全文获取类型
收费全文 | 6596篇 |
免费 | 1211篇 |
国内免费 | 1576篇 |
专业分类
航空 | 5665篇 |
航天技术 | 1439篇 |
综合类 | 1063篇 |
航天 | 1216篇 |
出版年
2024年 | 10篇 |
2023年 | 112篇 |
2022年 | 214篇 |
2021年 | 290篇 |
2020年 | 306篇 |
2019年 | 309篇 |
2018年 | 351篇 |
2017年 | 376篇 |
2016年 | 405篇 |
2015年 | 372篇 |
2014年 | 466篇 |
2013年 | 402篇 |
2012年 | 480篇 |
2011年 | 532篇 |
2010年 | 425篇 |
2009年 | 474篇 |
2008年 | 414篇 |
2007年 | 433篇 |
2006年 | 371篇 |
2005年 | 314篇 |
2004年 | 289篇 |
2003年 | 273篇 |
2002年 | 193篇 |
2001年 | 203篇 |
2000年 | 179篇 |
1999年 | 167篇 |
1998年 | 146篇 |
1997年 | 107篇 |
1996年 | 127篇 |
1995年 | 97篇 |
1994年 | 109篇 |
1993年 | 98篇 |
1992年 | 66篇 |
1991年 | 79篇 |
1990年 | 67篇 |
1989年 | 66篇 |
1988年 | 41篇 |
1987年 | 15篇 |
1986年 | 5篇 |
排序方式: 共有9383条查询结果,搜索用时 875 毫秒
961.
962.
提出了一种基于LSTM (Long Short Time Memory)模型的飞行历史数据挖掘模型的构建方法,此模型可以将飞行数据中有价值的目标数据自动提取出来。首先,通过滑动窗口法获得待检测数据;然后,将预先做好的训练样本数据输入到所构造的LSTM模型中进行训练,得到数据挖掘模型;最后,将待检测数据导入到训练好的LSTM模型中进行模式识别,将目标数据片段挖掘出来。结果表明,基于LSTM模型的飞行数据挖掘模型构建方法通用化程度高,可用于挖掘不同类型的目标数据,且识别率高,具有很高的工程应用价值。 相似文献
963.
《中国航空学报》2021,34(6):162-177
In the manufacturing of thin wall components for aerospace industry, apart from the side wall contour error, the Remaining Bottom Thickness Error (RBTE) for the thin-wall pocket component (e.g. rocket shell) is of the same importance but overlooked in current research. If the RBTE reduces by 30%, the weight reduction of the entire component will reach up to tens of kilograms while improving the dynamic balance performance of the large component. Current RBTE control requires the off-process measurement of limited discrete points on the component bottom to provide the reference value for compensation. This leads to incompleteness in the remaining bottom thickness control and redundant measurement in manufacturing. In this paper, the framework of data-driven physics based model is proposed and developed for the real-time prediction of critical quality for large components, which enables accurate prediction and compensation of RBTE value for the thin wall components. The physics based model considers the primary root cause, in terms of tool deflection and clamping stiffness induced Axial Material Removal Thickness (AMRT) variation, for the RBTE formation. And to incorporate the dynamic and inherent coupling of the complicated manufacturing system, the multi-feature fusion and machine learning algorithm, i.e. kernel Principal Component Analysis (kPCA) and kernel Support Vector Regression (kSVR), are incorporated with the physics based model. Therefore, the proposed data-driven physics based model combines both process mechanism and the system disturbance to achieve better prediction accuracy. The final verification experiment is implemented to validate the effectiveness of the proposed method for dimensional accuracy prediction in pocket milling, and the prediction accuracy of AMRT achieves 0.014 mm and 0.019 mm for straight and corner milling, respectively. 相似文献
964.
《中国航空学报》2021,34(6):141-150
Hobbing is one of the crucial gear manufacturing processes with high precision and high efficiency. In order to improve the accuracy of hobbing and hob relief grinding, more precise grinding wheels are demanded for relief grinding in the production of gear hobs. In this paper, a new and accurate mathematical method for calculating the axial profile of grinding wheel based on the corresponding gear hob to be ground is proposed. Considering that most researches have been conducted to focus on the optimization of hob geometric feature and only can be applied to a specific type of hand of helix and rake angle of gear hobs. The method in this paper can be served as a general algorithm for generating axial profile of grinding wheels on the basis of the spatial envelope theory, the principle of coordinate system transformation, and studies on normal profile of single-tooth. The accuracy of grinding hobs is based on applying the approach in practical manufacturing. Taking two typical different kinds of pre-grinding gear hobs as examples for calculation and experiment, the results of tooth profile errors strengthen the position that the validity and feasibility of this method, it can be employed for gear hob design and grinding processing. 相似文献
965.
《中国航空学报》2021,34(7):62-72
Delamination represents one of the most severe failure modes in composite laminates, especially when they are subjected to uniaxial compression loads. The evaluation of the delamination damage has always been an essential issue of composite laminates for durability and damage tolerance in engineering practice. Focusing on the most typical and representative elliptical delamination issue, an analytical model simultaneously considering the conservative buckling process and non-conservative delamination propagation process is implemented. Various computational cases considering different delamination depths, directions, aspect ratios, and areas are established, and the predicted results based on the analytical model are carefully compared. Effects of these geometrical delamination parameters on the buckling, delamination propagation, and failure behaviors of composite laminates are thoroughly analyzed, and innovative evaluation principles of the delamination damage have been concluded. It is found that the delamination area is the key factor that truly affecting the failure behaviors of delaminated composites, and the local / global buckling and failure loads show clear linearity with the delamination area, whilst the delamination depth and direction only have slight effects. 相似文献
966.
一种高光谱图像的双压缩感知模型 总被引:1,自引:0,他引:1
高光谱图像因其海量数据性,给存储、传输及后续分析处理带来了挑战。压缩感知理论提供了一种全新的信号采集框架。针对高光谱数据的三维特性,提出一种双压缩感知的采样与重构模型。该模型在采样阶段兼顾高光谱数据的空间和谱间稀疏特性,构造了能同时实现空间和谱间压缩采样的感知矩阵;重构阶段不同于传统的压缩感知重构方法直接重构高光谱数据,而是将高光谱数据分离成端元和丰度分别进行重构,然后利用重构的端元和丰度信息合成高光谱数据。实验结果表明,所提双压缩感知在低采样率下重构精度较三维压缩采样提高了10 dB以上,更为显著的是运算速度提升了3个数量级,同时该方法还便于获得端元和丰度信息。 相似文献
967.
针对民用航空发动机钛合金整体叶盘常用材料TA19开展其母材试件与电子束焊焊接试件在20,300,450℃的疲劳试验,通过焊接试件的焊缝材料断口与母材断口形貌的比较探讨了焊缝材料的疲劳破坏机理,并在104~106循环的疲劳寿命区间内采用Basquin模型分别建立了焊缝材料和母材的应力-疲劳寿命(S-N)曲线,结果显示母材试件与焊接试件的试验疲劳寿命大部分都落在了对应模型计算疲劳寿命的2倍线之内,表明试验得到的S-N曲线是合理的.焊接试件与母材试件的S-N曲线的对比分析表明,20℃时焊接试件的疲劳性能比母材试件略高,而在300℃和450℃时焊接试件与母材试件的疲劳性能差异随应力水平发生变化.但总地说来,在所关注疲劳寿命区间内,母材试件与焊接试件的计算疲劳寿命差异也在2倍线以内,初步表明两者的疲劳性能相当. 相似文献
968.
969.
旋翼非定常气动特性CFD模拟的通用运动嵌套网格方法 总被引:7,自引:4,他引:3
针对直升机旋翼非定常气动特性CFD模拟中的网格生成难题,提出了一套高效、通用的运动嵌套网格生成方法.首先,基于Poisson方程求解和翻折法生成旋翼桨叶的正交贴体网格.其次,针对旋翼桨叶的扭转分布及变距、挥舞等复杂运动,建立了一套通用的洞单元识别的扰动衍射法;为保证洞包络面的封闭性,完善了挖洞过程中网格加密策略;在洞边界确立基础上,提出了一种高效、鲁棒的最小距离法贡献单元搜索的改进方法.在此基础上,建立了基于RANS(Reynolds-averaged Navier-Stokes)方程的旋翼非定常流场CFD模拟方法.最后,采用所建立的方法分别对悬停和前飞状态下的C-T(Caradonna-Tung)旋翼和7A(Helishape 7A)旋翼的气动特性、桨尖涡的位置进行了计算,计算结果与试验值误差小于5%,验证了该运动嵌套网格生成方法在旋翼非定常气动特性CFD模拟中的有效性. 相似文献
970.