全文获取类型
收费全文 | 83781篇 |
免费 | 15911篇 |
国内免费 | 11361篇 |
专业分类
航空 | 61835篇 |
航天技术 | 18545篇 |
综合类 | 7910篇 |
航天 | 22763篇 |
出版年
2024年 | 355篇 |
2023年 | 1126篇 |
2022年 | 3045篇 |
2021年 | 3599篇 |
2020年 | 3416篇 |
2019年 | 2980篇 |
2018年 | 3298篇 |
2017年 | 3722篇 |
2016年 | 2749篇 |
2015年 | 3553篇 |
2014年 | 4556篇 |
2013年 | 4779篇 |
2012年 | 5437篇 |
2011年 | 6153篇 |
2010年 | 6124篇 |
2009年 | 6431篇 |
2008年 | 6255篇 |
2007年 | 5568篇 |
2006年 | 5138篇 |
2005年 | 4186篇 |
2004年 | 3090篇 |
2003年 | 2526篇 |
2002年 | 2238篇 |
2001年 | 2384篇 |
2000年 | 2025篇 |
1999年 | 2047篇 |
1998年 | 1519篇 |
1997年 | 1119篇 |
1996年 | 1171篇 |
1995年 | 1260篇 |
1994年 | 1296篇 |
1993年 | 678篇 |
1992年 | 676篇 |
1991年 | 398篇 |
1990年 | 360篇 |
1989年 | 495篇 |
1988年 | 288篇 |
1987年 | 387篇 |
1986年 | 274篇 |
1985年 | 511篇 |
1984年 | 425篇 |
1983年 | 338篇 |
1982年 | 341篇 |
1981年 | 481篇 |
1980年 | 203篇 |
1979年 | 163篇 |
1978年 | 175篇 |
1975年 | 162篇 |
1974年 | 162篇 |
1972年 | 156篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
ected g 《桂林航天工业高等专科学校学报》2006,(2)
with primary goat embryonic fibroblast showed no difference from traditional feederlayer-based culture method used in mouse and human. The putative primary EG colonies were multilayer clumps ofcompact cel 相似文献
192.
本文结合Protel 99 SE在高频PCB设计中的应用,着重探讨在电路原理图的绘制上需要重点注意的一些特殊问题,并提出解决问题的方法,尽可能地减小对高频PCB设计的影响,提高PCB设计的效率。 相似文献
193.
194.
D L Stephens L W Townsend J Miller C Zeitlin L Heilbronn 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2002,30(4):901-905
Deep-space manned flight as a reality depends on a viable solution to the radiation problem. Both acute and chronic radiation health threats are known to exist, with solar particle events as an example of the former and galactic cosmic rays (GCR) of the latter. In this experiment Iron ions of 1A GeV are used to simulate GCR and to determine the secondary radiation field created as the GCR-like particles interact with a thick target. A NASA prepared food pantry locker was subjected to the iron beam and the secondary fluence recorded. A modified version of the Monte Carlo heavy ion transport code developed by Zeitlin at LBNL is compared with experimental fluence. The foodstuff is modeled as mixed nuts as defined by the 71st edition of the Chemical Rubber Company (CRC) Handbook of Physics and Chemistry. The results indicate a good agreement between the experimental data and the model. The agreement between model and experiment is determined using a linear fit to ordered pairs of data. The intercept is forced to zero. The slope fit is 0.825 and the R2 value is 0.429 over the resolved fluence region. The removal of an outlier, Z=14, gives values of 0.888 and 0.705 for slope and R2 respectively. 相似文献
195.
De Gaudenzi R. Fanucci L. Giannetti F. Luise M. Rovini M. 《Aerospace and Electronic Systems Magazine, IEEE》2003,18(8):23-30
Since 1999, ESA has conducted a number of system studies and technological developments to support the European and Canadian industry in the definition of a Satellite UMTS (S-UMTS) component development strategy, identifying critical technological areas and promoting S-UMTS demonstrations. In particular, the MUSIC project has successfully demonstrated advanced digital signal processing techniques to mitigate CDMA interference in spread-spectrum receivers, thus increasing the capacity and/or quality of service of a wireless communication network. The low-complexity solution for interference mitigation investigated and developed in the project is particularly suited for being implemented in mobile terminals. 相似文献
196.
Conte E. De Maio A. Ricci G. 《IEEE transactions on aerospace and electronic systems》2002,38(2):415-426
We address the estimation of the structure of the covariance matrix and its application to adaptive radar detection of coherent pulse trains in clutter-dominated disturbance modeled as a compound-Gaussian process. For estimation purposes we resort to range cells in spatial proximity with that under test and assume that these cells, free of signal components, can be clustered into groups of data with one and the same value of the texture. We prove that, plugging the proposed estimator of the structure of the covariance matrix into a previously derived detector, based upon the generalized likelihood ratio test (GLRT), leads to an adaptive detector which ensures the constant false alarm rate (CFAR) property with respect to the clutter covariance matrix as well as the statistics of the texture. Finally, we show that this adaptive receiver has an acceptable loss with respect to its nonadaptive counterpart in cases of relevant interest for radar applications 相似文献
197.
198.
M. I. Becka A. Jurewicz 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1996,17(12)
Currently conducted studies on modelling of scattered solar radiation in the 0.350-1.00 μm range along the Phobos orbit around Mars are presented. Our calculations include various types of grains, various densities and scattering angles. The calculations are performed with the aid of LOWTRAN7 program. These studies are directly related to the photometer coupled to PFS (Planetary Fourier Spectrometer) planned for the Mars-96 mission. 相似文献
199.
P.B. Marty S. Bardeau O. Czoske H. Ebeling J.P. Kneib R. Sadat I. Smail 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2004,34(12):2509-2515
We present an analysis of seven clusters observed by XMM-Newton as part of our survey of 17 most X-ray luminous clusters of galaxies at z 0.2 selected for a comprehensive and unbiased study of the mass distribution in massive clusters. Using the public software FTOOLS and XMMSAS we have set up an automated pipeline to reduce the EPIC MOS and pn spectro-imaging data, optimized for extended sources analysis. We also developped a code to perform intensive spectral and imaging analysis particularly focussing on proper background estimate and removal. XMM-Newton deep spectro-imaging of these clusters allowed us to fit a standard β-model to their gas emission profiles as well as a standard MEKAL emission model to their extracted spectra, and test their inferred characteristics against already calibrated relations. 相似文献
200.
对利用3D资源在快速开发虚拟环境系统中的方法进行了研究。在开发虚拟环境系统的过程中,复杂模型的建立是必不可少的,仅仅利用OpenGL函数编程来实现仿真是很困难的,针对该问题提出了利用3D资源进行3D文件读取和转换的两种方案,分析了虚拟环境中复杂模型的建立以及处理的基本方法,并对数控车床的仿真进行了详细介绍。 相似文献