全文获取类型
收费全文 | 399篇 |
免费 | 21篇 |
国内免费 | 99篇 |
专业分类
化学 | 479篇 |
晶体学 | 11篇 |
综合类 | 7篇 |
物理学 | 22篇 |
出版年
2024年 | 1篇 |
2023年 | 1篇 |
2022年 | 1篇 |
2021年 | 11篇 |
2020年 | 7篇 |
2019年 | 10篇 |
2018年 | 17篇 |
2017年 | 17篇 |
2016年 | 11篇 |
2015年 | 10篇 |
2014年 | 17篇 |
2013年 | 74篇 |
2012年 | 35篇 |
2011年 | 15篇 |
2010年 | 13篇 |
2009年 | 24篇 |
2008年 | 29篇 |
2007年 | 27篇 |
2006年 | 31篇 |
2005年 | 29篇 |
2004年 | 20篇 |
2003年 | 16篇 |
2002年 | 16篇 |
2001年 | 8篇 |
2000年 | 10篇 |
1999年 | 8篇 |
1998年 | 8篇 |
1997年 | 6篇 |
1996年 | 11篇 |
1995年 | 6篇 |
1994年 | 9篇 |
1993年 | 3篇 |
1992年 | 9篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1984年 | 1篇 |
1982年 | 2篇 |
排序方式: 共有519条查询结果,搜索用时 343 毫秒
71.
Enantioselective Sulfur‐Michael Addition of Thioacetic Acid to Nitroalkenes Catalyzed by Bifunctional Amine‐Thiourea Catalysts 下载免费PDF全文
An enantioselective Michael addition of thioacetic acid (AcSH) to nitroalkenes, catalyzed by a leucine‐derived bifunctional amine? thiourea, was developed with high yields and moderate enantioselectivities. The thiourea‐ammonium salt formed in the reaction is identified as the active catalyst, and the multiple H‐bonding system is responsible for the stereocontrol. The resulting thioester products are useful intermediates for the synthesis of enantiomerically enriched S‐containing compounds. 相似文献
72.
Zhi Guo Qiao Tian Hua Shen Zhen Fang Fu Jun Qi Li Hong Wang Qing Bao Song 《中国化学快报》2011,22(11):1265-1268
A series of C2-symmetric and asymmetric chiral thiourea derivatives were synthesized from commercial L-phenylalanine.All of the new compounds have been fully characterized by IR,1H NMR,13C NMR,MS spectra and elemental analyses.The chiral thioureas were used as chiral ligands in the catalytic enantioselective ethylation of aldehydes with diethylzinc,the corresponding sec-alcohols were gained with excellent enantioselectivities(up to 87.1%ee) and high yields(up to 76.7%) after the conditions were optimized. 相似文献
73.
本文探讨了硫脲浸出银的微观机理及银和硫脲的E-pH图,在25℃下,硫脲浓度,Fe^3+浓度及pH是影响浸出平衡的主要因素,试验确定硫脲浸出银的适宜条件。 相似文献
74.
A novel cellulose solvent, 1.5 M NaOH/0.65 M thiourea aqueous solution, was used to dissolve cotton linters having a molecular weight of 10.1 × 104 to prepare cellulose solution. Regenerated cellulose (RC) films were obtained from the cellulose solution by coagulating with sulfuric acid (H2SO4) aqueous solution with a concentration from 2 to 30 wt %. Solubility of cellulose, structure, and mechanical properties of the RC films were examined by infrared spectroscopy, X‐ray diffraction, scanning electron microscopy, 13C NMR, and tensile tests. 13C NMR analysis indicated that the novel solvent of cellulose is a nonderivative aqueous solution system. The presence of thiourea enhanced significantly the solubility of cellulose in NaOH aqueous solution and reduced the formation of cellulose gel; as a result, thiourea prevented the association between cellulose molecules, leading to the solvation of cellulose. The RC film obtained by coagulating with 5 wt % H2SO4 aqueous solution for 5 min exhibited higher mechanical properties than that with other H2SO4 concentrations and a homogenous porous structure with a mean pore size of 186 nm for free surface in the wet state. The RC film plasticized with 10% glycerin for 5 min had a tensile strength of 107 MPa and breaking elongation of 10%, and about 1% glycerin in the RC film plays an important role in the enhancement of the mechanical properties. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1521–1529, 2002 相似文献
75.
Rotational barriers of the NH2 group in thiourea and benzylurea in solution become slightly larger in the presence of anionic hydrogen‐bond acceptors. The interactions between the N? H bond and different anions were investigated in acetonitrile solution using 1H{14N} variable‐temperature NMR. Line‐shape analyses of the spectra show a weakly anion‐dependent increase in ΔG? of rotation, with benzoate having the strongest effect and iodide the weakest. Hydrogen‐bonding acidities of benzylurea and thiourea were also measured on the Abraham solute hydrogen‐bond acidity scale by proton NMR. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
76.
The asymmetric aza-Henry reaction of fluoromethyl imines derived from 4-methoxyaniline with nitromethane was achieved under mild conditions using cinchona-derived bifunctional thiourea as catalyst. A series of chiral fluoromethylated β-nitroamines were synthesized and their transformation to optically pure 4-fluoromethyl-2-imidazolidones was illustrated. 相似文献
77.
在B3LYP/6.31 G(2DF,2PD)水平优化气相中的尿素和硫脲分子构型,得到C2点群的非平面分子.对此构型的尿素和硫脲分子用CPHF和FF方法进行了非线性光学性质的计算,比较了尿素和硫脲非线性光学性质,讨论了极化函数、弥散函数和相关效应对(超)极化率的影响,还与固定C2v对称相同水平优化得到的平面分子计算结果进行了比较. 相似文献
78.
Faizan Ur Rahman Maryam Bibi Ezzat Khan Abdul Bari Shah Mian Muhammad Muhammad Nawaz Tahir Adnan Shahzad Farhat Ullah Muhammad Zahoor Salman Alamery Gaber El-Saber Batiha 《Molecules (Basel, Switzerland)》2021,26(15)
In this study six unsymmetrical thiourea derivatives, 1-isobutyl-3-cyclohexylthiourea (1), 1-tert-butyl-3-cyclohexylthiourea (2), 1-(3-chlorophenyl)-3-cyclohexylthiourea (3), 1-(1,1-dibutyl)-3-phenylthiourea (4), 1-(2-chlorophenyl)-3-phenylthiourea (5) and 1-(4-chlorophenyl)-3-phenylthiourea (6) were obtained in the laboratory under aerobic conditions. Compounds 3 and 4 are crystalline and their structure was determined for their single crystal. Compounds 3 is monoclinic system with space group P21/n while compound 4 is trigonal, space group R3:H. Compounds (1–6) were tested for their anti-cholinesterase activity against acetylcholinesterase and butyrylcholinesterase (hereafter abbreviated as, AChE and BChE, respectively). Potentials (all compounds) as sensing probes for determination of deadly toxic metal (mercury) using spectrofluorimetric technique were also investigated. Compound 3 exhibited better enzyme inhibition IC50 values of 50, and 60 µg/mL against AChE and BChE with docking score of −10.01, and −8.04 kJ/mol, respectively. The compound also showed moderate sensitivity during fluorescence studies. 相似文献
79.
J. M. Salas M. A. Romero J. A. Rodríguez R. Faure 《Journal of chemical crystallography》1996,26(12):847-851
The title compounds palladium(II) and platinum(II) tetrakisthiourea dichloride bis(7-hydroxy-5-methyl[1,2,4]triazolo[1,5a]pyrimidine (Hmtpo)) dihydrate solvates, have been synthesized by reacting thecis-[MCl2(Hmtpo)2] (where M=Pt(II), Pd(II)) complexes with an excess of thiourea (tu) and the structure of the palladium compound was solved by X-ray diffraction. Crystals of [Pd(tu)4]Cl2·2Hmtpo·2H2O are triclinic with space groupP and unit cell dimensionsa=7.972(1),b=9.049(1),c=11.808(2)Å, =88.20(1), =75.15(1), =76.54(1)o. The cation [Pd(tu)4]2+ is centrosymmetric involving four sulfur thiourea atoms in a near square planar environment. The triazolopyrimidine molecules, chloride anions and water molecules do not take part in the metal center coordination but interact by hydrogen bonding between them and the thiourea moieties. A comparison between powder diffraction data of palladium(II) and platinum(II) compounds clearly indicates that both compounds are isomorphous. 相似文献
80.
Ummuhan Solmaz Gun Binzet Omer Celik Gulten Kavak Balci Aylin Dogen 《Journal of Coordination Chemistry》2018,71(2):200-218
N,N-Di-R-N′-(4-chlorobenzoyl)thiourea (Di-R: diethyl, di-n-propyl, di-n-butyl and diphenyl) ligands (HL1–4) and their Pt(II) complexes (cis-[Pt(L1–4-S,O)2]) have been synthesized and structurally characterized by elemental analyses, FT-IR and NMR spectroscopy. HL2 ligand and cis-[Pt(L4-S,O)2] metal complex have been also characterized by a single-crystal X-ray diffraction study. HL2, C14H19ClN2OS, crystallizes in the monoclinic space group P21/n (no. 14), with Z = 4, and unit cell parameters, a = 11.1405(16) Å, b = 9.7015(12) Å, c = 14.790(2) Å, β = 106.547(7)°. The cis-[Pt(L4-S,O)2], C40H28Cl2N4O2PtS2: triclinic, space group P-1 (no. 2), a = 8.9919(3) Å, b = 14.7159(6) Å, c = 15.7954(6) Å, α = 113.9317(18)°, β = 97.4490(18)°, and γ = 105.0492(16)°. Single crystal analysis of complex, cis-[Pt(L1–4-S,O)2], revealed that a square planar coordination geometry is formed around the platinum atom by two sulfur and two oxygen atoms of the related ligands, which are in a cis configuration. In addition, the thiourea derivative ligands and their complexes were evaluated for both their in-vitro antibacterial and antifungal activity. The results have been reported, explained, and compared with fluconazole and ampicillin, used as reference drugs. 相似文献