全文获取类型
收费全文 | 9951篇 |
免费 | 47篇 |
国内免费 | 15篇 |
专业分类
航空 | 4781篇 |
航天技术 | 3243篇 |
综合类 | 200篇 |
航天 | 1789篇 |
出版年
2021年 | 92篇 |
2019年 | 57篇 |
2018年 | 236篇 |
2017年 | 140篇 |
2016年 | 130篇 |
2015年 | 58篇 |
2014年 | 204篇 |
2013年 | 263篇 |
2012年 | 267篇 |
2011年 | 408篇 |
2010年 | 279篇 |
2009年 | 434篇 |
2008年 | 459篇 |
2007年 | 276篇 |
2006年 | 198篇 |
2005年 | 233篇 |
2004年 | 245篇 |
2003年 | 293篇 |
2002年 | 293篇 |
2001年 | 379篇 |
2000年 | 187篇 |
1999年 | 232篇 |
1998年 | 284篇 |
1997年 | 174篇 |
1996年 | 253篇 |
1995年 | 303篇 |
1994年 | 284篇 |
1993年 | 173篇 |
1992年 | 224篇 |
1991年 | 92篇 |
1990年 | 101篇 |
1989年 | 225篇 |
1988年 | 101篇 |
1987年 | 101篇 |
1986年 | 100篇 |
1985年 | 276篇 |
1984年 | 222篇 |
1983年 | 183篇 |
1982年 | 195篇 |
1981年 | 306篇 |
1980年 | 95篇 |
1979年 | 83篇 |
1978年 | 95篇 |
1977年 | 68篇 |
1976年 | 61篇 |
1975年 | 84篇 |
1974年 | 73篇 |
1972年 | 80篇 |
1971年 | 69篇 |
1970年 | 60篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
V. A. Olaev 《Russian Aeronautics (Iz VUZ)》2009,52(2):214-220
The algorithmic support of a small-sized navigation system on the basis of the magnetoinertial course transmitter is considered; the support makes it possible to significantly reduce accumulating errors that are due to incomplete data on wind parameters and decrease requirements for random errors of initial data sensors. 相似文献
992.
An analysis is presented that forms the basis for an algorithm for calculating the IGBT losses in a power factor correction (PFC) circuit. The method employs experimental data from an off-line test circuit that closely resembles the switching conditions in the actual PFC. This technique provides calculated values of both the conduction and switching losses of the main transistor in a boost-type PFC circuit. Results for a 6 kW PFC are included 相似文献
993.
Amirmehrabi H. Viswanathan R. 《IEEE transactions on aerospace and electronic systems》1997,33(1):85-97
A new constant false alarm rate (CFAR) test termed signal-plus-order statistic CFAR (S+OS) using distributed sensors is developed. The sensor modeling assumes that the returns of the test cells of different sensors are all independent and identically distributed In the S+OS scheme, each sensor transmits its test sample and a designated order statistic of its surrounding observations to the fusion center. At the fusion center, the sum of the samples of the test cells is compared with a constant multiplied by a function of the order statistics. For a two-sensor network, the functions considered are the minimum of the order statistics (mOS) and the maximum of the order statistics (MOS). For detecting a Rayleigh fluctuating target in Gaussian noise, closed-form expressions for the false alarm and detection probabilities are obtained. The numerical results indicate that the performance of the MOS detector is very close to that of a centralized OS-CFAR and it performs considerably better than the OS-CFAR detector with the AND or the OR fusion rule. Extension to an N-sensor network is also considered, and general equations for the false alarm probabilities under homogeneous and nonhomogeneous background noise are presented. 相似文献
994.
A model of the main support of the aircraft landing gear is presented and its dynamics is studied using the equations for the distributed motion of a wheel equipped with a brake. Stability of the support wheel rolling motion is analyzed and the brake parameter values which may cause stability loss are found. The results of numerical experiments are presented. 相似文献
995.
Recent data and theory for type II solar radio bursts are reviewed, focusing on a recent analytic quantitative theory for
interplanetary type II bursts. The theory addresses electron reflection and acceleration at the type II shock, formation of
electron beams in the foreshock, and generation of Langmuir waves and the type II radiation there. The theory's predictions
as functions of the shock and plasma parameters are summarized and discussed in terms of space weather events. The theory
is consistent with available data, has explanations for radio-loud/quiet coronal mass ejections (CMEs) and why type IIs are
bursty, and can account for empirical correlations between type IIs, CMEs, and interplanetary disturbances.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
996.
An analysis is done to determine the maximum power transfer conditions for full-wave rectifier circuits. Potential applications noted are implanted medical instruments, inductive power transfer to weapons, power transfer using space reflectors, and power generation in space. Three types of series impedances are considered: resistive/inductive (RL), resistive/capacitive (RC), and resistive/inductive/capacitive (RLC). The optimum ratio of ac-to-dc voltage output is determined for each type. For the case that involves all three impedance types, the optimum turning condition is also determined. The differential equations describing the circuits are solved in nondimensional form. The solutions involve partial differential equations, closed-form relationships, and simultaneous equations that are solved by numerical methods. The optimum ratio of peak ac-to-dc voltage ranges from 2.0 to 2.8, depending upon the circuit. The optimum turning differs significantly from the usual resonant conditions, especially for low Q. 相似文献
997.
The historical development of terrestrial atmospheric electricity is described, from its beginnings with the first observations of the potential gradient to the global electric circuit model proposed by C.T.R. Wilson in the early 20th century. The properties of the terrestrial global circuit are summarised. Concepts originally needed to develop the idea of a global circuit are identified as “central tenets”, for example, the importance of radio science in establishing the conducting upper layer. The central tenets are distinguished from additional findings that merely corroborate, or are explained by, the global circuit model. Using this analysis it is possible to specify which observations are preferable for detecting global circuits in extraterrestrial atmospheres. Schumann resonances, the extremely low frequency signals generated by excitation of the surface-ionosphere cavity by electrical discharges, are identified as the most useful single measurement of electrical activity in a planetary atmosphere. 相似文献
998.
A problem of transverse bending of elastic isotropic parallelogram plates under the action of uniformly distributed load is considered. The plate sides are either pivoted or rigidly restrained. To determine the value of maximum plate deflection, it is proposed that an interpolation technique with respect to form factor be used; and as a geometrical argument, an inner-outer conformal radius ratio can be applied instead of the form factor. 相似文献
999.
A summary of research and development work on high-power microwave filters is given here: first, design considerations in high-power microwave filters?power handling capacity, waveform distortion, multimode suppression, and stop and pass band characteristics; second, a discussion of filtering devices and techniques in two broad categories-dominant mode filters and harmonic filters (discussion covers methods of operation and significant characteristics of each filter developed to date); and third, a discussion of applications and limitations of filters in various systems and interference situations. Also included are the availability, cost, size, weight, etc. as functions of frequency for the various filter types. 相似文献
1000.
Recent developments in the physics input for iron core collapse models of type II supernovae are reviewed. The effect of these developments on collapse calculations is also discussed. The inner core collapses homologously, with little change in specific entropy, bounces in the neighborhood of nuclear density, and sets up an outward moving shock. In adiabatic models an explosion may result. The Inclusion of neutrino effects may produce substantial shock damping. Current results indicate that core collapse, bounce and shock propagation does not produce an explosion when neutrino effects are included. 相似文献