全文获取类型
收费全文 | 426篇 |
免费 | 22篇 |
国内免费 | 9篇 |
专业分类
化学 | 268篇 |
晶体学 | 4篇 |
力学 | 31篇 |
数学 | 70篇 |
物理学 | 84篇 |
出版年
2023年 | 1篇 |
2022年 | 6篇 |
2021年 | 16篇 |
2020年 | 14篇 |
2019年 | 28篇 |
2018年 | 31篇 |
2017年 | 24篇 |
2016年 | 28篇 |
2015年 | 13篇 |
2014年 | 26篇 |
2013年 | 54篇 |
2012年 | 37篇 |
2011年 | 29篇 |
2010年 | 13篇 |
2009年 | 29篇 |
2008年 | 22篇 |
2007年 | 22篇 |
2006年 | 14篇 |
2005年 | 9篇 |
2004年 | 7篇 |
2003年 | 7篇 |
2002年 | 2篇 |
2001年 | 5篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1994年 | 1篇 |
1989年 | 2篇 |
1985年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1978年 | 4篇 |
1977年 | 2篇 |
1975年 | 1篇 |
1974年 | 2篇 |
排序方式: 共有457条查询结果,搜索用时 234 毫秒
101.
The chemical composition of a hydrodistilled oil of Stachys inflata Benth. growing wild in Iran was examined by GC/MS. Thirty-nine constituents were identified. The major components of the oil were germacrene-D (16.9%), bicyclogermacrene (16.6%), -pinene (11.3%), -phellandrene (9.8%), bicycloelemene (6.6%), -pinene (5.6%), and spathulenol (3.2%). 相似文献
102.
Shohreh Nafisi Fatemeh Ghoreyshi Kahangi Ebrahim Azizi Nader Zebarjad Heidar-Ali Tajmir-Riahi 《Journal of Molecular Structure》2007,830(1-3):182-187
Zanamivir (ZAN) is the first of a new generation of influenza virus-specific drugs known as neuraminidase inhibitors, which acts by interfering with life cycles of influenza viruses A and B. It prevents the virus spreading infection to other cells by blocking the neuraminidase enzyme present on the surface of the virus. The aim of this study was to examine the stability and structural features of calf thymus DNA and yeast RNA complexes with zanamivir in aqueous solution, using constant DNA or RNA concentration (12.5 mM) and various zanamivir/polynucleotide (P) ratios of 1/20, 1/10, 1/4, and 1/2. FTIR and UV–visible spectroscopy are used to determine the drug external binding modes, the binding constant and the stability of zanamivir–DNA and RNA complexes in aqueous solution. Structural analysis showed major interaction of zanamivir with G-C (major groove) and A-T (minor groove) base pairs and minor perturbations of the backbone PO2 group with overall binding constants of Kzanamivir–DNA = 1.30 × 104 M−1 and Kzanamivir–RNA = 1.38 × 104 M−1. The drug interaction induces a partial B to A-DNA transition, while RNA remains in A-conformation. 相似文献
103.
A. J. Blotcky F. G. Hamel A. Stranik A. Ebrahim R. B. Sharma E. P. Rack S. S. Solomon 《Journal of Radioanalytical and Nuclear Chemistry》1989,131(2):319-329
A method is described for determination of vanadium in biological tissues. This method consists of a wet digestion of the tissue with nitric acid followed by anion exchange chromatography, neutron irradiation, and radioassay. The chromatographic separation will allow the decontamination of vanadium from radioactivatable sodium and chlorine which are present in large quantities in biological tissues. The validity of the method is evaluated by employing NBS-SRM 157 and 157a Bovine Liver employing the method of standard additions. The method is successfully applied to human, cow and rat liver specimens. The detection limit of the method is one ppb. 相似文献
104.
A. A. El-Shazly M. M. H. El-Naby M. A. Kenawy M. M. El-Nahass H. T. El-Shair A. M. Ebrahim 《Applied Physics A: Materials Science & Processing》1985,36(1):51-53
Ternary ZnSxSe1–x polycrystalline thin films were prepared by evaporation in vacuum of 10–5 Torr. The molecular fractionx varied in the region ox1. The optical constants (the refractive indexn, the absorption indexk, and the absorption coefficient) were determined in the wavelength range 300–1600nm. A plot representing
2=f(hv) shows that the ZnSxSe1–x polycrystalline thin films of different compositions have two direct transitions corresponding to the energy gapsE andE+. The variation in eitherE orE+ withx indicates that this system belongs to the amalgamation type. Such variation follows a quadratic equation. The bowing parameter was found to be 0.456 eV, roughly equal to the calculated value 0.60 eV using the empirical pseudopotential method based on the virtual-crystal approximation, in which the disorder effect has not been taken into account. 相似文献
105.
A highly selective and sensitive anodic stripping differential pulse polarographic method has been developed for the determination of trace amount of bismuth in various samples after adsorption of its 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol complex on amberlite XAD-2 resin in the pH range of 2.0-3.0. The retained analyte on the resin recovered with 10.0 ml of 2 M hydrochloric acid and bismuth is determined by anodic stripping differential pulse polarography. In this case, 0.15 μg of bismuth can be concentrated in the column from 1100 ml of aqueous sample, where its concentration is as low as 0.14 ng ml−1 and the linearity is maintained in the concentration range 0.05-160 μg ml−1 in final solution with a correlation coefficient of 0.999 and relative standard deviation of ±1.2%. Various parameters such as the effect of pH, flow rate, and interference of number of metal ions on the determination of bismuth have been studied in detail to optimize the conditions for determination of bismuth in standard alloys: Nippon Keikinzoku Kogyo (NKK CRM No. 916 aluminum alloy); (NKK CRM No. 1021 Al, Si, Cu, Zn alloy); and (NKK CRM No. 920 aluminum alloy), biological samples: National Institute for Environmental Studies (NIES, No. 5 human hair; NIES, No. 7 tea leaves) and water samples: (spring water, river water; Kerman water; and Shiraz water). 相似文献
106.
An efficient one-pot synthesis of tetrahydrobenzo[b]pyran is described. This involved the three-component reaction of aromatic aldehydes, molononitrile, and dimedone in the presence of a catalytic amount of Caro's acid supported on silica gel in ethanol/water under reflux. 相似文献
107.
Structural Chemistry - Acidity changes of p-aminobenzoic acid (pABA) after π-stacking with substituted benzenes (SB) have been investigated using quantum mechanical calculations at the... 相似文献
108.
109.
Ebrahim Karkhaneei Mohammad Hasan Zebarjadian Mojtaba Shamsipur 《Journal of solution chemistry》2001,30(4):323-333
[7Li] NMR measurements were used to determine the stoichiometry and stability of Li+ complexes with 18-crown-6 and dicyclohexyl-18-crown-6 in nitromethane and acetonitrile solutions. A competitive [7Li] NMR technique was also employed to probe the complexation of Ba2+, Pb2+, Cd2+, and UO22+ ions with the same crown ethers–solvent systems. All the resulting 1 : 1 complexes were more stable in nitromethane than acetonitrile solution. In all cases, the stability of both crown complexes in nitromethane and acetonitrile varied in the order Pb2+ > Ba2+ > Li+ > Cd2+ > UO22+. 相似文献
110.
Substituted 5-Antipyrinylazo-4-phenyl-2-aminothiazoles as Disperse Dyes for Dyeing Polyester Fabrics
Mohamed A. Metwally Amira Metwally Ebrahim Abdel-Galil Fathy A. Amer 《Monatshefte für Chemie / Chemical Monthly》2008,139(1):35-42
Summary. A series of some new substituted 5-antipyrinylazo-4-phenyl-2-aminothiazole disperse dyes was synthesized by diazocoupling
of 4-antipyrinyldiazonium chloride with aminothiazole derivatives. The synthesized dyes were characterized by UV-Vis absorption,
IR, 1H NMR, and MS spectroscopy. The dyes gave orange to reddish-violet shades with very good depth and levelness when applied
to polyester fabrics as disperse dyes and their fastness properties were evaluated on polyester fibers. Also the position
of color in CIELAB coordinates (L*, a*, b*, H*, and C*) was assessed. 相似文献