全文获取类型
收费全文 | 864篇 |
免费 | 180篇 |
国内免费 | 204篇 |
专业分类
航空 | 717篇 |
航天技术 | 254篇 |
综合类 | 107篇 |
航天 | 170篇 |
出版年
2024年 | 2篇 |
2023年 | 30篇 |
2022年 | 34篇 |
2021年 | 42篇 |
2020年 | 53篇 |
2019年 | 52篇 |
2018年 | 58篇 |
2017年 | 65篇 |
2016年 | 63篇 |
2015年 | 57篇 |
2014年 | 66篇 |
2013年 | 56篇 |
2012年 | 70篇 |
2011年 | 71篇 |
2010年 | 74篇 |
2009年 | 51篇 |
2008年 | 62篇 |
2007年 | 49篇 |
2006年 | 50篇 |
2005年 | 39篇 |
2004年 | 37篇 |
2003年 | 34篇 |
2002年 | 27篇 |
2001年 | 23篇 |
2000年 | 17篇 |
1999年 | 19篇 |
1998年 | 17篇 |
1997年 | 7篇 |
1996年 | 4篇 |
1995年 | 5篇 |
1993年 | 2篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 3篇 |
1989年 | 1篇 |
1988年 | 1篇 |
排序方式: 共有1248条查询结果,搜索用时 468 毫秒
261.
Gaseous cavity at the base of an underwater projectile 总被引:1,自引:0,他引:1
A Dyment J.P Flodrops J.B Paquet D Dupuis D Marchand 《Aerospace Science and Technology》1998,2(8):489-504
The problem of the behavior of the gaseous cavity which is formed at the base of an underwater launched projectile is treated using different approaches. Asymptotic analysis is used to yield expressions for similarity parameters and a simplified hydrodynamic model of the initial stretching phase. A laboratory facility is described, in which launches can be simulated and analyzed by means of pressure measurements and high speed visualizations. Complete calculations are also performed using a numerical “Volume of Fluid” model solving the unsteady Navier-Stokes equations. Results from the three approaches are presented and compared during the cavity stretching phase. Finally, the thermodynamic aspects of the problem are examined. 相似文献
262.
A.M. Jorgensen D. Ober J. Koller R.H.W. Friedel 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
In this paper we report on initial work toward data assimilative modeling of the Earth’s plasmasphere. As the medium of propagation for waves which are responsible for acceleration and decay of the radiation belts, an accurate assimilative model of the plasmasphere is crucial for optimizing the accurate prediction of the radiation environments encountered by satellites. On longer time-scales the plasmasphere exhibits significant dynamics. Although these dynamics are modeled well by existing models, they require detailed global knowledge of magnetospheric configuration which is not always readily available. For that reason data assimilation can be expected to be an effective tool in improving the modeling accuracy of the plasmasphere. In this paper we demonstrate that a relatively modest number of measurements, combined with a simple data assimilation scheme, inspired by the ensemble Kalman filtering data assimilation technique does a good job of reproducing the overall structure of the plasmasphere including plume development. This raises hopes that data assimilation will be an effective method for accurately representing the configuration of the plasmasphere for space weather applications. 相似文献
263.
Differentmodels are proposed for the study ofhybrid systems that are composed of interactingcontinuous and discrete parts as,for instance,inRef.[1 ].Generally,the discrete part is modelledby an automation,and the continuous part by dif-ferent sets of state equations.Jump functions canbe added to represent the discontinuities.But noindication is given about the relations between thedifferent models and the jump functions. This paper isconcerned with the modelling forphysical systems with sw… 相似文献
264.
It is commonly believed that comets are made of primordial material. As a consequence, they can reveal more information about
the origin of our solar system. To interpret the coma composition measurements of comet Churyumov–Gerasimenko that will be
collected by the Rosetta mission, models of the coma chemistry have to be constructed. However, programming the chemistry
of a cometary coma is extremely complex due to the large number of species and reactions involved. Moreover, such a program
needs to be very flexible as one may want to extend, change, or update the set of species, reactions, and reaction rates.
Therefore, we developed software to manage a database of species and reactions and to generate code automatically to compute
source/loss balances. This database includes the data from the UMIST database and the ion–molecule reactions collected by
V.G. Anicich. To use all these databases together, a lot of practical problems need to be solved, but the result is an enormous
source of information about chemical reactions that can be used in chemical models, not only for comets but also for other
applications. 相似文献
265.
MATLAB与C++结合复杂动态对象仿真建模方法 总被引:1,自引:0,他引:1
MATLAB/S imu link是一个强大的自动控制系统工程仿真工具,但在进行复杂动态对象仿真建模时需要大量的S imu link模块的堆叠,难度之大使得实现建模上花费的时间预计占系统开发周期的大半,而且得到的仿真模块通常具有可读性差、容易出错等缺点,运行时占用大量的系统时间和内存空间,对其进行调试和修改也很困难。本文介绍了作者探寻的使用MATLAB/S imu link结合C++编写成的现成类库进行复杂对象仿真建模方法,详细论述了C++m ex函数工程创建编译的过程和利用m ex函数和S imu link S-function进行复杂动态对象整体仿真建模的思路。通过应用实践表明,这种仿真建模方法不但减少了重复劳动的代价,加速了自动控制系统设计周期,使得复杂动态对象仿真模块简洁高效,还可以起到保护数据安全和知识产权的作用。 相似文献
266.
岳忠玉 《西安航空技术高等专科学校学报》2002,20(1):55-58
本论述了数学模型的一般概念,讨论了数学模型的分类及数学模型的步骤和方法,通过两个建模实例,结合作辅导建模竞赛的经验,研究了建模竞赛的组织与训练问题。 相似文献
267.
268.
复杂系统可靠度综合计算平台的设计实现 总被引:1,自引:0,他引:1
鉴于复杂大系统可靠度综合计算面临诸多困难 ,分析了其复杂性特征 ,提出了一种一体化建模方法———复合逻辑树模型 (CompositeLogicTreeModel,简称CLTM)及其递归调度综合算法 ,并采用面向对象的思想和技术 ,设计实现了可视化的系统可靠度CLTM综合建模与计算软件平台。介绍了软件的总体框架及其功能 ,并通过实例阐明了相应的系统可靠度综合分析方法 相似文献
269.
非定常气动力的结构自适应神经网络建模方法 总被引:3,自引:0,他引:3
讨论了非线性非定常气动力的结构自适应神经网络模型建模方法,该方法具有同时进行结构辨识与参数辨识的优点;利用纵向大振幅强迫振荡风洞试验数据,验证了建模方法及所建模型的有效性,结果表明:结构自适应神经网络模型对非定常气动力有很好的逼近能力,由于采用飞行参数的时间离散数据作为输入量,模型可直接应用于飞行仿真研究。 相似文献
270.
仿真软件AMESim应用研究 总被引:12,自引:0,他引:12
AMESim软件是由法国IMAGINE公司推出一种用于机械液压系统建模与仿真的软件,近年来才开始在我国机械液压行业中应用,在航空发动机领域的应用还不多见.该文首先对AMESim软件进行了介绍.然后用燃油调节器中的一个元件为例,说明了AMESim软件在航空发动机燃油系统研究中具有应用潜力. 相似文献