全文获取类型
收费全文 | 225篇 |
免费 | 61篇 |
国内免费 | 28篇 |
专业分类
化学 | 95篇 |
晶体学 | 1篇 |
力学 | 24篇 |
综合类 | 1篇 |
数学 | 54篇 |
物理学 | 139篇 |
出版年
2023年 | 3篇 |
2022年 | 4篇 |
2021年 | 4篇 |
2020年 | 6篇 |
2019年 | 3篇 |
2018年 | 9篇 |
2017年 | 3篇 |
2016年 | 8篇 |
2015年 | 7篇 |
2014年 | 19篇 |
2013年 | 21篇 |
2012年 | 34篇 |
2011年 | 32篇 |
2010年 | 32篇 |
2009年 | 17篇 |
2008年 | 11篇 |
2007年 | 12篇 |
2006年 | 8篇 |
2005年 | 6篇 |
2004年 | 3篇 |
2003年 | 6篇 |
2002年 | 5篇 |
2001年 | 5篇 |
2000年 | 6篇 |
1999年 | 7篇 |
1998年 | 7篇 |
1997年 | 5篇 |
1996年 | 1篇 |
1995年 | 5篇 |
1994年 | 6篇 |
1993年 | 3篇 |
1992年 | 2篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1986年 | 1篇 |
排序方式: 共有314条查询结果,搜索用时 15 毫秒
41.
区域品牌作为一种公共物品,同其他公共物品一样具有非竞争性和非排他性的性质,现有理论和研究表明,这种性质决定了区域品牌具有“公共地悲剧”风险,这种风险表现为过度使用.但通过构建博弈模型,对比模型的纳什均衡解和帕累托最优解,可以发现区域品牌化过程中的“公共地悲剧”风险不仅表现为过度使用,也表现为投入不足,即具有双重性.并通过对这种双重性的内在机理进行分析,提出有效防范和规避“公共地悲剧”风险的政策建议. 相似文献
42.
理论分析了射流抛光的紊动冲击射流特点,构建了射流抛光的垂直冲击射流模型和斜冲击射流模型。根据射流抛光冲击射流的特点,比较各种流体模型后,采用RNG k-e 模型应用于射流抛光模型的计算。利用计算流体力学理论的二阶迎风格式对抛光模型方程离散,用SIMPLEC数值计算方法对射流抛光过程的紊动冲击射流和离散相磨粒分布进行数值模拟,得到了射流抛光过程的连续流场和离散相磨粒与水溶液的耦合流场,同时计算出了抛光液射流在工件壁面上的压力、速度、紊动强度、剪切力分布和磨粒体积质量分布,分析了垂直射流抛光模型和斜冲击射流抛光模型紊流流场的特点。 相似文献
43.
In this paper, a new global optimization approach based on the filled function method is proposed for solving box-constrained systems of nonlinear equations. We first convert the nonlinear system into an equivalent global optimization problem, and then propose a new filled function method to solve the converted global optimization problem. Several numerical examples are presented and solved by using different local minimization methods, which illustrate the efficiency of the present approach. 相似文献
44.
采用多种色谱分离技术对藏药柳茶叶80%乙醇提取物进行分离纯化,得到了9个化合物。 根据其理化性质与NMR谱数据对化合物进行了结构鉴定,分别为金丝桃苷(hyperoside,Ⅰ)、槲皮素(quercetin,Ⅱ)、芸香苷(rutin,Ⅲ)、槲皮素3-O-β-D-吡喃葡萄糖苷(quercetin-3-O-β-D-glucopyranoside,Ⅳ)、儿茶素(catechin,Ⅴ)、香草酸(vanillic acid,Ⅵ)、熊果苷(arbutin,Ⅶ)、异阿魏酸(isoferulic acid,Ⅷ)和胡萝卜苷(daucosterol,Ⅸ)。 化合物中除Ⅳ、Ⅷ和Ⅸ外,其余6个化合物为首次从该属植物中分离鉴别。 相似文献
45.
Yongjian Liu 《Nonlinear dynamics》2012,67(1):89-96
This paper studies the problem of the circuit implementation and the finite-time synchronization for the 4D (four-dimensional)
Rabinovich hyperchaotic system. The electronic circuit of 4D hyperchaotic system is designed. It is rigorously proven that
global finite-time synchronization can be achieved for hyperchaotic systems which have uncertain parameters. 相似文献
46.
47.
Anatolij Dvurečenskij Yongjian Xie 《International Journal of Theoretical Physics》2014,53(10):3380-3390
An n-perfect pseudo effect algebra means that it can be decomposed into n+1 comparable slices. We show that such a pseudo effect algebra satisfying a Riesz Decomposition Property type corresponds to the lexicographic product of a cyclic group \(\frac{1}{n}\mathbb{Z}\) with some po-group. The analogous result will be proved for strong \(\mathbb{Q}\) -perfect pseudo effect algebras. 相似文献
48.
Zao Yi Xibin Xu Qi Fang Yuying Wang Xibo Li Xiulan Tan Jiangshan Luo Xiaodong Jiang Weidong Wu Yougen Yi Yongjian Tang 《Applied Physics A: Materials Science & Processing》2014,114(2):485-493
Silver nanosheets (NSs) have been synthesized by an electroless plating approach using a complexation mechanism of triethanolamine (TEA) and Ag+ to reduce the oxidation–reduction potential difference and slow down the deposition speed of Ag on quartz glass substrates. The synthesized Ag NSs with 500 nm in edge length and 30 nm in thickness stand on the substrates and are dispersed uniformly. The formation mechanism of Ag NSs is proposed. The formation of Ag NSs is attributed to the molar ratio of AgNO3 to TEA, the concentration of AgNO3 and the influence of reaction temperature. This study is important in vertical immobilization Ag NSs on solid substrates, which could provide substrates for catalysis or surface-enhanced Raman scattering. 相似文献
49.
Retail service for mixed retail and E-tail channels 总被引:1,自引:0,他引:1
Together with regular retail channel, a firm can distribute products directly through Internet (referred to as an “e-tail”
distribution channel). The competitive edge of the retail channel lies in more value-added services, some of which are unavailable
through the e-tail channel. We consider a model mixed with retailing and e-tailing distribution channels where the service
level and price decision are made, respectively, ex ante and ex post demand realizations. From the firm’s perspective of managing
the two channels, we acquire the optimal decisions and characterize the effects of the demand uncertainty on the firm’s optimal
retail service and expected profit. Applying stochastic comparison method, we show the firm’s retail service and profit both
increase in the demand mean, and the firm profits from the increase of the convex order of the demand by decreasing his service
level. Further, if the coefficient of the demand increases, we characterize that the firm benefits from it. Finally, several
numerical studies are presented to gain insights. 相似文献
50.