全文获取类型
收费全文 | 617篇 |
免费 | 5篇 |
国内免费 | 24篇 |
专业分类
化学 | 273篇 |
力学 | 36篇 |
数学 | 302篇 |
物理学 | 35篇 |
出版年
2023年 | 9篇 |
2022年 | 7篇 |
2021年 | 10篇 |
2020年 | 2篇 |
2019年 | 15篇 |
2018年 | 16篇 |
2017年 | 12篇 |
2016年 | 9篇 |
2015年 | 9篇 |
2014年 | 24篇 |
2013年 | 60篇 |
2012年 | 33篇 |
2011年 | 37篇 |
2010年 | 28篇 |
2009年 | 52篇 |
2008年 | 45篇 |
2007年 | 49篇 |
2006年 | 27篇 |
2005年 | 39篇 |
2004年 | 27篇 |
2003年 | 9篇 |
2002年 | 10篇 |
2001年 | 10篇 |
2000年 | 6篇 |
1999年 | 9篇 |
1998年 | 9篇 |
1997年 | 9篇 |
1996年 | 6篇 |
1995年 | 4篇 |
1994年 | 12篇 |
1993年 | 7篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 5篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 5篇 |
排序方式: 共有646条查询结果,搜索用时 312 毫秒
641.
5-Methylenehydantoin, as well as the N-mono- and N,N-di-protected derivatives, can be obtained by different synthetic routes. These compounds can undergo a large variety of reactions, such as Diels-Alder, epoxidation, methanol addition and conjugate addition reactions of different types of nucleophiles, including carbon (cyanide), nitrogen (piperidine) and sulfur (thiols, thioacetate) nucleophiles. The reactivity with electrophilic reagents, such as m-CPBA or methanol in acidic medium, and the need for Lewis acids to promote the conjugate addition reactions indicate that hydantoin is a poor electron-withdrawing group. 相似文献
642.
Andrew Dahao Yeung 《Journal of organometallic chemistry》2011,696(1):112-117
Three cis-chelating di-N-heterocyclic carbene palladium(II) complexes [PdX2(diNHC)] (X = I, 1; X = SCN, 2; X = CF3CO2, 3) bearing different anionic co-ligands were synthesized and fully characterized. A comparison of their catalytic activities in the Mizoroki-Heck reaction and conjugate addition of arylboronic acids to cyclic enones revealed increasing efficiency in the order SCN− < I− < CF3CO2−. The di(trifluoroacetato) complex 3 showed the best activity in both transformations highlighting the importance of co-ligands effects in catalysis. In addition, the molecular structure of an unusual poly-heteronuclear complex salt 4 is reported, which has been isolated as a byproduct in the synthesis of complex 3. 相似文献
643.
The aim of the paper was to investigate the effect of ultrasonic emulsification treatment on the fabrication mechanism and stability of the emulsion. The covalent conjugate made with rice bran protein hydrolysate (RBPH) and ferulic acid (FA) was used as the emulsifier. The effects of high intensity ultrasound (HIU) power with different level (0 W, 150 W, 300 W, 450 W and 600 W) on the stability of emulsion were evaluated. The results showed that ultrasonic emulsification can significantly improve the stability of the emulsions (p < 0.05). The emulsion gained better stability and emulsifying property at 300 W. It was able to fabricate emulsion with smaller particle size, more uniform distribution and higher interfacial protein content. It was confirmed by fluorescent microscopy and cryo-scanning electron microscopy (cryo-SEM) furtherly. And it was also proved that the emulsion treated by proper HIU treatment at 300 W had better storage stability. Excessive HIU treatment (450 W, 600 W) had negative effects on the stability of emulsion. The stability of emulsion (300 W) against different environmental stresses was further explored, which established a theoretical basis for the industrial application of emulsion in food industry. 相似文献
644.
1.IntroductionInthispaperwewillgivesomesuitablesufficientconditionswhichassuretheclosednesspropertyofthedifferenceoftwoclosedconvexsetsingeneralBanachspaces,notnecessarilyrenekive.Theclosednessproblemweareconcernedwithisfrequentlyencounteredindifferentbranchesofappliedmathematics;forexample,thesolvabilityoflinearsystemsoverconeandthedualitytheoryofabstractmathematicalprogramming.OurmotivationcomesfromaBaiocchi-Gastaldi-TomarelliIsresult13]concernedwiththecaseofHilbertspace.FurlhermorelK5th.… 相似文献
645.
一种混合的HS-DY共轭梯度法 总被引:22,自引:3,他引:19
本文在HS方法和DY方法的基础上,综合两者的优势,提出了一种求解无约束优化问题的新的混合共轭梯度法.在Wolfe线搜索下,不需给定下降条件,证明了算法的全局收敛性.数值试验表明,新算法较之HS方法和PR方法更加有效. 相似文献
646.
WeiWang Lian-shengZhang Yi-fanXu 《计算数学(英文版)》2005,23(2):217-224
A revised conjugate gradient projection method for nonlinear inequality constrained optimization problems is proposed in the paper, since the search direction is the combination of the conjugate projection gradient and the quasi-Newton direction. It has two merits. The one is that the amount of computation is lower because the gradient matrix only needs to be computed one time at each iteration. The other is that the algorithm is of global convergence and locally superlinear convergence without strict complementary condition under some mild assumptions. In addition the search direction is explicit. 相似文献