全文获取类型
收费全文 | 15141篇 |
免费 | 2973篇 |
国内免费 | 2486篇 |
专业分类
化学 | 11555篇 |
晶体学 | 349篇 |
力学 | 786篇 |
综合类 | 186篇 |
数学 | 1455篇 |
物理学 | 6269篇 |
出版年
2024年 | 42篇 |
2023年 | 334篇 |
2022年 | 609篇 |
2021年 | 712篇 |
2020年 | 840篇 |
2019年 | 797篇 |
2018年 | 674篇 |
2017年 | 672篇 |
2016年 | 855篇 |
2015年 | 908篇 |
2014年 | 1111篇 |
2013年 | 1344篇 |
2012年 | 1535篇 |
2011年 | 1555篇 |
2010年 | 1151篇 |
2009年 | 1045篇 |
2008年 | 1183篇 |
2007年 | 938篇 |
2006年 | 829篇 |
2005年 | 632篇 |
2004年 | 514篇 |
2003年 | 372篇 |
2002年 | 313篇 |
2001年 | 249篇 |
2000年 | 216篇 |
1999年 | 193篇 |
1998年 | 145篇 |
1997年 | 109篇 |
1996年 | 142篇 |
1995年 | 89篇 |
1994年 | 78篇 |
1993年 | 70篇 |
1992年 | 54篇 |
1991年 | 60篇 |
1990年 | 34篇 |
1989年 | 36篇 |
1988年 | 22篇 |
1987年 | 14篇 |
1986年 | 31篇 |
1985年 | 21篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1976年 | 5篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
221.
Hang GONG Nian Fa YANG? Wei Jun TANG Qing Hua FAN Li Wen YANG The College of Chemistry Xiangtan University Xiangtan Laboratory of Chemical Biology Center for Molecular Science Institute of Chemistry Chinese Academy of Sciences Beijing 《中国化学快报》2005,16(8)
Among the reactions in which C-C bonds are formed, the Baylis-Hillman coupling of aldehydes with α, β-unsaturated carbonylic compounds is currently attracting much interest due to the atom economy, the mild conditions and the generation of functional groups1,2. Furthermore, compared to the Heck, Suzuki and other palladium catalyzed C-C bond forming reaction3, the Baylis-Hillman reaction can be promoted by using organic bases in the complete absence of any metal4. However, almost all the … 相似文献
222.
223.
An all-atom dimethyl sulfoxide (DMSO) model and a TIP5P water model have been adopted for molecular dynamics simulation. Two new qualities ηrelE and ηrel are introduced to describe the anomalous nonideal behaviors of DMSO–water mixtures. The simulation is compared with chemical shift and excess enthalpy of mixing, which shows good concentration dependences. In addition, our all-atom simulation also indicates that the C–H groups of DMSO may interact with the oxygen atoms of water and DMSO. The weak C–HO contacts and the strong O–HO hydrogen bonds represent the consistent concentration dependences, which exhibits the cooperation effect. 相似文献
224.
A novel and efficient ionic liquid supported synthesis of oligosaccharides with a general protocol of coupling and purification is described. The method represents an attractive alternative to the classical solid- and fluorous-phase synthesis strategies and combines the advantage of performing homogeneous chemistry on a relatively large scale while avoiding large excesses of reagents. 相似文献
225.
226.
227.
Yb3+:KY(WO4)2晶体生长与光谱性能 总被引:5,自引:4,他引:5
采用泡生法生长YbKYW晶体, 通过XRD分析确认所生长的晶体为β-YbKYW. TG-DTA测量结果表明, 晶体的熔点为1045 ℃, 相变温度为1010 ℃. 测得晶体红外光谱和拉曼光谱, 对其峰值所属振动的归属进行了指认, 并测量了晶体的吸收光谱和荧光光谱. 结果表明, YbKYW晶体在940, 980 nm附近有很强的吸收峰, 主峰980 nm处的吸收截面积为1.34×10-19 cm2;该晶体在990, 1010, 1030 nm附近都有较强的荧光发射峰, 其中最强发射峰1030 nm的发射线宽高达16 nm, 有望作为可调谐激光器的增益介质. 计算得其1030 nm受激发射截面积为3.1×10-20 cm2. 相似文献
228.
Chun Hua Ge Xiang Dong Zhang Yong Chao Ma Lei Guan Chun Yue Shi Xiao Yan Zhang Ya Nan Guo Qi Tao Liu College of Chemistry Liaoning University Shenyang China 《中国化学快报》2007,(11)
The preparation and crystal structure of complex Co(Hsae)_2·2H_2O (1,H_2sae=N-salicylidene-2-iminoethanol) are reported.X- ray analysis revealed that every six Co(Hsae)_2 forms a cyclic chip and every 12 water forms a novel gear-like cluster.Acting as building blocks,the gear-like water cluster and complex chip are connected in A-B fashion and extend into one-dimensional supramolecular chain.Hydrogen bond is the primary bridging force in the formation of supramolecular framework. 相似文献
229.
Liping Heng Jin Zhai Yong Zhao Jinjie Xu Xianliang Sheng Lei Jiang 《Chemphyschem》2006,7(12):2520-2525
A light-emitting poly (distyryldimethylbenzene-co-triethylene glycol) rod-coil block copolymer was used to fabricate films with three-dimensionally ordered honeycomb structures by the breath-figure method. Photocurrent generation and photovoltaic performance are studied, and the dependence of photocurrent on applied electric field is investigated. Introducing the ordered porous structure significantly improves the photoelectric conversion behavior, because porous structures not only enhance the light-harvesting efficiency but also benefit charge separation and charge transfer. This phenomenon may have great prospects for enhancing the photovoltaic behavior of organic thin-film devices. 相似文献
230.