全文获取类型
收费全文 | 315篇 |
免费 | 2篇 |
国内免费 | 6篇 |
专业分类
化学 | 259篇 |
晶体学 | 2篇 |
力学 | 1篇 |
数学 | 1篇 |
物理学 | 60篇 |
出版年
2024年 | 6篇 |
2023年 | 85篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2019年 | 5篇 |
2017年 | 1篇 |
2015年 | 4篇 |
2014年 | 1篇 |
2013年 | 55篇 |
2012年 | 19篇 |
2010年 | 4篇 |
2009年 | 7篇 |
2008年 | 4篇 |
2007年 | 10篇 |
2006年 | 5篇 |
2005年 | 10篇 |
2004年 | 4篇 |
2003年 | 6篇 |
2002年 | 4篇 |
2001年 | 6篇 |
2000年 | 8篇 |
1999年 | 12篇 |
1998年 | 15篇 |
1997年 | 6篇 |
1996年 | 6篇 |
1995年 | 4篇 |
1994年 | 8篇 |
1993年 | 4篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有323条查询结果,搜索用时 0 毫秒
1.
2.
Matthias Freytag Frank T. Edelmann Ludger Ernst Peter G. Jones Reinhard Schmutzler 《无机化学与普通化学杂志》2004,630(3):377-383
The reaction of the symmetric diphosphene 2, 4, 6‐(CF3)3‐C6H2‐P=P‐C6H2‐2, 4, 6‐(CF3)3 4 with Ru3(CO)12 led to the 50‐electron Ru3P2 nido‐cluster Ru3(CO)9[μ‐P‐C6H2‐2, 4, 6‐(CF3)3]2 5 , which in solution at room temperature displays hindered rotation of the aromatic rings about the C(aryl)—P bonds. The structure of 5 was determined by X‐ray crystal structure analysis; its Ru3P2 centre forms a distorted square pyramid with one ruthenium atom at the apex. One of the two C6H2(CF3)3 groups is also appreciably distorted. Temperature‐dependent 19F NMR studies of the [A3M3X]2 spin system (A = M = CF3, X = 31P) of 5 indicated a rotational barrier ΔG≠ of 82.3 kJ mol‐1 at 141 °C. The same Ru3P2 core was obtained by the reaction of the unsymmetric diphosphene Mes*‐P=P‐Mes 11 with Ru3(CO)12; hindered rotation about the C(aryl)—P bonds was also observed, in this case. 相似文献
3.
Eu5Ge3 and EuIrGe2 were prepared from the elements in tantalum tubes, and their crystal structures were determined from single crystal X-ray data. Eu5Ge3 adopts the structure of Cr5B3: I4/mcm, a = 799.0(1)pm, c = 1 536.7(1)pm, Z = 4, wR2 = 0.0421 for 669 F2 values and 16 variables. The structure of Eu5Ge3 contains isolated germanium atoms and germanium atom pairs with a Ge? Ge distance of 256.0 pm. Eu5Ge3 may be described as a Zintl phase with the formulation [5 Eu2+]10+[Ge]4?[Ge2]6?. Magnetic investigations of Eu5Ge3 show Curie-Weiss behaviour above 50 K with a magnetic moment of μexp = 7.6(1) μB which is close to the free ion value of μeff = 7.94 μB for Eu2+. EuIrGe2 is isotypic with CeNiSi2: Cmcm, a = 445.5(2) pm, b = 1 737.4(4) pm, c = 426.6(1) pm, Z = 4, wR2 = 0.0507 for 295 F2 values and 18 variables. The structure of EuIrGe2 is an intergrowth of ThCr2Si2-like slabs with composition EuIr2Ge2 and AlB2-like slabs with composition EuGe2 in an AB stacking sequence. Both slabs are distorted when compared to the symmetry of the prototypes. The Ge? Ge distance of 256.6 pm in the AlB2-like fragment is comparable to that in Eu5Ge3. 相似文献
4.
Sc2Ni2In was prepared by a reaction of the elemental components in an are furnace and subsequent annealing at 1070 K. Sc2Ni2In is a Pauli paramagnet and a poor metallic conductor with a specific resistivity of 224 mΩcm at room temperature. Its crystal structure was refined from X-ray powder data: P4/mbm, a = 716.79(1) pm, c = 333.154(8) pm, Z = 2, Rwp = 0.040, and RB(I) = 0.026. Sc2Ni2In crystallizes with a ternary ordered version of the U3Si2-type structure. The nickel and indium atoms occupy [NiSc6] trigonal prisms and [InSc8] square prisms, respectively. These structural fragments are derived from the AlB2 and CsCl-type structures. Semi-empirical band structure calculations reveal Sc2Ni2In to be a nickelide, and the strongest bonding interactions are found for the Sc? Ni contacts, followed by Sc? In and Ni? In. A rigidband model suggests the existence of the isotypic phase Sc2Ni2Sb. 相似文献
5.
Syntheses and Crystal Structures of [Pd9As8(PPh2)8] and [Pd9Sb6(PPh3)8] [PdCl2(PPh3)2] reacts with As(SiMe3)3 to give the new cluster [Pd9As8(PPh3)8] ( 4 ). 4 has been characterized by X-ray crystal structure analysis. It is a molecule in which four [Pd2(PPh3)2]-units are bridged by As2-units. A further Pd atom is located in the centre of the cluster. 4 crystallizes in the space group C2/c with four formula units per unit cell. The lattice constants at 200 K are: a = 3 970.6(3), b = 1 648.90(16), c = 3 266.30(20) pm, β = 131,44(4)°. The reaction of [PdCl2(PPh3)2] with Sb(SiMe3)3 yields [Pd9Sb6(PPh3)8] ( 5 ). 5 consists of a body centred cubic Pd9-cluster. All of the cube faces are capped by μ4-Sb-ligands. 5 crystallizes in the space group Pn3 with two formula units per unit cell. The lattice constants at 200 K are: a = b = c = 1 995.4(2) pm. 相似文献
6.
Fluoridolysis of Diphosphoryl Compounds The behaviour of diphosphoryl compounds [X2(O)P]2Y in fluoridolysis reactions is decisively determined by the nature of the bridging group Y. In the cases of Y = NH and CH2 and X = Cl [F2P(O)]2N? and [F2P(O)]2CH2 are obtained quantitatively. For Y = NPh, O, and CH2 the formation of phosphorylated pentafluorophosphates [F5P? Y? POX2]? is observed. Amido and ester derivatives containing fluorine (see table 2) are obtained from the corresponding chloro compounds by Cl/F exchange. Fluoridolysis of the azadiphosphetidine 19 results in the formation of acyclic 19 a . 相似文献
7.
讨论了用共沸蒸馏法浓缩处理水、土壤、固废样品或其萃取液中不易吹除、具挥发性、且易溶于水的非卤代挥发性有机物,并用气相色谱质谱联用仪定性定量的方法. 相似文献
8.
Zucheng Wu Ying Sing Fung 《International journal of environmental analytical chemistry》2013,93(7):431-442
The preconcentration technique of purge-and-trap has been investigated in the present work for quantitative adsorption of volatile organic pollutants purged from water samples. A dynamic purging device with variable volume size has been constructed and tested to purge different concentrations of organic compounds. With Tenax GR as the adsorbent, a dynamic purge-and-trap technique was developed combining on-column preconcentration procedures using ambient trapping/thermal desorption/cryogenic focusing/back-flash injection prior to separation and determination using capillary gas chromatography. Various aromatic compounds in water were determined, giving linear working ranges over five orders of magnitude from 0.02 to 5000 µg/L. The analytical procedures were optimized under the assistance of ultrasonication with results validated for the determination of organic contaminants in underground water and tap water, giving over 93% recoveries and a detection limit of 0.01 µg/L, two orders of magnitude lower than those obtained using commercial available instruments with on-line configuration to minimize cross-contamination. The technique provides a potential automated method for in situ monitoring of volatile organic compounds in water. 相似文献
9.
Majid M. Heravi Nasrin Farhangi Yahya Sh. Beheshtiha Karim Assadolah Mitra Ghassemzadeh Koroush Tabar-Hydar 《Phosphorus, sulfur, and silicon and the related elements》2013,188(12):2883-2885
In an environmentally benign system, alcohols are rapidly oxidized to carbonyl compounds using CrO 3 supported onto wet silica gel as an oxidant under microwave irradiation. 相似文献
10.
Majid M. Heravi Mohammad Rahimizadeh Effat Iravani Mitra Ghassemzadeh 《Phosphorus, sulfur, and silicon and the related elements》2013,188(4):797-802
The synthesis of bicyclic compounds derived from benzo[1,2,4]triazines is described. 相似文献