全文获取类型
收费全文 | 1732篇 |
免费 | 108篇 |
国内免费 | 401篇 |
专业分类
化学 | 2126篇 |
晶体学 | 29篇 |
力学 | 2篇 |
综合类 | 12篇 |
物理学 | 72篇 |
出版年
2024年 | 2篇 |
2023年 | 13篇 |
2022年 | 22篇 |
2021年 | 26篇 |
2020年 | 54篇 |
2019年 | 52篇 |
2018年 | 54篇 |
2017年 | 49篇 |
2016年 | 68篇 |
2015年 | 71篇 |
2014年 | 87篇 |
2013年 | 223篇 |
2012年 | 115篇 |
2011年 | 91篇 |
2010年 | 69篇 |
2009年 | 90篇 |
2008年 | 106篇 |
2007年 | 99篇 |
2006年 | 105篇 |
2005年 | 120篇 |
2004年 | 122篇 |
2003年 | 113篇 |
2002年 | 65篇 |
2001年 | 55篇 |
2000年 | 35篇 |
1999年 | 31篇 |
1998年 | 32篇 |
1997年 | 24篇 |
1996年 | 27篇 |
1995年 | 33篇 |
1994年 | 28篇 |
1993年 | 29篇 |
1992年 | 35篇 |
1991年 | 17篇 |
1990年 | 7篇 |
1989年 | 8篇 |
1988年 | 16篇 |
1987年 | 6篇 |
1985年 | 3篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 6篇 |
1980年 | 2篇 |
1979年 | 5篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有2241条查询结果,搜索用时 15 毫秒
81.
以2-氯-5-氯甲基吡啶(CCMP)、无水乙二胺和硝基胍为原料,运用串联反应方法合成了吡虫啉[化学名:1-(6-氯-3-吡啶甲基)-N-硝基-2-咪唑啉亚胺]。该方法反应中间体无需纯化处理,操作简单,同时解决了活性中间体进一步进行副反应的难题。通过单因素实验,探讨了pH、反应溶剂、温度以及时间等因素对产物收率的影响,得到的优化工艺条件为:以乙腈为溶剂,nCCMP∶n无水乙二胺∶n硝基胍=1∶5∶1,于30℃反应120min,产率可达96.35%。其结构经1H NMR、13C NMR、IR表征。 相似文献
82.
Direct X‐ray Observation of Trapped CO2 in a Predesigned Porphyrinic Metal–Organic Framework 下载免费PDF全文
Jacob A. Johnson Dr. Shuang Chen Tyler C. Reeson Dr. Yu‐Sheng Chen Prof. Xiao Cheng Zeng Prof. Jian Zhang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(25):7632-7637
Metal–organic frameworks (MOFs) are emerging microporous materials that are promising for capture and sequestration of CO2 due to their tailorable binding properties. However, it remains a grand challenge to pre‐design a MOF with a precise, multivalent binding environment at the molecular level to enhance CO2 capture. Here, we report the design, synthesis, and direct X‐ray crystallographic observation of a porphyrinic MOF, UNLPF‐2, that contains CO2‐specific single molecular traps. Assembled from an octatopic porphyrin ligand with [Co2(COO)4] paddlewheel clusters, UNLPF‐2 provides an appropriate distance between the coordinatively unsaturated metal centers, which serve as the ideal binding sites for in situ generated CO2. The coordination of CoII in the porphyrin macrocycle is crucial and responsible for the formation of the required topology to trap CO2. By repeatedly releasing and recapturing CO2, UNLPL‐2 also exhibits recyclability. 相似文献
83.
Colette Lebrun Dr. Matthieu Starck Vicky Gathu Yves Chenavier Dr. Pascale Delangle 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(50):16566-16573
Peptides are interesting tools to rationalize uranyl–protein interactions, which are relevant to uranium toxicity in vivo. Structured cyclic peptide scaffolds were chosen as promising candidates to coordinate uranyl thanks to four amino acid side chains pre‐oriented towards the dioxo cation equatorial plane. The binding of uranyl by a series of decapeptides has been investigated with complementary analytical and spectroscopic methods to determine the key parameters for the formation of stable uranyl–peptide complexes. The molar ellipticity of the uranyl complex at 195 nm is directly correlated to its stability, which demonstrates that the β‐sheet structure is optimal for high stability in the peptide series. Cyclodecapeptides with four glutamate residues exhibit the highest affinities for uranyl with log KC=8.0–8.4 and, therefore, appear as good starting points for the design of high‐affinity uranyl‐chelating peptides. 相似文献
84.
Organotin–Oxido Cluster‐Based Multiferrocenyl Complexes Obtained by Hydrolysis of Ferrocenyl‐Functionalized Organotin Chlorides 下载免费PDF全文
Zhiliang You Robert Möckel Jakob Bergunde Prof. Dr. Stefanie Dehnen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(42):13491-13496
Three organotin–oxido clusters were formed by hydrolysis of ferrocenyl‐functionalized organotin chloride precursors in the presence of NaEPh (E=S, Se). [RFcSnCl3?HCl] ( C ; RFc = CMe2CH2C(Me)?N?N?C(Me)Fc) and [SnCl6]2? formed {(RFcSnCl2)3[Sn(OH)6]}[SnCl3] ( 3 a ) and {(RFcSnCl2)3[Sn(OH)6]}[PhSeO3] ( 3 b ), bearing an unprecedented [Sn4O6] unit, in a one‐pot synthesis or stepwise through [(RFcSnCl2)2Se] ( 1 ) plus [(RFcSnCl2)SePh] ( 2 ). A one‐pot reaction starting out from FcSnCl3 gave [(FcSn)9(OH)6O8Cl5] ( 4 ), which represents the largest Fc‐decorated Sn/O cluster reported to date. 相似文献
85.
Charanjeet Kaur Mangat 《Journal of Dispersion Science and Technology》2014,35(11):1528-1536
New pyridinium gemini surfactants have been synthesized by esterification of renewable fatty acids with mercaptoethanol furnishing respective esters (mercaptomethyl decanoate, mercaptomethyl dodecanoate, mercaptomethyl tetradecanoate, mercaptomethyl hexadecanoate) followed by their subsequent treatment with 4-dimethyl amino pyridine resulting in the formation of title gemini surfactants: 1-(5-(decanoyloxy)-2-hydroxypentyl)-4-((5-(decanoyloxy)-2-hydroxypentyl)dimethyl ammonio)pyridin-1-ium chloride (9), 1-(5-(dodecanoyloxy)-2-hydroxypentyl)-4-((5-(dodecanoyloxy)-2-hydroxypentyl)dimethyl ammonio)pyridin-1-ium chloride (10), 1-(5-(tetradecanoyloxy)-2-hydroxypentyl)-4-((5-(tetradecanoyloxy)-2-hydroxypentyl)dimethyl ammonio)pyridin-1-ium chloride (11), and 1-(5-(hexadecanoyloxy)-2-hydroxypentyl)-4-((5-(hexadecanoyloxy)-2-hydroxypentyl)dimethyl ammonio)pyridin-1-ium chloride (12). Their identifications are based on infrared, 1H NMR, 13C NMR, distortionless enhanced polarization transfer, co-relational spectroscopy (COSY), and mass spectral studies. Their surface active properties are also evaluated on the basis of surface tension and conductivity measurements. Thermal stability of these long chain cationic gemini surfactants have been measured by thermal gravimetric analysis under nitrogen atmosphere. 相似文献
86.
Jian‐Hua Zou Da‐Liang Zhu Fei‐Fei Li Fu‐Song Li He Wu Qiao‐Yun Li Gao‐Wen Yang Ping Zhang Yun‐Xia Miao Jian Xie 《无机化学与普通化学杂志》2014,640(11):2226-2231
Reactions of three tetrazole containing carboxylic acid ligands, namely, Hpztza, Htzpya, and Hpytza [Hpztza = 5‐(2‐pyrazinyl)tetrazole‐2‐acetic acid, Htzpya = 3‐(5‐tetrazolyl)pyridine‐1‐acetic acid, Hpytza = 5‐(3‐pyridyl)tetrazole‐2‐acetic acid] with NdCl3 · 6H2O under hydrothermal conditions, afforded the complexes [Nd(pztza)2(H2O)6] · pztza · 3H2O ( 1 ), [Nd2(tzpya)2(H2O)12]Cl4 · 2H2O ( 2 ), and [Nd(pytza)2Cl(H2O)2] ( 3 ). The compounds were structurally characterized by elemental analysis, IR spectroscopy and single‐crystal X‐ray diffraction. X‐ray diffraction analyses revealed that compound 1 displays a mononuclear structure, 2 shows a dinuclear structure, and 3 features a 1D polymeric chain structure via pytza as linker. Furthermore, the luminescent properties investigated at room temperature in the solid state show that compound 2 has an obvious decrease in its luminescence, when compared to the ligand. 相似文献
87.
A convenient and highly convergent method for the synthesis of new imidazo[1,2-a]pyridine-based coelenterazine analogues is reported. The imidazo[1,2-a]pyridine core was constructed through a condensation between 2-aminopyridine analogues and arylglyoxals. Additionally, a new approach to the synthesis of benzylglyoxals was introduced. The imidazo[1,2-a]pyridines display moderate antioxidant activities at a low micromolar level in 2,2-diphenyl-1-picrylhydrazyl (DPPH). 相似文献
88.
利用三有机锡氢氧化物和手性配体(4R)-3-[[(2S)-5-氧-2-吡咯烷基]羰基]-4-噻唑烷甲酸(HL)反应合成了3个三有机锡(4R)-3-[[(2S)-5-氧-2-吡咯烷基]羰基]-4-噻唑烷甲酸酯R3SnL[1,R=c-C6H11(a),C6H5(b),C6H5C(CH3)2CH2(c)],通过元素分析、IR、1H NMR和X-射线单晶衍射表征了其结构。化合物1a属正交晶系,P212121空间群;化合物1b属单斜晶系,P21空间群。二者均为由羧基氧和内酰胺羰基氧桥联配位形成的右螺旋链状有机锡配位聚合物,锡原子具有五配位[SnC3O2]畸变三角双锥构型。化合物1a和1b对体外2种人癌细胞Colo205和Bcap37增殖均有强的抑制作用,其活性为1b1a。 相似文献
89.
以2,6-二(甲基苯并咪唑)吡啶和2,2′-联吡啶为配体,合成了一个钴的配合物[Co(mbzimpy)(bipy)Cl]Cl O4·1.3H2O(1)和一个镨的配合物[Pr(mbzimpy)2(NO3)2]Cl O4·2CH3COCH3(2),(mbzimpy=2,6-bis(methylbenzimidazol-2-yl)pyridine,bipy=2,2′-bipyridine)并利用单晶衍射对其结构进行了表征。还对配合物1和2的荧光和电化学性质进行了研究。晶体结构中C-H…O氢键和π-π芳环堆积作用将每个单核分子连接成一个三维的空间结构。配合物1的TD-DFT理论计算的结果表明:实验得到的紫外谱图和理论计算的紫外谱图较好地吻合。通过循环伏安图可以了解金属中心的氧化和还原电子对。在不同偶极矩的溶剂中研究其荧光性能。 相似文献
90.
在含水甲苯中,2,4-二氯苄与锡粉反应合成了二(2,4-二氯苄基)二氯化锡,将其分别与2-羰基丙酸(苯甲酰基)腙及2-羰基丙酸(水杨酰基)腙反应,合成了2个取代苄基锡配合物(C2、C3),配合物C2和C3通过元素分析、1H NMR、13C NMR、IR、UV-Vis等表征,运用X-射线单晶衍射测试了2个有机锡配合物的分子结构,结构分析表明,锡与配位原子形成变形五角双锥构型的双核有机锡配合物,分子以Sn2O2四元环为中心对称。热分析结果表明,在空气氛下,配合物C2在121℃、C3在128℃以下可稳定存在;在Tris-HCl缓冲溶液中,以EB做为荧光探针,用荧光光谱法初步研究了配合物与鲱鱼精DNA的相互作用,结果表明配合物与鲱鱼精DNA作用是插入结合与静电结合共同作用所致。 相似文献