全文获取类型
收费全文 | 184篇 |
免费 | 15篇 |
国内免费 | 3篇 |
专业分类
化学 | 171篇 |
晶体学 | 4篇 |
力学 | 1篇 |
数学 | 9篇 |
物理学 | 17篇 |
出版年
2023年 | 2篇 |
2022年 | 6篇 |
2021年 | 8篇 |
2020年 | 9篇 |
2019年 | 11篇 |
2018年 | 12篇 |
2017年 | 8篇 |
2016年 | 13篇 |
2015年 | 13篇 |
2014年 | 10篇 |
2013年 | 12篇 |
2012年 | 12篇 |
2011年 | 16篇 |
2010年 | 8篇 |
2009年 | 9篇 |
2008年 | 12篇 |
2007年 | 9篇 |
2006年 | 6篇 |
2005年 | 6篇 |
2004年 | 7篇 |
2003年 | 1篇 |
2002年 | 1篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1988年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1971年 | 2篇 |
1969年 | 1篇 |
排序方式: 共有202条查询结果,搜索用时 15 毫秒
31.
Farhat Jubeen Sania Zafar Iqbal Nusrat Shafiq Maryam Khan Shagufta Parveen Munawar Iqbal 《合成通讯》2018,48(6):601-625
Among all heterocyclic compounds, pyrimidine is of prime interest, exhibit broad spectrum of biological activities, because of its occurrence in deoxyribonucleic acid bases. The bioactive moiety pyrimidine has a voluminous therapeutic profile as it is a vital component of a series of natural composites and chemotherapeutic drugs. Since from last 50–60 years, this motif has been used commendably against bacterial, tuberculosis viral, malarial, fungal, and cancerous contagions. Recently, numerous pyrimidine derivatives were synthesized and discussed here, fused with other heterocyclic moieties, pyrazole, coumarine, triazole, alkenyloxindole, hydrazine and others, were also investigated for their bioactivities. Amid all recently reported compounds, several exhibit potentials against breast cancer cell lines. Intensive research has been performed and is going ahead with distinctive emphasis on antineoplastic potential of pyrimidine. These widespread medicinal attributes impulse scientists to synthesize more and more biologically active pyrimidine composites by following simple and eco-friendly routes. 相似文献
32.
Mehtab Parveen Raza Murad Ghalib Sayed Hasan Mehdi Rayees Ul Hasan Mattu Mohammed Ali 《Journal of Saudi Chemical Society》2009,13(3):287-290
The chloroform extract of the leaves of Ficus benjamina (var. comosa) (Moraceae) afforded a new triterpenic acid named as (9,11), (18,19)-disecoolean-12-en-28-oic acid (1) along with β-amyrin (2). Their structures were established on the basis of chemical and physical evidences (IR, 1H NMR, and MS data). The compound 1 exhibited significant antimicrobial activity against Salmonella typhimurium (MTCC-98), Candida albicans (IAO-109), Staphylococcus aureus (IAO-SA-22), Escherichia coli (K-12) and low activity against Aspergillus niger (lab isolate ICAR) and Aspergillus brassicola. 相似文献
33.
The new experimental results on the effective quantum numbers and term energies of the highly excited odd-parity 4s4d 3D1,2,3 →4snf 3F2,3,4 Rydberg transitions of zinc have been presented. The experiment was performed using the three dye lasers simultaneously pumped by the second harmonic (532?nm) of the Q-switched Nd:YAG laser. The new observation includes the 4snf 3F3 (12?≤n?≤?50) series excited from the 4s4d 3D2 intermediate level. In addition, the 4snf 3F2 (12?≤n?≤?28) and 4snf3F4 (12?≤n?≤?33) series are observed from the thermally populated 4s4d 3D1,3 fine structure components. The ionization potential of zinc has been determined from the unperturbed 4snf 3F3 series as 75769.31?±?0.15?cm?1, which is in excellent agreement with the previously reported value. 相似文献
34.
Parveen S Arjmand F 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2012,85(1):53-60
Novel ternary dizinc(II) complexes 1-3, derived from 1,2-bis(1H-benzimidazol-2-yl)ethane-1,2-diol and l-form of amino acids (viz., tryptophan, leucine and valine) were synthesized and characterized by spectroscopic (IR, (1)H NMR, UV-vis, ESI-MS) and other analytical methods. To evaluate the biological preference of chiral drugs for inherently chiral target DNA, interaction of 1-3 with calf thymus DNA in Tris-HCl buffer was studied by various biophysical techniques which reveal that all these complexes bind to CT DNA non-covalently via electrostatic interaction. The higher K(b) value of L-tryptophan complex 1 suggested greater DNA binding propensity. Further, to evaluate the mode of action at the molecular level, interaction studies of complexes 1 and 2 with nucleotides (5'-GMP and 5'-TMP) were carried out by UV-vis titrations, (1)H and (31)P NMR which implicates the preferential selectivity of these complexes to N3 of thymine rather than N7 of guanine. Furthermore, complex 1 exhibits efficient DNA cleavage with supercoiled pBR322. The complex 1 cleaves DNA efficiently involving hydrolytic cleavage pathway. Such chiral synthetic hydrolytic nucleases with asymmetric centers are gaining considerable attention owing to their importance in biotechnology and drug design, in particular to cleave DNA with sequence selectivity different from that of the natural enzymes. 相似文献
35.
Yali Yuan Haijuan Li Shuang Han Lianzhe Hu Saima Parveen Haoran Cai Guobao Xu 《Analytica chimica acta》2012
Electrochemiluminescence (ECL) of ruthenium complexes has broad applications and the immobilization of Ru(bpy)32+ has received extensive attention. In comparison with Ru(bpy)32+, Ru(phen)32+ can be immobilized more easily because of its better adsorbability. In this study, immobilization of Ru(phen)32+ for ECL analysis has been demonstrated for the first time by using graphene oxide (GO) as an immobilization matrix. The immobilization of Ru(phen)32+ is achieved easily by mixing Ru(phen)32+ with GO without using any ion exchange polymer or covalent method. The strong binding of Ru(phen)32+ with GO is attributed to both the π–π stacking interaction and the electrostatic interaction. The Ru(phen)32+/GO modified electrode was characterized by using tripropylamine (TPA) as the coreactant. The linear range of TPA is from 3 × 10−7 to 3 × 10−2 mol L−1 with the detection limit of 3 × 10−7 mol L−1. The ECL sensor demonstrates outstanding long-term stability. After the storage in the ambient environment for 90 days, the ECL response remains comparable with its original signal. 相似文献
36.
Investigations into the variation of self-diffusivity with solute radius, density, and degree of disorder of the host medium is explored. The system consists of a binary mixture of a relatively smaller sized solute, whose size is varied and a larger sized solvent interacting via Lennard-Jones potential. Calculations have been performed at three different reduced densities of 0.7, 0.8, and 0.933. These simulations show that diffusivity exhibits a maximum for some intermediate size of the solute when the solute diameter is varied. The maximum is found at the same size of the solute at all densities which is at variance with the prediction of the levitation effect. In order to understand this anomaly, additional simulations were carried out in which the degree of disorder has been varied while keeping the density constant. The results show that the diffusivity maximum gradually disappears with increase in disorder. Disorder has been characterized by means of the minimal spanning tree. Simulations have also been carried out in which the degree of disorder is constant and only the density is altered. The results from these simulations show that the maximum in diffusivity now shifts to larger distances with decrease in density. This is in agreement with the changes in void and neck distribution with density of the host medium. These results are in excellent agreement with the predictions of the levitation effect. They suggest that the effect of disorder is to shift the maximum in diffusivity towards smaller solute radius while that of the decrease in density is to shift it towards larger solute radius. Thus, in real systems where the degree of disorder is lower at higher density and vice versa, the effect due to density and disorder have opposing influences. These are confirmed by the changes seen in the velocity autocorrelation function, self part of the intermediate scattering function and activation energy. 相似文献
37.
Masood Parvez Atta‐ur‐Rahman M. Iqbal Choudhary Shehnaz Parveen Syed Abdul Majid Ayatollahi 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(2):233-234
In the title compound, 3β‐(dimethylamino)‐16α‐hydroxy‐14‐methyl‐4‐methylene‐9,19‐cyclo‐5α‐pregnan‐20‐one monohydrate, C25H39NO2·H2O, the pentacyclo steroidal alkaloid is composed of three six‐membered, one five‐membered and one three‐membered ring. The molecular dimensions are as expected. The structure is stabilized by hydrogen bonds involving H and O atoms of water and the alkaloid molecules, with strong N?O [2.829 (7) Å] and O?O [2.790 (6) and 2.949 (7) Å] interactions. 相似文献
38.
Simple Organic Salts Having a Naphthalenediimide (NDI) Core Display Multifunctional Properties: Gelation,Anticancer and Semiconducting Properties 下载免费PDF全文
Following a supramolecular synthon rationale, a dicarboxylic acid derivative having a naphthalenediimide (NDI) core, namely, bis‐N‐carboxymethyl naphthalenediimide ( NDI‐G ), was reacted with n‐alkyl amines with varying alkyl chain lengths to generate a new series of primary ammonium dicarboxylate (PAD) salts. The majority of the salts (≈85 %) were found to gel various polar solvents. The gels were characterized by dynamic rheology and high‐resolution electron microscopy. Single‐crystal and powder X‐ray diffraction analyses were used to study the supramolecular synthon present in one of the gelator salts (i.e., S8 ). Charge‐transfer (CT)‐induced gelation with donor molecules such as anthracene methanol ( Ant ) and pyrene ( Py ) was also possible with S8 . The CT complex ( S8.Ant ) displayed anticancer activity as probed by cell migration assay on the highly aggresive breast cancer cell line MDA‐MB‐231 . The DMSO gel of S8.Ant also displayed semiconducting behavior. To the best of our knowledge, simple organic salts with an NDI core that display such mulitifunctional properties are hitherto unknown. 相似文献
39.
A simple precise method is described for the determination of isonicotinic acid hydrazide (isoniazid) alone, and in mixtures with aspirin, paracetamol and streptomycin, by reaction with vanillin in the Weisz ring-oven technique; 0.1–15 μg of isoniazid can be determined with errors of 2–2.7%. 相似文献
40.
Mohammad Shakir Shama Parveen Nishat Begum Yasser Azim 《Transition Metal Chemistry》2004,29(8):916-920
A series of transition metal complexes of the type [M(ah)3](ClO4)2 (1–6) [M = MnII, FeII, CoII, NiII, CuII and ZnII, ah = acetylhydrazine] have been prepared by the reaction of M(ClO4)2 · 6H2O with acetylhydrazine formed in situ by the reaction of hydrazine hydrate and acetylsalicylic acid methyl ester. The chelating behaviour of acetylhydrazine and overall geometry of these complexes have been spectroscopically investigated by means of FT-IR, 1H-n.m.r. and electronic spectral techniques, as well as by elemental analysis data, molar conductance values and magnetic susceptibility measurements. Single X-ray structure determination of complex (4) revealed three acetylhydrazine ligands coordinated to nickel ion in a bidentate manner maintaining an octahedral environment. In all other complexes too, an octahedral geometry has been proposed on the basis of results obtained by various physico-chemical studies. 相似文献