全文获取类型
收费全文 | 2026篇 |
免费 | 544篇 |
国内免费 | 324篇 |
出版年
2024年 | 5篇 |
2023年 | 16篇 |
2022年 | 19篇 |
2021年 | 37篇 |
2020年 | 42篇 |
2019年 | 34篇 |
2018年 | 30篇 |
2017年 | 96篇 |
2016年 | 146篇 |
2015年 | 92篇 |
2014年 | 174篇 |
2013年 | 185篇 |
2012年 | 183篇 |
2011年 | 167篇 |
2010年 | 105篇 |
2009年 | 179篇 |
2008年 | 116篇 |
2007年 | 165篇 |
2006年 | 200篇 |
2005年 | 157篇 |
2004年 | 148篇 |
2003年 | 103篇 |
2002年 | 94篇 |
2001年 | 82篇 |
2000年 | 55篇 |
1999年 | 63篇 |
1998年 | 43篇 |
1997年 | 34篇 |
1996年 | 22篇 |
1995年 | 19篇 |
1994年 | 15篇 |
1993年 | 15篇 |
1992年 | 17篇 |
1991年 | 15篇 |
1990年 | 15篇 |
1989年 | 5篇 |
1987年 | 1篇 |
排序方式: 共有2894条查询结果,搜索用时 15 毫秒
911.
现有文献中的翼伞建模方法多数是针对不带动力情况下的翼伞建模,不能适应动力翼伞的飞行控制。为了实现动力伞的有效控制,首先要建立合理的动力学模型。假设翼伞承载物和软翼之间具有2个自由度,分别建立软翼和承载物体坐标系下的作用力和力矩的平衡方程,通过体坐标系转换和消除翼伞内部状态量,得到有利于实现翼伞控制的8自由度非线性状态方程。仿真表明模型的飞行曲线与飞行实验的结果相一致,验证了模型的有效性。 相似文献
912.
913.
914.
915.
根据当前地空导弹武器系统受干扰吊舱和反辐射导弹威胁导致其作战能力下降的作战实践,本文首先提出了一种可有效打击进犯之敌、保全自身的侧击战术;其次,对该侧击战术进行军事建模,分析了飞行器从开始转弯到照射制导雷达进入其攻击范围期间,飞行器速度、攻击角度范围、转弯时的坡度角及航线与雷达间的航路捷径等因素对飞行器转弯时间造成的影响,并结合防空作战过程、避开空中威胁相关因素,给出了照射制导雷达辐射时机的标准;最后提出了确保侧击战术成功运用应的意见建议,并根据其操作难度指出人工智能运用于军事领域的必要性。希冀本研究能够为地面防空兵应对干扰吊舱和反辐射导弹的侧击战术提供一定理论参考。 相似文献
916.
实弹发射是复杂的系统性军事训练活动,在实施前要对其进行风险评估,实施的全过程中要进行风险管理,首要工作是运用科学方法进行风险分析。本文运用系统工程的思想,针对实弹发射这一复杂系统活动,识别得到环境、交通、技术、管理、人员、任务、装备、保障和通信这9类风险情景,进一步分析建立了实弹发射风险等级全息模型(HHM)。在此基础上,运用风险过滤、评级与管理框架(RFRM),通过初步情景过滤、双重标准过滤、多重标准过滤、主要风险情景的定量评级等步骤对以上风险情景进行过滤分析,得到了环境因素、装备因素和管理因素这3种最重要的风险因素。通过综合运用HHM和RFRM方法分析出的风险因素,能够为决策者进行有针对性的风险评估和风险管理提供一定理论支持。 相似文献
917.
Ammonium nitrate and fuel oil (ANFO) based explosive is a classic example of non-ideal high explosives. Its detonation is characterized by a strong dependence of detonation parameters on explosive charge diameter, presence and characteristics of confinement, as well as incomplete consumption of explosive at the sonic point.In this work we propose a detonation model based on the Wood-Kirkwood (WK) theory coupled with the thermochemical code EXPLO5 and supplemented with reaction rate models. Our objective is to analyze the validity of the model for highly non-ideal ANFO explosives, with emphasis on effect of reaction rate models.It was found that both single-step and two-step pressure-based models can be calibrated to reproduce experimental detonation velocity-charge radius data of ANFO at radii significantly above the failure radius (i.e. for D/Did > ∼0.6). Single-step pressure-based model, with the pressure exponent equal to 1.4, proved to be the most accurate, even in the vicinity of the failure radius. The impact of the rate models is most evident on temporal (and spatial) distribution of flow parameters in detonation driving zone, especially when it comes to the conversion and width of detonation driving zone. 相似文献
918.
919.
In order to accurately describe the transverse relaxation characteristic and stress relaxation modulus of HTPB coating during pre-strain thermal aging process, a one month thermal aging test was carried out at 70 C with pre-strain of 0%, 3%, 6% and 9%, respectively. The low-field 1H NMR and stress relaxation modulus tests were carried out for HTPB coating at different aging stages. The stress relaxation model considering the molecular chains was proposed according to the changes of crosslinking chain and dangling chain of HTPB coating during pre-strain aging. The results showed that with the increase of aging time, the decay rate of transverse relaxation curve became faster, the transverse relaxation time decreased, the value of combined parameter qMrl increased, the proportion of crosslinking chain decreased, while the proportion of dangling chain increased. Moreover, the stress relaxation modulus increased, the crosslinking network structure of HTPB coating became denser and the degree of cross-linking increased. At the initial aging stage, the pre-strain will destroy the crosslinking network structure of HTPB coating to a certain extent. With the increase of aging time, the effect of pre-strain will gradually weaken and the influence of aging on materials will gradually increase. The correlations between the stress relaxation model considering the molecular chains and the test results were more than 0.9950, which can accurately describe the stress relaxation modulus of HTPB coating during the pre-strain thermal aging process. 相似文献
920.