全文获取类型
收费全文 | 5330篇 |
免费 | 825篇 |
国内免费 | 519篇 |
专业分类
化学 | 3532篇 |
晶体学 | 62篇 |
力学 | 401篇 |
综合类 | 34篇 |
数学 | 653篇 |
物理学 | 1992篇 |
出版年
2024年 | 6篇 |
2023年 | 139篇 |
2022年 | 124篇 |
2021年 | 217篇 |
2020年 | 217篇 |
2019年 | 227篇 |
2018年 | 200篇 |
2017年 | 164篇 |
2016年 | 273篇 |
2015年 | 249篇 |
2014年 | 302篇 |
2013年 | 379篇 |
2012年 | 495篇 |
2011年 | 503篇 |
2010年 | 330篇 |
2009年 | 296篇 |
2008年 | 325篇 |
2007年 | 312篇 |
2006年 | 321篇 |
2005年 | 266篇 |
2004年 | 180篇 |
2003年 | 139篇 |
2002年 | 113篇 |
2001年 | 98篇 |
2000年 | 109篇 |
1999年 | 93篇 |
1998年 | 83篇 |
1997年 | 76篇 |
1996年 | 93篇 |
1995年 | 74篇 |
1994年 | 45篇 |
1993年 | 54篇 |
1992年 | 43篇 |
1991年 | 29篇 |
1990年 | 27篇 |
1989年 | 19篇 |
1988年 | 10篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1985年 | 11篇 |
1984年 | 1篇 |
1983年 | 6篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1971年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有6674条查询结果,搜索用时 15 毫秒
71.
72.
用超临界流体干燥法制备出大孔高比表面高分散态Fe/ZrO_2气凝胶超细粒子催化剂,研究了在其制备过程中织构性质、颗粒大小、体相和表面结构的变化,并与普通浸渍法制备的Fe/ZrO_2催化剂作了对比。对几种Fe/ZrO_2催化剂的F-T反应性能考察表明,Fe/ZeO_2气凝胶超细催化剂显示出高的反应活性;随载体ZrO_2颗粒尺寸减小,活性组分铁的分散度变大,其颗粒尺寸变小,催化剂比表面积增大,反应活性增大,甲烷和低碳烃生成量增加,重质组分减少,认为产物烃分布主要受催化剂活性相颗粒尺寸效应制约。 相似文献
73.
74.
75.
76.
77.
The keto-enol tautomerization of p-hydroxyphenylpyruvic acid (pHPP) in aqueous solutions and the complexation reaction between enolic pHPP and boric acid have been studied by electrochemical techniques including linear sweep voltammetry (LSV), pulse voltammetry, and cyclic voltammetry (CV), combining with UV spectrometry. Electrochemical techniques reveal that in aqueous solution, there are two tautomers of pHPP: enolic form and ketonic form; the former exists mainly in freshly prepared pHPP solution, and the latter exists mainly in equilibrium solution. Both enolic and ketonic pHPP are electroactive. The electrochemical oxidation of enolic pHPP gives rise to two anodic waves, I(a) and II(a), while the electrochemical oxidation of ketonic pHPP only results in the observation of the second wave II(a). The oxidation process I(a) is revealed to be associated with the quasi-reversible, two-electron two-proton oxidation of "C=C"group at the side chain of enolic pHPP, and the oxidation process II(a) is proposed to result from the irreversible oxidation of phenolic hydroxyl group. It is observed that in aqueous solution, enolic pHPP can quickly complex with boric acid to yield enol-borate complex that can also oxidize at a glassy carbon electrode to yield an anodic wave. 相似文献
78.
Liu J Kharitonova EP Duan CG Mei WN Smith RW Hardy JR 《The Journal of chemical physics》2005,122(14):144503
We studied temperature dependence of complex capacitance, impedance, and polarized Raman spectra of single crystal Cs2Nb4O11. First, we observed a sharp lambda-shaped peak at 165 degrees C in the complex capacitance, then found drastic changes in the Raman spectra in the same temperature range. Utilizing the pseudosymmetry search of structure space group, we attributed the observed anomalies to a structural change from the room temperature orthorhombic Pnn2 to another orthorhombic Imm2. We also measured room temperature polarized Raman spectra in different symmetries of normal vibrations and assigned high wavenumber Raman bands to the internal vibrations of NbO6 octahedra and NbO4 tetrahedra. 相似文献
79.
Using FcCOONa (Fc = (eta(5)-C(5)H(5))Fe(eta(5)-C(5)H(4))) as starting material, we obtained an unprecedented metal-organic coordination polymer containing ferrocenecarboxylate components [[Pb(2)(FcCOO)(eta(2)-FcCOO)(mu(2)-eta(2)-FcCOO)(mu(3)-eta(2)-FcCOO)(CH(3)OH)].1.5CH(3)OH.H(2)O](n) (1), tetramer [Zn(4)(mu(2)-FcCOO)(6)(mu(4)-O)] (2), and coordination polymers [Pb(FcCOO)(mu(2)-FcCOO)(bpe)](n) (3) (bpe = 1,2-bis(4-pyridyl)ethene), [[Zn(FcCOO)(2)(bpt)].2.5H(2)O](n) (4) (bpt = N,N'-bis(3-pyridylmethyl)thiourea), and [Zn(FcCOO)(eta(2)-FcCOO)(bbp)](n) (5) (bbp = 4,4'-trimethylene-dipyridine). Compounds 1 and 2 are formed by ferrocenecarboxylate units coordinating with Pb(II) or Zn(II). In polymer 1, ferrocenecarboxylate units have four kinds of coordinate modes; just these novel coordinate modes lead to the unprecedented one-dimensional polymer where two kinds of rhomboids are arranged alternatively along the chain. Compound 2 is a tetramer, in which a distinct connectivity of the six ferrocene units is established through the four Zn atoms. Compounds 3-5 are obtained by organic ligands bridging Pb(II) or Zn(II), leading to a new type of metal-organic coordination polymer. 相似文献
80.