全文获取类型
收费全文 | 474篇 |
免费 | 16篇 |
国内免费 | 1篇 |
专业分类
化学 | 408篇 |
晶体学 | 5篇 |
力学 | 5篇 |
综合类 | 1篇 |
数学 | 26篇 |
物理学 | 46篇 |
出版年
2023年 | 4篇 |
2022年 | 47篇 |
2021年 | 22篇 |
2020年 | 18篇 |
2019年 | 20篇 |
2018年 | 17篇 |
2017年 | 14篇 |
2016年 | 17篇 |
2015年 | 16篇 |
2014年 | 17篇 |
2013年 | 29篇 |
2012年 | 17篇 |
2011年 | 47篇 |
2010年 | 19篇 |
2009年 | 18篇 |
2008年 | 26篇 |
2007年 | 27篇 |
2006年 | 12篇 |
2005年 | 17篇 |
2004年 | 17篇 |
2003年 | 10篇 |
2002年 | 11篇 |
2000年 | 10篇 |
1999年 | 4篇 |
1997年 | 1篇 |
1996年 | 2篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 2篇 |
1988年 | 1篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1982年 | 1篇 |
1975年 | 1篇 |
1964年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有491条查询结果,搜索用时 15 毫秒
41.
Studies and X‐ray Determinations with 2‐(Acetonylthio)benzothiazole: Synthesis of 2‐(Benzothiazol‐2‐ylthio)‐1‐phenylethanone and 2‐(Acetonylthio)Benzothiazole by C―S Bond Cleavage of 2‐(Acetonylthio)benzothiazole in KOH
下载免费PDF全文
![点击此处可从《Journal of heterocyclic chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
New route for the synthesis of 2‐(benzothiazol‐2‐ylthio)‐1‐phenylethanone ( 6 ) and 2‐(acetonylthio)benzothiazole ( 1 ) by using phenacyl bromide and α‐chloroacetone, respectively, through carbon–sulfur bond cleavage reactions in a basic medium has been generated. Treatment of 1 with malononitrile and elemental sulfur afforded the corresponding derivative of 2‐amino‐3‐cyanothiophene ( 12 ), whereas treatment of 1 with cyanoacetohydrazide afforded the corresponding derivative of cyanoacetylhydrazone derivative ( 13 ). The structure of the synthesis compounds has been established on the basis of elemental analyses, 1H‐NMR, 13C‐NMR, correlation spectroscopy, heteronuclear single quantum coherence, MS spectra, and X‐ray crystallographic investigations. 相似文献
42.
Dielectrophoresis (DEP) has been used for many years for the analysis of the electrophysiological properties of cells. However, such analyses have in the past been time-consuming, such that it can take 30 min or more to collect sufficient data to make valid interpretations from a single DEP spectrum. This has limited the application of the technology to a rapid tool for non-invasive, label-free research in areas from drug discovery to diagnostics. In this paper we present the development of a programmable, multi-channel DEP system for rapid biophysical assessment of populations of biological cells. A new assay format has been developed for continuous near-real-time monitoring, using simultaneous application of up to eight alternating current electrical signals to independently addressable dot microelectrodes in an array format, allowing a DEP spectrum to be measured in 20?s, with a total cycle time between measurements of 90?s. To demonstrate the system, human leukaemic K562 cells were monitored after exposure to staurosporine and valinomycin. The DEP response curves showed the timing and manner in which the membrane properties changed for the actions of these two drugs at the early phase of induction. This technology shows the great potential for increasing our understanding of the role of electrophysiology in drug action, by observing the changes in electrical characteristics as they occur. 相似文献
43.
ZAKNROU Zohra 《高等学校化学研究》2011,27(1):99-103
The authors investigated the regulation of human aquaporin 1(hAQP1) and the involvement of aquaporin 1(AQP1) in the migration of human hepatocellular carcinoma SMMC-7221 cells using RNA intereference technology. Firstly, two short hairpin RNA(shRNA) constructs in PBSU6 vector were reconstructed and their knockdown effects were identified in SMMC-7221 cells. Next, the involvement of endogenous hAQP1 in regulating the migration of SMMC-7221 cells was investigated via siRNA technology. HAQP1-shRNA can specific... 相似文献
44.
Arjmand F Sayeed F Muddassir M 《Journal of photochemistry and photobiology. B, Biology》2011,103(2):166-179
New Schiff base ligand L derived from the condensation reaction of 2-amino-3-formylchromone with (R)-2-amino-2-phenylethanol was synthesized and characterized which involves combination element of ammine functionality and naturally occurring heterocyclic chromone, 4H-benzopyran-4-one. Subsequently, their complexes 1 and 2 with Cu(NO?)? and Zn(NO?)?, respectively were prepared. The DNA binding studies of the ligand L and complexes 1 and 2 with CT-DNA as compared to classical anticancer drug cisplatin were carried out by employing different optical methods viz, UV-vis, fluorescence, circular dichroism and viscosity measurements. Furthermore, the absorption studies, 1H and 31P with mononucleotides were also monitored to examine the base specific interactions of the transition metal complexes which revealed a higher propensity of copper(II) complex 1 for 5'-GMP while for zinc(II) complex 2 towards 5'-TMP involving groove binding mechanism of the complexes towards DNA. The complex 1 exhibits a remarkable DNA cleavage activity with pBR322 DNA in presence of different activators and cleavage reaction involves various oxygen species suggesting the involvement of active oxygen species for the DNA scission. 相似文献
45.
Structure and dynamics of highly PEG-ylated sterically stabilized micelles in aqueous media 总被引:1,自引:0,他引:1
Vuković L Khatib FA Drake SP Madriaga A Brandenburg KS Král P Onyuksel H 《Journal of the American Chemical Society》2011,133(34):13481-13488
Molecular assemblies of highly PEG-ylated phospholipids are important in many biomedical applications. We have studied sterically stabilized micelles (SSMs) of self-assembled DSPE–PEG2000 in pure water and isotonic HEPES-buffered saline solution. The observed SSM sizes of 2–15 nm largely depend on the solvent and the lipid concentration used. The critical micelle concentration of DSPE–PEG2000 is 10 times higher in water than in buffer, and the viscosity of the dispersion dramatically increases with the lipid concentration. To explain the experimentally observed results, we performed atomistic molecular dynamics simulations of solvated SSMs. Our modeling revealed that the observed assemblies have very different aggregation numbers (N(agg) ≈ 90 in saline solution and N(agg) < 8 in water) because of very different screening of their charged PO4(–) groups. We also demonstrate that the micelle cores can inflate and their coronas can fluctuate strongly, thus allowing storage and delivery of molecules with different chemistries. 相似文献
46.
Caragisides A–C ( 1 – 3 , resp.), three new isoflavone glucosides, were isolated from the BuOH sub‐fraction of the EtOH extract of the whole plant of Caragana conferta, along with ononoside ( 4 ), reported for the first time from this species. The structures of the new compounds were elucidated by spectroscopic techniques including MS and 2D‐NMR spectroscopy. Compounds 1 – 3 showed significant inhibition of platelet aggregation. 相似文献
47.
Fatima Bi Seema Iqbal Muhammad Arman Amanat Ali Mahmood-ul Hassan 《Journal of Saudi Chemical Society》2011,15(3):269-273
The effects of polysaccharide elicitor k-carrageenan obtained from Hypnea musciformis, red algae on the production of Induced Secondary Metabolites, ISMs (the disease resistance compounds) and on various growth characters of chickpea and maize plants were studied. Experiments were conducted in the field of PCSIR Laboratories Complex Karachi during December 2008–April 2009 in randomized complete block design with three replications. Three elicitor treatments were used, a solid preparation in which the elicitor was mixed with soil (T2 1 mg/g) and applied around the seeds in the soil. The two other preparations were liquid, T1 and T3 at a concentration of 100 μg glc eq ml−1 and were applied around the sowing seeds and as a foliar spray on the plants, respectively. Statistical analysis of the data revealed that these treatments significantly enhanced all the growth characters of chickpea except T2 that gave the nonsignificant difference in the plant height. Maximum plant height (80.3 cm), number of pods plant−1 (76.2), number of branches plant−1 (25.0), number of leaves plant−1 (125.6), earlier flowering and high ISMs contents in leaves, stem and grains of chickpea were recorded in T1 treated chickpea plants. In maize plants only T1 and T3 treatments (with minor exceptions) had significant effects on few characters like plant height, stem diameter, number of leaves plant−1 and on ISMs contents in leaves while number of cobs plant−1 and flowering time were nonsignificantly affected by these treatments. These results suggested that k-carrageenan elicitor can be used as a potent plant protectant as well as growth promoting agent especially for chickpea plants. 相似文献
48.
Othman MK Al-Qadri FA Al-Yusufy FA 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2011,78(5):1342-1348
Two new chelating resins possessing multiple functional groups capable of coordinating with several metal ions are reported. The resins were synthesized by condensing Schiff bases derived from 2-aminophenol, 2-hydroxy-5-chloroaniline and terephthaldehyde with formaldehyde in an alkaline medium. The effects of pH and contact time of the Cu(2+) and Pb(2+) in aqueous solutions on the uptake behavior of the resins were studied. The metal ion uptake behavior of the resins was investigated by the batch method. Both the uptake and the selectivity of the resins towards the investigated metal ions were related to the structure of the resins, type of the metal ion and the uptake conditions. The resins showed maximum uptake capacity for Cu(2+) and Pb(2+) at pH 10. Cu(2+) was seen to undergo preferential adsorption in separate and mixture solutions of Cu(2+) and Pb(2+). Kinetic studies for the resins using Langmiur equation were also performed. The Schiff base monomers and their formaldehyde resins were characterized by elemental analyses, FTIR and (1)H NMR spectroscopy. The thermal stability of the resins was studied using TGA/DTG analysis. 相似文献
49.
Maria de Fatima Pereira 《Tetrahedron》2007,63(4):847-854
The work described in this paper is a further example of the utility of Appel's salt in the conception of novel heterocyclic rings. We confirmed that primary alkyldiamines may react easily with the methyl N-(4-chloro-5H-1,2,3-dithiazol-5-ylidene)-anthranilates to afford quinazolines, which are very interesting starting materials for the access to novel 2,3-condensed quinazolin-4-ones. On the other side, aromatic amines allow the synthesis of polycyclic molecules, which are structurally close to the model natural products (e.g., rutaecarpine, luotonine, tryptanthrine and vasicinone). 相似文献
50.
Summary A TLC method has been developed for the separation of Zn(II) from Cd(II) and Cu(II) on silica gel alyers with mixed organic solvents containing s-butylamine. The separation of Zn(II) from Cd(II) in the presence of certain anions and at various pH values of sample solution was examined. A mixture containign s-butylamine, acetone and formic acid in 262 was found to be the best solvent. 相似文献