全文获取类型
收费全文 | 1374篇 |
免费 | 32篇 |
国内免费 | 238篇 |
专业分类
化学 | 1504篇 |
晶体学 | 12篇 |
力学 | 2篇 |
综合类 | 7篇 |
数学 | 1篇 |
物理学 | 118篇 |
出版年
2023年 | 7篇 |
2022年 | 23篇 |
2021年 | 18篇 |
2020年 | 26篇 |
2019年 | 31篇 |
2018年 | 33篇 |
2017年 | 21篇 |
2016年 | 23篇 |
2015年 | 20篇 |
2014年 | 48篇 |
2013年 | 149篇 |
2012年 | 83篇 |
2011年 | 79篇 |
2010年 | 57篇 |
2009年 | 73篇 |
2008年 | 81篇 |
2007年 | 100篇 |
2006年 | 97篇 |
2005年 | 83篇 |
2004年 | 67篇 |
2003年 | 65篇 |
2002年 | 48篇 |
2001年 | 53篇 |
2000年 | 35篇 |
1999年 | 46篇 |
1998年 | 33篇 |
1997年 | 27篇 |
1996年 | 25篇 |
1995年 | 24篇 |
1994年 | 21篇 |
1993年 | 21篇 |
1992年 | 17篇 |
1991年 | 15篇 |
1990年 | 13篇 |
1989年 | 17篇 |
1988年 | 11篇 |
1987年 | 16篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1984年 | 6篇 |
1982年 | 4篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1974年 | 3篇 |
1973年 | 3篇 |
1972年 | 2篇 |
排序方式: 共有1644条查询结果,搜索用时 187 毫秒
1.
A string of four new hetero binuclear Ru(III) complexes of ferrocenecarboxaldehyde-4(N)-substituted thiosemicarbazones were synthesized and characterized by various spectral (infrared, ultraviolet–visible, Electron Paramagnetic Resonance (EPR) and High Resolution Mass Spectrometry (HR-MS) techniques. The binding abilities of the ligands/complexes with nucleic acid (calf thymus DNA, CT-DNA) and bovine serum albumin (BSA) were analyzed by absorption and emission titration methods. The complexes exhibited better DNA binding affinity than their parent ligands. The interaction with CT-DNA was found to be intercalative and with BSA static quenching mechanism was observed. All the synthesized Ru(III) complexes were subjected to study their in vitro cytotoxicity against MCF-7 (human breast cancer) and HT-29 (human colon cancer) cell lines. Among the four complexes, complex 3 [RuCp (FF-etsc)PPh3]Cl exhibited the highest cytotoxicity in MCF-7 cells and complex 4 [RuCp (FF-ptsc)PPh3]Cl was the most active on HT-29 cells. 相似文献
2.
Controlled dilithiation of propargyl bromide with two equivalents of n-butyllithium, in the presence of TMEDA, produces the operational equivalent of the dianion 1,3-dilithiopropyne. The latter reacts efficiently with acid chlorides to produce bishomopropargylic alcohols in a single step route and with high regioselectivity and moderate yields. 相似文献
3.
《印度化学会志》2021,98(10):100142
A simple and low cost method for extraction and preconcentration of Arsenazo-III (ARS-III) and Magdala Red (MR) was developed by an efficient cloud point extraction (CPE) method using mixed micelles of Triton X–114 (TX–114) and cetyltrimethyl ammonium bromide (CTAB). Various parameters, such as pH/concentration of H2SO4, surfactant concentrations (TX-114 and CTAB), equilibrium temperature and time have been studied to maximise efficiency. Thermodynamic quantities like change in Gibbs free energy (ΔG0), change in enthalpy (ΔH0) and change in entropy (ΔS0) were calculated. The results show that the CPE of ARS-III and MR dye is feasible, spontaneous, and endothermic in the temperature range of (50–80) °C indicating good recoveries for the developed method. The effect of temperature, surfactant concentration and dye concentration on various thermodynamic quantities was investigated and it was found that ΔG0 values increased with temperature but decreased with surfactant and dye concentration. ΔH0 and ΔS0 values increased as surfactant concentration increased and decreased as dye concentration decreased. The recoveries were found to be the range from 90.02 – 101.03 % for ARS-III and 86.07–99.46 % for MR dyes which proves that the method is highly efficient. 相似文献
4.
Regioselective One‐pot Synthesis of New Unsymmetric Spiro Dihydrofurans in the Reaction of Mixed Two Different Cyclic β‐Dicarbonyl Compounds with BrCN and Aldehydes in the Presence of Et3N 下载免费PDF全文
Crossed one‐pot reaction of mixed cyclic β‐dicarbonyl with various aldehydes in the presence of cyano gen bromide and triethylamine leads to the selective and efficient formation of crossed new unsymmetri cal spiro dihydrofurans at room temperature. The products were obtained in good to excellent yields. Structure elucidation was carried out by 1H NMR, 13C NMR, FT‐IR spectroscopy, Mass analyses and X‐ray crystallography technique. A proposed mechanism was discussed for the formation of products. 相似文献
5.
Novel and Stereospecific Synthesis of (2S)‐3‐(2,4,5‐Trifluorophenyl)propane‐1,2‐diol from D‐Mannitol 下载免费PDF全文
Derya Aktaş Meryem Fıstıkçı Özlem Gündoğdu Hasan Seçen M. Fethi Şahin Ramazan Altundaş Yunus Kara 《Helvetica chimica acta》2015,98(8):1127-1131
A stereospecific synthesis of (2S)‐3‐(2,4,5‐trifluorophenyl)propane‐1,2‐diol from D ‐mannitol has been developed. The reaction of 2,3‐O‐isopropylidene‐D ‐glyceraldehyde with 2,4,5‐trifluorophenylmagnesium bromide gave [(4R)‐2,2‐dimethyl‐1,3‐dioxolan‐4‐yl](2,4,5‐trifluorophenyl)methanol in 65% yield as a mixture of diastereoisomers (1 : 1). The Ph3P catalyzed reaction of the latter with C2Cl6 followed by reduction with Pd/C‐catalyzed hydrogenation gave (2S)‐3‐(2,4,5‐trifluorophenyl)propane‐1,2‐diol with >99% ee and 65% yield. 相似文献
6.
Equilibria of EuO dissolution and dissociation in molten (NaBr + NaI) mixtures of 0.77:0.23 and 0.31:0.69 compositions at T = 973 K were studied by potentiometric titration method using Pt(O2)|ZrO2(Y2O3) indicator electrode. The solubility product indices of EuO are (7.81 ± 0.08) and (8.43 ± 0.16) in the melts of 0.77:0.23 and 0.31:0.69 compositions. The corresponding dissociation constant indices are (4.96 ± 0.04) and (5.54 ± 0.06), respectively (all the parameters are in molality). Non-dissociated EuO is the prevailing form in all the saturated solutions of europium monoxide. The decrease of the iodide ion concentration in the melts results in strengthening of EuO dissociation that is explained by introduction of harder Pearson’s base (Br−) in sodium iodide melt. In its turn this increases the fixation degree of Eu2+ in mixed halide complexes. The total solubility of EuO decreases going from NaI melt to the (bromide + iodide) mixtures that is caused by the decrease of ‘physical’ solubility of non-dissociated oxide which occupies hollow spaces of enough large size in the ionic solvents. The quantity of these hollow spaces diminishes at the sequential Br− → I− substitution. 相似文献
7.
Nucleic acid staining dyes are used for detecting nucleic acids in electrophoresis gels. Historically, the most common dye used for gel staining is ethidium bromide, however due to its toxicity and mutagenicity other dyes that are safer to the user and the environment are preferred. This Short Communication details the properties of dyes now available and their sensitivity for detection of DNA and their ability to permeate the cell membrane. It was found that GelRed? was the most sensitive and safest dye to use with UV light excitation, and both GelGreen? and Diamond? Nucleic Acid Dye were sensitive and the safer dyes using blue light excitation. 相似文献
8.
A novel, cost‐effective, and simple electrocatalyst based on a Pt‐modified glassy carbon electrode (GCE), using cetyltrimethylammonium bromide (CTAB) as a cationic surfactant, is reported. Am‐phiphilic... 相似文献
9.
We report in this work new results concerning the temperature dependence of the non-Newtonian viscosity of semi-diluted aqueous micellar solutions of cetyltrimethylammonium bromide (CTAB) in the presence of potassium bromide (KBr). Two structural transitions are responsible for the unusual flow curves obtained. The first transition induced by the shear flow corresponds to an induced liquid crystalline phase of the nematic type; the second corresponds to the disappearing of this phase with increase of the temperature. 相似文献
10.
The electrochemical bromination of 4-methoxy toluene by two-phase electrolysis yields 3-bromo 4-methoxy toluene at first, which subsequently undergoes side-chain bromination to give 3-bromo 4-methoxy benzyl bromide as a final product in 86% yield. The two-phase electrolysis consists of 25–50% NaBr as aqueous electrolyte and CHCl3 containing aromatic compound as organic phase. The reaction temperature is maintained at 10–25 °C. The probable orientation of bromine atom in an alkyl aromatic compound (nuclear versus side chain) is explained from the experimental result. 相似文献