全文获取类型
收费全文 | 13669篇 |
免费 | 2040篇 |
国内免费 | 2668篇 |
专业分类
化学 | 12547篇 |
晶体学 | 251篇 |
力学 | 345篇 |
综合类 | 103篇 |
数学 | 241篇 |
物理学 | 4890篇 |
出版年
2024年 | 66篇 |
2023年 | 220篇 |
2022年 | 422篇 |
2021年 | 544篇 |
2020年 | 789篇 |
2019年 | 540篇 |
2018年 | 515篇 |
2017年 | 502篇 |
2016年 | 730篇 |
2015年 | 617篇 |
2014年 | 768篇 |
2013年 | 1285篇 |
2012年 | 946篇 |
2011年 | 871篇 |
2010年 | 640篇 |
2009年 | 826篇 |
2008年 | 827篇 |
2007年 | 851篇 |
2006年 | 825篇 |
2005年 | 697篇 |
2004年 | 673篇 |
2003年 | 586篇 |
2002年 | 534篇 |
2001年 | 382篇 |
2000年 | 383篇 |
1999年 | 319篇 |
1998年 | 272篇 |
1997年 | 250篇 |
1996年 | 220篇 |
1995年 | 211篇 |
1994年 | 161篇 |
1993年 | 158篇 |
1992年 | 154篇 |
1991年 | 84篇 |
1990年 | 70篇 |
1989年 | 64篇 |
1988年 | 71篇 |
1987年 | 40篇 |
1986年 | 38篇 |
1985年 | 25篇 |
1984年 | 23篇 |
1983年 | 19篇 |
1982年 | 26篇 |
1981年 | 12篇 |
1980年 | 19篇 |
1979年 | 25篇 |
1978年 | 17篇 |
1977年 | 14篇 |
1976年 | 20篇 |
1972年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
102.
Summary Several -cyclodextrin (CD)-bonded stationary phases for high performance liquid chromatography (HPLC) were prepared, based on silica beads coated with a poly(alkylamine), [poly(ethyleneimine)(PEI)]. In order to obtain stationary phases with a high content of CD and maximum accessibility of the CD cavity, the functionalization was carried out after the coating, using the mono-tosyl derivative of CD as the intermediate. The ability of these supports to separate ortho, meta and para isomers of some disubstituted benzene derivatives was examined. The contribution of the amino groups of the polymer and of the CD cavity to the separation process is discussed. The resolution is mainly based on the difference in the stability of the complexes of the various isomers with CD. The influence of the amount of CD on the height of the theoretical plate is also studied. 相似文献
103.
104.
在所有电极过程中研究最多的是析氢反应,其重要性一直为化学界所关注。提高电极活性的各种方法中,普遍采用电沉积法,它价廉简便、效果明显。但涂层不够牢固,在使用过程中易脱落,使用寿命短。为了克服上述缺点,作者将电沉积和离子注入技术联合使用,即在Ni、W镀层上注入Mo离子,利用Mo离子的能量将Ni、W打入表面内层,进行离子束混合。这既 相似文献
105.
HUANG Xiao-wen SHI Peng-fei 《高等学校化学研究》2006,22(1):73-75
IntroductionLithium ion batteries are key components of mobiletelephones and portable computers.Among the knownLi-intercalation materials for lithium ion battery cath-odes,LiCoO2,LiNiO2,and LiMn2O4have been stud-ied extensively[1—3].LiCoO2is nowused in c… 相似文献
106.
Thermodynamics of the dissociation of 2-aminopyridinium ion in synthetic seawater and a standard for pH in marine systems 总被引:1,自引:0,他引:1
Buffer solutions composed of 2-aminopyridinium chloride and 2-aminopyridine in synthetic seawater are useful as a supplement to buffers of Tris (pH 8.2) and Bis (pH 8.8) in standardizing measurements of hydrogen ion concentration (pm
H
or pH(SWS)) in oceanography. The dissociation constant of 2-amino-pyridinium ion over the range of salinities (S) from 30 to 40 has now been determined from the emf of cells without liquid junction at eight temperatures (T) from 278.15 to 313.15 K. The results fit the equation pK=2498.31/T–15.3274+2.4050 lnT+S(0.012928–2.9417×10–5T) with a standard deviation of 0.0023. Thermodynamic constants for the dissociation process and standard reference values of pm
H
and pH(SWS) were derived from the data. The pm
H
of the buffer consisting of 2-aminopyridinium chloride and 2-aminopyridine (each 0.04 molal) in synthetic seawater of salinity 35 varies from 7.356 at 278.15 K to 6.601 at 313.15 K. 相似文献
107.
108.
Takehiko Yamato Masashi Yasumatsu Yoshiyuki Saruwatari Louis Korbla Doamekpor 《Journal of inclusion phenomena and macrocyclic chemistry》1994,19(1-4):315-331
Novel macrocyclic compounds, hexahydroxy[1.0.1.0.1.0]- (2b) and octahydroxy[1.0.1.0.1.0.1.0]metacyclophane (2c) have been prepared in 50–70% yield by base-catalyzed condensation of 5,5-di-tert-butyl-2,2-dihydroxybiphenyl (1) with formaldehyde in refluxing xylene. An attempted alkylation of the flexible macrocycles2b and2c with ethyl bromoacetate in the presence of Cs2CO3 under acetonitrile reflux gave only one pure stereoisomer3 and4, respectively, while other possible isomers were not observed. The structural characterization of these products is also discussed. The two-phase solvent extraction data indicated that hexaethyl ester3 and octaethyl ester4 show strong metal affinity, comparable with that of the corresponding calix[n]arenes, and a high K+ selectivity was observed for octaethyl ester4.1H-NMR titration of hexaethyl ester3 and octaethyl ester4 with KSCN clearly demonstrate that a 11 complex is formed which is stable on the NMR time scale.This paper is dedicated to the commemorative issue on the 50th anniversary of calixarenes. 相似文献
109.
《Electroanalysis》2004,16(16):1359-1365
Electrochemical oxidation of catechols has been studied in the presence of cyanide ion as nucleophile in aqueous solution, by means of cyclic voltammetry and controlled‐potential coulometry. The results indicate that the participation of catechols in the Michael reaction with cyanide ion to form the corresponding o‐dihydroxybenzonitrile. Based on an EC mechanism, the homogeneous rate constants were estimated by comparing the experimental cyclic voltammetric responses with the digital simulated results. 相似文献
110.
低共熔混合锂盐相图的绘制及应用 总被引:3,自引:0,他引:3
采用热分析法对不同组成的混合锂盐二元体系进行研究, 绘制了混合锂盐体系的步冷曲线和T-x相图, 结果表明体系均为具有最低共熔点的二元体系. LiOH-LiNO3、LiOH-LiCl、LiOH-Li2CO3及LiNO3-LiCl体系的最低共熔点分别为175.7、294.5、418.2及221.6 ℃. 利用低共熔混合物LiNO3-LiOH为锂盐与不同前驱体反应, 制备出了层状结构良好的锂离子电池正极材料LiNiO2、LiNi0.8Co0.2O2及LiNi1/3Co1/3Mn1/3O2. X射线衍射分析表明, 合成的材料具有规整的层状NaFeO2结构, 且XRD衍射峰强度之比I(003)/I(104)>2.0, 电性能测试表明, 在2.7-4.3 V(vs Li/Li+)的电压范围内进行0.1C倍率充放电, LiNiO2、LiNi0.8Co0.2O2、LiNi1/3Co1/3Mn1/3O2首次充电比容量分别达168.0、225.4、194.0 mAh·g-1, 放电比容量分别为138.4、165.8、157.7 mAh·g-1. 相似文献