全文获取类型
收费全文 | 1040篇 |
免费 | 278篇 |
国内免费 | 184篇 |
专业分类
航空 | 866篇 |
航天技术 | 310篇 |
综合类 | 80篇 |
航天 | 246篇 |
出版年
2024年 | 3篇 |
2023年 | 46篇 |
2022年 | 81篇 |
2021年 | 74篇 |
2020年 | 62篇 |
2019年 | 62篇 |
2018年 | 44篇 |
2017年 | 52篇 |
2016年 | 68篇 |
2015年 | 42篇 |
2014年 | 73篇 |
2013年 | 64篇 |
2012年 | 69篇 |
2011年 | 71篇 |
2010年 | 49篇 |
2009年 | 55篇 |
2008年 | 51篇 |
2007年 | 61篇 |
2006年 | 63篇 |
2005年 | 35篇 |
2004年 | 30篇 |
2003年 | 38篇 |
2002年 | 26篇 |
2001年 | 23篇 |
2000年 | 34篇 |
1999年 | 36篇 |
1998年 | 28篇 |
1997年 | 29篇 |
1996年 | 18篇 |
1995年 | 23篇 |
1994年 | 15篇 |
1993年 | 14篇 |
1992年 | 16篇 |
1991年 | 7篇 |
1990年 | 13篇 |
1989年 | 11篇 |
1988年 | 9篇 |
1987年 | 7篇 |
排序方式: 共有1502条查询结果,搜索用时 296 毫秒
631.
632.
W. Wang A.G. Burns S. Solomon T.L. Killeen 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2005,36(12):2486-2491
Current first-principles global models of the coupled thermosphere–ionosphere (T–I) system use grids that are too coarse to simulate the mesoscale and small-scale structures that occur in this complex system. These small-scale and mesoscale structures have a great effect on global-scale neutral and plasma distributions and have important consequences for daily space weather. In this paper, we present a new first-principles, high-resolution, T–I nested grid (TING) polar cap model that incorporates multiple nesting levels and two-way interaction. The TING model simulation of the electron densities and temperatures demonstrates the importance of high spatial resolution. It is found that both the mid-latitude electron density trough and its associated dawn electron temperature peak are more pronounced and structured in the nested grid than in the coarse grid. Using the TING model to simulate ionospheric F2 region electron density variations with geomagnetic activity and universal time (UT) is also discussed. 相似文献
633.
B. Schmieder P. DémoulinG. Aulanier 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Solar filament eruptions play a crucial role in triggering coronal mass ejections (CMEs). More than 80% of eruptions lead to a CME. This correlation has been studied extensively during the past solar cycles and the last long solar minimum. The statistics made on events occurring during the rising phase of the new solar cycle 24 is in agreement with this finding. Both filaments and CMEs have been related to twisted magnetic fields. Therefore, nearly all the MHD CME models include a twisted flux tube, called a flux rope. Either the flux rope is present long before the eruption, or it is built up by reconnection of a sheared arcade from the beginning of the eruption. 相似文献
634.
The convection of heat-generating fluid in a rotating horizontal cylinder is experimentally investigated. The threshold of convection excitation, the structure of convective flows and the heat transfer in the cylinder depending on the heat release capacity, liquid viscosity and aspect ratio of the cavity are studied. It is found that the average convection is excited by the thermovibrational mechanism —the gravity force, rotating in the cavity frame, produces the oscillations of non-isothermal fluid relative to the wall, which in turn result in excitation of mean convective flows. It is shown that the structure of convective flows depends on the dimensionless velocity of rotation. At relatively low rotation velocity the convection develops in the form of a periodic system of vortices regularly distributed along the cylinder axis. The threshold of excitation (critical value of vibration parameter) of three-dimensional vortex structures grows with rotation velocity. Above some definite rotation velocity the convection develops as two-dimensional rolls parallel to the axis of rotation. The threshold of two-dimensional structures excitation does not depend on the rotation velocity. Besides the structure of thermal convective flows the analysis of the relatively weak currents generated by the inertial waves below the threshold of convection is performed. 相似文献
635.
曲面积分在三重积分中的应用 总被引:2,自引:0,他引:2
得到了把一类三重积分化为曲面积分的一个定理,并给出定理的一些应用。 相似文献
636.
叙述某型导弹的新型结构--斜燕尾槽配合的具有高协调要求的镀镍、机加工的工艺方法。改进后的“镀前加工协调尺寸预先补偿法”,已成功应用于某型导弹的批产。在同类协调零件制造过程中,该种方法具有较大的借鉴作用。 相似文献
637.
在设计变结构控制器的过程中,确定对象不确定性的范围是一个重要的前提步聚。但是,在某些情况下要确定其边界是相当困难的,或者存在不能精确描述的外部扰动不可能得到其变化的准确范围。针对上述问题,在传统的变结构控制器中加入了对应不确定因素的自适应环节,并证明了该方法设计之控制器的稳定性。仿真结果表明了该法的有效性。 相似文献
638.
采用胶接方式连接的复合结构在生产制造过程中容易出现脱粘问题,将严重影响产品的结构完整性.采用新型检测方法对脱粘缺陷进行定量测量对于保障产品质量、提高检测效率起到至关重要的作用.本文介绍了激光剪切散斑方法的检测原理、蜂窝夹层结构中脱粘缺陷的形成原因与结构特点及对脱粘缺陷的验收规范.利用激光剪切散斑方法对脱粘缺陷进行检测,分析激光剪切散斑方法对脱粘缺陷进行定量测量的检测精度.通过对已知间距缺陷进行定量测量,检测结果与实际缺陷尺寸吻合较好,检测精度在10%以内.结果表明该方法对脱粘缺陷的检测精度能够满足实际生产的检测需要. 相似文献
639.
640.
Stability analysis of explicit guidance laws for space launch vehicles with varying thrust integrals
Eun-Jung Song Sang-bum ChoChang-Su Park Woong-Rae RohMiok Joh 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
In this study, a stability analysis of the explicit guidance laws for space launch vehicles is performed with consideration of varying thrust integrals. Among various forms of explicit guidance, linear tangent guidance in its general form is selected and six different acceleration profiles are considered for this numerical experiment. A linear system modeling which includes all of the significant dynamic elements of a space launcher is performed to analyze the effect of the characteristics of thrust integrals on stability margins. Numerical results show that in an aspect of guidance stability, it is advantageous to have thrust integrals derived from increasing acceleration profiles, such as constant thrust case, which may be considered in the development of propulsion systems. Finally, time-domain simulation with the original nonlinear models is performed to verify the approach and the result shows that the nonlinear dynamics of the system is conserved well in the linear model. 相似文献