全文获取类型
收费全文 | 623篇 |
免费 | 167篇 |
国内免费 | 40篇 |
专业分类
830篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 13篇 |
2021年 | 38篇 |
2020年 | 9篇 |
2019年 | 6篇 |
2018年 | 11篇 |
2017年 | 17篇 |
2016年 | 10篇 |
2015年 | 33篇 |
2014年 | 47篇 |
2013年 | 39篇 |
2012年 | 34篇 |
2011年 | 40篇 |
2010年 | 63篇 |
2009年 | 46篇 |
2008年 | 51篇 |
2007年 | 49篇 |
2006年 | 30篇 |
2005年 | 39篇 |
2004年 | 16篇 |
2003年 | 7篇 |
2002年 | 7篇 |
2001年 | 10篇 |
2000年 | 11篇 |
1999年 | 36篇 |
1998年 | 24篇 |
1997年 | 24篇 |
1996年 | 20篇 |
1995年 | 29篇 |
1994年 | 13篇 |
1993年 | 9篇 |
1992年 | 11篇 |
1991年 | 11篇 |
1990年 | 6篇 |
1989年 | 2篇 |
1988年 | 5篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1983年 | 1篇 |
排序方式: 共有830条查询结果,搜索用时 0 毫秒
281.
介绍了艺术图形生成方法及其遗传算法在艺术图形生成过程中的作用.每种算法都是基于给定初始条件的迭代过程,并通过遗传算法控制初始条件和迭代方式来改变迭代过程,获得更复杂的图形. 相似文献
282.
研究一类二次Hamilton系统在周期扰动下的动力学性质,应用Melnikov方法给出了该系统产生混优与次谐分枝的参数范围。 相似文献
283.
284.
鱼雷在作空间运动时是一个复杂的动力学系统,其动力学行为有很强的非线性.文章综述了鱼雷非线性控制系统的研究进展,探讨了其今后的发展方向,揭示了现代微分动力系统理论在鱼雷非线性系统及控制领域的应用前景. 相似文献
285.
Cheng-ai Wang Jian-bing Xu Yun Shen Yue-ting Wang Teng-long Yang Ze-hua Zhang Fu-wei Li Rui-qi Shen Ying-hua Ye 《防务技术》2021,17(3):741-747
The storage stability of energetic materials is important for its application. Here, the storage stability of Al/CuO nanothermite, which was prepared by electrospray method and stored with different storage time, was systematically researched. The activation energy of Al/CuO nanothermite was calculated by differential scanning calorimetry (DSC). The ignition temperature and the curve pressure history of Al/CuO nanothermite was measured using ignition temperature measuring device and constant-volume pressurization tests, respectively. Further, the thermites were characterized by X-ray Diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and Transmission electron microscopy (TEM). The results show that the morphology of the thermites did not change significantly. The activation energy was decreased from 254.1 kJ/mol to 181.8 kJ/mol after storage for 13 months. When stored for 0, 7 and 13 months, the peak pressures of Al/CuO nanothermite were 685.8 kPa, 626.3 kPa and 625.5 kPa, respectively. In addition to the ignition temperature, it was 775 ℃, 739 ℃ and 754 ℃, respectively. This result indicated that the ignition and combustion properties of Al/CuO nano-thermite are obviously reduced when stored for a long time, at room temperature. 相似文献
286.
Zeng Liu Cheng-lei Fan Zhu Ming Chao Chen Ang Liu Chun-li Yang San-bao Lin Lang-ping Wang 《防务技术》2021,17(3):923-931
High nitrogen stainless steel with nitrogen content of 0.75%was welded by gas metal arc welding with Ar—N2-O2 ternary shielding gas. The effect of the ternary shielding gas on the retention and improvement of nitrogen content in the weld was identified. Surfacing test was conducted first to compare the ability of O2 and CO2 in prompting nitrogen dissolution. The nitrogen content of the surfacing metal with O2 is slightly higher than CO2. And then Ar—N2-O2 shielding gas was applied to weld high nitrogen stainless steel. After using N2-containing shielding gas, the nitrogen content of the weld was improved by 0.1 wt%. As N2 continued to increase, the increment of nitrogen content was not obvious, but the ferrite decreased from the top to the bottom. When the proportion of N2 reached 20%, a full austenitic weld was obtained and the tensile strength was improved by 8.7%. Combined with the results of surfacing test and welding test, it is concluded that the main effect of N2 is to inhibit the escape of nitrogen and suppress the ni-trogen diffusion from bottom to the top in the molten pool. 相似文献
287.
Zhi Yang Ke Wang Peng Zhu Peng Liu Qiu Zhang Cong Xu Hao-tian Jian Rui-qi Shen 《防务技术》2021,17(4):1572-1578
Triggered spark-gap switch is a popular discharge switch for pulse power systems. Previous studies have focused on planarizing this switch using thin film techniques in order to meet the requirements of compact size in the systems. Such switches are one-shot due to electrodes being too thin to sufficiently resist spark-erosion. Additionally, these switches did not employ any structures in securing internal gas composition, resulting in inconsistent performance under harsh atmospheres. In this work, a novel planar triggered spark-gap switch (PTS) with a hermetically sealed cavity was batched-prepared with printed circuit board (PCB) technology, to achieve reusability with low cost. The proposed PTS was inspected by micro-computed tomography to ensure PCB techniques meet the requirements of machining precision. The results from electrical experiments demonstrated that PCB PTS were consistent and reusable with lifespan over 20 times. The calculated switch voltage and circuit current were consistent with those derived from real-world measurements. Finally, PCB PTS was used to introduce hexanitrostilbene (HNS) pellets in a pulse power system to verify its performance. 相似文献
288.
289.
根据信息战的内容和特点,分析了信息因素和兵力因素在信息战过程中相互作用的关系,结合系统动力学理论,建立了信息战系统动力学模型;并结合仿真实例对信息战的相关因素进行了定量与定性相结合的分析,说明了制信息权在信息战中的决定性作用,为信息战研究提供了理论参考. 相似文献
290.