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   158篇
  免费   3篇
化学   126篇
力学   5篇
数学   12篇
物理学   18篇
  2024年   1篇
  2023年   1篇
  2022年   23篇
  2021年   12篇
  2020年   4篇
  2019年   2篇
  2018年   4篇
  2017年   3篇
  2016年   8篇
  2015年   5篇
  2014年   4篇
  2013年   10篇
  2012年   9篇
  2011年   9篇
  2010年   3篇
  2009年   4篇
  2008年   6篇
  2007年   10篇
  2006年   10篇
  2005年   8篇
  2004年   2篇
  2003年   5篇
  2002年   5篇
  2000年   2篇
  1999年   2篇
  1998年   1篇
  1996年   1篇
  1995年   1篇
  1994年   1篇
  1993年   1篇
  1992年   2篇
  1986年   1篇
  1974年   1篇
排序方式: 共有161条查询结果,搜索用时 0 毫秒
11.
A multinational company may move production to a foreign country to take advantage of low manufacturing cost, and/or experience tax savings. Transfer prices play an important and strategic role on income shifting by multinational companies. In this paper, we construct a framework for optimal decision making in global supply chains with uncertain and price-dependent demand, propose methods to improve global supply chain parties’ performance, and explore schemes to integrate global supply chains. The optimal pricing and offshoring decisions are investigated for different situations where the low foreign production cost and low foreign tax rate exist or only one of them is available. The case of low foreign tax rate without the advantage of low foreign production cost provides the most interesting findings that partial offshoring dominates when a certain threshold is met. In addition, the double marginalization is examined in decentralized global supply chains similar to the mechanism in newsvendor problems. Due to the existence of the tax jurisdiction, the double marginalization cannot be completely eliminated by coordinating schemes. Finally, the traditional buy back contract is found to be unable to coordinate global supply chains, while a modified sales sharing contract can improve the performance of the global supply chain.  相似文献   
12.
13.
The ZnO:Fe nanoparticles of mean size 3-10 nm were synthesized at room temperature by simple co-precipitation method. The crystallite structure, morphology and size estimation were performed by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM). The wurtzite structure of ZnO gradually degrades with the increasing Fe doping concentration. The magnetic behavior of the nanoparticles of ZnO with varying Fe doping concentration was investigated using a vibrating sample magnetometer (VSM). Initially these nanoparticles showed strong ferromagnetic behavior, however at higher doping percentage of Fe, the ferromagnetic behavior was suppressed and paramagnetic nature was observed. The enhanced antiferromagnetic interaction between neighboring Fe-Fe ions suppressed the ferromagnetism at higher doping concentrations of Fe. Room-temperature Mössbauer spectroscopy investigation showed Fe3+ nature of the iron atom in ZnO matrix.  相似文献   
14.
[Reaction: see text]. A highly efficient synthetic method of carotenoid compounds has been developed on the basis of the sulfone coupling and double-elimination strategy. This method highlighted the sulfone-mediated coupling with the novel C(10) dialdehyde, 2,7-dimethyl-4-octenedial, which was easily prepared and efficiently utilized in the synthesis of the conjugated polyene chains.  相似文献   
15.
16.
The symmetrical vinamidinium salts were allowed to react with malononitrile in refluxing ethanol in the presence of ammonium acetate for 12 h to afford the 2‐amino‐5‐aryl or formylpyridine‐3‐carbonitriles.  相似文献   
17.
The Baylis-Hillman reaction of a sesquiterpene lactone parthenin with various aldehydes gave unexpected products containing a 1,3-dioxolane moiety. Both small aliphatic and aromatic aldehydes produced 1,3-dioxolanes, whereas higher aliphatic aldehydes produced normal Baylis-Hillman products.  相似文献   
18.
The chiral Zn(II) complex [ZnLCl(2)], 1 {L = 4-methyl-2,6-di[(S)-(+)-1-phenylethyliminomethyl] phenol}, self-assembles via C-H...Cl hydrogen bonding into supramolecular helices. Complex 1 exhibits emission in solution at room temperature in the visible range. Crystal data for 1: orthorhombic space group P2(1)2(1)2(1), a = 9.614(2) A, b = 13.825(3) A, c = 18.667(3) A, V = 2481.1(8) A(3), Z = 4.  相似文献   
19.
[MoVIO2(S2C2(CN)2)2]2− (┘1) and [MoIVO(S2C2(CN)2)2]2− (2) mimick oxidoreductase enzymatic activities of sulphite oxidase with biological electron donor, SO 3 2− , andin vitro electron acceptor, [Fe(CN)6]3−, demonstrating proton coupled electron transfer reaction in water and inhibition of the oxidation of (2) in the presence of KCN. The sulphite exidizing system is characterized by substrate saturation kinetics indicating the biological significance of the reactions  相似文献   
20.
Chemotherapy is an aggressive form of chemical drug therapy aiming to destroy cancer cells. Adjuvant therapy may reduce hazards of chemotherapy and help in destroying these cells when obtained from natural products, such as medical plants. In this study, the potential therapeutic effect of Rosa damascena callus crude extract produced in vitamin-enhanced media is investigated on colorectal cancer cell line Caco-2. Two elicitors, i.e., L-ascorbic acid and citric acid at a concentration of 0.5 g/L were added to the callus induction medium. Callus extraction and the GC–MS analysis of methanolic crude extracts were also determined. Cytotoxicity, clonogenicity, proliferation and migration of Caco-2 colorectal cancer cells were investigated using MTT cytotoxicity, colony-forming, Ki-67 flow cytometry proliferation and Migration Scratch assays, respectively. Our results indicated that L-ascorbic acid treatment enhanced callus growth parameters and improved secondary metabolite contents. It showed the least IC50 value of 137 ug/mL compared to 237 ug/mL and 180 ug/mL in the citric acid-treated and control group. We can conclude that R. damascena callus elicited by L-ascorbic acid improved growth and secondary metabolite contents as well as having an efficient antiproliferative, anti-clonogenic and anti-migratory effect on Caco-2 cancer cells, thus, can be used as an adjuvant anti-cancer therapy.  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