全文获取类型
收费全文 | 350篇 |
免费 | 22篇 |
专业分类
化学 | 252篇 |
晶体学 | 34篇 |
力学 | 3篇 |
数学 | 45篇 |
物理学 | 38篇 |
出版年
2023年 | 1篇 |
2022年 | 4篇 |
2021年 | 8篇 |
2020年 | 4篇 |
2019年 | 8篇 |
2018年 | 2篇 |
2017年 | 9篇 |
2016年 | 6篇 |
2015年 | 9篇 |
2014年 | 16篇 |
2013年 | 31篇 |
2012年 | 23篇 |
2011年 | 16篇 |
2010年 | 12篇 |
2009年 | 21篇 |
2008年 | 21篇 |
2007年 | 18篇 |
2006年 | 6篇 |
2005年 | 14篇 |
2004年 | 10篇 |
2003年 | 10篇 |
2002年 | 16篇 |
2001年 | 4篇 |
2000年 | 9篇 |
1999年 | 12篇 |
1998年 | 13篇 |
1997年 | 9篇 |
1996年 | 19篇 |
1995年 | 12篇 |
1994年 | 1篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 4篇 |
1989年 | 7篇 |
1988年 | 5篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1973年 | 1篇 |
1925年 | 1篇 |
排序方式: 共有372条查询结果,搜索用时 640 毫秒
1.
2.
Amorín M Castedo L Granja JR 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(22):6543-6551
Here we report the preparation and structural characteristics of self-assembling peptide tubelets composed of 32-membered rings formed of alternating alpha-amino acids and cis-3-aminocyclohexanecarboxylic acids. The tubelets possess a partial hydrophobic core environment, provided by the projection of the cyclohexane C2 methylene moiety into the lumen, and a Van der Waals pore diameter of about 7 A. 相似文献
3.
4.
Pablo Ríos Javier Borge Francisco Fernndez de Crdova Giuseppe Sciortino Agustí Lleds Amor Rodríguez 《Chemical science》2021,12(7):2540
The concept of metal–ligand cooperation opens new avenues for the design of catalytic systems that may offer alternative reactivity patterns to the existing ones. Investigations of this concept with ligands bearing a boron center in their skeleton established mechanistic pathways for the activation of small molecules in which the boron atom usually performs as an electrophile. Here, we show how this electrophilic behavior can be modified by the ligand trans to the boron center, evincing its ambiphilic nature. Treatment of diphosphinoboryl (PBP) nickel–methyl complex 1 with bis(catecholato)diboron (B2Cat2) allows for the synthesis of nickel(ii) bis-boryl complex 3 that promotes the clean and reversible heterolytic cleavage of dihydrogen leading to the formation of dihydroborate nickel complex 4. Density functional theory analysis of this reaction revealed that the heterolytic activation of H2 is facilitated by the cooperation of both boryl moieties and the metal atom in a concerted mechanism that involves a Ni(ii)/Ni(0)/Ni(ii) process. Contrary to 1, the boron atom from the PBP ligand in 3 behaves as a nucleophile, accepting a formally protic hydrogen, whereas the catecholboryl moiety acts as an electrophile, receiving the attack from the hydride-like fragment. This manifests the dramatic change in the electronic properties of a ligand by tuning the substituent trans to it and constitutes an unprecedented cooperative mechanism that involves two boryl ligands in the same molecule operating differently, one as a Lewis acid and the other one as a Lewis base, in cooperation with the metal. In addition, reactivity towards different nucleophiles such as amines or ammonia confirmed the electrophilic nature of the Bcat moiety, allowing the formation of aminoboranes.A bis(boryl)nickel complex promotes the facile and reversible activation of H2 through a cooperative mechanism that involves the metal and both boryl moieties in a concerted five-center process. 相似文献
5.
L. Poul S. Ammar N. Jouini F. Fievet F. Villain 《Journal of Sol-Gel Science and Technology》2003,26(1-3):261-265
A new route for the preparation of powdery metal, oxide and hydroxide materials is presented as a chimie douce alternative to the sol-gel method. It consists in the reduction or the hydrolysis of a metal salt dissolved and heated in a polyol medium. It appears through zinc and cobalt examples that the use of acetate precursors contrarily to chloride or sulfate ones leads to the precipitation of a solid (metal, oxide, hydroxide) whose nature depends on two main factors: the hydrolysis ratio, defined by the water to metal molar ratio, and the reaction temperature. As in the sol-gel method, acetate leads to the formation of intermediate alkoxyacetate complex. The absence of water favors metal formation while its presence favors oxide or hydroxyacetate formation. 相似文献
6.
7.
Cimpeanu V Parvulescu VI Amorós P Beltrán D Thompson JM Hardacre C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,10(18):4640-4646
Heterogeneous catalytic oxidation of a series of thioethers (2-thiomethylpyrimidine, 2-thiomethyl-4,6-dimethyl-pyrimidine, 2-thiobenzylpyrimidine, 2-thiobenzyl-4,6-dimethylpyrimidine, thioanisole, and n-heptyl methyl sulfide) was performed in ionic liquids by using MCM-41 and UVM-type mesoporous catalysts containing Ti, or Ti and Ge. A range of triflate, tetrafluoroborate, trifluoroacetate, lactate and bis(trifluoromethanesulfonyl)imide-based ionic liquids were used. The oxidations were carried out by using anhydrous hydrogen peroxide or the urea-hydrogen peroxide adduct and showed that ionic liquids are very effective solvents, achieving greater reactivity and selectivity than reactions performed in dioxane. The effects of halide and acid impurities on the reactions were also investigated. Recycling experiments on catalysts were carried out in order to evaluate Ti leaching and its effect on activity and selectivity. 相似文献
8.
Mohamed Mongi Ftini Mohamed Krifa Haddad Amor 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(8):i106-i108
The title compounds, potassium pentamolybdenum oxide, KMo5O13, and potassium niobate antimonate or potassium niobium antimony oxide (1/1.76/3.24), KNb1.76Sb3.24O13, were synthesized by solid‐state reactions and are isomorphous in space group Cmcm. The structure of the Mo complex has three unique Mo atoms and consists of MoO6 octahedra sharing edges to form Mo2O6 pairs and Mo3O9 triplets, which, in turn, form layers by sharing corners. These layers are linked together in the [100] direction, yielding a three‐dimensional network similar to that of KSb5O13. This framework delimits interconnected tunnels, running approximately along the [110] and [10] directions, in which K+ ions are located. In the isomorphous KNb1.76Sb3.24O13 structure, one of the Mo sites in KMo5O13 is replaced by Sb and the other two Mo sites have been replaced by Nb/Sb. 相似文献
9.
10.