全文获取类型
收费全文 | 26116篇 |
免费 | 2922篇 |
国内免费 | 1684篇 |
专业分类
化学 | 18892篇 |
晶体学 | 226篇 |
力学 | 77篇 |
综合类 | 38篇 |
数学 | 19篇 |
物理学 | 11470篇 |
出版年
2024年 | 33篇 |
2023年 | 183篇 |
2022年 | 530篇 |
2021年 | 715篇 |
2020年 | 841篇 |
2019年 | 822篇 |
2018年 | 696篇 |
2017年 | 783篇 |
2016年 | 1258篇 |
2015年 | 1248篇 |
2014年 | 1248篇 |
2013年 | 2230篇 |
2012年 | 1592篇 |
2011年 | 1739篇 |
2010年 | 1450篇 |
2009年 | 1853篇 |
2008年 | 1734篇 |
2007年 | 1837篇 |
2006年 | 1682篇 |
2005年 | 1333篇 |
2004年 | 1139篇 |
2003年 | 961篇 |
2002年 | 741篇 |
2001年 | 594篇 |
2000年 | 532篇 |
1999年 | 492篇 |
1998年 | 404篇 |
1997年 | 374篇 |
1996年 | 299篇 |
1995年 | 257篇 |
1994年 | 184篇 |
1993年 | 174篇 |
1992年 | 144篇 |
1991年 | 108篇 |
1990年 | 66篇 |
1989年 | 58篇 |
1988年 | 108篇 |
1987年 | 48篇 |
1986年 | 30篇 |
1985年 | 28篇 |
1984年 | 31篇 |
1982年 | 26篇 |
1981年 | 28篇 |
1980年 | 22篇 |
1979年 | 7篇 |
1978年 | 9篇 |
1976年 | 7篇 |
1973年 | 10篇 |
1972年 | 7篇 |
1971年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 30 毫秒
21.
Dr. Si-Yong Qin Yan Jiang Dr. Han Sun Han Liu Prof. Ai-Qing Zhang Prof. Xinxiang Lei 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(39):17245-17251
Residual dipolar coupling (RDC), a robust anisotropic NMR parameter for structural elucidation of organic molecules, is only accessible in an anisotropic environment. Herein, we introduce a novel alignment medium based on the molecular self-assembly of oligopeptide amphiphile (OPA). This medium is compatible with different intermediate and polar solvent systems, such as CD3OD, [D6]DMSO, and D2O. The preparation of the OPA-based medium is simple and rapid, while only very weak background signals were observed from OPAs. Furthermore, we show that the purity of OPA has only a minor influence on the quality of the RDC data. These advantages allow RDC measurements of organic molecules with different polarities and solubilities with high efficiency and accuracy. 相似文献
22.
D. J. Plazek C. A. Bero S. Neumeister G. Floudas G. Fytas K. L. Ngai 《Colloid and polymer science》1994,272(11):1430-1438
By making creep and recoverable creep measurements of a nearly monodisperse low molecular weight poly(methyl phenyl siloxane) sample, we have found on decreasing temperature towardsT
g that there is continuously a change in the viscoelastic spectrum concomitant with a decrease of the steadystate recoverable compliance. This behavior is exactly the same as previously observed in low molecular weight poly(styrene), proving that this spectacular anomaly in the viscoelasticity of low molecular weight polymers is general and deserves an explanation. Photon correlation spectroscopic measurements performed on the same sample have extended the observation of the viscoelastic response to shorter times and the result corroborates the trend of variation established by the creep data.Dedicated to Prof.Dr. E. W. Fischer on his 65th Birthday. Prof.Dr. Fischer is known for his valuable contribution to fosterine, international collaboration of research in polymer science. This work is an example of his contribution because it would not be possible without him bringing us together. One of us (KLN) would like to take this opportunity to thank Prof. Dr. Fischer for his unwaiving support of the 1st (Crete) and the 2nd (Alicante) International Discussion Meeting on Relaxations in Complex Systems 相似文献
23.
24.
本文研究了胆绿素的表面增强拉曼光谱。结果表明,在溶液酸度不同时,拉曼光谱特征频率的变化表现出胆绿素的质子化。铜离子与胆绿素的相互作用实验结果说明金属铜离子可与胆绿素生成金属配合物。 相似文献
25.
The characterization of the clusters formed on alkaline hydrolysis of [PdCl4]2– was performed using17O,23Na,35Cl,133Cs NMR and UV spectroscopy. The chemical composition of the clusters was found to be [Pd(OH)2]
n
·nNaCl. No mononuclear oxo- or hydroxocomplexes were detected. The spatial structure of the clusters is stabilized by alkali metal cations.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 675–679, April, 1993. 相似文献
26.
高分辨(e,2e)谱仪采用二维位置灵敏探测器同时对能量和角度进行多道测量.二维位置灵敏探测器由级联使用的微通道板和电阻阳极板组成,由于电阻阳极板的边缘效应和制造工艺的缺陷,测量得到的位置图像与实际图像总会有一定的形变,存在一定的非线性.本文针对高分辨(e,2e)谱仪二维位置灵敏探测器输出图像的“桶形”畸变及位置非线性,采用一种简易的冷刻法(用脉冲信号来模拟真实电子束团),检验了二维位置灵敏探测器的Gear型电阻阳极板的线性好坏,并用分割成小三角形的方法找出测量得到的畸变图像与原始真实图像的映射关系,再用此关系对其它测量得到的畸变图像进行修正,并对修正的结果进行了评估.通过修正,由“桶形”畸变所造成的图像扭曲得到明显改善.修正后的x方向非线性由修正前的2.1%变为0.59%.这种检验和修正方法对其它领域类似探测器输出图像的修正也有一定的指导意义. 相似文献
27.
Methylcyanide, CH3CN, is an important interstellar species, and therefore the accurate knowledge of precise rest frequencies for rotational transitions as well as ground-state rotational and hyperfine constants is needed. In this work the hyperfine structure of the millimeter- and submillimeter-wave spectra of CH3CN has been further investigated. In addition, accurate THz measurements have been carried out for the first time. Consequently, the present investigation allowed us to provide the most accurate ground state rotational and hyperfine parameters known at the moment for CH3C14N. To resolve the hyperfine structure of the rotational transitions observed, the Lamb-dip technique has been exploited. Both frequency-modulated and video-type detections have been employed. 相似文献
28.
29.
More than 250 rotationally resolved vibrational bands of the A2B2-X2A1 electronic transition of 15NO2 have been observed in the 14 300-18 000 cm−1 range. The bands have been recorded in a recently constructed setup designed for high resolution spectroscopy of jet cooled molecules by combining time gated fluorescence spectroscopy and molecular beam techniques. The majority of the observed bands has been rotationally assigned and can be identified as transitions starting from the vibrational ground state or from vibrationally excited (hot band) states. An exceptionally strong band is located at 14 851 cm−1 and studied in more detail as a typical benchmark transition to monitor 15NO2 in atmospheric remote sensing experiments. Standard rotational fit routines provide band origins, rotational and spin rotation constants. A subset of 177 vibronic levels of 2B2 vibronic symmetry has been analyzed in the energy range between 14 300 and 17 250 cm−1, in terms of integrated density and using Next Neighbor Distribution. It is found that the overall statistical properties and polyad structure of 15NO2 are comparable to those of 14NO2 but that the internal structures of the polyads are completely different. This is a direct consequence of the X2A1-A2B2 vibronic mixing. 相似文献
30.