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31.
A. Najafi F. Golestani-Fard H. R. Rezaie N. Ehsani 《Journal of Sol-Gel Science and Technology》2011,59(2):205-214
Nano sized β-SiC particles were synthesized from sol–gel process. Mono dispersed β-SiC nano particles with semi spherical
morphology were obtained by employing APC as a dispersant agent and adjusting pH in the range of 2.5–4. Phenolic resin and
TEOS were employed as precursors and heat treatment was conducted up to 1500 °C. Different techniques such as XRD, DTA, FTIR,
PSA, SEM and TEM were used to characterize the formation of β-SiC. The (Si–O-C) bonds were formed by hydrolysis and condensation
reactions in the gel while the nucleation of crystalline β-SiC was found to be initiated at 1400 °C. The primary particles
in the sol were found to be (< 10 nm) while the size distribution in the final product was recorded in the range of 30–50 nm. 相似文献
32.
The results of the innovative study on a new stationary phase with high efficiency based on ZnO nano and micro rod coating on fused silica are reported in this paper. ZnO nanorods with a diameter in the range of 70–300 nm and the length of about 500 nm, have been grown on fused silica fibers using a hydrothermal process. The extraction properties of the fiber were investigated using headspace solid-phase microextraction (HS-SPME) mode coupled with gas chromatography–mass spectrometry detection (GC–MS) for 1,4-dichloro-nitrobenzene, biphenyl and acenaphthene. The calibration curves were linear up to 102–107 ng L−1 (R2 > 0.995) with detection limits of 10−3 ng L−1 for biphenyl and acenaphthene and 10 ng L−1 for 1,4-dichloro-nitrobenzene. The RSD for single fiber and fiber-to-fiber were less than 7.0 and 11.5%, respectively. The high stability of the ZnO coating is proved at relatively high temperatures (up to 300 °C) with a high extraction capacity and long lifespan (more than 100 times). Promising recoveries (91–102%) were obtained in environmental water samples analysis by applying the proposed technique. 相似文献
33.
Reactions of SnCl2 with the complexes cis‐[PtCl2(P2)] (P2=dppf (1,1′‐bis(diphenylphosphino)ferrocene), dppp (1,3‐bis(diphenylphosphino)propane=1,1′‐(propane‐1,3‐diyl)bis[1,1‐diphenylphosphine]), dppb (1,4‐bis(diphenylphosphino)butane=1,1′‐(butane‐1,4‐diyl)bis[1,1‐diphenylphosphine]), and dpppe (1,5‐bis(diphenylphosphino)pentane=1,1′‐(pentane‐1,5‐diyl)bis[1,1‐diphenylphosphine])) resulted in the insertion of SnCl2 into the Pt? Cl bond to afford the cis‐[PtCl(SnCl3)(P2)] complexes. However, the reaction of the complexes cis‐[PtCl2(P2)] (P2=dppf, dppm (bis(diphenylphosphino)methane=1,1′‐methylenebis[1,1‐diphenylphosphine]), dppe (1,2‐bis(diphenylphosphino)ethane=1,1′‐(ethane‐1,2‐diyl)bis[1,1‐diphenylphosphine]), dppp, dppb, and dpppe; P=Ph3P and (MeO)3P) with SnX2 (X=Br or I) resulted in the halogen exchange to yield the complexes [PtX2(P2)]. In contrast, treatment of cis‐[PtBr2(dppm)] with SnBr2 resulted in the insertion of SnBr2 into the Pt? Br bond to form cis‐[Pt(SnBr3)2(dppm)], and this product was in equilibrium with the starting complex cis‐[PtBr2(dppm)]. Moreover, the reaction of cis‐[PtCl2(dppb)] with a mixture SnCl2/SnI2 in a 2 : 1 mol ratio resulted in the formation of cis‐[PtI2(dppb)] as a consequence of the selective halogen‐exchange reaction. 31P‐NMR Data for all complexes are reported, and a correlation between the chemical shifts and the coupling constants was established for mono‐ and bis(trichlorostannyl)platinum complexes. The effect of the alkane chain length of the ligand and SnII halide is described. 相似文献
34.
Rafati AA Bagheri A Khanchi AR Ghasemian E Najafi M 《Journal of colloid and interface science》2011,361(1):252-258
The specific sorption of Eu(III) and Y(III) on γ-alumina was investigated with solid-state (1)H NMR. Solution pH was shown to influence the recorded (1)H NMR spectra of γ-alumina, and thus, metal ion-containing samples were prepared under constant pH conditions, 8.00±0.05. The metal ion concentration in the samples was varied between 6.58×10(-7) M - 3.95×10(-4) M in case of Y(3+) and 6.58×10(-8) M - 1.32×10(-4) M in case of Eu(3+). The mineral concentration was kept constant at 4 g/l. After separation of the liquid phase, the samples were dried under vacuum to remove physisorbed water from the mineral surface. However, even after 48 h of drying at 150°C and 20 mTorr, water was still detected in the proton spectra as two distinct peaks with chemical shifts at 1.3 and 0.9 ppm. The europium addition to the γ-alumina samples induced significant spectral changes in comparison with yttrium-containing samples. These changes were attributed to the paramagnetism of europium rather than to complexation reactions occurring on the mineral surface. Proton spectra obtained for yttrium samples were therefore used to detect the spectral changes induced by the sorption reaction itself. The results revealed a large distribution of protons being removed from the mineral surface upon yttrium complexation. Removed protons were assigned to both bridging surface hydroxyls such as (Al(VI))(2)-OH as well as to terminal hydroxyls, e.g., of type Al(VI)-OH. Acidic protons belonging to (Al(VI))(3)-OH groups were not observed to participate in the surface reaction. 相似文献
35.
M.Z. Kassaee Z. Najafi F.A. Shakib M.R. Momeni 《Journal of organometallic chemistry》2011,696(10):2059-2064
The effects of alkyl, amino, phosphino, oxy, and thio moieties on the stability, multiplicity and reactivity of α-cyclopropylsilylenes with acyclic, cyclic, and unsaturated cyclic structures are compared and contrasted at B3LYP/AUG-cc-pVTZ//B3LYP/6-31G∗ level. The simultaneous stabilizing effects of heteroatom and cyclopropyl α-substituents on the above silylenes create the following trend of singlet-triplet energy gaps (?ES-T): amino ≈ oxy > thio > alkyl > phosphino. The ΔES-T values for all the above silylenes increase through cyclization, because cyclization stabilizes singlet states of all our α-heteroatom substitued silylenes while destabilizes their corresponding triplet states. The ΔES-T values for all the heteroatom substituted cyclic silylenes decrease upon unsaturation, due to the higher stabilization of triplet compared to the singlet state. Interestingly, isodesmic reactions showed the phosphino substituents stabilize the triplet more than the corresponding singlet states, not only in the unsaturated form but also in the acyclic and cyclic structures. This is in contrast to cyclopropyl which stabilizes singlet considerably more than the corresponding triplet states. The reactivity of the above silylenes is discussed in terms of nucleophilicity, and electrophilicity; showing phosphino- and aminocyclopropylsilylenes more nucleophilic than oxy- and thiocyclopropylsilylenes. 相似文献
36.
Mohammadi-Manesh H Alavi S Woo TK Najafi B 《Physical chemistry chemical physics : PCCP》2011,13(6):2367-2377
We perform molecular dynamics simulations (up to 6 ns) for the structure I clathrate hydrates of linear molecules CS, CS(2), OCS, and C(2)H(2) in large cages at different temperatures in the stability range to determine the angular distribution and dynamics of the guests in the large cages. The long axes of linear guest molecules in the oblate large structure I clathrate hydrate cages are primarily confined near the equatorial plane of the cage rather than axial regions. This non-uniform spatial distribution leads to well-known anisotropic lineshapes in the solid-state NMR spectra of the guest species. We use the dynamic distribution of guest orientations in the cages during the MD simulations at different temperatures to predict the (13)C NMR powder lineshapes of the guests in the large cages. The length of the guests and intermolecular interactions of the guests in the water cages determine the angular distribution and the mobility of the guests in the sI large cages at different temperatures. At low temperatures the range of motion of the guests in the cages are limited and this is reflected in the skew of the predicted (13)C lineshapes. As the guest molecules reach the fast motion limit at higher temperatures, the lineshapes for CS, OCS, and C(2)H(2) are predicted to have the "standard" powder lineshapes of guest molecules. 相似文献
37.
A. Najafi R. Golestanian 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,34(1):99-103
Dynamics of an array of line defects interacting with a background elastic medium is studied in the linear regime. It is shown that the inertial coupling between the defects and the ambient phonons leads to an anomalous response behavior for the deformation modes of a defect-lattice, in the form of anisotropic and anomalous mass and elastic constants, resonant dissipation through excitation of phonons, and instabilities. The case of a single fluctuating line defect is also studied, and it is shown that it could lead to formation of shock waves in the elastic medium for sufficiently high frequency deformation modes.Received: 18 February 2003, Published online: 23 July 2003PACS:
63.20.Mt Phonon-defect interactions -
61.72.Bb Theories and models of crystal defects -
66.30.Lw Diffusion of other defects 相似文献
38.
The problem of gamma ray spectrum analysis has been is studied. The difficulties encountered by different methods are explained. An empirical method which uses an experimental peak for the analysis of spectrum is developed. This method utilizes the simple algorithm of linear least squares and is able to analyze the multiplets. It gives more accurate results than other ones. It is well adapted for automatic treatment of gamma ray spectra by small computers. 相似文献
39.
40.
Periodica Mathematica Hungarica - In this paper, we define a weaker notion of Douglas metrics, namely weakly Douglas metrics. A Finsler metric satisfies a projectively invariant equation... 相似文献