全文获取类型
收费全文 | 662篇 |
免费 | 31篇 |
国内免费 | 1篇 |
专业分类
化学 | 493篇 |
晶体学 | 4篇 |
力学 | 27篇 |
数学 | 36篇 |
物理学 | 134篇 |
出版年
2024年 | 1篇 |
2023年 | 15篇 |
2022年 | 13篇 |
2021年 | 17篇 |
2020年 | 26篇 |
2019年 | 21篇 |
2018年 | 26篇 |
2017年 | 19篇 |
2016年 | 26篇 |
2015年 | 22篇 |
2014年 | 33篇 |
2013年 | 36篇 |
2012年 | 47篇 |
2011年 | 55篇 |
2010年 | 28篇 |
2009年 | 26篇 |
2008年 | 47篇 |
2007年 | 29篇 |
2006年 | 25篇 |
2005年 | 37篇 |
2004年 | 23篇 |
2003年 | 13篇 |
2002年 | 8篇 |
2001年 | 5篇 |
2000年 | 6篇 |
1998年 | 4篇 |
1997年 | 1篇 |
1996年 | 3篇 |
1995年 | 7篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1990年 | 2篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 12篇 |
1982年 | 2篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 3篇 |
1974年 | 1篇 |
排序方式: 共有694条查询结果,搜索用时 16 毫秒
21.
The inclusion complexes of a series of 4-arylidenamino-5-phenyl-4H-1, 2, 4-triazole-3-thiols have been prepared with β-cyclodextrin. The compounds and their inclusion complexes have been characterized by studying their physical and spectral properties. The thermodynamic stability constant and free energy of activation have been determined to know the stability of inclusion complexes and type of host-guest relation. Finally, absorption, excitation and emission spectra of the compounds (4-arylidenamino-5-phenyl-4H-1, 2, 4-triazole-3-thiols) and their inclusion complexes have been taken. It is found that inclusion complex formation brings about a drastic change in absorption and fluorescence characteristic (both excitation and emission spectra) of newly synthesized compounds. 相似文献
22.
Dr. Jagadeesh Yerri Dr. José Dias Dr. Mallikajurna Reddy Nimmakayala Franck Razafindrainibe Charlotte Courageux Anne-Julie Gastellier Johanne Jegoux Dr. Caroline Coisne Dr. Christophe Landry Dr. Fabien Gosselet Johan Hachani Dr. Jean-François Goossens Prof. Marie-Pierre Dehouck Dr. Florian Nachon Dr. Rachid Baati 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(65):15035-15044
Novel 6-alkyl- and 6-alkenyl-3-fluoro-2-pyridinaldoximes have been synthesised by using a mild and efficient chemoselective hydrogenation of 6-alkynyl-3-fluoro-2-pyridinaldoxime scaffolds, without altering the reducible, unprotected, sensitive oxime functionality and the C−F bond. These novel 6-alkyl-3-fluoro-2-pyridinaldoximes may find medicinal application as antidotes to organophosphate poisoning. Indeed, one low-molecular-weight compound exhibited increased affinity for sarin-inhibited acetylcholinesterase (hAChE) and greater reactivation efficiency or resurrection for sarin-inhibited hAChE, compared with those of 2-pyridinaldoxime (2-PAM) and 1-({[4-(aminocarbonyl)pyridinio]methoxy}methyl)-2-[(hydroxyimino)methyl]pyridinium chloride (HI-6), two pyridinium salts currently used as antidote by several countries. In addition, the uncharged 3-fluorinated bifunctional hybrid showed increased in vitro blood–brain barrier permeability compared with those of 2-PAM, HI-6 and obidoxime. These promising features of novel low-molecular-weight alkylfluoropyridinaldoxime open up a new era for the design, synthesis and discovery of central non-quaternary broad spectrum reactivators for organophosphate-inhibited cholinesterases. 相似文献
23.
24.
25.
26.
Maravanji S. Balakrishna Srinivasan Priya Rashmishree Panda 《Phosphorus, sulfur, and silicon and the related elements》2013,188(4-5):911-914
Ten-membered heterocycles of the type PhN(PCl2){OC6H2(R)2 (μ-S(CH2))((R)2─C6H2O─)} (R = Me, iPr or tBu) have been prepared and their transition metal chemistry is explored. Functionalised phosphines react with transition metals to give interesting metallacycles. Several Group 6, ruthenium, platinum metals and novel titanium(IV) metallacycles have been structurally characterized. 相似文献
27.
Adwait K. Pradhan Gadadhar Panda Nrusingha C. Patl Padma L. Nayak 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(2):501-512
The graft copolymerization of methyl methacrylate onto silk fibers initiated by the ferric chloride-eysteine redox system has been investigated in aqueous medium. The rate of grafting was calculated by varying the concentrations of monomer, initiator, acidity of the medium, cysteine, and temperature. The percentage of grafting increases with an increase of Fe3+ concentration up to 2,5 × 10?3 mol/L and thereafter it decreases. The graft yield increases steadily upon increasing the monomer concentration. The graft yield also increases with increasing cysteine concentration up to 0.5 × 10?3 mol/L and then decreases. The effect of the perchloric acid concentration, temperature, solvents, and certain neutral salts on graft yield has also been investigated and a suitable reaction scheme has been proposed. 相似文献
28.
A series of 4-arylidenamino-5-phenyl-4H-1,2,4-triazole-3-thiols have been synthesised and their inclusion complexes have been prepared with β-cyclodextrin. The compounds and their inclusion complexes have been characterised by studying their physical and spectral properties. The thermodynamic stability constant and free energy of activation have been determined to know the stability of inclusion complexes. Finally, the compounds and their inclusion complexes are screened for antibacterial, antioxidant and anthelmintic activities. It is found that inclusion complexes of the newly synthesised compounds have appreciable stability and inclusion complex formation increases the antibacterial, antioxidant and anthelmintic activities significantly as compared to naked compound. 相似文献
29.
D. P. Maurya M. Aqil B. P. Panda A. Ali 《Journal of Dispersion Science and Technology》2013,34(3):424-432
The main objective of the present work was to formulate and optimize a microparticulate sustained release drug delivery system of isoniazid by using a novel, alkaline extracted ispaghula husk as a polymer. Isoniazid microspheres of alkaline extracted ispaghula husk were prepared by emulsification internal ionic gelation method. Results of preliminary trials indicated that the polymer concentration, cross-linking agent and stirring speed had a noticeable effect on size and surface morphology. A four-factor three-level Box-Behnken design was employed to study the effect of independent variables on dependent variables. The particle size and entrapment efficiency varied from 30.75 to 61.78 µm and 62.27% to 85.80% respectively, depending on the polymer concentration, concentration of cross-linker and stirring speed. Optimized microspheres batch based on point prediction tool of design software exhibited 83.43% drug entrapment and 51.53 µm particle size with 97.80% and 96.37% validity, respectively at the following conditions: sodium alginate (3.55% w/v), alkaline extracted ispaghula husk (3.60% w/v), cross-linker concentration (7.82% w/v), and stirring speed (1200 rpm). The optimized formulation showed controlled drug release for more than 12 hours. The drug release followed Higuchi kinetics via a non-Fickian diffusion. 相似文献
30.
Satyanarayana Reddy Jaggavarapu Anand Solomon Kamalakaran Jagadeesh Babu Nanubolu Venkata Prasad Jalli Sravan Kumar Gangisetty Gopikrishna Gaddamanugu 《Tetrahedron letters》2014
Efficient and facile synthesis of 7H-benzopyrano[3,2-c]coumarins has been achieved by mild base promoted reaction of 4-chloro-3-formylcoumarin with diversely functionalized resorcinols. All the products were obtained as pure precipitates from the reaction mixture and the structure of the product was confirmed by X-ray analysis. 相似文献