全文获取类型
收费全文 | 24667篇 |
免费 | 1181篇 |
国内免费 | 1382篇 |
专业分类
航空 | 13955篇 |
航天技术 | 7033篇 |
综合类 | 1332篇 |
航天 | 4910篇 |
出版年
2021年 | 300篇 |
2020年 | 192篇 |
2019年 | 217篇 |
2018年 | 326篇 |
2017年 | 208篇 |
2016年 | 287篇 |
2015年 | 317篇 |
2014年 | 786篇 |
2013年 | 889篇 |
2012年 | 885篇 |
2011年 | 1109篇 |
2010年 | 979篇 |
2009年 | 1328篇 |
2008年 | 1315篇 |
2007年 | 866篇 |
2006年 | 821篇 |
2005年 | 742篇 |
2004年 | 702篇 |
2003年 | 747篇 |
2002年 | 715篇 |
2001年 | 781篇 |
2000年 | 614篇 |
1999年 | 743篇 |
1998年 | 699篇 |
1997年 | 552篇 |
1996年 | 542篇 |
1995年 | 590篇 |
1994年 | 604篇 |
1993年 | 494篇 |
1992年 | 447篇 |
1991年 | 372篇 |
1990年 | 324篇 |
1989年 | 478篇 |
1988年 | 263篇 |
1987年 | 280篇 |
1986年 | 253篇 |
1985年 | 648篇 |
1984年 | 524篇 |
1983年 | 410篇 |
1982年 | 495篇 |
1981年 | 616篇 |
1980年 | 248篇 |
1979年 | 185篇 |
1978年 | 189篇 |
1976年 | 156篇 |
1975年 | 187篇 |
1974年 | 182篇 |
1973年 | 161篇 |
1972年 | 188篇 |
1971年 | 148篇 |
排序方式: 共有10000条查询结果,搜索用时 125 毫秒
301.
大尺寸工件测量中的温度误差修正 总被引:1,自引:0,他引:1
着重讨论了大尺寸工件测量中影响温度误差修正精度的主要因素,修正精度主要受模型误差、温度误差、线膨胀系数误差和温度梯度影响,其中,线膨胀系数误差对精度影响最大。引入微分膨胀系数,提出了更精确的温度误差修正模型,利用此模型对自研的形心轴线、型面点坐标测量系统的纵轴测量数据进行了温度误差修正,有效地提高了测量精度,降低了温度误差修正后的不确定度,确保了大尺寸高精度测量的实现。 相似文献
302.
303.
The transport characteristics of macroparticles, charged by the solar radiation under microgravity conditions, were investigated by analyzing the videorecords of experiments carried out onboard the Mirorbital station. The temperature, distributions of velocities, charge, friction coefficient, and diffusion coefficient were obtained for bronze particles. 相似文献
304.
The first of a series of problems of the optimization of correction of satellite systems, moving over near-circular orbits, is considered. The correction is accomplished by means of low-thrust engines and is supposed to be flexible, where only the parameters of the relative motion of satellites must be corrected. The problem has a large dimension, but is invariant with respect to renumbering of satellites. This allows us to decompose the problem, i.e., to find new variables, linearly dependent on old ones, in which the problem breaks down into a series of independent subproblems of low dimension. The decomposition is accomplished by means of the technique [1] based on the theory of linear representations of groups. 相似文献
305.
The strain–stress state of the solid propellant rocket engines (SPREs) is simulated under impact. The effect of orientation of elastic and strength properties of orthotropic organoplastic shell material on the strain–stress state of the solid propellant is investigated. Normal and oblique impact of single steel cylinder projectiles, both simultaneous and at different times of multiple, converging steel spheric particles with SPRE are investigated in this study. The investigation is conducted numerically. The numerical modeling was carried out in a three-dimensional formulation by the method of finite elements for the continuous approach of the mechanics of a deformable solid. The destruction of the anisotropic material is described by the tensor-polynomial criterion of the fourth degree, which takes into account the influence of hydrostatic pressure. 相似文献
306.
DS1620芯片是一种新型的测量温度和调节温度的器件。它本身就是一个数字温度计,能够输出9位二进制的温度值;同时,借助其三个温度报警输出和控制信号,DS1620也可作为温度调节器使用。本文详细阐述了DS1620数字温度计/温度调节器的特点、结构和原理,并结合具体例子介绍了DS1620的应用。文中给出了相关电路和程序框图。 相似文献
307.
308.
Using a novel space platform-based manipulator with slewing and deployable links, the paper addresses two issues of considerable importance: (a) How important is it to model flexibility of the system? (b) How many modes are needed to adequately represent the elastic character? Results suggest that the fundamental mode is able to capture physics of the response quite accurately. Due to its massive character, the platform dynamics is virtually unaffected, even by severe maneuvers of the manipulator. Hence, treating the platform as rigid would save the computational cost without affecting the accuracy. Although the link flexibility does affect the manipulator's tip vibration, the joint and platform vibrations remain negligible. The revolute joint flexibility appears to be an important parameter affecting both the joint as well as tip responses. The information should prove useful in the design of this new class of manipulators. 相似文献
309.
L. M. Zelenyi M. S. Dolgonosov A. A. Bykov V. Yu. Popov Kh. V. Malova 《Cosmic Research》2002,40(4):357-366
Using both analytical and numerical models of the collisionless anisotropic current sheet generated by the impinging flows of transient ions, we have studied the self-consistent solutions taking the plasma trapped in the sheet into account. It is demonstrated that there exists a limited window in the space of system parameters where self-consistent solutions can exist. When the density of the quasi-trapped plasma is sufficiently large, a redistribution of the total current can be a cause of the sheet decay, when the local current of the trapped particles compensate (totally or in part) the main current in the center and at the edges of the sheet, while the total current generated by ions on the trapped trajectories vanishes. 相似文献
310.
The US RLV program aims to stimulate commercial development of a next-generation heavy-lift launcher and lower launch costs by one order of magnitude from the Space Shuttle. This paper discusses the incentives needed to encourage private investment — income tax relief, investment mitigation, financing assistance — in the venture and uses a specifically developed case study model to evaluate their effectiveness. It finds that an R&D tax credit would be the most practical incentive. Directions for future work are provided. 相似文献