全文获取类型
收费全文 | 2877篇 |
免费 | 75篇 |
国内免费 | 8篇 |
专业分类
化学 | 1957篇 |
晶体学 | 45篇 |
力学 | 107篇 |
数学 | 594篇 |
物理学 | 257篇 |
出版年
2023年 | 14篇 |
2022年 | 52篇 |
2021年 | 70篇 |
2020年 | 55篇 |
2019年 | 55篇 |
2018年 | 33篇 |
2017年 | 24篇 |
2016年 | 77篇 |
2015年 | 74篇 |
2014年 | 63篇 |
2013年 | 138篇 |
2012年 | 126篇 |
2011年 | 174篇 |
2010年 | 106篇 |
2009年 | 98篇 |
2008年 | 152篇 |
2007年 | 128篇 |
2006年 | 154篇 |
2005年 | 145篇 |
2004年 | 135篇 |
2003年 | 114篇 |
2002年 | 110篇 |
2001年 | 35篇 |
2000年 | 17篇 |
1999年 | 27篇 |
1998年 | 20篇 |
1997年 | 27篇 |
1996年 | 49篇 |
1995年 | 27篇 |
1994年 | 37篇 |
1993年 | 31篇 |
1992年 | 25篇 |
1991年 | 27篇 |
1990年 | 21篇 |
1989年 | 14篇 |
1988年 | 19篇 |
1987年 | 17篇 |
1985年 | 29篇 |
1984年 | 22篇 |
1983年 | 26篇 |
1982年 | 24篇 |
1981年 | 24篇 |
1980年 | 36篇 |
1979年 | 30篇 |
1978年 | 20篇 |
1977年 | 9篇 |
1976年 | 15篇 |
1975年 | 13篇 |
1974年 | 9篇 |
1915年 | 9篇 |
排序方式: 共有2960条查询结果,搜索用时 0 毫秒
101.
Luigi Mondello 《Analytical and bioanalytical chemistry》2013,405(13):4589-4590
102.
The purpose of this work is to discuss a methodology for the interpretation of experimental data and its application, in the context of thermo-elasto-dynamics, to the investigation of the time dependence of variables, such as the resonance frequency of a consolidated granular sample, subjected to various protocols of varying temperature. An analytical equation is deduced, which fits extremely well the experimental curves and has the expected asymptotic behavior of the dependent variable. It also predicts the observed asymmetry in the response to the sign of the temperature variation. 相似文献
103.
104.
Christopher Lombardi Dr. Richard P. Rucker Dr. Robert D. J. Froese Dr. Sepideh Sharif Prof. Pier Alexandre Champagne Prof. Michael G. Organ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(62):14223-14229
The relative rates of arylation of primary alkylamines with different Pd-NHC catalysts have been measured, as have the relative rates of arylation of the secondary aniline product in an attempt to understand the key ligand design features necessary to have high selectivity for the monoarylated amine product. As the substituents on the N-aryl ring of the NHC increase in size, selectivity for monoarylation increases and this is further enhanced by chlorinating the back of the NHC ring. Computations have been performed on the catalytic cycle of this transformation in order to understand the selectivity obtained with the different catalysts. 相似文献
105.
Pier G. Desideri Luciano Lepri Roberto Udisti Leonardo Checchini Massimo Del Bubba Renato Cini 《International journal of environmental analytical chemistry》2013,93(3-4):331-351
Abstract Organic compounds extractable with n-hexane were identified and quantitatively determined in pack, surface and deep snow samples taken at different depths and collected at several altitudes above sea level from Antarctica during the 1993/94 Italian expedition. The comparison between the composition of organic compounds in snow and the ones in pack and sea-water samples pointed out that the three matrices substantially contain the same biogenic and anthropogenic organic compounds. The contribution of marine aerosol to organic content in the snow is confirmed by the enrichment ratios calculated for the more representative classes of identified compounds (n-alkanes, phthalates and low molecular weight alkylbenzenes). The changes in the composition of organic compounds in snow as the altitude increases seem to depend on the dimensional spectrum of the aerosol. Thus, smallest particles, richest in surfactant material, reach the highest altitudes. 相似文献
106.
107.
Giacomo Luigi Petretto Carlo Ignazio G. Tuberoso Gina Vlahopoulou Alessandro Atzei Alberto Mannu Saadia Zrira 《Natural product research》2016,30(3):286-292
Seven commercial Moroccan honeys were considered for chemical characterisation. Volatile fraction, total polyphenols content, antioxidant and antiradical activities were evaluated by employing different analytical methodologies. Several physical parameters such as refractive index, pH, water content, solids content and colour were measured. Volatile fraction revealed an abundant presence of cis- and trans-linalool oxide in the seven studied samples. The presence of high levels of compounds related to the Maillard reaction, like furfural and hydroxymethylfurfural, could be the result of thermal treatments used to liquefy commercial honeys or of long storage times. The CIE L*a*b*Cab*hab° chromatic coordinates confirmed the advanced stage of the Maillard reaction, showing L* values lower than the common values found for honey of similar typologies. 相似文献
108.
109.
Marina Russo Filomena Cichello Carla Ragonese Paola Donato Francesco Cacciola Paola Dugo Luigi Mondello 《Analytical and bioanalytical chemistry》2013,405(13):4617-4626
In this work, a high-performance liquid chromatography with evaporative light scattering detection method has been developed and applied for quantification of the polar content of the lipid fraction in milk samples of different origin. From a chromatographic stand-point, a 4.6-mm I.D. hydrophilic interaction liquid chromatography column was employed to attain a baseline separation of major phospholipid classes contained in the various milk samples tested. Quantitative analysis was performed by the external calibration method using reference material solutions in the 5–100 mg/L concentration range. Analytical recoveries ranging from 57 to 100 %, and repeatability data lower than 8.04 % were obtained on a skimmed cow’s milk sample. The crude cow milk was the most abundant (0.04 %) in phospholipids and donkey milk was the poorest (0.004 %). Quantitative differences were determined in the phospholipid content of the milk samples tested. Finally, characterization of phospholipid profile and fatty acid composition of the different samples was carried out by an ion trap-time of flight mass spectrometer and gas chromatography coupled to flame ionization and mass spectrometry detection. A thorough screening of the polar lipid composition of milk samples of different origin is here outlined, for the first time. 相似文献
110.
The synthesis of (±)10H-phenothiazine-10-propanoyl-1′-myo-inositol was accomplished in order to test it as inhibitor of phosphatidylinositol specfic phospholipase C (PI-PLC). 相似文献