全文获取类型
收费全文 | 1931篇 |
免费 | 250篇 |
国内免费 | 38篇 |
专业分类
化学 | 70篇 |
晶体学 | 4篇 |
力学 | 106篇 |
综合类 | 16篇 |
数学 | 58篇 |
物理学 | 179篇 |
无线电 | 1786篇 |
出版年
2024年 | 5篇 |
2023年 | 26篇 |
2022年 | 51篇 |
2021年 | 58篇 |
2020年 | 68篇 |
2019年 | 52篇 |
2018年 | 48篇 |
2017年 | 72篇 |
2016年 | 87篇 |
2015年 | 104篇 |
2014年 | 173篇 |
2013年 | 117篇 |
2012年 | 162篇 |
2011年 | 156篇 |
2010年 | 123篇 |
2009年 | 147篇 |
2008年 | 141篇 |
2007年 | 131篇 |
2006年 | 95篇 |
2005年 | 83篇 |
2004年 | 79篇 |
2003年 | 50篇 |
2002年 | 38篇 |
2001年 | 24篇 |
2000年 | 31篇 |
1999年 | 24篇 |
1998年 | 10篇 |
1997年 | 14篇 |
1996年 | 9篇 |
1995年 | 10篇 |
1994年 | 6篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有2219条查询结果,搜索用时 0 毫秒
1.
在综述光电对抗内涵的基础上,论述光电对抗在现代战争作战平台中的具体应用,并着重从电子战的角度论述了光电对抗在现代防空作战中的最新应用。最后指出光电对抗技术在未来电子战中的作用和发展方向。 相似文献
2.
3.
因特网防御DoS攻击技术评述Ⅰ--攻击分类与特征·包过滤·攻击检测与防御 总被引:1,自引:0,他引:1
概述了因特网上DoS攻击的相应分类及基本特征,评述了包过滤、攻击检测及防御技术的最新成果.前一部分介绍了入口过滤、基于路由的过滤网和有效源地址强制协议.后一方面主要讨论了适合于检测攻击包的技术,介绍了新近提出的频谱分析方法和泛滥检测系统.简要评述了已有的防御SYN泛滥攻击的技术措施,介绍了Cisco的TCP拦截技术,提出了改进策略. 相似文献
4.
C. Acero J. M. Ribó R. Solé F. R. Trull 《Monatshefte für Chemie / Chemical Monthly》1993,124(4):401-417
Summary Characteristic oxidation reactions of bilin-1,19-diones (biliverdins) and biladien-ac-1,19-diones (bilirubins) were reinvestigated. These include bromine and iodine oxidation of biliverdin IX, bilirubin IX and their Zn(II) complexes, the reaction described by Siedel (1941) of mesobilirubin XIII dimethyl ester with nitric acid (Gmelin reaction) and Smith's oxidation (1977) of etiobiliverdin IV using Tl triacetate and Pb tetra-acetate. For some of these reaction products new structures were assigned on the basis of their spectrometric data. These structures agreed with the expected reactivity pattern of biliverdins and bilirubins.
Reaktivität von Pyrrolpigmenten, 15 Mitt.: Über die Oxidation von Bilirubinen und Biliverdinen
Zusammenfassung Einige bekannte Oxydationen von Bilin-1,19-dionen (Biliverdinen) und Biladien-ac-dionen (Bilirubinen) wurden neuerlich untersucht, und zwar die Brom- und Jodoxydation von Biliverdin IX und Bilirubin IX sowie der entsprechenden Zn(II)-Komplexe, die Reaktion des Dimethylesters von Mesobilirubin XIII mit HNO3 (Gmelinreaktion; Siedel 1941) und Smith's Oxydation von Etiobiliverdin IV mit Thaliumtriacetat und Bleitetraacetat. Für einige Reaktionsprodukte wurden aufgrund spektroskopischer Daten neue Strukturen-konsistent mit dem bekannten Reaktionsverhalten von Biliverdinen und Bilirubinen-formuliert.相似文献
5.
6.
A JPEG image encryption with the adaptive key and run consistency of MCUs is proposed. The chosen-plaintext attack (CPA) is given here on this encryption scheme. First, the adaptive key can be reproduced from the encrypted image, so that the plaintext images with the same adaptive key can be constructed. Second, the existence of run consistency of MCUs (RCM) between the original image and the encrypted image facilitates rapid estimation. In addition, the single swap for the runs of MCUs with RCM is designed for more accurate estimation. Detailed cryptanalytic results suggest that this encryption scheme can only be used to realize perceptual encryption but not to provide content protection for digital images. Furthermore, applications of the CPA to break other encryption schemes with RCM are presented. 相似文献
7.
While malicious samples are widely found in many application fields of machine learning, suitable countermeasures have been investigated in the field of adversarial machine learning. Due to the importance and popularity of Support Vector Machines (SVMs), we first describe the evasion attack against SVM classification and then propose a defense strategy in this paper. The evasion attack utilizes the classification surface of SVM to iteratively find the minimal perturbations that mislead the nonlinear classifier. Specially, we propose what is called a vulnerability function to measure the vulnerability of the SVM classifiers. Utilizing this vulnerability function, we put forward an effective defense strategy based on the kernel optimization of SVMs with Gaussian kernel against the evasion attack. Our defense method is verified to be very effective on the benchmark datasets, and the SVM classifier becomes more robust after using our kernel optimization scheme. 相似文献
8.
9.
Rosario Torregrosa 《Tetrahedron》2007,63(2):469-473
The reaction of different epoxides with commercially available imidazole at 60 °C leads to the formation of the corresponding 1-(β-hydroxyalkyl)imidazoles in a regioselective manner. When the reaction is applied to a chiral epoxide [(R)-styrene oxide], the expected chiral alcohol is isolated with the same enantiomeric excess. The use of benzimidazole as the heterocyclic component in the same process also allows the simple preparation of the corresponding 1-(β-hydroxyalkyl)benzimidazoles. 相似文献
10.
Density functional theory calculations were carried out for the title reactions. Ethylene oxide and methylamine were adopted as reactants. Amine clusters (dimer, trimer, tetramer, and pentamer) were considered, because the combination of one oxide and one amine molecule gave a large activation energy. An amine tetramer was found to react favorably with the oxide via various zwitterionic intermediates. A back-side S(N)2 nucleophilic attack of one amine and the subsequent proton relay up to the front side provide a stabilized reaction field. The amine-alcohol mixed reactant may react readily with the oxide, because the alcoholic O-H group is in contact with the oxide oxygen with the strong hydrogen-bond stabilization. 相似文献