全文获取类型
收费全文 | 38240篇 |
免费 | 7124篇 |
国内免费 | 6028篇 |
专业分类
化学 | 28244篇 |
晶体学 | 603篇 |
力学 | 2445篇 |
综合类 | 418篇 |
数学 | 4223篇 |
物理学 | 15459篇 |
出版年
2024年 | 121篇 |
2023年 | 699篇 |
2022年 | 1397篇 |
2021年 | 1499篇 |
2020年 | 1585篇 |
2019年 | 1618篇 |
2018年 | 1427篇 |
2017年 | 1455篇 |
2016年 | 1914篇 |
2015年 | 2092篇 |
2014年 | 2539篇 |
2013年 | 3170篇 |
2012年 | 3691篇 |
2011年 | 3699篇 |
2010年 | 2742篇 |
2009年 | 2775篇 |
2008年 | 2982篇 |
2007年 | 2471篇 |
2006年 | 2283篇 |
2005年 | 1854篇 |
2004年 | 1394篇 |
2003年 | 1168篇 |
2002年 | 1187篇 |
2001年 | 964篇 |
2000年 | 789篇 |
1999年 | 660篇 |
1998年 | 466篇 |
1997年 | 426篇 |
1996年 | 376篇 |
1995年 | 301篇 |
1994年 | 298篇 |
1993年 | 232篇 |
1992年 | 185篇 |
1991年 | 153篇 |
1990年 | 141篇 |
1989年 | 96篇 |
1988年 | 87篇 |
1987年 | 65篇 |
1986年 | 72篇 |
1985年 | 50篇 |
1984年 | 28篇 |
1983年 | 31篇 |
1982年 | 20篇 |
1981年 | 17篇 |
1980年 | 10篇 |
1979年 | 21篇 |
1977年 | 14篇 |
1957年 | 9篇 |
1936年 | 7篇 |
1925年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
131.
A concise method to synthesize benzo[c]phenanthridine alkaloid, nornitidine, was developed utilizing nickel- or palladium-catalyzed iminoannulation of an internal alkyne. The advantages of this strategy included readily available starting materials, inexpensive reagents, short reaction steps, and good yields. 相似文献
132.
Reaction of transition metal formate M(HCOO)(2).2H2O (M = Mn, Co, Ni) with 4,4'-bpy (4,4-bipyridine) has led to four new compounds with the formula M(HCOO)2(4,4'-bpy).nH2O (M = Mn, Co (1.Mn, 2.Co), n = 0; M = Co, Ni (3.Co, 4.Ni), n = 5). Compounds 1.Mn and 2.Co are isomorphous and crystallized in the tetragonal crystal system with the chiral space group P4(1)2(1)2. They are of three-dimensional diamondoid structure connected by anti-anti formate with 4,4'-bpy in the cavities of the framework reinforcing the intermetallic connections; the diamond-like net was observed also in their azide analogue (Mn(N3)2(4,4'-bpy)). Compounds 3.Co and 4.Ni are isomorphous also but crystallized in the monoclinic crystal system with the space group Cc. Both structures are uninterpenetrated 3D "CdSO4" type with big channels, constructed by anti-anti formate and 4,4'-bpy. This type of net was not observed in their azide analogue. Residing in the channels, water molecules form a new type of 1D tape constructed by vertex-sharing cyclic pentamers. Magnetic measurements were performed on all of these four compounds. 1.Mn and 2.Co are weak ferromagnets with the critical temperature Tc = 5.3 and 7.4 K, respectively. 3.Co is an antiferromagnet with Neel temperature TN = 3.0 K, and 4.Ni is a weak ferromagnet below 20 K. Hysteresis loop can be observed for 2.Co and 4.Ni at 1.8 K. As an analogue of azide, formate can be used to construct molecular architectures, which structurally and magnetically have great similarities to and also differences from those of azide. This offers a promising method for the design of new molecular architectures with formate. 相似文献
133.
134.
Wei ZHANG Ni SONG Zhong Zhen LI Ying Xia LI 《中国化学快报》2006,17(3):285-288
Obyanamide 1 is a cyclic depsipeptide that was recently isolated from the marine cyanobacterium Lyngbya confervoides by Moore and co-workers1. This compound displayed a potent inhibitory effect on both KB and LoVo cells in vitro. Several structural analog… 相似文献
135.
Hae‐Jeong Lee Christopher L. Soles Da‐Wei Liu Barry J. Bauer Wen‐Li Wu 《Journal of Polymer Science.Polymer Physics》2002,40(19):2170-2177
X‐ray reflectivity has been used to determine the mass uptake of probe molecules in porous thin films supported on thick silicon wafers. The adsorption occurs by capillary condensation when the films are exposed to probe vapor at controlled partial vapor pressures. The probe solvent partial pressure was varied by mixing saturated air and dry air at constant temperature or by changing sample temperature at a constant vapor concentration. Pore size distribution in the films can be calculated from the probe uptake with typical porosimetric approaches such as the application of the Kelvin equation to convert partial pressure into pore size. For illustration, the pore size distribution of three different nanoporous thin films, the primary candidate of ultra‐low‐k interlevel dielectrics in the next generation of integrated circuit chips, was determined with this technique. These samples represent different generations of low‐k dielectrics developed by industry. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2170–2177, 2002 相似文献
136.
137.
138.
139.
Hai-Bin Tian Duan-Zhi Yin Lan Zhang Li-Hua Wang Chun-Fu Zhang Jun-Ling Li Wei Zhou Chun-Ying Wu Yong-Xian Wang 《Journal of Radioanalytical and Nuclear Chemistry》2004,262(2):383-389
The compound 3-{[4-(4-[18F]fluorophenyl)methyl]piperazin-1-yl}-methyl-1H-pyrrolo[2,3-b]pyridine ([18F]3), which is an analogue of L-745,870 binding D4
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
140.