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971.
C. Oliveira J. Salgado F. G. Carvalho 《Journal of Radioanalytical and Nuclear Chemistry》1997,216(2):191-198
A simulation study of a PGNAA measuring arrangement with a252Cf neutron source for the characterization of cement raw materials was carried out using the MCNP code to investigate the effect on the system response of varying the bulk density and the water contentv
w of samples of fixed dry composition. The source is placed at the centre of a lead cylinder of extemal radiusR
Pb. This cylinder is enclosed in a coaxial cylinder of polyethylene moderator of extermal radiusR
in. The sample material is confined to the space between an outer cylindrical surface of radiusR
out and the moderator cylinder. The first series of simulation runs was carried out for different sets of values ofR
in,R
out and , and constantv
w. The system specific responseS (count rate per wt%) shows a broad maximum aroundT
M=R
in-R
Pb=4 cm andT
S=R
out-R
in=8.5 cm and a dependence on that is almost linear in the region of the maximum. In a second series of runs the dependence ofS onv
w was studied for a geometry corresponding to a real experiment described elsewhere and for a geometry for which the density saturation effect is already apparent. It is shown that when the sensitivity of the system is optimized both andv
w must be used as calibration parameters while in the low-sensitivity design regionv
w can be used as the only calibration parameter. 相似文献
972.
The separation and detection of common mono- and disaccharides by capillary electrophoresis (CE) with contactless conductivity detection (CCD) is presented. At high values of pH, the sugars are converted to anionic species that can be separated by CE and indirectly detected by CCD. The main anionic species present in the running electrolytes are hydroxide and phosphate, which have greater mobility than the ionized sugars, and, thus, the indirect detection is possible. The method was applied to analysis of glucose, fructose, and sucrose in soft drinks, isotonic beverages, fruit juice, and sugarcane spirits. Galactose was used as internal standard in all cases. Plate numbers range from ca. 70,700 to 168,200 and the limits of detection from 13 to 31 microM. 相似文献
973.
D. Bohrer P. C. do Nascimento S. Garcia Pomblum E. Seibert L. Machado de Carvalho 《Analytical and bioanalytical chemistry》1998,361(8):780-783
A method for the determination of cyanide in blood plasma by differential pulse polarography (DPP) is described without a drastic acidification of the sample. Cyanide was determined as tetracyanonickelate(II)-anion complex after a microwave-acid assisted cleanup and a selective complex extraction in a polyethylene methylene blue (PE-MB) impregnated column. The cyano complex was eluted from the column with water/acetonitrile and determined by pulse-polarography at –380 mV (Ag/AgCl). The linear range of calibration was obtained from 1.2 to 9.6 μg of cyanide with r = 0.99 and RSD = 9% of 1.2 μg of cyanide. A detection limit of 40 μg L–1 was calculated and the recoveries of cyanide from spiked samples were about 80%. This method was compared with the classical pyridine-pyrazolone method. 相似文献
974.
D. Bohrer P. C. do Nascimento S. Garcia Pomblum E. Seibert L. Machado de Carvalho 《Fresenius' Journal of Analytical Chemistry》1998,361(8):780-783
A method for the determination of cyanide in blood plasma by differential pulse polarography (DPP) is described without a
drastic acidification of the sample. Cyanide was determined as tetracyanonickelate(II)-anion complex after a microwave-acid
assisted cleanup and a selective complex extraction in a polyethylene methylene blue (PE-MB) impregnated column. The cyano
complex was eluted from the column with water/acetonitrile and determined by pulse-polarography at –380 mV (Ag/AgCl). The
linear range of calibration was obtained from 1.2 to 9.6 μg of cyanide with r = 0.99 and RSD = 9% of 1.2 μg of cyanide. A
detection limit of 40 μg L–1 was calculated and the recoveries of cyanide from spiked samples were about 80%. This method was compared with the classical
pyridine-pyrazolone method.
Received: 3 September 1997 / Revised: 21 January 1998 / Accepted: 24 January 1998 相似文献
975.
E. A. Oliveira M. P. C. Silva Z. M. B. Flgueiredo L. B. Carvalho 《Applied biochemistry and biotechnology》1989,22(1):109-114
Dacron (polyethylenetherephthalate) in the form of plates if proposed as a maxtrix to immobilized proteins. A three-step procedure is used to activate this support and to fix the protein on it. Amyloglucosidase was used as a model to test this method, and it showed advantages compared to the powder form of Dacron. 相似文献
976.
J. J. C. Teixeira-Dias R. Fausto L. A. E. Batista de Carvalho 《Journal of computational chemistry》1991,12(9):1047-1057
The Cα? C internal rotation in 2-methylpropionic, 2-methylthiopropionic (thiol and thion forms) and 2-methyldithiopropionic acids was studied by the ab initio SCF-MO method using 3-21G and 3-21G + d(0.65S) basis sets. Energies and structures of several conformations of these molecules, determined by gradient geometry refinement, are reported and used to assess the effects of oxygen-by-sulphur substitution on molecular properties. The nature and relative importance of intramolecular interactions involving both the α-methyl substituents and the C(?X)Y (X, Y? O or S) fragment are also discussed. 相似文献
977.
do Nascimento PC Bohrer D Rohlfes AL de Carvalho LM Ramirez A 《Fresenius' Journal of Analytical Chemistry》2001,370(1):92-96
A method has been developed for the chromatographic determination of methanethiol (MT) and ethanethiol (ET) as contaminants in amino acid parenteral nutrition (PN) solutions. The clean-up of the samples before chromatographic analysis was investigated by solid-phase extraction (SPE) on pre-columns filled with polyethylene powder (PE), aluminium oxide (AlOx), silica (SiOx), or polyurethane foam (PUF) as adsorbents. The thiols were more efficiently separated from the matrices by SPE on PUF pre-columns. Simultaneous derivatization and elution with DTNB (5,5'-dithiobis(2-nitrobenzoic acid)) enabled further discrimination between MT and ET by reversed-phase HPLC with spectrophotometric detection. The retention times for the derivatized MT and ET species were 12.5 and 23.0 min, respectively. Recoveries from spiked PN samples were calculated to be approximately 90%, and the MT and ET content of commercial PN solutions was determined using the methodology described. Detection limits of 15 and 10 microg L(-1) were calculated for MT and ET, respectively. 相似文献
978.
Ruben Dario Sinisterra Renata Vicentini Mielli Carlos Alberto Alves de Carvalho Wendel Gomes da Silva Antonio Salvio Mangrich Ana Maria da Costa Ferreira 《Journal of inclusion phenomena and macrocyclic chemistry》1999,33(2):203-216
The compound formed by the copper-Schiff base complex salicylideneserinatecopper(II), [Cu(sal-ser)(H2O)], interacting with -cyclodextrin was prepared, and characterized in the solid state by infrared, UV-visible and EPR spectroscopies, X- ray diffraction, and thermoanalytical techniques. The catalytic activity of this compound, [Cu(sal-ser)CD], in the decomposition of hydrogen peroxide, and in the dismutation of superoxide radicals was also verified, in comparison with the reactivity of the free complex, in aqueous solution. In both cases, a decreasing in the reaction rate was observed for the CD-containing compound. The results of structural characterization, in addition to the substantial differences observed in the catalytic activities of the compounds, are indicative of partial insertion of the copper complex in the cavity of the oligosaccharide. 相似文献
979.
A. O. Porto W. F. Magalhães C. F. Carvalho J. C. Machado 《Journal of Radioanalytical and Nuclear Chemistry》1995,198(1):151-159
Positron Lifetime Spectroscopy (LS) measurements were performed in a series of binary molecular solid solutions of the general formula M1–x
G
x
L3, where L(ligand)=acetylacetone, dipivaloylmethane, or N-benzoyl-N-phenylhydroxylamine, M=Al(III), Ga(III) or In(III), as matrix, and G=Cr(III), Mn(III), Fe(III), Co(III), Ru(III), Rh(III) and Ir(III), as guest molecules, and the corresponding mechanical mixtures. For the solid solutions, the o-Ps yield values (I
3) decrease very rapidly with the increase of the guest mole fraction, showing a high efficient Ps inhibition process, while for the corresponding mechanical mixtures, these values decrease linearly with the increase of the guest molecule concentration, indicating the presence of two distinct phases. These results confirm our previous proposal that the LS technique is able to characterize solid solutions formed by one matrix, in whichI
3 values are high, and one guest, in which theI
3 values are very low. 相似文献
980.
Karl E. Bessler Elisabeth B. Dourado Myller de S. Carvalho Sebastio S. Lemos Javier Ellena 《无机化学与普通化学杂志》2005,631(10):1935-1940
A convenient method for the preparation of diphenylboron chelates from ammonium tetraphenylborate is described. A variety of five‐ or six‐membered O,O‐, N,O‐ and N,N‐chelates were obtained in yields from 60 to 90 %. The isolated compounds were characterized by elemental analysis, IR spectroscopy and multinuclear magnetic resonance spectroscopy (1H, 13C, and 11B). The crystal and molecular structures of (pyridine‐2‐acetyloximato)diphenylboron and (1‐phenylazo‐2‐naphtholato)diphenylboron were determined by X‐ray diffraction on single crystals. 相似文献