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271.
In order to study the influences of confining pressure and strain rate on the mechanical properties of the Nitrate Ester Plasticized Polyether (NEPE) propellant, uniaxial tensile tests were conducted using the self-made confining pressure system and material testing machine. The stress-strain responses of the NEPE propellant under different confining pressure conditions and strain rates were obtained and analyzed. The results show that confining pressure and strain rate have a remarkably influence on the mechanical responses of the NEPE propellant. As confining pressure increases (from 0 to 5.4 MPa), the maximum tensile stress and ultimate strain increase gradually. With the coupled effects of confining pressure and strain rate, the value of the maximum tensile stress and ultimate strain at 5.4 MPa and 0.0667 s−1 is 2.03 times and 2.19 times of their values under 0 MPa and 0.00333 s−1, respectively. Afterwards, the influence mechanism of confining pressure on the NEPE propellant was analyzed. Finally, based on the viscoelastic theory and continuous damage theory, a nonlinear constitutive model considering confining pressure and strain rate was developed. The damage was considered to be rate-dependent and pressure-dependent. The constitutive model was validated by comparing experimental data with predictions of the constitutive model. The whole maximum stress errors of the model predictions are lower than 4% and the corresponding strain errors are lower than 7%. The results show that confining pressure can suppress the damage initiation and evolution of the NEPE propellant and the nonlinear constitutive model can describe the mechanical responses of the NEPE propellant under various confining pressure conditions and strain rates. This research can lay a theoretical foundation for analyzing the structural integrity of propellant grain accurately under working pressure loading. 相似文献
272.
Hai-bin Xu Long-kui Chen De-zhi Zhang Fang-ping Zhang Zhao-wu Shen Wen-xiang Liu Sheng-hong Huang 《防务技术》2021,17(3):1071-1080
The mitigation of blast shock with water has broad application prospects. Understanding the mitigation effects on the reflected overpressure of the explosion shock with water surrounding an explosive in a confined space is of great significance for military explosives safety applications. To estimate the effects of the parameters on the reflected overpressure of blasted shock wave, a series of experiments were carried out in confined containers with spherical explosives immersed in a certain thickness of water, and numerical simulations were conducted to explore the corresponding mechanisms. The results reveal that the reflected overpressure is abnormally aggravated at a small scaled distance. This aggravation is due to the high impulse of the bulk accelerated water shell converted from the explosion. With increasing scaled distance, the energy will be gradually dissipated. The mitigation effects will appear with the dispersed water phase front impacting at a larger scaled distance, except in the case of a dense water phase state. A critical scaled distance range of 0.7—0.8 m/kg1/3 for effective mitigation was found. It is suggested that the scaled distance of space walls should be larger than the critical value for a certain water-to-explosive weight ratio range (5—20). 相似文献
273.
This study investigates and quantifies some possible sources affecting the position of impact points of small caliber spin-stabilized projectiles (such as 12.7 mm bullets). A comparative experiment utilizing the control variable method was designed to figure out the influence of tiny eccentric centroids on the projectiles. The study critically analyzes data obtained from characteristic parameter measurements and precision trials. It also combines Sobol's algorithm with an artificial intelligence algorithm—Adaptive Neuro-Fuzzy Inference Systems (ANFIS)—in order to conduct global sensitivity analysis and determine which parameters were most influential. The results indicate that the impact points of projectiles with an entry angle of 0° deflected to the left to that of projectiles with an entry angle of 90°. The difference of the mean coordinates of impact points was about 12.61 cm at a target range of 200 m. Variance analysis indicated that the entry angle — i.e. the initial position of mass eccentricity — had a notable influence. After global sensitivity analysis, the significance of the effect of mass eccentricity was confirmed again and the most influential factors were determined to be the axial moment and transverse moment of inertia (Izz Iyy), the mass of a projectile (m), the distance between nose and center of mass along the symmetry axis for a projectile (Lm), and the eccentric distance of the centroid (Lr). The results imply that the control scheme by means of modifying mass center (moving mass or mass eccentricity) is promising for designing small-caliber spin-stabilized projectiles. 相似文献
274.
275.
针对现代空战效能评估多层次、多因素、非线性耦合的复杂特点,提出一种基于有监督局部保留投影(SLPP)和最小二乘支持向量机(LSSVM)的空战效能综合评估模型.先利用SLPP对数据局部信息和类别信息的处理能力,提取空战效能数据中有辨识力的低维特征;利用获取的低维特征构建LSSVM空战效能综合评估模型;通过构建的模型,对空战效能进行评估.计算分析表明,所提出模型的评估结果与专家的评估结果相一致,没有出现错判,不同参数下结果输出也很稳定.因此,将该模型用于空战效能评估是有效和可行的,也为空战效能评估提供了一种可靠的技术途径. 相似文献
276.
美国信息安全战略的基本要素与实施原则探析 总被引:2,自引:0,他引:2
美国作为信息霸权国家,为了保护其信息设施安全,不断强化其信息优势,通过长期实践与应用,总结了一系列与国家信息安全战略相关的理论。本文通过分析21世纪以来,美国涉及信息安全领域的实施条例以及在信息安全领域的实际性行动,探析其信息安全战略基本要素及实施原则,将可以为我国制定与实施国家信息安全战略提供一定借鉴。 相似文献
277.
机场道面抢修应急起降带的确定 总被引:1,自引:0,他引:1
应急起降带的确定是战时机场道面抢修的基础性工作,对抢修工程量、抢修效率、抢修进程都有着重大影响.首先介绍了应急起降带合理尺寸的确定;然后提出了应急起降带最佳抢修位置的确定原则;为了实现应急起降带方案的快速优选,用VB编写了方案优选程序,改变了传统的人工优选法费时费力的现状.从文中的实例分析可以得出结论:该方案优选程序的运算结果满足实际抢修施工需要. 相似文献
278.
279.
金属/SiO2复合气凝胶催化剂对一氧化碳氧化的催化 总被引:3,自引:0,他引:3
采用溶胶-凝胶法和超临界干燥法制备了Cu/SiO2 和Co/SiO2 气凝胶催化剂, 对其结构和形貌进行了XRD、TEM 和比表面分析, 并考察了其对CO氧化的催化性能。实验结果表明, 制得的Cu/SiO2 和Co/SiO2 气凝胶催化剂均保留了气凝胶的纳米网络和高比表面积, 活性组份均匀地分散在纳米级二氧化硅气凝胶载体中, 对CO的氧化均表现出高的催化活性。 相似文献
280.
智能理论在BIT设计与故障诊断中的应用 总被引:20,自引:0,他引:20
近20年来机内测试(BIT)技术从理论到应用取得了显著进展,已成为提高产品测试性和诊断能力的有效途径。本文概述了BIT技术的特点,分析了国内外BIT的发展趋势,对BIT智能化从系统设计、信息处理到综合决策各阶段进行概括,对专家系统、神经网络、模糊理论、信息融合等智能理论在BIT中的应用进行了综合分析,并初步建立智能BIT的理论框架 相似文献