全文获取类型
收费全文 | 264篇 |
免费 | 59篇 |
国内免费 | 31篇 |
出版年
2024年 | 1篇 |
2022年 | 6篇 |
2021年 | 8篇 |
2020年 | 4篇 |
2019年 | 2篇 |
2018年 | 2篇 |
2017年 | 6篇 |
2016年 | 21篇 |
2015年 | 12篇 |
2014年 | 12篇 |
2013年 | 11篇 |
2012年 | 20篇 |
2011年 | 17篇 |
2010年 | 17篇 |
2009年 | 23篇 |
2008年 | 5篇 |
2007年 | 10篇 |
2006年 | 25篇 |
2005年 | 21篇 |
2004年 | 16篇 |
2003年 | 15篇 |
2002年 | 13篇 |
2001年 | 10篇 |
2000年 | 16篇 |
1999年 | 13篇 |
1998年 | 11篇 |
1997年 | 6篇 |
1996年 | 7篇 |
1995年 | 8篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 1篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 1篇 |
排序方式: 共有354条查询结果,搜索用时 375 毫秒
151.
李银奎 《国防科技大学学报》1991,13(1):38-44
本文以(Ph_3P)_2 PdCl_2为催化剂,用各种比例的对二乙炔苯(DEB)与1,4-丁炔二醇(BD)合成出共聚物及两种单体的均聚物。共聚物为褐黑色,不溶不熔。单体配比中DEB比例越高,共聚物交联度和比重越大,产率越高,溶胀度越小。单体摩尔比DEB/BD≥1/2时,共聚物最良溶剂为苯,溶度参数(δP)为9.15卡~(0.5)·cm~(-1.5),而DEB/BD=1/5时,共聚物最良溶剂为无水乙醇,8p=12.7卡~(0.5)·cm~(-1.5).对均聚物及共聚物做了红外光谱表征并讨论了聚合反应机理。 相似文献
152.
Riley M. Moore 《Small Wars & Insurgencies》2013,24(5):857-878
As a consequence of intervention in Iraq and Afghanistan, force ratio for counterinsurgency (COIN) has come under increased scrutiny. Reduced to its essence, the issue is simply, ‘How many troops does it take to get the job done?’ This answer has been sought by the US military, academia, and think tanks. There have been numerous responses, culminating in several ‘plug-and-play’ equations for minimum force ratios in COIN operations. Due to the impossibility of determining precisely how many insurgent forces there are, it has become common to base force ratios on the population of the country. In the realm of policy, the question above is posed as, ‘How many of our troops does it take to get the job done?’ 相似文献
153.
Vadim Kolnogorov 《战略研究杂志》2013,36(2):339-359
Few issues were as contentious in the development of the Soviet Navy as the role of aircraft carriers and sea-based aviation. Despite the continued insistence by the highest naval authorities and scientific experts that surface combatants simply could not be protected in the open ocean without the support of ship-borne aviation, Soviet leaders – for a variety of reasons – resisted aircraft carrier development until the final decades of the Cold War. In examining one of the most defining and telling asymmetries of the Cold War at sea, the author argues that while the USSR was economically and technologically capable of building aircraft carriers of any class, bureaucratic infighting, misperceptions of cost and practicality, and the inherent flaws of a totalitarian system ultimately created an impossible gap in capabilities between the two sides. The priorities and direction of Soviet weapons and defense technology development during the Cold War was largely a factor of the military-political situation taking shape at home, and in the world. As a rule, the navy was assigned missions that corresponded to its capabilities at a given point in time, rather than the other way around. Often, the navy lacked the material resources needed to implement its core mission. The availability of these resources, in turn, depended on the country's economic situation, its scientific potential, the technological state of its industry, as well as the subjective influence of political and military leaders on the priorities of technological development. The impact of the country's socioeconomic imperatives was undoubtedly also felt in the sluggish pace of development of ship-borne aviation and aircraft carriers in the USSR. 相似文献
154.
This paper provides a contribution to the growing corpus of knowledge and understanding of the interaction between economic growth and defence spending in South Africa by specifying a Keynesian simultaneous equation model and estimating the system for the period 1961 to 1997. The model contains a growth equation, a savings equation, a trade balance equation and a military burden equation and when estimated by single equation and systems estimation methods is relatively well specified. There is evidence of an overall negative effect of military spending on the economy over this period, though the significance of individual coefficients is low. There is certainly no evidence of any positive impact, suggesting that cuts in military spending do present an opportunity for improved macroeconomic performance. 相似文献
155.
156.
157.
城市交通流量预测对交通管理和公共安全具有重要意义。然而,交通栅格流量数据中的规律在时刻变化,在城市中存在全局范围的时空间关系,并且不同特征通道在每个城市区域上有不同的重要性。为解决这些挑战并做出更准确的预测,设计了一种新颖的时空神经网络模型——3D通道注意力网络(three-dimensional channel-wise attention networks,3D-CANet)。提出一个3D通道内注意力(three-dimensional inner channel attention,3D-InnerCA)单元来动态捕获各个通道中不同的全局时空相关性,同时设计通道间注意力(inter channel attention,InterCA)单元来自适应地重校准每个区域上不同特征通道的贡献。在3个真实交通栅格流量数据集上的实验结果表明,3D-CANet模型的预测能力优于其他对比方法,证明了模型的有效性。 相似文献
158.
贾玲 《中国人民武装警察部队学院学报》2007,23(12):87-89
数据库设计是数据库应用领域的主要研究课题,是继需求分析后的一个非常重要的环节。关系数据库设计的重点难点就是数据库的规范化理论,必须深入透彻的理解规范化理论,才能设计出一个高质量的数据库。根据数据库设计理论和应用要求,通过通俗易懂的实例详尽地说明了1NF、2NF、3NF和BCNF在数据库设计中的具体操作步骤和方法,对于数据库设计有重要的指导意义。 相似文献
159.
C3I系统是一个复杂的人机大系统,对其评估是一个非常复杂的问题。首先建立了C3I系统评价指标体系,根据粗糙集理论对系统属性进行约简,通过MATLAB编写的程序计算出指标权重,确定了影响系统的最佳指标。最后提出了C3I系统作战能力综合指数计算方法,结果显示粗糙集理论对C3I系统评估能取得非常好的效果。 相似文献
160.
鲁棒性多视图三角化方法通常借助重投影误差经验阈值来剔除图像对应中的错误匹配,该经验阈值的选取直接影响三维重构场景点的数量和精度。在分析图像特征点定位噪声及对极传递几何原理的基础上,建立对极传递过程不确定性的传递模型,提出一种基于核密度估计的最优噪声尺度估算方法,并将该噪声尺度作为多视图三角化中错误匹配筛选的依据。实验结果表明,该方法可以获得准确的噪声尺度估计,从而有效提升多视图三角化方法的三维重构质量。 相似文献