全文获取类型
收费全文 | 9894篇 |
免费 | 1492篇 |
国内免费 | 1184篇 |
专业分类
化学 | 7006篇 |
晶体学 | 94篇 |
力学 | 463篇 |
综合类 | 113篇 |
数学 | 1132篇 |
物理学 | 3762篇 |
出版年
2024年 | 26篇 |
2023年 | 208篇 |
2022年 | 355篇 |
2021年 | 354篇 |
2020年 | 410篇 |
2019年 | 389篇 |
2018年 | 330篇 |
2017年 | 320篇 |
2016年 | 469篇 |
2015年 | 458篇 |
2014年 | 581篇 |
2013年 | 702篇 |
2012年 | 873篇 |
2011年 | 851篇 |
2010年 | 567篇 |
2009年 | 525篇 |
2008年 | 639篇 |
2007年 | 619篇 |
2006年 | 521篇 |
2005年 | 468篇 |
2004年 | 319篇 |
2003年 | 275篇 |
2002年 | 252篇 |
2001年 | 228篇 |
2000年 | 232篇 |
1999年 | 198篇 |
1998年 | 206篇 |
1997年 | 159篇 |
1996年 | 175篇 |
1995年 | 163篇 |
1994年 | 124篇 |
1993年 | 107篇 |
1992年 | 82篇 |
1991年 | 64篇 |
1990年 | 65篇 |
1989年 | 41篇 |
1988年 | 41篇 |
1987年 | 32篇 |
1986年 | 26篇 |
1985年 | 36篇 |
1984年 | 15篇 |
1983年 | 14篇 |
1982年 | 15篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1962年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
911.
Huaifen?Li Tao?Xie Lingling?Ye Yanwei?Wang Chenggen?XieEmail author 《Mikrochimica acta》2017,184(4):1011-1019
The authors report on a surface molecular imprinting strategy for synthesizing magnetic and molecularly imprinted core-shell polymer nanoparticles (MMIPs) with a typical size of 320 nm. The triazophos-imprinted polymer shell on 180-nm magnetite particles (modified with 3-methacryloxypropyl trimethoxysilane) was obtained by radical polymerization of ethylene glycol dimethacrylate in the presence of triazophos, this followed by extractive removal of triazophos. The resulting MMIPs possess large binding capacity, high recognition selectivity, and fast binding kinetics for triazophos. They can be easily separated from a solution by using a magnet. These features result in a convenient and selective solid-phase extraction procedure for triazophos prior to its determination by UV spectrometry or by GC analysis. The method was successfully applied to the extraction and clean-up of triazophos residues in spiked homogenates of vegetables with recoveries in the range of 89.2 ~ 99.0%. The detection limits for triazophos by the UV assay and GC assay are 0.93 nM and 0.32 nM, respectively. 相似文献
912.
In this paper, we wish to report an environment friendly synthetic method for β-ketothioesters from a dodecylbenzenesulfonic acid (DBSA)-catalyzed hydrolysis reaction of chain α-oxo ketene dithioacetals in water. It was shown that the hydrolysis reaction of chain α-oxo ketene dithioacetals could efficiently occur in the presence of 7.5?mol% DBSA at 100?°C in water, affording the desired β-keto thioesters in excellent yields. 相似文献
913.
Jie Ren Chao Fan Yi-Gong Guo Shi-Kai Yan Richard D. Ye Yan Zhang Hui-Zi Jin Wei-Dong Zhang 《Tetrahedron》2017,73(12):1611-1617
A phytochemical investigation of the whole plant of Liparis regnieri Finet led to the isolation of one new biphenantherene (1) and ten new nervogenic acid derivatives (2–11), together with nine known compounds. Their structures were elucidated mainly by extensive analyses of 1D and 2D NMR spectroscopic data and chemical reactions. Additionally, for the first time a previously unreported biphenantherene was discovered to effectively suppress TNF-α induced expression of NF-κB-Luc in Hela cells with the IC50 value of 1.80 μM and the structure-activity relationshipwas also discussed. 相似文献
914.
He Yanfang Niu Xiangheng Shi Libo Zhao Hongli Li Xin Zhang Wenchi Pan Jianming Zhang Xifeng Yan Yongsheng Lan Minbo 《Mikrochimica acta》2017,184(7):2181-2189
Microchimica Acta - The authors describe a photometric method for the determination of free cholesterol based on the oxidation of cholesterol by the catalytic action of the enzyme... 相似文献
915.
Wang Jia Liu Yuan Deng Xiling Zhao Na Ying Xue Ye Bang-Ce Li Yingchun 《Mikrochimica acta》2017,184(10):3893-3900
Microchimica Acta - The authors describe an electrochemical sensor for ultrasensitive voltammetric of histamine (HA) by using a gold electrode that was modified with a film consisting of... 相似文献
916.
Double Michael addition of nitromethane to divinyl ketones: A remarkably positive effect of additive
Yongqi Yao Yingying Liu Ling Ye Feng Chen Xinying Li Zhigang Zhao Xuefeng Li 《Tetrahedron》2017,73(16):2311-2315
An efficient double Michael addition of nitromethane to divinyl ketones was established in good to high yields (75–99%). A wide range of cyclohexanones were obtained with excellent diastereocontrol (up to >20:1 dr) and enantioinduction (91–99% ee) in a one-pot fashion. The involvement of basic additive significantly enhanced the reactivity of this cascade sequence. 相似文献
917.
Shuai Zong Lan Li Jinglei Li Farnaz Shaikh Liu Yang Ming Ye 《Applied biochemistry and biotechnology》2017,182(2):669-686
In the present study, an intracellular melanin, named LIM205, was separated from Lachnum YM205 mycelia and was purified on a Sephadex G-15 column. The molecular weight of LIM205 was determined as 522 Da, and its molecular formula was speculated as C28H14N2O7S. The possible chemical structure of LIM205 was determined according to the results of Fourier transform infrared (FT-IR), 1H NMR, 13C NMR, and pyrolysis/GC-MS analysis. With the aim to increase its water solubility, its carboxymethylated derivative, named CLIM205, was formed by the substitution of hydrogen atoms in LIM205 with one, two, and three carboxymethylate groups. FT-IR, UV, and ESI-MS analysis demonstrated that the carboxymethylate groups were conjugated onto LIM205. The lead detoxification activities of LIM205 and CLIM205 had also been investigated. In vivo test showed that both LIM205 and CLIM205 reduced the tissue lead concentration, enhanced lead excretion, and reversed lead-induced alterations in superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and malondialdehyde (MDA) concentrations in mice, with CLIM205 showed better efficacy. The study indicates that LIM205 and CLIM205 have significant lead detoxification effect which will contribute to solve related problems. 相似文献
918.
Reaction of 1,2‐di(thiophen‐2‐yl)ethane‐1,2‐dione and (1R,2R)‐(−)‐diaminocyclohexane afforded a homochiral quinoxaline derivative (4aR,8aR)‐2,3‐di(thiophen‐2‐yl)‐decahydroquinoxaline ( 1 ). Fluorescent analysis exhibits an intense blue emission band at 386 nm. Crystallographic analysis showed that it belongs to chiral space group P21 with ferroelectric behavior, and a typical ferroelectric feature of electric hysteresis loop was obtained. The dielectric constant of compound 1 was measured at room temperature. 相似文献
919.
<正>A high-performance capillary electrophoresis with amperometric detection(CE-AD) method has been developed for the analysis of seven bioactive ingredients,namely ferulic acid(FA),vanillin,vanillic acid,p-hydroxybenzoic acid,caffeic acid,gallic acid and protocatechuic acid,in Rhizoma Chuanxiong.The effects of several factors such as the acidity and concentration of running buffer,the separation voltage,the applied potential to working electrode and the injection time were investigated.Under the optimum conditions,the seven analytes could be well separated within 21 min at the separation voltage of 16 kV in a 60 mmol/L borax running buffer(pH 8.7).A 300μm diameter carbon disk electrode has a good response at potential of +950 mV(vs.SCE) for all analytes.Good linear relationship was established over three orders of magnitude with detection limits(S/N = 3) ranged from 3.3×10~(-7) to 6.7×10~(-9)g/mL.This proposed method has been successfully applied for the determination and comparison of different batches of Rhizoma Chuanxiong samples based on their characteristic electrochemical profiles. 相似文献
920.