全文获取类型
收费全文 | 3459篇 |
免费 | 280篇 |
国内免费 | 465篇 |
专业分类
化学 | 3830篇 |
晶体学 | 16篇 |
力学 | 24篇 |
综合类 | 30篇 |
数学 | 24篇 |
物理学 | 280篇 |
出版年
2024年 | 7篇 |
2023年 | 29篇 |
2022年 | 101篇 |
2021年 | 104篇 |
2020年 | 173篇 |
2019年 | 128篇 |
2018年 | 109篇 |
2017年 | 124篇 |
2016年 | 140篇 |
2015年 | 142篇 |
2014年 | 162篇 |
2013年 | 316篇 |
2012年 | 196篇 |
2011年 | 169篇 |
2010年 | 153篇 |
2009年 | 167篇 |
2008年 | 169篇 |
2007年 | 162篇 |
2006年 | 155篇 |
2005年 | 159篇 |
2004年 | 172篇 |
2003年 | 155篇 |
2002年 | 110篇 |
2001年 | 80篇 |
2000年 | 78篇 |
1999年 | 78篇 |
1998年 | 88篇 |
1997年 | 62篇 |
1996年 | 88篇 |
1995年 | 59篇 |
1994年 | 63篇 |
1993年 | 58篇 |
1992年 | 51篇 |
1991年 | 33篇 |
1990年 | 24篇 |
1989年 | 18篇 |
1988年 | 18篇 |
1987年 | 11篇 |
1986年 | 18篇 |
1985年 | 12篇 |
1984年 | 15篇 |
1983年 | 9篇 |
1982年 | 11篇 |
1981年 | 8篇 |
1980年 | 7篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1973年 | 2篇 |
1972年 | 1篇 |
排序方式: 共有4204条查询结果,搜索用时 15 毫秒
111.
By using the relationship equation of Partition coefficients with water solubilities for polycyclic aromatic hydrocarbons (PAHs), we have estimated the solubilities of PAHs. In addition the high-performance liquid chromatograph (HPLC) method has been used for the indirect determination of solubilities of PAHs. t3ased on the di-region theory, We have studied the relationship of the solubilities of PAHs with carcinogenicity and introduced the solubility parameter into the di-region theory equation. The calculated carcinogenicity of PAHs from the obtained equation shows little difference from that calculated from Dai Qianhuan's equation. 相似文献
112.
Helicenes form a subclass of polyhexes and correspond to hydrocarbons of considerable chemical interest. This paper is the first part of a general graph-theoretical treatment of helicenes. The invariants are studied: the relations between them, their possible values, and their upper and lower bounds in helicenes. Extremal helicenes and circular helicenes are useful definitions of subclasses of the systems under consideration. Finally an account of symmetry of helicenes is given.On leave from: Department of Mathematics, Xinjiang University, Wulumuqi Xinjiang 830046, People's Republic of China. 相似文献
113.
The crystalline morphology of a thermotropic aromatic polyester has been studied by microscopy techniques. Spherulites with ringed structure under polarizing micioscope were observed for solution cast specimens, They were composed of radially growing crystalline lamellae of thickness around 100. It was found that the molecules were packed in the thickness direction. Banded texture was observed in randomly packed domains for melt cast specimens. The bands have the same width and internal structure as those usually observed in oriented specimens of these polymers obtained by shearing their mesomorphic melt. 相似文献
114.
115.
C. André L. Ismaili M. Thomassin T. T. Truong B. Refouvelet Y. C. Guillaume 《Chromatographia》2003,58(3-4):165-170
Summary Lithium chloride (LiCl) effect on the retention process of a phenol derivative series was investigated on two types of fluorinated stationary phase (i.e. a silica grafted with fluorinated linear alkyl chain (L-FSP) and a silica grafted with fluorinated aromatic ring stationary phase (A-FSP)). The results showed that the solute retention is enhanced when the A-FSP was used instead of the L-FSP due to additional – interactions. For the two fluorinated stationary phases (FSPs), the phenol-FSP association process can be divided into two LiCl concentration domains demonstrated that it was important to take into account the adsorbtion of Cl– anion on the FSPs. As well, enthalpy-entropy compensation revealed that the solute retention mechanism was independent of the solute molecular structure and confirmed a change on the solute retention mechanism at a critical LiCl concentration value around 0.02M. 相似文献
116.
芳香酸淋洗液的单柱阳离子色谱法测定碱金属,铵离子和烷基胺 总被引:7,自引:0,他引:7
研究了邻苯二甲酸、苯甲酸和对羟基苯甲酸3种芳香酸分别做淋洗液的单柱阳离子色谱法分离测定Li+、Na+、NH4+、K+、甲胺、乙胺和正丙胺7种物质。3种芳香酸做淋洗液均可将7种物质分离开,且分离结果差异不大。在淋洗液浓度相同的条件下,邻苯二甲酸做淋洗液测定的检出限较低。选择3.0 mmol/L邻苯二甲酸做淋洗液测得了上述7种物质的检出限和线性范围,并进行了叶面肥试样分析,7种物质的加标回收率在96.4%~98.6%之间。 相似文献
117.
LING Daren LIU Bing WU Guoqi Department of Applied Chemistry Jiangsu Institute of Petrochemical Technology Changzhou China 《Chinese Journal of Reactive Polymers》2002,(1)
1. INTRODUCTION When investigating contaminated sites it is often essential to determine specific pollutants in a large number of ambient air samples. Amongst these sites, polycylic aromatic hydrocarbons (PAHs) are a major class of compounds that hav… 相似文献
118.
A. M. Churakov O. Yu. Smirnov S. L. Ioffe Yu. A. Strelenko V. A. Tartakovsky 《Russian Chemical Bulletin》1994,43(9):1532-1535
2-(tert-Butyl-NNO-azoxy)aniline was prepared by selective reduction of 2-(tert-butyl-NNO-azoxy)nitrobenzene. Its bromination yielded the correspondingpara-bromo- andortho, para-dibromoanilines (3a,b).meta-Bromoanilines (6a,b) were synthesized by selective replacement of theortho-bromine atoms in ortho,para-bromo(tert-butylazoxy)benzenes (5a,b) by ammonia in toluene under pressure.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1620–1623, September, 1994.This work was carried out with the financial support of the Russian Foundation for Basic Research (Project No. 93-03-18461). 相似文献
119.
本文报道用环加成-芳构化串连反应制备多取代芳香族化合物的方法。将1-氯-2-卤-3-苯硒基-1,3-丁二烯(5)与丁炔二酸二甲酯进行Diels-Alder反应时,能直接生成多取代的芳香族化合物4-苯硒基-5-卤代邻苯二甲酸二甲酯(4)。若用2-卤素-3-苯硒基-1,3-丁二烯(1)与丁炔二酸二甲酯进行Diels-Alder反应,只得到正常的加成产物4-苯硒基-5-卤素-1,4-环己二烯-1,2-二甲酸二甲酯(3),需再用DDQ处理,才得到多取代芳香族化合物(4)。 相似文献
120.
An oxidation method (sulfone method) for the determination of polycyclic aromatic sulfur heterocycles (PASH) in diesel fuel is presented. The aromatic fraction of a diesel fuel, isolated by solid phase extraction, is oxidized under controlled conditions with hydrogen peroxide. The oxidation products, mainly methylated dibenzosulfone, are determined and quantified directly, without further clean-up, by HPLC with photodiode-array detection. 相似文献