全文获取类型
收费全文 | 4834篇 |
免费 | 1000篇 |
国内免费 | 1785篇 |
专业分类
化学 | 3543篇 |
晶体学 | 244篇 |
力学 | 426篇 |
综合类 | 172篇 |
数学 | 599篇 |
物理学 | 2635篇 |
出版年
2024年 | 11篇 |
2023年 | 51篇 |
2022年 | 157篇 |
2021年 | 170篇 |
2020年 | 189篇 |
2019年 | 181篇 |
2018年 | 183篇 |
2017年 | 233篇 |
2016年 | 198篇 |
2015年 | 251篇 |
2014年 | 303篇 |
2013年 | 393篇 |
2012年 | 414篇 |
2011年 | 424篇 |
2010年 | 449篇 |
2009年 | 492篇 |
2008年 | 461篇 |
2007年 | 459篇 |
2006年 | 405篇 |
2005年 | 353篇 |
2004年 | 268篇 |
2003年 | 229篇 |
2002年 | 187篇 |
2001年 | 207篇 |
2000年 | 236篇 |
1999年 | 149篇 |
1998年 | 62篇 |
1997年 | 50篇 |
1996年 | 64篇 |
1995年 | 40篇 |
1994年 | 45篇 |
1993年 | 40篇 |
1992年 | 33篇 |
1991年 | 25篇 |
1990年 | 36篇 |
1989年 | 31篇 |
1988年 | 22篇 |
1987年 | 28篇 |
1986年 | 17篇 |
1985年 | 18篇 |
1984年 | 14篇 |
1983年 | 13篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有7619条查询结果,搜索用时 31 毫秒
1.
The stable phase equilibria of quaternary systems LiBr-NaBr-MgBr2-H2O and LiBr-KBr-MgBr2-H2O at 298.15 K were studied by both experimental measurement(isothermal solution saturation method) and theoretical prediction(Pitzer model). The solubilities of the saturated solution have been determined experimentally and two stable phase diagrams and relevant water diagrams of the two quaternary systems were obtained. Results show that quaternary system LiBr-NaBr-MgBr2-H2O is hydrate II type as NaBr and NaBr·2H2O coexistence. Its phase diagram consists of only one invariant point, four univariant curves, and five crystallization fields. The quaternary system LiBr-KBr-MgBr2-H2O is a complex type as the double salt KBr·MgBr2·6H2O formed. In addition to this double salt, the three single salts LiBr·2H2O, KBr and MgBr2·6H2O also crystallize. In this paper, the solubilities of phase equilibria in above quaternary systems were also calculated by the Pitzer's electrolyte solution model. All the needed parameters can be obtained from the literature or be fitted by experimental data. On the Basis of the experimental and calculated results, the phase diagram of the quaternary system was plotted for comparison. It shows that the calculation results are consistent with the experimental ones. 相似文献
2.
The drawbacks of our earlier report of preparing fuel cell catalyst arrays by borohydride reduction of inkjet prepared arrays of metal salts are discussed along with the need for inclusion of state-of-the-art metrics in all array screening. An alternative method for screening of hydrogen/air cathode catalysts, direct methanol fuel cell (DMFC) anode catalysts, and catalyst loading studies is provided. State-of-the-art Johnson Matthey catalysts were used in control experiments to demonstrate the utility of the array fuel cell for high throughput screening of fuel cell catalysts in the 3-4 mg/cm2 range. This report lays out hard learned rules for high throughput screening and demonstrates that the array fuel cell can be used for very precise screening of libraries of membrane electrode assembly (MEA) components without the pitfalls discussed in the introduction. 相似文献
3.
4.
Junhua Chen 《Journal of organometallic chemistry》2006,691(3):470-474
Four novel hexadentate imidazolium salts were synthesized from hexakis(bromomethyl)benzene and 1-substituted imidazole. The arylation of aldehydes with arylboronic acids was effected conveniently and in high yields by a catalyst system generated in situ from these hexadentate imidazolium salts, [Rh(COD)Cl]2 and a base. 相似文献
5.
6.
7.
8.
9.
The catalytic activities of SO42-/TiO2-MoO3 in synthesizing cyclohexanone ethylene ketal,cyclohexanone 1,2-propanediol ketal, 2-propyl-1,3-dioxolane, 4-methyl-2-isopropyl-1,3-dioxolane,2-isopropyl-1,3-dioxolane, 4-methyl-2-isopropyl-1,3-dioxolane, butanone ethy-lene ketal and butanone 1,2-propanediol ketal were reported. It has been demonstrated that SO42-/TiO2-MoO3 is an excellent catalyst. Various factors concerned in this reaction have been investigated. The optimum conditions have been found, that is, the molar ratio of aldehyde/ketone to alcohol was 1:1.5 or 1:1.3,the mass ratio of the catalyst used to the reactants was 0.25~1.5%, and the reaction time was 45~60 min. Under this conditions, the yield of cyclohexanone ethylene ketal is 82.7%, cyclohexanone 1,2-propanediol ketal is 83.4%, the yield of 2-propyl-1,3-dioxolane is 68.1%,4-methyl-2-isopropyl-1,3-dioxolane is 87.5%, the yield of 2-isopropyl-1,3-dioxolane is 70.7%,4-methyl-2-isopropyl-1,3-dioxolane is 82.5%, the yield of butanone ethylene ketal is 74.1%, and butanone 1,2-propanediol ketal is 94.9%.Some equation and experiment results concerned of the synthetic acetals or ketals were listed as follows. 相似文献
10.