全文获取类型
收费全文 | 412篇 |
免费 | 44篇 |
国内免费 | 73篇 |
专业分类
化学 | 279篇 |
晶体学 | 4篇 |
力学 | 45篇 |
数学 | 57篇 |
物理学 | 144篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 9篇 |
2021年 | 15篇 |
2020年 | 19篇 |
2019年 | 18篇 |
2018年 | 10篇 |
2017年 | 11篇 |
2016年 | 21篇 |
2015年 | 21篇 |
2014年 | 17篇 |
2013年 | 28篇 |
2012年 | 33篇 |
2011年 | 21篇 |
2010年 | 21篇 |
2009年 | 24篇 |
2008年 | 14篇 |
2007年 | 24篇 |
2006年 | 23篇 |
2005年 | 25篇 |
2004年 | 18篇 |
2003年 | 11篇 |
2002年 | 12篇 |
2001年 | 7篇 |
2000年 | 14篇 |
1999年 | 16篇 |
1998年 | 19篇 |
1997年 | 13篇 |
1996年 | 18篇 |
1995年 | 13篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 1篇 |
1986年 | 2篇 |
排序方式: 共有529条查询结果,搜索用时 15 毫秒
81.
82.
83.
用离子抑制色谱法分析二(2,2,6,6—四甲基—4—哌啶基)马来酸酯合?… 总被引:4,自引:0,他引:4
建立了用离子抑制色谱法分析二(2,2,6,6-四甲基-4-哌啶基)马来酸酯合成反应液的方法。平均回收率为98.8%,相对标准偏差为0.56%,测量的平均相对偏差不大于5.0%,方法简单,快速,可用于工艺条件的选择和质量检测。 相似文献
84.
As various errors result from manufacture and assembly processes or wear effect, clearance joint widely exists in mechanical system as a base component. The coupling analysis of tribology and dynamics of clearance joint is important to the reliability of mechanical system. A nonlinear contact pressure distribution mode (NLCP) is proposed to combine dynamics analysis with wear calculation together in this paper. The discrete thought of Winkler model is adopted to deal with contact problem with a high conformal rate. The contact relationship in a local microcontact area can be regarded as the contact between cylinder and plane. And the local contact pressure is acquired based on Hertz contact theory. The NLCP model has not only described the nonlinear relationship between contact pressure and penetration depth, but also avoided the complexity in contact pressure computation. The performance of NLCP model is demonstrated in comparison with asymmetric Winkler model, revealing that NLCP model has enhanced the calculation accuracy with a good efficiency. A comprehensive experimental study on the wear calculation of a slider–crank mechanism with clearance joint is presented and discussed to provide an experimental verification for NLCP model. The paper’s work has solved the contact problem with a high conformal rate and has described the nonlinear relationship between contact pressure and penetration depth. It has great value to the wear analysis of clearance joint. 相似文献
85.
Li Huaifan Zhang Shengli Wu Yueqin Zhang Lichun Zhao Ren 《The European Physical Journal C - Particles and Fields》2009,63(1):133-138
We extend the classical Damour–Ruffini method and discuss Hawking radiation in Kerr–Newman–de Sitter (KNdS) black hole. Under the condition that the total energy, angular momentum and charge of spacetime are conserved, taking the reaction of the radiation of the particle to the spacetime and the relation between the black hole event horizon and the cosmological horizon into consideration, we derive the black hole radiation spectrum. The radiation spectrum is no longer a pure thermal one. It is related to the change of the Bekenstein–Hawking entropy corresponding the black hole event horizon and the cosmological horizon. It is consistent with the underlying unitary theory. 相似文献
86.
以4-硝基对苯腈,氨水和铜盐反应于在原位水热条件下合成了二(2,4-二(对硝基苯)-1,3,5-环戊二烯铜配合物,通过单晶X射线衍射,元素分析,红外,核磁光谱和热重分析等手段对其进行了表征。结构分析表明,铜与四个源自原位合成的配体上的氮原子配位形成平面四边形构型。基于密度泛函的理论计算对配合物的热力学稳定性进行了阐释。 相似文献
87.
Qi Yang Sanping Chen Shengli Gao 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2009,83(3):357-360
Fourteen new complexes with the general formula of Ln(Hmna)3(phen) (H2mna = 2-mercaptonicotinic acid and phen = 1,10-phenanthroline) were synthesized and characterized by elemental analyses, IR
spectra and thermogravimetric analyses. In addition, molar specific heat capacities were determined by a microcalorimeter
at 298.15 K. The IR spectra of the complexes showed that the Ln3+ coordinated with the oxygen atoms of H2mna and the nitrogen atoms of phen. The complexes decomposed directly to oxides Ln2O3, CeO2, Pr6O11, and Tb4O7 in one step. The values of molar specific heat capacities for fourteen solid complexes were plotted against the atomic numbers
of lanthanide, which presented as “tripartite effect”. It suggested a certain amount of covalent character existed in the
bond of Ln3+ and ligands, according with nephelauxetic effect of 4f electrons of rare earth ions.
The article is published in the original. 相似文献
88.
以邻苯二胺为起始原料,经5步反应合成了富马酸依美斯汀(1)。 采用加入相转移催化剂的方法,改进了2个关键中间体2-氯-1-(2-乙氧基乙基)苯并咪唑(4)和依美斯汀(5)的合成工艺。 反应无需控制水分,中间体4和5的收率分别提高至67.9%和74.9%。 产物的结构经IR、1H NMR、13C NMR、质谱、元素分析、差热分析及X射线粉末衍射证实。 相似文献
89.
Polytetrafluoroethylene-modified silica/12-silicotungstic acid (abbreviated as HSiW/SiO2-PTFE) catalyst was prepared by the ultrasonic impregnation method. The SEM results reveal there are a number of nanowires connecting microspheres with others, botryoidal structure. The diameters of these nanowires vary mainly from 30 nm to 60 nm. An asymmetric ESR signal is found in the ESR spectra of HSiW/SiO2-30 wt% PTFE, which can be concluded to be peroxyl radical by spectral line shapes, g factor (2.0132). 相似文献
90.
Shengli Yang 《Chinese Journal of Lasers》1992,1(3):249-254
A novel phenomenon is reported for the first time that the generation of the newlongitudinal modes in amplifying multi-longitudinal mode laser in a dye amplifier.The newmodes are located on the violet side within the gain band of the amplifing medium.The phe-nomenon is explained by the theory of third-order nonlinear polarization in the case of four-wave resonances.The intensity of the new modes created are comparable with or even higherthan that of the original modes.The effect can be expected to serve as a new method for ex-tention of spectral tuning ranges of laser. 相似文献