全文获取类型
收费全文 | 14462篇 |
免费 | 2502篇 |
国内免费 | 2310篇 |
专业分类
化学 | 11095篇 |
晶体学 | 211篇 |
力学 | 880篇 |
综合类 | 171篇 |
数学 | 1573篇 |
物理学 | 5344篇 |
出版年
2024年 | 36篇 |
2023年 | 228篇 |
2022年 | 392篇 |
2021年 | 455篇 |
2020年 | 512篇 |
2019年 | 555篇 |
2018年 | 482篇 |
2017年 | 404篇 |
2016年 | 747篇 |
2015年 | 729篇 |
2014年 | 897篇 |
2013年 | 1099篇 |
2012年 | 1238篇 |
2011年 | 1322篇 |
2010年 | 996篇 |
2009年 | 984篇 |
2008年 | 1138篇 |
2007年 | 980篇 |
2006年 | 900篇 |
2005年 | 738篇 |
2004年 | 644篇 |
2003年 | 516篇 |
2002年 | 647篇 |
2001年 | 525篇 |
2000年 | 451篇 |
1999年 | 293篇 |
1998年 | 221篇 |
1997年 | 164篇 |
1996年 | 178篇 |
1995年 | 147篇 |
1994年 | 113篇 |
1993年 | 125篇 |
1992年 | 86篇 |
1991年 | 70篇 |
1990年 | 46篇 |
1989年 | 37篇 |
1988年 | 34篇 |
1987年 | 26篇 |
1986年 | 19篇 |
1985年 | 25篇 |
1984年 | 10篇 |
1983年 | 18篇 |
1982年 | 3篇 |
1981年 | 10篇 |
1980年 | 5篇 |
1979年 | 10篇 |
1978年 | 7篇 |
1977年 | 2篇 |
1974年 | 3篇 |
1957年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
Ye Qing Li Ming Lu Chun Xu Lu Sai Jian Zhu Qi Fa Liu 《中国化学快报》2007,18(11):1313-1315
A novel and simple procedure for synthesis of azanucleoside by Mitsunobu reaction between N-(p-nitrobenzyloxycarbonyl)- trans-4-hydroxy-D-proline methyl ester obtained from trans-4-hydroxy-L-proline after six-step reaction and 2-fluoro-6-azidopurine is described,and azanucleoside is fluorinated by new fluridizer 2,2-difluoro-1,3-dimethylimidazolidine (DFI).All reactions could be carded out under mild condition. 相似文献
72.
73.
Shuang‐Jun Lin Chang‐Heng Tan Shan‐Hao Jiang Yi‐Ming Li Da‐Yuan Zhu 《Helvetica chimica acta》2006,89(11):2789-2793
Four new iridoids, buergerinins B–E ( 1 – 4 ), along with three known iridoids, were isolated from the roots of Scrophularia buergeriana. Their structures were identified on the basis of spectroscopic analysis. 相似文献
74.
Lei Qiao Chao Zhang Xiang‐Wen Zhang Zi‐Chuan Wang Haolin Yin Zhong‐Ming Sun 《中国化学》2020,38(3):295-304
The polypnictide complexes of rare earth cations have drawn the attention of the scientific community for their uncommon bonding modes and potential applications. Herein, we present a systematic and comprehensive summary on recent advances in the field of rare earth polypnictides, focusing on their synthesis, structures, and reactivities. The structural stabilizing effects imposed by the electropositive rare earth cations as well as the reducing capability of rare earth precursors in the synthesis of these polypnictide complexes are described in this review. We also disscuss in detail the bonding interactions and coordination modes between rare earth cations and polypnictide clusters as well as the similarities and the peculiarity of some structures. 相似文献
75.
76.
用自旋-晶格弛豫时间(T1)研究了溶胀的交联聚丙烯酰胺-丙烯酸网络和线型聚苯乙烯溶液中质子的弛豫行为。交联网络中,随着交联度增大,T1CH/T1CH2的值由1.17逐渐趋近于1;而线型聚苯乙烯溶液中,T1CH/T1CH2的值由最稀浓度下的1.7过渡到1。说明在交联网络中,交联度很低时,链段的运动已经相当受约束;但交联度很大时,充分溶胀的交联网络中链段运动仍有一定自由度。而在线型高分子浓溶液中,链段的运动严重受阻,导致自旋扩散效应非常完全,彻底平均掉了各质子间T1时间的差异。 相似文献
77.
六甲氧基甲基三聚氰胺(HMMM)-多元醇-丙烯酸酯-酸催化剂的混合体系在较高温度下同时进行缩聚和自由基聚合并表现出协同效应,DSC研究结果表明,丙烯酸酯在HMMM和酸的催化作用下可在较低温度下发生自由基聚合反应,并把反应释放出来的大量的热量有效地传递给缩聚发反应,满足缩聚反应吸热的要求,从而节省固化所需要的能量,为了提高储存稳定性。本文以潜酸催化剂作为酸的来源,对该混杂聚合体系进行了研究,仍有明显的热互补效应。 相似文献
78.
The anodic polymerization of 3-aminophthalhydrazide (luminol) and iron(II) tris 5-aminophenanthroline (Fe(phen-NH2)3(2+)) has been reported in this paper. A bilayer electrode was developed based on these polymers and the ITO conductive glass (denoted ITO[Fe(phen-NH2)3(2+)]luminol electrode). This electrode emitted light (lambdaem: 430 nm) as it was brought into contact with H2O2. At pH 10, the resulting electrochemiluminescence (ECL) showed a linear relationship with the concentration of H2O2 in the range of 10 microM(-1) mM. This bilayer electrode also showed an application potential for the detection of glucose after being further modified with glucose oxidase (denoted ITO[Fe(phen-NH2)3(2+)]luminol]GOx electrode). Although the resulting ECL decayed more rapidly in concentrated glucose solutions (e.g., I M) because of the consumption of luminol during use, the decay became less severe in diluted glucose solutions (e.g., 10 mM). According to the flow injection analysis, a linear relationship existed between the ECL and the concentration of glucose from 10(-5)-10(-3) M at pH 9. The detection limit could reach a level of 5 x 10(-5) M at this pH. 相似文献
79.
80.
The secondary reduction in the direct and oxazaborolidine‐catalyzed asymmetric borane reduction of ketones was investigated by the use of GC/MS tracing titration and control experiments. The results indicate that the secondary reduction affects the enantioselectivity only in noncoordinated solvents at low temperature and not under the usual catalytic reduction conditions because the intermediate alkoxyborane is unstable and quickly converts to borane and dialkoxyborane. The function of an alcohol additive in the asymmetric borane reduction of ketones is to consume excess borane in the reduction system thus inhibiting noncatalytic reduction, which leads to increased enantioselectivity in the catalytic reduction. 相似文献