全文获取类型
收费全文 | 101698篇 |
免费 | 24566篇 |
国内免费 | 6786篇 |
专业分类
化学 | 80030篇 |
晶体学 | 558篇 |
力学 | 3236篇 |
综合类 | 427篇 |
数学 | 5859篇 |
物理学 | 15863篇 |
综合类 | 27077篇 |
出版年
2024年 | 598篇 |
2023年 | 4808篇 |
2022年 | 3022篇 |
2021年 | 4165篇 |
2020年 | 6218篇 |
2019年 | 3790篇 |
2018年 | 3699篇 |
2017年 | 2053篇 |
2016年 | 7519篇 |
2015年 | 7774篇 |
2014年 | 7909篇 |
2013年 | 8711篇 |
2012年 | 7467篇 |
2011年 | 5647篇 |
2010年 | 6917篇 |
2009年 | 6908篇 |
2008年 | 5107篇 |
2007年 | 4584篇 |
2006年 | 3782篇 |
2005年 | 3314篇 |
2004年 | 2882篇 |
2003年 | 2573篇 |
2002年 | 3030篇 |
2001年 | 2529篇 |
2000年 | 1948篇 |
1999年 | 1958篇 |
1998年 | 1521篇 |
1997年 | 1489篇 |
1996年 | 1273篇 |
1995年 | 1190篇 |
1994年 | 1017篇 |
1993年 | 986篇 |
1992年 | 775篇 |
1991年 | 701篇 |
1990年 | 573篇 |
1989年 | 565篇 |
1988年 | 439篇 |
1987年 | 329篇 |
1986年 | 223篇 |
1985年 | 172篇 |
1980年 | 124篇 |
1977年 | 173篇 |
1976年 | 192篇 |
1975年 | 197篇 |
1974年 | 201篇 |
1972年 | 161篇 |
1971年 | 126篇 |
1970年 | 211篇 |
1969年 | 125篇 |
1968年 | 135篇 |
排序方式: 共有10000条查询结果,搜索用时 17 毫秒
991.
Jing XU Lan Hua ZHAO Xin Guo WU Hong Mei WANG Ru Xiu CAI College of Chemistry Molecular Science Wuhan University Wuhan Stuff of Chemistry Yunyang Medical College Shiyan College of Resources Environmental Science Wuhan University Wuhan 《中国化学快报》2006,17(7):949-952
Quantification of free radical formation is critical for evaluation and interpretation of many radical-mediated biological processes1-4. Numerous studies have been devoted to the determination of free radicals, but the most of the reports have been focuse… 相似文献
992.
Gejihu De Weiping Qin Jisen Zhang Yan Wang Chunyan Cao Yang Cui 《Journal of solid state chemistry》2006,179(3):955-958
In this work, we used the hydrothermal method to synthesize Eu3+ ion-doped cubic BaF2 nanorods, which is a luminescent material. The clubbed structures were well crystallized and exhibited face-centred cubic structures, as indicated by powder X-ray diffraction, scanning electron microscopy, electron diffraction, and transmission electron microscopy. The luminescent properties were studied, and local symmetry surrounding Eu3+ ions and electronic transition processes included. The results indicated that Eu3+ occupied only one C4ν site in nanorods. 相似文献
993.
利用傅立叶变换红外(FT-IR)和拉曼(FT-Raman)光谱研究了高浓度磷脂酰胆碱(PC)与牛血清白蛋白(BSA)的相互作用,及Eu3+对该作用的影响.FT-IR结果显示,PC/BSA混合体系中二者的相互作用主要发生在PC头部极性基团,且这一作用随BSA含量的增加而增强,作用后蛋白质二级结构中α螺旋的比例有所增加. FT-Raman光谱说明PC与BSA的相互作用影响磷脂CH链的排列有序程度. PC/BSA/Eu3+体系的红外光谱显示, Eu3+与PC的磷氧键发生了强相互作用,并使蛋白α螺旋的比例进一步增加. 相似文献
994.
三正辛胺修饰电极伏安测定痕量金的研究 总被引:3,自引:0,他引:3
用化学修饰电极伏安测定痕量金,Kalcher K等曾采用阴离子交换剂碳糊修饰电极及打萨宗碳糊修饰电极检测100~300μg/L的金。本文采用三正辛胺(TOA)修饰玻碳电极,在1.5 mol/L介质中,Au(Ⅲ)在+0.16 V(vs SCE)处有一灵敏的不可逆还原峰。检出限为0.1μg/L。灵敏度比文献方法高千倍。Au(Ⅲ)浓度在5×10~(-7)~5×10~(-9)mol/L范围内峰高与浓度 相似文献
995.
The ESR signals of bilirubin-IXα were studied including the samples treated with free radical generating and inhibiting systems, i.e.X-X0., Fe/EDTA, SOD, mannitol/ascorbate, DTPA, KCN et al.These stable signals all comprise those originated from a semiquinone radical(g=2.0012)and superoxide radical(g11=2.041, g⊥=2.0040).The latter is shown to be bound with metal ionsespecially iron, chelated by bilirubin.The iron probably comes from bilirubin precursor---hemootobin.Active oxygen free radical scavengers may destroy these radicals.Kinetic curves of regeneration of the bilirubin radicals have been determined.Bilirubin is discussed as"active oxygen trap"in mammatians. 相似文献
996.
997.
Thermal analysis supported by kinetic calculations was applied exhaustively to these compounds. Under dynamic conditions, tetrafluorometallates(III), which as intermediates, could not be isolated, for the first three compounds. In each case, the final step was the pure metal(III) fluoride. Ammonium hexafluorochromate(III) decomposed directly to the pure chromium(III) fluoride. The decomposition rate of all compounds slowed down towards the end, probably for kinetic reasons. Polymorphic transitions of ammonium hexafluorotitanate(III) were observed at 35 and 100°C. Ammoniumhexafluoroscandate(III) underwent polymorphic transition at 47°C. The decomposition patterns for all these compounds were similar. Conditions for the preparation of pure ammonium tetrafluorometallates(III) of Sc, Ti and V are described. 相似文献
998.
The diffusion length of charge carriers in the active layer of a perovskite solar cell (PSC) of the structure Glass/PEDOT: PSS/CH3NH3PbI3/PC60BM/Al is modelled. It is found that the diffusion length depends on the position x in the active layer measured from the PEDOT: PSS interface, Urbach energy and temperature. By varying the voltage in the range from zero to , it is shown that the dependence of diffusion length on the position x in the active layer reduces at higher voltage. The combined influence of applied voltage and temperature on the diffusion length of charge carriers is investigated and it is found that in the low voltage range the diffusion length is temperature independent, but it becomes significantly temperature dependent at higher voltages. Also, it is found that the diffusion length decreases as the applied voltage increases and this reduction becomes much more significant at higher voltage and temperatures. The combined influence of applied voltage and Urbach energy on diffusion length of charge carriers reveals that the diffusion length decreases when both the applied voltage and Urbach energy increase. However, the reduction in the diffusion length due to the increase in Urbach energy becomes less significant at higher voltage. 相似文献
999.
Prof. I. G. Csizmadia Prof. M. C. Harrison Prof. B. T. Sutcliffe 《Theoretical chemistry accounts》1966,6(3):191-216
This paper (Part I) describes the theoretical and computational bases of some non-empirical calculations on small organic molecules to be reported in later papers (Parts II et seq). Approximate solutions for the usual fixed nucleus electronic Hamiltonian, in the term of wave functions composed of Slater determinants, are discussed, with particular emphasis on their computational utility. Possible choices of basis functions, from which to form the determinants are examined, and the advantages of Gaussian type functions (GTF) centered on the component atoms are pointed out. Some of the properties of molecules which can be calculated using such approximate wave functions are outlined. Finally an attempt is made to discuss the current limitations of non-empirical calculations of the type described here, and some guesses are made about their future. Brief outlines as a set of appendices are given of the mathematical formalism and computational details of the calculations. 相似文献
1000.
A simple and accurate RP-HPLC method using photodiode array detection (PAD) was developed for the simultaneous determination of four flavonoids, namely quercetin (QU),luteolin(LU),apigenin(AP) and isorhamnetin (IS) in pigeonpea leaves.Extract samples were separated on HIQ SIL C18V column using methanol-acetonitrile-water(31:10:59, v/v/v) as mobile phase.The flavonoids were detected at 254.5 nm for QU and IS, and at 345 nm for LU and AP.Contents were determined with satisfactory repeatability (R. S. D. < 2.2%) and recovery (97.27 – 99.98%). The developed method was found to be simple and efficient. 相似文献