全文获取类型
收费全文 | 561篇 |
免费 | 14篇 |
国内免费 | 12篇 |
专业分类
化学 | 397篇 |
晶体学 | 3篇 |
力学 | 25篇 |
数学 | 87篇 |
物理学 | 75篇 |
出版年
2023年 | 4篇 |
2022年 | 7篇 |
2021年 | 4篇 |
2020年 | 5篇 |
2019年 | 5篇 |
2018年 | 11篇 |
2017年 | 3篇 |
2016年 | 20篇 |
2015年 | 14篇 |
2014年 | 25篇 |
2013年 | 31篇 |
2012年 | 30篇 |
2011年 | 33篇 |
2010年 | 16篇 |
2009年 | 11篇 |
2008年 | 19篇 |
2007年 | 22篇 |
2006年 | 19篇 |
2005年 | 20篇 |
2004年 | 19篇 |
2003年 | 29篇 |
2002年 | 40篇 |
2001年 | 29篇 |
2000年 | 51篇 |
1999年 | 7篇 |
1998年 | 5篇 |
1997年 | 4篇 |
1996年 | 6篇 |
1995年 | 6篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 3篇 |
1991年 | 3篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 5篇 |
1987年 | 9篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 3篇 |
1982年 | 11篇 |
1981年 | 6篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 5篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1957年 | 4篇 |
排序方式: 共有587条查询结果,搜索用时 281 毫秒
511.
Jiang‐Lin Fang Wei Huang Suchada Chantrapromma S. Shanmuga Sundara Raj Ibrahim Abdul Razak Hoong‐Kun Fun Shao‐Hua Gou Hong‐Sen Wang 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(12):1429-1430
A donor–acceptor compound, diaqua‐1κO,2κO‐[μ‐11,23‐dimethyl‐3,7,15,19‐tetraazatricyclo[19.3.1.19,13]hexacosa‐1(25),2,7,9,11,13(26),14,19,21,23‐decaene‐25,26‐diolato‐1κ4N3,N7,O25,O26:2κ4N15,N19,O25,O26]dizinc(II) diperchlorate bis(8‐methylquinoline) ethanol disolvate, [Zn2(C24H26N4O2)(H2O)2](ClO4)2·2C10H9N·2C2H6O, obtained by the reaction of a dinuclear zinc(II) complex of a Robson macrocycle (acceptor) and 8‐methylquinoline (donor), lies about an inversion centre and the coordination about the unique Zn atom is a distorted square pyramid. The fifth coordination site is occupied by the water molecule, Zn—O = 2.016 (2) Å, and the average macrocyclic Zn—O and Zn—N distances are 2.059 (6) and 2.059 (3) Å, respectively. 相似文献
512.
合成了2 个以1 ,1 ,2 ,2四乙酰基乙烷阴离子( T A E2 - ) 为桥联的双核铜配合物[(bipy Cu)(bipy Cu H2 O) T A E]( Cl O4)2 ·2 H2 O( Ⅰ) 和(bipy Cu)2 T A E( P F6)2 ·3 H2 O( Ⅱ) 及1 个多核铜配合物[ Cu T A E·2 H2 O]n( Ⅲ) ,并进行了表征。对配合物( Ⅰ) 进行了 X射线晶体结构分析,该配合物属于单斜晶系,空间群为 P21/ n ,晶胞参数为a = 7 .923(1) .465(5) 〓, b = 16 .068(3) 〓, c = 30 .182(7) 〓, β= 93 .18(2)°,晶胞体积 V= 3836 .5(12) 〓3 , Z= 4 , 最终偏离因子 R1 = 0 .1135 ,w R2 = 0 .3121 。磁性质研究表明在这两个双核铜配合物中两个金属铜之间存在弱的反铁磁性相互作用。 相似文献
513.
Yun Shan Peng Han Sheng Xu Pance Naumov S. Shanmuga Sundara Raj Hoong‐Kun Fun Ibrahim Abdul Razak Seik Weng Ng 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(11):1386-1388
The title compound, C10H9NO2Se, crystallizes as flat molecules linked by selenium–oxygen interactions [Se?O = 3.189 (4) Å] into a linear chain along the a axis of the triclinic cell. The bond dimensions that are derived from ab initio geometry optimization calculations are similar to those determined from the diffraction measurements. 相似文献
514.
Xinping Hou Kok Siong Siow Zhiqiang Gao 《Journal of Solid State Electrochemistry》1999,3(7-8):387-391
One of the approaches to improving the ionic conductivity and the mechanical strength of a solid polymer electrolyte is to
use polymers in modified forms, such as polymer blends, copolymers and cross-linked polymers. In this study, a new polymer
electrolyte based on the acrylonitrile-butadiene-styrene (ABS) copolymer has been prepared. The ionic conductivity, electrochemical
stability and interfacial characteristics of the polymer electrolyte in contact with a lithium electrode have been investigated.
The temperature dependence of the conductivity below 20 °C can be described by the Arrhenius equation, and above 20 °C by
the VTF equation. Lithium passivation appeared to have taken place in the system. The conductivity and electrochemical characteristics
of the system are somewhat similar to those of PAN-based polymer electrolytes.
Received: 9 December 1998 / Accepted: 9 March 1999 相似文献
515.
W J Boeve T Kok A M Tegzess W J van Son R J Ploeg W J Sluiter R L Kamman 《Magnetic resonance imaging》2001,19(5):595-607
To evaluate whether combined contrast enhanced MRA and MRI (ce-MRA-MRI) has the potential to replace intra-arterial DSA (i.a.DSA) in patients with impaired graft function or suspected of vascular complications after pancreas and/or kidney transplantation. 7 patients after combined pancreas-kidney and 22 patients after kidney transplantation underwent ce-MRA-MRI and i.a.DSA within a 3 days interval. Qualitative and quantitative comparison of the arterial and venous supply, the parenchyma and urinary collecting system was made. Both ce-MRA and i.a.DSA showed good results in the detection of arterial stenoses. However, ce-MRA falsely suggested stenoses if vascular clips were used; on the other hand, i.a.DSA was less informative if the graft arteries were very tortuous. Ce-MRA was superior in depicting the venous anatomy (p < 0.001) and the parenchymal enhancement of the pancreatic grafts. For the assessment of the contrast excretion, the pyelocalyceal system and the ureter of the renal graft ce-MRA-MRI was superior (p < 0.001), for small caliber arteries in the renal grafts i.a.DSA was of greater value (p < 0.001). The combination of ce-MRA and MRI is reliable for evaluating the vascular anatomy and has several advantages over i.a.DSA after pancreas and/or kidney transplantation. It can replace i.a.DSA in patients with impaired graft function or suspected of vascular complications after pancreas and/or kidney transplantation. 相似文献
516.
Pan
e Naumov Gligor Jovanovski Sheng‐Zhi Hu Il‐Hwan Suh Ibrahim Abdul Razak Suchada Chantrapromma Hoong‐Kun Fun Seik Weng Ng 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(9):1016-1019
The short carbonyl bond in the title compound, [Cu2(C7H4NO3S)4(C3H4N2)4] [Liu, Huang, Li & Lin (1991). Acta Cryst. C 47 , 41–43], is an artifact of disorder in the isothiazol‐3(2H)‐one 1,1‐dioxide part of the 1,2‐benzisothiazol‐3(2H)‐one entity. In the present redetermination, all bond dimensions in the centrosymmetric dinuclear molecule are normal. The five‐coordinate Cu atom shows trigonal–bipyramidal coordination. Hydrogen bonds from the imidazole donor ligand link adjacent molecules into a two‐dimensional layer structure. 相似文献
517.
二价锰盐和1,4,8,11-环十四四氮烷(cyclam)在溶液中自组装生成双核双(μ-氧桥)锰(Ⅲ/Ⅳ)配合物:犤(cyclam)MnO犦2(ClO4)2(NO3)。该配合物被晶体结构表征,低温EPR表明其具有16条Mn?/Mn?二聚体的特征信号。磁性研究确认有强的反铁磁性,J/k=-680K,g=2.0。 相似文献
518.
519.
P. Kok P. De Clercq M. Vandewale J.P. Declercq G. Germain M. Van Meerssche 《Tetrahedron letters》1979,20(22):2063-2066
The synthesis of perhydroazulenic lactone , a potential precursor for several helenaholides is described. Its structure is determined by X-ray diffraction of the corresponding alcohol . 相似文献
520.
The absorption spectra of normal and deuterated diacetylene trapped in solid argon at 9 K were investigated in the near-ultraviolet region between 2000 and 3000 Å. The vibrational structure observed at low temperature for the band system at 2448 Å, which was previously reported by Haink and Jungen in the gas phase, and identified as a 1Δu ← X1Σg+ transition, was analyzed. A comparison between the spectra for C4H2 and C4D2 suggests some revisions in the upper-state vibrational assignments. The possibility that the upper state assumes a C2htrans configuration of 1Au symmetry is examined. The matrix spectra also appear to indicate that the absorption spectrum observed at 2576 Å in the gas phase and which has been assigned to a 1Σu? ← X1Σg+ transition may not originate in the ground state of C4H2. 相似文献