全文获取类型
收费全文 | 1373篇 |
免费 | 151篇 |
国内免费 | 183篇 |
专业分类
化学 | 1651篇 |
晶体学 | 9篇 |
力学 | 8篇 |
综合类 | 1篇 |
物理学 | 38篇 |
出版年
2024年 | 1篇 |
2023年 | 19篇 |
2022年 | 24篇 |
2021年 | 38篇 |
2020年 | 59篇 |
2019年 | 49篇 |
2018年 | 57篇 |
2017年 | 50篇 |
2016年 | 74篇 |
2015年 | 40篇 |
2014年 | 87篇 |
2013年 | 115篇 |
2012年 | 125篇 |
2011年 | 93篇 |
2010年 | 69篇 |
2009年 | 85篇 |
2008年 | 70篇 |
2007年 | 103篇 |
2006年 | 85篇 |
2005年 | 85篇 |
2004年 | 66篇 |
2003年 | 47篇 |
2002年 | 66篇 |
2001年 | 27篇 |
2000年 | 21篇 |
1999年 | 20篇 |
1998年 | 17篇 |
1997年 | 19篇 |
1996年 | 23篇 |
1995年 | 10篇 |
1994年 | 14篇 |
1993年 | 13篇 |
1992年 | 11篇 |
1991年 | 2篇 |
1990年 | 6篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 2篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有1707条查询结果,搜索用时 250 毫秒
71.
Six pentacyclic triterpene acids, ursolic acid, oleanolic acid, betulinic acid, 23-hydroxybetulinic acid, glycyrrhetinic acid, and senegenin, were metabolized by the microbe Nocardia sp. NRRL 5646 to selectively furnish their corresponding 28-methyl esters. Notably, ursolic acid (1) was converted to oleanolic acid methyl ester (4) via two intermediates, oleanolic acid (2), and ursolic acid methyl ester (3), which are formed by participation of ‘retro-biosynthetic’ methyl migration from C-19 to C-20. Senegenin (11) was selectively converted to a nortriterpene methyl ester, senegenic acid methyl ester (12), via an unprecedented C-C bond cleavage. The stereochemical assignments of compounds 11 and 12 were made unambiguously for the first time using 2D NMR spectroscopy. 相似文献
72.
Fe_3(CO)_(12)与配位基前体P(NEt_2)_2Cl反应,给出4个新的两核和三核铁羰基簇合衍生物:Fe_2(CO)_6(μ-Cl)[μ-P(NEt_2)_2](Ⅰ),Fe_2(CO)_6[μ-P(NEt_2)_2]_2(Ⅱ),Fe_3(CO)_9(μ-CO)(μ_3-PNEt_2)(Ⅲ)和Fe_3(CO)_9(μ_3-PNEt_2)[P(NEt_2)_3](Ⅳ)。在反应期间,配前体分子中的P-Cl和P-N键劈开,形成的分子片Cl、PNEt_2、P(NEt_2)_2和P(NEt_2)_3作为配体与铁羰合物重新组建成上述簇合物。利用X射线衍射法测定了它们的晶体结构。Ⅰ属三斜晶系,P1空间群,晶胞参数a=0.8745(6)nm,b=0.9601(7)nm,c=1.3996(10)nm,α=74.131(11)°,β=79.480(12)°,γ=69.727(12)°,V=1.0553(13)nm~3,D_c=1.543g·cm~(-3),Z=2,R=0.0443,wR=0.0831。Ⅱ属正交晶系,Pbcn空间群,晶胞参数a=1.0153(3)nm,b=1.7543(5)nm,c=1.6860(5)nm,V=3.0031(15)nm~3,D_c=1.394g·cm~(-3),Z=4,R=0.0519,wR=0.1035。Ⅲ属单斜晶系,P2_1/c空间群,晶胞参数a=1.0280(5)nm,b=1.2113(5)nm,c=1.9192(7)nm,β=93.560(7)°,V=2.1366(16)nm~3,D_c=1.712g·cm~(-3),Z=4。Ⅳ属单斜晶系,Cc空间群,晶胞参数a=1.5875(7)nm,b=1.0359(5)nm,C=2.1919(9)nm,β=101.266(8)°,V=3.535(3)nm~3,Dc=1.443g·cm~(-3),Z=4。Ⅰ和Ⅱ为两核铁簇,其簇骨架Fe_2PCl和Fe_2P_2呈蝶状。Ⅲ和Ⅳ 相似文献
73.
Synthesis,characterization and biological screening studies of mixed ligand complexes using flavonoids as precursors
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)
Flavonoids are a group of plant phenolics that provide various health benefits through cell signalling pathways and antioxidant effects. In the present study, a new series of mixed ligand complexes of Co(II), Ni(II), Cu(II) and Zn(II) were synthesized by incorporating curcumin and quercetin flavonoid precursors. The structural features of the synthesized complexes were explored using elemental analysis, thermogravimetric analysis, UV–visible, infrared, NMR, mass and electron paramagnetic resonance spectral analyses and conductivity measurements. These data support an octahedral geometry of the synthesized complexes. In silico biological activity score for the ligand was predicted using PASS online software. ADMET properties were studied using VLS3D online software. Anti‐inflammatory and antioxidant activities were experimentally validated which prove that theoretical predictions are in agreement with the experimental results. Interestingly the synthesized complexes interact with calf thymus DNA through groove binding mode. Moreover, they have good potential to cleave pUC19 DNA. Minimum inhibitory concentration values of the synthesized complexes reveal that they have better antimicrobial efficacy than the ligands. 相似文献
74.
《Journal of Coordination Chemistry》2012,65(4):714-727
Four dioxomolybdenum(VI) complexes were synthesized by reaction of [MoO2(acac)2] with thiosemicarbazones derived from 5-allyl-2-hydroxy-3-methoxybenzaldehyde (1), 2-hydroxynaphthaldehyde (2), 2,3-dihydroxybenzaldehyde (3), or 5-tert-butyl-2-hydroxybenzaldehyde (4). The ligands were coordinated to molybdenum as tridentate ONS donors. X-ray crystallography showed that the distorted octahedral coordination of molybdenum is completed by methanol (D) in 1a, 3a, and 4a or H2O in 2a. The molecular structures of 1, 3, and 4, and the complexes were determined by single-crystal X-ray crystallography. Binding of the ligand and complexes with calf thymus DNA were investigated by UV, fluorescence titrations, and viscosity measurements. Gel electrophoresis revealed that all the complexes can cleave pBR322 plasmid DNA. The cytotoxic properties of the complexes against human colorectal (HCT 116) cell line showed strong antiproliferative activities in relative order 4a?>?3a?>?1a?>?2a with IC50 values of 1.6, 4.0, 4.8, and 6.7?μM, respectively. The complexes exhibited more activity than the standard reference drug, 5-fluorouracil (IC50 7.3?μM). These studies show that dioxomolybdenum(VI) complexes have potential use in chemotherapy. 相似文献
75.
76.
77.
Trans‐1,2‐cyclohexanediol and trans‐2‐aminocycloxexanol are useful chiral auxiliaries. Simple chemical resolution procedures for these molecules are presented. 相似文献
78.
A reliable method for direct synthesis of β‐dichlorosubstituted acetanilides is reported. The key transformation involves the oxidative and catalytic cleavage of a carbon‐carbon bond in the presence of iodine trichloride (ICl3). In this protocol ICl3 is used not only as the catalyst but also as the oxidant which widely broadens the scope of its application in organic synthetic chemistry. 相似文献
79.
S. Munavalli D. K. Rohrbaugh H. D. Durst 《Phosphorus, sulfur, and silicon and the related elements》2013,188(8):1657-1671
Trifluoromethylthiocopper has been found to catalyze the opening of the epoxide ring and to furnish not-so-easily accessible novel trifluoromethylthiolated α-hydroxy compounds. This communication presents the mechanism of the formation of the various compounds and their mass spectral data. 相似文献
80.
Peng Yao 《应用有机金属化学》2014,28(3):194-197
An efficient and simple synthetic method for biaryl synthesis was developed using Pd(OAc)2 as catalyst from aryl hydrazides under O2. Various biaryls were synthesized in good yields, offering an expedient protocol for the synthesis of symmetrical biaryl molecules via C―N cleavage. The reactions were performed in component solvent of toluene and acetone without using any pro‐oxidant. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献