全文获取类型
收费全文 | 1213篇 |
免费 | 22篇 |
国内免费 | 3篇 |
专业分类
化学 | 589篇 |
晶体学 | 18篇 |
力学 | 61篇 |
数学 | 108篇 |
物理学 | 462篇 |
出版年
2022年 | 15篇 |
2021年 | 10篇 |
2020年 | 19篇 |
2019年 | 25篇 |
2018年 | 16篇 |
2017年 | 24篇 |
2016年 | 41篇 |
2015年 | 19篇 |
2014年 | 34篇 |
2013年 | 56篇 |
2012年 | 73篇 |
2011年 | 78篇 |
2010年 | 61篇 |
2009年 | 41篇 |
2008年 | 72篇 |
2007年 | 73篇 |
2006年 | 57篇 |
2005年 | 46篇 |
2004年 | 35篇 |
2003年 | 37篇 |
2002年 | 32篇 |
2001年 | 20篇 |
2000年 | 23篇 |
1999年 | 11篇 |
1998年 | 17篇 |
1997年 | 15篇 |
1996年 | 17篇 |
1995年 | 14篇 |
1994年 | 13篇 |
1993年 | 19篇 |
1992年 | 11篇 |
1991年 | 5篇 |
1990年 | 11篇 |
1989年 | 18篇 |
1988年 | 6篇 |
1987年 | 19篇 |
1986年 | 7篇 |
1985年 | 14篇 |
1984年 | 12篇 |
1983年 | 13篇 |
1982年 | 13篇 |
1981年 | 10篇 |
1980年 | 11篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1977年 | 5篇 |
1975年 | 4篇 |
1972年 | 4篇 |
1960年 | 4篇 |
1954年 | 5篇 |
排序方式: 共有1238条查询结果,搜索用时 562 毫秒
751.
Hexamethylenetetramine/acetic anhydride-promoted α-methylenation of aryl alkyl ketones followed by acid-catalyzed cyclization of the resulting acrylophenones produce 2-alkyl indanones in excellent yields. 相似文献
752.
Sandeep Pimparkar Trisha Bhattacharya Dr. Arun Maji Argha Saha Dr. Ramasamy Jayarajan Dr. Uttam Dutta Dr. Gang Lu Prof. David W. Lupton Dr. Debabrata Maiti 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(50):11558-11564
The significance of site selective functionalization stands upon the superior selectivity, easy synthesis and diverse product utility. In this work, we demonstrate the para-selective introduction of versatile nitrile moiety, enabled by a detachable and reusable H-bonded auxiliary. The methodology holds its efficiency irrespective of substrate electronic bias. The conspicuous shift in the step energetics was probed by both experimental and computational mechanistic tools, which heralds the inception of para-deuteration. The synthetic impact of the methodology was highlighted with reusability of directing group and post synthetic modifications. 相似文献
753.
J. Bhattacharya N. Chakravarty S. Pattnaik W.D. Slafer R. Biswas V. Dalal 《Journal of Non》2012,358(17):2313-2318
Light trapping is essential to harvest long-wavelength red and near-infrared photons in thin film silicon solar cells. Light trapping in p-i-n thin film cells is commonly achieved with back-reflectors, and in n-i-p cells with textured front transparent conductors. We systematically compare the optical properties and performance of randomly roughened back reflectors with periodic plasmonic-photonic back-reflectors in p-i-n solar cells. The randomly textured back reflectors were prepared to have very high diffuse reflectance comparable to the state of the art. The periodic back reflectors of tapered nano-pillars/bumps show enhanced quantum efficiency and optical absorption over randomly structured back reflectors using the same solar cell architecture in nc-Si solar cells. The strong diffraction and light concentration in periodic back reflectors may be more beneficial than the light scattering offered by randomly textured back reflectors. 相似文献
754.
Mounir Zeitouny Petr Balling Petr Ken Pavel Maika Ronald C. Horsten Stefan T. Persijn H. Paul Urbach Nandini Bhattacharya 《Annalen der Physik》2013,525(6):437-442
An instrument achieving 100 KHz spectral precision using multiple correlation Fourier transform spectroscopy has been demonstrated. The instrument can measure the individual frequency comb modes of 100 MHz frequency comb lasers in air. The experiments show ~400,000 resolved modes at linewidths of 85 MHz in the region of 829 nm and ~ 182,000 resolved modes at linewidths of 28 MHz in the region of 1.5 μm, with a recording time of few minutes. The precision of the instrument, defined by the frequency positioning, attains sub‐MHz even when the scan is performed in air. 相似文献
755.
756.
The study of recrystallization texture of a cold deformed Fe–Mn–Al–Si–C alloy, with about 30% Mn, has been discussed in this paper. The alloy is fully austenitic at room temperature, and therefore, principal FCC rolling textures were developed in this material at different stages of cold rolling. The present study was undertaken to observe the transformation of FCC rolling texture during recrystallization of a heavily cold deformed specimen. It was observed that isothermal annealing at 750 °C led to a weak recrystallisation texture, which was quite similar to the deformation texture developed at the early stage of cold rolling. During recovery stage, a strong Bs/Goss-type texture was developed, which was identified as a new observation in this work. 相似文献
757.
758.
759.
760.
In the present work we have made use of polarization phase shifting in digital holographic microscopy (DHM) for three dimensional phase profiling of transmissive and reflecting microscopic samples. The Mach–Zehnder arrangement with proper polarizing elements (polarizer-masked cube beam splitter, quarter wave plate and a linear polarizer) is used for recording the phase-shifted digital holograms. The suggested procedure is simple and accurate and obviates the need of piezo devices for phase shifting. The phase profile of the specimen is reconstructed from the holograms by using standard phase shifting algorithms. 相似文献