全文获取类型
收费全文 | 1740篇 |
免费 | 230篇 |
国内免费 | 300篇 |
专业分类
航空 | 1277篇 |
航天技术 | 312篇 |
综合类 | 293篇 |
航天 | 388篇 |
出版年
2024年 | 6篇 |
2023年 | 28篇 |
2022年 | 39篇 |
2021年 | 48篇 |
2020年 | 55篇 |
2019年 | 60篇 |
2018年 | 50篇 |
2017年 | 60篇 |
2016年 | 84篇 |
2015年 | 76篇 |
2014年 | 116篇 |
2013年 | 102篇 |
2012年 | 123篇 |
2011年 | 140篇 |
2010年 | 84篇 |
2009年 | 109篇 |
2008年 | 118篇 |
2007年 | 114篇 |
2006年 | 105篇 |
2005年 | 90篇 |
2004年 | 74篇 |
2003年 | 86篇 |
2002年 | 68篇 |
2001年 | 67篇 |
2000年 | 48篇 |
1999年 | 39篇 |
1998年 | 44篇 |
1997年 | 32篇 |
1996年 | 19篇 |
1995年 | 20篇 |
1994年 | 33篇 |
1993年 | 25篇 |
1992年 | 24篇 |
1991年 | 24篇 |
1990年 | 24篇 |
1989年 | 14篇 |
1988年 | 14篇 |
1987年 | 6篇 |
1986年 | 2篇 |
排序方式: 共有2270条查询结果,搜索用时 15 毫秒
991.
改革开放以来,外商直接投资从无到有、从小到大,为国家经济发展和现代化建设做出了不可或缺的重要贡献。近几年,外商在中国的直接投资已暴露出了一些问题,为了提升我国利用外商直接投资的质量和水平,必须解决这些问题。 相似文献
992.
通过识别企业产品/技术研发过程中的技术活动,探讨了企业以高风险、领先发展模式为大背景、为降低技术风险而采取的基于技术成熟度的科研管理模式框架,分析了这种模式向企业自主创新科研管理模式转变的必然趋势。 相似文献
993.
介绍在AutoCAD2004平台上,利用二次开发系统及其下拉菜单、VLISP语言等控制模块程序而开发轴类零件图绘制系统。软件采用下拉式菜单技术和屏幕图形可视化,使用户方便快捷地进行绘制各种轴类零件图,从而减轻设计人员在绘制轴类零件图的重复性工作,具有交互性好、使用方便及扩展性好等特点。 相似文献
994.
Lo J S K Quality & Reliability Centre Advisory Committee The Hong Kong Polytechnic University Hung Hom Kowloon Hong Kong 《南京航空航天大学学报(英文版)》1998,(1)
ISO9000质量管理系统往往存在一种神秘性。一般认为它只适用于大型公司,对小型公司而言,该系统实在是太昂贵了,本文澄清了这种错误的想法,并说明了ISO9000系统内在之属性事实上是灵活的,不论任何行业的小型公司均可适用。此外,它亦指出了认证审核员和质量管理顾问应对那些易犯的错误提高警觉。 相似文献
995.
疲劳裂纹扩展是结构健康监测的主要问题之一,为了保证金属结构的可靠和安全运行,实时监测结构的疲劳裂纹扩展过程十分必要。针对结构裂纹扩展的问题,采用压电传感器(PZT)和电阻应变片两种传感器,提出结合能够连续监测结构损伤的被动监测方法以及对微小损伤敏感的主动监测方法对裂纹扩展进行综合监测,以提高裂纹扩展的监测水平。采用随机森林算法对裂纹长度进行识别,并使用D-S证据理论对两种传感器的识别结果进行数据融合,得到比单一传感器更准确、可靠的裂纹扩展识别结果。进行了基于应变和主动Lamb波的裂纹扩展监测实验研究,验证了该方法对提高裂纹扩展监测识别准确率的有效性和实用性。 相似文献
996.
997.
U.M. Leloglu E. Kocaoglan 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008
Although it is generally agreed that the outer space should be used for the benefit of all mankind, only a fraction of the countries have the necessary technological base for accessing space. Space technology, with its implications on science, economy and well-being of citizens, is mostly chosen as one of the priority areas for technological development by developing countries. However, there is already an over-capacity in global space industry and there are doubts on necessity of additional capacity establishment by developing countries. In this study, the importance and benefits of capacity-building in these countries are emphasized and the advantages and disadvantages that developing countries have in the framework of space technology acquisition are briefly presented. The feasibility of certain levels of space technology is discussed and the necessity of combining existing indigenous capabilities with technology obtained from foreign sources in the optimal way is stressed. We have also mentioned various general mechanisms of technology transfer and argued the importance of licensing in catching-up developed countries. After considering the necessary conditions of efficiency of technology, such as establishment of regional centers of space science and technology education by United Nations, joint development of space systems, complete technology transfer packages, cooperative space projects within regional organizations, coordinated constellations and special agreements with large space agencies, which are specific mechanisms already in use, are reviewed. Some typical examples of mechanisms are also given with special emphasize on small satellite technology that makes access to space affordable for many countries. Through sharing and analyzing the experience of developing countries in their odyssey of space capacity-building, the difficulties can be negotiated and the vicious circles can be broken. This study, in our view, is a step to incite a general discussion of obstacles and opportunities for developing countries, that could help them in using their limited resources effectively, hence, enable them to offer better conditions to their citizens and to contribute space science to a larger extend. 相似文献
998.
Robert J. Rovetto 《Space Policy》2013,29(4):225-228
The question is: should the United States and nations at large pursue a human spaceflight program (and if so, why)? I offer an unwavering positive answer to this question, and state the reasons for it while considering the broad challenges and benefits of (human) spaceflight. Space exploration is a human activity that is intrinsically forward-looking, and as such, has positive potential. Both national and international space programs can galvanize the population, inspire the youth, foster job-creation, and motivate the existing workforce. The nature of the enterprises involved—their scale, novelty, and complexity—requires a steady and continuous upward progression toward greater societal, scientific and technological development. That is, in order to overcome the challenges of human spaceflight, progress is required. More to the point, the survival of humanity depends on expanding beyond the confines of our planet. Human spaceflight, in short, presents us with an opportunity to significantly advance the nation and the global community. 相似文献
999.
霍秀红 《郑州航空工业管理学院学报(管理科学版)》2006,24(6):21-25
20世纪70年代以后,随着滞胀现象的出现和新古典宏观经济学的兴起,凯恩斯主义面临理论和实践的双重挑战,政府能否、怎样干预经济活动以及政府政策是否有效,成为西方经济学界争论的热点问题之一。文章把政府作为市场经济中与企业、居民并列的市场行为主体,对政府管制的收益成本进行比较,以管制经济学的视角从微观的角度对政府和市场的关系进行分析,并以市场绩效为主线,从经济学的视角对政府管制进行了理论探讨。 相似文献
1000.