全文获取类型
收费全文 | 231篇 |
免费 | 15篇 |
国内免费 | 1篇 |
专业分类
化学 | 173篇 |
晶体学 | 3篇 |
数学 | 14篇 |
物理学 | 57篇 |
出版年
2024年 | 4篇 |
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 6篇 |
2020年 | 6篇 |
2019年 | 11篇 |
2018年 | 12篇 |
2017年 | 5篇 |
2016年 | 5篇 |
2015年 | 12篇 |
2014年 | 19篇 |
2013年 | 21篇 |
2012年 | 7篇 |
2011年 | 16篇 |
2010年 | 14篇 |
2009年 | 13篇 |
2008年 | 12篇 |
2007年 | 14篇 |
2006年 | 4篇 |
2005年 | 6篇 |
2004年 | 9篇 |
2003年 | 2篇 |
2002年 | 10篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1998年 | 2篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1987年 | 2篇 |
1986年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1975年 | 2篇 |
1973年 | 1篇 |
1968年 | 1篇 |
1967年 | 2篇 |
1957年 | 2篇 |
1956年 | 1篇 |
排序方式: 共有247条查询结果,搜索用时 31 毫秒
71.
Manisha Samanta Koushik Pal Umesh V. Waghmare Kanishka Biswas 《Angewandte Chemie (International ed. in English)》2020,59(12):4822-4829
A challenge in thermoelectrics is to achieve intrinsically low thermal conductivity in crystalline solids while maintaining a high carrier mobility (μ). Topological quantum materials, such as the topological insulator (TI) or topological crystalline insulator (TCI) can exhibit high μ. Weak topological insulators (WTI) are of interest because of their layered hetero‐structural nature which has a low lattice thermal conductivity (κlat). BiTe, a unique member of the (Bi2)m(Bi2Te3)n homologous series (m:n=1:2), has both the quantum states, TCI and WTI, which is distinct from the conventional strong TI, Bi2Te3 (where m:n=0:1). Herein, we report intrinsically low κlat of 0.47–0.8 W m?1 K?1 in the 300–650 K range in BiTe resulting from low energy optical phonon branches which originate primarily from the localized vibrations of Bi bilayer. It has high μ≈516 cm2 V?1 s?1 and 707 cm2 V?1 s?1 along parallel and perpendicular to the spark plasma sintering (SPS) directions, respectively, at room temperature. 相似文献
72.
Chandra B. Bhargava Amarendra N. Vishnoi Umesh C. Srivastava 《Transition Metal Chemistry》1981,6(2):114-118
Summary X-ray (K-) absorption edge spectrometric (XAES) investigations of some copper(II) chelates involving amino acids and a carbonato complex have been carried out employing a curved crystal spectrograph. Experimental edgewidths have been used to bear on the number of nearest neighbours around the central metal atom in the complexes in the solid state. Comparisons in respect of the nature of the metal-ligand bond have been made between inferences drawn on the basis of XAES, i.r. and optical spectral data. Average radii of the coordination sphere in the amino acid chelates have been reported using extended fine structure energy separations (Levy's method). In the carbonato complex, the possibility of determining different metal-donor distances within the coordination sphere has been suggested for the first time. 相似文献
73.
Aspy Mehta Umesh Gaur Bernhard Wunderlich 《Journal of Polymer Science.Polymer Physics》1978,16(2):289-296
The equilibrium melting temperature, volume, and enthalpy and entropy changes on melting of poly(ethylene terephthalate) have been analyzed and heats of fusion have been newly measured with an automated scanning calorimeter to yield the following data: 553°K, 16.9 cm3/mole, 2.69 kJ/mole, and 48.6 J/deg/mole, respectively. A more detailed discussion of annealed samples obtained from etched starting materials shows that the density of the noncrystalline regions may be variable. 相似文献
74.
Abhinay S. Chillal Rajesh T. Bhawale Dr. Umesh A. Kshirsagar 《European journal of organic chemistry》2023,26(34):e202300665
A lenient approach for regioselective C3−H chalcogenation and thiocyanation of 4H-pyrido[1,2-a] pyrimidin-4-ones is developed using visible light photocatalysis. This operationally straightforward method furnishes a broad array of C-3, Ar−S/Ar−Se and -SCN functionalized derivatives in moderate to high yields. This protocol employs visible light as an environmentally friendly energy source, cost effective inorganic persulfate-based oxidant and easily procurable dichalcogenides for regioselective C−H chalcogenation of the substrate at room temperature. Further, regioselective thiocyanation of 4H-pyrido[1,2-a] pyrimidin-4-ones was also developed. Mechanistic path for these transformations has been proposed based on light on/off and Stern-Volmer studies as well as quantum yield calculations. 相似文献
75.
One‐Pot Three‐Component Synthesis of 2‐Amino Pyrimidines in Aqueous PEG‐400 at Ambient Temperature
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)
Dhanaji V. Jawale Umesh R. Pratap Manisha R. Bhosale Ramrao A. Mane 《Journal of heterocyclic chemistry》2016,53(5):1626-1630
Amino pyrimidines have been synthesized by a one‐pot procedure under environmentally friendly reaction conditions at room temperature. The use of aqueous PEG‐400 circumvents the problems associated with the toxic, hazardous organic solvents and oxidizing agents. 相似文献
76.
Rodriguez EE Poineau F Llobet A Sattelberger AP Bhattacharjee J Waghmare UV Hartmann T Cheetham AK 《Journal of the American Chemical Society》2007,129(33):10244-10248
Crystalline technetium dioxide was prepared and for the first time its crystal structure determined by neutron powder diffraction. In addition, electronic structure calculations using density functional theory were performed to further elucidate the bonding mechanisms in TcO2. The crystal structure determined by Rietveld analysis with the NPD data is of a distorted rutile type, similar to that of MoO2; space group P21/c, a = 5.6891(1), b = 4.7546(1), c = 5.5195(1) A, and beta = 121.453(1) degrees . The NPD analysis also establishes a new neutron scattering length of 6.00(3) fm for 99Tc. Our results clearly show metal-metal bonding between Tc pairs along the edge-sharing chains of TcO6 octahedra. The Tc-Tc bond was found to be 2.622(1) A from NPD profile analysis and 2.59 A from first-principles DFT calculations. The bond is somewhat longer than expected from earlier predictions, suggesting that the nature of the Tc-Tc interaction is weaker than anticipated for the Tc(IV) cation with three outer electrons. The NPD results supported by the DFT calculations suggest that the filling of antibonding orbitals and the influence of the crystal field stabilization of the d3 Tc cations lead to more regular TcO6 octahedra and diminish the metal-metal bond strength compared with closely related oxides such MoO2 and WO2. 相似文献
77.
Sanjay Dashrath Vaidya Bobba Venkata Siva Kumar Ramanatham Vinod Kumar Umesh Nanasaheb Bhise Uday Chandrakant Mashelkar 《Journal of heterocyclic chemistry》2007,44(3):685-691
78.
Agarwal Umesh P. Ralph Sally A. Baez Carlos Reiner Richard S. 《Cellulose (London, England)》2021,28(14):9069-9079
Cellulose - In cellulose materials, the cellulose II allomorph is often present either exclusively or in conjunction with cellulose I, the natural cellulose. Moreover, in regenerated and mercerized... 相似文献
79.
Chao Jia Liheng Chen Ziqiang Shao Umesh P. Agarwal Liangbing Hu J. Y. Zhu 《Cellulose (London, England)》2017,24(6):2483-2498
We fabricated cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) from different cellulose materials (bleached eucalyptus pulp (BEP), spruce dissolving pulp (SDP) and cotton based qualitative filter paper (QFP) using concentrated oxalic acid hydrolysis and subsequent mechanical fibrillation (for CNFs). The process was green as acid can be easily recovered, and the prepared cellulose nanomaterials were carboxylated and thermally stable. In detail, the CNC yield from the different materials was similar. After hydrolysis, the DP of the cellulose materials decreased substantially, whereas the mechanical fibrillation of the cellulosic solid residues (CSRs) did not dramatically reduce the DP of cellulose. CNCs with different aspect ratios were produced from different starting materials by oxalic acid hydrolysis. The CNCs and CNFs obtained from BEP and QFP possessed more uniform dimensions than those from SDP. On the other hand, CNFs derived from SDP presented the best suspension stability. FTIR analyses verified esterification of cellulose by oxalic acid hydrolysis. The results from both XRD and Raman spectroscopy indicated that whereas XRD crystallinity of CNCs from BEP and QFP did not change significantly, there was some change in Raman crystallinity of these samples. Raman spectra of SDP CNCs indicated that the acid hydrolysis preferably removed cellulose I portion of the samples and therefore the CNCs became cellulose II enriched. TGA revealed that the CNCs obtained from QFP exhibited higher thermal stability compared to those from BEP and SDP, and all the CNCs possessed better thermal stability than that of CNCs from sulfuric acid hydrolysis. The excellent properties of prepared cellulose nanomaterials will be conducive to their application in different fields. 相似文献
80.
Umesh A. Fegade Suban K. Sahoo Amanpreet Singh Narinder Singh Sanjay B. Attarde Anil S. Kuwar 《Analytica chimica acta》2015
A fluorescent based receptor (4Z)-4-(4-diethylamino)-2-hydroxybenzylidene amino)-1,2dihydro-1,5-dimethyl-2-phenylpyrazol-3-one (receptor 3) was developed for the highly selective and sensitive detection of Cu2+ and Zn2+ in semi-aqueous system. The fluorescence of receptor 3 was enhanced and quenched, respectively, with the addition of Zn2+ and Cu2+ ions over other surveyed cations. The receptor formed host-guest complexes in 1:1 stoichiometry with the detection limit of 5 nM and 15 nM for Cu2+ and Zn2+ ions, respectively. Further, we have effectively utilized the two metal ions (Cu2+ and Zn2+) as chemical inputs for the manufacture of INHIBIT type logic gate at molecular level using the fluorescence responses of receptor 3 at 450 nm. 相似文献