全文获取类型
收费全文 | 255篇 |
免费 | 89篇 |
国内免费 | 9篇 |
出版年
2022年 | 4篇 |
2021年 | 17篇 |
2019年 | 1篇 |
2018年 | 4篇 |
2017年 | 4篇 |
2016年 | 4篇 |
2015年 | 7篇 |
2014年 | 10篇 |
2013年 | 8篇 |
2012年 | 5篇 |
2011年 | 12篇 |
2010年 | 19篇 |
2009年 | 26篇 |
2008年 | 10篇 |
2007年 | 14篇 |
2006年 | 13篇 |
2005年 | 15篇 |
2004年 | 2篇 |
2003年 | 1篇 |
2002年 | 1篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 31篇 |
1998年 | 26篇 |
1997年 | 13篇 |
1996年 | 21篇 |
1995年 | 13篇 |
1994年 | 10篇 |
1993年 | 13篇 |
1992年 | 10篇 |
1991年 | 6篇 |
1990年 | 11篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1985年 | 3篇 |
1982年 | 2篇 |
排序方式: 共有353条查询结果,搜索用时 0 毫秒
351.
In this work, NH2-substituted oxazoles and NO2/NF2/NHNO2-substituted ethylenes/acetylenes were designed and used as dienes and dienophiles, respectively, in order to develop new bridge-ring insensitive high energy compounds through the Diels-Alder reaction between them. The reaction type, reaction feasibility and performance of reaction products were investigated in detail theoretically. The results showed that dienes most possibly react with dienophiles through the HOMO-diene controlled normal Diels-Alder reaction at relatively low energy barrier. Tetranitroethylene could react with the designed dienes much more easily than other dienophiles, and was employed to further design 29 new bridge-ring energetic compounds. Due to high heat of formation, density and oxygen balance, all designed bridge-ring energetic compounds have outstanding detonation performance, 16 of them have higher energy than HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocine) and 2 others even possess comparative energy with the representative of high energy compounds CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane). The predicted average h50 value of these bridge-ring energetic compounds is 83 cm, showing their low impact sensitivity. The NH2 groups could obviously impel the proceeding of Diels-Alder reactions, but would slightly decrease the energy and sensitivity performance. In all, the new designed bridge-ring compounds have both high energy and low sensitivity, and may be produced through Diels-Alder reactions at relatively low energy barrier. This paper may be helpful for the theoretical design and experiment synthesis of new advanced insensitive high energy compounds. 相似文献
352.
To deal with the radio frequency threat posed by modern complex radar networks to aircraft, we researched the unmanned aerial vehicle (UAV) formations radar countermeasures, aiming at the solution of radar jamming resource allocation under system countermeasures. A jamming resource allocation method based on an improved firefly algorithm (FA) is proposed. Firstly, the comprehensive factors affecting the level of threat and interference efficiency of radiation source are quantified by a fuzzy comprehensive evaluation. Besides, the interference efficiency matrix and the objective function of the allocation model are determined to establish the interference resource allocation model. Finally, A mutation operator and an adaptive heuristic are integtated into the FA algorithm, which searches an interference resource allocation scheme. The simulation results show that the improved FA algorithm can compensate for the deficiencies of the FA algorithm. The improved FA algorithm provides a more sci-entific and reasonable decision-making plan for aircraft mission allocation and can effectively deal with the battlefield threats of the enemy radar network. Moreover, in terms of convergence accuracy and speed as well as algorithm stability, the improved FA algorithm is superior to the simulated annealing algorithm (SA), the niche genetic algorithm (NGA), the improved discrete cuckoo algorithm (IDCS), the mutant firefly algorithm (MFA), the cuckoo search and fireflies algorithm (CSFA), and the best neighbor firefly algorithm (BNFA). 相似文献
353.