全文获取类型
收费全文 | 4175篇 |
免费 | 775篇 |
国内免费 | 301篇 |
出版年
2024年 | 7篇 |
2023年 | 15篇 |
2022年 | 42篇 |
2021年 | 75篇 |
2020年 | 79篇 |
2019年 | 92篇 |
2018年 | 97篇 |
2017年 | 213篇 |
2016年 | 169篇 |
2015年 | 133篇 |
2014年 | 364篇 |
2013年 | 398篇 |
2012年 | 288篇 |
2011年 | 384篇 |
2010年 | 293篇 |
2009年 | 344篇 |
2008年 | 264篇 |
2007年 | 300篇 |
2006年 | 271篇 |
2005年 | 244篇 |
2004年 | 226篇 |
2003年 | 168篇 |
2002年 | 129篇 |
2001年 | 128篇 |
2000年 | 75篇 |
1999年 | 71篇 |
1998年 | 57篇 |
1997年 | 39篇 |
1996年 | 45篇 |
1995年 | 45篇 |
1994年 | 49篇 |
1993年 | 21篇 |
1992年 | 33篇 |
1991年 | 25篇 |
1990年 | 34篇 |
1989年 | 18篇 |
1988年 | 12篇 |
1987年 | 3篇 |
1975年 | 1篇 |
排序方式: 共有5251条查询结果,搜索用时 140 毫秒
961.
根据传热学理论和热网络法,以某型直升机尾减速器弧齿锥齿轮传动系统为研究对象,建立了其温度场Simulink仿真计算模型。基于该模型,计算获得该传动系统正常润滑条件下的稳态温度场,并以它作为初始条件计算分析该传动系统失去润滑条件下的瞬态温度场,为预测该弧齿锥齿轮传动系统在失去润滑条件下的干运转生存能力提供理论依据。 相似文献
962.
963.
964.
实际环境中观测系统的噪声,同时存在着白噪、色噪声和尖点噪声的影响.已有的研究都仅考虑白噪或色噪声,首次将实际系统中可能出现的所有噪声纳入观测方程,推导出统一的带白噪形式的观测方程.新观测方程在色噪声ARMA辨识基础上,可以直接用于传统的卡尔曼滤波算法,避免了扩维滤波.于是状态参数的稳健估计归结为ARMA参数的辨识.重点研究了自由参数选取与输入噪声之间的关系,将鲁棒支持向量回归机的优化问题转换成最大后验估计问题,为合理选择自由参数提供了理论依据.仿真结果验证了新算法的有效性. 相似文献
965.
966.
Serkan Eryilmaz 《海军后勤学研究》2013,60(4):313-320
Measuring the relative importance of components in a mechanical system is useful for various purposes. In this article, we study Birnbaum and Barlow‐Proschan importance measures for two frequently studied system designs: linear consecutive k ‐out‐of‐ n and m ‐consecutive‐ k ‐out‐of‐ n systems. We obtain explicit expressions for the component importance measures for systems consisting of exchangeable components. We illustrate the results for a system whose components have a Lomax type lifetime distribution. © 2013 Wiley Periodicals, Inc. Naval Research Logistics, 2013 相似文献
967.
Paolo Tripodi 《Small Wars & Insurgencies》2013,24(2):221-236
This study develops the concepts of fourth generation operations and the associated principles. First, the concept of fourth generation operations is introduced and defined. Fourth generation operations are the evolution and extension of third and fourth generation warfare based on a change of tactics, technology, and combatants. These operations are currently ongoing in Afghanistan and Iraq, and with the global war on terrorism. Based on the framework of US joint doctrine, the supporting principles of fourth generation operations are developed. This requires the introduction of the principle of Population Perception. 相似文献
968.
By running life tests at higher stress levels than normal operating conditions, accelerated life testing (ALT) quickly yields information on the lifetime distribution of a test unit. The lifetime at the design stress is then estimated through extrapolation using a regression model. In constant‐stress testing, a unit is tested at a fixed stress level until failure or the termination time point of test, whereas step‐stress testing allows the experimenter to gradually increase the stress levels at some prefixed time points during the test. In this work, the optimal k‐level constant‐stress and step‐stress ALTs are compared for the exponential failure data under complete sampling and Type‐I censoring. The objective is to quantify the advantage of using the step‐stress testing relative to the constant‐stress one. Assuming a log‐linear life–stress relationship with the cumulative exposure model for the effect of changing stress in step‐stress testing, the optimal design points are determined under C/D/A‐optimality criteria. The efficiency of step‐stress testing to constant‐stress one is then discussed in terms of the ratio of optimal objective functions based on the information matrix. © 2013 Wiley Periodicals, Inc. Naval Research Logistics 00: 000–000, 2013 相似文献
969.
Elena Pokalova 《Small Wars & Insurgencies》2013,24(2):335-337
ABSTRACTThis article discusses the Rhodesian Front regime propaganda warfare strategy during Zimbabwe’s war of liberation. It uses the case of the Chilonga area of Chiredzi located in the south-east of Zimbabwe to demonstrate that propaganda warfare was introduced as a measure to counter guerrilla infiltration and civilian cooperation with them. Drawing on ideas of military anthropology vis-à-vis the importance of cultural awareness in counterinsurgency, the paper argues that the efforts of the Rhodesian Front regime to use propaganda were fruitless. This is because they mostly ignored the culture of the Shangani, local people. Despite that, there were other reasons for the failure of the Rhodesian Front’s propaganda strategy, including the lack of conformity between politics and military action. 相似文献
970.
James Horncastle 《Small Wars & Insurgencies》2013,24(5):744-763
Croatia's successful bid for independence was one of the defining moments of the immediate post-Cold War period. Nevertheless, the means that Croatia used to obtain independence remains relatively unexamined by academics. This article focuses on the early period of Croatia's bid for secession, and specifically the role that Yugoslavia's policy of Total National Defence played in facilitating its independence. Unlike in Slovenia, where the legacies of Total National Defence facilitated Slovenia's bid for secession, in Croatia the decision of its political leaders meant that the country largely neglected its positive legacies, resulting in a protracted four-year struggle. 相似文献