全文获取类型
收费全文 | 4484篇 |
免费 | 821篇 |
国内免费 | 493篇 |
专业分类
化学 | 3358篇 |
晶体学 | 40篇 |
力学 | 219篇 |
综合类 | 44篇 |
数学 | 483篇 |
物理学 | 1654篇 |
出版年
2024年 | 13篇 |
2023年 | 75篇 |
2022年 | 161篇 |
2021年 | 130篇 |
2020年 | 178篇 |
2019年 | 196篇 |
2018年 | 155篇 |
2017年 | 132篇 |
2016年 | 248篇 |
2015年 | 208篇 |
2014年 | 271篇 |
2013年 | 306篇 |
2012年 | 374篇 |
2011年 | 368篇 |
2010年 | 272篇 |
2009年 | 291篇 |
2008年 | 307篇 |
2007年 | 268篇 |
2006年 | 254篇 |
2005年 | 223篇 |
2004年 | 163篇 |
2003年 | 143篇 |
2002年 | 181篇 |
2001年 | 152篇 |
2000年 | 92篇 |
1999年 | 103篇 |
1998年 | 64篇 |
1997年 | 61篇 |
1996年 | 70篇 |
1995年 | 43篇 |
1994年 | 56篇 |
1993年 | 32篇 |
1992年 | 20篇 |
1991年 | 42篇 |
1990年 | 37篇 |
1989年 | 29篇 |
1988年 | 12篇 |
1987年 | 12篇 |
1986年 | 11篇 |
1985年 | 19篇 |
1984年 | 6篇 |
1983年 | 6篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1970年 | 1篇 |
1966年 | 1篇 |
1964年 | 1篇 |
1962年 | 1篇 |
1959年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有5798条查询结果,搜索用时 15 毫秒
71.
The successful separation of 2- and 3-methyl-substituted positional isomers of butanol, butyl acetate, and butanoic acid and its ethyl ester, is reported. These compounds are of interest in the study of wine flavour, however the separation of the 2- and 3-methyl isomers may present problems, and more so in the presence of the wine matrix components, when single capillary column gas chromatography (GC) is used. The strategy to achieve separation was based on the use of shape-selective cyclodextrin derivative (CDD) capillary columns (commonly referred to as chiral columns). These columns provide simultaneous resolution of the enantiomeric pairs of the 2-methyl isomers, and at the same time the ability to separate the 3-methyl isomer from the 2-methyl is achieved in all but the case of the ( S)-2- and 3-methylbutanol. The advantages of using shape-selective columns to perform this study is demonstrated, with coupling of two CDD columns giving improved separations of these compounds. Although these compounds are relatively volatile, cryogenic modulated comprehensive two-dimensional GC was shown to provide good pulsed peak profiles with chiral separation in the first dimension when a thicker film trapping column segment was employed. The components of interest were well separated from other wine matrix components. 相似文献
72.
ZheMingNI WeiHuaYU ShaoFenZHAO ZhongHuaGE 《中国化学快报》2004,15(8):989-992
Magnesium aluminium hydrotalcite (Mg-Al-HT) with molar ratio of Mg-to-Al of 3 to 1 was prepared and characterized by X-ray diffraction (XRD) and infrared spectra (IR). The performances of Mg-Al-HT for the adsorption and desorption of NOx were studied. The results indicated that the adsorption capacity of the hydrotalcite for NOx was 1398.2mg/g, and it was higher than the acticarbon‘s. The adsorption capacities depended on adsorption time and temperature.Mg-Al-HT could be regenerated by thermal decomposition, and the adsorption efficiency had not changed markedly after three cycles. 相似文献
73.
The anodic reaction of Ni in an alkaline solution was studied by the tip–substrate voltammetry mode of scanning electrochemical microscopy (SECM) and cyclic voltammetry (CV). A platinum microdisc electrode was selected as the tip electrode, which functioned as a pH sensor with transient response capability. The pH value of the solution near the Ni electrode surface varied while the Ni substrate oxidation reaction occurred, and the pH variation could be detected by the tip faradic current. The cyclic voltammogram results showed that two types of hydroxides: i.e. α‐Ni(OH)2 and β‐Ni(OH)2 were formed during Ni oxidation in the lower potential region. In the proceedings of α‐Ni(OH)2 → γ‐NiOOH and β‐Ni(OH)2 → β‐NiOOH, the process of OH? concentration decrease in the solution was ahead and behind of electron transfer in the solid phase, respectively. These results indicate that the OH? adsorption process occurs as an elementary step in the former reaction and the H+ diffusion process from the inner to the outer layer of the solid phase occurs as a subsequent step in the latter reaction. The results also revealed that the oxide film on the Ni surface has a two‐layer structure. The real potential of the oxygen evolution reaction (OER) on the Ni surface with different cycles is also analyzed in the paper. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
74.
本文用P204-兰113A-煤油组成的滤膜体系处理钒(Ⅳ)的溶液,并考察了表面活性剂、载体、外相pH值、内相酸度、起始钒(Ⅳ)浓度以及乳水比等因素对分离的影响。 相似文献
75.
76.
某些分子光谱分析法测定核酸的进展 总被引:36,自引:3,他引:36
对近年来利用分光光度法、荧光法和共振光散射法定量测定核酸的现状进行了评述,表中列出了重要的反应体系及分析特征,引用文献77篇。 相似文献
77.
LBL分子沉积法制备葡萄糖氧化酶电极 总被引:1,自引:0,他引:1
采用以静电力为主的逐层分子交替沉积技术制备葡萄糖氧化酶(GOD)电极.通过带有正电荷的聚二甲基二烯丙基铵盐酸盐(PDDA)和带有负电荷的GOD交替沉积在修饰有3-巯基-1-丙基磺酸钠(MPS)的金电极表面.以甲酸二茂铁为电子媒介体,用循环伏安法检测GOD电极对葡萄糖的响应.结果表明,当GOD电极组装层数小于4时,电流响应随着层数的增加而增大,超过4层时电流响应减小.其中4层GOD修饰电极的线性范围为0.55~6.63 mmol•L-1,当pH为7.0时,响应最大.同时电极的检测重现性能良好,相对标准偏差为2.4%. 相似文献
78.
Li Yan Liang Shao Ping Ren Yi Quan Zheng Man Geng Lu Guangzhou Institute of Chemistry Chinese Academy of Sciences Guangzhou China Key Laboratory of Polymer Materials for Electronics Guangdong China Graduate School of the Chinese Academy of Sciences Beijing China 《中国化学快报》2007,18(2):225-228
A series of novel liquid crystalline epoxides with lateral substituents were cured with anhydrides and the cure kinetics was investigated by non-isothermal DSC technique. The results showed that the lengths of lateral substituents have great effect on the value of Ea. The curing reaction became less active, when the liquid crystalline epoxides have long lateral substituents and were controlled by diffusion at the late stage of cure. A nematic structure was observed by POM and XRD. 相似文献
79.
The three new lignanoids 1 – 3 and the five new phyllocladane diterpenoids 7 – 11 were isolated from the leaves of Callicarpa furfuraceae, together with two known lignanoids, lariciresinol ( 4 ) and (+)‐sesamin ( 5 ), and five known diterpenoids, 17‐norphyllocladane‐3,16‐dion ( 6 ), calliterpenone ( 12 ), calliterpenone 17‐acetate ( 13 ), (3β,16α)‐phyllocladane‐3,16,17‐triol ( 14 ), and (3β,16α)‐phyllocladane‐3,16,17‐triol 17‐acetate ( 15 ). Their structures were established by spectral‐data interpretation. 相似文献
80.
This paper describes the design and synthesis of a family of pore-forming amphiphiles. Two of these amphiphiles, which are derived from cholic acid, lysine, and p-phenylenediamine, can produce pores in lipid bilayers as individual molecules. In sharp contrast, analogous amphiphiles that do not contain a rigid 1,4-phenylenediamide moiety favor the formation of dimer-based pores. Kinetic evidence in support of monomer- and dimer-based pores has been obtained from Na+ transport measurements across bilayers made from 1-palmitoyl-2-oleoyl-2-sn-glycero-3-phosphocholine (POPC). Structure-activity studies that have been carried out with pore-forming, dimer-based amphiphiles have also revealed a significant activity dependence on their overall compactness. The practical potential of pore-forming amphiphiles with controllable supramolecular properties is briefly discussed. 相似文献