全文获取类型
收费全文 | 2882篇 |
免费 | 89篇 |
国内免费 | 390篇 |
专业分类
化学 | 2432篇 |
晶体学 | 17篇 |
力学 | 46篇 |
数学 | 7篇 |
物理学 | 859篇 |
出版年
2024年 | 2篇 |
2023年 | 56篇 |
2022年 | 56篇 |
2021年 | 61篇 |
2020年 | 73篇 |
2019年 | 78篇 |
2018年 | 52篇 |
2017年 | 95篇 |
2016年 | 103篇 |
2015年 | 106篇 |
2014年 | 141篇 |
2013年 | 149篇 |
2012年 | 206篇 |
2011年 | 251篇 |
2010年 | 203篇 |
2009年 | 282篇 |
2008年 | 224篇 |
2007年 | 241篇 |
2006年 | 191篇 |
2005年 | 125篇 |
2004年 | 107篇 |
2003年 | 107篇 |
2002年 | 68篇 |
2001年 | 56篇 |
2000年 | 45篇 |
1999年 | 43篇 |
1998年 | 41篇 |
1997年 | 28篇 |
1996年 | 29篇 |
1995年 | 31篇 |
1994年 | 23篇 |
1993年 | 19篇 |
1992年 | 18篇 |
1991年 | 17篇 |
1990年 | 13篇 |
1989年 | 8篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1982年 | 1篇 |
1980年 | 2篇 |
1978年 | 1篇 |
排序方式: 共有3361条查询结果,搜索用时 109 毫秒
21.
22.
In the absence of ligand, copper and amine, a recoverable nanoparticle palladium(0) catalyzed Sonogashira reaction of aryl iodides and bromides with terminal alkynes was developed. The protocol involved the use of an environmental-friendly reaction system with ethanol as the solvent, potassium carbonate as a base, and poly(vinylpyrrolidone) (PVP) supported nanosized palladium metal colloids as the catalyst. The palladium metal was recovered and recycled by a simple decantation of the reaction solution and used for eight consecutive trials without significant loss of its reactivity. 相似文献
23.
Silver halide (AgX) microcrystal was used as template to synthesize hollow polyelectrolyte capsules. These hollow capsules were characterized by laser light scattering (LLS) used to measure the size of the capsules in solution. The ratio of hydrodynamic radius (Rh) from dynamic LLS to the radius of gyration (Rg) from static LLS is almost unity, revealing that the entities are hollow in solution. The results suggest that the LLS method can be regarded as a good complement to the confocal laser scanning microscopy (CLSM) method for the characterization of small hollow capsules, and it possesses the advantage of not needing fluorescence labeling. 相似文献
24.
25.
通过紫外吸收光谱、导数光谱以及溶液电导率的变化研究了紫色光对[PtCl6]2-水解过程的影响规律. 相似文献
26.
Sevim?Hamamci Veysel?T.?YilmazEmail author William?T.?A.?Harrison 《Structural chemistry》2005,16(4):379-383
The first silver(I) complex of saccharinate (sac) with pyridine (py), [Ag(sac)(py)]n has been synthesized and characterized by elemental analysis, IR spectroscopy and single crystal X-ray diffractometry. The complex crystallizes in chiral, trigonal space group P3121 (No. 152) with unit cell parameters of a = 11.2605(2) Å, c = 17.3300(4) Å, V = 1903.02(6) Å3 and Z = 6. [Ag(sac)(py)]n contains monomeric [Ag(sac)(py)] units linked into infinite helices by way of Ag⋅sAg interactions [d(Ag⋅sAg) = 2.909(2) and 2.985(1) Å]. The distorted square-planar environment of Ag is completed by an N-bonded sac [Ag—N = 2.084(2) Å] and a py molecule [Ag—N = 2.116(2) Å]. The Nsac—Ag—Npy angle is 173.85(10)∘. The one-dimensional chains are crosslinked by C—H⋅sO interactions involving the carbonyl and sulfonyl O atoms of sac and aromatic-ring hydrogen atoms of both sac and py. The thermal stability of the title complex was investigated using thermogravimetry and differential thermal analysis in a static atmosphere of air. The first decomposition stage between 90 and 160∘C corresponds to removal of the py molecule in a single stage, while the degradation of the sac moiety occurs at two stages in the temperature range 370–515∘C, giving an end product of metallic Ag. 相似文献
27.
A typical silver cubane-like heteroselenometallic cluster, (μ3-WSe4)Ag3(PPh3)3Cl·0.5SePPh3, was synthesized from reaction of [Et4N]2[WSe4] and Ag(PPh3)2(NO3) in CH2Cl2 solution and structurally characterized by X-ray crystallography. The compound crystallizes in the trigonal space group R3 with a=16.258(4), b=22.80(3) Å, V=5217(7) Å3, and Z=3. The structure contains a strongly distorted cubane-like {WAg3Se3Cl} core. The coordination geometries of the W center and each Ag atom are tetrahedral. The mean W-Ag separation is 3.010(3) Å. Optical nonlinearity of this cubane-like cluster was studied. Large optical limiting effect with threshold of 0.45 J/cm2 was observed with the laser pulses of 7 ns at 532 nm. 相似文献
28.
A new salicylic-based open-chain crown ether ligand, 1,10-bis(2′-carboxylphenyl)-1,4,7,10-tetraoxadecane (BCPTD) was synthesized. Solutions of its complex with Tb3+ can emit the intrinsic fluorescence of Tb3+. The fluorescence intensity of the complex in KCl solution was enhanced by the addition of silver(I), leading to a new fluorescence enhancement phenomenon. The spectrofluorimetric determination of traces of silver(I) based on the above phenomenon was carried out. The excitation and emission wavelengths are 298 and 545 nm, respectively. Under optimal conditions, the differential value of fluorescence intensity in the absence and presence of Ag+ was proportional to the concentration of silver(I) in the range 0.5-20 μg ml−1. The method was applied to the determination of silver(I) in a standard ore sample. The analytical performance is investigated in detail by using common aromatic carboxylic acids or synthetic analogues of BCPTD as ligands to replace BCPTD. It was found that Tb-aromatic acid complexes did not result in fluorescence enhancement of Tb3+ in AgCl collosol. The phenomenon was only observed in Tb(III) with BCPTD or its open-chain crown ether analogues solutions.In addition, the enhancement of the fluorescence intensity of terbium(III) in these complexes depends on the extent of formation of the AgCl collosol. 相似文献
29.
30.
The coordination of silver cation to diphosphene Mes*P=PMes* ( 1 , Mes* = tBu3C6H2) was investigated in detail. The reaction of 1 with Ag[Al(ORF)4] (ORF = OC(CF3)3) in the ratios of 2 : 1, 3 : 2 and 1 : 2 led to the formation of the first cationic silver linked diphosphene complexes 2 — 4 . Complexes 2 and 3 contain two and three diphosphene molecules linked by the linear Ag(I) cation, respectively, and they feature unusual zig‐zag topologies. Complex 4 is a dinuclear silver complex, and each Ag(I) center features a tetrahedral geometry, coordinated by one phosphorus atom of diphosphene 1 and three chloro atoms of two CH2Cl2 molecules. 相似文献