全文获取类型
收费全文 | 25118篇 |
免费 | 1184篇 |
国内免费 | 1382篇 |
专业分类
航空 | 14005篇 |
航天技术 | 7247篇 |
综合类 | 1337篇 |
航天 | 5095篇 |
出版年
2021年 | 302篇 |
2020年 | 192篇 |
2019年 | 217篇 |
2018年 | 342篇 |
2017年 | 213篇 |
2016年 | 287篇 |
2015年 | 320篇 |
2014年 | 787篇 |
2013年 | 890篇 |
2012年 | 891篇 |
2011年 | 1121篇 |
2010年 | 989篇 |
2009年 | 1329篇 |
2008年 | 1327篇 |
2007年 | 870篇 |
2006年 | 831篇 |
2005年 | 760篇 |
2004年 | 712篇 |
2003年 | 771篇 |
2002年 | 721篇 |
2001年 | 808篇 |
2000年 | 623篇 |
1999年 | 756篇 |
1998年 | 722篇 |
1997年 | 564篇 |
1996年 | 566篇 |
1995年 | 626篇 |
1994年 | 649篇 |
1993年 | 499篇 |
1992年 | 479篇 |
1991年 | 375篇 |
1990年 | 331篇 |
1989年 | 505篇 |
1988年 | 268篇 |
1987年 | 286篇 |
1986年 | 259篇 |
1985年 | 648篇 |
1984年 | 530篇 |
1983年 | 417篇 |
1982年 | 497篇 |
1981年 | 617篇 |
1980年 | 249篇 |
1979年 | 194篇 |
1978年 | 189篇 |
1976年 | 156篇 |
1975年 | 193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 484 毫秒
251.
252.
A multiple model adaptive estimator (MMAE) has been formulated to estimate the state of a dynamic system modeled by a linear stochastic differential equation, from which measurements, described as a noise-corrupted space-time point process functionally related to that state, are extracted. Assumed certainty equivalence is used to combine such an estimator with the LQ full-state feedback controller to synthesize a practical, implementable controller. Performance of the estimator and resultant controller characteristics are investigated via simulation as a function of approximation method used to limit the full-scale estimator to finite dimensionality and also as a function of important parameters defining the dynamics and observation processes. 相似文献
253.
Nazar R. Ikhsanov Chul-Sung Choi 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,38(12):2901-2902
The state of subsonic propeller is intermediate between the states of supersonic propeller and accretor in the evolutionary tracks of magnetized compact stars. The rotational rate of a star at this stage decelerates due to the interaction between its magnetosphere and the surrounding hot, quasi-static plasma envelope. The magnetospheric radius is smaller than the corotation radius and the boundary of the magnetosphere is stable with respect to interchange instabilities. The rate of the mass flux from the inner radius of the envelope to the stellar surface is limited by the rate of plasma diffusion into the magnetic field of the star. As a result, the subsonic propeller would appear as a low-luminosity accretion-powered pulsar with a soft X-ray spectrum. 相似文献
254.
Michel D. Ingham Robert D. Rasmussen Matthew B. Bennett Alex C. Moncada 《Acta Astronautica》2006,58(12):648-661
It has become clear that spacecraft system complexity is reaching a threshold where customary methods of control are no longer affordable or sufficiently reliable. At the heart of this problem are the conventional approaches to systems and software engineering based on subsystem-level functional decomposition, which fail to scale in the tangled web of interactions typically encountered in complex spacecraft designs. Furthermore, there is a fundamental gap between the requirements on software specified by systems engineers and the implementation of these requirements by software engineers. Software engineers must perform the translation of requirements into software code, hoping to accurately capture the systems engineer's understanding of the system behavior, which is not always explicitly specified. This gap opens up the possibility for misinterpretation of the systems engineer's intent, potentially leading to software errors. This problem is addressed by a systems engineering methodology called State Analysis, which provides a process for capturing system and software requirements in the form of explicit models. This paper describes how requirements for complex aerospace systems can be developed using State Analysis, using representative spacecraft examples. 相似文献
255.
文章介绍了CBERS -1卫星红外多光谱扫描仪(IRMSS)关键部件扫描子系统研制与应用情况。 相似文献
256.
Tikhomirov AA Ushakova SA Manukovsky NS Lisovsky GM Kudenko YA Kovalev VS Gribovskaya IV Tirrannen LS Zolotukhin IG Gros JB Lasseur Ch 《Acta Astronautica》2003,53(4-10):249-257
The paper considers problems of biosynthesis of higher plants' biomass and "biological incineration" of plant wastes in a working physical model of biological LSS. The plant wastes are "biologically incinerated" in a special heterotrophic block involving Californian worms, mushrooms and straw. The block processes plant wastes (straw, haulms) to produce soil-like substrate (SLS) on which plants (wheat, radish) are grown. Gas exchange in such a system consists of respiratory gas exchange of SLS and photosynthesis and respiration of plants. Specifics of gas exchange dynamics of high plants--SLS complex has been considered. Relationship between such a gas exchange and PAR irradiance and age of plants has been established. Nitrogen and iron were found to the first to limit plants' growth on SLS when process conditions are deranged. The SLS microflora has been found to have different kinds of ammonifying and denitrifying bacteria which is indicative of intensive transformation of nitrogen-containing compounds. The number of physiological groups of microorganisms in SLS was, on the whole, steady. As a result, organic substances--products of exchange of plants and microorganisms were not accumulated in the medium, but mineralized and assimilated by the biocenosis. Experiments showed that the developed model of a man-made ecosystem realized complete utilization of plant wastes and involved them into the intrasystem turnover. 相似文献
257.
258.
259.
以毫米波主被动复合探测器为工程应用背景,通过分析信号的特点,提出一种基于移步预测思想的快速算法来消除脉冲调制信号对被动通道信号的串扰。仿真分析和实验结果表明,该方法对改善信噪比效果明显,而且具有成本低、速度快和易于工程化实现的优点。 相似文献
260.
一组能够描述各种组合发动机系统工作的通用方程组已用于弹道计算的通用程序包TC系列,使得通用程序包TC对各种类型的火箭和空间飞行器的弹车员道仿真方便又准确。本文是第2部分。 相似文献