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Nanocrystalline cobalt ferrites with nominal composition CoCrxFe2−xO4 ranging from x=0.0 to 0.5 with step increment of 0.25 were prepared by sol–gel auto combustion and chemical co-precipitation techniques. A comparative study of structural, electrical and magnetic properties of these ferrites has been measured using different characterization techniques. Structural and micro-structural studies were measured using X-ray diffraction, Fourier transform infra-red spectroscopy (FTIR), scanning electron microscopy and atomic force microscopy. Crystallite sizes of the series are within the range of 12–29±2 nm. Lattice parameters decrease by increasing Cr3+ concentration. FTIR confirms the presence of two lattice absorption bands. DC electrical resistivity increases to a value of ∼1010 Ω-cm with increase in Cr3+ concentration, but the most significant increase is in samples prepared by sol–gel combustion. Dielectric properties have been measured as a function of frequency at room temperature. Dielectric loss decreases to 0.1037 and 0.0108 at 5 MHz for chemical co-precipitation and sol–gel combustion, respectively. Impedance measurements further helped in analyzing the electrical properties and to separate the grain and grain boundary resistance effects using a complex impedance analysis. Magnetic parameters were studied using a vibrating sample magnetometer in the applied field of 10 kOe. The saturation magnetization decreased from 63 to 10.8 emu/gm with increase in Cr3+ concentration. 相似文献
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Urea dimethacrylates functionalized with bisphosphonate/bisphosphonic acid for improved dental materials 下载免费PDF全文
Melek Naz Guven Ece Akyol Fatma Demir Duman Havva Yagci Acar Ozlem Karahan Duygu Avci 《Journal of polymer science. Part A, Polymer chemistry》2017,55(19):3195-3204
Incorporation of bisphosphonate/bisphosphonic acid groups in dental monomer structures should increase interaction of these monomers with dental tissue as these groups have strong affinity for hydroxyapatite. Therefore, new urea dimethacrylates functionalized with bisphosphonate (1a, 1b) and bisphosphonic acid (2a, 2b) groups are synthesized and evaluated for dental applications. Monomers 1a and 1b are synthesized from 2‐isocyanatoethyl methacrylate (IEM) and two bisphosphonated amines (BPA1 and BPA2), prepared as reported elsewhere. Selective dealkylation of the bisphosphonate ester groups of 1a and 1b using trimethylsilyl bromide (TMSBr) gives monomers (2a and 2b) with bisphosphonic acid functionality. X‐ray diffractometer (XRD), Raman spectroscopy, and X‐ray photoelectron spectroscopy (XPS) analyses of monomer‐treated HAP particles show that 2a induces formation of stable monomer‐calcium salts, similar to 10‐methacryloyloxydecyl dihydrogen phosphate (MDP), with higher chemical interaction than 2b. The photopolymerization studies indicate good copolymerizability with commercial dental monomers. In vitro studies on NIH 3T3 mouse embryonic fibroblast cells have clearly shown that the tested monomers (1b and 2b) are not toxic according to the MTT standards. All these properties make these monomers suitable as biocompatible cross‐linkers/adhesives for dental applications. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3195–3204 相似文献
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L. V. Mikhal’chenko M. A. Syroeshkin M. Yu. Leonova A. S. Mendkovich A. I. Rusakov V. P. Gul’tyai 《Russian Journal of Electrochemistry》2011,47(11):1205-1210
The electrochemical behavior of 2-, 3-, and 4-nitrosonitrobenzenes (NNB) in DMF (with Bu4NClO4 suppoting salt) in the presence and in the absence of different proton donors (water, phenol, benzoic, acetic, chloroacetic,
and sulfuric acids) is studied by the methods of cyclic voltammetry, chronoamperometry and also by electrolysis at the controlled
potential. The electrochemical reduction of these compounds is shown to preferentially afford either monomeric (N-nitrophenylhydroxylamines)
or dimeric (azoxy compounds) products, which is determined by the interplay between reactions of protonation and dimerization
of NNB radical anions. The dimerization reactions proceed fast and reversibly to afford the corresponding dimeric dianions
with the basicity much higher as compared with NNB radical anions as the result of which the monomeric products are formed
in the presence of “strong” proton donors and the dimeric products form in the presence of “weak” proton donors. Like the
effective rate of formation of dimeric products, the basicity of radical anions increases in the row 4- < 3- < 2-NNB. 相似文献
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Y. G. Abov M. I. Bulgakov S. P. Borovlev F. S. Dzheparov A. D. Gul’ko V. M. Garochkin V. E. Shestopal S. V. Stepanov S. S. Trostin 《Hyperfine Interactions》1990,61(1-4):1319-1326
The experimental investigations of the polarization transport in the disordered spin system8Li −6Li in LiF crystal are considered. This process is initiated by one originally polarized beta-active8Li nucleus produced in a nuclear reaction. The autocorrelation function Foo(t) for the ran dom-walks-in-disordered-system
problem has been measured over the range Foo(t)≥0.1 Foo(0) by analysing the β-emission anisotropy. The influence of the resonance
process at double larmor frequency and of the thermal translational motion of8Li and6Li spins is studied. Results are in a good agre ement with the theory. 相似文献