全文获取类型
收费全文 | 26198篇 |
免费 | 2781篇 |
国内免费 | 2169篇 |
专业分类
化学 | 12641篇 |
晶体学 | 191篇 |
力学 | 811篇 |
综合类 | 265篇 |
数学 | 12049篇 |
物理学 | 5191篇 |
出版年
2023年 | 391篇 |
2022年 | 401篇 |
2021年 | 534篇 |
2020年 | 831篇 |
2019年 | 776篇 |
2018年 | 783篇 |
2017年 | 664篇 |
2016年 | 958篇 |
2015年 | 926篇 |
2014年 | 1456篇 |
2013年 | 2262篇 |
2012年 | 1341篇 |
2011年 | 1575篇 |
2010年 | 1358篇 |
2009年 | 1593篇 |
2008年 | 1750篇 |
2007年 | 1724篇 |
2006年 | 1427篇 |
2005年 | 1161篇 |
2004年 | 1042篇 |
2003年 | 1060篇 |
2002年 | 880篇 |
2001年 | 726篇 |
2000年 | 666篇 |
1999年 | 627篇 |
1998年 | 577篇 |
1997年 | 436篇 |
1996年 | 417篇 |
1995年 | 402篇 |
1994年 | 341篇 |
1993年 | 237篇 |
1992年 | 227篇 |
1991年 | 156篇 |
1990年 | 129篇 |
1989年 | 119篇 |
1988年 | 129篇 |
1987年 | 89篇 |
1986年 | 79篇 |
1985年 | 123篇 |
1984年 | 102篇 |
1983年 | 49篇 |
1982年 | 108篇 |
1981年 | 78篇 |
1980年 | 54篇 |
1979年 | 77篇 |
1978年 | 65篇 |
1977年 | 59篇 |
1976年 | 55篇 |
1975年 | 29篇 |
1973年 | 35篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
1.
《Mendeleev Communications》2022,32(5):629-631
The Michael–Mannich cascade cyclization of cyano olefins, ethyl 4,4,4-trifluoro-3-oxobutanoate, aromatic aldehydes and ammonium acetate provides convenient stereoselective formation of ethyl 5,5-dicyano-4,6-diaryl-2-hydroxy-2-(trifluoromethyl)piperidine-3-carboxylates with fourstereogenic centers and dialkyl 4,6-diaryl-5-cyano-2-hydroxy-2-(trifluoromethyl)piperidine-3,5-dicarboxylates with five stereogenic centers. Ammonium acetate plays dual role, acting as a base and as a nitrogen source. 相似文献
2.
3.
为提高煤与瓦斯突出矿井瓦斯抽放效果,建立了3个一级指标、14个二级指标的突出矿井瓦斯抽放限制影响因素评价指标体系,利用AHP和熵权法分别确定指标因子主、客观权重.通过实地调研分析和反馈验证了AHP-熵权法的可行性和正确性,利用加权平均法确定评价模型的综合权重.研究表明:封孔方式、钻孔半径、抽放时间、煤体裂隙发育程度和抽放负压是目前影响煤矿瓦斯抽放效果的主控因素. 相似文献
4.
Tapasi Chand Laxmikanta Khamari Deepak Chopra Saptarshi Mukherjee Manmohan Kapur 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(43):e202200723
A one-step Rh-catalyzed site-selective ortho-C−H alkynylation of perylene as well as naphthalene mono- and diimides is reported. A single step regioselective access to ortho-C−H alkynylated derivatives of these ryleneimides not only increases the step economy of the ortho-functionalization on these dyes but also provides a quick access route towards highly functionalized dyes that have potential optoelectronic applications. Increased solubility of tetra(triisopropylsilyl)acetylenyl PDIs in organic solvents greatly enhances their utility for further derivatization. 相似文献
5.
6.
In this work, a vanillin complex is immobilized onto MCM-41 and characterized by FT-IR, X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, thermogravimetric analysis, and BET techniques. This supported Schiff base complex was found to be an efficient and recoverable catalyst for the chemoselective oxidation of sulfides into sulfoxides and thiols into their corresponding disulfides (using hydrogen peroxide as a green oxidant) and also a suitable catalyst for the preparation of 2,3-dihydroquinazolin-4(1H)-one derivatives in water at 90°C. Using this protocol, we show that a variety of disulfides, sulfoxides, and 2,3-dihydroquinazolin-4(1H)-one derivatives can be synthesized in green conditions. The catalyst can be recovered and recycled for further reactions without appreciable loss of catalytic performance. 相似文献
7.
8.
Caesium carbonate supported on hydroxyapatite‐encapsulated Ni0.5Zn0.5Fe2O4 nanocrystallites as a novel magnetically basic catalyst for the one‐pot synthesis of pyrazolo[1,2‐b]phthalazine‐5,10‐diones
下载免费PDF全文
![点击此处可从《应用有机金属化学》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Behrooz Maleki Samaneh Barat Nam Chalaki Samaneh Sedigh Ashrafi Esmail Rezaee Seresht Farid Moeinpour Amir Khojastehnezhad Reza Tayebee 《应用有机金属化学》2015,29(5):290-295
A novel nanomagnetic basic catalyst of caesium carbonate supported on hydroxyapatite‐coated Ni0.5Zn0.5Fe2O4 magnetic nanoparticles (Ni0.5Zn0.5Fe2O4@HAP‐Cs2CO3) was prepared. This new catalyst was fully characterized using Fourier transform infrared spectroscopy, transmission and scanning electron microscopy, X‐ray diffraction and vibrating sample magnetometry techniques, and then the catalytic activity of this catalyst was investigated in the synthesis of 1H‐pyrazolo[1,2‐b]phthalazine‐5,10‐dione derivatives. Also, Ni0.5Zn0.5Fe2O4@HAP‐Cs2CO3 could be reused at least five times without significant loss of activity and could be recovered easily by applying an external magnet. Thus, the developed nanomagnetic catalyst is potentially useful for the green and economic production of organic compounds. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
9.
Inside Cover: Ru‐Catalysed CH Arylation of Indoles and Pyrroles with Boronic Acids: Scope and Mechanistic Studies (Chem. Eur. J. 14/2015)
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
10.