全文获取类型
收费全文 | 6091篇 |
免费 | 1080篇 |
国内免费 | 587篇 |
专业分类
化学 | 6274篇 |
晶体学 | 26篇 |
力学 | 374篇 |
综合类 | 80篇 |
数学 | 224篇 |
物理学 | 780篇 |
出版年
2024年 | 5篇 |
2023年 | 114篇 |
2022年 | 119篇 |
2021年 | 325篇 |
2020年 | 352篇 |
2019年 | 270篇 |
2018年 | 258篇 |
2017年 | 207篇 |
2016年 | 517篇 |
2015年 | 472篇 |
2014年 | 475篇 |
2013年 | 655篇 |
2012年 | 497篇 |
2011年 | 361篇 |
2010年 | 237篇 |
2009年 | 257篇 |
2008年 | 237篇 |
2007年 | 326篇 |
2006年 | 282篇 |
2005年 | 240篇 |
2004年 | 254篇 |
2003年 | 202篇 |
2002年 | 138篇 |
2001年 | 141篇 |
2000年 | 96篇 |
1999年 | 91篇 |
1998年 | 55篇 |
1997年 | 76篇 |
1996年 | 93篇 |
1995年 | 56篇 |
1994年 | 61篇 |
1993年 | 40篇 |
1992年 | 48篇 |
1991年 | 38篇 |
1990年 | 31篇 |
1989年 | 26篇 |
1988年 | 24篇 |
1987年 | 14篇 |
1986年 | 11篇 |
1985年 | 15篇 |
1984年 | 14篇 |
1983年 | 7篇 |
1982年 | 15篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1957年 | 1篇 |
排序方式: 共有7758条查询结果,搜索用时 203 毫秒
101.
Summary The essential oils have been isolated from tobacco leaves using a simple gas co-distillation apparatus. The method involves co-distillation with water under the continuous stream of an inert gas with subsequent single solvent extraction of the distillate. The extract is analysed on GC and GC/MS in splitless injection mode without further concentration. The method was evaluated for reproducibility using n-octadecane as an internal standard. The distillation-extraction procedure was reporducible with an average deviation of ±3% for the major constituents. The present method was applied to the analyses of the essential oils of other agricultural products.Dedicated to Dr. L. S. Ettre on the occasion of his 60th birthday. 相似文献
102.
In this study we describe the activation with chloroformates of Trisacryl-GF-2000, a new synthetic gel support that is stable,
hydrophilic, and contains large amounts of hydroxyl groups available for activation.
Of all the reagents tested, the activation withN-hydroxysuccinimide-chloroformate andp-nitrophenylchloroformate in organic solvents provides the best activation yield and subsequent coupling. When Trisacryl was
activated in acetone with the chloroformates in the presence of 4-dimethylaminopyridine as base and catalyst, up to 30% of
the hydroxyl groups, (i.e., 1/repeating unit) could be activated. Amino-containing ligands and proteins could be coupled to
these carriers at pH 8 or higher. For better results in affinitychromatographic applications, spacers of ε-amino caproic acid
or diaminohexane were introduced. The efficacy of these columns was demonstrated by purification of enzymes, antibodies, and
antigens. The performance of these new columns were compared with that of Sepharose columns activated in various ways. In
every case, the properties of the Trisacryl support proved superior with particular reference to the purity of the product
obtained. 相似文献
104.
Structure determination of triglycerides according to their number of unsaturated fatty acids (N.U.F.A.) is more easily achieved after ozonolysis of their mixtures (fats and oils) than by capillary gas chromatographic analysis of the mixture as such. Analyses performed before and after ozonolysis of cocoa buttel, hazelnut oil, and a mixture of both fats illustrate the potential of this approach to the structure elucidation of triglycerides by chromatographic techniques. 相似文献
105.
The needle oil of the Algerian maritime pine (Pinus pinaster Ait.) growing in natural habitats in Sidi Feradj (Algiers region) was obtained by hydrodistillation in 0.3% yield and analyzed
by GC and GC/MS. More than 46 compounds amounting to 65.2% of the total oil were identified. The main components were β-caryophyllene
(26.6%), allo-aromadendrene (12.5%), and α-humulene (4.3%).
__________
Published in Kimiya Prirodnikh Soedinenii, No. 5, pp. 445–447, September–October, 2005. 相似文献
106.
The composition of the essential oil of Bifora radians, an aldehyde-producing weed, has been investigated by capillary gas chromatography, coupled gas chromatography – mass spectrometry, on-line catalytic hydrogenation and coupled gas chromatography – infrared spectrometry. The nineteen compounds identified included eighteen aldehydes: seven alkanals (C6, C9, C10, C11, C12, C13, and C14), ten alkenals, including five (E)-2-alkenals (C12, C13, C14, C15, and C16), and one (E,E)-2,4-alkadienal (C13). Typical Bifora odors were attributed to three major (E)-2-alkenals, C12, C13, and C14. 相似文献
107.
利用维生素A、D3、E均有电化学活性的特点,采用电化学安培检测,建立了HPLC检测奶粉中的脂溶性维生素A、D3、E的新方法.流动相为甲醇∶水=95∶5(V/V),含0.05 mol/L高氯酸钠.检测器采用玻碳电极,直流安培模式(DC),氧化电位 1.3 V.方法检测限为:VA、VD3、-αVE、-γVE、-δVE分别为0.08、2.3、0.16、0.19、0.28ng.回收率分别为:90.2%~98.2%、91.2%~103%、92.7%~99.5%、92.6%~97.4%、90.7%~98.0%.同紫外检测比较,方法具有灵敏度高、抗干扰强的特点. 相似文献
108.
Yoshihiko Kondo Ken Endo Nobuhiko Iki Sotaro Miyano Fumio Hamada 《Journal of inclusion phenomena and macrocyclic chemistry》2005,52(1-2):45-49
Even though it was obtained in poor yield, p-tert-butylthiacalix[8]arene (TC8A) has been synthesized as a new member of thiacalix[n]arenes by the terephthalate-induced cyclization of a mixture of acyclic oligomers, which was obtained by the reaction between p-tert-butylphenol and sulfur with CaO in ethylene glycol/diphenyl ether system. Slow evaporation of the chloroform solution of TC8A afforded guest-free crystals consisting of TC8A itself. The close-packed crystal structure of TC8A resembles that of p-tert-butylcalix[8]arene (C8A) closely, containing a plated loop molecular structure.This revised version was published online in July 2005 with a corrected issue number. 相似文献
109.
110.