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   224篇
  免费   27篇
  国内免费   9篇
化学   161篇
力学   2篇
综合类   2篇
数学   56篇
物理学   39篇
  2024年   1篇
  2023年   2篇
  2022年   12篇
  2021年   13篇
  2020年   9篇
  2019年   8篇
  2018年   5篇
  2017年   6篇
  2016年   9篇
  2015年   18篇
  2014年   12篇
  2013年   19篇
  2012年   14篇
  2011年   16篇
  2010年   14篇
  2009年   18篇
  2008年   5篇
  2007年   10篇
  2006年   14篇
  2005年   14篇
  2004年   20篇
  2003年   6篇
  2002年   1篇
  2001年   3篇
  2000年   2篇
  1999年   1篇
  1997年   1篇
  1992年   2篇
  1991年   2篇
  1990年   1篇
  1986年   2篇
排序方式: 共有260条查询结果,搜索用时 125 毫秒
81.
Increasingly, customer service, rapid response to customer requirements, and flexibility to handle uncertainties in both demand and supply are becoming strategic differentiators in the marketplace. Organizations that want to achieve these benchmarks require sophisticated approaches to conduct order promising and fulfillment, especially in today’s high-mix low-volume production environment. Motivated by these challenges, the Available-to-Promise (ATP) function has migrated from a set of availability records in a Master Production Schedule (MPS) toward an advanced real-time decision support system to enhance decision responsiveness and quality in Assembly To Order (ATO) or Configuration To Order (CTO) environments. Advanced ATP models and systems must directly link customer orders with various forms of available resources, including both material and production capacity. In this paper, we describe a set of enhancements carried out to adapt previously published mixed-integer-programming (MIP) models to the specific requirements posed by an electronic product supply chain within Toshiba Corporation. This model can provide individual order delivery quantities and due dates, together with production schedules, for a batch of customer orders that arrive within a predefined batching interval. The model considers multi-resource availability including manufacturing orders, production capability and production capacity. In addition, the model also takes into account a variety of realistic order promising issues such as order splitting, model decomposition and resource expediting and de-expediting. We conclude this paper with comparison of our model execution results vs. actual historical performance of systems currently in place.  相似文献   
82.
Polyclonal rabbit antibodies against nonylphenol (NP), the main product of nonionic surfactants destruction, were obtained and applied for immunoenzyme assay (ELISA). Two approaches to immunogen synthesis were compared. The first was direct coupling of a mixture of NP isomers to the carrier protein by Mannich reaction. The second was formation of amide bonds between 7-(p-hydroxyphenyl)heptanoic acid (HHA), a linear carboxylated analog of NP, and the carrier protein. Anti-HHA antibodies showed a low affinity to technical NP, whereas with Mannich synthesis it was possible to generate antibodies specific to branched NP molecules. An indirect competitive ELISA was developed based on the anti-NP antibodies. The detection limit of the analysis is 10 ng/mL, with a total duration of around 3 h. The developed ELISA can be applied for group-specific determination of nonionic surfactants and their toxic metabolites. The possibility of NP detection in environmental water matrices using the proposed ELISA without loss of sensitivity is explored.  相似文献   
83.
The voltammetry of some estrogenic compounds (estradiol, nonylphenol, bisphenol A, ethynylestradiol, estrone, estriol) in aqueous solution at boron doped diamond electrodes is reported. For oxidised (hydrophilic) electrodes electrochemically irreversible kinetics were observed for the diffusing molecules allowing the inference of diffusion coefficients and transfer coefficients. In contrast for hydrogen terminated (hydrophobic) surfaces significant adsorption was observed. A limit of detection of 1–100 µM for the estrogenic compounds was found using the oxidised diamond electrode. Surface modification of the oxidised diamond with nano‐Carbon (so‐called Carbon Black) allowed preconcentration of the target by adsorption onto the Carbon Black prior to analysis and a corresponding reduction of the limit of detection by ca three orders of magnitude to 5–100 nM.  相似文献   
84.
针对两个制造商与一个零售商组成的二级供应链,建立了制造商一方与零售商联盟,制造商另一方与之竞争、零售商类型为其私人信息下的博弈模型,从系统优化的角度研究了供应链系统批发价格如何应对突发事件.首先证明稳定条件下,零售商成本信息为非对称信息时,批发价格契约能实现集中控制与分散控制下-该供应链的协调.当突发事件造成零售商的成本分布变化时,通过求解突发事件下供应链系统最优利润的Karush-Kuhn-Tucker(KKT)条件,提出了供应链应对突发事件的最优策略,进一步证明了改进的批发价格契约可以协调突发事件下分散化决策的供应链系统.数值仿真表明,当零售商的成本在一个较小的范围内扰动时,原有契约机制具有一定的鲁棒性,而当扰动较大时,需要对原来的生产计划进行调整.  相似文献   
85.
A robust solid‐phase microextraction fiber was fabricated by electropolymerization of thiophene on a stainless steel wire. This fiber was applied for the determination of endocrine‐disruptor pesticides, namely, chlorpyrifos, penconazole, procymidone, bromopropylate, and λ‐cyhalothrin in well waters by a headspace solid‐phase microextraction procedure. Operational parameters, namely, pH, sample volume, adsorption temperature and time, desorption temperature, stirring rate, and salt amount were optimized as 7.0, 8 mL, 70°C and 20 min, 250°C, 600 rpm, and 0.3 g/mL, respectively. The separation power of GC was coupled with the excellent sensitivity of the developed fiber enabling us to determine pesticide mixtures simultaneously in a ng/mL range. The LOD was in the range of 0.02–0.64 ng/mL. The method was successfully applied for the selective and sensitive determination of target pesticides in well water samples with acceptable recovery values (92–110%). The polythiophene fiber gives satisfactory results compared with commercial fibers. Commonly used pesticides with different polarities were chosen as representative compounds to search the applicability of the fiber for well water analysis collected from vineyards.  相似文献   
86.
We report a structure–property relationship study of four 9,9′-spirobifluorene (SBF) derivatives (4-5Pm-SBF, 2-5Pm-SBF, 4-Ph-SBF and 2-Ph-SBF), substituted with either phenyl or pyrimidine at the C2 or C4 position of the SBF core. Structural, thermal, electrochemical and photophysical properties have been examined and correlated to theoretical calculations in order to study the influence of the nature and the position of the substituent. The emission properties of 4- versus 2-substituted SBFs are noticeably different highlighting, in the excited state, the remarkable effect of substitution in ortho position of SBF. All compounds have been used as host material for green dopant in PhOLEDs with very high performances (2-5Pm-SBF: CE>58 cd/A, PE>35 lm/W, EQE>14%). More importantly, the two 4-substituted SBFs have been used as host materials in blue PhOLEDs, displaying high performance and a decrease of VTH for 4-5Pm-SBF due to the incorporation of the electron-withdrawing pyrimidine.  相似文献   
87.
The endocrine system that provides communication and maintains homeostasis, is an important part of the body. Any defects or disruptions that affect the endocrine system may cause serious problems in the actions and functions of the body. Endocrine disruptive chemicals (EDCs) are exogenous chemicals or mixtures of chemicals that affects normal functions of the endocrine system by interfering with endogenous hormones and hormonal pathways and disrupting homeostasis. Numerous compounds are considered as endocrine disruptors such as bisphenols (BPs), phthalates, pesticides etc. and they are widely used for industrial purposes in many commercial products. Therefore, human exposure is almost inevitable. Besides that, EDCs may cause environmental pollution and are found in surface waters, wastewater, soil etc. To prevent exposure and hazardous effect, there are legislative regulations including restrictions and prohibitions of the use of EDCs. Due to these reasons; it is crucial to develop highly sensitive, low-cost, easy-to-use, and rapid sensors for the determination of EDCs in commercial and environmental samples. Although there are mostly chromatographic and spectrometric methods for the EDCs monitoring, electrochemistry surpasses them with advantageous properties such as easy application procedure, high sensitivity, very low limit of detection (LOD) values and low-cost.In this review, major groups of EDCs will be explained with their recent and novel electrochemical sensor applications for their detection in commercial and environmental samples.  相似文献   
88.
投资决策中的0-1背包问题的扰动修复   总被引:1,自引:0,他引:1  
针对投资决策中的0-1背包问题,提出了在应急管理下0-1背包问题的扰动修复的多目标决策模型,此模型反映了多变的经济条件下,公司或企业的项目投资资金分配计划受到扰动时积极应对扰动的决策需要.本文利用线性加权和法将其转化为单目标决策优化模型,并证明这个单目标决策优化模型为0-1背包问题,采用分枝定界方法求解,并对权系数取值进行了分析,同时结合实例验证了模型的合理性和有效性.  相似文献   
89.
采用高Z杂质注入HL-1M等离子体中, 触发等离子体电流衰竭的实验已经施行.用激光吹气注入高Z杂质能够增加辐射冷却,等离子体在-3ms时间内迅速冷却而且在电流终止之前电子温度损失约80%.实验证明:它是一种使得大型聚变实验装置上在放电破裂之前显著减少等离子体中热能而且安全终止放电的简单、快速和有效的途径. 关键词: 高Z杂质 破裂 等离子体终止 激光吹气  相似文献   
90.
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