全文获取类型
收费全文 | 3881篇 |
免费 | 433篇 |
国内免费 | 204篇 |
专业分类
化学 | 1238篇 |
晶体学 | 32篇 |
力学 | 1158篇 |
综合类 | 22篇 |
数学 | 468篇 |
物理学 | 1600篇 |
出版年
2024年 | 6篇 |
2023年 | 24篇 |
2022年 | 70篇 |
2021年 | 58篇 |
2020年 | 87篇 |
2019年 | 99篇 |
2018年 | 89篇 |
2017年 | 107篇 |
2016年 | 123篇 |
2015年 | 109篇 |
2014年 | 161篇 |
2013年 | 343篇 |
2012年 | 161篇 |
2011年 | 198篇 |
2010年 | 191篇 |
2009年 | 256篇 |
2008年 | 269篇 |
2007年 | 260篇 |
2006年 | 232篇 |
2005年 | 214篇 |
2004年 | 200篇 |
2003年 | 194篇 |
2002年 | 153篇 |
2001年 | 118篇 |
2000年 | 89篇 |
1999年 | 79篇 |
1998年 | 83篇 |
1997年 | 92篇 |
1996年 | 73篇 |
1995年 | 53篇 |
1994年 | 53篇 |
1993年 | 45篇 |
1992年 | 46篇 |
1991年 | 29篇 |
1990年 | 25篇 |
1989年 | 18篇 |
1988年 | 24篇 |
1987年 | 21篇 |
1986年 | 11篇 |
1985年 | 15篇 |
1984年 | 15篇 |
1982年 | 11篇 |
1981年 | 5篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有4518条查询结果,搜索用时 15 毫秒
141.
A convenient one-pot synthesis of benzo[f]pyrimido[4,5-b]quinoline derivatives is described via three-component reaction of benzaldehydes, naphthalen-2-amine, and barbituric acid at room temperature in aqueous media catalyzed by iodine. Compared with other methods, this three-component reaction used a green solvent, gave good yields, and was operationally simple. 相似文献
142.
A general and practical one‐pot synthesis of naphthopyran derivatives using hexadecyltrimethylammonium bromide (HTMAB) as catalyst (10 mol%) is described. This method provides several advantages such as neutral conditions, high yields and simple workup procedure. The catalyst is low cost, facile, active, environmentally friendly, and reusable. In addition, water is chosen as a green solvent. 相似文献
143.
Three-component reaction of aromatic aldehyde, 2-naphthalenamine, and 1,2-diphenylethanone in aqueous media catalyzed by triethylbenzylammonium chloride (TEBAC) at 90 °C gave 3-aryl-3-(naphthalen-2-ylamino)-1,2-diphenylpropan-1-one derivatives. The enol form of 1,2-diphenylethanone was tentatively proposed to participate in the formation of the products. Compared with previous methods, this three-component reaction has the advantages of green solvent, good yields, and operational simplicity. 相似文献
144.
A new and efficient method to synthesize a 3,3,6,6,9‐aryl‐1,8‐dioxo‐octahydroxanthene derivative using diammonium hydrogen phosphate as catalyst was performed in water at room temperature in a short periods. 相似文献
145.
Saeed Balalaie Morteza Bararjanian Masoumeh Sheikh‐Ahmadi Shohreh Hekmat Peyman Salehi 《合成通讯》2013,43(7):1097-1108
Diammonium hydrogen phosphate was used as a mild, efficient, neutral, and cheap catalyst for the synthesis of various 4H‐benzo[b]pyran derivatives via a one‐pot, three‐component condensation of aromatic aldehydes, active methylene compounds, and dimedone in aqueous media. 相似文献
146.
A simple, mild, and ecofriendly method has been developed for the synthesis of 3-vinylchromones from 4-oxo-4H-1-benzopyran-3-carboxaldehyde (3-formylchromone) by simple Knoevenagel condensation with various active methylene compounds (AMC) in aqueous micellar media in the presence of catalytic amounts of cetyl trimethylammonium bromide (CTAB) and 1,4-diazabicyclo[2.2.2]octane (DABCO). In the case of malonic acid as AMC, the reaction resulted in formation of only Doebner decarboxylated products under the standard reaction condition. It has been also observed that 3-formylchromone derivatives primarily undergo tandem Knoevenagel and Michael reactions in the presence of > 2 equiv. of ethyl acetoacetate to produce benzophenone derivatives, by opening of pyran ring, as the sole product in good yields. 相似文献
147.
《合成通讯》2013,43(24):4557-4563
Abstract 6‐Amino‐5‐cyano‐4‐aryl‐1,4‐dihydropyrano[2,3‐c]pyrazoles were synthesized by three‐component reaction of aromatic aldehydes, malononitrile, and 3‐methyl‐1‐phenyl‐2‐pyrazolin‐5‐one using triethylbenzylammonium chloride (TEBA) as catalyst in aqueous media. The reaction has the advantages of good yield, less pollution, ease of separation, and of being environment friendly. 相似文献
148.
Ji Li Ming Wei Qingyang Du Weifeng Liu Guoshun Jiang Changfei Zhu 《Surface and interface analysis : SIA》2013,45(2):682-684
Band alignment at CdS/Cu2ZnSnSe4 heterojunction interface is studied by X‐ray photoemission spectroscopy. The Cu2ZnSnSe4 thin films are prepared by selenization of electrodeposited Cu‐Zn‐Sn precursors. CdS overlayers with different thickness are sequentially grown on the Cu2ZnSnSe4 substrate by pulsed laser deposition process. Photoemission spectra are obtained before and after each growth to study the conduction and valence band offsets at the heterojunction interface. The determined conduction band offset of 0.34 eV indicates a spike‐like ‘type I’ band alignment at CdS/Cu2ZnSnSe4 interface. The spike will avoid interface recombination, and it is low enough that electron could transfer from the Cu2ZnSnSe4 layer to the buffer layer which is suitable for solar cell's fabrication. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
149.
150.
Three diamine monomers with different derivatives of imidazole heterocyclic ring and meta-linked aryl ethers were synthesized and used in polycodensation reaction with various commercial dianhydrides for preparation of a series of novel poly(ether-imide) (PEI)s. The polycodensation reactions were carried out by using conventional method and in a green medium of ionic liquid (IL) without using NMP-pyridine-acetic anhydride. The PEIs were obtained in good yields (80% 96%) with moderate viscosity (0.48 0.66 dL/g) in a shorter reaction time (10 h) in IL as compared with the conventional method (36 h). All of the polymers were amorphous in nature, showed excellent solubility in amide-type polar aprotic solvents with ability to form tough and flexible films, and excellent thermal stability with Tgs in the range of 212 340 ℃ and 10% weight loss temperature (T10) up to 570℃ in N 2 and 528 ℃ in air. 相似文献