全文获取类型
收费全文 | 1854篇 |
免费 | 375篇 |
国内免费 | 423篇 |
专业分类
航空 | 1478篇 |
航天技术 | 538篇 |
综合类 | 226篇 |
航天 | 410篇 |
出版年
2024年 | 7篇 |
2023年 | 43篇 |
2022年 | 62篇 |
2021年 | 99篇 |
2020年 | 92篇 |
2019年 | 101篇 |
2018年 | 115篇 |
2017年 | 115篇 |
2016年 | 120篇 |
2015年 | 104篇 |
2014年 | 149篇 |
2013年 | 112篇 |
2012年 | 168篇 |
2011年 | 153篇 |
2010年 | 101篇 |
2009年 | 106篇 |
2008年 | 103篇 |
2007年 | 106篇 |
2006年 | 90篇 |
2005年 | 87篇 |
2004年 | 68篇 |
2003年 | 50篇 |
2002年 | 67篇 |
2001年 | 53篇 |
2000年 | 43篇 |
1999年 | 36篇 |
1998年 | 45篇 |
1997年 | 32篇 |
1996年 | 39篇 |
1995年 | 24篇 |
1994年 | 39篇 |
1993年 | 28篇 |
1992年 | 22篇 |
1991年 | 22篇 |
1990年 | 26篇 |
1989年 | 12篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 2篇 |
排序方式: 共有2652条查询结果,搜索用时 312 毫秒
1.
《中国航空学报》2021,34(5):617-627
In this paper, a progressive approach to predict the multiple shot peening process parameters for complex integral panel is proposed. Firstly, the invariable parameters in the forming process including shot size, mass flow, peening distance and peening angle are determined according to the empirical and machine type. Then, the optimal value of air pressure for the whole shot peening is selected by the experimental data. Finally, the feeding speed for every shot peening path is predicted by regression equation. The integral panel part with thickness from 2 mm to 5 mm and curvature radius from 3200 mm to 16000 mm is taken as a research object, and four experiments are conducted. In order to design specimens for acquiring the forming data, one experiment is conducted to compare the curvature radius of the plate and stringer-structural specimens, which were peened along the middle of the two stringers. The most striking finding of this experiment is that the outer shape error range is below 3.9%, so the plate specimens can be used in predicting feeding speed of the integral panel. The second experiment is performed and results show that when the coverage reaches the limit of 80%, the minimum feeding speed is 50 mm/s. By this feeding speed, the forming curvature radius of the specimens with different thickness from the third experiment is measured and compared with the research object, and the optimal air pressure is 0.15 MPa. Then, the plate specimens with thickness from 2 mm to 5 mm are peened in the fourth experiment, and the measured curvature radius data are used to calculate the feeding speed of different shot peening path by regressive analysis method. The algorithm is validated by forming a test part and the average deviation is 0.496 mm. It is shown that the approach can realize the forming of the integral panel precisely. 相似文献
2.
《中国航空学报》2020,33(2):391-406
A thermal-solid-liquid complex operational environment induces structural interface developing a typical coupling sliding/impact wear behavior. It results in contact damage until systems fail, which may cause significant economic losses and catastrophic consequences. The key point of solving this problem is to reveal the coupling damage mechanism of the sliding/impact behavior in typical systems and life characterization under a complicate evolving environment. This has been a hot topic in the area of mechanical reliability. The main work in this paper can be concluded as follows. Firstly, the main industries in which the “sliding/impact behavior” takes place have been introduced. Then, existing studies on the wear mechanism and degree analysis are presented, which includes surface morphology analysis, wear debris analysis, and wear degree measurement. Meanwhile, existing problems in theoretical modeling and experiments in current research are summarized, so as to point out a bright direction for future research on wear prediction. They include interface contact modeling, mathematic coupling mechanism modeling, wear equation establishment, and wear life characterization, which can provide some new ideas for improving the existing studies on the sliding/impact wear behavior. 相似文献
3.
4.
就十种典型的精密平面形状误差测量-分离方法的权函数及其零点,作了分析比较。按形状误差谐波抑制最小准则,论证了五点式正交逐次三点法、九点式正交逐次三点法、复合三点法、不对称二维混合法和不对称四点法优于其他方法,不对称四点法则较为理想。 相似文献
5.
6.
证明了最小二乘直线函数是一种严格的凸函数。F(a,b)=∑(y-ax_i-b)~2是一个椭圆抛物面。a=[n∑x_iy_i-∑x_i∑y_i]/[n∑x_i^2-(∑x_i)~2]和b=[∑x_i^2∑y_i-∑x_i∑x_i∑y_i]/[n∑x_i^2-(∑x_i)~2]仅表示极值点。a=∑x_iy_i/∑x_i和 b=[∑x_i^2∑y_i-∑x_i∑x_iy_i]/[n∑x_i^2]在某些情况下可以是极值点,但不是在每种情况下都是极值点。 相似文献
7.
高精度圆度仪误差分离装置研制及测量不确定度分析 总被引:3,自引:0,他引:3
介绍了一种由程控型多齿分度台和高精度圆度仪组合而成的全自动误差分离装置,该装置能够使圆度仪主轴回转误差从被测工件测量结果中可靠分离,从而极大地提高了圆度测量不确定度,本文对该装置测量不确定度进行了分析。 相似文献
8.
复杂系统的可靠性分析方法研究 总被引:1,自引:1,他引:0
本文对未来的运载器的复杂控制系统的可靠性建模、分配和预计的一般方法和程序及综合分析方法进行了讨论和研究。并简述了复杂系统的计算机辅助可靠性分析。 相似文献
9.
经过对误差分离技术理论进行了分析之后,又对误差补偿技术进行了研究,并建立了多点法测量形状误差的补偿控制系统。通过补偿主轴径向误差运动,提高了工件的圆度误差和圆柱度误差。 相似文献
10.
在采用点值图确定门限区间个数的基础上,对门自回归模型中门限值、滞后步长、各门限区间模型阶数,利用正交设计方法寻优,计算工作量锐减,却可得到精度较高的预报模型。 相似文献