全文获取类型
收费全文 | 794篇 |
免费 | 63篇 |
国内免费 | 113篇 |
专业分类
化学 | 907篇 |
晶体学 | 26篇 |
力学 | 4篇 |
综合类 | 3篇 |
数学 | 9篇 |
物理学 | 21篇 |
出版年
2024年 | 1篇 |
2023年 | 16篇 |
2022年 | 15篇 |
2021年 | 20篇 |
2020年 | 37篇 |
2019年 | 30篇 |
2018年 | 28篇 |
2017年 | 23篇 |
2016年 | 36篇 |
2015年 | 25篇 |
2014年 | 42篇 |
2013年 | 96篇 |
2012年 | 49篇 |
2011年 | 45篇 |
2010年 | 24篇 |
2009年 | 37篇 |
2008年 | 40篇 |
2007年 | 38篇 |
2006年 | 37篇 |
2005年 | 46篇 |
2004年 | 47篇 |
2003年 | 25篇 |
2002年 | 21篇 |
2001年 | 20篇 |
2000年 | 27篇 |
1999年 | 12篇 |
1998年 | 16篇 |
1997年 | 18篇 |
1996年 | 27篇 |
1995年 | 8篇 |
1994年 | 9篇 |
1993年 | 12篇 |
1992年 | 8篇 |
1991年 | 4篇 |
1990年 | 9篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1977年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有970条查询结果,搜索用时 12 毫秒
961.
Efficient Synthesis of (−)‐Corynoline by Enantioselective Palladium‐Catalyzed α‐Arylation with Sterically Hindered Substrates
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Xiaofeng Rao Dr. Naikai Li Heng Bai Chaodi Dai Dr. Zheng Wang Prof. Dr. Wenjun Tang 《Angewandte Chemie (International ed. in English)》2018,57(38):12328-12332
Sterically hindered substrates can be employed in an enantioselective palladium‐catalyzed α‐arylation with the chiral monophosphorus ligand BI‐DIME. This process enabled an efficient synthesis of the antidepressant (S)‐nafenodone, a four‐step enantioselective synthesis of the Sceletium alkaloid (+)‐sceletium A‐4, a concise five‐step enantioselective synthesis of (?)‐corynoline, as well as a three‐step preparation of (?)‐DeN‐corynoline. 相似文献
962.
Additive Effects in the Palladium‐Catalyzed Carboiodination of Chiral N‐Allyl Carboxamides
下载免费PDF全文
![点击此处可从《Angewandte Chemie (International ed. in English)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
David A. Petrone Hyung Yoon Dr. Harald Weinstabl Prof. Dr. Mark Lautens 《Angewandte Chemie (International ed. in English)》2014,53(30):7908-7912
The use of Pd catalysis as a means to synthesize organic halides has recently received increased attention. Among the reported methods is the Pd‐catalyzed carboiodination, which uses extremely bulky ligands to facilitate carbon–halogen reductive elimination from PdII as the key catalytic step. When approaching substrates exhibiting low stereoselectivity, catalyst troubleshooting becomes difficult as there are few ligands known to promote the key reductive elimination. Herein, we present our finding that tertiary amines act as weakly coordinating ligands which significantly enhance diastereoselectivity in the Pd/QPhos‐catalyzed carboiodination of chiral N‐allyl carboxamides. This methodology allows efficient access to enantioenriched and densely functionalized dihydroisoquinolinones, and has been applied toward the asymmetric formal synthesis of (+)‐corynoline. 相似文献
963.
DFT calculations at the BP86/TZ2P level were carried out to analyze quantitatively the metal–ligand bonding in transition‐metal complexes that contain imidazole (IMID), imidazol‐2‐ylidene (nNHC), or imidazol‐4‐ylidene (aNHC). The calculated complexes are [Cl4TM(L)] (TM=Ti, Zr, Hf), [(CO)5TM(L)] (TM=Cr, Mo, W), [(CO)4TM(L)] (TM=Fe, Ru, Os), and [ClTM(L)] (TM=Cu, Ag, Au). The relative energies of the free ligands increase in the order IMID<nNHC<aNHC. The energy levels of the carbon σ lone‐pair orbitals suggest the trend aNHC>nNHC>IMID for the donor strength, which is in agreement with the progression of the metal–ligand bond‐dissociation energy (BDE) for the three ligands for all metals of Groups 4, 6, 8, and 10. The electrostatic attraction can also be decisive in determining trends in ligand–metal bond strength. The comparison of the results of energy decomposition analysis for the Group 6 complexes [(CO)5TM(L)] (L=nNHC, aNHC, IMID) with phosphine complexes (L=PMe3 and PCl3) shows that the phosphine ligands are weaker σ donors and better π acceptors than the NHC tautomers nNHC, aNHC, and IMID. 相似文献
964.
965.
《Journal of Saudi Chemical Society》2023,27(2):101621
An environmentally benign highly atom-economic protocol for the construction of the CC bond has been developed under catalyst- and solvent-free conditions. This protocol involves the efficient coupling of 2-methyl quinazolinones with 3-(trifluoroacetyl)coumarins for the access of quinazolinone derivatives in excellent yields (up to 90 %). The crystal structure of compound 3di was investigated by X-ray diffraction analysis. The biological activities, such as in vitro antifungal activity of the quinazolinone derivatives against Fusarium graminearum, Fusarium moniliforme, Fusarium oxysporum, Phytophthora parasitica var nicotianae, and Rhizoctonia solani Kuhn, were investigated. The bioassay results indicated that most of the target products exhibited promising fungicidal activities, and compound 3 cl exhibited 95 % fungicidal activity against R. solani, with an EC50 value of 10.6 μg/mL. 相似文献
966.
Changjiang Li Zhaozhou Li Kunpeng Tan Prof. Dr. Guodu Liu 《European journal of organic chemistry》2023,26(33):e202300398
Rhodium-catalyzed hydroformylation of olefins is an important method for synthesizing aldehydes, and it is worth noting that regioselectivity and enantioselectivity of the product controlled by ligand are the most commonly used strategies. The modular synthesis of phosphite and phosphoramidite ligands have significant advantages of simple synthesis and high catalytic activity, which was why these ligands have been widely used in hydroformylation reactions. Herein, we focus on the synthesis methods and design ideas of such ligands, as well as their application effects in hydroformylation reactions. This review aims to provide a reference for the design and synthesis of ligands in hydroformylation subsequently. 相似文献
967.
Chen-Hui Yuan Xiao-Xia Wang Prof. Dr. Lei Jiao 《Angewandte Chemie (International ed. in English)》2023,62(17):e202300854
Amide is one of the most widespread functional groups in organic and bioorganic chemistry, and it would be valuable to achieve stereoselective C(sp3)−H functionalization in amide molecules. Palladium(II) catalysis has been prevalently used in the C−H activation chemistry in the past decades, however, due to the weakly-coordinating feature of simple amides, it is challenging to achieve their direct C(sp3)−H functionalization with enantiocontrol by PdII catalysis. Our group has developed sulfoxide-2-hydroxypridine (SOHP) ligands, which exhibited remarkable activity in Pd-catalyzed C(sp2)−H activation. In this work, we demonstrate that chiral SOHP ligands served as an ideal solution to enantioselective C(sp3)−H activation in simple amides. Herein, we report an efficient asymmetric PdII/SOHP-catalyzed β-C(sp3)−H arylation of aliphatic tertiary amides, in which the SOHP ligand plays a key role in the stereoselective C−H deprotonation-metalation step. 相似文献
968.
通过直接计算分子配分函数并将常温下的无转动跃迁偶极矩平方近似为一常数应用到高温,计算了对称陀螺分子PH3 0010-0000跃迁的高温线强度。在296K,计算的分子总配分函数与HITRAN数据库的结果符合很好,只有-0.075%的百分误差。计算的跃迁线强度在2000 K和3000 K的高温与HITRAN数据库的结果也吻合较好,表明分子配分函数和线强度的高温计算是可靠的。在此基础上,进一步计算了更高温度4000和5000 K的跃迁线强度,报道了对称陀螺分子PH3 0010-0000跃迁在极端高温4000和5000 K的模拟光谱。计算结果对大气分子高温光谱的实验测量和理论研究均有一定的参考价值。 相似文献
969.
合成了四(三苯基氧膦)合硫氰酸钕配合物,通过元素分析及分子量测定,确定了该配合物的化学式为Nd(NCS)3·4ph3P=O。经x射线单晶衍射测定了该配合物的结构,晶体属单斜晶系,P21/C空间群,晶体学参数如下: a=13.221(7)Å v=6943Å3 b=23.544(14)Å z=4 c=22.821(18)Å d实验值=1.375g/cm3 β=102.19(5)° d计算值=1.370g/cm3 F(0,0,0,0)=2924e 吸收系数μ=9.8cm-1(MoKa) 钕的配位数为七,三个NCS-根以氮与钕配位,平均键长2.50Å,四个三苯基氧膦以膦酰基上的氧与钕配位,平均Nd—O键长2.39Å。分子具有近似的C8对称性。 相似文献
970.
Recent findings in the use of multidentate phosphines to synthesise porous coordination polymers (metal-organic frameworks) and their possible precursor cages are reviewed. Additional recent investigations into using large adamantoid Age cages as polymer vertices in giant diamandoid structures are also presented. The results are discussed in terms of possible strategies for the controled synthesis of porous coordination polymers. 相似文献