全文获取类型
收费全文 | 8107篇 |
免费 | 1279篇 |
国内免费 | 1627篇 |
专业分类
航空 | 4826篇 |
航天技术 | 2259篇 |
综合类 | 1487篇 |
航天 | 2441篇 |
出版年
2024年 | 6篇 |
2023年 | 38篇 |
2022年 | 129篇 |
2021年 | 121篇 |
2020年 | 199篇 |
2019年 | 79篇 |
2018年 | 121篇 |
2017年 | 116篇 |
2016年 | 109篇 |
2015年 | 250篇 |
2014年 | 442篇 |
2013年 | 467篇 |
2012年 | 480篇 |
2011年 | 520篇 |
2010年 | 645篇 |
2009年 | 628篇 |
2008年 | 574篇 |
2007年 | 552篇 |
2006年 | 457篇 |
2005年 | 392篇 |
2004年 | 287篇 |
2003年 | 227篇 |
2002年 | 268篇 |
2001年 | 305篇 |
2000年 | 323篇 |
1999年 | 437篇 |
1998年 | 400篇 |
1997年 | 333篇 |
1996年 | 330篇 |
1995年 | 247篇 |
1994年 | 274篇 |
1993年 | 245篇 |
1992年 | 221篇 |
1991年 | 186篇 |
1990年 | 152篇 |
1989年 | 135篇 |
1988年 | 103篇 |
1987年 | 92篇 |
1986年 | 42篇 |
1985年 | 22篇 |
1984年 | 12篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1972年 | 2篇 |
1970年 | 1篇 |
1965年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
The hierarchical porous N/O co-functionalized carbon(HPNOC)was scalably prepared by using the lowcost and renewable blighted grains as the raw material coupled with mild KHCO_3 activation for electrochemical capacitors(ECs).The elemental N was in situ doped in the obtained HPNOC without any N-containing additives.Remarkably,the obtained HPNOC was endowed with a large specific surface area(about 2 624m~2·g~(-1)),high pore volume(about 1.35cm~3·g~(-1)),as well as high-content N/O functionalization(about 1.9%(in atom)N and about 10.2%(in atom)O.Furthermore,the as-resulted HPNOC electrode with a high mass loading of 5mg·cm~(-2 )exhibited competitive gravimetric capacitances of about 373.6F·g~(-1 )at 0.5A·g~(-1),and even about 260.4F·g~(-1 )at a high rate of 10A·g~(-1);superior capacitance retention of about 98.8%at 1A·g~(-1 )over 10 000consecutive cycles;and high specific energy of about 9.6W·h·kg~(-1 )at a power of 500W·kg~(-1),when evaluated as a promising electrode in 6mol KOH for advanced electrochemical supercapacitors.More encouragingly,the green synthetic strategy we developed holds a huge promise in generalizing for other biomass-derived carbon materials for versatile energy-related applications. 相似文献
2.
Automotive collision avoidance technology can effectively avoid the accidents caused by dangerous traffic conditions or driver's manipulation errors.Moreover,it can promote the development of autonomous driving for intelligent vehicle in intelligent transportation.We present a collision avoidance system,which is composed of an evasive trajectory planner and a path following controller.Considering the stability of the vehicle in the conflict-free process,the evasive trajectory planner is designed by polynomial parametric method and optimized by genetic algorithm.The path following controller is proposed to make the car drive along the designed path by controlling the vehicle's lateral movement.Simulation results show that the vehicle with the proposed controller has good stability in the collision process,and it can ensure the vehicle driving in accordance with the planned trajectory at different speeds.The research results can provide a certain basis for the research and development of automotive collision avoidance technology. 相似文献
3.
Pengbin Guo Jian Sun Shuling Hu Ju Xue 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(3):787-798
Pulsar navigation is a promising navigation method for high-altitude orbit space tasks or deep space exploration. At present, an important reason for restricting the development of pulsar navigation is that navigation accuracy is not high due to the slow update of the measurements. In order to improve the accuracy of pulsar navigation, an asynchronous observation model which can improve the update rate of the measurements is proposed on the basis of satellite constellation which has a broad space for development because of its visibility and reliability. The simulation results show that the asynchronous observation model improves the positioning accuracy by 31.48% and velocity accuracy by 24.75% than that of the synchronous observation model. With the new Doppler effects compensation method in the asynchronous observation model proposed in this paper, the positioning accuracy is improved by 32.27%, and the velocity accuracy is improved by 34.07% than that of the traditional method. The simulation results show that without considering the clock error will result in a filtering divergence. 相似文献
4.
6.
L O Bjorn S Widell T Wang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2002,30(6):1557-1562
Plants have evolved under the influence of UV-B radiation and have acquired systems for monitoring it and investing appropriate resources for protection against it, i.e., filters, quenchers of radicals and reactive oxygen species, and repair systems. An hypothesis for how plants monitor radiation has been presented. 相似文献
7.
晶体管h参数微变等效电路是电子技术中求解低频、小信号放大电路常用的分析方法.本文通过具体分析,将模拟放大电路进行了新的分类,并且明确而系统地给出运用微变等效电路求解各类模拟放大电路动态指标Av、ri和γ0公式、解题难点及规律. 相似文献
8.
本文建立了包括非线性环节在内的横航向驾驶员—操纵系统—飞机本体组合系统的数学模型,采用闭环控制原理,对JJ-7飞机横航向驾驶员诱发振荡PIO问题进行了研究,并详细地讨论了驾驶员参数及其各种操纵动作、操纵系统和飞机本体气动参数对横航向PIO的影响,探讨了横航向PIO产生的机理。文中以JJ-7飞机为例,采用时域法在整个飞行包线各点进行了检查,并用固基飞行模拟器进行模拟验证。其结果与理论计算结果相一致。 相似文献
9.
对H5飞机经过了计算、论证、试飞,在此基础上提出了一种既安全又能充分发挥飞机飞行性能,同时又使动作程序化的调油方法--规划调油法。用这种调油就可以大大地减少飞行员操纵飞机进的注意力分散,更利于集中精力操纵飞机,以保证飞行的安全。 相似文献
10.
论述了我国加入世界贸易组织后,如何搞好航空产品的包装和包装标准化工作,以提高航空工业军品和民品在国际市场的竞争能力。 相似文献