首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   156篇
  免费   9篇
化学   138篇
力学   1篇
数学   3篇
物理学   7篇
无线电   16篇
  2023年   2篇
  2022年   7篇
  2021年   2篇
  2020年   1篇
  2019年   4篇
  2018年   4篇
  2017年   2篇
  2016年   5篇
  2015年   3篇
  2014年   2篇
  2013年   13篇
  2012年   5篇
  2011年   8篇
  2010年   11篇
  2009年   14篇
  2008年   8篇
  2007年   6篇
  2006年   9篇
  2005年   10篇
  2004年   2篇
  2003年   4篇
  2002年   6篇
  2001年   2篇
  2000年   2篇
  1999年   2篇
  1997年   2篇
  1996年   1篇
  1994年   1篇
  1992年   2篇
  1990年   1篇
  1987年   1篇
  1984年   1篇
  1982年   3篇
  1980年   2篇
  1979年   2篇
  1978年   1篇
  1977年   2篇
  1975年   1篇
  1974年   1篇
  1971年   2篇
  1966年   1篇
  1932年   4篇
  1931年   1篇
  1917年   2篇
排序方式: 共有165条查询结果,搜索用时 125 毫秒
151.

Security and privacy are useful concerns in the context of big data. The Internet of Things (IoT) serves both to bolster and to ease security worries. IoT gadgets raise immense new security challenges, particularly with regards to things like basic framework. Be that as it may, they additionally offer approaches to help keep clients progressively secure by adding additional obstructions of safeguard to information and people. In order to sustain the integrity of data and to provide in order to implicit security for any big database, data slicing is constructive. Data slicing implicitly provides the preservation and the query performance to the database users. The sliced data are stored at servers in a distributed system to protect the data from the attackers. In this article, an intelligent and efficient model is developed to partition the polynomial data securely and to store at various servers in a distributed system. An auto-key generator spawns an encryption key to encrypt the polynomial data as a higher level security. Encrypted data is partitioned by an efficient Fast Fourier transform Technique. A novel clustering methodology entitled as Binary Reverse Clustering is introduced to optimize the performance as well as to reduce the servers’ requisition. Moreover, the novel clustering technique is compared with the traditional clustering algorithm.

  相似文献   
152.
153.
154.
Two individual examples of pyrazolo[3,4‐b]pyridine‐5‐carbonyl azides and hydrazides were reacted with various nucleophilic reagents. Different unexpected behaviors was observed. NMR, IR, mass spectra together with elemental analyses and X‐ray structure analyses, were used to prove the structure of the obtained products.  相似文献   
155.
In this paper, the chaos-based hash function is analyzed, then an improved version of chaos-based hash function is presented and discussed using chaotic neural networks. It is based on the piecewise linear chaotic map that is used as a transfer function in the input and output of the neural network layer. The security of the improved hash function is also discussed and a novel type of collision resistant hash function called semi-collision attack is proposed, which is based on the collision percentage between the two hash values. In the proposed attack particle swarm optimization algorithm is used to define the fitness function parameters. Finally, numerical and simulation results provides strong collision resistance and high performance efficiency.  相似文献   
156.
Nanostructured ceria doped with other rare earth elements is a good oxygen ion conductor, which gives rise to various catalytic applications such as the construction of membranes for syngas production by partial oxidation of methane. This article focuses on the Gd-doped cerium dioxides, which can be modified with Pt or Pd to enhance the reactivity of the lattice oxygen in interaction with methane. The aim of the work is the elucidation of correlations between the structural, electronic, and chemical properties of these nanomaterials. Detailed studies were performed for a series of samples with and without surface modification by noble metals using a complex combination of physicochemical methods: XRD, TEM, CH(4) TPR, XPS, SIMS, and FTIR spectroscopy of adsorbed CO. XPS and TPR data revealed that surface modification with noble metals enhances the reducibility of the doped ceria support, where the effect is more pronounced for Pd than for Pt. The formation of highly cationic Pd species due to strong metal support interactions provides a possible explanation for this behavior. Furthermore, the results obtained in the present work for the Gd-doped ceria system are compared to those obtained previously for the Pr-doped ceria system.  相似文献   
157.
For a system of functional differential equations of an arbitrary order the conditions are established for the initial value problem to be solvable on an infinite interval, and the structure of the set of solutions to this problem is studied.  相似文献   
158.
159.
In this communication we present the synthesis of the inverse crown ether complex [Li(2)O(2)·Li(4){CH(2)(N(Me)CH(2)S(NtBu)(2))(2)}(2)] (1) which is able to accommodate peroxide in a torus of lithium ions.  相似文献   
160.
Electrophilic trisubstituted ethylene monomers, halogen ring‐substituted 2‐cyano‐N,N‐dimethyl‐3‐phenyl‐2‐propenamides, RC6H4CH [dbnd]C(CN)CON(CH3)2 (where R is 2‐Br, 3‐Br, 4‐Br, 2‐Cl, 3‐Cl, 4‐Cl, 2‐F, 3‐F, 4‐F), were synthesized by potassium hydroxide catalyzed Knoevenagel condensation of ring‐substituted benzaldehydes and N,N‐dimethyl cyanoacetamide, and characterized by CHN elemental analysis, IR, 1H‐ and 13C‐NMR. Novel copolymers of the ethylenes and styrene were prepared at equimolar monomer feed composition by solution copolymerization in the presence of a radical initiator, ABCN at 70°C. The composition of the copolymers was calculated from nitrogen analysis, and the structures were analyzed by IR, 1H and 13C NMR, GPC, DSC, and TGA. High T g of the copolymers in comparison with that of polystyrene indicates a substantial decrease in chain mobility of the copolymer due to the high dipolar character of the trisubstituted ethylene monomer unit. The gravimetric analysis indicated that the copolymers decompose in the 300–450°C range.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号