全文获取类型
收费全文 | 1928篇 |
免费 | 100篇 |
国内免费 | 181篇 |
专业分类
化学 | 2125篇 |
晶体学 | 6篇 |
数学 | 1篇 |
物理学 | 77篇 |
出版年
2024年 | 2篇 |
2023年 | 51篇 |
2022年 | 21篇 |
2021年 | 30篇 |
2020年 | 39篇 |
2019年 | 43篇 |
2018年 | 49篇 |
2017年 | 41篇 |
2016年 | 58篇 |
2015年 | 63篇 |
2014年 | 104篇 |
2013年 | 258篇 |
2012年 | 111篇 |
2011年 | 138篇 |
2010年 | 97篇 |
2009年 | 118篇 |
2008年 | 120篇 |
2007年 | 113篇 |
2006年 | 106篇 |
2005年 | 88篇 |
2004年 | 92篇 |
2003年 | 78篇 |
2002年 | 76篇 |
2001年 | 31篇 |
2000年 | 37篇 |
1999年 | 24篇 |
1998年 | 28篇 |
1997年 | 25篇 |
1996年 | 22篇 |
1995年 | 22篇 |
1994年 | 20篇 |
1993年 | 16篇 |
1992年 | 12篇 |
1991年 | 10篇 |
1990年 | 12篇 |
1989年 | 9篇 |
1988年 | 11篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有2209条查询结果,搜索用时 0 毫秒
71.
利用电动势法得到了牛血清白蛋白(BSA)与十二烷基硫酸钠(SDS)相互作用的结合等温线. 通过四阶导数紫外光谱法和荧光光谱法研究了相互作用过程中芳香族氨基酸残基微环境极性的变化. 通过研究发现, 随着SDS浓度的逐渐增大, SDS在BSA上的平均结合数(v)逐渐增大, 色氨酸(Trp)残基所处微环境的极性在减弱后保持基本不变, 酪氨酸残基所处微环境的极性在明显增强后稍有减弱, 苯丙氨酸残基所处微环境的极性略有增强. 结果表明, 当v由0增大到14时, SDS主要结合在BSA的Trp-213附近并逐渐形成聚集体, 从而诱导BSA由结构域ⅡA 开始逐渐展开. 此后, SDS呈正协同作用的特点与BSA 结合, v急剧增大. 当v约为302 时, SDS在BSA上的结合基本达到饱和, BSA的构象趋于稳定. 相似文献
72.
Rahul D. Shingte Deepshikha Chatterjee Bhausaheb V. Tawade Bharat Shrimant 《高分子科学杂志,A辑:纯化学与应用化学》2019,56(2):136-145
Three bisphenols containing cardo perhydrocumyl cyclohexylidene group, namely; 1,1-bis(4-hydroxyphenyl)-4-perhydrocumylcyclohexane, 1,1-bis(4-hydroxy-3-methylphenyl)-4-perhydrocumylcyclohexane and 1,1-bis(4-hydroxy-3,5-dimethylphenyl)-4-perhydrocumylcyclohexane were synthesized starting from p-cumyl phenol. Each of these bisphenols was polycondensed with both terephthaloyl chloride and isophthaloyl chloride by phase transfer-catalyzed interfacial polymerization to obtain a series of new aromatic polyesters. Inherent viscosities and number average molecular weights of polyesters were in the range 0.51-0.64 dL/g and 17390-41430?g/mol, respectively which indicated the formation of reasonably high molecular weight polymers. The detailed NMR studies revealed that axial and equatorial identity of the phenyl rings of bisphenols was retained in polyesters resulting in constitutional isomerism. Polyesters containing perhydrocumyl cyclohexylidene groups showed excellent solubility in organic solvents viz, chloroform, dichloromethane, 1,1,2,2-tetrachloroethane and tetrahydrofuran. The self-standing films of polyesters could be cast from their chloroform solution. The 10% weight loss temperatures and glass transition temperatures of polyesters were in the range 453–485?°C and 201–267?°C, respectively demonstrating their excellent thermal characteristics. The gas permeability study of polyesters was carried out for He, H2 and N2 by variable-volume method. An improvement in permeability and decrease in selectivity was observed due to symmetric methyl substituents while reverse trend was observed in case of polyesters with asymmetric methyl substituents. 相似文献
73.
74.
《高分子科学杂志,A辑:纯化学与应用化学》2013,50(7):779-790
Abstract 5‐tert‐Butyl‐isophthalic acid (TIPA) was polycondensed with three different aromatic diamines by means of triphenylphosphite (TPP) and pyridine. The resulting polyamides were characterized by solution viscosities and MALDI‐TOF mass spectra (m.s.). These m.s. revealed significant fractions of cyclic oligo‐ and polyamides in all samples. In polyamides of high molecular weight, only cycles were detectable (observed up to masses of 13,000 Da). Three poly(amide‐imide)s were prepared by TPP‐mediated polycondensation of trimellitic anhydride (TMA) and three aromatic diamines. Although relatively high molar masses were obtained, the MALDI‐TOF m.s. displayed the peaks of linear chains in addition to those of cyclic polymers. The results together suggest that the side reactions mainly occur at the amino endgroups. 相似文献
75.
76.
含羧酸共生稀土光敏剂的低密度聚乙烯膜紫外光氧化降解 总被引:3,自引:0,他引:3
含羧酸共生稀土光敏剂的低密度聚乙烯膜紫外光氧化降解林宜超(福建省测试技术研究所福州350003)近年来,许多作者先后研究并开发出含硬脂酸铈(CeSt3)光敏剂的可控光降解低密度聚乙烯(LDPE)[1,2]、高密度聚乙烯[3]、聚丙烯[4]、聚苯乙烯... 相似文献
77.
78.
固相微萃取法在禁用偶氮染料检测中的应用初探 总被引:4,自引:1,他引:4
将固相微萃取技术应用于出口染色纺织品及皮革制品中禁用偶氮染料检验,偶染料经连二亚硫酸钠还原成芳胺后,用固相微萃取技术萃取富集后,用GC-MS分析。实验了萃取方式、萃取纤维、pH值、浓度、温度、萃取时间及色谱条件等因素对萃取与测定的影响。 相似文献
79.
Jinwei Sun Xinrui Yang Yun Liu Yi Wang Yi Pan 《Journal of heterocyclic chemistry》2020,57(3):1449-1455
An efficient synthesis of 3-nitroimidazo[1,2-a]pyridines has been developed via N-iodosuccinimide (NIS)-mediated multicomponents reaction of 2-aminopyridines, aldehydes, and nitromethane under metal-free conditions. This protocol has many advantages such as broad substituent scope, mild and eco-friendly conditions, high step economy, and good yields. 相似文献
80.
IRMPD Spectra of Protonated Hydroxybenzaldehydes: Evidence of Torsional Barriers in Carboxonium Ions
Prof. Barbara Chiavarino Prof. Otto Dopfer Prof. Maria Elisa Crestoni Dr. Davide Corinti Dr. Philippe Maître Prof. Simonetta Fornarini 《Chemphyschem》2020,21(8):749-761
Protonation at the formyl oxygen atom of benzaldehydes leading to the formation of carboxonium ions yields two distinct isomers, depending on the relative orientation of the proton either cis or trans with respect to the hydrogen atom on the adjacent carbon. In this context, the IR multiple photon dissociation (IRMPD) spectra of protonated ortho, meta, and para-hydroxybenzaldehydes ( OH−BZH+ ), delivered into the gas phase by electrospray ionization of hydro-alcoholic solutions, are reported in the 3200–3700 cm−1 spectral range. This range is characteristic of O−H stretching modes and thus able to differentiate cis and trans carboxonium isomers. Comparison between IRMPD spectra and DFT calculations at the B3LYP/6-311++G(2df2p) level suggests that for both p- OH−BZH+ and m- OH−BZH+ only cis conformers are present in the ion population analyzed. For o- OH−BZH+ , IRMPD spectroscopy points to a mixture comprising one trans and more than one cis conformers. The energy barrier for cis–trans isomerization calculated for each OH−BZH+ isomer is a measure of the degree of π-electron delocalization. Furthermore, IRMPD spectra of p- OH−BZH+ , m- OH−BZH+ and protonated phenol (this last used as reference) were recorded also in the fingerprint range. Both the observed C−O and O−H stretching vibrations appear to be a measure of π-electron delocalization in the ions. 相似文献