全文获取类型
收费全文 | 4828篇 |
免费 | 256篇 |
国内免费 | 32篇 |
专业分类
化学 | 3308篇 |
晶体学 | 57篇 |
力学 | 170篇 |
数学 | 751篇 |
物理学 | 830篇 |
出版年
2023年 | 34篇 |
2022年 | 137篇 |
2021年 | 143篇 |
2020年 | 97篇 |
2019年 | 188篇 |
2018年 | 151篇 |
2017年 | 107篇 |
2016年 | 240篇 |
2015年 | 154篇 |
2014年 | 246篇 |
2013年 | 475篇 |
2012年 | 280篇 |
2011年 | 292篇 |
2010年 | 207篇 |
2009年 | 198篇 |
2008年 | 213篇 |
2007年 | 202篇 |
2006年 | 200篇 |
2005年 | 168篇 |
2004年 | 153篇 |
2003年 | 129篇 |
2002年 | 171篇 |
2001年 | 72篇 |
2000年 | 109篇 |
1999年 | 63篇 |
1998年 | 40篇 |
1997年 | 46篇 |
1996年 | 35篇 |
1995年 | 36篇 |
1994年 | 35篇 |
1993年 | 37篇 |
1992年 | 32篇 |
1991年 | 23篇 |
1990年 | 16篇 |
1989年 | 29篇 |
1988年 | 27篇 |
1987年 | 20篇 |
1986年 | 17篇 |
1985年 | 29篇 |
1984年 | 24篇 |
1983年 | 21篇 |
1982年 | 20篇 |
1981年 | 26篇 |
1980年 | 16篇 |
1979年 | 15篇 |
1978年 | 15篇 |
1977年 | 9篇 |
1976年 | 13篇 |
1975年 | 16篇 |
1959年 | 8篇 |
排序方式: 共有5116条查询结果,搜索用时 0 毫秒
101.
M. M. Ghorab N. E. Amin M. S. A. El Gaby N. M. H. Taha M. A. Shehab I. M. I. Faker 《Phosphorus, sulfur, and silicon and the related elements》2013,188(12):2918-2928
The key intermediate diisothiocyanate 2 was allowed to react with 5-amino-3-methyl-pyrazole-4-carbonitrile 3, ethyl 5-amino-1-phenyl-pyrazole-4-carboxylate 6, 2-amino-tetrahydrobenzo[b]thiophene-3-car-bonitrile 9, ethyl-2-amino-tetra-hydrobenzo[b]thiophene-3-carboxylate 12, and/or 1,2,4-triazole 15 to give the corresponding biscompounds 4, 5, 7, 8, 10, 11, 13, 14, and 16, respectively. The structure of the synthesized compounds was elucidated by elemental analyses and spectral data. Some of the prepared compounds were tested for their antimicrobial and antitumor activities. 相似文献
102.
Marwa F. Mansour Ehab F. El‐Kady Nabawia M. El‐Guindi Samir M. El‐Moghazy Ann Van Schepdael 《Journal of separation science》2013,36(20):3432-3439
A simple CE method was developed and validated for the simultaneous determination of chlordiazepoxide (CHL), amitriptyline, and nortriptyline (mixture I) or the determination of CHL and imipramine (mixture II) using the same BGE. Sertraline and amitriptyline were used as internal standards for the first and second mixtures, respectively. The method allows amitriptyline to be completely separated from its impurity and main metabolite nortriptyline, which can be quantified from 0.2 μg/mL. The separation was achieved using 20 mM potassium phosphate buffer pH 5 containing 12 mM β‐cyclodextrin and 1 mM carboxymethyl‐β‐cyclodextrin. UV detection was performed at 200 nm and a voltage of 15 kV was applied on an uncoated fused‐silica capillary at 25°C. These experimental conditions allowed separation of the compounds to be obtained in 7 min. Calibration graphs proved the linearity up to 40 μg/mL for CHL, up to 100 μg/mL for amitriptyline and imipramine, and up to 5 μg/mL for nortriptyline. The accuracy and precision of the method have been determined by analyzing synthetic mixtures and pharmaceutical formulations. The analytical results were quite good in all cases indicating that the method was linear, sensitive, precise, accurate, and selective for both mixtures. 相似文献
103.
Paweł Szymański Robert Skibiński Małgorzata Liszka Izabela Jargieło Elżbieta Mikiciuk-Olasik Łukasz Komsta 《Central European Journal of Chemistry》2013,11(6):927-934
The lipophilicity of thirty-two novel acetylcholinesterase (AChE) inhibitors — 1,2,3,4-tetrahydroacridine and 2,3-dihydro-1H-cyclopenta[b]quinoline derivatives was studied by thin layer chromatography. The analyzed compounds were chromatographed on RP-18, RP-8, RP-2, CN and NH2 stationary phases with dioxane — citric buffer pH 3.0 binary mobile phases containing different proportions of dioxane. RM values for pure water were extrapolated from the linear Soczewiński-Wachtmeister equation and six compounds with known literature log P values were used as reference calibration data set for computation of experimental log P values. The obtained results were compared with computationally calculated partition coefficients values (AlogPs, AClogP, AlogP, MlogP, KOWWIN, XlogP2, XlogP3) by PCA and significant differences between them were observed. 相似文献
104.
Nabil Abdul‐kader Saleh Hussein El‐abd Saltani Fadhil Abbas Al‐Issa Al‐Sadek Gomaa Melad 《中国化学会会志》2013,60(10):1234-1240
The antimicrobial activity of thirteen newly synthesized 4‐thiazolidinones (TZONs) and four dithiolane derivatives was assessed against susceptible and resistant bacteria, including MRSA, as well as Candida albicans. The structure‐activity relationships revealed that 4‐Thiazolidinone derivatives harboring p‐chlorophenyl and dicarboxyethyl at the 2‐ethenyl and 5‐arylidine positions of the thiazolidinone ring display considerable antibacterial properties. No antifungal activity was recorded by all tested compounds against Candida albicans. The possible potentiative (synergistic) effect of the most active compounds to a few commercial antibiotics was also investigated. 相似文献
105.
Nabil Abdul‐Kader Saleh Hussein El‐Abd Saltani Fadhil Abbas Al‐Issa Ahmad Abul‐kasem Errabie Al‐Sadek Gomaa Melad 《中国化学会会志》2013,60(11):1353-1358
The antifungal and antioxidant activities of thirty newly synthesized 4‐thiazolidinone (TZON) derivatives were assessed against some fungal species including Candida albicans and Aspergillus niger. The introduction of different arylidene moieties at 5‐positions of the thiazolidinone ring successfully enhanced its biological activity. The structure–activity relationships revealed that 4‐thiazolidinone derivatives harboring dicarboxyethyl (at the 2‐ethenyl) and p‐nitrophenylhydrazyl arm (at the 5‐arylidine positions of the thiazolidinone ring) display considerable antifungal and antioxidant properties. 相似文献
106.
Benoit Rigo Philippe Gautret Anne Legrand Samira El Ghammarti Daniel Couturier 《合成通讯》2013,43(18):2609-2615
Starting from the readily available N,O-bis trimethylsilyl pyroglutamate, an easy high yield one pot synthesis of ketone 1 was described. 相似文献
107.
Use of microwave irradiation in the synthesis of arylidenemalononitrile and benzopyran derivatives in water without catalyst is a clean method with high yield. 相似文献
108.
Synthesis of allylic ethers from various aldehyde alcohols and β-hydroxylated phosphonium salts was carried out in a single manipulation and with excellent yields. 相似文献
109.
Tarek A. Salama Saad S. Elmorsy Abdel‐Galel M. Khalil Margret M. Girges Abdel‐Aziz S. El‐Ahl 《合成通讯》2013,43(8):1313-1319
A combination of tetrachlorosilane and potassium cyanide (in situ trichlorosilyl cyanide) was found to work efficiently for hydrocyanation of ketones to afford the corresponding cyanohydrins in high yield under mild conditions. 相似文献
110.
Aryl–heteroaryl and heteroaryl–heteroaryl compounds are obtained through the Suzuki–Miyaura cross-coupling reactions between diazonium salts and potassium trifluoroborates using PdCl2(CH3CN)2 as the catalyst in water and in the absence of any additive, ligand or base. In addition, the same mild catalytic system is effective for the Matsuda–Heck reaction between several monoolefins with aryldiazonium salts. 相似文献