全文获取类型
收费全文 | 33961篇 |
免费 | 4562篇 |
国内免费 | 6270篇 |
专业分类
化学 | 29418篇 |
晶体学 | 2753篇 |
力学 | 837篇 |
综合类 | 192篇 |
数学 | 1184篇 |
物理学 | 10409篇 |
出版年
2024年 | 68篇 |
2023年 | 332篇 |
2022年 | 689篇 |
2021年 | 1013篇 |
2020年 | 1371篇 |
2019年 | 1210篇 |
2018年 | 1023篇 |
2017年 | 1228篇 |
2016年 | 1473篇 |
2015年 | 1348篇 |
2014年 | 1885篇 |
2013年 | 3261篇 |
2012年 | 2112篇 |
2011年 | 1983篇 |
2010年 | 1749篇 |
2009年 | 2007篇 |
2008年 | 2119篇 |
2007年 | 2232篇 |
2006年 | 2280篇 |
2005年 | 2014篇 |
2004年 | 2057篇 |
2003年 | 1634篇 |
2002年 | 1441篇 |
2001年 | 1014篇 |
2000年 | 970篇 |
1999年 | 896篇 |
1998年 | 774篇 |
1997年 | 706篇 |
1996年 | 675篇 |
1995年 | 627篇 |
1994年 | 557篇 |
1993年 | 450篇 |
1992年 | 424篇 |
1991年 | 271篇 |
1990年 | 150篇 |
1989年 | 124篇 |
1988年 | 120篇 |
1987年 | 107篇 |
1986年 | 55篇 |
1985年 | 76篇 |
1984年 | 49篇 |
1983年 | 31篇 |
1982年 | 34篇 |
1981年 | 36篇 |
1980年 | 30篇 |
1979年 | 24篇 |
1978年 | 14篇 |
1977年 | 11篇 |
1976年 | 15篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 466 毫秒
991.
Limberg C 《Angewandte Chemie (International ed. in English)》2003,42(48):5932-5954
The oxo-functionalization of organic substrates with the aid of metal oxo moieties is of fundamental importance not only in nature but also in academic and industrial research. Nevertheless the corresponding reaction mechanisms remain among the most enigmatic in chemistry and few of them are understood in detail. Recent research efforts have resulted in significantly improved information: in the cases of many oxygenation reactions evidence has been provided for the occurrence radical intermediates, even though the high selectivity observed suggests to a different mechanism. Examples stem from various areas of chemistry and include processes involving molecular metal oxo complexes, gas-phase and matrix-isolated species, metalloenzymes, and solid-state oxide surfaces. This review treats this seemingly wide variety of systems with the aim of providing an overview of common reactivity patterns and principles, as well as open problems. 相似文献
992.
1 INTRODUCTION Recently, the low-spin square-planar nickel(II) complexes and high-spin octahedral nickel(II) complexes with Schiff base ligands have received much attention in optical materials[1~3]. Some nic- kel(II) complexes are widely used as lubricating oil, rubber industry additives, a fire-resistant additive and fungicide for leather[4~7]. Also, their adducts with nitrogen have attracted broad attention due to their potential applications as organic conductors and magnetic mate… 相似文献
993.
994.
利用Bridgman-Stockbarger方法在氩气气氛下生长出KZnF3:Eu^3+单晶,测定了晶体的激发光谱、荧光发射光谱和ESR谱,讨论了Eu离子的取代格位。 相似文献
995.
笼形聚偕胺肟树脂的研究—酚处理对树脂吸附贵金属性能的影响 总被引:5,自引:0,他引:5
研究了笼形聚偕胺肟树脂(CAO)和酸式(ACAO)及碱式(BCAO)树脂对于苯酚、对-氨基酚、对-硝基酚、对-甲氨基酚和对-苯二酚的吸附和吸留作用,测定了酚处理树脂的中和当量。它反映了笼形树脂吸留外来物的特性。酚处理树脂有效地吸附Ag 、AuCl4-、PtCl62-、PdCl42-和IrCl62-等贵金属离子,吸附方式似乎与溶液的pH值有关。SEM观察表明,Ag 、Au-Cl4-和IrCl62-离子在吸附过程中被还原为零价态,在树脂表面生成形态各异的结晶。 相似文献
996.
离子交换树脂在湿法冶金中的应用 总被引:14,自引:0,他引:14
本文简要综述了离子交换树脂在贵金属、稀有金属、稀土金属、铀及其它放射性核素等金属的湿法提取分离与纯化中的应用。 相似文献
997.
Adi Wolfson Ivo F.J. Vankelecom Pierre A. Jacobs 《Journal of organometallic chemistry》2005,690(15):3558-3566
When ionic liquids (ILs) are employed as solvents for transition metal complex (TMC) catalyzed reductions, a second solvent can be added to increase the efficiency of the catalytic cycle and the solubility of the reactant in the IL phase. Two industrially relevant asymmetric hydrogenations, the enantioselective reductions of methyl 2-acetamidoacrylate with Rh-EtDuPHOS and methyl acetoacetate with Ru-BINAP, were performed in different catalytic systems including 1-butyl-3-methylimidazolium hexafluorophosphate/ tetrafluoroborate as ILs. Product separation and TMC recycling was performed by extracting the product from the reaction mixture. This can be accomplished by cooling the system, by adding an excess of the second solvent or by adding a third solvent. A high solubility of the second solvent in the IL catalytic phase favors the reaction activity, but can induce leaching of the IL and TMC. 相似文献
998.
The novel coordination polymer [Pr(BYBA)3(H2O)2]·[Pr(BYBA)3(H2O)] (BYBAH = 2-benzoylbenzoic acid) was yielded by hydrothermal synthesis, determined by single-crystal X-ray diffraction, and characterized by FT-IR and UV-Vis spectra. The crystal crystallizes in the triclinic system, space group P with a = 9.112(3), b = 14.644(5), c = 27.076(11) (A), α = 84.223(3), β = 87.816(4), γ = 88.902(4)o, V = 3592(2) (A)3, C84H60O21Pr2, Mr = 1687.14, Z = 2, F(000) = 1700, Dc = 1.560 g/cm3, μ = 1.419 mm-1, the final R = 0.0485 and wR = 0.1258 for 13035 observed reflections with I>2((I). The compound contains two different building units, [Pr2(BYBA)6(H2O)4] and [Pr2(BYBA)6(H2O)2]. It is noticeable that [Pr2(BYBA)6(H2O)4] is an isolated binuclear building block, in which the Pr3 ion centers are both located in an eight-coordinated environment. However, in [Pr2(BYBA)6(H2O)2] the Pr3 ion centers are located in a nine-coordinated environment and connected by BYBA ligands to form 1D chains. 相似文献
999.
Raman phonon spectroscopy has been used to study photodimerization reaction inp-chloro cinnamic acid (pCCA) crystal. The β-form of the crystal yields the 4,4′-dichloro-β-truxinic acid dimer. Six distinct low frequency phonon
bands are observed in thepCCA monomer crystal. On reaction progress, these bands show a monotonic shift to lower frequencies and broaden out. Finally,
in the dimer crystal the phonon spectrum shows two weak broad bands. These results suggest that the reaction is homogeneous
in the initial stages and, as the product concentration increases, the lattice becomes highly disordered. The reactant and
the product were characterised by infrared and Raman spectroscopy. The disappearance of aliphatic C=C bond stretching vibration
and appearance of cyclobutane ring deformation and cyclobutane ring-breathing vibrations on reaction confirm photodimerization
by cyclobutane ring formation. The large Stoke's shift between the absorption and emission band suggest strong exciton-phonon
coupling in the monomer lattice. This reaction seems to be phonon-mediated. 相似文献
1000.