全文获取类型
收费全文 | 196127篇 |
免费 | 2052篇 |
国内免费 | 559篇 |
专业分类
化学 | 106468篇 |
晶体学 | 2591篇 |
力学 | 8110篇 |
综合类 | 6篇 |
数学 | 19820篇 |
物理学 | 61743篇 |
出版年
2020年 | 1596篇 |
2019年 | 1701篇 |
2018年 | 2202篇 |
2017年 | 2223篇 |
2016年 | 3378篇 |
2015年 | 1973篇 |
2014年 | 2992篇 |
2013年 | 7900篇 |
2012年 | 6138篇 |
2011年 | 7512篇 |
2010年 | 5275篇 |
2009年 | 5072篇 |
2008年 | 6779篇 |
2007年 | 6698篇 |
2006年 | 6623篇 |
2005年 | 6198篇 |
2004年 | 5549篇 |
2003年 | 5107篇 |
2002年 | 5061篇 |
2001年 | 5642篇 |
2000年 | 4186篇 |
1999年 | 3368篇 |
1998年 | 2928篇 |
1997年 | 2848篇 |
1996年 | 2644篇 |
1995年 | 2552篇 |
1994年 | 2311篇 |
1993年 | 2307篇 |
1992年 | 2584篇 |
1991年 | 2520篇 |
1990年 | 2417篇 |
1989年 | 2426篇 |
1988年 | 2362篇 |
1987年 | 2331篇 |
1986年 | 2183篇 |
1985年 | 2888篇 |
1984年 | 3082篇 |
1983年 | 2576篇 |
1982年 | 2910篇 |
1981年 | 2669篇 |
1980年 | 2666篇 |
1979年 | 2726篇 |
1978年 | 2967篇 |
1977年 | 2885篇 |
1976年 | 2823篇 |
1975年 | 2730篇 |
1974年 | 2586篇 |
1973年 | 2778篇 |
1972年 | 1774篇 |
1967年 | 1464篇 |
排序方式: 共有10000条查询结果,搜索用时 18 毫秒
61.
Mark Edgar Dee Hayward Fatemeh Zeinali Shahzad Riaz George W. Weaver 《Magnetic resonance in chemistry : MRC》2020,58(2):170-185
A simple to use nuclear magnetic resonance analysis method has been tested on complex 1H, 19F, and 13C multiplets. This open-source line-shape analysis method analysis of total lineshape (ANATOLIA)1 provides some significant advantages over traditional assign-iterate methods of NMR spectral analysis by avoiding false minima and progressing optimisation to the global minimum. The target molecules are 1-perfluorotol-4-yl-2-perfluorotol-4-yl-oxymethyl-1H-benzimidazole (molecule-I) and 1-tetrafluoropyrid-4-yl-2-tetrafluoropyrid-4-yl-thio-1H-benzimidazole (molecule-II) which were produced as part of a family of fluorinated drug scaffolds prepared for anticancer and antiparasitic screening. Spectra display significant second-order effects with 1H Δδ = 3.68 and 4.67 Hz for the aromatic hydrogen “triplets”, with 19F 4JAA', 4JBB', 4JXX', and 4JYY' coupling constants range from +4.8 to −14.0 Hz and for 13C-isotopomers 19F Δδ of up to 111.56 Hz. A spin-system of six coupling nuclei (HaHbHcHd FYFY') was analysed in 12 s, a spin-system of nine coupling fluorine nuclei (AA'BB'CCC-YY') was analysed within 2 min, and 10 coupling nuclei (XX'YY'ZZZ-BB'-Hd) was optimised in 6 min using a laptop computer. ANATOLIA was also robust enough to be able to yield accurate spectral values from inaccurate input values. In both compounds, a fluorine–fluorine coupling constant was identified between the two fluoro-aromatic rings (FBB' and FYY') of +4.05 and +4.67 Hz and attributed to a through-space interaction. Ab initio structure optimisations and coupling constant calculations provided useful input data for spectral analysis. A modern 19F nuclear magnetic resonance spectrum of perfluorotoluene (octafluorotoluene) and analysis from 1975 was used as a test data set to assess ANATOLIA. 相似文献
62.
Valentin A. Semenov Dmitry O. Samultsev Leonid B. Krivdin 《Magnetic resonance in chemistry : MRC》2020,58(6):532-539
The density functional theory calculation of 1H and 13C NMR chemical shifts in a series of ten 10 classically known Strychnos alkaloids with a strychnine skeleton was performed at the PBE0/pcSseg-2//pcseg-2 level. It was found that calculated 1H and 13C NMR chemical shifts provided a markedly good correlation with experiment characterized by a mean absolute error of 0.08 ppm in the range of 7 ppm for protons and 1.67 ppm in the range of 150 ppm for carbons, so that a mean absolute percentage error was as small as ~1% in both cases. 相似文献
63.
Rogozhkin S. V. Khomich A. A. Bogachev A. A. Nikitin A. A. Khoroshilov V. V. Kulevoy T. V. Fedin P. A. Pryanishnikov K. E. Lukyanchuk A. A. Raznitsyn O. A. Shutov A. S. Zaluzhnyi A. G. Vasiliev A. L. Presniakov M. Yu. 《Physics of Atomic Nuclei》2020,83(11):1519-1528
Physics of Atomic Nuclei - Improved mechanical properties of oxide dispersion strengthened (ODS) steels, the advanced materials for the reactor core, are due to the high density of uniformly... 相似文献
64.
Lithium Insertion Mechanism in Iron-Based Oxyfluorides with Anionic Vacancies Probed by PDF Analysis
Dr. Damien Dambournet Dr. Karena W Chapman Dr. Mathieu Duttine Dr. Olaf Borkiewicz Dr. Peter J Chupas Dr. Henri Groult 《ChemistryOpen》2015,4(4):443-447
The mechanism of lithium insertion that occurs in an iron oxyfluoride sample with a hexagonal–tungsten–bronze (HTB)-type structure was investigated by the pair distribution function. This study reveals that upon lithiation, the HTB framework collapses to yield disordered rutile and rock salt phases followed by a conversion reaction of the fluoride phase toward lithium fluoride and nanometer-sized metallic iron. The occurrence of anionic vacancies in the pristine framework was shown to strongly impact the electrochemical activity, that is, the reversible capacity scales with the content of anionic vacancies. Similar to FeOF-type electrodes, upon de-lithiation, a disordered rutile phase forms, showing that the anionic chemistry dictates the atomic arrangement of the re-oxidized phase. Finally, it was shown that the nanoscaling and structural rearrangement induced by the conversion reaction allow the in situ formation of new electrode materials with enhanced electrochemical properties. 相似文献
65.
JETP Letters - At the resonant passage of a plane elastic shear wave through an acoustically continuous heterostructure consisting of magnetic and nonmagnetic layers in a symmetric nonmagnetic... 相似文献
66.
Radiophysics and Quantum Electronics - We analyze the features of energetic electron precipitation (with the maximum energy E ≥ 150 keV) from the Earth’s radiation belt into a... 相似文献
67.
68.
S. V. Panin I. V. Vlasov V. P. Sergeev B. B. Ovechkin P. O. Marushchak Sunder Ramasubbu P. S. Lyubutin V. V. Titkov 《Physical Mesomechanics》2015,18(3):261-272
The structure and properties of 12Cr1MoV steel irradiated with a zirconium ion beam were studied by optical microscopy, scanning electron microscopy, and micro- and nanoindentation. It is shown that the modification covers the entire cross-section of the irradiated specimens to a depth of 1 mm. The data on irradiation-induced structural changes are used to interpret the changes in mechanical properties of the irradiated specimens under static and cyclic loading. Particular attention is given to analysis of strain estimation by the digital image correlation method. 相似文献
69.
Kondakov N. N. Mel´nikova T. M. Chekryzhova T. V. Mel´nikova M. V. Zinin A. I. Torgov V. I. Chizhov A. O. Kononov L. O. 《Russian Chemical Bulletin》2015,64(5):1142-1148
Russian Chemical Bulletin - Terminal disaccharide fragment of phenolic glycolipid from Mycobacterium leprae (PGL-I) was synthesized as a glycoside with 4-(2-aminoethoxy)phenyl aglycon. The obtained... 相似文献
70.