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71.
Renormalization group calculations ind = 4 andd = 4 – are performed for a system of finite size. A form of mean-field theory is used which yields a rounded transition for a finite system, and this allows a sensible expansion in fluctuations. A combination of Ewald and Poisson sum techniques is used to produce explicit numerical results for the specific heat ind = 4 which, with the setting of two nonuniversal metrical factors and the fourth-order coupling constant may be compared with simulations. The numerical visibility of logarithmic corrections is investigated. The universal scaling function for the specific heat to relativeO() is also evaluated numerically. 相似文献
72.
73.
Victor A.?ZammitEmail author Nigel T.?Price Vicky N.?Jackson Byun-Sung?Park 《Monatshefte für Chemie / Chemical Monthly》2005,136(8):1299-1309
Summary. Carnitine acyltransferases catalyse equilibria between acyl-CoA esters and the respective acylcarnitines. Therefore, they act not only as pathway enzymes, but also as modulators of acyl-CoA concentrations within individual sub-cellular compartments. Because acyl-CoA esters are potent biologically active metabolites, carnitine acyltransferase activities are potentially able to affect a diverse range of physiological processes, ranging from insulin secretion, to appetite control, and insulin sensitivity of tissues. The distinctive subcellular distributions of the different types of carnitine acyltransferases also enables them to participate in the transfer of acyl moieties across intracellular membranes, and of particular acylcarnitine esters across the plasma membrane and into the plasma. Pharmacological strategies that make use of these properties to improve cell function are discussed. 相似文献
74.
H. A. v. Derschau und H. Prugger 《Fresenius' Journal of Analytical Chemistry》1969,247(1-2):8-12
Zusammenfassung Die 42 wichtigsten, durch Atomabsorption erfaßbaren Elemente wurden nach einem einheitlichen Verfahren hinsichtlich der günstigsten Betriebsbedingungen untersucht. Die Elemente der 1. und 2. Neben gruppe und der 2. Hauptgruppe werden mit möglichst geringem Strom der Hohlkathodenlampe am empfind lichsten nachgewiesen. Alle übrigen Elemente liefern bei maximalem Lampenstrom günstigste Ergebnisse. In den einzelnen Gruppen kann man eine Abnahme der notwendigen Flammentemperatur zur Probenverdampfung mit Zunahme der Periode feststellen. Bei den Elementen der 4. Nebengruppe (Ti, Zr, Hf) kann Mußsäure und in geringem Maße Salzsäure die Verdampfungsblockierung durch Bildung von Oxiden vermindern.
Optimum conditions of atomic absorption, illustrated by means of the periodic system
The 42 most important elements which can be determined by atomic absorption were examined according to a common method in order to establish the most favourable working conditions. The elements of groups IB and IIA and IIB were determined with the highest sensitivity at the lowest possible current of the hollow cathode lamp. All other elements yielded optimum results at maximum lamp current. In the individual groups the flame temperature required for sample evaporation decreased as the period increased. With the elements of group IVA (Ti, Zr, Hf) the evaporation blocking by formation of oxides could be reduced by hydrofluoric acid and, to a lesser extent, hydrochloric acid.相似文献
75.
V. Spěvá?ková J. Jhn M. Pra?ská 《Journal of Radioanalytical and Nuclear Chemistry》1983,80(1-2):115-120
The determination of uranium in natural waters by XRF analysis after its preconcentration with some organic precipitants is described.109Cd source is used for the excitation of L-series X-rays of uranium. Separation yield, kinetics of coprecipitation and the possibility of preparing thin-layer samples for XRF analysis were studied in detail for uranium concentration with α-nitroso-β-naphtol, methylene blue with ammonium thiocyanate, tannin with urotropine and other precipitants. A procedure using coprecipitation of uranium with α-nitroso-β-naphtol from 500 ml samples of surface or waste, waters is proposed. 相似文献
76.
P. Bersier und F. v. Sturm 《Fresenius' Journal of Analytical Chemistry》1966,224(1):317-332
Zusammenfassung Die Möglichkeit der gleichzeitigen Bestimmung von Niob und Zinn mit Hilfe der Polarographie wird untersucht. Es wird gefunden, daß die Bestimmung zwar nicht gleichspannungspolarographisch, wohl aber square-wave-polarographisch durchführbar ist. Zur Analyse der binären Nb-Sn-Legierungen (etwa Nb3Sn) ist 8,0±0,1 m HCl+10 Vol-% Äthylenglykol als Grundelektrolyt geeignet. In diesem Elektrolyten erscheinen die erste Reduktionswelle des Niobs, NbVIV, und die zweite Reduktionswelle des Zinns, SnIISn, gut getrennt und vermeßbar. Die Differenz der Spitzenpotentiale (E
pNbV/IV= -0.26V, E
pSnII/O= -0.46V gegen Quecksilber-Bodenelektrode) beträgt 200 mV.Die beschriebene Methode hat im Vergleich zu den bekannten nichtpolarographischen Analysenvorschriften den Vorzug, eine bis zu 100 mal kleinere Einwaage (bei vergleichbarer Reproduzierbarkeit) und einen verringerten Zeitaufwand zu erfordern.Bei Einwaagen von 2–14 mg beträgt die Genauigkeit der Niobbestimmung 1% rel., die der Zinnbestimmung 2% rel. Eine einzelne Niob-Zinn-Simultanbestimmung dauert 4 Std.
Herrn Prof. Dr. M. von Stackelberg zum 70. Geburtstag gewidmet. 相似文献
Summary The possibility of a simultaneous polarographic determination of niob and tin is investigated.It has been found that the determination cannot be carried out by direct current polarography, but square-wave polarography yields good results.8.0±0.1 M HCl+10 vol-% ethylene glycol is suitable as supporting electrolyte for the analysis of the binary Nb-Sn-alloys (Nb3Sn).In this supporting electrolyte the first reduction-wave of niobium NbVNbIV, and the second reduction wave of tin, SnIISn0, are well developed and separated. The difference of the peak potential (E pNbV/IV= -0.26V, E pSnII/O= -0.46V vs. mercury-pool electrode) is 200 mV. Compared with conventional methods the method described has the advantage of requiring smaller amounts of sample (up to 100 times smaller by weight at comparable reproducibility) with a saving of time.With sample amounts of 2 to 14 mg the accuracy of the niobium determination is 1% rel., that of the tin determination is 2% rel. One single simultaneous determination of niobium and tin takes about four hours.
Herrn Prof. Dr. M. von Stackelberg zum 70. Geburtstag gewidmet. 相似文献
77.
Diphenylphosphorylazide N3P(O)(OPh)2 reacts with Pt(PPh3)3, Pt(PPh3)2(C2H4), trans-RhCl(CO)(PPh3)2, Ru(CO)3(PPh3)2, CoCl2(PPh3)2 and CuCl(PPh3)2 to give the azido complexes Pt(PPh3)2(N3)R, Pt(PPh3)2(N3)2R2, the urylene complex RhCl(PPh3)2(RNCONR) and the phosphine imine complexes Ru(CO)3(RPPh3)2, CoCl2(RNPPh3)2, CuCl(RNPPh3)2, respectively, (RP(O)(OPh)2). The oxidative addition of n-C6F13SO2N3 to Pt(PPh3)4 and Pt(PPh3)2(C2H4) affords the complexes Pt(PPh3)2(N3)R and Pt(PPh3)2(N3)2R2, respectively, (RSO2C6F13. The compounds are characterized by elemental analysis and by their IR spectra. 相似文献
78.
R. v. Hentig T. Goldbrunner F. v. Feilitzsch G. Angloher 《Analytical and bioanalytical chemistry》1998,360(6):664-668
For the determination of trace elements in organic liquids radiochemical neutron activation analysis has been combined with counting methods geared to various decay modes of indicator radionuclides leading to a high sensitivity required for ultrapure samples. The activation parameters such as irradiation time, sample mass and neutron flux have been enlarged to the maximum possible in the available irradiation facility. Separation yields and adsorption losses have been studied in detail for a set of elements in order to rule out losses during the separation process. The attainable limits of detection are 2 · 10–16g/g for U and Lu, in the 5 · 10–15g/g range for Th and Sm, in the 1 · 10–14g/g region for La, 5 · 10–13g/g for Rb, Cd and 2 · 10–12g/g for K and In. Although the analysis focused on traces of naturally occurring radioisotopes, results for Cr, Fe, W and Zn are presented as well. 相似文献
79.
80.
A chiral stationary phase (CSP) has been prepared by chemically bonding a chiral pseudo-18-crown-6 type host having a 1-phenyl-1,2-cyclohexanediol unit to 3-aminopropyl silica gel. The chiral column was prepared by the slurry-packing method in a stainless steel HPLC column. Normal mobile phases can be used with this CSP in contrast to conventional dynamic coating type CSPs. Enantiomers of 20 out of 30 amino compounds, including 20 amino acids, 2 amino acid methyl esters, 6 amino alcohols, and 2 lipophilic amines, were efficiently separated on columns with this CSP. It is noteworthy that 15 amino compounds out of 30 were separated with better separation factors and shorter retention times compared to the corresponding CSP having pseudo-18-crown-6 with 1-phenyl-1,2-ethanediol as a chiral unit. In view of the correlation between the enantiomer selectivities observed in chromatography and those obtained in gas phase FABMS-EL methods and solution phase titrations, chiral recognition in the host-guest interaction likely contributes to enantiomer separation. 相似文献