全文获取类型
收费全文 | 118篇 |
免费 | 3篇 |
国内免费 | 19篇 |
专业分类
化学 | 84篇 |
力学 | 1篇 |
数学 | 33篇 |
物理学 | 22篇 |
出版年
2023年 | 2篇 |
2022年 | 1篇 |
2021年 | 5篇 |
2020年 | 2篇 |
2019年 | 6篇 |
2018年 | 6篇 |
2017年 | 3篇 |
2016年 | 6篇 |
2014年 | 7篇 |
2013年 | 4篇 |
2012年 | 10篇 |
2011年 | 9篇 |
2010年 | 7篇 |
2009年 | 5篇 |
2008年 | 14篇 |
2007年 | 10篇 |
2006年 | 4篇 |
2005年 | 8篇 |
2004年 | 2篇 |
2003年 | 5篇 |
2002年 | 2篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 9篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 1篇 |
1992年 | 1篇 |
1989年 | 1篇 |
1986年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有140条查询结果,搜索用时 187 毫秒
91.
The measurement accuracy of a parallel-plate interferometer for angular displacement measurement is analyzed. The measurement accuracy of angular displacement is not only related to the accuracy of phase extraction, but also related to initial incident angle, refraction index and thickness of plane-parallel plate as well as wavelength's stability of laser diode, etc. Theoretical analysis and computer simulation show that the measurement error of the angular displacement bears a minimum value when choosing an optimal initial incident angle in a large range. These analytical results serve as a guide in practical measurement. In this interferometer, reducing the refraction index or increasing the thickness of the parallel plate can improve the measurement accuracy; and the relative error of the phase measurement is 3.0×10−4 corresponding to 1 °C temperature variation. Based on these theoretical and experimental results, the measurement accuracy of the parallel-plate interferometer is up to an order of 10−8 rad. 相似文献
92.
基于分支设置的质量导引相位展开算法 总被引:3,自引:0,他引:3
二维相位展开方法是近年来较为活跃、引起关注的一个研究课题,它在许多测量应用中有着重要的作用。尽管掩膜阻断算法在多个领域都有成功应用实例,该算法存在着固有的缺陷。为了克服掩膜阻断算法的缺陷,综合分支阻断方法和质量导引方法的优点,提出一种基于分支设置的质量导引相位展开新算法。它先以一个初始质量图来引导分支的设置,然后把分支对应的相位质量设置为最低,从而产生一个新的质量图,最后按新质量图来引导相位展开,并使用几个包裹相位图来验证此方法的有效性。计算机模拟相位图和实际相位图的相位展开结果表明,在存在复杂轮廓不连续和高噪声的情况下,该算法优于模板阻断算法,能得到较好的相位展开结果。 相似文献
93.
Hang Huo Yanqiu Jiang Tingting Zhao Junlei Wang Defeng Li Xianzhu Xu Kaifeng Lin 《化学:亚洲杂志》2019,14(9):1496-1505
In this work, three organosilica precursors functionalized with carbamate moieties were synthesized by condensing of 3‐isocyanatopropyltriethoxysilane and coupling regents of either hydroquinone (HQ), bisphenol A (BPA), or 1,1′‐bi‐2‐naphthol (BN). These organosilica precursors were covalently bonded in the framework of periodic mesoporous organosilicas by co‐condensation and hydrolysis with tetraethyl orthosilicate (TEOS) under hydrothermal treatment. The compositions and physical properties were characterized with FTIR, XRD, thermogravimetric/differential thermal analysis (TG/DTA), 29Si NMR, 13C NMR spectroscopies, SEM, TEM, and BET technologies. These characterizations suggest that three different structures were formed as the result of different sizes and compositions of the organosilica precursors. The three mesoporous organosilicas were applied as heterogeneous catalysts in the one‐pot cascade Knoevenagel and Michael cyclopropanic reactions for the synthesis of cyclopropanic derivatives and showed excellent activity and selectivity. The highest conversion was obtained with mesoporous catalyst (MC)‐HQ owing to its ordered mesostructure, highest surface area, and weakest stereo effect of the organic linking groups compared with MC‐BAP and MC‐BN. This methodology employed cheaper and more easily obtainable raw materials as reagents over the traditional alkene additive system and these heterogeneous catalysts exhibit superior performance and recyclability than typical homogeneous organic catalysts. 相似文献
94.
Improving the convergence of non-interior point algorithms for nonlinear complementarity problems 总被引:1,自引:0,他引:1
Recently, based upon the Chen-Harker-Kanzow-Smale smoothing function and the trajectory and the neighbourhood techniques, Hotta and Yoshise proposed a noninterior point algorithm for solving the nonlinear complementarity problem. Their algorithm is globally convergent under a relatively mild condition. In this paper, we modify their algorithm and combine it with the superlinear convergence theory for nonlinear equations. We provide a globally linearly convergent result for a slightly updated version of the Hotta-Yoshise algorithm and show that a further modified Hotta-Yoshise algorithm is globally and superlinearly convergent, with a convergence -order , under suitable conditions, where is an additional parameter.
95.
Zhengyi Li Jinbei Yan Yue Yin Zhihui Zhang Zhiming Wang Defeng Xu Xiaoqiang Sun 《中国化学》2016,34(7):657-661
A simple and nontoxic fluorescent chemosensor of di‐O‐methyl curcumin has been prepared from curcumin. The sensor exhibited selective and sensitive fluorescent responses toward Al3+ over a wide range of metal ions, such as Mn2+, Ce3+, Pt2+, Sn4+, Hg+, Sb3+, K+, Ca2+, Mg2+, Ba2+, Cu2+, Ni2+, Na+, NH4+, Ag+, Pb2+, Zn2+, Fe2+, Fe3+, Hg2+ and Cr3+ in ethanol/water. The free ligand showed quite weak fluorescence emission due to the isomerization of C?O double bond in the excited state, however, after addition of Al3+, fluorescence emission results in a prominent fluorescence enhancement. 相似文献
96.
Polycarbonate/clay nanocomposites (PCNs) were prepared by melt intercalation using epoxy resin as a compatibilizer. The intercalated structure of PCNs was investigated using XRD and TEM. The linear and nonlinear dynamic rheological properties of PCNs were measured by the use of a parallel plate rheometer. The results reveal that the presence of epoxy influences rheological behavior of PCNs significantly. Addition of epoxy can improve dispersion of clay, enhancing the low-frequency viscoelastic responses; while high loadings of epoxy lead to a severe degradation of PC matrix, decreasing the high-frequency responses together with the plasticizing effect of excessive epoxy. Both of these two effects result in invalidity of time-temperature superposition. Moreover, all samples show high sensitivity to both the quiescent and large amplitude oscillatory shear (LAOS) deformation, despite enhanced percolation of tactoids due to the compatibilization of epoxy. 相似文献
97.
98.
High-temperature synthesis of stable ordered mesoporous silica materials by using fluorocarbon-hydrocarbon surfactant mixtures 总被引:3,自引:0,他引:3
Li D Han Y Song J Zhao L Xu X Di Y Xiao FS 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(23):5911-5922
Highly ordered hexagonal mesoporous silica materials (JLU-20) with uniform pore sizes have been successfully synthesized at high temperature (150-220 degrees C) by using fluorocarbon-hydrocarbon surfactant mixtures. The fluorocarbon-hydrocarbon surfactant mixtures combine the advantages of both stable fluorocarbon surfactants and ordered hydrocarbon surfactants, giving ordered and stable mixed micelles at high temperature (150-220 degrees C). Mesoporous JLU-20 shows extraordinary stability towards hydrothermal treatment (100 % steam at 800 degrees C for 2 h or boiling water for 80 h), thermal treatment (calcination at 1000 degrees C for 4 h), and toward mechanical treatment (compressed at 740 MPa). Transmission electron microscopy images of JLU-20 show well-ordered hexagonal arrays of mesopores with one-dimensional (1D) channels and further confirm that JLU-20 has a two-dimensional (2D) hexagonal (P6 mm) mesostructure. 29Si HR MAS NMR spectra of as-synthesized JLU-20 shows that JLU-20 is primarily made up of fully condensed Q4 silica units (delta=-112 ppm) with a small contribution from incompletely cross-linked Q3 (delta=-102 ppm) as deduced from the very high Q4/Q3 ratio of 6.5, indicating that the mesoporous walls of JLU-20 are fully condensed. Such unique structural features should be directly attributed to the high-temperature synthesis, which is responsible for the observed high thermal, hydrothermal, and mechanical stability of the mesoporous silica materials with well-ordered hexagonal symmetry. Furthermore, the concept of "high-temperature synthesis" is successfully extended to the preparation of three-dimensional (3D) cubic mesoporous silica materials by the assistance of a fluorocarbon surfactant as a co-template. The obtained material, designated JLU-21, has a well-ordered cubic Im3m mesostructure with fully condensed pore walls and shows unusually high hydrothermal stability, as compared with conventional cubic mesoporous silica materials such as SBA-16. 相似文献
99.
We analyze the rate of local convergence of the augmented Lagrangian method in nonlinear semidefinite optimization. The presence
of the positive semidefinite cone constraint requires extensive tools such as the singular value decomposition of matrices,
an implicit function theorem for semismooth functions, and variational analysis on the projection operator in the symmetric
matrix space. Without requiring strict complementarity, we prove that, under the constraint nondegeneracy condition and the
strong second order sufficient condition, the rate of convergence is linear and the ratio constant is proportional to 1/c, where c is the penalty parameter that exceeds a threshold .
The research of Defeng Sun is partly supported by the Academic Research Fund from the National University of Singapore. The
research of Jie Sun and Liwei Zhang is partly supported by Singapore–MIT Alliance and by Grants RP314000-042/057-112 of the
National University of Singapore. The research of Liwei Zhang is also supported by the National Natural Science Foundation
of China under project grant no. 10471015 and by the Scientific Research Foundation for the Returned Overseas Chinese Scholars,
State Education Ministry, China. 相似文献
100.
Defeng Qi Prof. Jie Xu Dr. Yitong Zhou Dr. Hao Zhang Jianqiao Shi Prof. Kun He Prof. Yifei Yuan Prof. Jun Luo Prof. Shun Wang Prof. Yong Wang 《Angewandte Chemie (International ed. in English)》2023,62(37):e202307355
Co-based material catalysts have shown attractive application prospects in the 2 e− oxygen reduction reaction (ORR). However, for the industrial synthesis of H2O2, there is still lack of Co-based catalysts with high production yield rate. Here, novel cyclodextrin-supported Co(OH)2 cluster catalysts were prepared via a mild and facile method. The catalyst exhibited remarkable H2O2 selectivity (94.2 % ~ 98.2 %), good stability (99 % activity retention after 35 h), and ultra-high H2O2 production yield rate (5.58 mol gcatalyst−1 h−1 in the H-type electrolytic cell), demonstrating its promising industrial application potential. Density functional theory (DFT) reveals that the cyclodextrin-mediated Co(OH)2 electronic structure optimizes the adsorption of OOH* intermediates and significantly enhances the activation energy barrier for dissociation, leading to the high reactivity and selectivity for the 2 e− ORR. This work offers a valuable and practical strategy to design Co-based electrocatalysts for H2O2 production. 相似文献