全文获取类型
收费全文 | 1075篇 |
免费 | 51篇 |
国内免费 | 2篇 |
专业分类
化学 | 786篇 |
晶体学 | 14篇 |
力学 | 13篇 |
数学 | 57篇 |
物理学 | 258篇 |
出版年
2024年 | 2篇 |
2023年 | 18篇 |
2022年 | 36篇 |
2021年 | 36篇 |
2020年 | 44篇 |
2019年 | 61篇 |
2018年 | 53篇 |
2017年 | 36篇 |
2016年 | 57篇 |
2015年 | 41篇 |
2014年 | 101篇 |
2013年 | 109篇 |
2012年 | 75篇 |
2011年 | 70篇 |
2010年 | 38篇 |
2009年 | 29篇 |
2008年 | 44篇 |
2007年 | 32篇 |
2006年 | 30篇 |
2005年 | 27篇 |
2004年 | 30篇 |
2003年 | 17篇 |
2002年 | 22篇 |
2001年 | 14篇 |
2000年 | 7篇 |
1999年 | 10篇 |
1998年 | 4篇 |
1997年 | 3篇 |
1996年 | 7篇 |
1995年 | 9篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 6篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 9篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1982年 | 9篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1939年 | 1篇 |
排序方式: 共有1128条查询结果,搜索用时 15 毫秒
1.
Conductivity, viscosity, turbidity, and NMR measurements were performed over most of the mole fraction range for sodium deoxycholate (SDC) with hexadecyltrimethylammonium bromide (HTAB), hexadecylpyridinium bromide (HPyBr), and hexadecylpyridinium chloride (HPyCl). All studies demonstrate that the mixed-micelle formation is more favorable in SDC plus HTAB rather than SDC plus HPyBr or SDC plus HPyCl mixtures. The results showed that the bulky pyridinium head groups of HPyBr or HPyCl create steric incompatibility with rigid SDC monomers in the mixed state. 相似文献
2.
Adamovich MI Aggarwal MM Alexandrov YA Ameeva ZV Andreeva NP Anzon ZV Arora R Badyal SK Bhalla KB Bhasin A Bhatia VS Bubnov VI Burnett TH Cai X Chasnikov IY Chernova LP Chernyavski MM Dressel B Eligbaeva GZ Eremenko LE Friedlander EM Gadzhieva SI Gaitinov AS Ganssauge ER Garpman S Gerassimov SG Gill A Grote JG Gulamov KG Gulyamov UG Gupta VK Hackel S Heckman HH Haung H Judek B Kachroo S Kadyrov FG Kalyachkina GS Kanygina EK Kaul GL Kaur M Kharlamov SP Koss T Kumar V Lal P Larionova VG 《Physical review letters》1990,65(4):412-415
3.
tert-Butyl 2-hydroxyalkyl sulfides, prepared by reaction of epoxides with 2-methylpropane-2-thiol, are converted directly to 1,3-oxathiolanes upon treatment with pivalaldehyde and boron trifluoride diethyl etherate in the presence of thioanisole. 相似文献
4.
Cloud point (C(P)) was measured for ternary mixtures of different ionic surfactants such as sodium dodecyl sulfate (SDS), dodecyltrimethylammonium bromide (DTAB), and dimethylene bis(dodecyldimethylammonium bromide) (12-2-12) plus triblock polymer (TBP) ((PEO)(2)(PPO)(15.5)(PEO)(2)) plus water, keeping the concentration of TBP constant and varying the surfactant concentration from pre- to postmicellar regions. These experiments were also performed in the presence of different fixed amounts of NaBr to evaluate the salt effect on the clouding behavior of these ternary mixtures. The C(P) value of TBP exhibits a drastic change at the cmc of each surfactant. The cmc values thus obtained both in the absence and in the presence of NaBr were used to evaluate counterion binding (beta) with the Corrin-Harkins method. beta values were also used to evaluate the thermodynamic parameters of these ionic surfactants. The results suggest that the beta values evaluated using this method, especially at low [TBP], are in good agreement with those reported in the literature. 相似文献
5.
Navjeet Kaur Yamini Verma Pooja Grewal Neha Ahlawat Pranshu Bhardwaj Nirmala Kumari Jangid 《合成通讯》2020,50(9):1286-1334
AbstractFew conversions cannot take place with ground-state reactions even with the help of a catalyst, therefore they are made to occur under photochemical conditions. The transfer of electrons took place even with the photochemical excitement of one molecule where redox reaction cannot occur at the ground state. The ground-state reactions resulted in the formation of side products. The substrates did not require any sort of chemical activation for C–N bond construction in the course of photochemical reactions. The source of energy; light has always been the interest of researchers in order to induce chemical reactions ever since the starting of scientific chemistry. The present review encloses the chemistry of photochemical transformations with a focus on their synthetic uses. The organic photochemical reactions prevent the polluting or harmful reagents thus, provides a possibility for sustainable procedures as well as green chemistry. This review article displays the formation of numerous of five-membered fused nitrogen-heterocyclic compounds. 相似文献
6.
Attempts to cyclise o-chlorophenyl benzyl ether, sulphide, sulphoxide and sulphone by treatment with KNH2/NH3 were unsuccessful. Similar reaction of 1-(o-chlorophenyl)-2,2-diphenylethane led to amination whereas α-(o-chlorobenzyl)phenylacetic acid gave a dihydrocoumarin. Reaction of 4- and 2-(o-chlorophenethyl)-pyridines, however, afforded products comprising benzisoquinolines and 1-pyridylbenzocyclobutenes. 相似文献
7.
Prakash O Kaur H Batra H Rani N Singh SP Moriarty RM 《The Journal of organic chemistry》2001,66(6):2019-2023
The combination reagent (dichloroiodo)benzene and lead(II) thiocyanate in dichloromethane effects oxidation of various enol silyl ethers, ketene silyl acetals, and beta-dicarbonyl compounds, thereby providing an efficient and convenient method for alpha-thiocyanation of carbonyl and beta-dicarbonyl compounds. 相似文献
8.
Herein we describe a strategy for the preparation of artificial alpha-helices involving replacement of one of the main-chain hydrogen bonds with a covalent linkage. To mimic the C=O...H-N hydrogen bond as closely as possible, we envisioned a covalent bond of the type C=X-Y-N, where X and Y are two carbon atoms connected through an olefin metathesis reaction. Our results demonstrate that the replacement of a hydrogen bond between the i and i + 4 residues at the N-terminus of a short peptide with a carbon-carbon bond results in a highly stable constrained alpha-helix at physiological conditions as indicated by CD and NMR spectroscopies. The advantage of this strategy is that it allows access to short alpha-helices with strict preservation of molecular recognition surfaces required for biomolecular interactions. 相似文献
9.
A new series of N-substituted bis-(tetrahydropapaverine) ring systems have been synthesised in expectation of better antispasmodic activity in comparison with papaverine. The synthesis of the targeted heterocycles is described along with a discussion of their structure activity relationship. The general synthetic methods of bis-(tetrahydropapaverine) analogues involve tetrahydropapaverine, various piperazines, diisocyanates and diisothiocyanates as starting materials. Pharmacological evaluation involves the in vitro antispasmodic activity on a freshly removed guinea pig ileum using a force displacement transducer amplifier connected to a physiograph. Among the analogues synthesized in the present study, N,N'-bis-[2-carbamoyl-1-(3,4-dimethoxybenzyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolinyl]piperazine (22), was found to be the most potent muscle relaxant (IC(50): 0.31 microM). 相似文献
10.
P. V. Bharatam Amita D. Kaur P. Senthil Kumar 《International journal of quantum chemistry》2006,106(5):1237-1249
The potential energy surface (PES) of thionylimide has been searched using ab initio MO and density functional calculations. The electronic structures of the isomers of HNSO have been studied using the HF/6‐31+G*, MP2(full)/6‐31+G*, and B3LYP/6‐31+G* levels. Final energies of these molecules have been calculated at the high‐accuracy G2 and CBS‐Q levels. The probable pathways of isomerization of thionylimide to its isomers (e.g., thiocyanic acid, HONS, nitrosothiols) have been explored by studying the three‐ or four‐membered transition states. This study identified total eight possible isomers ( 1–8 ) of HNSO, of which four ( 1–4 ) have already been realized experimentally. Of the remaining four ( 5–8 ), at least two ( 5, 7 ) can be generated experimentally. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 相似文献