全文获取类型
收费全文 | 35486篇 |
免费 | 8242篇 |
国内免费 | 1408篇 |
专业分类
化学 | 40515篇 |
晶体学 | 313篇 |
力学 | 428篇 |
数学 | 1809篇 |
物理学 | 2071篇 |
出版年
2024年 | 4篇 |
2023年 | 7篇 |
2022年 | 31篇 |
2021年 | 167篇 |
2020年 | 1266篇 |
2019年 | 2613篇 |
2018年 | 1071篇 |
2017年 | 670篇 |
2016年 | 3405篇 |
2015年 | 3545篇 |
2014年 | 3456篇 |
2013年 | 4104篇 |
2012年 | 2884篇 |
2011年 | 2084篇 |
2010年 | 2806篇 |
2009年 | 2786篇 |
2008年 | 2269篇 |
2007年 | 1647篇 |
2006年 | 1332篇 |
2005年 | 1525篇 |
2004年 | 1334篇 |
2003年 | 1239篇 |
2002年 | 1932篇 |
2001年 | 1326篇 |
2000年 | 1245篇 |
1999年 | 335篇 |
1998年 | 26篇 |
1997年 | 20篇 |
1994年 | 1篇 |
1991年 | 1篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1976年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
941.
942.
943.
944.
Philippe Mongondry Chantal Bonnans‐Plaisance Martine Jean Jean Franois Tassin 《Macromolecular rapid communications》2003,24(11):681-685
The hydroxyl end groups of poly(ethylene glycol) (PEG) have been transformed easily and quantitatively into amino groups via the Mitsunobu reaction. Phthalimide was alkylated with PEGs and the hydrazinolysis of the resulting phthalimido‐PEGs gave the amino compounds in high yields. Quaternization of the amino groups leads to hydrophilic polymer chains bearing a positive charge on one or two ends, depending on the chosen PEG. Such products can be used to protect sterically, negatively charged particles such as clays.
945.
Riadh Neffati Alexander Alexeev Sergey Saunin Jos C. M. Brokken‐Zijp Daan Wouters Stefan Schmatloch Ulrich S. Schubert Joachim Loos 《Macromolecular rapid communications》2003,24(1):113-117
A systematic investigation into the surface properties of siloxane rubber/carbon black (CB) nanocomposites has been performed, using an automated scanning probe microscope. In this way the influence of CB concentration and curing rate of the siloxane rubber matrix on roughness and conductivity of the composites was studied. Decreasing the curing rate while keeping the CB concentration resulted in a decrease in both roughness and surface conductivity, which can be explained by an additional siloxane‐rubber layer formed during curing.
946.
947.
Hong‐Ping Xiao Zhan Shi Long‐Guan Zhu Ru‐Ren Xu Wen‐Qin Pang 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(3):m82-m83
The reaction of nickel(II) nitrate with terephthalic acid and 2,2′‐bipyridine in dimethylformamide solution gives the title complex, [Ni(C10H8N2)(H2O)4](C8H4O4). The NiII ion is octahedrally coordinated to one 2,2′‐bipyridine and four water molecules and does not coordinate to the terephthalate anion. Hydrogen bonds between the terephthalate anions and the [Ni(2,2′‐bipy)(H2O)4]2+ cations produce a two‐dimensional hydrogen‐bonding architecture with double sheets. 相似文献
948.
A. Subbiah Pandi D. Velmurugan S. Shanmuga Sundara Raj Hoong‐Kun Fun M. C. Bansal 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(6):o302-o304
The title compound, C19H20O6, crystallizes in the centrosymmetric space group P21/c with one molecule in the asymmetric unit. The molecule is approximately planar and the dihedral angle between the phenyl rings is 11.0 (1)°. The H atoms of the central propenone group are trans. There is an intramolecular O—H⃛O hydrogen bond and the molecules are crosslinked by four intermolecular C—H⃛O hydrogen bonds, producing a three‐dimensional network. 相似文献
949.
Jun Ni Yi‐Zhi Li Wen‐Bin Qi Yong‐Jiang Liu Hui‐Lan Chen Zhi‐Lin Wang 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(8):o470-o472
The title compound, 3,3′‐(4‐pyridylimino)dipropanenitrile, C11H12N4, has a twofold axis and consists of a pyridine ring head and two cyanoethyl tails, the three groups being linked by an N atom. The planar geometry around the amino N atom suggests conjugation with the π‐system of the pyridine ring. The molecules are stacked in a layer structure via relatively weak to very weak intermolecular C—H⃛π and C—H⃛N hydrogen‐bond interactions. 相似文献
950.
Shan‐Bao Qiao Chang‐Mei Jiao Qing‐Feng Xu Yong Zhang Bao‐Long Li Jian‐Ping Lang 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(11):m465-m466
The reaction of CuCN and KCN with (NH4)2[WS4] followed by cation exchange with PPh4Br produced the title compound, (C24H20P)2[Cu2WS4(CN)2]·CH3CN·H2O or (PPh4)2[(NC)Cu(μ‐S)2W(μ‐S)2Cu(CN)]·MeCN·H2O. In the structure of the dianion, [(NC)Cu(μ‐S)2W(μ‐S)2Cu(CN)]2−, the WS4 moiety acts as a bidentate ligand that binds two CuCN groups, thus forming a slightly bent WCu2 core with approximate D2d symmetry. The W—Cu distances are in the range 2.6463 (6)–2.6545 (6) Å. 相似文献