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171.
A systematic quantum mechanical study of the possible conformations, their relative stabilities, vibrational and electronic
spectra and thermodynamic parameters of methyl-3-methoxy-2-propenoate has been reported for the electronic ground (S0) and first excited (S1) states using time-dependent and time-independent Density Functional Theory (DFT) and RHF methods in extended basis sets.
Detailed studies have been restricted to the E-isomer, which is found to be substantially more stable than the Z-isomer. Four
possible conformers c′Cc, c′Tc, t′Cc, t′Tc, of which the first two are most stable, have been identified in the S0 and S1 states. Electronic excitation to S1 state is accompanied with a reversal in the relative stability of the c′Cc and c′Tc conformers and a substantial reduction
in the rotational barrier between them, as compared with the S0 state. Optimized geometries of these conformers in the S0 and S1 states are being reported. Based on suitably scaled RHF/6-31G** and DFT/6-311G** calculations, assignments have been provided to the fundamental vibrational bands of both these conformers in terms of frequency,
form and intensity of vibrations and potential energy distribution across the symmetry coordinates in the S0 state. A complete interpretation of the electronic spectra of the conformers has been provided. 相似文献
172.
Poly(vinyl chloride) (PVC)-based membrane of pentathia-15-crown-5 exhibits good potentiometric response for Hg2+ over a wide concentration range (2.51 × 10−5 to 1.00 × 10−1 mol dm−3) with a slope of 32.1 mV per decade of Hg2+ concentration. The response time of the sensor is as fast as 20 s. The electrode has been used for a period of six weeks and exhibits fairly good discriminating ability towards Hg2+ in comparison to alkali, alkaline and some heavy metal ions. The electrode can be used in the pH range from 2.7 to 5.0. 相似文献
173.
A highly sensitive spectrophotometric method for the determination of nitrite in water and soil has been developed. The reaction of nitrite with acidified potassium iodide to liberate iodine which oxidizes leuco‐crystal violet (LCV) to form crystal violet having absorption maxima at 590 nm forms the bases of this method. In aqueous medium the system obeys Beer's law in the range of 0.1 to 1.0 μg per 25 mL (0.004–0.04 ppm), while in an extractive system the range is 0.025–0.25 μg in 100 mL (0.00025–0.0025 ppm). The molar absorptivity and Sandell's sensitivity were found to be 1.54 × 106 1 mol?1 cm?1 and 44 pg cm?2, respectively. 相似文献
174.
Samik Gupta Anil Kumar Barik Sachindranath Pal Arijit Hazra Somnath Roy Ray J. Butcher Susanta Kumar Kar 《Polyhedron》2007
Four cis-dioxomolybdenum complexes of general formula [MoO2(Ln)EtOH] (n = 1–4) and one oxomolybdenum(IV) complex [MoO(L4)EtOH], with potentially tridentate Schiff bases derived from 5-methyl pyrazole-3-carbohydrazide and salicylaldehyde/substituted salicylaldehyde/o-hydroxy acetophenone have been prepared. The Mo(IV) complex is derived from the Mo(VI) dioxo complex by oxotransfer reaction with PPh3. The complexes are characterized by elemental analysis, electronic spectra, IR, 1H NMR, and by cyclic voltammetry. All the Mo(VI) species are crystallographically characterized. The complexes have a distorted octahedral structure in which the ligand behaves as a binegative donor one, leaving the pyrazole –N uncoordinated towards the metal center. It is also revealed from the crystal structure that the Mo(VI) center enjoys an NO5 donor environment. 相似文献
175.
A detailed study for the spectrophotometric readout method for L-threonine powder, [CH3CH(OH)CH(NH2)COOH], was done. In this method, 400 mg unirradiated/irradiated L-threonine powder was dissolved in 10 ml of a solution which contains 3×10−4 mol dm−3 ferrous ammonium sulphate and 1.7×10−4 mol dm−3 xylenol orange (XO) in aerated aqueous 0.17 mol dm−3 sulphuric acid (FX). The peroxy radicals produced from irradiated threonine oxidize ferrous ions and XO forms a complex with ferric ions as well as controls the chain length of ferrous ion oxidation. The plot of absorbance at 556 nm against dose is linear in the dose range 20–400 Gy and doses down to about 1 Gy can be measured using 10-cm path cells. Response of the dosimeter is independent of irradiation temperature above 20. A dose of 50 Gy–10 kGy can be measured dissolving 50 mg threonine powder in 10 ml of a solution which contains 3×10−4 mol dm−3 ferrous ammonium sulphate and 1.3×10−4 mol dm−3 XO in aerated aqueous 0.06 mol dm−3 sulphuric acid (FX). The plot of absorbance at 552 nm against dose is non-linear. However dosimeter shows linear dose response up to 1000 Gy. Irradiated threonine powder is stable for about 3 months. The reproducibility of the method is better than ±2%. This dosimeter is very useful as transfer dosimeter for food irradiation programme. 相似文献
176.
Manju Gupta 《Talanta》2007,71(3):1039-1046
The aim of present work was to optimize the experimental parameters in single drop microextraction under solution immersion (SDME) and headspace (HS-SDME) extraction modes for the determination of periodate using guaifenesine [3-(2′-methoxyphenoxy)-1,2-propane diol] and norephedrine (phenylpropanolamine) as new and alternative reagents for the Malaprade reaction. The reactions were complete within 5 min resulting in the formation of 2-(2′-methoxyphenoxy)-acetaldehyde and benzaldehyde, respectively. SDME/HS-SDME of oxidation products with 2 μl of anisole or 1 μl of toluene, respectively, has permitted the determination of periodate at μg l−1 concentration levels. The results indicated that HS-SDME (range 0.01-10 mg l−1, r2 = 0.9990; limit of detection 1.55 μg l−1) was more sensitive than SDME (range 0.05-50 mg l−1, r2 = 0.9984; limit of detection 3.42 μg l−1), and was inexpensive, rapid and convenient. Tolerance of excess of iodate has permitted the application of this method in the determination of ethylene glycol in motor oil; the average recovery on spiked sample was 98.6% with R.S.D. of 4.2%. 相似文献
177.
A high-performance thin layer chromatographic (HPTLC) method for the rapid and simple quantification of the four major anthraquinone derivatives i.e. physcion, chrysophanol, emodin and chrysophanol glycoside in Rheum emodi is described. HPTLC of anthraquinone derivatives was performed on pre-coated RP-18 F254S HPTLC plates. For achieving good separation, the mobile phase of methanol-water-formic acid (80:19:1, v/v/v) was used. The densitometric determination of anthraquinone derivatives was carried out at 445 nm in reflection/absorption mode. The calibration curves were linear in the range of 20-100 ng for physcion, 80-400 ng for chrysophanol and emodin, and 200-1000 ng for chrysophanol glycoside. The method was found to be reproducible and convenient for quantitative analysis of anthraquinone derivatives in the methanolic extract of rhizomes of R. emodi collected from three different locations of Western Himalaya, India. 相似文献
178.
Summary Copper, palladium and nickel can be titrated amperometrically with 2,5-dihydroxyacetophenone oxime at –0.15, –0.4 and, –1.2 V vs. S. C. E. respectively, the optimum pH values being 4.6, 4.0, and 9.0. Alkali and alkaline earth metals, Al, Bi, Cd, Co, Cr. Fe(II), Hg, Mn, Ni, Pb, Th, Zn, UO, W, and Zr do not interfere with the estimation of copper and palladium. The interferences due to the presence of silver and iron(III) can be eliminated by adding excess of KCl and KF respectively. Most heavy metals interfere with the estimation of nickel and should be eliminated before titration.
Zusammenfassung Kupfer, Palladium und Nickel können mit 2,5-Dihydroxyaeetophenonoxim bei –0,15, –0,4 bzw. –1,2 V gegen eine gesättigte Kalomelelektrode amperometrisch titriert werden, wobei man das pH am besten auf 4,6, 4,0 bzw. 9,0 hält. Alkalimetalle, Erdalkalien, Al, Bi, Cd, Co, Cr, Fe(II), Hg, Mn, Ni, Pb, Th, Zn, UO2, W und Zr stören die Bestimmung des Kupfers und des Palladiums. Silber und Eisen können mit Kaliumchlorid gefällt bzw. mit Kaliumfluorid maskiert werden. Die meisten Schwermetalle stören die Nickelbestimmung und müssen daher vor der Titration entfernt werden.相似文献
179.
C.N.R. Rao D.D. Sarma P.R. Sarode E.V. Sampathkumaran L.C. Gupta R. Vijayaraghavan 《Chemical physics letters》1980,76(3):413-415
The valence state of Yb in some of its intermetallics, YbNi2Ge2, YbCu2Si2 and YbPd2Si2 has been investigated by LIII(Yb) absorption edges and X-ray pnotoelectron spectra in the 4f and 4d regions. These studies establish the presence of mixed valence in all three systems and illustrate the utility of 4f and 4d spectra in the study of mixed valence in Yb compounds. 相似文献
180.