全文获取类型
收费全文 | 381篇 |
免费 | 14篇 |
国内免费 | 9篇 |
专业分类
化学 | 282篇 |
晶体学 | 1篇 |
力学 | 13篇 |
数学 | 27篇 |
物理学 | 81篇 |
出版年
2023年 | 1篇 |
2022年 | 8篇 |
2021年 | 13篇 |
2020年 | 17篇 |
2019年 | 12篇 |
2018年 | 16篇 |
2017年 | 10篇 |
2016年 | 18篇 |
2015年 | 10篇 |
2014年 | 18篇 |
2013年 | 37篇 |
2012年 | 30篇 |
2011年 | 34篇 |
2010年 | 24篇 |
2009年 | 18篇 |
2008年 | 23篇 |
2007年 | 17篇 |
2006年 | 31篇 |
2005年 | 18篇 |
2004年 | 11篇 |
2003年 | 5篇 |
2002年 | 8篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 3篇 |
1998年 | 3篇 |
1997年 | 1篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1980年 | 3篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有404条查询结果,搜索用时 0 毫秒
261.
Ghorbani-Vaghei Ramin Malaekehpoor Seyedeh Mina Hasanein Parisa Karamyan Roya Asadbegy Mostafa 《Research on Chemical Intermediates》2016,42(5):4715-4731
Research on Chemical Intermediates - N,N,N′,N′-Tetrachlorobenzene-1,3-disulfonamide and poly(N,N′-dichloro-N-ethyl-benzene-1,3-disulfonamide) are new catalysts promoted by... 相似文献
262.
Shock formation due to flow compressibility and its interaction with boundary layers has adverse effects on aerodynamic characteristics, such as drag increase and flow separation. The objective of this paper is to appraise the prac-ticability of weakening shock waves and, hence, reducing the wave drag in transonic flight regime using a two-dimensional jagged wall and thereby to gain an appropriate jagged wall shape for future empirical study. Different shapes of the jagged wall, including rectangular, circular, and triangular shapes, were employed. The numerical method was validated by experimental and numerical studies involving transonic flow over the NACA0012 airfoil, and the results presented here closely match previous experimental and numerical results. The impact of parameters, including shape and the length-to-spacing ratio of a jagged wall, was studied on aerodynamic forces and flow field. The results revealed that applying a jagged wall method on the upper surface of an airfoil changes the shock structure significantly and disinte-grates it, which in turn leads to a decrease in wave drag. It was also found that the maximum drag coefficient decrease of around 17%occurs with a triangular shape, while the max-imum increase in aerodynamic efficiency (lift-to-drag ratio) of around 10%happens with a rectangular shape at an angle of attack of 2.26?. 相似文献
263.
Reza Sedaghat Herati Ramin Sedaghat Herati 《Journal of polymer science. Part A, Polymer chemistry》2004,42(8):1934-1938
A new poly(ethylene glycol) derivative, 1‐methoxypoly(oxyethylene)benzocyclobutene ( 1 ) was prepared from the reaction of 1‐benzocyclobutenyl 1‐hydroxyethyl ether with mesylate of methoxypoly(oxyethylene) in tetrahydrofuran. The degree of end‐group conversion, as determined by NMR, was 100%. The Diels–Alder reactions of 1 with maleic anhydride and N‐phenylmaleimide were carried out in refluxing toluene to obtain the corresponding adducts ( 2 and 3 , respectively) in excellent yields. NMR analyses of 2 and 3 indicated complete conversion of 1 to the corresponding products. The reaction of 2 with o‐toluidine resulted in complete conversion of the anhydride adduct to the corresponding products. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1934–1938, 2004 相似文献
264.
Gouher Rabani Georgina M. Rosair Arno Kraft 《Journal of polymer science. Part A, Polymer chemistry》2004,42(6):1449-1460
Thermoplastic polyamide elastomers were obtained by polymerization of aminobenzoyl‐substituted telechelics derived from poly(tetrahydrofuran)‐diols (number‐average molecular weight: 1400 or 2000 g mol?1) with several diacid dichlorides (terephthaloyl dichloride, 4,4′‐biphenyldicarbonyl dichloride, or 2,6‐naphthalenedicarbonyl dichloride) and chlorotrimethylsilane in N,N‐dimethylacetamide at 0–20 °C. The as‐prepared polymers had melting temperatures above 190 °C and exhibited elastic properties at room temperature, as evidenced by dynamic mechanical analysis and stress–strain measurements. The polymer with 2,6‐naphthalenedicarboxamide hard segments had the widest rubbery plateau within the series, the highest extension at break, and good recovery properties. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1449–1460, 2004 相似文献
265.
Ramin Ghahremanzadeh Somayyeh Ahadi Maryam Sayyafi Ayoob Bazgir 《Tetrahedron letters》2008,49(29-30):4479-4482
Some new phthalazine derivatives were prepared by reaction of phthalhydrazide and dialkyl acetylenedicarboxylates in the presence of N-heterocycles. 相似文献
266.
Tahmineh Akbarzadeh Saeedeh Noushini Somayeh Taban Mohammad Mahdavi Mahsima Khoshneviszadeh Mina Saeedi Saeed Emami Mohammad Eghtedari Yaghoub Sarrafi Mehdi Khoshneviszadeh Maliheh Safavi Kouros Divsalar Mohammad Hassan Moshafi Ali Asadipour Reyhaneh Sabourian Najmeh Edraki Omidreza Firouzi Ramin Miri Abbas Shafiee Alireza Foroumadi 《Molecular diversity》2015,19(2):273-281
267.
Ramin Faghih 《Journal of carbohydrate chemistry》2013,32(4):619-624
Abstract 2-Deoxy-2-C-methyl-D-glucose (11) was prepared from levoglucosan (4) as an analogue of 2-deoxy-D-glucose (1) in study of the metabolism of glucose in brain. 相似文献
268.
Hadi Adibi Mohammad Bagher Majnooni Sherita Shahidi Maryam Afshar Ramin Abiri 《合成通讯》2013,43(18):2753-2766
Efficient N-acylation of sulfonamides with both readily available carboxylic acid chlorides and anhydrides has been carried out with catalysis by bismuth(III) salts including BiCl3 and Bi (OTf)3. The reactions proceed rapidly in both heterogeneous and solvent-free conditions and afforded the corresponding N-acylsulfonamides in good to excellent yields. The mild reaction conditions and low toxicity of bismuth salts make this procedure attractive and in close agreement with the goals of green chemistry. Some of the synthesized compounds were evaluated in vitro as antimicrobial agents against representative strains of Gram-positive (Staphylococcus aureus ATCC 25922, clinical strains of Staphylococcus aureus VISA and Enterococcus spp.) and Gram-negative bacteria (Pseudomonas aeruginosa ATCC 27853, clinical strains of Klebsiella pneumonia and Escherichia coli) and as antifungal agents against Candida albicans (clinically isolated) by both disc diffusion and minimal inhibition concentration (MIC) methods. All these bacteria and fungi studied were screened against some antibiotics to compare with our chemicals' zone diameters. 相似文献
269.
Ranjbar Saeed Masoumi Hamid Haghighi Khoshkhoo Ramin Mirfendereski Mojtaba 《Journal of Thermal Analysis and Calorimetry》2020,140(5):2505-2518
Journal of Thermal Analysis and Calorimetry - The biggest challenge in dispersion of nanoparticles in phase change materials (PCMs) is the physical stability of these particles in PCM. Numerous... 相似文献
270.
Mirzaei-Mosbat Maryam Ghorbani-Vaghei Ramin Karamshahi Zahra 《Research on Chemical Intermediates》2020,46(2):1613-1628
Research on Chemical Intermediates - In this research, the synthesis route of ZnCr-layered double hydroxides functionalized with poly(p-phenylenediamine) and Cu(II) was described. LDHs@PpPDA@Cu was... 相似文献