全文获取类型
收费全文 | 1035篇 |
免费 | 107篇 |
国内免费 | 109篇 |
专业分类
航空 | 600篇 |
航天技术 | 334篇 |
综合类 | 93篇 |
航天 | 224篇 |
出版年
2024年 | 4篇 |
2023年 | 9篇 |
2022年 | 9篇 |
2021年 | 43篇 |
2020年 | 32篇 |
2019年 | 26篇 |
2018年 | 20篇 |
2017年 | 40篇 |
2016年 | 40篇 |
2015年 | 51篇 |
2014年 | 60篇 |
2013年 | 55篇 |
2012年 | 65篇 |
2011年 | 69篇 |
2010年 | 58篇 |
2009年 | 58篇 |
2008年 | 56篇 |
2007年 | 44篇 |
2006年 | 62篇 |
2005年 | 58篇 |
2004年 | 51篇 |
2003年 | 71篇 |
2002年 | 52篇 |
2001年 | 36篇 |
2000年 | 27篇 |
1999年 | 18篇 |
1998年 | 29篇 |
1997年 | 26篇 |
1996年 | 8篇 |
1995年 | 15篇 |
1994年 | 17篇 |
1993年 | 8篇 |
1992年 | 8篇 |
1991年 | 8篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 2篇 |
1984年 | 2篇 |
排序方式: 共有1251条查询结果,搜索用时 15 毫秒
561.
为解决采用静态框架描述故障案例存在的问题,提出一种基于知网的软件故障案例语义表示方法.通过分析案例的语义匹配准则,给出表示方法的具体语法描述规范.在此基础上,结合实际案例,分析软件故障领域中实体、事件、属性和属性值4类义原及其相互关系,并用KDML语言进行统一描述.实验表明,与传统基于关键字的模糊匹配方法相比,采用基于... 相似文献
562.
功率控制对于允许次用户和主用户之间频谱共享的认知无线电网络来说是关键的,针对具有干扰限制的认知网络最大总容量得到一种最优的分步式功率控制策略,对于系统效用的非凸性,引入几何规划把非凸最优化问题转换为凸最优化问题,引入辅助变量和额外等式约束,把效用之间的关联转化为约束之间的关联,提出了功率控制策略的解决方法,显示了整体最... 相似文献
563.
Katinka Geréb Sándor Frey 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
The point source list of the Wilkinson Microwave Anisotropy Probe (WMAP) is a uniform, all-sky catalogue of bright sources with flux density measurements at high (up to 94 GHz) radio frequencies. We investigated the five-year WMAP list to compile a new catalogue of bright and compact extragalactic radio sources to be potentially studied with Very Long Baseline Interferometry at millimeter wavelengths (mm-VLBI) and Space VLBI (SVLBI). After comparing the WMAP data with the existing mm-VLBI catalogues, we sorted out the yet unexplored sources. Using the 41, 61 and 94 GHz WMAP flux densities, we calculated the spectral indices. By collecting optical identifications, lower-frequency radio flux densities and VLBI images from the literature, we created a list of objects which have not been investigated with VLBI at 86 GHz before. With total flux density at least 1 Jy and declination above −40°, we found 37 suitable new targets. It is a nearly 25% addition to the known mm-VLBI sources. Such objects are also potentially useful as phase-reference calibrators for the future Japanese SVLBI mission ASTRO-G at its highest observing frequency (43 GHz). The phase-referencing capability of ASTRO-G would allow long integrations and hence better sensitivity for observing faint target sources close to suitable phase calibrators in the sky. 相似文献
564.
G. P. Chernov 《Space Science Reviews》2006,127(1-4):195-326
This review covers fairly comprehensively experimental and theoretical research on the fine structure of types zebra pattern
(ZP) and fiber bursts (FB) in solar type II + IV radio bursts. The basic attention is given to the latest experimental data.
A comparative analysis of several recent solar type IV radio outbursts with these fine structure in dynamical radio spectra
is carried out using available ground-based and satellite data (Yohkoh, SOHO, TRACE, RHESSI). New data on microwave zebra
structures and fiber bursts testifies that they are analogous to similar structures observed at meter wavelengths. The discovery
of the superfine structure, in the form of millisecond spikes is the most significant new effect in the cm range. All basic
theoretical models of the zebra pattern and fiber bursts are discussed critically. Two main models are studied for their interpretation:
(i) interactions between electrostatic plasma waves and whistlers, (ii) radio emission at double plasma resonance (DPR). The
relative significance of several possible mechanisms remains uncertain. 相似文献
565.
566.
Jeongwoo Lee 《Space Science Reviews》2007,133(1-4):73-102
Solar active region coronae are known for strong magnetic fields permeating tenuous plasma, which makes them an ideal astronomical
laboratory for magnetohydrodynamics research. It is, however, relatively less known that this physical condition also permits
a very efficient radiation mechanism, gyro-resonant emission, produced by hot electrons gyrating in the coronal magnetic field.
As a resonant mechanism, gyro-emission produces high enough opacity to fully reveal the coronal temperature, and is concentrated
at a few harmonics of the local gyrofrequency to serve as an excellent indicator of the magnetic field. In addition, the polarization
of the ubiquitous free–free emission and a phenomenon of depolarization due to mode coupling extend the magnetic field diagnostic
to a wide range of coronal heights. The ability to measure the coronal temperature and magnetic field without the complications
that arise in other radiative inversion problems is a particular advantage for the active region radio emissions available
only at these wavelengths. This article reviews the efforts to understand these radiative processes, and use them as diagnostic
tools to address a number of critical issues involved with active regions. 相似文献
567.
简要叙述了航空计量信息管理系统ORACLE6应用软件向ORACLE7升级的过程中遇到的一些问题和解决办法,以及升级后的效果。 相似文献
568.
根据气象卫星地面测试对成像终端软件的要求,对成像终端软件的设计与工程实现进行了研究。给出了成像终端软件的接口要求、设计思想、实现方法和可靠性设计等。整星测试结果表明,成像终端软件的设计原理和实现方法合理可行。 相似文献
569.
】阐述了高等数学标准化测试计算机辅助教学软件开发的环境,它是在Win-dows中文环境中,利用FoxPro数据库软件和Word字处理软件编制的。介绍了高等数学标准化测试CAI软件的功能及特点,通过DDE技术实现高等数学标准化测试试题的输入输出的方法 相似文献
570.
作者运用Authorware、3Dmax、Premiere等多媒体制作工具,把文字、图片、动画、音频、视频等信息有机地结合起来,制作完成了新颖、实用、交互性强、功能强大的工科《大学物理》CAI课件制作并投入使用,解决了教师难教、学生难学的问题,得到了学生的极大欢迎并取得了良好的教学效果。本文介绍了作者制作中的技术手段及运用的体会。 相似文献