全文获取类型
收费全文 | 3072篇 |
免费 | 100篇 |
国内免费 | 11篇 |
专业分类
化学 | 1762篇 |
晶体学 | 47篇 |
力学 | 126篇 |
数学 | 654篇 |
物理学 | 594篇 |
出版年
2023年 | 19篇 |
2022年 | 44篇 |
2021年 | 77篇 |
2020年 | 63篇 |
2019年 | 81篇 |
2018年 | 113篇 |
2017年 | 118篇 |
2016年 | 145篇 |
2015年 | 105篇 |
2014年 | 151篇 |
2013年 | 412篇 |
2012年 | 198篇 |
2011年 | 199篇 |
2010年 | 187篇 |
2009年 | 137篇 |
2008年 | 182篇 |
2007年 | 179篇 |
2006年 | 111篇 |
2005年 | 95篇 |
2004年 | 84篇 |
2003年 | 63篇 |
2002年 | 46篇 |
2001年 | 25篇 |
2000年 | 26篇 |
1999年 | 22篇 |
1998年 | 22篇 |
1997年 | 21篇 |
1996年 | 21篇 |
1995年 | 11篇 |
1994年 | 9篇 |
1993年 | 9篇 |
1992年 | 7篇 |
1990年 | 7篇 |
1989年 | 8篇 |
1988年 | 10篇 |
1987年 | 10篇 |
1986年 | 13篇 |
1985年 | 17篇 |
1984年 | 13篇 |
1983年 | 13篇 |
1982年 | 10篇 |
1981年 | 17篇 |
1980年 | 6篇 |
1979年 | 10篇 |
1977年 | 7篇 |
1976年 | 12篇 |
1975年 | 5篇 |
1974年 | 10篇 |
1973年 | 9篇 |
1968年 | 10篇 |
排序方式: 共有3183条查询结果,搜索用时 15 毫秒
101.
Marco Reichel Mara Egenhöfer Burkhard Krumm Konstantin Karaghiosoff 《无机化学与普通化学杂志》2020,646(6):328-331
Fluoromethylating agents are a highly studied and controversely discussed class of compounds. New fluoromethyl pseudohalides FCH2N3, FCH2SCN, and FCH2SeCN were prepared for the first time and their physical and spectroscopic properties investigated. Their synthesis is performed conveniently by fluoromethylation of the respective silver or potassium pseudohalogenides with fluoroiodomethane. 相似文献
102.
A series of piperidoimidazolinium salts which differ in the chain lengths (butyl, octyl, dodecyl, octadecyl) and their Pd–N‐heterocyclic carbene complexes with pyridine were synthesized and characterized using elemental analysis and spectroscopic methods. The effects of these ligands on catalyst activation and the performance of the complexes were studied in Suzuki–Miyaura reactions of arylboronic acid with aryl chlorides. The complex with the ligand having the longest chain length was found to be most active. The results demonstrated that the length of the alkyl chain of the piperidoimidazolin‐2‐ylidene controlled the dispersion and composition of the nanoparticles and it affected the catalytic activity. The impact of alkyl chain length of piperidoimidazolin‐2‐ylidene on the Suzuki–Miyaura reactions of arylboronic acid with aryl halides was systematically investigated. 相似文献
103.
In this study, in order to explain solvent proton relaxation mechanism, the spin-lattice relaxation time (T1) of agar solutions was measured as a function of agar concentration. Relaxation measurements were carried out by a FT-NMR spectrometer operating at 60 MHz and inversion recovery pulse squence was used. Relaxation rate(1/T1a) was linearly proportional to concentration of agar solution (C), and the T1 mechanism of solvent water protons in agar solutions should be caused by the chemical exchange of water protons between free and bound water. 相似文献
104.
105.
106.
Identification of radical structures on 1‐pentamethylbenzyl‐3‐ethylimidazoliumsilver(I)bromide and 1,3‐bis(pentamethylbenzyl)‐4,5‐dimethylbenzimidazoliumsilver(I)bromide exposed to gamma rays: an EPR study
下载免费PDF全文
![点击此处可从《Magnetic resonance in chemistry : MRC》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Yusuf Ceylan Keziban Usta Ahmet Kunduracioglu Ayhan Usta Bekir Cetinkaya 《Magnetic resonance in chemistry : MRC》2016,54(11):864-869
1‐Pentamethylbenzyl‐3‐ethylimidazoliumsilver(I)bromide and 1,3‐bis(pentamethylbenzyl)‐4,5dimethylbenzimidazoliumsilver(I)bromide and their Ag+ complexes were synthesized and their polycrystal forms were produced by recrystallization in dichloromethane/Et2O solvent system. Structural determinations were carried out by 1H NMR and 13C NMR with a Varian 400 NMR system using tetramethylsilane as internal standard and CDCl3 as solvent. The disappearance of acidic N‐heterocyclic carbene proton showed the formation of Ag(I) complexes. Also, elemental analyses were carried out. Electron paramagnetic resonance (EPR) measurements were performed to determine the formed radical structure on the samples irradiated at the room temperature for 72 h by using 60Co‐source with dose rate of 0.680 kGy. The EPR measurements were carried out in the temperature range of 200 K–450 K. Identical radicals were determined on the irradiated compounds. It was observed that the shapes of the spectra of the samples were independent of the temperature but, the resonance line intensities changed linearly with the temperature. Also, it was detected that the free radical on the 1‐pentamethylbenzyl‐3‐ethylimidazoliumsilver(I)bromide is not stable compared to that on the 1,3‐bis(pentamethylbenzyl)‐4,5dimethylbenzimidazoliumsilver(I)bromide. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
107.
Estefanía Moreno-Gordaliza Sven J. van der Lee Ayşe Demirkan Cornelia M. van Duijn Johan Kuiper Petrus W. Lindenburg Thomas Hankemeier 《Analytica chimica acta》2016
A new capillary isotachophoresis (cITP) method for lipoprotein profiling with superior lipoprotein coverage compared to previous methods has been developed, resolving twice as many lipoprotein species (18 peaks/fractions) in serum or plasma in less than 9.5 min. For this, a novel mixture of 24 spacers, including amino acids, dipeptides and sulfonic acids, was developed and fine-tuned, using predictive software (PeakMaster) and testing of spiked serum samples. Lipoprotein peaks were identified by serum-spiking with reference lipoproteins. Compatibility with common lipophilic stains for selective lipoprotein detection with either UV/Vis or laser-induced fluorescence was demonstrated. A special new capillary with a neutral coating (combining water-compatible OV1701-OH deactivation and methylation) was used for the first time for electrodriven separations, allowing very stable separations in a pH 8.8–9.4 gradient system, being functional for more than 100 injections. Excellent reproducibility was achieved, with coefficients of variation lower than 2.6% for absolute migration times. Comparison was performed with human plasma samples analyzed by NMR, leading to similar results with cITP after multivariate statistics, regarding group-clustering and lipoprotein species correlation. The new cITP method was applied to the analysis of serum samples from a LDL receptor knock-out mice model fed either a normal diet or a western-type diet. Differences in the lipoprotein levels and in the sublipoprotein types were detected, showing a shift to more atherogenic particles due to the high cholesterol diet. In summary, this novel method will allow more detailed and informative profiling of lipoprotein particle subtypes for cardiovascular disease research. 相似文献
108.
109.
Monica Roşiu 《复变函数与椭圆型方程》2015,60(2):181-190
We extend the notion and basic properties of quadratic differential divisors to a Klein surface, using the corresponding form’s divisors from the double cover of the Klein surface. 相似文献
110.