全文获取类型
收费全文 | 2164篇 |
免费 | 110篇 |
国内免费 | 17篇 |
专业分类
化学 | 1646篇 |
晶体学 | 11篇 |
力学 | 33篇 |
综合类 | 16篇 |
数学 | 240篇 |
物理学 | 345篇 |
出版年
2023年 | 18篇 |
2022年 | 12篇 |
2021年 | 36篇 |
2020年 | 44篇 |
2019年 | 57篇 |
2018年 | 38篇 |
2017年 | 25篇 |
2016年 | 57篇 |
2015年 | 52篇 |
2014年 | 59篇 |
2013年 | 119篇 |
2012年 | 149篇 |
2011年 | 154篇 |
2010年 | 78篇 |
2009年 | 102篇 |
2008年 | 162篇 |
2007年 | 144篇 |
2006年 | 132篇 |
2005年 | 146篇 |
2004年 | 122篇 |
2003年 | 85篇 |
2002年 | 98篇 |
2001年 | 25篇 |
2000年 | 32篇 |
1999年 | 22篇 |
1998年 | 26篇 |
1997年 | 23篇 |
1996年 | 20篇 |
1995年 | 9篇 |
1994年 | 12篇 |
1993年 | 11篇 |
1992年 | 8篇 |
1991年 | 8篇 |
1990年 | 16篇 |
1989年 | 12篇 |
1988年 | 11篇 |
1987年 | 9篇 |
1986年 | 6篇 |
1985年 | 20篇 |
1984年 | 14篇 |
1983年 | 13篇 |
1982年 | 16篇 |
1981年 | 17篇 |
1980年 | 16篇 |
1979年 | 14篇 |
1978年 | 8篇 |
1977年 | 8篇 |
1976年 | 6篇 |
1975年 | 4篇 |
1974年 | 5篇 |
排序方式: 共有2291条查询结果,搜索用时 15 毫秒
51.
The structure of gilmicolin and mycorrhizinol, two new metabolites isolated from culture filtrates of Gilmaniella humicola BARRON , have been shown to be 3 and 15 respectively by spectral and chemical studies. The X-ray analysis of gilmicolin ( 3 ) is also reported. 相似文献
52.
[reaction: see text] A gram-scale approach toward (-)-epibatidine (1, naturally occurring enantiomer), a novel class of amphibian alkaloid, has been developed from readily available starting materials using mild and easily controlled reactions. The entire synthetic route is straightforward and convenient for gram-scale synthesis. 相似文献
53.
Hosoya K Hira N Watabe Y Tanaka N Kubo T Kaya K 《Analytical and bioanalytical chemistry》2004,380(2):343-345
Thiacalix[4]arene (5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrahydroxy-2,8,14,20-tetrathiacalix[4]arene) is an amphiphilic molecule comprising four p-tert-butylphenol-like groups ortho-linked by single sulfur atoms. This molecule has a high electron density area owing to the close proximity of the hydroxyl groups and sulfur atoms. We studied the applicability of this interesting compound as a selector for high-performance liquid chromatography (HPLC) thereby presumably exploiting this feature. Firstly, uniformly sized polymer particles were prepared by using a multi-step swelling and polymerization method with ethylene glycol dimethacrylate (EDMA) as a cross-linker. Methacrylic acid (MAA) was introduced onto the surface of the resulting polymer particles through a new modification method. Thiacalix[4]arene was chemically bonded through the MAA group by using 1,4-dibromobutane as a spacer to reduce steric hindrance around the MAA and the polymer particle itself. The performance of the prepared polymer-based thiacalix[4]arene-modified stationary phase was evaluated with HPLC. Specific chromatographic retention behavior was observed for catechol relative to positional isomers of xylene, cresol, and benzene-diol. Catecholamine and catechol showed specific chromatographic retention behavior. 相似文献
54.
[reaction: see text] A bridged N,N-di(aryl)-1,2,4,5-benzenediimide was synthesized in which restricted rotation led to two diasteriomeric conformations at room temperature. The more stable syn-macrocycle is achiral, whereas the strained anti-macrocycle possesses planar chirality similar to that of trans-cyclooctene. The structure was characterized by X-ray crystallography, and the enantiomers were resolved by chiral chromatography. 相似文献
55.
Muranaka A Okuda M Kobayashi N Somers K Ceulemans A 《Journal of the American Chemical Society》2004,126(14):4596-4604
Oxo-titanium phthalocyanine (TiOPc) derivatives of catechin and hematoxylin (natural ortho-diol type chiral compounds) have been prepared and characterized by spectral and chromatographic techniques. It is demonstrated that the TiOPc unit is an excellent template for chiral recognition through its isolated Q-transitions. The formation of a helical dimeric complex with hematoxylin induces strong CD-activity in the Q-band region. Ab initio geometry optimizations were combined with a Kuhn-Kirkwood coupled-oscillator mechanism to obtain the absolute configuration of hematoxylin. In addition, it is shown that the described chiroptical recognition method is sensitive to slight conformational changes. 相似文献
56.
The structure and configuration of gilmaniellin, a metabolite of Gilmaniella humicola BARRON , has been shown to be 2 by X-ray analysis. By comparison of spectral data structure 1 has been assigned to dechlorogilmaniellin. 相似文献
57.
Ken Ohwada 《Polyhedron》1983,2(5):423-424
It is shown that the Pauling electronegativity scale χ is closely related to the electrostatic potential near the physical meaningful boundary between the core and valence regions in an atom, and is well reproduced by the relationship: where Nν is the valence electron number and the factor f(n) is empirically given by n being the periodic number. 相似文献
58.
A simple and automated methodology for a sensitive electrochemical detection of enzyme immunoassays that employ alkaline phosphatase (AP) as label has been developed. A flow injection system with programmable pump, valve and cell functions, amperometric detection of indigo and screen-printed electrodes (SPEs) are responsible for the advantages of this methodology. Amperometric detection at a low potential of indigo, the product of the enzymatic hydrolysis of the substrate 3-indoxyl phosphate (IP), is combined with a flow injection system. This incorporates in the flow cell a disposable screen-printed board provided with a graphite working electrode. No electrode pretreatment is necessary to obtain reproducible signals. The system was applied to the determination by an enzyme-linked immunosorbent assays (ELISA) of pneumolysin (PLY), a toxin related to respiratory infections. Linear calibration curves for low and high concentration ranges were obtained. These were also performed in a proteic matrix and linearity was also obtained. 相似文献
59.
The assembly strategy to prepare a monolayer of bovine serum albumin on the surface of silica gel supported gold nanoparticles is described. The stereo‐specific recognition ability of this material was evaluated by enantioresolution of Dansyl‐norvaline. For enantiomeric separation, the influences of buffer concentration and the concentration of organic modifier on the separation performance were investigated. A better separation in terms of enantioresolution and peak shape was found with the phosphate concentration at 30 mM. Moreover, the peak shape and resolution can be improved by the addition of methanol solution. Enantioresolution of Dansyl‐norvaline was obtained from this material at optimized conditions. It appears that the immobilization of a monolayer of bovine serum albumin on gold nanoparticles as the chiral selector of Dansyl‐derivative amino acid is promising. 相似文献
60.
The standardization of EDTA solution against metallic copper as primary standard is studied. Six indicators were examined; titration with PAN as indicator at pH 6 is recommended. 相似文献