全文获取类型
收费全文 | 5659篇 |
免费 | 244篇 |
国内免费 | 52篇 |
专业分类
化学 | 4251篇 |
晶体学 | 42篇 |
力学 | 221篇 |
综合类 | 2篇 |
数学 | 777篇 |
物理学 | 662篇 |
出版年
2024年 | 9篇 |
2023年 | 43篇 |
2022年 | 212篇 |
2021年 | 307篇 |
2020年 | 207篇 |
2019年 | 230篇 |
2018年 | 218篇 |
2017年 | 169篇 |
2016年 | 292篇 |
2015年 | 202篇 |
2014年 | 211篇 |
2013年 | 533篇 |
2012年 | 359篇 |
2011年 | 384篇 |
2010年 | 238篇 |
2009年 | 204篇 |
2008年 | 258篇 |
2007年 | 259篇 |
2006年 | 207篇 |
2005年 | 181篇 |
2004年 | 164篇 |
2003年 | 140篇 |
2002年 | 144篇 |
2001年 | 54篇 |
2000年 | 63篇 |
1999年 | 44篇 |
1998年 | 30篇 |
1997年 | 44篇 |
1996年 | 40篇 |
1995年 | 32篇 |
1994年 | 39篇 |
1993年 | 31篇 |
1992年 | 32篇 |
1991年 | 28篇 |
1990年 | 43篇 |
1989年 | 26篇 |
1988年 | 22篇 |
1987年 | 26篇 |
1986年 | 27篇 |
1985年 | 32篇 |
1984年 | 19篇 |
1983年 | 17篇 |
1982年 | 25篇 |
1981年 | 20篇 |
1980年 | 14篇 |
1979年 | 16篇 |
1978年 | 11篇 |
1977年 | 12篇 |
1976年 | 9篇 |
1975年 | 6篇 |
排序方式: 共有5955条查询结果,搜索用时 15 毫秒
191.
192.
193.
194.
Metal complexes of novel Schiff base derived from the condensation of 2‐quinoline carboxaldehyde and ambroxol drug with some transition metal ions
下载免费PDF全文
![点击此处可从《应用有机金属化学》网站下载免费的PDF全文](/ch/ext_images/free.gif)
A new Schiff base was prepared as the condensation product of the reaction of 2‐quinoline carboxaldehyde and ambroxol drug. The Schiff base ligand thus obtained (HL; trans‐4‐[(2‐(2‐quinolinoimino)‐3,5‐dibromobenzyl)amino]cyclohexanol) was further employed as a tridentate ligand for the synthesis of new complexes through reaction with Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) metal ions. The synthesized HL and its metal complexes were characterized using various physicochemical techniques including elemental analysis, Fourier transform infrared and UV–visible spectroscopies, conductimetric and magnetic susceptibility measurements, mass spectrometry and thermal analyses. 1H NMR data indicated that complex formation was through the amino group rather than the aliphatic hydroxyl group. Thermal analysis gave an idea about the decomposition pattern of HL and its complexes. Also, it revealed the number of water molecules in the inner and outer spheres of the complexes. An octahedral geometry for all the complexes has been suggested. HL and its complexes were screened for their antimicrobial activity against various species of bacteria and fungi using the disc diffusion method. The Cr(III) complex had the highest antimicrobial activity. 相似文献
195.
Shereen Mowaka Matthias Ziehe Dalia Mohamed Ulrike Hochkirch Jürgen Thomale Michael W. Linscheid 《Journal of mass spectrometry : JMS》2012,47(10):1282-1293
Oxaliplatin, [(1R,2R)‐cyclohexane‐1,2‐diamine](ethanedioato‐O,O')platinum(II) shows a great efficiency against colorectal cancer. Although the mode of action of oxaliplatin is not yet understood, it is commonly accepted that binding of oxaliplatin to DNA prevents DNA synthesis and alters protein to DNA binding. In order to elucidate the modified DNA–protein interaction and thus to understand the mechanisms leading to cellular misinterpretation of DNA information and apoptosis, we have identified the preferential binding sites and the dynamics of the oxaliplatin‐DNA intrastrand and interstrand adducts at the oligomer level using high‐performance liquid chromatography/electrospray ionization‐tandem mass spectrometry (HPLC/ESI‐MS/MS) and HPLC/inductively coupled plasma‐MS for quantitative studies. We used a combination of benzonase, alkaline phosphatase and Nuclease S1 for digestion. This digestion procedure allows the study of platinated oligomeric nucleotides and more complex interstrand adducts. The digestion products were mostly chromatographically separated and characterized using HPLC/ESI‐ion trap MS/MS experiments. We could show that the adducts to guanine and adenine are quite dynamic; that is, the ratios are changing for several days. In addition, the resulting adducts provide evidence for the action of the digesting enzymes and indicate that the adduct spectrum at the oligomeric level is different to that at the commonly studies dinucleotide level. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
196.
Mohamed Baqar Tarek Agag Hatsuo Ishida Syed Qutubuddin 《Journal of polymer science. Part A, Polymer chemistry》2012,50(11):2275-2285
A new class of high‐performance resins of combined molecular structure of both traditional phenolics and benzoxazines has been developed. The monomers termed as methylol‐functional benzoxazines were synthesized through Mannich condensation reaction of methylol‐functional phenols and aromatic amines, including methylenedianiline (4,4′‐diaminodiphenylmethane) and oxydianiline (4,4′‐diaminodiphenyl ether), in the presence of paraformaldehyde. For comparison, other series of benzoxazine monomers were prepared from phenol, corresponding aromatic amines, and paraformaldehyde. The as‐synthesized monomers are characterized by their high purity as judged from 1H NMR and Fourier transform infrared spectra. Differential scanning calorimetric thermograms of the novel monomers show two exothermic peaks associated with condensation reaction of methylol groups and ring‐opening polymerization of benzoxazines. The position of methylol group relative to benzoxazine structure plays a significant role in accelerating polymerization. Viscoelastic and thermogravimetric analyses of the crosslinked polymers reveal high Tg (274–343 °C) and excellent thermal stability when compared with the traditional polybenzoxazines. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012 相似文献
197.
Hanifa Daoui Yasmine Bouhamidi Ahmed Boucherit Mohamed Zouikri 《International Journal of Polymer Analysis and Characterization》2018,23(5):463-473
The fundamental understanding of the behavior of a solid is intimately related to the understanding of the interactions on the surface of the latter, a major challenge in particular if the material is natural and ecological. The infinite dilution-inverse gas chromatography was used to evaluate the surface thermodynamic properties of several phases (grafted and/or coated) diatomite. A series of non- or polar-solute probes were injected at temperatures of 45?°C and 90?°C. The dispersive surface free energies values of the supports decrease with increasing temperature and their active surface is amphoteric with predominantly acidic character. 相似文献
198.
Catalytic activity of nickel(II), copper(II) and oxovanadium(II)‐dihydroindolone complexes towards homogeneous oxidation reactions
下载免费PDF全文
![点击此处可从《应用有机金属化学》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Mohamed Shaker S. Adam 《应用有机金属化学》2018,32(4)
Three novel paramagnetic metal complexes (MH2ID) of Ni2+, Cu2+ and VO2+ ions with 3‐hydroxy‐3,3’‐biindoline‐2,2’‐dione (dihydroindolone, H4ID) were synthesized and characterized by different spectroscopic methods. The ligand (H4ID) was synthesized via homocoupling reaction of isatin in presence of phenylalanine in methanol. Complexation of low valent Ni2+, Cu2+ ions and high valent VO2+ ions with H4ID carried out in 1: 2 molar ratios. A comparison in the catalytic potential of paramagnetic complexes of low and high valent metal ion was explored in the oxidation processes of cis‐cyclooctene, benzyl alcohol and thiophene by an aqueous H2O2, as a green terminal oxidant, in the presence and absence of acetonitrile, as an organic solvent, at 85 °C. NiH2ID, CuH2ID and VOH2ID show good catalytic activity, i.e. good chemo‐ and regioselectivity. VOH2ID has the highest catalytic potential compared to both Ni2+‐ and Cu2+‐species in the same homogenous aerobic atmosphere. Catalytic oxidation of other alkenes and alcohols was also studied using NiH2ID, CuH2ID or VOH2ID as a pre‐catalyst by an aqueous H2O2. A mechanistic pathway for those oxidation processes was proposed. 相似文献
199.
Coordination compounds of Fe(III), Zn(II), Ni(II), Co(II), Cu(II), Cd(II) and Mn(II) ions were synthesized from the ligand [4,4′‐((((ethane‐1,2‐diylbis(oxy))bis(2,1‐phenylene))bis(methanylylidene))bis(azanylylidene))diphenol]ethane (H2L) derived from the condensation of bisaldehyde and 4‐aminophenol. Microanalysis, magnetic susceptibility, infrared, 1H NMR and mass spectroscopies, molar conductance, X ray powder diffraction and thermal analysis were used to confirm the structure of the synthesized chelates. According to the data obtained, the composition of the 1:1 metal ion–bis‐Schiff base ligand was found to be [M(H2L)(H2O)2]Cln (M = Zn(II), Ni(II), Co(II), Cu(II), Cd(II) and Mn(II), n = 2; Fe(III), n = 3). Magnetic susceptibility measurements and reflectance spectra suggested an octahedral geometry for the complexes. Central metals ions and bis‐Schiff base coordinated together via O2 and N2 donor sites which as evident from infrared spectra. The Gaussian09 program was applied to optimize the structural formula for the investigated Schiff base ligand. The energy gaps and other important theoretical parameters were calculated applying the DFT/B3LYP method. Molecular docking using AutoDock tools was utilized to explain the experimental behaviour of the Schiff base ligand towards proteins of Bacillus subtilis (5 h67), Escherichia coli (3 t88), Proteus vulgaris (5i39) and Staphylococcus aureus (3ty7) microorganisms through theoretical calculations. The docked protein receptors were investigated and the energies of hydrogen bonding were calculated. These complexes were then subjected to in vitro antibacterial studies against several organisms, both Gram negative (P. vulgaris and E. coli) and Gram positive (S. pyogones and B. subtilis). The ligand and metal complexes exhibited good microbial activity against the Gram‐positive and Gram‐negative bacteria. 相似文献
200.