全文获取类型
收费全文 | 351篇 |
免费 | 16篇 |
国内免费 | 60篇 |
专业分类
化学 | 223篇 |
晶体学 | 3篇 |
力学 | 16篇 |
综合类 | 2篇 |
数学 | 54篇 |
物理学 | 129篇 |
出版年
2022年 | 3篇 |
2021年 | 3篇 |
2020年 | 2篇 |
2019年 | 1篇 |
2018年 | 2篇 |
2017年 | 1篇 |
2016年 | 2篇 |
2015年 | 4篇 |
2014年 | 4篇 |
2013年 | 8篇 |
2012年 | 9篇 |
2011年 | 42篇 |
2010年 | 19篇 |
2009年 | 20篇 |
2008年 | 7篇 |
2007年 | 16篇 |
2006年 | 12篇 |
2005年 | 30篇 |
2004年 | 59篇 |
2003年 | 19篇 |
2002年 | 25篇 |
2001年 | 19篇 |
2000年 | 5篇 |
1999年 | 13篇 |
1998年 | 11篇 |
1997年 | 11篇 |
1996年 | 12篇 |
1995年 | 10篇 |
1994年 | 3篇 |
1993年 | 8篇 |
1992年 | 8篇 |
1991年 | 11篇 |
1990年 | 6篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 7篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1967年 | 1篇 |
1964年 | 3篇 |
排序方式: 共有427条查询结果,搜索用时 15 毫秒
41.
The computational results for curcumin at the B3LYP/6-31G(d,p) level show that the enol form of curcumin is more stable than the diketo form because of an intramolecular hydrogen bond, which extends the conjugation effect in the enol chain, formed in the enol structure. Cis-diketone form can not be obtained, presumably due to the strong repulsion between the carbonyl dipoles aligned in parallel. According to the phenolic O-H bond dissociation enthalpy, curcumin in its most stable form can be suggested to be a relatively good antioxidant. In order to avoid overcoming H-bond interaction and to improve the antioxidant activity of curcumin, a catechol moiety was incorporated into curcumin for designing a novel antioxidant. It is found that the designed molecule is much more efficient to scavenge radical than curcumin, comparable to vitamin E. Moreover, the ionization potential of the designed molecule is similar to that of curcumin, indicating that the designed molecule can not display the prooxidant effect. 相似文献
42.
A new quantum scattering approach (linear combination of arrangement channels-scattering wavefunction,LCAC-SW) proposed by Deng and his co-workers is used to calculate collinear state-to-state reaction probabilities for the F + H-2(v)→HF(v')+H system.Several interesting problems such as threshold energy,compound states and enhance by translational energy of the reactants and the vibration excitation of products are discussed and they are compared with other theoretical investigations reported in the literature.It is shown that the LCAC-SW approach is the successful one of quantum scattering methods. 相似文献
43.
On the basis of the common feature among the electron transfer process and the ion hydration process as well as the relevant experimental kinetic data of electron transfer reaction,a new accurate hydration potential function scheme for the determination of electron transfer coupling matrix element is presented.The coupling matrix element between two hydrated ions of the reacting system in solution is calculated.The results and the applicability of this scheme are discussed. 相似文献
44.
A series of novel solution-processable small-molecule host materials: 2DPF-TCz, 2SBF-TCz, 27DPF-TCz, and 27SBF-TCz comprising a fluorene monomer as the rigid core and tri-carbazole as the periphery have been designed and synthesized, and their optical, electrochemical, and thermal properties have been fully characterized. The host materials exhibit high glass-transition temperatures (231–310 °C) and high triplet energy levels (2.61–2.73 eV). High-quality amorphous thin films can be obtained by spin-coating the host materials from solutions. It is found that the HOMO level of the host materials can be tuned by linking the tri-carbazole unit to the 2,7 positions of the fluorine core, resulting in appropriate HOMO energy levels (−5.36 to −5.23 eV) for improved hole-injection in the device. Solution-processed blue and green electrophosphorescent devices bases on the developed host materials exhibit high efficiencies of 21.2 and 34.8 cd A−1, respectively. 相似文献
45.
LONG Hao WANG Tian-hong ZHANG Ying-kuan State Key Laboratory of Microbial Technology Sh ong University Jinan P. R. China 《高等学校化学研究》2008,24(5):565-569
Two uridine auxotrophic mutants of Trichoderma reesei were isolated by resistance to 5-fluoroorotic acid after UV mutagenesis. One mutant, called M23, was complemented with the Aspergillus niger pyrG gene carried by plasmid pAB4-1. A mutated pyrG gene of M23 was cloned and DNA sequencing analysis indicated that a cytosine was inserted into the 934―939 oligo dC position of the pyrG coding region, resulted in a frameshift mutation. Transformation efficiency was approximately 200―300 transformants per microgram of DNA with plasmid pAB4-1. Stable transformants were obtained by monosporic culture and showed to be prototroph after successive propagation. Vitreoscilla hemoglobin expression plasmid pUCVHb was cotransformed with plasmid pAB4-1 and attained a transformation efficiency of 71.8% or of 26.1% with pAN7-1. Southern blot analysis of the transformants demonstrated that plasmid pUCVHb was integrated into the chromosomal DNA. The experimental results demonstrated that the pyrG-based system was more efficient and timesaving than the conventional hygromycin B resistance-based transformation system. 相似文献
46.
CHU Yongbao GAO Baoyu YUE Qinyan WANG Yan & WANG Shuguang . School of Environmental Science Engineering Shandong University Jinan China . College of Material Environment Qingdao University of Science Technology Qingdao China 《中国科学B辑(英文版)》2006,(4)
Polyaluminum chloride (PAC) coagulant has been developed and widely used in water and wastewater treatment industry since the 1980s[1]. PAC is normally made by partial hydrolysis of acid aluminum chloride solution using slow alkaline titration method. However, this method would result in many different Al species. Among these Al species, it seems that tridecamer (Al13O4(OH) 724 , often denoted by Al13) is the most effective and stable polymeric Al species for water and wastewater treatme… 相似文献
47.
高温煤焦油的超临界萃取分馏研究 总被引:5,自引:0,他引:5
采用正戊烷溶剂,在超临界状态下,于220℃和5MPa~15MPa循序升压条件下,将高温煤焦油萃取分馏为10个液相窄馏分和1个固相沥青产物;切割深度达78.36%,萃余沥青收率为21.64%,明显低于常规蒸馏沥青收率。研究发现,所用高温煤焦油的初馏分萃取收率最高,随着萃取压力的增加,较低压力段一次萃取液相馏分的收率迅速减少;压力达到10 MPa,液相馏分总收率趋于峰值。元素分析和色质联用分析数据表明,随着萃取压力的增加,一次萃取获得窄馏分的碳氢原子比逐渐增加,平均环数和相对分子质量均逐渐增大,萃取馏分逐渐变重。 相似文献
48.
近年来,紧束缚模型方法被广泛应用于计算生物大分子体系.本文从第一性原理出发,根据紧束缚近似的思想,推导出生物大分子体系中的单电子运动方程.在此基础上给出了紧束缚模型方法中所涉及参数(在位能和迁移积分)的计算公式,在理论上完善了紧束缚模型方法.我们将所提出的参数化方法应用于理想B型DNA分子,给出了各种序列组合下的在位能和迁移积分.此外,我们还计算了周期性DNA分子poly(A)-poly(T)和poly(G)-poly(C)中空穴在位能和迁移积分随格点间距离的变化,为改进现有的SSH极化子模型提供了新的思路,有助于DNA中电荷输运的极化子机理的研究. 相似文献
49.
Precipitation polymerizations of divinylbenzene(DVB) in pure supercritical carbon dioxide,and parallel runs with presence of a cosolvent were carried out.The results showed that use of acetone as the cosolvent contributed greatly to the formation of the monodisperse microspheres.PDVB microspheres,with obviously higher uniformity than reported up to date,were achieved using 6-7 mL of acetone in a reactor of 50 mL with DVB concentration of 0.4 mol/L under 16 MPa,a much lower pressure than previously reported without use of cosolvent. 相似文献
50.
Hai Guang Zhang Xu Tang Tao Kao Shan Chen Chun Xue Yuan Shi Na Yan Min Hua Jiang 《中国化学快报》2011,22(6):647-650
A new acid-base fluorescent switch containing both imidazo[4,5-f][1,10]-phenanthroline and triphenylamine groups has been synthesized.Its fluorescence emissions and absorptions can be reversibiy changed through protonation/deprotonation of imidazole and amine moiety by controlling the intramolecular charge transfer(ICT) process,leading to off-on-off fluorescent molecular switching. 相似文献