全文获取类型
收费全文 | 508篇 |
免费 | 39篇 |
国内免费 | 44篇 |
专业分类
化学 | 278篇 |
晶体学 | 3篇 |
力学 | 108篇 |
综合类 | 27篇 |
数学 | 89篇 |
物理学 | 86篇 |
出版年
2024年 | 2篇 |
2023年 | 8篇 |
2022年 | 14篇 |
2021年 | 23篇 |
2020年 | 29篇 |
2019年 | 21篇 |
2018年 | 16篇 |
2017年 | 18篇 |
2016年 | 27篇 |
2015年 | 11篇 |
2014年 | 23篇 |
2013年 | 45篇 |
2012年 | 21篇 |
2011年 | 26篇 |
2010年 | 26篇 |
2009年 | 23篇 |
2008年 | 25篇 |
2007年 | 33篇 |
2006年 | 25篇 |
2005年 | 23篇 |
2004年 | 20篇 |
2003年 | 27篇 |
2002年 | 18篇 |
2001年 | 12篇 |
2000年 | 11篇 |
1999年 | 17篇 |
1998年 | 7篇 |
1997年 | 5篇 |
1996年 | 4篇 |
1995年 | 9篇 |
1994年 | 5篇 |
1993年 | 7篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1989年 | 2篇 |
1986年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有591条查询结果,搜索用时 0 毫秒
41.
以固体废弃物钼尾矿为主要原料,辅以适量的粘土与石英,制备出了建筑陶瓷砖,并研究了不同烧成温度、保温时间对陶瓷砖性能的影响.结果表明,以钼尾矿为主要原料,采用压制成型法,在烧成温度1165 ℃、保温时间120 min条件下,可制备出抗折强度为46.85 MPa、吸水率为0.43;、体积密度为2.23 g/cm3的高性能陶瓷砖.以钼尾矿为原料制备建筑陶瓷砖,将固体废弃物转化为一种产品,形成一个闭合的产品生产链,可消耗大量的工业固体废弃物,减少其对环境的污染,具有良好的环保效益. 相似文献
42.
Matthias Müller Dr. Silke Koser Olena Tverskoy Dr. Frank Rominger Dr. Jan Freudenberg Prof. Dr. Uwe H. F. Bunz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(24):6082-6086
This work reports the synthesis and characterization of bis- and tetrakis(thiadiazolo)-appended di- and tetraazaacenes, displaying up to seven catenated benzene/pyrazine rings. The targets are obtained by condensation of benzo-bis(thiadiazole)-4,5-dione with aromatic di- and tetraamines. The condensation products—up to a heptacene-like species—are stable but can be insoluble. Soluble derivatives are readily processible, but do not show enhanced electron affinities, as the two or four attached benzothiadiazole units are effectively resonance-separated from the acene body, maximizing the number of Clar-sextets. 相似文献
43.
Dr. Ya‐Qian Lan Dr. Shun‐Li Li Dr. Hai‐Long Jiang Prof. Dr. Qiang Xu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(26):8076-8083
In this work, we have demonstrated a family of diamondoid metal–organic frameworks (MOFs) based on functionalized molecular building blocks and length‐adjustable organic linkers by using a stepwise synthesis strategy. We have successfully achieved not only “design” and “control” to synthesize MOFs, but also the functionalization of both secondary building units (SBUs) and organic linkers in the same MOF for the first time. Furthermore, the results of N2 and H2 adsorption show that their surface areas and hydrogen uptake capacities are determined by the most optimal combination of functional groups from SBUs and organic linkers, interpenetration, and free volume in this system. A member of this series, DMOF‐6 exhibits the highest surface area and H2 adsorption capacity among this family of MOFs. 相似文献
44.
Dr. Michael L. Lejkowski Dr. Ronald Lindner Dr. Takeharu Kageyama Dr. Gabriella É. Bódizs Dipl.‐Chem. Philipp N. Plessow Dr. Imke B. Müller Dr. Ansgar Schäfer Dr. Frank Rominger Prof. Dr. Peter Hofmann Dr. Cornelia Futter Dr. Stephan A. Schunk Dr. Michael Limbach 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(44):14017-14025
For more than three decades the catalytic synthesis of acrylates from the cheap and abundantly available C1 building block carbon dioxide and alkenes has been an unsolved problem in catalysis research, both in academia and industry. Herein, we describe a homogeneous catalyst based on nickel that permits the catalytic synthesis of the industrially highly relevant acrylate sodium acrylate from CO2, ethylene, and a base, as demonstrated, at this stage, by a turnover number of greater than 10 with respect to the metal. 相似文献
45.
Duringthelastdecade,1,3-dioltypechiralbuildingbIocksofvariousconfigurationshavebeensynthesizedandappliedwidelyinthetotalsynthesisofnaturalpolyenemacrolideantibiotics1'2andla,25-dihydroxyvitaminD3analogues'.RecentlyWeigandandBrucker4synthesizedachiralbuildingblock(4R,6R)-2,2-dimethyl-5-tert-butyldip4-hydroxymethyl-l,3-dioxane1inlOsteps.Herein,wereportasyntheticrouteofnewbuildingblock(4S,6S)-2,2-dimethyl-5-tert-butyldip2,anenantiomerofl,startingfromreadilyavailableandinexpensiveD( )-xylose3i… 相似文献
46.
Firoz A. Jaipuri 《Tetrahedron letters》2004,45(21):4149-4152
A versatile route for the modular synthesis of (R)-3-hydroxyalkanoic acids, constituents of the naturally biodegradable poly(3-hydroxyalkanoate) polymers, and its application to the synthesis of (R)-3-hydroxydecanoic acid is described. Key steps include a microwave-assisted catalytic transfer hydrogenation and a facile microwave-assisted hydrolysis of an N-methoxy-N-methyl (Weinreb) amide, which enhances the practicality of this protecting group for carboxylic acids. 相似文献
47.
A metal-organic framework,Ce-FDM-50,was constructed by employing gallic acid featuring both carboxylate and pyrogallate as the coordinating sites and Ce(Ⅲ).The co-assembly of the carboxylates and pyrogallates with two metal ions have achieved a new type of paddle wheel secondary building unit.These building units were further joined by organic struts to obtain frameworks in sql topology.This synthetic approach could be expanded to five different lanthanide metals(Nd,Eu,Gd,Tb,Yb)for the construction of a series of isoreticular MOFs based on FDM-50,and even MTV-MOFs in which mixed lanthanide metals with specific ratios were distributed.In addition,featuring the lanthanide metals as the inorganic nodes in the network,Tb-FDM-50 showed distinct luminescence properties that could be furtherly tuned for variable applications. 相似文献
48.
49.
Li‐Na Wang Zhen‐Xun Zhou Dr. Xiao‐Na Li Dr. Tong‐Mei Ma Prof. Sheng‐Gui He 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(18):6957-6961
In addition to generation of a methyl radical, formation of a formaldehyde molecule was observed in the thermal reaction of methane with AuNbO3+ heteronuclear oxide cluster cations. The clusters were prepared by laser ablation and mass‐selected to react with CH4 in an ion‐trap reactor under thermal collision conditions. The reaction was studied by mass spectrometry and DFT calculations. The latter indicated that the gold atom promotes formaldehyde formation through transformation of an Au?O bond into an Au?Nb bond during the reaction. 相似文献
50.
分别以2种硝基羧酸配体EBNB(1,2-二(3-硝基苯甲酸)-乙烯)和NPA(3-硝基邻苯二甲酸)与BPY(4,4′-联吡啶)及金属锌反应,配位溶剂热法合成了2种具有硝基基团修饰的二核金属簇为基本构筑单元的金属有机框架化合物[Zn2(EBNB)2(BPY)2·2H2O]n(1)和[Zn2(NPA)2(BPY)2·H2O]n(2)。通过X-射线单晶衍射法测定了2种配合物的结构,其中配合物1属于三斜晶系,P1空间群,a=0.818 62(9)nm,b=1.142 20(14)nm,c=1.428 63(17)nm,α=96.803 0(10)°,β=93.045 0(10)°,γ=102.472(2)°,V=1.290 8(3)nm3,Z=2,Mr=595.81,Dc=1.533 g·cm-3,μ=1.01 mm-1,F(000)=608,T=293(2)K;配合物2属于三斜晶系,P1空间群,a=1.154 06(14)nm,b=1.190 86(16)nm,c=1.459 52(19)nm,α=98.029(1)°,β=98.749(1)°,γ=113.579(2)°,V=1.771 9(4)nm3,Z=2,Mr=879.35,Dc=1.648 g·cm-3,μ=1.43 mm-1,F(000)=892,T=293(2)K。同时也对2种配合物的发光性能进行了测试,测试结果表明2种配合物具有较好的荧光性能。 相似文献