全文获取类型
收费全文 | 24222篇 |
免费 | 4088篇 |
国内免费 | 3488篇 |
专业分类
化学 | 17726篇 |
晶体学 | 408篇 |
力学 | 1405篇 |
综合类 | 222篇 |
数学 | 2529篇 |
物理学 | 9508篇 |
出版年
2024年 | 110篇 |
2023年 | 559篇 |
2022年 | 976篇 |
2021年 | 1081篇 |
2020年 | 1134篇 |
2019年 | 1143篇 |
2018年 | 979篇 |
2017年 | 979篇 |
2016年 | 1275篇 |
2015年 | 1337篇 |
2014年 | 1587篇 |
2013年 | 2067篇 |
2012年 | 2293篇 |
2011年 | 2330篇 |
2010年 | 1675篇 |
2009年 | 1512篇 |
2008年 | 1759篇 |
2007年 | 1422篇 |
2006年 | 1272篇 |
2005年 | 959篇 |
2004年 | 818篇 |
2003年 | 597篇 |
2002年 | 573篇 |
2001年 | 427篇 |
2000年 | 390篇 |
1999年 | 431篇 |
1998年 | 304篇 |
1997年 | 220篇 |
1996年 | 250篇 |
1995年 | 204篇 |
1994年 | 173篇 |
1993年 | 174篇 |
1992年 | 138篇 |
1991年 | 137篇 |
1990年 | 106篇 |
1989年 | 90篇 |
1988年 | 60篇 |
1987年 | 50篇 |
1986年 | 48篇 |
1985年 | 49篇 |
1984年 | 24篇 |
1983年 | 18篇 |
1982年 | 16篇 |
1981年 | 8篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 5篇 |
1976年 | 5篇 |
1975年 | 5篇 |
1957年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
92.
Amide-water mixtures are studied by all-atom molecular dynamics (MD) simulations and the relative temperature-dependent NMR experiment. The weak C-H...O contacts are found in the amide-water systems theoretically and experimentally. The statistical results of the average numbers of hydrogen bonds indicate that the methyl groups in amide molecules represent different capabilities in forming the weak C-H...O contacts. The statistics also imply that the C-H...O contacts are more obvious in the amide-rich region than those in the water-rich region. The temperature-dependent NMR spectra are also adopted to investigate the weak C-H...O contacts in the amide-water systems. The relative chemical shifts of the methyl groups are in good agreement with the MD simulations. 相似文献
93.
本文研究了离子对反相液相色谱分析氨基酚异构体的可能性、影响因素和色谱条件,发现以含4×10-8mol/L四丁基碘化铵、0.184mol/L醋酸钠的甲醇水溶液(23:77)作为流动相,ODS为固定相时可以实现氨基酚异构体的良好分离。 相似文献
94.
CUI Wei HUANG Lei LI Wei WANG Li-ping 《高等学校化学研究》2006,22(2):236-238
Introduction S Adenosylmethionine(SAM)isabiologicallyac tivecompoundwidelydistributedinthebodytissues andfluids.Itisinvolvedinanumberofbiochemical reactions.Asamethylgroupdonor,itisimportantin transmethylationreactions,whichcontributestothe synthesesofsuc… 相似文献
95.
含活性基团的醛可与烯丙碘和锡粉直接进行亲核加成反应,得到高烯丙基的醇,水的存在不利于此反应的进行,与烯丙基溴相比,烯丙基碘反应活性更强,可在短时间内得较高的产率。 相似文献
96.
Binding of wogonin to human serum albumin: a common binding site of wogonin in subdomain IIA 总被引:4,自引:0,他引:4
Tian J Liu J Xie J Yao X Hu Z Chen X 《Journal of photochemistry and photobiology. B, Biology》2004,74(1):39-45
The binding of wogonin to human serum albumin (HSA) has been studied by spectroscopic method including circular dichroism (CD), infrared spectra (IR) and fluorescence spectra. The fluorescence properties of HSA were examined in presence of wogonin and the fluorescence intensity of HSA was significantly decreased in the presence of wogonin. The binding parameters of wogonin were studied from the fluorescence decreasing of HSA by the fluoremetric titrations. The Stern-Volmer plots indicated that the binding of wogonin to HSA at 296, 303, 310 K is characterized by one binding site with the binding constant K(S-V) at 1.872 x 10(5), 1.561 x 10(5), 1.392 x 10(5), respectively, which are good agreement with the results from the Scatchard plots. The binding process was exothermic, enthalpy driven and spontaneous, as indicated by the thermodynamic analyses, and the major part of the binding energy is hydrophobic interaction, which were consistent with the result of molecule modelling study, and there are also a numbers of hydrogen bonds between wogonin and HSA. Furthermore, the displacement experiments indicate that wogonin can bind to the subdomain IIA, that is, the site I of HSA, which is also good agreement with the result of molecule modelling study. 相似文献
97.
应用分子动力学模拟了25 ℃和50 ℃时新型室温熔盐二(三氟甲基磺酸酰)亚胺锂[LiN(SO2CF3)2, LiTFSI]与尿素(摩尔比为1:3.6)体系的结构与动力学性质. 在两个温度下体系的微观结构基本相同, Li+的配位数约为5, 且都是与溶剂和阴离子中的氧原子发生配位. 对TFSI-的研究表明, 每个TFSI-只提供四个氧中的一个与Li+配位; 而且在Li+的配位层中, TFSI-具有顺、反和gauche 等不同的构象, 并且不同构象出现的几率会随着温度的改变而改变. 相似文献
98.
Yao Zhu Siyuan Fang Shaoqin Chen Youjie Tong Chunling Wang Yun Hang Hu 《Chemical science》2021,12(16):5825
Photocatalytic ethane conversion into value-added chemicals is a great challenge especially under visible light irradiation. The production of ethyl hydroperoxide (CH3CH2OOH), which is a promising radical reservoir for regulating the oxidative stress in cells, is even more challenging due to its facile decomposition. Here, we demonstrated a design of a highly efficient visible-light-responsive photocatalyst, Au/WO3, for ethane oxidation into CH3CH2OOH, achieving an impressive yield of 1887 μmol gcat−1 in two hours under visible light irradiation at room temperature for the first time. Furthermore, thermal energy was introduced into the photocatalytic system to increase the driving force for ethane oxidation, enhancing CH3CH2OOH production by six times to 11 233 μmol gcat−1 at 100 °C and achieving a significant apparent quantum efficiency of 17.9% at 450 nm. In addition, trapping active species and isotope-labeling reactants revealed the reaction pathway. These findings pave the way for scalable ethane conversion into CH3CH2OOH as a potential anticancer drug.Highly efficient visible-light driven photocatalytic oxidation of ethane into ethyl hydroperoxide was realized for the first time over Au/WO3. 相似文献
99.
100.
Mao-fengZhang Qiao-hongYao Chun-huiHuang Wei-xiaoCao 《高分子科学》2005,(1):27-27
A kind of azo-containing resin (Azo-R) was synthesized by a simple way through the coupling reaction of 2-nitro-N-methyldiphenylamine-4-diazoresin (NDR) with phenol, and a new covalentely attached multilayer film from Azo-R as H-donor and photosensitive diazoresin, diphenylamine-4-diazoresin (DR) as H-acceptor via H-bonding attraction by selfassembly technique has been fabricated. Following the decomposition of diazonium group of DR under exposure to UV light, the H-bonds between the layers of the film convert to covalent bonds and the film becomes very stable toward polar solvents or electrolyte aqueous solutions. Thus the UV-irradiated azo-containing films can be used to measure photocurrent in a conventional three-electrode photoelectrochemical cell using KCl as supporting electrolyte. It was confirmed that the azo-containing multilayer film is responsible for the photocurrent generation. 相似文献