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991.
分析化学中的非线性校准 总被引:15,自引:0,他引:15
对分析化学中的非线性校准作了系统的讨论,对近年来分析化学中非线性及有关问题的方法和研究进展作了较全面的评述,各种非线性校准方法可不同程度地成功地用于解决非线性问题,迄今为止,人工神经网络(ANN)被认为是解决非线性校准问题的最优方法之一。 相似文献
992.
R. Kirchner M. Rodriguez de Rivera J. Seidel V. Torra 《Journal of Thermal Analysis and Calorimetry》2005,82(1):179-184
Summary Using an RC model, the behavior of a TAM high-performance calorimeter (Thermometric AB, Sweden) equipped with a flow-mixing
insertion vessel using independent pumps for each reactant is studied. The model shows a reliable sensitivity behavior for
mixtures realized inside the cell. The model behavior is compared with experimental measurements.</o:p> 相似文献
993.
A spectrofluorometric method for the quantitative determination of flufenamic, mefenamic and meclofenamic acids in mixtures has been developed by recording emission fluorescence spectra between 370 and 550 nm with an excitation wavelength of 352 nm. The excitation–emission spectra of these compounds are deeply overlapped which does not allow their direct determination without previous separation. The proposed method applies partial least squares (PLS) multivariate calibration to the resolution of this mixture using a set of wavelengths previously selected by Kohonen artificial neural networks (K-ANN). The linear calibration graphs used to construct the calibration matrix were selected in the ranges from 0.25 to 1.00 μg ml−1 for flufenamic and meclofenamic acids, and from 1.00 to 4.00 μg ml−1 for mefenamic acid. A cross-validation procedure was used to select the number of factors. The selected calibration model has been applied to the determination of these compounds in synthetic mixtures and pharmaceutical formulations. 相似文献
994.
Kaiser J Park S Boering KA Brenninkmeijer CA Hilkert A Röckmann T 《Analytical and bioanalytical chemistry》2004,378(2):256-269
A mass spectrometric method to determine the absolute intramolecular (position-dependent) nitrogen isotope ratios of nitrous oxide (N2O) has been developed. It is based on the addition of different amounts of doubly labeled 15N2O to an N2O sample of the isotope ratio mass spectrometer reference gas, and subsequent measurement of the relative ion current ratios of species with mass 30, 31, 44, 45, and 46. All relevant quantities are measured by isotope ratio mass spectrometers, which means that the machines inherent high precision of the order of 10–5 can be fully exploited. External determination of dilution factors with generally lower precision is avoided. The method itself can be implemented within a day, but a calibration of the oxygen and average nitrogen isotope ratios relative to a primary isotopic reference material of known absolute isotopic composition has to be performed separately. The underlying theoretical framework is explored in depth. The effect of interferences due to 14N15N16O and 15N14N16O in the 15N2O sample and due to 15N
2
+
formation are fully accounted for in the calculation of the final position-dependent nitrogen isotope ratios. Considering all known statistical uncertainties of measured quantities and absolute isotope ratios of primary isotopic reference materials, we achieve an overall uncertainty of 0.9 (1). Using tropospheric N2O as common reference point for intercomparison purposes, we find a substantially higher relative enrichment of 15N at the central nitrogen atom over 15N at the terminal nitrogen atom than measured previously for tropospheric N2O based on a chemical conversion method: 46.3±1.4 as opposed to 18.7±2.2. However, our method depends critically on the absolute isotope ratios of the primary isotopic reference materials air–N2 and VSMOW. If they are systematically wrong, our estimates will also necessarily be incorrect. 相似文献
995.
介绍气相色谱-质谱联用仪的常见故障:与质谱仪调谐相关的故障、与校准和灵敏度相关的故障及与色谱图和质谱图相关的故障,给出了产生故障的可能原因,提出了故障排除的方法。 相似文献
996.
997.
998.
Several organic compounds like phenanthrene, benzanilide, anisic acid, triphenylene, 2-chloroanthraquinone, hexachlorobenzene, carbazole, 4-iodobenzoic acid, perylene, anthraquinone, as new reference materials for temperature and energy calibration of DTA and DSC apparatuses were studied in the range 300—600 K.
Zusammenfassung Als neue Referenzsubstanzen für Temperatur- und Energiekalibrierung von DTA- und DSC-Geräten wurden im Temperaturbereich 300–600 K einige organische Verbindungen, wie z.B. Phenanthren, Benzanilid, Anissäure, Triphenylen, 2-Chloranthrachinon, Hexachlorbenzol, Karbazol, 4-Jodbenzoesäure, Perylen und Anthrachinon untersucht.相似文献
999.
The second-order correlation energy of M?ller–Plesset perturbation theory is computed for the neon atom using a wave function
that depends explicitly on the interelectronic coordinates (MP2-R12). The resolution-of-identity (RI) approximation, which
is invoked in the standard formulation of MP2-R12 theory, is largely avoided by rigorously computing the necessary three-electron
integrals. The basis-set limit for the second-order correlation energy is reached to within 0.1 mE
h. A comparison with the conventional RI-based MP2-R12 method shows that only three-electron integrals over s and p orbitals need to be computed exactly, indicating that the RI approximation can be safely used for integrals involving orbitals
of higher angular momentum.
Received: 9 May 2001 / Accepted: 31 October 2001 / Published online: 9 January 2002 相似文献
1000.
Ab initio calculations of the structure, atomic charges, natural bond orbital and thermodynamic functions have been performed at HF/6-311G** and B3LYP/6-311G** levels of theory for the title compound of 4-phenyl-1-(1-phenylethylidene) thiosemicarbazide. The calculated results show
that the sulfur atom and all of the nitrogen atoms have bigger negative charges and that they are the potential sites to react
with the metallic ions, which make the title compound a multidentate ligand. The coordination ability of the sulfur atom and
the nitrogen atom of C=N double bond increases with the increase of polarity of the solvent. Electronic absorption spectra
have been calculated by time-dependent density functional theory (TD-DFT) method. The calculation of the second-order optical
nonlinearity has also been carried out with the PM3 semi-empirical method, resulting in the molecular hyperpolarisability
is 5.477×10−30 esu. 相似文献