首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   280篇
  免费   37篇
  国内免费   14篇
化学   139篇
晶体学   1篇
力学   5篇
综合类   25篇
数学   91篇
物理学   70篇
  2024年   1篇
  2023年   6篇
  2022年   24篇
  2021年   31篇
  2020年   13篇
  2019年   6篇
  2018年   7篇
  2017年   8篇
  2016年   5篇
  2015年   18篇
  2014年   17篇
  2013年   21篇
  2012年   18篇
  2011年   20篇
  2010年   23篇
  2009年   20篇
  2008年   12篇
  2007年   14篇
  2006年   4篇
  2005年   13篇
  2004年   6篇
  2003年   9篇
  2002年   7篇
  2001年   1篇
  2000年   6篇
  1999年   6篇
  1998年   2篇
  1997年   3篇
  1996年   2篇
  1995年   1篇
  1993年   1篇
  1991年   1篇
  1990年   1篇
  1989年   1篇
  1988年   2篇
  1987年   1篇
排序方式: 共有331条查询结果,搜索用时 46 毫秒
51.
We consider several two-agent scheduling problems with controllable job processing times, where agents A and B have to share either a single machine or two identical machines in parallel while processing their jobs. The processing times of the jobs of agent A are compressible at additional cost. The objective function for agent B is always the same, namely a regular function fmaxfmax. Several different objective functions are considered for agent A, including the total completion time plus compression cost, the maximum tardiness plus compression cost, the maximum lateness plus compression cost and the total compression cost subject to deadline constraints (the imprecise computation model). All problems are to minimize the objective function of agent A subject to a given upper bound on the objective function of agent B. These problems have various applications in computer systems as well as in operations management. We provide NP-hardness proofs for the more general problems and polynomial-time algorithms for several special cases of the problems.  相似文献   
52.
在生物学、社会科学、保险理赔、可靠性和人口统计学等的研究中,我们经常会遇到复发事件数据的处理.最近一段时间以来,两个相邻复发事件的时间间隔的一个纵向数据模型已经引起统计工作者的广泛兴趣.本文中,我们提议另一个复发事件时间间隔模型,它可以用来模拟生存数据中带有所谓的持久生存者.非参数方法将用于我们所提议模型的统计推断,模拟和现实数据的例子将用来评价模型和提议估计方法的小样本性质.  相似文献   
53.
资金限制条件下的原油采购策略研究   总被引:3,自引:0,他引:3  
闫超  陈国华  宋科 《运筹与管理》2010,19(3):100-105
在对原油采购市场的复杂性和生产商面临的采购风险进行深入分析的基础上,综合考虑影响企业采购的因素,强调原油供应链中资金流的限制,引入合同组合管理的方法,构建了一个简单的原油供应链系统,并借助供应链Agent建模仿真技术实现了该原油供应链系统。仿真结果的分析证明,相比较于传统的数学模型、系统动力学等方法,Agent的自主性、适应性和分布性等特点更适合于描述此类难以求解的供应链复杂性问题。随着采购进程的演化,生产商Agent通过对油价和需求变化规律的学习给出基于预测的最优合同组合策略,该策略在保证利润最大化的同时能够有效控制采购风险,平衡库存采购成本和财务成本,增强企业的可持续发展能力。  相似文献   
54.
Considerable research has been conducted on the topic of unidirectional evacuations from exits. However, few studies aim at simulating counter flow through a bottleneck with complex conflict. This paper proposes an agent-based model to investigate bidirectional flow evacuation. Pedestrian speed is determined by the speed of the leading agent and the surrounding agents. The moving direction of pedestrian originates from four forces, namely, gradient force, repulsive force, resistance force, and random force. These four forces dominate the main stream of the pedestrian moving trajectory, the interaction between pedestrians and their local environment, the resistance or disinclination to movement, and the random variations and chaotic nature of pedestrian dynamics. The novelty of this research is in the agent-based model that combines the agent and forces while providing insights for the simulation of the pedestrian dynamic on the cognitive level. The experiment results show that the behavior that arises from this model is consistent with the observations from Guangzhou Metro and that this model could help capture the essence of pedestrian behavior near egresses.  相似文献   
55.
Abstract

We consider a setting where a large number of agents are trading commodity bundles. Assuming that agents of the same type have a certain utility attached to each transaction, we construct a statistical equilibrium which in turn implies prices on the different commodities. Our basic question is then the following. Assuming that some commodities come out with prices that are socially unacceptable, is it possible to change these prices systematically if a new type of agent is paid to enter the market? We will consider explicit examples where this can be done.  相似文献   
56.
57.
Human immunodeficiency virus (HIV) especially HIV-1 infection and its progression to acquired immune deficiency syndrome (AIDS) remains a significant global health challenge. The advent of the highly active antiretroviral therapy (HAART) has greatly extended the life expectancy of patients living with HIV, but it has become evident that long-term HAART will not eliminate the HIV reservoir and cure the infection. Moreover, the drug resistance and undesirable side effects hamper efficacious therapy, creating an urgent need to develop novel, more effective and less toxic anti-HIV therapeutics. Imidazole, oxazole and thiazole with two heteroatoms at meta-position of five-membered rings are fascinating structures and constitute an important class of heterocycles in drug discovery. Their derivatives could exert the anti-HIV activity through diverse mechanisms and possess promising antiviral activity against both drug-sensitive and drug-resistant HIV strains. This review summarizes the research progress made regarding the anti-HIV potential of imidazole, oxazole and thiazole hybrids, and the structure–activity relationships (SARs) are also discussed to facilitate further rational design of more effective candidates, covering articles published from 2012 to 2022.  相似文献   
58.
Disease progression in Tuberculosis (TB) is dependent on host’s immune system. Phyllanthus niruri, a traditional herb, has long been used to boost immune system in Indonesian society. This study aimed to observe the potential role of P. niruri in inducing immune cells activity in TB patients by in vitro approach. Peripheral blood mononuclear cells (PBMCs) and macrophages were collected from active pulmonary TB patients. After stimulation with graded doses of P. niruri aqueous extract, cell proliferation, phagocytic activity and nitric oxide (NO) release were analysed. P. niruri aqueous extract induced proliferation of PBMCs, increased NO release, and improved macrophages phagocytic activity. These effects were observed in a dose-dependent manner. This may lead to further research for the potential role of P. niruri as immunomodulatory adjuvant therapy for TB patients.  相似文献   
59.
锌是机体必需的微量元素,它对动物免疫系统的正常发育和功能方面有重要作用。综述了微量元素锌对动物免疫器官、免疫细胞和免疫分子等的可能作用机制和对免疫功能的影响。  相似文献   
60.
The accumulation of amyloid plaques, or misfolded fragments of proteins, leads to the development of a condition known as amyloidosis, which is clinically recognized as a systemic disease. Amyloidosis plays a special role in the pathogenesis of neurodegenerative diseases such as Alzheimer’s disease (AD), Parkinson’s disease, and rheumatoid arthritis (RA). The occurrence of amyloidosis correlates with the aging process of the organism, and since nowadays, old age is determined by the comfort of functioning and the elimination of unpleasant disease symptoms in the elderly, exposure to this subject is justified. In Alzheimer’s disease, amyloid plaques negatively affect glutaminergic and cholinergic transmission and loss of sympathetic protein, while in RA, amyloids stimulated by the activity of the immune system affect the degradation of the osteoarticular bond. The following monograph draws attention to the over-reactivity of the immune system in AD and RA, describes the functionality of the blood–brain barrier as an intermediary medium between RA and AD, and indicates the direction of research to date, focusing on determining the relationship and the cause–effect link between these disorders. The paper presents possible directions for the treatment of amyloidosis, with particular emphasis on innovative therapies.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号