全文获取类型
收费全文 | 3101篇 |
免费 | 92篇 |
国内免费 | 642篇 |
专业分类
化学 | 1556篇 |
晶体学 | 7篇 |
力学 | 20篇 |
综合类 | 2篇 |
数学 | 22篇 |
物理学 | 2228篇 |
出版年
2024年 | 11篇 |
2023年 | 59篇 |
2022年 | 46篇 |
2021年 | 49篇 |
2020年 | 83篇 |
2019年 | 72篇 |
2018年 | 93篇 |
2017年 | 77篇 |
2016年 | 118篇 |
2015年 | 124篇 |
2014年 | 136篇 |
2013年 | 184篇 |
2012年 | 234篇 |
2011年 | 362篇 |
2010年 | 203篇 |
2009年 | 248篇 |
2008年 | 228篇 |
2007年 | 227篇 |
2006年 | 200篇 |
2005年 | 128篇 |
2004年 | 114篇 |
2003年 | 119篇 |
2002年 | 122篇 |
2001年 | 96篇 |
2000年 | 71篇 |
1999年 | 56篇 |
1998年 | 62篇 |
1997年 | 36篇 |
1996年 | 31篇 |
1995年 | 36篇 |
1994年 | 27篇 |
1993年 | 24篇 |
1992年 | 25篇 |
1991年 | 34篇 |
1990年 | 12篇 |
1989年 | 12篇 |
1988年 | 7篇 |
1987年 | 12篇 |
1986年 | 4篇 |
1985年 | 10篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 9篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 1篇 |
1974年 | 3篇 |
1973年 | 5篇 |
排序方式: 共有3835条查询结果,搜索用时 171 毫秒
51.
Wolfgang Schattke 《Progress in Surface Science》1997,54(3-4):211-227
Photoemission in the vacuum ultraviolet photon regime has proved to be an effective tool for the investigation of valence band surface electronic structure. The interpretation cannot be exclusively confined to the valence bands but has to consider cross sections with realistic final states consistently designed within the one-step model. Therefore especially in the surface sensitive photoemission, several effects hide the final goal of deducing the energetic and wavefunction structure together with microscopic potential parameters through a convincing agreement of calculated with measured spectra. The final states band structure is much less well understood than the valence band structure under consideration. The optical potential, which controls the surface sensitivity through the underlying damping mechanisms, widely relies on empirical assumptions. Furthermore, the photon field is not only strongly influenced but in the vicinity of the plasma frequency also deteriorated by the electronic response. In view of high resolution spectroscopy the accuracy of the data interpretation is affected, and in fact, band-mapping methods are no longer valid. Examples of recent calculations to account for these effects are reviewed. 相似文献
52.
53.
硝基烃光异构化反应的密度泛函理论计算 总被引:3,自引:0,他引:3
采用DFT(B3LYP)计算方法, 在6-31G*水平上获得了反式-β-硝基苯乙烯、硝基乙烯和硝基甲烷基态异构化反应时的过渡态分子结构, 并计算了异构化能垒及激发态电子跃迁能. 结果显示, 反式-β-硝基苯乙烯和硝基苯与硝基甲烷相比具有较短的过渡态C—N键长, 较低的异构化能垒, 并且随着不饱和度的增加, 硝基苯和反式-β-硝基苯乙烯电子垂直跃迁能与基态异构化反应过渡态之间能量的差值ΔE迅速减小. 从能量的角度分析, 取代基的不饱和度越大, 越有利于激发态势能面与异构化反应势能面发生锥型或漏斗交叉, 因而越有利于光化学反应沿光异构化通道进行. 激发态分子的初始电子运动的定域或离域特征的差别可能是导致硝基苯等硝基芳烃与硝基甲烷等硝基烷烃光解通道不同的一个重要原因. 相似文献
54.
In this paper we study theoretically the molecular structure of [Be(C5Me5)2], with special interest in similarities and differences found in the computed geometric parameters, depending on the treatment of the electron correlation used. Given the low energy differences found between the different configurations studied (less than 4 kcal mol−1), and the high fluxionality found in experimental studies for this compound, we analyzed the dynamics of the system by means of first principles molecular dynamics calculations. A complex dynamics is found and analyzed in terms of two molecular rearrangement processes: 1,2-sigmatropic intraring rearrangement and a ring inversion mechanism that interchanges the roles (with regard to their coordination to the central Be atom) of the two rings.Dedicated to Dr. Jeal Paul Malrieu on occasion of his 65th birthday. 相似文献
55.
Angle-resolved photoelectron spectra were measured for a single-domain monolayer film of naphthalene-1,4,5,8-tetracarboxylic dianhydride (NTCDA) prepared on a cleaved GeS(0 0 1) surface using synchrotron radiation. The observed photoelectron angular distributions were analyzed by a calculation using the single-scattering approximation combined with molecular orbital calculation. With the help of the low-energy electron diffraction pattern, the structure of the NTCDA monolayer on GeS(0 0 1) was estimated quantitatively. 相似文献
56.
Zn3V3O8 two-dimensional micro sheets are successfully synthesized by combination of solvothermal method and heat treatment. The Zn3V3O8 has better electrochemical performances after calcinations. 相似文献
57.
V. A. Petukhov 《Russian Chemical Bulletin》1992,41(6):1055-1057
The correlation of the spectra of conjugated tetratomic and triatomic systems was examined by means of corrected Dewar rules.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 6, pp. 1353–1356, June, 1992. 相似文献
58.
Dimethyl 1′,1′-ureylenedi(1-ferrocenecarboxylate) (1) formed during the synthesis of 1-amino, 1′-ferrocenecarboxylic acid shows virtual molecular centrosymmetry. Electronic coupling between the two Fc groups through the ureylene bridge results in both Fc groups being individually oxidizable (ΔE1/2?0.14 V). The possible existence of intermolecular electronic communication has discussed. The oxidation was followed by spectroelectrochemistry. The separation between the two halfwave potentials ΔE1/2=137±5 mV and the comproportionation constant Kc=207. 相似文献
59.
Chemical sensors have been widely used for the analysis of volatile organic compounds. Employing chemical sensors in an array format with pattern recognition provides a higher degree of selectivity and reversibility leading to an extensive range of applications. When such systems are used for odour analysis they are termed electronic noses. Application of electronic noses ranges from the food industry, medical industry to environmental monitoring and process control. Many types of different gas sensors have been employed in the array. These include conducting polymers, metal oxide semiconductors, piezoelectric, optical fluorescence and amperometric gas sensors The transducer principle of these sensors is varied and is discussed in detail within this review. Examples of the current trends in sensor array technology as well as the applications to which the sensor-based noses have been applied are also discussed. 相似文献
60.
合成并测定了标题化合物的分子结构,Ca空间群,a=2.1933(2)nm,b=1.2447(3)nm,c=1.5912(5)nm,β=117.02(2)°,I'=3.8679 nm~3,Z=4,最后根据I>3G(I)的2849个独立衍射点的强度数据,把结构精修到R=0.036.在晶体结构测定基础上进行了EHMO计算,以研究其簇骼成键性质,结果表明,该分子虽不存在金属-金属键,但M与μ-O之间除了σ键外,还存在四中心d-ρπ键,它是该类化合物稳定的主要因素。 相似文献