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991.
In a previous work, the synthesis and structural-microstructural characterization of different nanocrystalline lithium metasilicate (Li2SiO3) samples were performed. Then, in this work, initially, a textural analysis was performed over the same samples. Li2SiO3 samples prepared with a non-ionic surfactant (TRITON X-114) presented the best textural properties. Therefore, this sample was selected to evaluate its water vapor (H2O) and carbon dioxide (CO2) sorption properties. Sorption experiments were performed at low temperatures (30-80 °C) in presence of water vapor using N2 or CO2 as carrier gases. Results clearly evidenced that CO2 sorption on these materials is highly improved by H2O vapor, and of course, textural properties enhanced the H2O-CO2 sorption efficiency, in comparison with the solid-state reference sample. 相似文献
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Wurstbauer U Majumder D Mandal SS Dujovne I Rhone TD Dennis BS Rigosi AF Jain JK Pinczuk A West KW Pfeiffer LN 《Physical review letters》2011,107(6):066804
We find unexpected low energy excitations of fully spin-polarized composite-fermion ferromagnets in the fractional quantum Hall liquid, resulting from a complex interplay between a topological order manifesting through new energy levels and a magnetic order due to spin polarization. The lowest energy modes, which involve spin reversal, are remarkable in displaying unconventional negative dispersion at small momenta followed by a deep roton minimum at larger momenta. This behavior results from a nontrivial mixing of spin-wave and spin-flip modes creating a spin-flip excitonic state of composite-fermion particle-hole pairs. The striking properties of spin-flip excitons imply highly tunable mode couplings that enable fine control of topological states of itinerant two-dimensional ferromagnets. 相似文献
996.
Impact of disorder on the 5/2 fractional quantum Hall state 总被引:1,自引:0,他引:1
Pan W Masuhara N Sullivan NS Baldwin KW West KW Pfeiffer LN Tsui DC 《Physical review letters》2011,106(20):206806
We compare the energy gap of the ν = 5/2 fractional quantum Hall effect state obtained in conventional high mobility modulation-doped quantum-well samples with those obtained in high quality GaAs transistors (heterojunction insulated gate field-effect transistors). We are able to identify the different roles that long-range and short-range disorders play in the 5/2 state and observe that the long-range potential fluctuations are more detrimental to the strength of the 5/2 state than short-range potential disorder. 相似文献
997.
The unsteady wake behind a hexagonal cylinder in cross-flow is investigated numerically. The time-dependent three-dimensional Navier-Stokes equations are solved for three different Reynolds numbers Re and for two different cylinder orientations. The topology of the vortex shedding depends on the orientation and the Strouhal frequency is generally higher in the wake of a face-oriented cylinder than behind a corner-oriented cylinder. For both orientations a higher Strouhal number St is observed when Re is increased from 100 to 500 whereas St is unaffected by a further increase up to Re=1000. The distinct variation of St with the orientation of the hexagonal cylinder relative to the oncoming flow is opposite of earlier findings for square cylinder wakes which exhibited a higher St with corner orientation than with face orientation. 相似文献
998.
Two explosive triazides of phosphorus(V), OP(N(3))(3) and SP(N(3))(3), have been prepared as neat substances and structurally characterized. Both compounds can be handled in gas, liquid, and solid states in submillimolar quantities. The melting points of OP(N(3))(3) and SP(N(3))(3) are +22 and -30 °C, respectively. The two triazides have been characterized by IR (Ar matrix and gas phase) and Raman (solid) spectroscopies. Their single-crystal structures were obtained by X-ray diffraction and found to be significantly distorted from the predicted ideal C(3) symmetry because of intermolecular interactions. The spectroscopic and structural properties are discussed in combination with density functional theory calculations. 相似文献
999.
Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is frequently used to identify and quantify drugs in human biological samples due to the high selectivity and sensitivity of this technique. However, ion suppression effects caused by co-eluting compounds: drugs, metabolites, matrix components, impurities and degradation products, are a major concern. Stable isotope labelled internal standards (SIL ISs), usually deuterium ((2)H) labelled, are often used to compensate for these effects. In many LC separations the retention times of (2)H labelled ISs and their analogues will differ. Ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) is increasingly being used for bio-analysis. With the better chromatographic resolution provided with sub 2 μm particles, larger separation between analytes and their (2)H labelled analogues can be expected, which might reduce the benefits of the SIL IS. There is a greater difference in physico-chemical properties between hydrogen isotopes than between isotopes of other elements. (13)C, (15)N and (18)O labelled ISs are more similar to their analytes than (2)H labelled ISs and thereby expected to behave more similarly in chromatographic separations. In this study we have investigated the use of (13)C and (2)H labelled ISs for the determination of amphetamine and methamphetamine by UPLC-MS/MS. The (13)C labelled ISs were co eluting with their analytes under different chromatographic conditions while the (2)H labelled ISs and their analytes were slightly separated. An improved ability to compensate for ion suppression effects were observed when the (13)C labelled ISs were used. Furthermore, an UPLC-MS/MS method for determination of amphetamine and methamphetamine in urine using (13)C labelled ISs has been developed and validated. Unfortunately, there are few (13)C labelled ISs commercial available today. If more (13)C labelled ISs become commercial available they may well be the coming solution to minimize ion suppression/enhancement effects in LC-MS/MS analyses of drugs in biological samples. 相似文献
1000.
Zeng X Beckers H Willner H Grote D Sander W 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(14):3977-3984
The elusive triplet fluorocarbonyl nitrene, FC(O)N (X3A′′), has been generated in high yield from matrix‐isolated FC(O)N3 by ArF excimer laser photolysis (λ=193 nm). As a side product FNCO was formed. The novel nitrene was characterized by IR, UV/Vis, EPR spectroscopy, and quantum‐chemical calculations. All six fundamental vibrations of FC(O)N at 1681.3, 1193.8, 879.8, 646.5, 588.7, and 434.8 cm?1 (argon matrix, 16 K), their 12/13C, 16/18O, and 14/15N isotopic shifts, and four electronic transitions at T0=13 890, 25 428, 29 166, and 30 900 cm?1 that exhibit vibrational fine structures have been detected. Under visible‐light irradiation at λ≥495 nm, FC(O)N reacted with molecular N2 in the matrix cage at 6 K to give back FC(O)N3, whereas near‐UV irradiation at λ≥335 nm yielded FNCO. The singlet–triplet energy gaps of different carbonyl nitrenes are discussed. 相似文献