全文获取类型
收费全文 | 543篇 |
免费 | 20篇 |
专业分类
化学 | 419篇 |
晶体学 | 15篇 |
力学 | 7篇 |
数学 | 28篇 |
物理学 | 94篇 |
出版年
2024年 | 2篇 |
2023年 | 10篇 |
2022年 | 23篇 |
2021年 | 13篇 |
2020年 | 15篇 |
2019年 | 17篇 |
2018年 | 21篇 |
2017年 | 17篇 |
2016年 | 20篇 |
2015年 | 16篇 |
2014年 | 24篇 |
2013年 | 48篇 |
2012年 | 40篇 |
2011年 | 36篇 |
2010年 | 22篇 |
2009年 | 16篇 |
2008年 | 29篇 |
2007年 | 15篇 |
2006年 | 16篇 |
2005年 | 20篇 |
2004年 | 15篇 |
2003年 | 13篇 |
2002年 | 9篇 |
2001年 | 9篇 |
2000年 | 7篇 |
1999年 | 3篇 |
1997年 | 7篇 |
1996年 | 4篇 |
1994年 | 5篇 |
1992年 | 2篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1988年 | 6篇 |
1986年 | 5篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 3篇 |
1981年 | 9篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 5篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1971年 | 2篇 |
1967年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有563条查询结果,搜索用时 15 毫秒
101.
Ashwani Vij Jennifer L. Palmer Kamlesh Chauhan Richard Vaughan Williams 《Journal of chemical crystallography》2000,30(10):621-626
2,6-Dimethyl-1,3,5,7-cyclooctatetraene-1,3,5,7-tetracarboxylic acid 3, C14H14O9, was prepared by thermolysis of the corresponding semibullvalene and characterized by spectroscopic and single-crystal X-ray diffraction studies. The monohydrate of 3 crystallizes in the tetrahedral space group P-4n2, a = 11.0924(3) Å, c = 12.6799(5) Å, V = 1560.15(9) Å3, Z = 4. The cyclooctatetraene ring adopts a tub-shaped conformation with a crystallograpically imposed twofold rotational symmetry, and is composed of localized C=C double bonds in the 1,3,5, and 7 positions with an average interatomic distance of 1.327 (5) Å and C–C single bonds with an average interatomic distance of 1.489(5) Å. The average C=C–C angle in the ring is 122.6(3)°. Each symmetry generated eight-membered ring contains four carboxyl groups, two of which are coplanar with the methyl groups across the C=C ring atoms. However, across the C–C bonds the carboxyl groups and the methyl groups show a torsion angle of 64.3(4)°. The presence of a water molecule in the crystal lattice generates a three-dimensional network of close hydrogen bondings between water and the carboxyl groups of multiple rings. This creates a network of orthogonal 10-membered rings between the 8-membered rings. Two given cyclooctatetraene rings are intermolecularly hydrogen bonded not only directly through their carboxyl groups but also via a bridging water molecule. This effect is rare in polycarboxylic acids and their monohydrates which bond only with water or among themselves. 相似文献
102.
Harsh Kumar Kanchan Bhardwaj Natlia Cruz-Martins Eugenie Nepovimova Patrik Oleksak Daljeet Singh Dhanjal Sonali Bhardwaj Reena Singh Chirag Chopra Rachna Verma Prem Parkash Chauhan Dinesh Kumar Kamil Ku
a 《Molecules (Basel, Switzerland)》2021,26(11)
The ingestion of contaminated water and food is known to cause food illness. Moreover, on assessing the patients suffering from foodborne disease has revealed the role of microbes in such diseases. Concerning which different methods have been developed for protecting food from microbes, the treatment of food with chemicals has been reported to exhibit an unwanted organoleptic effect while also affecting the nutritional value of food. Owing to these challenges, the demand for natural food preservatives has substantially increased. Therefore, the interest of researchers and food industries has shifted towards fruit polyphenols as potent inhibitors of foodborne bacteria. Recently, numerous fruit polyphenols have been acclaimed for their ability to avert toxin production and biofilm formation. Furthermore, various studies have recommended using fruit polyphenols solely or in combination with chemical disinfectants and food preservatives. Currently, different nanoparticles have been synthesized using fruit polyphenols to curb the growth of pathogenic microbes. Hence, this review intends to summarize the current knowledge about fruit polyphenols as antibacterial agents against foodborne pathogens. Additionally, the application of different fruit extracts in synthesizing functionalized nanoparticles has also been discussed. 相似文献
103.
Darko Kwabena Adu Zondi Nate John Alake Blessing Wisdom Ike Ruchika Chauhan Prof. Rajshekhar Karpoormath 《Electroanalysis》2023,35(3):e202200216
Solvothermally synthesized cobalt sulphide/reduced graphene oxide (CoS/rGO) was used to fabricate an electrochemical sensor for detection of artemisinin. Microscopic techniques were used to characterize CoS/rGO nanocomposite. The electrochemical sensor was fabricated by modifying the surface of glassy carbon electrode with CoS/rGO nanocomposite. [Fe(CN)6]3−/4− was used as a mediator to aid oxidation of artemisinin. Differential pulse voltammetric technique was used for the detection of artemisinin. A linear range of 30–100 μM was used. Experimentally, a detection limit of 0.5 μM was obtained. Therefore, the developed sensor can be used for quality control of artemisinin. 相似文献
104.
Mihir B. Banerjee R. G. Shandil S. S. Chauhan & Daleep Sharma 《Studies in Applied Mathematics》2000,105(1):31-34
Results of the previous paper with this title ( M. B. Banerjee et al., Stud. Appl. Math. 103:43–50) are extended to the case of neutrally stable perturbations. 相似文献
105.
Vishnu Chauhan T. Gupta Paramjit Singh P.D. Sahare N. Koratkar Rajesh Kumar 《Physics letters. A》2019,383(9):898-907
The calibrated and controlled swift heavy ions (SHI) beam irradiation generate defects which can cause modifications in various properties of the materials such as structural, optical, magnetic, morphological, and chemical etc. The passage of ion through the target material causes the nuclear energy losses () and electronic energy losses (). The dominates over in SHI irradiation. In the present study, ZrO2 thin films were grown on silicon and glass substrate by using RF sputtering deposition technique. For the purpose of modifications induced by swift heavy ions, these films were irradiated by a 120 MeV S9+ ion beam of 1 pnA current, with varying ion fluences from 5E12 to 1E13 ions/cm2, using the tandem accelerator at the Inter University Accelerator Center (IUAC), New Delhi, India. The X-ray diffraction (XRD) patterns confirmed the formation of monoclinic and tetragonal phases and it was observed that XRD peaks intensity increased up to the fluence of 5E12 ions/cm2 followed by opposite behavior at higher fluences. Atomic force microscope (AFM) study revealed the increased surface roughness after SHI irradiation. In addition to it, the formation of electronic transition states in optical band gap region and enhancement of absorption edge was observed from UV-visible spectroscopy (UV-Vis) results due to which direct band gap energy value decreased from those of un-irradiated samples. Photoluminescence (PL) broad emission spectra were determined using the excitation wavelength at 290 nm with the prominent peak at 415 nm which can be ascribed to Zr vacancies due to band edge emission as a result of free-exciton recombination. Rutherford backscattering spectrometry (RBS) technique was used for depth profiling and elemental composition in zirconia thin films. The expected role of electronic energy loss during ion irradiation is to modify the properties of the material has been discussed. 相似文献
106.
Surface films on metals and alloys often protect them from reaction with the environment, and hence a knowledge of their protective
properties and composition could be invaluable for predicting their corrosion behaviour. XPS (x-ray photoelectron spectroscopy)
could provide a quantitative analysis of the chemical composition, the nature of valence states and elemental distribution
within the surface films.
The present paper reviews the potential of this technique in corrosion studies. A brief review of the work done on the passivation
of iron and iron-chromium alloys and on the inhibition studies on copper base alloys has been given. A few examples of investigations
carried out at authors’ laboratory are also included. An attempt has been made to establish a correlation between the compositions
of the films formed and corrosion behaviour of carbon steel in 10.5 pH lithium hydroxide solution and of Cu-Ni alloys and
sacrificial Al-Zn-Sn alloys in synthetic sea-water. 相似文献
107.
X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) measurements have been done
at the K-edge of Cu in Cu-Ti glasses and on the K-edges of Ni and Zr in Ni-Zr glasses using a synchrotron radiation source.
The results are discussed in terms of the shape shift and intensity of the absorption edge as well as the principal absorption
maximum. The values of bondlength calculated by the one-electron multiple scattering XANES theory as well as the graphical
analysis EXAFS technique show good agreement. 相似文献
108.
A. V. Eremeev A. A. Romanova V. V. Servakh S. S. Chauhan 《Journal of Applied and Industrial Mathematics》2007,1(4):433-441
The problem is considered of optimizing the product delivery from suppliers to consumers. The size of each open supply is bounded both below and above, the size of consumption for each consumer is bounded below, the supply cost functions are linear for nonzero volumes of supply. A fully polynomial time approximation scheme is proposed for this problem in the case of one consumer, and the complexity of the problem is studied in the general case. 相似文献
109.
Ramesh B. Reddy Premansh Dudhe Priyanka Chauhan Sagnik Sengupta Venkatesh Chelvam 《Tetrahedron》2018,74(48):6946-6953
An efficient synthesis of N-Boc-tubuphenylalanine benzyl ester (N-Boc-Tup-OBn, 1a) and N-Boc-epi-tubuphenylalanine benzyl ester (N-Boc-epi-Tup-OBn, 1b) is reported herein. Regioselective aziridine 4 ring opening with carbon nucleophiles followed by hydroboration of 1,1-substituted aminoalkene 3 using 9-BBN and subsequent oxidation in an alkaline medium are used as the key steps to provide N-tosyl 1,4-aminoalcohols. The 1,4-aminoalcohols are successfully transformed into the desired products with an overall yield of 23% for 1a and 11% for 1b over 8 consecutive steps separately. 相似文献
110.
Allium schoenoprasum L. (family Amaryllidaceae), commonly known as chives has great culinary value besides being used as ethnomedicine. This review emphasises on phytochemistry and pharmacological activities of A. schoenoprasum, and discusses the future opportunities for systematic investigations. Scientific evaluation of chives validates its traditional claims and demonstrates diverse pharmacological potential including an anti-inflammatory, anticancer, antioxidant, anthelmintic and antihypertensive. Though phytochemical studies revealed the presence of sulphur and phenolic compounds, flavonoids, saponin and steroidal glycosides yet methodical research to identify bioactive compounds is required. This review confirms the medicinal importance of A. schoenoprasum and could stimulate future research on its unexplored aspects, especially identification of bioactive compounds and related mechanisms and safety, which might develop it as a drug. 相似文献