全文获取类型
收费全文 | 919篇 |
免费 | 223篇 |
国内免费 | 159篇 |
专业分类
航空 | 770篇 |
航天技术 | 208篇 |
综合类 | 120篇 |
航天 | 203篇 |
出版年
2024年 | 5篇 |
2023年 | 34篇 |
2022年 | 35篇 |
2021年 | 62篇 |
2020年 | 55篇 |
2019年 | 47篇 |
2018年 | 49篇 |
2017年 | 50篇 |
2016年 | 73篇 |
2015年 | 46篇 |
2014年 | 66篇 |
2013年 | 40篇 |
2012年 | 67篇 |
2011年 | 52篇 |
2010年 | 49篇 |
2009年 | 65篇 |
2008年 | 68篇 |
2007年 | 69篇 |
2006年 | 88篇 |
2005年 | 38篇 |
2004年 | 51篇 |
2003年 | 30篇 |
2002年 | 23篇 |
2001年 | 11篇 |
2000年 | 24篇 |
1999年 | 17篇 |
1998年 | 19篇 |
1997年 | 14篇 |
1996年 | 6篇 |
1995年 | 15篇 |
1994年 | 9篇 |
1993年 | 9篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 4篇 |
1984年 | 4篇 |
排序方式: 共有1301条查询结果,搜索用时 15 毫秒
781.
E.G. Cordaro E. Olivares D. Galvez D. Salazar-Aravena D. Laroze 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
We present the results of three years of continuous operations and the principal characteristics of our new 3He neutron monitors installed in the Chilean Network of Cosmic-Ray Observatories. During the years 2004 and 2005, we began the construction of this International Geophysical Year (IGY)-type 3He neutron monitor, with the intention of replacing the older proportional tubes of the BF3. These new monitors are installed in stations at locations ranging from the near-equatorial zone to the Antarctic zone. As a reference system, we used our own BF3 neutron monitors and previously complemented the collected data with a Monte Carlo simulation for the proton-yield function response of the Putre neutron monitor. Herein, we present for the first time the data obtained from our new high-mountain observatory located in the Altiplanic zone. 相似文献
782.
B.G.B. Solheim 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
The European Modular Cultivation System (EMCS) on the ISS allows long-term biological experiments, e.g. on plants. Video cameras provide near real-time 2D images from these experiments. A method to obtain 3D coordinates and stereoscopic images from these 2D images has been developed and is described in this paper. The procedure was developed to enhance the data output of the MULTIGEN-1 experiment in 2007. One of the main objectives of the experiment was to study growth movements of the Arabidopsis plants and the effect of gravity on these. 3D data were important during parts of the experiment and the paper presents the method developed to acquire 3D data, the accuracy of the data, limitations to the technique and ways to improve the accuracy. Sequences of 3D data obtained from the MULTIGEN-1 experiment are used to illustrate the potential of this newfound capability of the EMCS. In the experiment setup, a positional depth accuracy of about ±0.4 mm for relative object distances and an absolute depth accuracy of about ±1.4 mm for time dependent phenomena was reached. The ability to both view biological specimens in 3D as well as obtaining quantitative 3D data added greatly to the scientific output of the MULTIGEN-1 experiment. The uses of the technique to other researchers and their experiments are discussed. 相似文献
783.
784.
三维工序模型的演进式构建方法 总被引:1,自引:0,他引:1
为实现以三维工序模型为核心的三维工艺构建,基于从毛坯模型到最终产品模型的演进过程,对三维工序模型的生成方法进行研究.在制造特征信息模型的基础上,结合基准信息建立了面向工序模型生成的工序信息模型.提出制造特征信息在工序模型中的映射机制,解决该模式下工序模型信息缺失的问题.以工序信息模型为模板,首先定义加工特征基元,然后通过实例化实现工序模型的变换.最后,通过集成工艺决策系统,构建三维工序模型生成系统,为后续工艺尺寸标注和工艺展示提供模型支持. 相似文献
785.
多用酸洗缓蚀剂DSCH-1的研究 总被引:1,自引:0,他引:1
由含氮的脂肪胺、芳香胺等多种常用的有机缓蚀剂复配制成的DSCH-1 缓蚀剂,在硝酸中对20# 锅炉钢和紫铜的缓蚀效率达99.7% ,在盐酸中对20# 锅炉的钢的缓蚀效率达98.5% ,对紫铜的缓蚀效率也较高。Fe3+ 离子浓度对DSCH-1 缓蚀性能有较大的影响 相似文献
786.
S. Karakula W. Tkaczyk F. Giovannelli 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1984,3(10-12)
In the spherical accretion onto massive objects, the matter may be heated up to temperatures as high as 1012 °K. In such a hot plasma, the thermal bremsstrahlung (e-e and e-p) and π° decay from inelastic collisions of protons are the main γ-ray sources. We determined the γ -ray production spectra from the π° decay and from bremsstrahlung for different temperatures. The expected γ-ray spectra were evaluated too in order to fit experimental data. We have fitted COS B data from 3C 273 using a two temperatures plasma model. The best fit is for
(M8 is the black hole mass in 108 M) which gives
. The hard X-ray measurements do not contradict the bremsstrahlung spectrum. 相似文献
Full-size image (1K)
787.
本文介绍了一种基于虚拟听觉技术的新型告警系统,通过其原理算法介绍和原理样机实验表明了该系统的可实现性。 相似文献
788.
Quantification of spatial structure of human proximal tibial bone biopsies using 3D measures of complexity 总被引:2,自引:0,他引:2
Saparin PI Thomsen JS Prohaska S Zaikin A Kurths J Hege HC Gowin W 《Acta Astronautica》2005,56(9-12):820-830
Changes in trabecular bone composition during development of osteoporosis are used as a model for bone loss in microgravity conditions during a space flight. Symbolic dynamics and measures of complexity are proposed and applied to assess quantitatively the structural composition of bone tissue from 3D data sets of human tibia bone biopsies acquired by a micro-CT scanner. In order to justify the newly proposed approach, the measures of complexity of the bone architecture were compared with the results of traditional 2D bone histomorphometry. The proposed technique is able to quantify the structural loss of the bone tissue and may help to diagnose and to monitor changes in bone structure of patients on Earth as well as of the space-flying personnel. 相似文献
789.
790.