全文获取类型
收费全文 | 442篇 |
免费 | 112篇 |
国内免费 | 26篇 |
出版年
2022年 | 9篇 |
2021年 | 5篇 |
2020年 | 5篇 |
2019年 | 7篇 |
2018年 | 4篇 |
2017年 | 18篇 |
2016年 | 20篇 |
2015年 | 14篇 |
2014年 | 42篇 |
2013年 | 69篇 |
2012年 | 59篇 |
2011年 | 55篇 |
2010年 | 29篇 |
2009年 | 25篇 |
2008年 | 19篇 |
2007年 | 22篇 |
2006年 | 27篇 |
2005年 | 28篇 |
2004年 | 21篇 |
2003年 | 16篇 |
2002年 | 7篇 |
2001年 | 16篇 |
2000年 | 16篇 |
1999年 | 10篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 5篇 |
1995年 | 8篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1987年 | 1篇 |
排序方式: 共有580条查询结果,搜索用时 15 毫秒
251.
252.
S-Box是现行分组密码中唯一的非线性部件,主要提供了分组密码算法中必需的混淆作用,其密码强度决定了整个分组密码的安全强度。为进一步提高S-Box的强度,结合离散混沌系统的内在随机性、有界性、非周期性及对初始条件和参数极度敏感等特点,提出一种采用多混沌映射和交叉映射生成S-Box的生成算法。实验分析表明,该算法生成的样本密钥敏感性强,随机性好,既能较好地满足S-Box设计所要求的各项准则和特性,安全性高,同时又能降低计算复杂度,提高计算速度,且易于生成和扩展,因而是一种性能良好的S-Box候选算法。 相似文献
253.
Gaetano Joe Ilardi 《Small Wars & Insurgencies》2013,24(2):331-358
This article will seek to provide a detailed examination of the IRA's operational intelligence methodologies. Providing not only a lengthy discussion on the organization's intelligence collection protocols, it will also examine the interplay between intelligence and IRA decision-making. It will be contended that intelligence's influence resided in its ability to introduce a strong element of predictability into the IRA's decision-making process. This depended on an ability to construct a detailed intelligence picture of the target and its geographical milieu so as to minimize the likelihood of volunteers encountering unforeseen circumstances that could adversely affect planned or anticipated outcomes. 相似文献
254.
Thomas-Durell Young 《战略研究杂志》2013,36(7):1031-1057
By any objective measure, defense institutions in Central and Eastern Europe have all but universally been incapable of producing viable defense plans that are based on objective costing and operational planning data. This situation exists in spite the provision of considerable Western advice and assistance, let alone reporting to and receiving assessments by NATO’s International Staff under Partnership for Peace, as well as via the integrated defense planning and reporting systems. An explanation for this systematic failure across European post-Communist defense institutions can be found in the continued slow development of an over-arching policy framework which directs and approves all activities of the armed forces, as well as the de-centralization of financial decision-making down to capability providers. The essay ends with an examination of the adverse effects of the early introduction of planning programming, budgeting system (PPBS), have had on the development of effective policy and planning capabilities within these defense institutions. 相似文献
255.
魏静波 《国防科技大学学报》2013,35(4)
研究了利用小推力器进行航天器姿态控制问题。从理论上推导了在给定姿态控制精度、小推力器参数以及倾斜开关曲线参数的前提下,能够形成理想极限环控制效果的充分必要条件。对相关文献中倾斜开关曲线设计方法不能形成理想极限环的情况进行了理论分析,并提出了一种新的基于倾斜开关曲线的准极限环控制方法,并推导了其控制精度。研究对于航天器应用小推力器实现高精度姿态控制具有较大的工程应用价值。 相似文献
256.
Dimitris Hatzinikolaou 《Defence and Peace Economics》2013,24(6):577-579
AbstractThis paper explains and assesses the UK experience with determining prices and profitability for non-competitive defence contracts. Three periods are considered, namely pre-1968, the 1968 Profit Formula Agreement and the changes introduced in 2014. Two cases of ‘excessive’ profits were major determinants of the 1968 Profit Formula Agreement; but continued dissatisfaction with the 1968 Agreement led to changes in 2014. The historical overview of UK experience provides a basis for understanding current UK policy and offers insights for other countries facing similar policy challenges. A critique is presented of UK policy on single source pricing and profitability. 相似文献
257.
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
258.
建筑物内部电场强度分布特性数值模拟研究 总被引:1,自引:0,他引:1
为解决建筑物内部空间电场强度分布难以量化的问题,采用时域有限差分(FDTD)法,对以平面波为激励源,二阶Mur收边界条件的闭合规则建筑物、非规则加窗建筑物和含钢筋非规则加窗建筑物3种模型结构内部电场强度分布特性进行模拟,并通过FEKO软件对计算结果的有效性进行验证。结果表明:普通混凝土材质的建筑物对平面波电场几乎无屏蔽效能;吸波混凝土材质的建筑物对平面波电场的屏蔽效能也较为有限,且随激励源频率的增加,在建筑开窗区域附近的谐振性增强,屏蔽性减弱;通过对植入钢筋墙体建筑物采用细线FDTD法的场强分布计算,证明金属钢筋可提高建筑围护结构的屏蔽效能。 相似文献
259.
电离层不规则体导致星载合成孔径雷达(SAR)信号产生幅度及相位闪烁,严重影响低波段星载SAR的图像分辨性能。推导了具有普遍性的幂律谱对应的双频双点互相关函数。基于此研究了电离层对星载P波段SAR分辨性能的影响及其规律。研究表明,电离层不规则体导致星载P波段SAR两维分辨率恶化,图像峰值增益损失严重。电离层不规则体强度,谱指数,外尺度等参数的增大都会导致星载SAR图像分辨率及峰值增益进一步下降。基于相位屏技术的数值仿真结果验证了本文研究。 相似文献
260.
基于LDO稳压器在电磁干扰(EMI)下产生直流偏移失效的机理分析,展开敏感度建模与仿真方法研究。使用一款实验芯片,创新地引入片上电压传感器,用于测试EMI在LDO稳压器内部的传播特性。在敏感度建模中,建立等效电路模型,通过直流功能测试,Z参数阻抗特性测试验证模型的正确性,将该模型用于LDO稳压器的敏感度预测。在敏感度仿真过程中,通过分析关键子电路和不断增加寄生元件,仿真不同寄生因素对敏感度影响的权重。将仿真结果与传导直接注入法(DPI)片上测试结果对比,仿真结果与DPI测试在频域1MHz至1GHz匹配。 相似文献