全文获取类型
收费全文 | 846篇 |
免费 | 30篇 |
专业分类
化学 | 668篇 |
晶体学 | 10篇 |
力学 | 27篇 |
数学 | 60篇 |
物理学 | 111篇 |
出版年
2024年 | 2篇 |
2023年 | 8篇 |
2022年 | 25篇 |
2021年 | 22篇 |
2020年 | 23篇 |
2019年 | 40篇 |
2018年 | 40篇 |
2017年 | 29篇 |
2016年 | 47篇 |
2015年 | 32篇 |
2014年 | 46篇 |
2013年 | 74篇 |
2012年 | 66篇 |
2011年 | 69篇 |
2010年 | 28篇 |
2009年 | 32篇 |
2008年 | 45篇 |
2007年 | 42篇 |
2006年 | 27篇 |
2005年 | 37篇 |
2004年 | 18篇 |
2003年 | 14篇 |
2002年 | 15篇 |
2001年 | 5篇 |
2000年 | 7篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 7篇 |
1995年 | 7篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 4篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1985年 | 6篇 |
1983年 | 2篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1976年 | 3篇 |
1969年 | 2篇 |
1968年 | 3篇 |
1967年 | 2篇 |
1963年 | 1篇 |
1962年 | 2篇 |
1961年 | 5篇 |
1960年 | 1篇 |
1944年 | 1篇 |
1938年 | 1篇 |
1937年 | 1篇 |
排序方式: 共有876条查询结果,搜索用时 15 毫秒
11.
T. Raghavendra RaoCh. Rama Krishna U.S. Udayachandran ThampyCh. Venkata Reddy Y.P. ReddyP. Sambasiva Rao R.V.S.S.N. Ravikumar 《Physica B: Condensed Matter》2011,406(11):2132-2137
The effect of Li2O content in vanadyl doped 20ZnO+xLi2O+(30−x)Na2O+50B2O3 (5≤x≥25) glasses has been studied with respect to their physical and structural properties. The absence of sharp peaks in XRD spectra of these glass samples confirms the amorphous nature. The physical parameters like density, refractive index, ionic concentration and electronic polarizability vary non-linearly with x mol% depending on the diffusivities of alkali ions. EPR and optical absorption spectra reveal that the resonance signals are characteristics of VO2+ ions in tetragonally compressed octahedral site. Spin-Hamiltonian, crystal field, tetragonal field and bonding parameters are found to be in good agreement with the other reported glass systems. The tetragonal distortion (g⊥-g∥) and Dt reveals that their values vary non-linearly with Li2O content and reaches a minimum at x=10 mol%. An anomaly of character has been observed in all the properties of vanadyl doped glass systems, which gives a clear indication of mixed alkali effect. 相似文献
12.
Y.P. Venkata Subbaiah 《Applied Surface Science》2006,253(5):2409-2415
ZnS films have been deposited on glass substrates by close-spaced evaporation (CSE) technique. The films were grown at different temperatures in the range, 200-350 °C. The layers have been characterized with X-ray diffractometer (XRD), atomic force microscope (AFM), energy dispersive analysis of X-rays (EDAX) and optical spectrophotometer to evaluate the quality of the layers for photovoltaic applications. The studies showed that the optimum substrate temperature for the growth of ZnS layers was 300 °C. The films grown at these temperatures exhibited cubic structure with nearly stoichiometric composition. The AFM data revealed that the films had nano-sized grains with a grain size of ∼40 nm. The optical studies exhibited direct allowed transition with an energy band gap of 3.61 eV. The other structural and optical parameters such as lattice stress, dislocation density, refractive index and extinction coefficient were also evaluated. The temperature-dependent conductivity measured in the range, 303-523 K showed a change in the conduction mechanism at 120 °C. The activation energy values evaluated using the temperature dependence of electrical conductivity are 7 and 29 meV at low and high temperature regions, respectively. 相似文献
13.
Indhumathi Kulandhaisamy Dinesh Babu Rajendran Malathi Kanagasabai Gunasekaran Gurusamy Balaji Moorthy Jithila V. George 《Waves in Random and Complex Media》2017,27(1):38-46
In this paper, an analog multiband phase shifter using slotline configuration is proposed. To implement the design, a pair of modified Split Ring Resonator (SRR) is employed. The periodic property of SRR provides multiband characteristics, whether the coupling slot gives the phase variations over the bands. The operation is well explained with an equivalent circuit model and its characteristics have been studied both in simulation and measurement. The prototype operates in 1.77–2.16, 3.5–3.97, 5.08–5.33, 6.43–6.93, and 8.01–8.59 GHz frequency bands which can be utilized for GSM, GPS, WLAN, C-band, and X-band applications, respectively. 相似文献
14.
15.
16.
Konkala Karnakar Katla Ramesh Sabbavarapu Narayana Murthy Yadavalli Venkata Durga Nageswar 《Helvetica chimica acta》2013,96(12):2276-2281
The first example of the stereoselective synthesis of (Z)‐ and (E)‐allyl aryl sulfides and selenides from Baylis? Hillman acetates under neutral conditions in H2O by supramolecular catalysis involving β‐cyclodextrin is reported. β‐Cyclodextrin can be recovered and reused. The reaction is very efficient in providing allyl aryl sulfides and selenides in good‐to‐excellent yields with clean reaction profiles under mild reaction conditions. 相似文献
17.
Nishtala Venkata Bharat Mahesh Chityala Bhargavi G. Pasala Vijay Kumar Basavoju Srinivas 《Molecular diversity》2020,24(4):1139-1147
Molecular Diversity - A series of new spirooxindolocarbamates 4a–l and 6a–d were synthesized by using the Betti reaction. All the target compounds were well characterized by IR, NMR and... 相似文献
18.
57Fe Mössbauer spectra of pulsed-laser deposited (PLD) films of CoFe2O4 of 0.3 µm thickness is investigated using transmission geometry is reported. Mössbauer parameters were determined for the tetrahedral (A) and octahedral (B) sites. The PLD processed films gave measurable spectra with no visible evidence of clustering or multiple phases present. Results on the films agreed with those of the bulk material. The films exhibited magnetic hyperfine and quadruple splittings similar to that of bulk CoFe2O4. This work demonstrates that measurable transmission Mössbauer spectra may be obtained for PLD deposited CoFe2O4 thick films. 相似文献
19.
Nagu A. Vasikerappa K. Gidyonu P. Prathap Ch. Venkata Rao M. Rama Rao K. S. David Raju B. 《Research on Chemical Intermediates》2020,46(5):2669-2681
Research on Chemical Intermediates - MgO-supported Ni catalysts were selectively catalysed by the hydrogenation of benzonitrile to benzylamine in continuous flow at atmospheric pressure without any... 相似文献
20.