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1.
This work extends our previous understanding concerning the nonlinear responses of entangled polymer solutions and melts to large external deformation in both simple shear and uniaxial extension. Many similarities have recently been identified for both step strain and startup continuous deformation, including elastic yielding, i.e., chain disentanglement after cessation of shear or extension, and emergence of a yield point during startup deformation that involves a deformation rate in excess of the dominant molecular relaxation rate. At a sufficiently high constant Hencky rate, uniaxial extension of an entangled melt is known to produce window-glass-like rupture. The present study provides evidence against the speculation that chain entanglements tie up into "dead knots" in constant-rate extension because of the exponentially growing chain stretching with time. In particular, it is shown that even Instron-style tensile stretching, i.e., extending a specimen by applying a constant velocity on both ends, results in rupture. Yet, in the same rate range, the same entangled melt only yields in simple shear, and the resulting shear banding is clearly not a characteristic of rupture. Thus, we conclude that chain entanglements respond to simple shear in the manner of yielding whereas uniaxial extension is rather effective in causing some entanglements to lock up, making it impossible for the entanglement network to yield at high rates. 相似文献
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Five entangled melts, with the number of entanglements per chain ranging from 25 to 160, have been studied to illustrate how cohesive strength can be overcome in either continuous or interrupted extension (i.e., during or after uniaxial stretching). The internal elastic stress due to chain deformation from imposed strain appears to be the cause of the observed yielding behavior that reveals scaling laws. The visual signature of the elastic breakup is the occurrence of nonuniform extension. The yield phenomena may be understood at a force level. 相似文献
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采用传统的熔融法制备了Er~(3+)掺杂的新型铋酸盐玻璃(Li_2O-SrO-ZnO-Bi_2O_3,LSZB),并对其光谱性质进行了表征,分析了玻璃的拉曼光谱、吸收光谱、荧光光谱,利用Judd-Ofelt理论研究了其荧光特性。LSZB玻璃样品中Er~(3+)的~4I_(13/2)→~4I_(15/2)跃迁发射峰位于1.53 μm处,半高宽约为78 nm。样品中Er~(3+)的~4I_(13/2)能级寿命为2.848 ms,量子效率为99.93%,受激发射截面达到9.76×10~(-21)cm~2。以上结果显示,Er~(3+)掺杂LSZB玻璃有良好的光谱特性。 相似文献
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研究了重金属氧氟硅铋酸盐玻璃 (50-x)SiO2 xBi2O3 50PbF2(x=0, 3, 5, 8, 10, 13, 15 mol%)中Er3+离子的吸收光谱、荧光光谱、荧光半高宽、荧光 寿命和热稳定性能.应用Judd Ofelt理论计算了玻璃的强度参数Ωt(t=2,4,6),应用 McCumber计算了能级4I13/2→4I15/2跃迁的受激发射截面. 结果发现荧光半高宽与Ω6有较大联系,Ω6越大,荧光半高宽越宽.对Er3+
关键词:
重金属氧氟硅铋酸盐玻璃
光谱性质
Er3+离子
Judd Ofelt参数 相似文献
6.
Comparative study of spectroscopic properties of Er^3+/Yb^3+-codoped tellurite glass and fibres under 980nm excitation* 下载免费PDF全文
A tellurite fibre of TeO_{2}-ZnO-La_{2}O_{3}-Li_{2}O glass codoped with 20000 ppm ytterbium and 5000 ppm erbium was fabricated by the suction casting and rod-in-tube technologies. The absorption spectrum of Er^{3+}/Yb^{3+} -codoped bulk glass has been measured. From the Judd-Ofelt intensity parameters, the spontaneous emission probability and radiative lifetime τ_{rad} of Er^{3+}:{}^{4}I_{13/2}→{}^{4}I_{15/2} transition for the bulk glass have been calculated. The emission fluorescence spectra and lifetimes around 1.5μm, and subsequent upconversion fluorescence in the range of 500-700nm were measured in fibres and compared with those in bulk glass. The changes in amplified spontaneous emission with fibre length and pumping power was also measured. It was found that the emission spectrum from erbium in fibres is almost twice as broad as the corresponding spectrum in bulk glass when pumped at 980nm. 相似文献
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Xu Jie-Cheng Cheng Ling-Ling Shen Wei-Zhen Wang Shi-Qing Qian Cui-He Huang Jia-Xin 《中国化学》1986,4(2):160-167
DSIP and its fourteen analogs as well as three short peptides were synthesized by solid phase method. The design of the analogs was based on the consideration of the introduction of D-amino acid into the molecules to inhibit the enzymatic hydrolysis and the introduction of amino acids with a hydrophobic side chain. The modification was placed on the position of 1, 3, 4, 5, 8 and 9, e.g. D- Trp1, Tyr1, Tyr1 Phe5, D-Trp1 Phe8, Trp3,4, D-Trp1,3,4 Phe8, D-Trp3,4 Phe8 D-Glu9, D-pF-Phe3,4 Phe8 D-Glu9, Phe5, Glu5 Asp9, Tyr6 Asp9, Asp9 and Ala7-DSIP as well as Trp-Ala-Gly-Gly-Asp, Trp-Ala-Gly-Gly-Glu and Trp-Gly-Glu. DSIP and Phe5-DSIP were also prepared by pentafluorophenyl ester method. The purity of the synthetic peptides was checked by amino acid analysis, elemental analysis, thin layer chromatography and paper electrophoresis. The biological assay showed that the analogs of D-Trp1, Tyr1, Tyr1 Phe5 and Ala7-DSIP as well as three short peptides were inactive whereas Phe5-DSIP showed similar activity as that of synthetic DSIP. 相似文献
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