首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   384580篇
  免费   3530篇
  国内免费   1167篇
化学   203027篇
晶体学   6025篇
力学   16621篇
综合类   9篇
数学   44037篇
物理学   119558篇
  2021年   3080篇
  2020年   3404篇
  2019年   3848篇
  2018年   5279篇
  2017年   5106篇
  2016年   7225篇
  2015年   4305篇
  2014年   6807篇
  2013年   16986篇
  2012年   12863篇
  2011年   15564篇
  2010年   11052篇
  2009年   10854篇
  2008年   14629篇
  2007年   14805篇
  2006年   13999篇
  2005年   12565篇
  2004年   11439篇
  2003年   10278篇
  2002年   10054篇
  2001年   11190篇
  2000年   8712篇
  1999年   6642篇
  1998年   5567篇
  1997年   5599篇
  1996年   5154篇
  1995年   4582篇
  1994年   4515篇
  1993年   4423篇
  1992年   4845篇
  1991年   4946篇
  1990年   4756篇
  1989年   4583篇
  1988年   4548篇
  1987年   4496篇
  1986年   4251篇
  1985年   5582篇
  1984年   5947篇
  1983年   4805篇
  1982年   5187篇
  1981年   5050篇
  1980年   4784篇
  1979年   5034篇
  1978年   5270篇
  1977年   5277篇
  1976年   5292篇
  1975年   4957篇
  1974年   4933篇
  1973年   5202篇
  1972年   3389篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Multilayer silicon structures with built-in layers of Ge nanoclusters were studied experimentally by Raman light scattering. The built-in layers were formed by the pulsed action of a low-energy beam of intrinsic ions during molecular-beam epitaxy. It is found that the ion-stimulated nucleation and the subsequent growth make it possible to obtain Ge nanoclusters almost free of Si.  相似文献   
992.
Abnormalities in the cochlear function usually cause broadening of the auditory filters which reduces the speech intelligibility. An attempt to apply a spectral enhancement algorithm has been undertaken to improve the identification of Polish vowels by subjects with cochlear-based hearing-impairment. The identification scores of natural (unprocessed) vowels and spectrally enhanced (processed) vowels has been measured for hearing-impaired subjects. It has been found that spectral enhancement improves vowel scores by about 10% for those subjects, however, a wide variation in individual performance among subjects has been observed. The overall vowels identification scores obtained were 85% for natural vowels and 96% for spectrally enhanced vowels.  相似文献   
993.
Optics and Spectroscopy - The fluorescence of the nematic liquid crystal n-butyl-n′-methoxyazoxybenzene (BMAOB) in the form of a layer and in porous glasses with pores of different diameter...  相似文献   
994.
Synthesis and Raman analysis of 1D-ZnO nanostructure via vapor phase growth   总被引:1,自引:0,他引:1  
1D-nanostructural zinc oxide (ZnO) with different shapes have been synthesized on p-type Si(1 0 0) and glass substrates via vapor phase growth by heating pure zinc powder at temperatures between 480 and 570 °C. The different ZnO nanostructures depend on the substrates and the growth temperatures. Scanning electron microscopy and X-ray diffraction revealed that a well-aligned nanowires array, which are vertical to the substrate of Si(1 0 0) with 18 sides on their heads, but six sides on their stems, has been formed at 480 °C. Raman study on the ZnO nanostructures shows that the coupling strength between electron and phonon determined by the ratio of the second- to the first-order Raman scattering cross-sections declines with decreasing diameter of the nanowires. However, a little changes of the coupling strength in terms of the width of the nanobelts have been observed.  相似文献   
995.
We construct commuting rank 2 formally self-adjoint ordinary differential operators corresponding to a curve of genus 2.  相似文献   
996.
997.
Data on the proteinase complex from Carica papaya latex were reviewed. The properties and applications of the domestic preparation cucumazyme and known medicinal preparations based on papaya proteinases (caripazyme, lecozyme, lecopain) were compared.  相似文献   
998.
999.
1000.
Using lower-cost lasers, 30% savings are possible for 10-Gb/s uncompensated metro transmission over NZDF, compared to G.652 fiber. We present WDM transmission results for a mixed plant of NZDF rings interconnected to G.652.C-fiber access laterals.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号