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81.
A procedure is described for the determination of the total concentration of organophosphorus pesticides in aqueous solution based on conversion of the compounds to orthophosphoric acid by oxygen-flask combustion and spectrophotometric determination as phosphomolybdenum blue. The procedure is particularly sensitive when preceded by efficient and selective accumulation of pesticides. The adsorption of malathion, parathion and phosalone on Amberlite XAD-4 resin from 1 l of 7–36 μM water solutions, followed by combustion of 500 μl of eluate yields of orthophosphoric acid with 90–105% recoveries. The detection limit is ca. 150 ng ml?1 pesticide in an aqueous sample. Inorganic phosphates and most of some commonly present non-pesticide phosphorus compounds are eliminated from the water sample during the adsorption step. In combination with a test for monitoring traces of cholinesterase inhibitors in surface waters, the determination of the total amount of organophosphorus pesticides as a cumulative parameter offers reliable information on the pollution level of the water environment. Application of such a combined procedure to a pond water from an apple orchard showed good correlation between phosphrus content and the cholinesterase inhibition. 相似文献
82.
Daniela Walterová Zdeně;K Stránský Vladimír Preininger Prof. Dr. Vilím Šimánek 《Electrophoresis》1985,6(3):128-132
The isotachophoretic behavior of quaternary benzo/c/phenanthridine, protoberberine and aporphine alkaloids in different electrolyte systems is described. The concentration of the leading ion and the pH value of the leading electrolyte affect the relative effective mobilities of the alkaloids. The system of pH 4.7, containing the leading ion K+ (0.005 M) counter ion acetate, and the terminating ion β-alanine (0.02 M), has been selected for the quantitative determination of the studied alkaloids in model mixtures and plant extracts. 相似文献
83.
J. Krištiak O. Šauša P. Bandžuch J. Bartoš 《Journal of Radioanalytical and Nuclear Chemistry》1996,210(2):563-570
The temperature dependence of positron annihilation characteristics,
3 andI
3, has been studied on sample of poly(butadiene), poly(isobutylene) and poly(chloroprene). The temperature range was between 15 and 470 K. The rate of expansion of holes or free-volume in all samples was deduced belowT
g as well aboveT
g as appr. 3·10–3 K–1 and 2·10–2 K–1, respectively. These values are very close to the rate of the mean squared displacement of scatterer<r
2>observed in neutron scattering experiments. A possibility to use an inverse value of free-volume,V
f
–1
for study of viscoelastic state of polymers is demonstrated. 相似文献
84.
Z. Šimša V. Roskovec F. Zounová P. Novotný W. Keilig 《Czechoslovak Journal of Physics》1977,27(1):88-98
An extended version of the noncollinear spin model bySawatzky et al. is developed to derive a dependence of the differential high field susceptibility on the degree of inversion of the ferrite MnFe2O4. Using the available data on the main molecular field coefficients it is shown that the present model imposes restrictions on values of. Determination of from the measurements of the field dependence of the saturated moments at low temperatures on samples with varying degrees of inversion reveals good quantitative agreement with the present model. 相似文献
85.
D. Šokčević Z. Lenac R. Brako M. Šunjić 《Zeitschrift für Physik B Condensed Matter》1977,28(4):273-281
We develop a theory of low energy electron loss spectroscopy of vibrational modes of molecules adsorbed on metal surfaces. Differential and total cross sections are calculated in the Distorted Wave Born Approximation, assuming i) strong elastic scattering on the metal surface, ii) direct electron-molecule interaction via the electric dipole field associated with the molecular vibration. The angular distributions are calculated and discussed for molecules adsorbed at various distances above the metal surface and for several electron energies and impact angles. The influence of electronic screening of dipolar oscillations is discussed and the consequences of the classical induced image dipoles are explored. It is shown that the metal surface selection rule known in IR spectroscopy is only approximately valid in electron scattering. Finally, we give numerical estimates of the inelastic scattering cross sections for the stretching vibrations of CO molecule adsorbed on transition metal surfaces, in reasonable agreement with experiments. 相似文献
86.
Instrumental neutron activation was used for the determination of 23 trace and minor elements in 4 different samples of brewer's
yeast. Detection limits for these elements vary from 2 ppb to 100 ppm. The following average concentrations were found (ppm,
dry weight): Al 597, Br 0.36, Cl 1473, Co 0.21, Cu 19, Fe 285, K 16 400, Mg 1355, Mn 8.4, Na 2330, Rb 19, Sb 0.053, Se 1.2,
V 2.2 and Zn 80. NBS standard 1569 was also analyzed and the following concentrations (in ppm) were measured: Al 2300, Br
0.65, Ce 0.23, Cl 460, Co 0.26, Cr 2.12, Cu 11, Fe 707, Gd 7.1, Hf 0.13, K 15 500, Mg 1780, Mn 7, Na 510, Rb 16, Sb 0.075,
Sc 0.18, Se 0.92, Th 3.7, Ti 38, U 0.49, V 4.1 and Zn 70. 相似文献
87.
Nataša Bukovec Peter Bukovec Jože Šiftar 《Monatshefte für Chemie / Chemical Monthly》1980,111(4):957-961
Compounds of the type CsLn(SO4)2, (Ln=La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) were prepared at 300°C. IR spectra were recorded in the range 4,000-250cm–1 and tentatively assigned. The number of observed bands exceeds the predicted number by site symmetry selection rules. Streching bands show bathochromic shifts whereas the deformations exibit hypsochromic shifts on going to heavier lanthanides. At the same time there is an increased splitting of these bands in the same direction. All these facts indicate an increased coupling in the layer structure which is in accordance with the lanthanide contraction.
N. Bukovec, P. Bukovec undJ. iftar, Vest. Slov. Kem. Drus.26, 103 (1979). 相似文献
88.
Jože Slivnik Mateja Žvanut Borka Sedej 《Monatshefte für Chemie / Chemical Monthly》1968,99(5):1713-1717
Zusammenfassung Die Reaktion zwischen MgCO3 und wässerigen Lösungen von Hydraziniumdifluorid und Flußsäure führt zum Hydraziniumfluoromagnesat. Diese Verbindung ist auch aus Magnesiumchlorid-und Hydraziniumdifluorid-Lösungen herstellbar. Es werden röntgenographische, IR-spektrographische und thermogravimetrische Untersuchungen dieser Verbindung angegeben.
Mit 3 Abbildungen 相似文献
Hydrazinium(+2) fluoromagnesate is formed in the reaction between MgCO3 and hydrazinium difluoride dissolved in hydrogen fluoride. The reaction of magnesium chloride and an aqueous solution of hydrazinium difluoride yields the same product. The results of X-ray diffraction studies, IR spectroscopical studies and thermogravimetrical investigation are given.
Mit 3 Abbildungen 相似文献
89.
Two new reagents for in situ peptide coupling based on the 2-mercaptopyrimidine core have been developed. The readily prepared thiouronium salts were found to promote both peptide and segment coupling efficiently with low racemization/epimerization levels. 相似文献
90.
Monooctyl--(4-carboxyanilino)benzylphosphonic acid (H2L) was investigated as a novel reagent for the extraction and separation of lead(II) and bismuth(III) from nitrate solutions. Stoichiometric ionization constants of H2L in ethanol — water mixtures determined by potentiometric NaOH titration had values pKa1 2.25 and pKa2 4.33. Ethanol and chloroform solutions of H2L followed Beer's law at 300 nm and 296 nm, molar absorptivities being 2.94·104 mol–1·l·cm–1 and 2.85·104 mol–1·l·cm–1, respectively. HNO3 and HCl were also extracted into chloroform solutions containing H2L. Bismuth(III) was quantitatively transferred into the chloroform H2L solution at pH 1, and lead(II) at 3.5. The value of the separation factor DBi/DPb is 160 at pH 1. 相似文献