全文获取类型
收费全文 | 1653篇 |
免费 | 166篇 |
国内免费 | 4篇 |
专业分类
化学 | 1210篇 |
晶体学 | 2篇 |
力学 | 53篇 |
数学 | 309篇 |
物理学 | 249篇 |
出版年
2023年 | 34篇 |
2022年 | 24篇 |
2021年 | 51篇 |
2020年 | 110篇 |
2019年 | 78篇 |
2018年 | 47篇 |
2017年 | 43篇 |
2016年 | 121篇 |
2015年 | 97篇 |
2014年 | 93篇 |
2013年 | 91篇 |
2012年 | 127篇 |
2011年 | 136篇 |
2010年 | 78篇 |
2009年 | 65篇 |
2008年 | 87篇 |
2007年 | 73篇 |
2006年 | 51篇 |
2005年 | 46篇 |
2004年 | 25篇 |
2003年 | 34篇 |
2002年 | 34篇 |
2001年 | 8篇 |
2000年 | 12篇 |
1999年 | 7篇 |
1998年 | 14篇 |
1997年 | 5篇 |
1996年 | 7篇 |
1995年 | 9篇 |
1994年 | 8篇 |
1992年 | 5篇 |
1991年 | 8篇 |
1989年 | 6篇 |
1986年 | 7篇 |
1984年 | 5篇 |
1978年 | 5篇 |
1977年 | 8篇 |
1976年 | 6篇 |
1974年 | 5篇 |
1970年 | 5篇 |
1967年 | 7篇 |
1964年 | 4篇 |
1963年 | 6篇 |
1933年 | 4篇 |
1930年 | 5篇 |
1916年 | 4篇 |
1914年 | 4篇 |
1912年 | 6篇 |
1911年 | 6篇 |
1909年 | 5篇 |
排序方式: 共有1823条查询结果,搜索用时 31 毫秒
1.
Edelsbacher Philipp Redhammer Gnther Monkowius Uwe 《Monatshefte für Chemie / Chemical Monthly》2020,151(4):543-547
Monatshefte für Chemie - Chemical Monthly - Four members of a new series of paddle-wheel copper(II) complexes bearing cyclobutanecarboxylate as bridging ligand with pyridine derived ligands in... 相似文献
2.
3.
4.
5.
6.
Albrecht H Binder U Harder G Lembke-Koppitz I Philipp A Schmidt-Parzefall W Schröder H Schulz HD Wurth R Donker JP Drescher A Matthiesen U Scheck H Spaan B Spengler J Wegener aD Gabriel JC Schubert KR Stiewe J Waldi R Weseler S Brown NN Edwards KW Frisken WR Fukunaga C Gilkinson DJ Gingrich DM Goddard M Kapitza H Kim PC Kutschke R MacFarlane DB McKenna JA McLean KW Nilsson AW Orr RS Padley P Patel PM Prentice JD Seywerd HC Stacey BJ Yoon T Yun JC Ammar R Coppage D Davis R Kanekal S Kwak N 《Physical review letters》1986,56(6):549-552
7.
rico Marlon de Moraes Flores Ana Paula Fleig Saidelles Eder Lisandro de Moraes Flores Mrcia Foster Mesko Mrcio Pozzobon Pedroso Valderi Luiz Dressler Celso Figueiredo Bittencourt Adilson Ben da Costa 《Microchemical Journal》2004,77(2):113-118
An alternative device for the direct solid analysis (DSA) for copper determination by flame atomic absorption spectrometry (FAAS) is proposed. Copper was directly determined in commercial medicinal plants used as dietary supplements. The determination of copper in solid samples by DSA–FAAS was made by using a conventional air–acetylene flame. Between 0.05 and 1.5 mg of each test, sample was weighed directly into a small polyethylene vial connected to the device used for solid introduction into the flame. Test samples were introduced into the flame as a dry aerosol using a T-quartz cell set between the burner and the optical path. The T-quartz cell has a slit in the superior part by which the solid aerosol passes to the flame. A transient signal, evaluated as integrated absorbance, is produced and it is totally integrated in 2 s. Background signals always presented absorbance values less than 0.1. It was found a characteristic mass of 0.8 ng Cu and absolute limit of detection of 1.2 ng (3 s), or 1.2 μg g−1 if a sample mass of 1 mg was used. Optimized conditions for air flow rate, flame stoichiometry, and so on were established as well. No excessive grinding of the samples was needed and samples with particle of size less than 80 μm were used throughout. No statistical difference between the results from the proposed system and those obtained by sample digestion and determination by conventional FAAS was observed. With the proposed procedure, more than 50 test samples can be analyzed in 1 h and it can be easily adapted to conventional spectrometers for FAAS. 相似文献
8.
Pablo Wessig Philipp Wettstein Bernd Giese Markus Neuburger Margaretha Zehnder 《Helvetica chimica acta》1994,77(3):829-837
The chiral N-(2-benzoylethyl)-N-tosylglycinamides 1a-c were prepared from the C2-symmetric pyrrolidines 5a-c . Irradiation of these ketones 1a-c gave cis-3-hydroxyprolinamides 10-12 in moderate to good yields (Scheme 3). The de of the photocyclizations depended on the size of the substituents in positions C(2) and C(5) of the chiral pyrrolidine auxiliaries. In addition, the de varied with the reaction temperature, allowing the determination of activation-parameter differences. The structure of products 10-12 were established by NMR and X-ray analyses. 相似文献
9.
Haiss W Raisch P Schiffrin DJ Bitsch L Nichols RJ 《Faraday discussions》2002,(121):167-80; discussion 229-51
In situ FTIR spectroscopy has been used in the attenuated total reflectance (ATR) mode to investigate the surface chemistry of etching Si(100) surfaces in aqueous KOH. The effect of solution concentration and electrode potential on the Si-H vibrations has been explored and the experimental results compared with density functional theory calculations. In addition. the kinetics of surface passivation of n-Si(100) has been investigated using FTIR spectroscopy. 相似文献
10.
Increased structural complexity leads to higher activity: peptides as efficient and versatile catalysts for asymmetric aldol reactions 总被引:3,自引:0,他引:3
[reaction: see text] Peptides containing a secondary amine and a carboxylic acid in a specific orientation to each other are presented as highly efficient catalysts for asymmetric aldol reactions: (1) their activity is considerably higher compared to that of proline, and (2) the enantioselectivity of the peptidic catalysts can be changed from (R)- to (S)-selectivity by simple modifications of the secondary structure. 相似文献