全文获取类型
收费全文 | 6064篇 |
免费 | 657篇 |
国内免费 | 484篇 |
专业分类
航空 | 3065篇 |
航天技术 | 1704篇 |
综合类 | 445篇 |
航天 | 1991篇 |
出版年
2024年 | 15篇 |
2023年 | 47篇 |
2022年 | 119篇 |
2021年 | 179篇 |
2020年 | 129篇 |
2019年 | 120篇 |
2018年 | 225篇 |
2017年 | 210篇 |
2016年 | 217篇 |
2015年 | 186篇 |
2014年 | 280篇 |
2013年 | 295篇 |
2012年 | 303篇 |
2011年 | 355篇 |
2010年 | 380篇 |
2009年 | 436篇 |
2008年 | 374篇 |
2007年 | 295篇 |
2006年 | 220篇 |
2005年 | 239篇 |
2004年 | 174篇 |
2003年 | 205篇 |
2002年 | 223篇 |
2001年 | 210篇 |
2000年 | 134篇 |
1999年 | 152篇 |
1998年 | 127篇 |
1997年 | 117篇 |
1996年 | 102篇 |
1995年 | 141篇 |
1994年 | 113篇 |
1993年 | 69篇 |
1992年 | 80篇 |
1991年 | 44篇 |
1990年 | 45篇 |
1989年 | 56篇 |
1988年 | 29篇 |
1987年 | 25篇 |
1986年 | 26篇 |
1985年 | 80篇 |
1984年 | 61篇 |
1983年 | 50篇 |
1982年 | 48篇 |
1981年 | 89篇 |
1980年 | 26篇 |
1979年 | 18篇 |
1978年 | 17篇 |
1977年 | 18篇 |
1976年 | 15篇 |
1972年 | 14篇 |
排序方式: 共有7205条查询结果,搜索用时 31 毫秒
11.
The results of the experimental studies of damping characteristics of a composite torsion bar in the helicopter main rotor
hingeless hub are presented. A variant of their improvement is considered. 相似文献
12.
We present an algorithm for calculating the shells of revolution with the branching meridian using the triangular finite elements, the rigidity matrices of which are formed based on the vector method of displacement interpolation [1]. The correct kinematic and static conditions of shell conjugation on the line of their coupling have been developed. The shell structure consisting of a cylinder and adjacent shells is calculated under various conditions of support. 相似文献
13.
以小车式起落架为例,利用ADAMS/Airc- raft建立了起落架滑跑试验仿真模型.给出了起落架滑跑运动方程,并进行了滑跑试验仿真分析。仿真结果与理论要求对比具有较好的一致性。 相似文献
14.
The problem of the optimal number of phased array faces for performing 360/spl deg/ horizon surveillance is considered. Assuming the detection performance is the same in all beam positions and the total number of T/R modules is constant, it is shown that the optimal number of array faces is three. This is true whether the arrays are operating simultaneously or sequentially. A parametric analysis is performed between the number of array faces operating simultaneously and the associated cost of simultaneous operation in terms of the size of the array. 相似文献
15.
16.
The problem of optimal data fusion in multiple detection systems is studied in the case where training examples are available, but no a priori information is available about the probability distributions of errors committed by the individual detectors. Earlier solutions to this problem require some knowledge of the error distributions of the detectors, for example, either in a parametric form or in a closed analytical form. Here we show that, given a sufficiently large training sample, an optimal fusion rule can be implemented with an arbitrary level of confidence. We first consider the classical cases of Bayesian rule and Neyman-Pearson test for a system of independent detectors. Then we show a general result that any test function with a suitable Lipschitz property can be implemented with arbitrary precision, based on a training sample whose size is a function of the Lipschitz constant, number of parameters, and empirical measures. The general case subsumes the cases of nonindependent and correlated detectors. 相似文献
17.
Stability of resonance rotation of a satellite with respect to its center of mass in the orbit plane
S. Yu. Sadov 《Cosmic Research》2006,44(2):160-171
The stability of resonance oscillations and rotations of a satellite in the plane of its orbit in the case when the difference of the moments of inertia with respect to the principal axes lying in the orbit plane is small is determined at a given rotation number m by the sign of function Φm(e), introduced by F.L. Chernous’ko in 1963. In this paper, convenient analytical representations of functions Φm(e) are described in the form of integrals and series of Bessel functions regular at e → 1?. Values of Φm(1) are calculated in explicit form. A theorem about the double asymptotic form of functions Φm(e) at m → ∞ and e → 1? is proved by the saddlepoint method. 相似文献
18.
Savkin A.V. Pathirana P.N. Faruqi F.A. 《IEEE transactions on aerospace and electronic systems》2003,39(3):901-910
Addressed here is the precision missile guidance problem where the successful intercept criterion has been defined in terms of both minimizing the miss distance and controlling the missile body attitude with respect to the target at the terminal point. We show that the H/sup /spl infin// control theory, when suitably modified, provides an effective framework for the precision missile guidance problem. The existence of feedback controllers (guidance laws) is investigated for the case of finite horizon and non-zero initial conditions. Both state feedback and output feedback implementations are explored. 相似文献
19.
L. V. Zasova V. I. Moroz V. M. Linkin I. V. Khatuntsev B. S. Maiorov 《Cosmic Research》2006,44(4):364-383
The goal of this paper is to summarize the experimental data on the atmosphere of Venus obtained after 1985, when the VIRA (Venus International Reference Atmosphere) or COSPAR model was published. Among the most important results that have appeared since then are the following: measurements of the vertical temperature profile by the VEGA spacecraft with high precision and high altitude resolution; measurements made with balloons of the VEGA spacecraft; radio occultation measurements of Magellan, Venera-15, and Venera-16; and temperature profiles derived from the data of infrared spectrometry obtained by Venera-15. The new result as compared to VIRA is the creation of a model of the atmosphere in the altitude range 55 to 100 km dependent on local time. This model is presented in our paper in tabulated form. 相似文献
20.
V D Kern F D Sack 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2001,27(5):941-949
Apical cells of moss protonemata represent a single-celled system that perceives and reacts to light (positive and negative phototropism) and to gravity (negative gravitropism). Phototropism completely overrides gravitropism when apical cells are laterally irradiated with relatively high red light intensities, but below a defined light intensity threshold gravitropism competes with the phototropic reaction. A 16 day-long exposure to microgravity conditions demonstrated that gravitropism is allowed when protonemata are laterally illuminated with light intensities below 140 nmol m-2s-1. Protonemata that were grown in darkness in microgravity expressed an endogenous tendency to grow in arcs so that the overall culture morphology resembled a clockwise spiral. However this phenomenon only was observed in cultures that had reached a critical age and/or size. Organelle positioning in dark-grown apical cells was significantly altered in microgravity. Gravisensing most likely involves the sedimentation of starch-filled amyloplasts in a well-defined area of the tip cell. Amyloplasts that at 1-g are sedimented were clustered at the apical part of the sedimentation zone in microgravity. Clustering observed in microgravity or during clino-rotation significantly differs from sedimentation-induced plastid aggregations after inversion of tip cells at 1-g. 相似文献