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31.
The viscoelastic properties of poly(n‐butyl acrylate), poly(ethyl acrylate) and poly(methyl acrylate) melts have been studied using samples that varied in both molar mass and the mol% branched repeat units, these properties having been previously determined by gel permeation chromatography and 13C NMR spectroscopy, respectively. Poly(n‐butyl acrylate) was studied most extensively using seven samples; one sample of poly(n‐butyl acrylate), two samples of poly(ethyl acrylate) and one sample of poly(methyl acrylate) were used to study the effect of side‐group size. Storage and loss moduli were measured over a range of frequency (1 × 10?3 to 1 × 102 rad s?1) at temperatures from Tg + 20 °C to Tg + 155 °C and then shifted to form master curves at Tg + 74 °C through use of standard superposition procedures. The plateau regions were not distinct due to the broad molar mass distributions of the polyacrylates. Hence, the upper and lower limits of shear storage modulus from the nominal ‘plateau’ region of the curves for the seven poly(n‐butyl acrylate) samples were used to calculate the chain molar mass between entanglements, Me, which gave the range 13.0 kg mol?1 < Me < 65.0 kg mol?1. The Graessley–Edwards dimensionless interaction density and dimensionless contour length concentration were calculated for poly(n‐butyl acrylate) using the mean value of plateau modulus (1.2 × 105 Pa) and three different methods for estimation of the Kuhn length; the data fitted closely to the Graessley–Edwards universal plot. The Williams–Landel–Ferry C1 and C2 parameters were determined for each of the polyacrylates; the data for the poly(n‐butyl acrylate) samples indicate an overall reduction in C1 and C2 as the degree of branching increases. Although the values of C1 and C2 were different for poly(n‐butyl acrylate), poly(ethyl acrylate) and poly(methyl acrylate), there is no trend for variation with structure. Thus the viscoelastic properties of the polyacrylate melts are similar to those for other polymer melts and, for the samples investigated, the effect of molar mass appears to dominate the effect of branching. © 2001 Society of Chemical Industry 相似文献
32.
Markus A. Cirone Aldo Delgado Dietmar G. Fischer Matthias Freyberger Holger Mack Michael Mussinger 《Quantum Information Processing》2002,1(5):303-326
We examine the problem of determining the parameters that describe a quantum channel. It is assumed that the users of the channel have at best only partial knowledge of it and make use of a finite amount of resources to estimate it. We discuss simple protocols for the estimation of the parameters of several classes of channels that are studied in the current literature. A quantitative measures of the quality of the estimation schemes can be given on the basis of the standard deviation or of the fidelity. Protocols that employ entangled particles are also discussed. The use of entangled particles as a nonclassical resource enhances the estimation quality of some classes of quantum channel. Further, the methods presented here can be extended to higher dimensional quantum systems.
PACS: 03.67.Hk 相似文献
33.
Mutual convertibility of bound entangled states under local quantum operations and classical communication (LOCC) is studied. We focus on states associated with unextendible product bases (UPB) in a system of three qubits. A complete classification of such UPBs is suggested. We prove that for any pair of UPBs S and T the associated bound entangled states S and T cannot be converted to each other by LOCC, unless S and T coincide up to local unitaries. More specifically, there exists a finite precision (S,T) > 0 such that for any LOCC protocol mapping S into a probabilistic ensemble (p, ), the fidelity between T and any possible final state satisfies F(T, ) = 1 - (S,T).PACS: 03.65.Bz; 03.67.-a; 89.70+c. 相似文献
34.
Wójcik Antoni Grudka Andrzej Chhajlany Ravindra W. 《Quantum Information Processing》2003,2(3):201-206
The notion of equivalence of maximally entangled bases of bipartite d–dimensional Hilbert spaces d d is introduced. An explicit method of inequivalent bases construction is presented.
PACS: 03.67.-a 相似文献
35.
提出了一个基于纠缠交换理论犤2~4犦的量子密钥分发协议。安全性分析证明此QKD协议是无条件安全,而且十分有效。 相似文献
36.
基于量子物理原理的量子密码术已被证明是保密通信中密钥安全分配的有效手段。本文介绍了量子密码的基本原理,介绍了实现量子加密的几种方案,并主要研究了基于EPR纠缠对的密钥分配机制,还讨论了量子密码通信的历史发展和指出现存在的问题以及未来的发展前景。 相似文献
37.
用量子信息理论研究具有原子运动的双光子Jaynes-Cummings模型中运动原子与光场的纠缠特性.结果表明:当运动原子的场模结构参数p取值较小时,系统的纠缠度不具有周期振荡特性,在p取值较大时,系统的纠缠度有明显的周期振荡特性,且振荡周期是原子静止情况下的2倍;在运动原子处于基态或激发态时,系统处于消纠缠状态,当运动原子处在相干叠加态时,原子才与场发生纠缠. 相似文献
38.
采用悬浮聚合法合成了甲基丙烯酸正丁酯、甲基丙烯酸β羟乙酯二元共聚树脂,采用冻胶纺丝技术制备了纤维状共聚物树脂,研究了甲基丙烯酸β羟乙酯含量对树脂饱和吸油率、吸油速率以及充分溶胀后树脂剩余率的影响,分别利用傅立叶变换红外光谱(FTIR)和动态热机械分析仪(DMA)对树脂的化学结构和动态力学性能进行了分析和讨论,利用软件materials studio对甲基丙烯酸正丁酯、甲基丙烯酸β羟乙酯共聚过程中的物理缠结能力进行了模拟预测。 相似文献
39.
40.
提出一种新的消息发送者和接收者同时匿名的经典消息通信方案.方案通过制备量子连续变量纠缠态,在参与者中移动式传输粒子,将1比特经典消息编码在不同的模式中.消息接收者可以计算得到匿名消息,然后通过不同模式的计算结果检验本次通信中的参与者诚实度,从而判断匿名消息是否有效.方案将传输和检测两个过程合并设计在同一轮通信中,通信信号和检测结论基于同一轮通信中的信道编码,可以验证具有自适应特征的参与者(检测过程和通信过程表现不一致的参与者)作弊.除了指数小的概率,发送者和接收者的匿名性和消息的私密性都得到保护. 相似文献