全文获取类型
收费全文 | 428篇 |
免费 | 70篇 |
国内免费 | 51篇 |
专业分类
化学 | 212篇 |
晶体学 | 10篇 |
力学 | 3篇 |
综合类 | 1篇 |
数学 | 102篇 |
物理学 | 221篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 2篇 |
2020年 | 3篇 |
2019年 | 5篇 |
2018年 | 3篇 |
2017年 | 8篇 |
2016年 | 12篇 |
2015年 | 14篇 |
2014年 | 42篇 |
2013年 | 37篇 |
2012年 | 70篇 |
2011年 | 57篇 |
2010年 | 53篇 |
2009年 | 59篇 |
2008年 | 42篇 |
2007年 | 53篇 |
2006年 | 29篇 |
2005年 | 11篇 |
2004年 | 14篇 |
2003年 | 11篇 |
2002年 | 8篇 |
2001年 | 3篇 |
2000年 | 4篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1996年 | 3篇 |
1995年 | 1篇 |
排序方式: 共有549条查询结果,搜索用时 31 毫秒
71.
72.
Liya?Wang Zhiliang?Liu Chenxi?Zhang Zhanquan?Liu Daizheng?Liao Zonghui?JiangEmail author Shiping?Yan 《中国科学B辑(英文版)》2003,46(6):533-541
A novel one-dimensional manganese(II) complex containing nitronyl nitroxide radical [Mn2(IM2-py)2(Ac)2(μ1,1-N3)(μ1,3-N3) · EtOH]
n
was synthesized and characterized structurally and magnetically. It crystallizes in the monoclinic space group p21/n. Each Mn(II) ion is six-coordinated in a distorted octahedral environment. The two N atoms of the nitronyl nitroxide radical
and the two O atoms of acetate ligands are in the equatorial plane, whereas the two different azido bridging ligands are in
trans axial position. Mn(II) ions are linked by nitrogen atom of μ1,1-azido and oxygen atoms of two carboxy groups to form a Mn-Mn unit. Mn-Mn units are linked by azido ligands through μ1,3 bridging style to form a one-dimensional chain. The compound is connected by the coordination bonds, π-π interactions and
hydrogen bonds as a three-dimensional structure. Magnetic susceptibility data support that there are stronger antiferromagnetic
interactions between the radical and Mn(II) ion, weak antiferromagnetic interactions between the Mn-R units, and very weak
antiferromagnetic interactions between the R-Mn-Mn-R units. 相似文献
73.
以2,4,6-吡啶三甲酸(H3ptc)和六水合高氯酸镍为原料用水热方法合成了三维超分子配合物[Ni(H2O)6]1.5.[Ni(ptc)(Hptc)].(H2O)4,并经X射线衍射分析确定了其单晶结构.该晶体属三斜晶系,P墿空间群,晶胞参数为:a=1.03058(16)nm,b=1.11852(17)nm,c=1.4689(2)nm,α=74.725(2)°,β=77.777(2)°,γ=64.734(2)°,V=1.4675(4)nm3,Mr=798.20,Z=2,ρ=1.806g/cm3,F(000)=822,μ=1.701mm-1,R1=0.0373,wR2=0.0993.结果表明,在组成该超分子体系的基本结构单元[Ni(ptc)(Hptc)]3-和[Ni(H2O)6]2+中,Ni(Ⅱ)离子均处于变形八面体配位环境中.配合物单元之间通过氢键相互连接,形成了无限延伸的三维超分子网状结构. 相似文献
74.
Li D Zhu M Xu C Chen J Ji B 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2011,78(1):74-79
The interaction of rutin to bovine serum albumin (BSA) in aqueous solution was investigated by fluorescence spectra and ultraviolet-visible (UV-vis) spectra at pH 7.40. There are also some metal ions present in blood plasma, thus the research about the effect of metal ions on the interaction of drugs with proteins is crucial. Therefore, we have studied the effect of Cu2+ or Fe3+ on the interaction between rutin and BSA by using spectroscopic technique at pH 7.40, for the first time. The results of fluorescence titration indicated that rutin could quench the intrinsic fluorescence of BSA in a static quenching way. The binding sites number (n), the binding constant (K) and the spatial-distance (r) of rutin with BSA without or with Cu2+ or Fe3+ at 310 K were calculated. The result showed that the presence of Cu2+ or Fe3+ increased the binding constant and changed the binding distance between the acceptor and the donor, which possibly results from the formation of metal ions-BSA complex. The effect of rutin on the conformation of BSA was also analyzed using UV under experimental conditions. Furthermore, the fluorescence displacement experiments indicated that rutin is situated within subdomain IIA of BSA. 相似文献
75.
Qi-Ying Lv Shu-Zhong Zhan Jian-Ge Wang An Ding 《Journal of organometallic chemistry》2008,693(7):1155-1158
In the presence of CoCl2 · 6H2O, the reaction of TCNE (tetracyanoethylene) with CH3OH forms a dicyanomethylacetate molecule, which has been obtained as one solvent molecule in one new compound {[Co(bpy)2CN2][(NC)2C-CO2CH3]} · 2H2O (1). It was characterized by IR spectra, UV-Vis spectra, and cyclic voltammogram. Its structure was determined by X-ray crystallography: 1 crystallizes in P2(1)/n with a = 13.3368(17), b = 12.5299(16), c = 16.074(2) Å, α = 90, β = 94.6320(10), γ = 90°, and Z = 2. 相似文献
76.
Li-Ya Wang Xiao-Qiang Wang Kai Jiang Jiu-Li Chang Yu-Fang Wang 《Journal of Molecular Structure》2007,840(1-3):14-21
A new nitronyl nitroxide NIT2-bithph (1) and its manganese(II) compound [Mn(hfac)2(IMHBithph)]2·(NIT2-bithph)(C6H14) (2) (hfac = hexafluoroacetylacetonate; NIT2-bithph = 4,4,5,5-tetramethyl-2-(bithiophenal-2-yl)imidazoline-1-oxyl-3-oxide; IMHBithph = 1-hydroxy-2-bithiophenal-4,4,5,5-tetramethyl-4,5-dihydro- 1H-imidazole) have been synthesized and structurally characterized by X-ray diffraction methods. The units of compound 1 were connected as one-dimensional chain by the intermolecular hydrogen bonds which afford an intermolecular antiferromagnetic interaction between nitronyl nitroxide radicals within the chain (J = −1.89 cm−1). Compound 2 resulting from the reaction of Mn(hfac)2·2H2O and NIT2-bithph is dinuclear and includes the reduced amidino-oxide form of NIT2-bithph, it is made up of three parts: a [Mn(hfac)2(IMHBithph)]2 dimer unit, an uncoordinated NIT2-bithph radical and a noncoordinated solvent molecule of hexane, the molecule of radical is hydrogen bonded to its reduced form. Two reduced IMHBithph ligands bridge the two manganese(II) ions through their amidino-oxide oxygen atoms resulting in a small intramolecular antiferromagnetic interaction between the manganese ions (J = −1.55 cm−1). 相似文献
77.
A novel one-dimensional manganese(Ⅱ) complex containing nitronyl nitroxide radical [Mn2(IM2-py)2(Ac)2((μ1.1-N3)(μ1,3-N3) . EtOH]n was synthesized and characterized structurally and magnetically. It crystallizes in the monoclinic space group p21/n. Each Mn(Ⅱ) ion is six-coordinated in a distorted octahedral environment. The two N atoms of the nitronyl nitroxide radical and the two O atoms of acetate ligands are in the equatorial plane, whereas the two different azido bridging ligands are in trans axial position. Mn(Ⅱ) ions are linked by nitrogen atom of μ1,1-azido and oxygen atoms of two carboxy groups to form a Mn-Mn unit. Mn-Mn units are linked by azido ligands through u1,3 bridging style to form a one-dimensional chain. The compound is connected by the coordination bonds,π-π interactions and hydrogen bonds as a three-dimensional structure. Magnetic susceptibility data support that there are stronger antiferromagnetic interactions between the radical and Mn(Ⅱ) ion, weak antiferromagnetic inter 相似文献
78.
A novel coordination polymer {[Zn(ts-gln)(bipy)]3H2O}n (ts-glnH2=N-p-toly-sulfonyl-glutamine,bipy=2,2-bipyridine) has been prepared and structurally characterized by X-ray diffraction method. It crystallizes in orthorhombic,space group P212121 with a=8.2622(5),b=16.6244(10),c=18.2807(10) ,V=2510.9(3) 3,C22H28N4O8SZn,Mr=573.91,Z=4,Dc= 1.518 g/cm3,μ(MoKa)=1.115 mm-1,F(000)=1192,the final R=0.0262 and wR=0.0662 for 5691 independent reflections with Rint=0.0240. The zinc(Ⅱ) atom is coordinated by N(3) and N(4) atoms of a bipy molecule,two carboxylate O(1) and O(2A) and amino N(1) atoms of ts-gln ligands,resulting in a square-pyramidal geometry. The title complex consists of an infinite zigzag chain of zinc(Ⅱ) ions linked by the carboxylate of N-p-tolysulfonyl-glutamine. 相似文献
79.
80.
《Arabian Journal of Chemistry》2022,15(12):104347
The high-pressure structures and properties of MH2 (M = Nb, Ta) are explored through an ab initio evolutionary algorithm for crystal structure prediction and first-principles calculations. It is found that NbH2 undergoes a phase transition from a cubic Fmm structure with regular NbH8 cubes to an orthorhombic Pnma structure with fascinating distorted NbH9 tetrakaidecahedrons at 48.8 GPa, while the phase transition pressure of TaH2 from a hexagonal P63mc phase with slightly distorted TaH7 decahedron to an orthorhombic Pnma phase with attractive distorted TaH9 tetrakaidecahedrons is about 90.0 GPa. Besides, the calculated electronic band structure and density of states demonstrate that all of these structures are metallic. The Poisson’s ratio, electron localization function, and Bader charge analysis suggest that these phases possess dominant ionic bonding character with the effective charges transferring from the metal atom to H. From our electron–phonon calculations, the calculated superconducting critical temperature Tc of the Pnma-NbH2 is 6.903 K at 50 GPa. Finally, via the quasi-harmonic approximation method, the phase diagrams at pressure up to 300 GPa and temperature up to 1000 K of MH2 (M = Nb, Ta) are established, where the transition pressure of Fmm-NbH2 → Pnma-NbH2 and P63mc-TaH2 → Pnma-TaH2 were found to decrease with increasing temperature. 相似文献