全文获取类型
收费全文 | 18122篇 |
免费 | 2538篇 |
国内免费 | 2951篇 |
专业分类
化学 | 14308篇 |
晶体学 | 280篇 |
力学 | 784篇 |
综合类 | 266篇 |
数学 | 2016篇 |
物理学 | 5957篇 |
出版年
2023年 | 179篇 |
2022年 | 268篇 |
2021年 | 425篇 |
2020年 | 521篇 |
2019年 | 564篇 |
2018年 | 469篇 |
2017年 | 421篇 |
2016年 | 736篇 |
2015年 | 793篇 |
2014年 | 927篇 |
2013年 | 1342篇 |
2012年 | 1517篇 |
2011年 | 1592篇 |
2010年 | 1208篇 |
2009年 | 1179篇 |
2008年 | 1434篇 |
2007年 | 1310篇 |
2006年 | 1204篇 |
2005年 | 999篇 |
2004年 | 928篇 |
2003年 | 818篇 |
2002年 | 883篇 |
2001年 | 731篇 |
2000年 | 524篇 |
1999年 | 429篇 |
1998年 | 267篇 |
1997年 | 284篇 |
1996年 | 229篇 |
1995年 | 218篇 |
1994年 | 188篇 |
1993年 | 186篇 |
1992年 | 170篇 |
1991年 | 121篇 |
1990年 | 106篇 |
1989年 | 93篇 |
1988年 | 56篇 |
1987年 | 56篇 |
1986年 | 41篇 |
1985年 | 40篇 |
1984年 | 27篇 |
1983年 | 17篇 |
1982年 | 14篇 |
1981年 | 15篇 |
1980年 | 13篇 |
1978年 | 12篇 |
1977年 | 8篇 |
1976年 | 9篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Zi‐Jing Li Hong‐Xiang Lou Wen‐Tao Yu Pei‐Hong Fan Dong‐Mei Ren Bin Ma Mei Ji 《Helvetica chimica acta》2005,88(10):2637-2640
The known 7,8‐secolabdane type diterpenoids neopallavicinin ( 1 ), pallavicinin ( 2 ), and 18‐hydroxypallavicinin ( 3 ) were isolated from Pallavicinia ambigua, and their structures were determined. The X‐ray crystal structure of 1 was solved, and, in combination with CD and NMR studies, the absolute configurations of 1 – 3 were established. A possible biogenetic pathway for 1 and 2 from a single labdane precursor is proposed. 相似文献
992.
993.
Fei Gao Bian‐Hong Meng Yi‐Bin Wei 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(7):m360-m362
The crystal structure of the title compound, [Mg(H2O)6]0.5[Mg2(C16H14ClN2O9)(H2O)4]·10H2O, shows that this binuclear complex consists of two Mg centres in distorted octahedral geometry, joined by an oxo bridge which is a derivative of the deprotoned hydroxy group of the phenolate in the ligand molecule. In the anion, the coordination sphere of each MgII ion is completed by two carboxylates, a tertiary N atom and two water molecules. The inner coordination spheres for the MgII ions are very similar, both in ligand sets and in geometry. Each unit of the binuclear complex has one negative charge neutralized by a neighbouring hydrated cation, [Mg(H2O)6]2+, in which the Mg atom lies on an inversion centre. In each cell, there are 34 water molecules and most of them participate in the formation of hydrogen bonds, which contribute greatly to the stability of the whole structure. 相似文献
994.
995.
996.
A sub-micron hydrophilic microchannel was fabricated on poly(dimethylsiloxane) (PDMS) in one step using vacuum ultraviolet light (VUV) lithography in vacuum. The topographies and properties of the irradiated PDMS surface were characterized and analyzed by atomic force microscopy (AFM), and the chemical composition changes on VUV-treated PDMS analyzed by X-ray photoelectron spectroscopy (XPS). The hydrophilic stability of irradiated PDMS surface was studied by static water contact angle. As demonstrated, the hydrophilicity on surface of PDMS microchannel can be kept for a longer term even three months after the treatment. 相似文献
997.
998.
Hong Ping HE Yue Mao SHEN Xiao Sheng YANG Bin Gui WANG Ling LI Xiao Jiang HAO * Laboratory of Phytochemistry Kunming Institute of Botany the Chinese Academy of Sciences Kunming . The Key Laboratory of Chemistry for Natural Prod 《中国化学快报》2001,(1)
Spiraea japonica L. (Rosaceae) is widely distributed in Yunnan Provence, P. R. China. Previous chemical investigations on S. japonica and its varieties have led to the report of 7 new atisane-type diterpenoids and 38 new diterpene alkaloids of atisine- and hetisine-type1-11. This paper describes the isolation and structure elucidation of two new diterpene alkaloids named spiratines A and B (1-2). Their structures were elucidated on the basis of 1D and 2D NMR experiments (HMQC, HMBC, 1… 相似文献
999.
1000.
Mylabris,thedriedbodyoftheChineseblisterbeetle,hasbeenusedasChinesemedicineforover2000years.Itsactiveconstituent,cantharidin,hasantitumoractivitiesandcausesleukocytosis'.Thesynthesisofcyclicglycerophospholipidcontainingcantharidinanalogueshassofarnotbeenreportedinliterature.Theconjugatesofthistypearenotonlynewprodrugsofcantharidinantitumoragentsbutalsomaygeneratetwocytotoxicgroupsagainstdifferenttargetsitesinsideaneoplasticcell'.Suchtypesofcompoundsmaybeofinterestinchemistry,biochemistryandph… 相似文献