全文获取类型
收费全文 | 175篇 |
免费 | 9篇 |
国内免费 | 5篇 |
专业分类
化学 | 112篇 |
晶体学 | 2篇 |
力学 | 15篇 |
数学 | 21篇 |
物理学 | 39篇 |
出版年
2023年 | 1篇 |
2022年 | 4篇 |
2021年 | 6篇 |
2020年 | 7篇 |
2019年 | 8篇 |
2018年 | 13篇 |
2017年 | 6篇 |
2016年 | 21篇 |
2015年 | 10篇 |
2014年 | 11篇 |
2013年 | 10篇 |
2012年 | 9篇 |
2011年 | 17篇 |
2010年 | 13篇 |
2009年 | 8篇 |
2008年 | 14篇 |
2007年 | 6篇 |
2006年 | 7篇 |
2005年 | 7篇 |
2003年 | 1篇 |
2002年 | 4篇 |
1999年 | 3篇 |
1982年 | 1篇 |
1978年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有189条查询结果,搜索用时 132 毫秒
91.
92.
93.
94.
Recent applications of game-theoretic analysis to supply chain efficiency have focused on constructs between a buyer (the retailer or manufacturer) and a seller (the supplier) in successive stages of a supply chain. If demand for the final product is stochastic then the supplier has an incentive to keep its capacity relatively low to avoid creating unneeded capacity. The manufacturer, on the other hand, prefers the supplier’s capacity to be high to ensure that the final demand is satisfied. The manufacturer therefore constructs a contract to induce the supplier to increase its production capacity. Most research examines contracting when final demand is realized after the manufacturer places its order to the supplier. However, if final demand is realized before the manufacturer places its order to the supplier, these types of contracts can be ineffective. This paper examines two contracts under the latter timing scenario: long-term contracts in which the business relationship is repeated, and penalty contracts in which the supplier is penalized for too little capacity. Results indicate long-term contracts increase the profit potential of the supply chain. Furthermore, the penalty contracts can ensure that the supplier chooses a capacity level such that the full profit potential is achieved. 相似文献
95.
96.
Gold nanoparticles exhibit unique optical, thermal, chemical and physical properties. The microorganisms have high potential
for production of nanoparticles with wide applications. Application of fungi to produce nanoparticles is potentially exciting
because of their ability to secrete large amounts of enzymes. In this study, we investigated biosynthesis of gold nanoparticles
by the fungus Epicoccum nigrum isolated from Andalian gold mine in north-west of Iran. The gold nanoparticles were produced intra and extracellular by reaction
of an aqueous solution of chloroauric acid with the biomass of fungus E. nigrum. The produced gold nanoparticles were in the size range of 5–50 nm in spherical and rod shapes. This is the first report
on the biosynthesis of gold nanoparticles by the fungus E. nigrum. 相似文献
97.
98.
99.
A simple and practical route is described for the synthesis of 2-efhoxy-(4H)-3,1 -benzoxazine-4-ones using the coupling reaction of anthranilic acid derivatives with diethyl dicarbonate following with fast cyclization of the carbamate adduct with a dehydrocyclization agent such as cyanuric chloride and N,N′-dicyclohexylcarbodiimide in PEG at room temperature.High yields of the products obtained under mild reaction conditions with simple work-up of the reaction mixture. 相似文献
100.
A simple sol‐gel method with and without surfactant was applied to prepare TiO2‐ZrO2 mixed oxides containing Ti and Zr at a molar ratio of 1:1. Several catalysts containing w=15% –35% H3PO4 were set up using these mixed oxides. The physical and chemical properties of catalysts were investigated by BET, SEM and pyridine adsorption‐desorption. The catalytic performance of each material was determined for the vapor‐phase acylation of veratrole (1,2‐dimethoxybenzene) to 3,4‐dimethoxyacetophenone (3,4‐DMAP), which was found to be the major product of the reaction of veratrole with ethyl acetate, with alkylated products being the minor products. 2,3‐Dimethoxyacetophenone (2,3‐DMAP) was not detected in the product stream. In the best experimental conditions, the alkylated products were less than 0.7%. This reaction may represent an environmentally friendly alternative to use the ethyl acetate as the acylating reagent. The feed molar ratios of veratrole/ethyl acetate were varied over a wide range of 0.1 to 1, and the optimum feed ratio of veratrole/ethyl acetate was 1:3. Space velocity employed in the veratrole acylation reported as WHSV (veratrole) was 1.2 h?1. The acylation reactions were carried out in the temperature range of 423 to 673 K and the optimum H3PO4 content for acylation was w=15%. 相似文献