全文获取类型
收费全文 | 592篇 |
免费 | 14篇 |
国内免费 | 87篇 |
专业分类
化学 | 481篇 |
晶体学 | 1篇 |
力学 | 31篇 |
数学 | 16篇 |
物理学 | 164篇 |
出版年
2023年 | 43篇 |
2022年 | 29篇 |
2021年 | 19篇 |
2020年 | 22篇 |
2019年 | 13篇 |
2018年 | 9篇 |
2017年 | 21篇 |
2016年 | 14篇 |
2015年 | 17篇 |
2014年 | 22篇 |
2013年 | 30篇 |
2012年 | 29篇 |
2011年 | 52篇 |
2010年 | 32篇 |
2009年 | 41篇 |
2008年 | 45篇 |
2007年 | 46篇 |
2006年 | 54篇 |
2005年 | 26篇 |
2004年 | 24篇 |
2003年 | 17篇 |
2002年 | 10篇 |
2001年 | 8篇 |
2000年 | 6篇 |
1999年 | 10篇 |
1998年 | 9篇 |
1997年 | 3篇 |
1996年 | 11篇 |
1995年 | 5篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有693条查询结果,搜索用时 375 毫秒
101.
Correlation between structure and photoluminescence in amorphous hydrogenated silicon nitride alloys
M. Molinari H. Rinnert M. Vergnat 《Physica E: Low-dimensional Systems and Nanostructures》2003,16(3-4):445
As-deposited a-SiNx:H (0.1<x<0.9) thin films prepared by evaporation of silicon under a flow of nitrogen and hydrogen ions exhibit visible photoluminescence at room temperature without any posttreatment. The nitrogen concentration was determined by X-ray photoemission spectroscopy. The structural characterization was performed with Fourier transform infrared absorption spectroscopy. The optical gap was obtained from transmission measurements in the ultraviolet–visible–near infrared range. These studies were correlated to the evolution of the photoluminescence properties. 相似文献
102.
反应挤出接枝共聚反应表观链增长常数的测量 总被引:4,自引:1,他引:3
以预辐照的LLDPE反应挤出接枝MAA作为研究对象,通过在双螺杆挤出机中的不同部位取样,用FFIR分析接枝物及均聚物的产量,并用ESR测试链增长自由基浓度,设计了测定接枝和均聚反应初始阶段的表观链增长常数的方法,结果表明,在本实验测试范围内表观接枝链增长常数不同于均聚链增长常数;所得的测量值符合理论预测值,证明测试方法适合高温熔融体系的研究。 相似文献
103.
Quantum chemical CI calculations with the semiempirical MO method SINDO1 are performed to study the rearrangement reactions of 1,2,6,7-octatetraen, 2,3-dimethylenebicyclo(2.2.0)hexane, 3,4-dimethylene-1,5-hexadiene and bicyclo(4.2.0)octa-1,5-diene. It is shown that the most favorable pathway of each of these six rearrangements involves the 2,3-dimethylene-1,4-cyclohexadiyl diradical as an interceptable intermediate. Two further intermediates, 1,2-divinyl-1-cyclobutene and 1,2-divinylylcyclobutane appear, but the latter with little importance. Energies and geometries of the four reactants resp. products, the three intermediates and twelve transitions states are presented. The mechanism of the rearrangements is discussed. 相似文献
104.
A. Hussain C.W. Ahn H.J. Lee I.W. Kim J.S. Lee S.J. Jeong S.K. Rout 《Current Applied Physics》2010,10(1):305-310
We have fabricated lead-free Bi0.5(Na0.75K0.25)0.5TiO3 (BNKT) ceramics by a conventional process (CP) and reactive templated grain growth (RTGG) methods. The effect of grain orientation on structure, dielectric, complex impedance and electrical properties was investigated. The phase formation and grain morphology of BNKT ceramics were examined by X-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. High dielectric constant and low dielectric loss was observed for grain oriented (textured) BNKT ceramics. Complex impedance, temperature dependent ac and dc conductivity were performed to explore the conduction behavior of the prepared BNKT ceramics. 相似文献
105.
Hirakawa K 《Analytical and bioanalytical chemistry》2006,386(2):244-248
Hydrogen peroxide (H2O2) is one of the most important reactive oxygen species. In the present study, a fluorometry method for detecting H2O2 utilizing folic acid was evaluated. Folic acid was decomposed by H2O2 in the presence of Cu(II) into pterine-6-carboxylic acid, leading to strong fluorescence enhancement. In the absence of the
metal ion, superoxide and H2O2 could not decompose folic acid. Also, H2O2 plus sodium hypochlorite (a source of singlet oxygen) could not induce fluorescence enhancement. These results demonstrate
that H2O2 can be selectively detected using folic acid plus Cu(II). The limit of detection (LOD; at S/N=3) for H2O2 is 0.5 μM. This method based on the fluorescence enhancement of folic acid was applied in order to determine small amounts
of H2O2 generated through the autooxidation of semicarbazide (generation rate: ∼0.01 μM min−1), a carcinogenic compound.
相似文献
106.
AlNxOy thin films were produced by DC reactive magnetron sputtering, using an atmosphere of argon and a reactive gas mixture of nitrogen and oxygen, for a wide range of partial pressures of reactive gas. During the deposition, the discharge current was kept constant and the discharge parameters were monitored. The deposition rate, chemical composition, morphology, structure and electrical resistivity of the coatings are strongly correlated with discharge parameters. Varying the reactive gas mixture partial pressure, the film properties change gradually from metallic-like films, for low reactive gas partial pressures, to stoichiometric amorphous Al2O3 insulator films, at high pressures. For intermediate reactive gas pressures, sub-stoichiometric AlNxOy films were obtained, with the electrical resistivity of the films increasing with the non-metallic/metallic ratio. 相似文献
107.
在样品池条件下,应用脉冲激光的泵浦-检测技术,研究了Rb(6~2D)激发态原子与H_2反应碰撞生成的RbH分子的振转能级的布居数密度分布及平均转动能、振动能、平动能的相对比值.发现RbH(X~1∑~+)只有v=0,1上有布居.转动带分布轮廓与池温下的统计分布接近,得到RbH的Boltzmann转动温度稍低于池温,而振动温度高.v=1和v=0上的布居数之比约为0.69,从而得到RbH(X~1∑~+)上平均转动能和平均振动能,由反应的有效能得到平均平动能,这三种能量的相对比值f_R:f_V: 相似文献
108.
在样品池条件下,用脉冲激光670.8 nm线激发Li原子基态至2P态,测量了的反应碰撞能量转移截面。池温保持在888 K,Li原子密度为10~(13)cm~(-3)量级,而H_2气压控制在60~300 Pa之间,测量时间分辨荧光光谱,它由两部分组成,在脉冲激光激发的瞬间(不超过10 ns),荧光迅速增强至最大值;激发结束后,荧光强度按指数衰减,由衰减曲线得到2P态原子在不同H_2气压下的有效寿命。根据Stern-Volmer方程,有效寿命与H_2气压成线性关系,由该直线的斜率给出了总的猝灭截面(25.1±4.0)×10~(-16)cm~2,而从直线的截距得到辐射寿命为(270±54)ns。总的猝灭截面是反应与非反应碰撞截面之和,由在不同H_2气压下记录的瞬态(10 ns)荧光快速增强信号得到反应截面为(0.2±0.1)×10~(-16)cm~2,虽只占总猝灭截面的1/125,但它在Li(2P)+H_2的碰撞传能中所起的作用是不能略去的。 相似文献
109.
Reactive Pulsed Laser Deposition is a single step process wherein the ablated elemental metal reacts with a low pressure ambient gas to form a compound. We report here a Secondary Ion Mass Spectrometry based analytical methodology to conduct minimum number of experiments to arrive at optimal process parameters to obtain high quality TiN thin film. Quality of these films was confirmed by electron microscopic analysis. This methodology can be extended for optimization of other process parameters and materials. 相似文献
110.
Titanium oxynitride (TiNxOy) films were deposited on polyethylene terephthalate (PET) substrates by means of a reactive radio frequency (RF) magnetron sputtering system in which the power density was the varied parameter. Experimental results show that the deposited TiNxOy films with a thickness of about 55 nm have similar contents of TiN, TiNxOy and TiO2 bonds, although they are deposited at different power densities. The TiNxOy films deposited at a lower power density have fewer internal defects and grain boundaries and possess higher activation energy and a lower rate of water vapor and oxygen transmission through TiNxOy/PET films. 相似文献