全文获取类型
收费全文 | 2277篇 |
免费 | 335篇 |
国内免费 | 168篇 |
出版年
2024年 | 2篇 |
2023年 | 9篇 |
2022年 | 19篇 |
2021年 | 51篇 |
2020年 | 53篇 |
2019年 | 40篇 |
2018年 | 74篇 |
2017年 | 114篇 |
2016年 | 102篇 |
2015年 | 75篇 |
2014年 | 187篇 |
2013年 | 220篇 |
2012年 | 164篇 |
2011年 | 196篇 |
2010年 | 142篇 |
2009年 | 180篇 |
2008年 | 132篇 |
2007年 | 144篇 |
2006年 | 164篇 |
2005年 | 151篇 |
2004年 | 127篇 |
2003年 | 80篇 |
2002年 | 69篇 |
2001年 | 67篇 |
2000年 | 44篇 |
1999年 | 33篇 |
1998年 | 27篇 |
1997年 | 16篇 |
1996年 | 18篇 |
1995年 | 20篇 |
1994年 | 18篇 |
1993年 | 7篇 |
1992年 | 12篇 |
1991年 | 8篇 |
1990年 | 7篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1975年 | 1篇 |
排序方式: 共有2780条查询结果,搜索用时 15 毫秒
991.
对于长径比较高的助推器来说,为了提高与芯级的连接可靠性,可采用超静定捆绑连接方式。这种捆绑连接方式增加了助推器动力学响应分析的难度。以超静定捆绑火箭助推器为研究对象,通过引入拉压双线性弹簧模拟捆绑连接装置,建立合理的动力学分析模型,对系统进行数值求解,获得径向冲击作用下助推器的动力学响应特性。通过与静定捆绑模型的对比,获得超静定捆绑助推器的广义位移、频谱和内力的响应,从而为工程应用提供一定的参考和理论支撑。 相似文献
992.
为提高高超声速翼身组合式飞行器的射程,研究了采用不同翼面变形模式时,飞行器在马赫数3~8内的气动特性和翼面效率。针对典型的轴对称翼身组合式外形,采用Navier-Stokes方程进行数值模拟,对伸缩、变后掠和二维折叠三种变形模式下的外形在超声速及高超声速来流条件下进行模拟,并对升阻比、翼面单位面积升阻比和操稳特性进行分析。结果表明:在超声速及高超声速范围内,变后掠变形模式在宽速域内升阻比提高明显,同时具备优良的翼面效率及操稳特性,其在马赫数3~8范围内具有最优的综合性能。研究成果能对高超声速翼身组合式变形飞行器布局设计提供参考,具有一定的指导意义。 相似文献
993.
Thomas-Durell Young 《战略研究杂志》2016,39(7):936-955
Traditionally, policy and planning have been institutionally weak in the Naval Staff (Office of the Chief of Naval Operations – OPNAV). In their place, the N8 (Programming) has dominated resource decision-making, and, by default, decisions relating to policy and planning. Recent uncertainty over defense authorization and appropriations has resulted in calls for a greater role to be played by the N3/5, Policy and Plans Directorate. The article argues that reform of the Department of the Navy’s planning process is urgently needed. OPNAV’s weak planning and overly dominant programming practices are compared with those of the Departments of the Army and Air Force and are shown to be out of conformance with them. The article concludes with specific and detailed recommendations for reform of both the current planning and programming processes. 相似文献
994.
We study the classical ranking and selection problem, where the ultimate goal is to find the unknown best alternative in terms of the probability of correct selection or expected opportunity cost. However, this paper adopts an alternative sampling approach to achieve this goal, where sampling decisions are made with the objective of maximizing information about the unknown best alternative, or equivalently, minimizing its Shannon entropy. This adaptive learning is formulated via a Bayesian stochastic dynamic programming problem, by which several properties of the learning problem are presented, including the monotonicity of the optimal value function in an information-seeking setting. Since the state space of the stochastic dynamic program is unbounded in the Gaussian setting, a one-step look-ahead approach is used to develop a policy. The proposed policy seeks to maximize the one-step information gain about the unknown best alternative, and therefore, it is called information gradient (IG). It is also proved that the IG policy is consistent, that is, as the sampling budget grows to infinity, the IG policy finds the true best alternative almost surely. Later, a computationally efficient estimate of the proposed policy, called approximated information gradient (AIG), is introduced and in the numerical experiments its performance is tested against recent benchmarks alongside several sensitivity analyses. Results show that AIG performs competitively against other algorithms from the literature. 相似文献
995.
程洪宝 《中国人民武装警察部队学院学报》2010,26(9):65-67
在突发事件的应急处置过程中,思想政治教育通过对处于突发事件中的人们进行心理救助、情绪调控、挫折调适以及心理引导,发挥心理调适功能。应急处置突发事件的思想政治教育心理调适机制包括:心理干预机制、情绪调控机制、挫折调适机制及心理引导机制。 相似文献
996.
科学技术的飞速发展及其在军事领域的广泛应用,物化出全新的武器装备。文章分析世界各军事强国在感知装备、主战平台、精确制导武器、信息对抗装备、太空及新概念武器等方面加大研发力度,呈现出的全新发展态势。它推动军事领域深层次变革,对现代战争产生广泛而深刻的影响。 相似文献
997.
Ugur Berk 《Defence and Peace Economics》2018,29(5):525-540
Previous studies on the relationship between individual’s enlistment decisions and their personal characteristics examined a number of variables such as age, marital status, gender, family background, geographical background, employment situation and education level. However, attitudes towards working, expectations from a good job and centrality of working are also important determinants in this process. This paper examines the profile of juveniles who seek a career as gendarmerie non-commissioned officers (NCO) in the Turkish Armed Forces and their attitudes and expectations towards working in general within the framework of Meaning of Working (MOW) researches. According to the results of the survey conducted with 500 NCO candidates in Turkey, learning something new, good relations with colleagues and employment guarantee are detected as the main expectations of juveniles who seek a career in military. Results also show that having a job is so important for these young people that they consider having a job even prior to their families. 相似文献
998.
本文分析了兵团语言生活的现状,着重就人们对说普通话的态度、普通话的使用情况和规范汉字的使用情况进行了分析,对进一步做好兵团语言文字规范工作提出了建议。 相似文献
999.
We consider a discrete time‐and‐space route‐optimization problem across a finite time horizon in which multiple searchers seek to detect one or more probabilistically moving targets. This article formulates a novel convex mixed‐integer nonlinear program for this problem that generalizes earlier models to situations with multiple targets, searcher deconfliction, and target‐ and location‐dependent search effectiveness. We present two solution approaches, one based on the cutting‐plane method and the other on linearization. These approaches result in the first practical exact algorithms for solving this important problem, which arises broadly in military, rescue, law enforcement, and border patrol operations. The cutting‐plane approach solves many realistically sized problem instances in a few minutes, while existing branch‐and‐bound algorithms fail. A specialized cut improves solution time by 50[percnt] in difficult problem instances. The approach based on linearization, which is applicable in important special cases, may further reduce solution time with one or two orders of magnitude. The solution time for the cutting‐plane approach tends to remain constant as the number of searchers grows. In part, then, we overcome the difficulty that earlier solution methods have with many searchers. © 2010 Wiley Periodicals, Inc. Naval Research Logistics, 2010 相似文献
1000.