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   2333篇
  免费   253篇
  国内免费   18篇
化学   230篇
力学   33篇
综合类   100篇
数学   1892篇
物理学   349篇
  2023年   12篇
  2022年   46篇
  2021年   57篇
  2020年   46篇
  2019年   58篇
  2018年   46篇
  2017年   83篇
  2016年   100篇
  2015年   105篇
  2014年   195篇
  2013年   201篇
  2012年   134篇
  2011年   164篇
  2010年   147篇
  2009年   174篇
  2008年   170篇
  2007年   205篇
  2006年   117篇
  2005年   87篇
  2004年   91篇
  2003年   55篇
  2002年   40篇
  2001年   38篇
  2000年   36篇
  1999年   26篇
  1998年   21篇
  1997年   18篇
  1996年   17篇
  1995年   9篇
  1994年   17篇
  1993年   10篇
  1992年   16篇
  1991年   8篇
  1990年   8篇
  1989年   2篇
  1988年   17篇
  1987年   3篇
  1986年   5篇
  1985年   7篇
  1984年   1篇
  1983年   2篇
  1982年   3篇
  1981年   3篇
  1980年   1篇
  1979年   2篇
  1977年   1篇
排序方式: 共有2604条查询结果,搜索用时 701 毫秒
21.
借鉴美国主流高校EHS体系建设我国的实验室安全文化   总被引:1,自引:0,他引:1  
以美国化学类专业排名前30的高等院校的环境安全与健康管理体系(Environment,HealthSafety,简写为EHS)为研究对象,进行了信息的收集、分析与整合,从中总结出美国高校EHS管理体系的6个特点;进一步介绍了美国高校EHS管理体系架构的确立与运作。结合目前我国高校实验室安全管理存在的主要问题,提出了建设、发展和丰富我国高校的实验室安全文化是当前最基础性的建设任务之一,以期引起高校管理部门对安全问题的真正重视并落实到行动中。  相似文献   
22.
The role of decision support systems in mitigating operational risks in firms is well established. However, there is a lack of investment in decision support systems in emerging markets, even though inadequate operational risk management is a key cause of discouraging external investment. This has also been exacerbated by insufficient understanding of operational risk in emerging markets, which can be attributed to past operational risk measurement techniques, limited studies on emerging markets and inadequate data.  相似文献   
23.
From the practices of Chinese consumer electronics market, we find there are two key issues in supply chain management: The first issue is the contract type of either wholesale price contracts or consignment contracts with revenue sharing, and the second issue is the decision right of sales promotion (such as advertising, on-site shopping assistance, rebates, and post-sales service) owned by either manufacturers or retailers. We model a supply chain with one manufacturer and one retailer who has limited capital and faces deterministic demand depending on retail price and sales promotion. The two issues interact with each other. We show that only the combination (called as chain business mode) of a consignment contract with the manufacturer’s right of sales promotion or a wholesale price contract with the retailer’s right of sales promotion is better for both members. Moreover, the latter chain business mode is realized only when the retailer has more power in the chain and has enough capital, otherwise the former one is realized. But which one is preferred by customers? We find that the former is preferred by customers who mainly enjoy low price, while the latter is preferred by those who enjoy high sales promotion level.  相似文献   
24.
We present a multispecies stochastic model that suggests optimal fishing policy for two species in a three‐species predator–prey ecosystem in the Barents Sea. We employ stochastic dynamic programming to solve a three‐dimensional model, in which the catch is optimized by using a multispecies feedback strategy. Applying the model to the cod, capelin, and herring ecosystem in the Barents Sea shows that the optimal catch for the stochastic interaction model is more conservative than that implied by the deterministic model. We also find that stochasticity has a stronger effect on the optimal exploitation policy for prey (capelin) than for predator (cod).  相似文献   
25.
Bioeconomic analyses of spatial fishery models have established that marine reserves can be economically optimal (i.e., maximize sustainable profit) when there is some type of spatial heterogeneity in the system. Analyses of spatially continuous models and models with more than two discrete patches have also demonstrated that marine reserves can be economically optimal even when the system is spatially homogeneous. In this note we analyze a spatially homogeneous two‐patch model and show that marine reserves can be economically optimal in this case as well. The model we study includes the possibility that fishing can damage habitat. In this model, marine reserves are necessary to maximize sustainable profit when dispersal between the patches is sufficiently high and habitat is especially vulnerable to damage.  相似文献   
26.
We consider the uncertain least cost shipping problem. The input is a multi-item supply chain network with time-evolving uncertain costs and capacities. Exploiting the operational law of uncertainty theory, a mathematical model of the problem is established and the indeterminacy factors are tackled. We use the scaling idea together with transformation approach and uncertainty programming to develop a hybrid algorithm to optimize and obtain the uncertainty distribution of the total shipping cost. We analyze the practical performance of the algorithm and present an illustrative example.  相似文献   
27.
朱斌  陈龙  强弢  程鲤 《应用声学》2015,23(1):1-3, 7
为借鉴国外状态预测与健康管理(PHM)技术的发展经验,促进大型平台实现从状态监控向健康管理过渡,本文回顾了美军PHM技术的发展概况,分析了F-35战斗机PHM的体系结构组成以及各模块的主要功能,总结了F-35战斗机PHM的工作流程,介绍了F-35战斗机PHM系统的发展现状及存在的主要问题,提出了对发展PHM技术的认识,为从事PHM技术工作者提供了参考。  相似文献   
28.
集成模块化航空电子架构(Integrated Modular Avionic, IMA)已成为主流航空电子系统。ARINC 653作为航空电子设备IMA架构的标准应用接口,成为研究航空电子软件编程方法的入口。最新研究表明,VxWorks能够为航空电子分区管理提供最优化的平台。然而,基于VxWorks的ARINC 653高效分区调度算法依然是研究的“盲区”。由此,设计了VxWorks内核态分层ARINC 653分区实时调度算法,提高了分区调度效率,为VxWorks内核ARINC 653完整性的研究提供非常有价值的参考。实验数据说明,相较于传统用户态分区管理模型,该调度算法使分区释放开销和分区释放抖动两项指标均显著降低。  相似文献   
29.
对民用船舶信息的管理是一项重要的工作,实现船舶信息管理的电子化,既减轻了管理人员的负担,又可以避免由于误操作而引起的错误。因此,对民用船舶数据库管理系统的开发和功能加以介绍,有助于其推广应用。  相似文献   
30.
For aerodynamic shape optimization, the approximation management framework (AMF) method is used to organize and manage the variable-fidelity models. The method can take full advantage of the low-fidelity, cheaper models to concentrate the main workload on the low-fidelity models in optimization iterative procedure. Furthermore, it can take high-fidelity, more expensive models to monitor the procedure to make the method globally convergent to a solution of high-fidelity problem. Finally, zero order variable-fidelity aerodynamic optimization management framework and search algorithm are demonstrated on an airfoil optimization of UAV with a flying wing. Compared to the original shape, the aerodynamic performance of the optimal shape is improved. The results show the method has good feasibility and applicability.  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