全文获取类型
收费全文 | 5411篇 |
免费 | 679篇 |
国内免费 | 560篇 |
专业分类
化学 | 4002篇 |
晶体学 | 79篇 |
力学 | 238篇 |
综合类 | 49篇 |
数学 | 861篇 |
物理学 | 1421篇 |
出版年
2024年 | 5篇 |
2023年 | 56篇 |
2022年 | 117篇 |
2021年 | 152篇 |
2020年 | 182篇 |
2019年 | 215篇 |
2018年 | 163篇 |
2017年 | 144篇 |
2016年 | 280篇 |
2015年 | 250篇 |
2014年 | 297篇 |
2013年 | 368篇 |
2012年 | 404篇 |
2011年 | 419篇 |
2010年 | 291篇 |
2009年 | 283篇 |
2008年 | 373篇 |
2007年 | 346篇 |
2006年 | 287篇 |
2005年 | 266篇 |
2004年 | 233篇 |
2003年 | 231篇 |
2002年 | 290篇 |
2001年 | 227篇 |
2000年 | 137篇 |
1999年 | 98篇 |
1998年 | 61篇 |
1997年 | 36篇 |
1996年 | 46篇 |
1995年 | 24篇 |
1994年 | 24篇 |
1993年 | 29篇 |
1992年 | 18篇 |
1991年 | 17篇 |
1990年 | 14篇 |
1989年 | 11篇 |
1988年 | 22篇 |
1987年 | 16篇 |
1986年 | 13篇 |
1985年 | 21篇 |
1984年 | 26篇 |
1983年 | 5篇 |
1982年 | 24篇 |
1981年 | 18篇 |
1980年 | 22篇 |
1979年 | 24篇 |
1978年 | 9篇 |
1977年 | 9篇 |
1976年 | 12篇 |
1975年 | 10篇 |
排序方式: 共有6650条查询结果,搜索用时 31 毫秒
41.
42.
设计并合成了2-(2’-羟基-3’-甲氧基苯基)-5,6-二硝基苯并咪唑化合物(1),通过X射线单晶衍射研究了该化合物的固态结构.利用紫外-可见光谱技术研究了其对阴离子的识别,发现化合物1能够在DMSO中对AcO^-,H2PO4^-,OH^-的3种离子进行有效识别,同时溶液由原来的黄色变成红色,实现裸眼检测. 相似文献
43.
Tran Quang Minh Léon Christiaens Pierre Grandclaudon Alain Lablache-Combier 《Tetrahedron》1977,33(17):2225-2229
Photoirradiated in presence of acetophenone, benzo[b]selenophene and its 3-methyl derivative add to dimethyl acetylenedicarboxylate. In each ease, the primary reaction product is unstable and has not been isolated. Photoexeited in its triplet state (the energy of which is in the neighbourhood of 69 ) benzo[b]selenophene and its 2- and 3-methyl, 2,3 dimethyl, 3 acetoxy and 2-methyl-3-acetoxy derivatives add to 1,2 dichloroethylene leading to cyclobutanes. Neither cyclo-addition occurs in absence of photosensitiser. Single-crystal X-ray analysis gave the structures of the two adducts of 3-acetoxybenzo[b]selenophene with trans-1,2-dichloroethylene. In both compounds the chlorine atoms are trans. 相似文献
44.
Li YS Xiao Y Wright PB Tran T 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2005,61(7):1675-1681
3-(Triethoxysilyl)propionitrile (TESPN) sol-gel has been prepared under different conditions. It was employed for coating the surfaces of quartz and aluminum. Infrared (IR) and Raman spectra of TESPN and TESPN sol-gels have been recorded in the study of the sol-gel process. Transmission and reflection absorption IR (RAIR) spectra of TESPN sol-gel coated quartz and aluminum have also been collected for better understanding the film formation on the substrate surfaces. Spectra collected at different temperatures indicated that the silane film on quartz decomposes at 700 degrees C. Results from thermal gravimetric analysis (TGA) supported this result. Based on the group frequencies and the spectral behavior in different states, some vibrational modes were assigned to the observed bands. The anticorrosion behavior of the sol-gel coated aluminum in comparison with the uncoated metal was evaluated by measuring the potentiodynamic polarization and electrochemical impedance spectra (EIS). 相似文献
45.
YiJianCHEN GuiYingXU ShiLingYUAN HaiYingSUN 《中国化学快报》2005,16(5):688-690
Molecular dynamics (MD) simulation are used to study the properties of gemini surfactant of ethyl-α,ω-bis(dodecyldimethylammonium bromide) (C12C2C12) and dodecyl-trimethylammonium bromide (DTAB) at the air/water interface, respectively. In the two systems,t he surfactant concentrations are both 28 wt.%, and other conditions are also the same. After reaching the thermodynamic equilibrium, the concentration profiles, the radial distributions functions (RDF) and the mean squared displacement (MSD) are investigated. The results reveal that the surface activity of C12C2C12 surfactant is higher than DTAB surfactant. 相似文献
46.
A New Asterosaponin from the Starfish Culcita novaeguineae 总被引:1,自引:0,他引:1
HaiFengTANG YangHuaYI LingLI PengSUN DaZhengZHOU BaoShuLIU 《中国化学快报》2005,16(5):619-622
A new asterosaponin named novaeguinoside A, along with a known saponin, asteronyl pentaglycoside sulfate, was isolated from the starfish Culcita novaeguineae. The new compound was identitied to be sodium 6α-O-{β-D-fucopyranosyl-(1→2)-β-D-fucopyranosyl-(1→4)-[β-D-quinovopyranosyl-(1→2)]-β-D-xylopyranosyl-(1→3)-[β-D-quinovopyranosyl}-5α-pregn-9(11)-en-20-one-3β-yl-sulfate by extensive spectral analysis and chemical evidence. 相似文献
47.
48.
49.
Vutukuri DR Bharathi P Yu Z Rajasekaran K Tran MH Thayumanavan S 《The Journal of organic chemistry》2003,68(3):1146-1149
A mild deprotection strategy for allyl ethers under basic conditions in the presence of a palladium catalyst is described. Under these conditions, aryl allyl ethers can be cleaved selectively in the presence of alkyl allyl ethers. These conditions are also effective in the deprotection of allyloxycarbonyl groups. The utility of the current methodology in sequence specific dendrimer synthesis is demonstrated. 相似文献
50.
Xin Gen Luo Hai Sheng Chen Shuang Liang Mao Huang Wei Dong Xuan Li Jin College of Pharmacy Second Military Medical University Shanghai China Department of Pharmacy Guangzhou Military General Hospital Guangzhou China Center of New Drug Evaluation Institute of Basic Medical Sciences Second Military Medical University Shanghai China 《中国化学快报》2007,18(6):697-699
Six indole alkaloids were isolated from the stems of Ervatamia yunnanensis. Among them, yunnanensine (I) is new. The other five are known alkaloids, namely: 19,20-E-vallesamine (II), 19s-heyneanine (HI), ibogaine (IV), ibogamine (V), coronaridine (VI). The structural elucidation of the alkaloids was based on spectral means. 相似文献