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131.
近年来, 旋光性高分子的广泛应用及其特有的功能已引起了广泛关注, 尤其在手性记忆功能材料[1~3]、液晶及手性催化等方面[4~6]皆表现出良好的应用前景. 用旋光性单体合成旋光性聚合物是最常用的方法之一. 早在20世纪70年代, 就有关于聚甲基丙烯酸薄荷酯(PMnMA)的研究[7], 但有关配体参与的阴离子聚合, 基团转移聚合(GTP)及其立构规整性的研究还未见报道. 相似文献
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134.
Soo Jin Adrian Koh Tiefeng Li Jinxiong Zhou Xuanhe Zhao Wei Hong Jian Zhu Zhigang Suo 《Journal of Polymer Science.Polymer Physics》2011,49(7):504-515
Subject to a voltage, a dielectric elastomer (DE) deforms. Voltage‐induced strains of above 100% have been observed when DEs are prestretched, and for DEs of certain network structures. Understanding mechanisms of large actuation strains is an active area of research. We propose that the voltage‐stretch response of DEs may be modified by prestretch, or by using polymers with “short” chains. This modification results in suppression or elimination of electromechanical instability, leading to large actuation strains. We propose a method to select and design a DE, such that the actuation strain is maximized. The theoretical predictions agree well with existing experimental data. The theory may contribute to the development of DEs with exceptional performance. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011 相似文献
135.
Two-phase monolayers adsorbed on crystalline substrates can form many patterns. After reviewing the experimentally observed patterns on various substrates, we extend a thermodynamic theory to account for the anisotropy in surface stress, substrate stiffness, and phase boundary energy. We solve the elastic field in the anisotropic substrate by using the Stroh formalism. We then focus on the pattern of periodic stripes, and determine the orientation of the stripes that minimizes the free energy. As an example, we examine in detail the (110) surface of a cubic crystal. Depending on the parameters that characterize anisotropy, the stripes can orient along either , or [001], or certain directions off the two crystalline axes. The transition between these orientations can be of either first or second order. The predications point to additional experiments that are needed to further the understanding. 相似文献
136.
In the microelectronic and photonic industries, temperature cycling has long been used as a reliability test to qualify integrated materials structures of small feature sizes. The test is time consuming, and is a bottleneck for innovation. Tremendous needs exist to understand various failure modes in the integrated structures caused by cyclic temperatures. This paper presents a systematic study of a failure mechanism recently discovered by the authors. In a thin film structure comprising both ductile and brittle materials, the thermal expansion mismatch can cause the ductile material to plastically yield in every temperature cycle. Under certain circumstances, the plastic deformation ratchets, namely, accumulates in the same direction as the temperature cycles. The ratcheting deformation in the ductile material may build up stress in the brittle materials, leading to cracking. The paper introduces an analogy between ratcheting and viscous flow. An analytical model is developed, which explains the experimental observations, and allows one to design the structure to avert this failure mode. Design rules with increasing levels of sophistication are described. Concepts presented here are generic to related phenomena in thin film structures. 相似文献
137.
An evolving material structure is in a non-equilibrium state, with free energy expressed by the generalized coordinates. A
global approach leads to robust computations for the generalized thermodynamic forces. Those forces drive various kinetic
processes, causing dissipation at spots, along curves, surfaces and interfaces, and within volumetric regions. The actual
evolution path, and therefore the final equilibrium state, is determined by the energetics and kinetics. A virtual work principle
links the free energy landscape and the kinetic processes, and assigns a viscous environment to every point on the landscape.
The approach leads to a dynamical system that governs the evolution of generalized coordinates. The microstructural evolution
is globally characterized by a basin map in the coordinate space; and by a diversity map and a variety map in the parameter
space. The control of basin boundaries raises the issue of energetic and kinetic bifurcations. The variation of basin boundaries
under different sets of controlling parameters provides an analytical way to plot the diversity maps of structural evolution.
The project supported by the National Science Foundation (USA) through grant MSS-9258115, and by the National Natural Science
Foundation of China 相似文献
138.
Acceleration target detection based on LFM radar 总被引:1,自引:0,他引:1
In radar systems, the echo signal caused by an accelerated target can be similarly considered as linear frequency modulation (LFM) signal. In high signal-to-noise ratio (SNR), discrete polynomial-phase transform (DPT) algorithm can be used to detect the echo signal, as it has low computation complexity and high real-time performance. However, in low SNR, the DPT algorithm has a large mean square error of the rate of frequency modulation and a low detection probability. In order to detect LFM signal in low SNR, this paper proposes a detection method, segment discrete polynomial-phase transform (SDPT), which means, at first, dividing the whole echo pulses into several segments with same duration in time domain, and then, using coherent accumulation method of DFT to segments, at last, processing this signal with DPT in intra-segment. In the case of a large number of segments, the SDPT can improve the output SNR. In addition, in a certain SNR, to the target signal with big sampling interval, large acceleration and less segments, this paper proposes an algorithm to detect the LFM signal generated from the combination of an improved DPT (IDPT) and fractional Fourier transform (FRFT). The output SNR of this algorithm is connected with the length of time delay. In the simulation, when the length of the time delay is 0.2 N, the output SNR is 2.5 dB more than that which results from directly using DPT. Finally, the detection performance and algorithm complexity of the proposed algorithm were analyzed, and the simulated and measured data verify the effectiveness of the algorithm. 相似文献
139.
Li Kang Jinmao You Zhiwei Sun Chengyan Wang Zhongyin Ji Yongping Gao Yourui Suo Yulin Li 《Chromatographia》2011,73(1-2):43-50
A pre-column derivatization method for the simple, sensitive determination of biogenic amines using 10-ethyl-acridine-3-sulfonyl chloride (EASC) as labeling reagent with fluorescence detection and mass spectrometry (MS) identification has been developed. After pre-column derivatization, the labeled biogenic amines were separated on a Hypersil BDS-C18 column by gradient elution. The derivatives showed an intense protonated molecular ion corresponding m/z [M + H]+ in positive-ion mode. The collision-induced dissociation of protonated molecular ion formed specific fragment ions at m/z 196.5, m/z 222.7, m/z 224.4 and m/z 272.5, m/z 286.2. Satisfactory linear responses were observed at the concentration range of 0.02?C10 ??mol L?1 with coefficients of >0.9993. Detection limits obtained by the analysis of a derivatized standard containing 0.2 pmol of each biogenic amine, were from 20.22 to 109.2 fmol (at a signal-to-noise ratio of 3). The relative standard deviations of retention times and peak areas for each biogenic amine were <0.96 and 3.22%, respectively. Recoveries except for PUT were in the range of 96.7?C103.6% for chicken sausage and 95.8?C104.6% for pork sausage The established method for the determination of biogenic amines except for PUT from real samples was satisfactory. 相似文献
140.
制备了用于温和条件下催化氧化去除工业废气中高浓度甲醛(HCHO)的1%Pt-4%CeO2/AC催化剂. 将高浓度甲醛的催化氧化过程与双甘膦氧化制备草甘膦的反应过程集成在一起,使草甘膦合成过程中产生和排放出来的甲醛(100-300 mg/m3)在通过催化剂床层时被完全除去. 系统研究了温度、空速和甲醛含量对甲醛去除率的影响. 在气体空速(GHSV)低于20000 h-1时废气中几乎所有的甲醛都被氧化,处理后的废气中的甲醛含量低于0.1 mg/m3,甲醛的转化率为99.1%-100%. 当GHSV为30000- h-1,催化剂床层温度为12℃时,生产废气通过催化剂床层后的甲醛含量小于1.5 mg/m3,甲醛的转化率为97.56%-99.99%. 1%Pt-4%CeO2/AC催化剂的中试试验结果表明,处理后最终尾气中甲醛含量小于10 mg/m3,有效地防止了甲醛对人们健康的危害,具有良好的产业化前景. 相似文献