellulose sulfate (SCS), dissolved in a 1M LiCl solution, were investigated by alternating current (AC)polarography. The SCS samples differed in the degree of substitution (DS), thedistribution of substituents within the anhydroglucose unit (AGU), and alongthechain, due to the method of synthesis. The goal was to study theelectrosorptionbehavior, characterized by the shape of the desorption wave in the polarogram,as a function of the chemical structure of the SCS samples. The shape of thedesorption wave reflects domains of different substitution. A superimpositionofparameters like DS and pattern of substitution on the electrosorption behaviorwas observed. The AC polarography method described can be used as a tool todistinguish between an even or uneven distribution of substituents along thecellulose chain. 相似文献
994.
A mathematical method for the calculation of the dead time (tm) in HPLC was evaluated using a computer simulation approach, in which artificial perturbations were introduced to Simulated homolog retention times. The calculation was based on a modified and extended Grobler and Bálisz (GB) method. Investigated wav how the precision of the calculated tM is affected by: statistical fluctuations in retention times and which, and how many homolog retention times are used. Based on these simulations a two-step procedure for the tM calculation is proposed: In the first step the linearity of log tR, n vs carbon number n is checked using as many homolog retention times as possible. The slope value bo of the first linear regression in the GB method is used for the selection of homolog retention times in the final tM calculation. In the second step the optimal selection of homologs is made and the final tM calculation is carried out. Guidelines for homolog selection are given. 相似文献
995.
R.J. Van De Nesse G.Ph. Hoornweg C. Gooijer U.A.Th. Brinkman N.H. Velthorst 《Analytica chimica acta》1989
Laser-induced fluorescence (LIF) detection in conventional-size column liquid chromatography is achieved at 257 nm with a frequency-doubled argon-ion laser. Short-wavelength excitation offers two important advantages: firstly, a wide variety of analytes can be excited, and secondly, the Raman scatter of the eluent does not interfere with the fluorescence of the analytes. A standard mixture of polynuclear aromatic hydrocarbons was studied, both with LIF detection and with a commercially available sensitive conventional fluorescence detector. The improvement in the detection limits ranges from about a factory of 4 to 30; the LIF detection limits are typically at the 50 ng l?1 level, which corresponds to an injected amount of 0.5 pg. 相似文献
996.
Inhaltsübersicht. Edukte von Typ M(CO)6 (M = Cr, Mo,W), N,N'-Bis(diphenylphosphino)-2,6-diaminopyridin (PNP) und Trimethylaminoxid setzen sich bei Raumtemperatur nicht zu dem bekannten Verbindungstyp mer-M(CO)3PNP, sondern zu Verbindungen der beiden Typen M(CO)4(PNP=O) mit zweizähnig koordinierten Liganden PNP=O und M(CO)5(NMe3) um. Die zu Vergleichszwecken untersuchte Oxidation eines koordinierten PNP-Liganden von mer-Mo(CO)3(PNP) in Tetramethylbenzollösung ergibt mit Luftsauerstoff bei 180°C eine Reaktion unter Spaltung der P–N-Bindung zur cubanartigen Verbindung Mo4(μ3-O)4(μ-Ph2PO2)4O4 (Ausbeute 48%). In einem Glaseinschlußrohr reagiert der ambidente N,N-Bis(diphenyIphosphino)-2-nminopyridin-Ligand (NPP) mit den Hexacarbonylen M(CO)6 in Toluollösung bei 140°C zu Verbindungen des Typs M(CO)4(NPP) mit zweizähniger Verknüpfung des NPP-Liganden. Hierbei bilden die beiden P-Donoratome am Aminstickstoffatom einen MP2N-Chelatvierring an Stelle des ebenfalls möglichen P, Npy-Chelatfünfrings. Der analoge Chelatvierring entsteht gleichfalls bei einer Ligandensubstitutions-reaktion zwischen Verbindungen des Zweikernkomplextyps MM′(CO)8(μ-PPh2)2 (M = M′ = W; M = Mo, M′ = W) bzw. \V(CO)4(μ-PPh2)2IrH(CO)(PPh3) und NPP. Er bildet sich außerdem bei der Thermolyse von Mo(CO)4(NPP) zu Mo2(CO)6(μ-PPh2)2(NPP). Die Identifizierung erfolgt im Falle der Verbindungen Mo(CO)4(PNP=O), Mo4(μ3-O)4(μ-Ph2PO2)4O4′ Mo2(CO)6(μ-PPh2)2(NPP) und W(CO)4(μ-PPh2)2IrH(CO)(NPP) durch Einkristall-Röntgenstrukturanalysen. Alle isolierten Produkte werden durch spektroskopische Messungen insbesondere 31P-NMR-Daten charakterisiert. Characterization of Properties of the Rigid Tridentate Chelate Ligand N,N′-Bis(diphenylphosphino)-2,6-diaminopyridine and N,N-Bis(diphenylphosphino)-2-aminopyridine with Transition Metals of the Chromium Group Hexacarbonyls M(CO)6 (M = Cr, Mo, W), N,N′-Bis(diphenylphosphino)-2,6-diaminopyridine (PNP) and trimethylamine oxide gave products of two types M(CO)4(PNP=O) having a bidentate ligand PNP=O and M(CO)5(NMe3) instead of the desired mer-M(CO)3PNP. For the purpose of a comparison, aerial oxidation of mer-Mo(CO)3PNP in tetramethyl benzene solution at 180°C was examined which resulted a P–N bond rupture under formation of the cubane-like product Mo4(μ3-O)4(μ-Ph2PO2C4O4){yield 48%). In sealed glass tubes the ambidentate ligand N,N-bis(diphenylphosphino)-2-aminopyridine (NPP) was reacted with the hexacarbonyls M(CO)6 in toluene solution at 140°C to products of the type M(CO)4NPP with NPP as bidentate ligand. Under this reaction conditions the four-membered chelate ring of the type MP2N was formed with the two P donor atoms attached to the amine N atom instead of the possible competitive five-membered chelate ring formation with a P and pyridyl nitrogen. The analogous four-membered chelate ring was formed in ligand substitution reactions between the substance NPP and each of the dinuclear coordination compounds MM′(CO)8(μ-PPh2)2 (M = M′ = W, M = Mo, M′ = W) including W(CO)4(μ-PPh2)2IrH(CO)(PPh3); Mo2(CO)6(μ-PPh2)2(NPP) was obtained via thermolysis of Mo(CO)4(PNP=O). The given structural identification of the compounds Mo(CO)4(PNP=O), Mo4(μ3-O)4(μ-Ph2PO2)4O4, Mo2(CO)6 (μ-PPh2)2(NPP) and W(CO)4(μ-PPh2)2IrH(CO) (NPP) was done by single-crystal X-ray analysis. All seperated products have been characterized by means of spectroscopic measurements especially 31P n.m.r. data. 相似文献
997.
The simultaneous determination of trace elements in animal organs offers improved possibilities to characterize the geographical origin of the animal by analyzing its pollution characteristics. Pb, Cd, Ni (GF-AAS) and Cu, Zn, Fe, Mn (F-AAS) in kidneys and livers of cows from different sites have been measured using simultaneous AAS. The correct allocation of cows to specific regions shows that multivariate data analysis provides efficient tools for the geographical classification. The consideration of absorbance rather than concentration as the data input simplified the analytical procedures by omitting the calibration step. 相似文献
998.
Summary The thermal decomposition of [CoCl2(-pic)2] was investigated over the 108°C to 222°C range and the Intennediates CoCl2(-pic) (s) and CoCl2 (s) were observed, with the evolution of (-pic) (g). Quantitative thermodynamic and kinetic data were obtained by performing dynamic and isothermal studies on the complex Additional thermodynamic data were obtained by studying the CoCl2/-pic system in acetone. The effect of the methylsubstituent on the metal-donor-N bond as well as on the thermodynamic quantities were discussed. 相似文献
999.
The weakly absorbed 1.2-μ combination band of water was accurately studied as a function of temperature, in both its profile and first derivative, to obtain information on the bulk properties of liquid water. Arrhenius plots of integrated component intensity ratios showed well aligned experimental points, except for a neatly defined break occurring in the 30 to 40°C temperature interval for pure water A similar break, shifted by some 18°C towards lower temperature, was found in the case of 1M NaClO4 aqueous solutions. The breaks are tentatively assumed to result from abrupt though subtle changes involving low-frequency modes. This tentative, assumption appears independent of specific models and assignments and, although in agreement with available neutron-scattering and NMR data, needs more direct verification. 相似文献
1000.
I. Trapp T. Famulok U. Risse A. Kettrup 《Fresenius' Journal of Analytical Chemistry》1998,362(4):409-414
Due to the complex composition of metal working fluids (MWF) the determination of all individual compounds is sometimes difficult
and very expensive. Today the widely used method for the quantification of airborne MWFs consists of a non specific IR analysis
of their C-H valence bands. With a new design of sample cell this inexpensive technique was extended to a more detailed screening
of the MWF composition, especially the detection of carbonyl compounds in MWFs and their aerosols and vapors. The screening
method was evaluated for the determination of concentrations of the aldehyde nonanal and the ketone diacetone alcohol in air
in laboratory experiments. In preliminary workplace studies the applicability of this method to the (semi-)quantitative determination
of carbonyl compounds in airborne MWFs is shown. The screening method was found to be very useful, specially to detect alterations
in the composition of the MWF due to industrial use.
Received: 16 January 1997 / Revised: 9 April 1998 / Accepted: 14 April 1998 相似文献