全文获取类型
收费全文 | 259篇 |
免费 | 46篇 |
国内免费 | 14篇 |
专业分类
化学 | 70篇 |
晶体学 | 2篇 |
力学 | 61篇 |
综合类 | 16篇 |
数学 | 44篇 |
物理学 | 126篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 18篇 |
2021年 | 10篇 |
2020年 | 9篇 |
2019年 | 4篇 |
2018年 | 6篇 |
2017年 | 6篇 |
2016年 | 12篇 |
2015年 | 9篇 |
2014年 | 29篇 |
2013年 | 22篇 |
2012年 | 19篇 |
2011年 | 15篇 |
2010年 | 13篇 |
2009年 | 11篇 |
2008年 | 19篇 |
2007年 | 22篇 |
2006年 | 13篇 |
2005年 | 12篇 |
2004年 | 18篇 |
2003年 | 4篇 |
2002年 | 7篇 |
2001年 | 1篇 |
2000年 | 6篇 |
1999年 | 5篇 |
1998年 | 1篇 |
1997年 | 4篇 |
1996年 | 4篇 |
1995年 | 3篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1984年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有319条查询结果,搜索用时 31 毫秒
81.
Based on orthogonal Latin cubes, an image cryptosystem with confusion–diffusion–confusion cipher architecture has been proposed recently (Inf. Sci. 2019, 478, 1–14). However, we find that there are four fatal vulnerabilities in this image cryptosystem, which leave open doors for cryptanalysis. In this paper, we propose a reference-validation inference algorithm and design screening-based rules to efficiently break the image cryptosystem. Compared with an existing cryptanalysis algorithm, the proposed method requires fewer pairs of chosen plain-cipher images, and behaves stably since different keys, positions of chosen bits and contents of plain images will not affect the cryptanalysis performance. Experimental results show that our cryptanalysis algorithm only requires pairs of chosen plain-cipher images, where represents the image’s resolution. Comparative studies demonstrate effectiveness and superiority of the proposed cryptanalysis algorithm. 相似文献
82.
N. O. Mahmoodi M. Mamaghani A. Ghanadzadeh M. Arvand M. Fesanghari 《Journal of Physical Organic Chemistry》2010,23(3):266-270
Synthesis of several ‘dyes’, analogs of retinal imine visual pigment via nucleophilic attack of some secondary amines to pyridinium salts following precyclic ring‐opening reaction, is discussed. The photochromic properties of these dyes have been studied by UV‐Vis spectroscopy under irradiation of UV light. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
83.
密码芯片运行时的光辐射可泄露其操作和数据的重要特征信息. 基于单光子探测技术, 设计并构建了针对CMOS半导体集成电路芯片光辐射信号的采集、传输、处理和分析的光电实验系统. 以AT89C52单片机作为实验对象, 采用时间相关单光子计数技术, 对不同工作电压下密码芯片的光辐射强度进行了对比, 分析了芯片指令级光辐射信息的操作依赖性和数据依赖性. 此外, 使用示波器对时间相关单光子计数技术在芯片光辐射分析上的可行性进行了验证. 实验结果表明, 采用时间相关单光子计数技术对密码芯片进行光辐射分析, 是一种直接有效的中低等代价光旁路分析攻击手段, 对密码芯片的安全构成了严重的现实威胁. 相似文献
84.
Chen Wang Yao Fu Prof. Qing‐Xiang Guo Prof. Lei Liu Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(8):2586-2598
Quantitative nucleophilicity scales are fundamental to organic chemistry and are usually constructed on the basis of Mayr’s equation [log k=s(N+E)] by using benzhydrylium ions as reference electrophiles. Here an ab initio protocol was developed for the first time to predict the nucleophilicity parameters N of various π nucleophiles in CH2Cl2 through transition‐state calculations. The optimized theoretical model (BH&HLYP/6‐311++G(3df,2p)//B3LYP/6‐311+G(d,p)/PCM/UAHF) could predict the N values of structurally unrelated π nucleophiles within a precision of ca. 1.14 units and therefore may find applications for the prediction of nucleophilicity of compounds that are not readily amenable to experimental characterization. The success in predicting N parameters from first principles also allowed us to analyze in depth the electrostatic, steric, and solvation energies involved in electrophile–nucleophile reactions. We found that solvation does not play an important role in the validity of Mayr’s equation. On the other hand, the correlations of the E, N, and log k values with the energies of the frontier molecular orbitals indicated that electrostatic/charge‐transfer interactions play vital roles in Mayr’s equation. Surprising correlations observed between the electrophile–nucleophile C? C distances in the transition state, the activation energy barriers, and the E and N parameters indicate the importance of steric interactions in Mayr’s equation. A method is then proposed to separate the attraction and repulsion energies in the nucleophile–electrophile interaction. It was found that the attraction energy correlated with N+E, whereas the repulsion energy correlated to the s parameter. 相似文献
85.
Faisal A.A. El-Orany 《Physics letters. A》2010,374(8):1097-1100
In [J.S. Shaari, M. Lucamarini, M.R.B. Wahiddin, Phys. Lett. A 358 (2006) 85] the deterministic six states protocol (6DP) for quantum communication has been developed. This protocol is based on three mutually unbiased bases and four encoding operators. Information is transmitted between the users via two qubits from different bases. Three attacks have been studied; namely intercept-resend attack (IRA), double-CNOT attack (2CNOTA) and quantum man-in-the-middle attack. In this Letter, we show that the IRA and 2CNOTA are not properly addressed. For instance, we show that the probability of detecting Eve in the control mode of the IRA is 70% instead of 50% in the previous study. Moreover, in the 2CNOTA, Eve can only obtain 50% of the data not all of it as argued earlier. 相似文献
86.
Simon G. Bott Sang-Woo Lee Kaiyuan Yang Michael G. Richmond 《Journal of chemical crystallography》2005,35(3):203-209
The reducing agent [Et3BH][Li] reacts with diag-CpRe(CO)2Br2 in THF at –78C by polyene ring attack to give the anionic rhenium(I) compound [(4-C5H6)Re(CO)2Br2]–. Monitoring the reaction by low-temperature IR spectroscopy has revealed that the reaction between diag-CpRe(CO)2Br2 and hydride is instantaneous and that the known compounds CpRe(CO)2Br– and CpRe(CO)2Br(H) are not formed as the principal reduction products. The reduced compound [(4-C5H6)Re(CO)2Br2]– is extremely temperature sensitive and decomposes upon warming to afford low yields of CpRe(CO)3. We have explored the reactivity of the hydride reduction product with added CO and have isolated and structurally characterized the anionic tetracarbonyl compound trans(Br)-[Re(CO)4Br2]– as the tetraphenylphosphonium salt. trans(Br)-[Re(CO)4Br2][PPh4] crystallizes in the monoclinic space group C2/c, a = 16.908(2) Å, b = 7.1579(7) Å, c = 23.543(2) Å, = 96.144(9), V = 2832.9(5) Å3, Z = 4, Dcacl = 1.870 g/cm3; R = 0.0419, Rw = 0.0450 for 1629 observed reflections with I > 3(I). The reaction between the product of hydride reduction and dppe is shown by IR and 31P NMR spectroscopies to produce mer-cis-BrRe(CO)2(2-dppe)(1-dppe). 相似文献
87.
昆虫自由飞行时翅膀攻角的光学测量 总被引:2,自引:0,他引:2
昆虫运动空气动力学研究需要测量昆虫运动的多种参数。其中 ,翅膀攻角是主要参数 ,是流体分析时主要的边界条件之一。由于昆虫的运动参数的测量同一般的测量相比具有一些特殊要求 ,它要求一定是非接触测量 ,因此成功的测量方法大都集中在光学测量方法上。本文以近年来有关昆虫自由飞行的实验为基础 ,着重介绍几种比较有特色的翅膀攻角的光学测量方法 相似文献
88.
End-stage renal diseases are affecting many patients and as a result, demand to receive dialysis service is growing annually. Morbidity and mortality rates are reported to be higher in comparison with healthy humans. The reason is reported to be the hemoincompatiblity of blood purification membranes, which hinders patients’ lives. Activation of different immune systems in the body, in case of blood-membrane interaction, results in several side effects, of which cardiovascular shocks have been mentioned to be a major one. Efforts to solve this issue have resulted in different generations of dialysis membranes. Zwitterionic immobilized membranes are the latest (third) generation, which owns a higher degree of hemocompatiblity with more stability of immobilized structures. This critical review intends to cover recent efforts conducted over the zwitterionization of polymeric membrane surfaces with the goal of improving hemocompatibility. Different aspects of third-generation membranes are discussed for a better understanding of the current gap and gathering the knowledge to further develop the field. Accordingly, this critical survey provides an in-depth understanding of blood purification membranes zwitterionization for paving the way for the optimum enhancement of hemodialysis membrane hemocompatibility. 相似文献
89.
Asymmetric vortices flow over slender body and its active control at high angle of attack 总被引:5,自引:0,他引:5
The studies of asymmetric vortices flow over slender body and its active control at high angles of attack have significant
importance for both academic field and engineering area. This paper attempts to provide an update state of art to the investigations
on the fields of forebody asymmetric vortices. This review emphasizes the correlation between micro-perturbation on the model
nose and its response and evolution behaviors of the asymmetric vortices. The critical issues are discussed, which include
the formation and evolution mechanism of asymmetric multi-vortices; main behaviors of asymmetric vortices flow including its
deterministic feature and vortices flow structure; the evolution and development of asymmetric vortices under the perturbation
on the model nose; forebody vortex active control especially discussed micro-perturbation active control concept and technique
in more detail. However present understanding in this area is still very limited and this paper tries to identify the key
unknown problems in the concluding remarks.
The project supported by the National Natural Science Foundation of China (10172017), Aeronautical Science Foundation of China
(02A51048) and Foundation of National Key Laboratory of Aerodynamic Design and Research (51462020504HK0101) 相似文献
90.