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   436070篇
  免费   4848篇
  国内免费   1230篇
化学   233773篇
晶体学   6489篇
力学   18764篇
综合类   13篇
数学   49932篇
物理学   133177篇
  2021年   3768篇
  2020年   4185篇
  2019年   4518篇
  2018年   5853篇
  2017年   5744篇
  2016年   8831篇
  2015年   5561篇
  2014年   8542篇
  2013年   20184篇
  2012年   15647篇
  2011年   19261篇
  2010年   13497篇
  2009年   13350篇
  2008年   17647篇
  2007年   17541篇
  2006年   16255篇
  2005年   14551篇
  2004年   13527篇
  2003年   11892篇
  2002年   11728篇
  2001年   13429篇
  2000年   10086篇
  1999年   7917篇
  1998年   6569篇
  1997年   6317篇
  1996年   6081篇
  1995年   5470篇
  1994年   5392篇
  1993年   5199篇
  1992年   5828篇
  1991年   5926篇
  1990年   5664篇
  1989年   5473篇
  1988年   5493篇
  1987年   5374篇
  1986年   5091篇
  1985年   6561篇
  1984年   6696篇
  1983年   5301篇
  1982年   5387篇
  1981年   5368篇
  1980年   4956篇
  1979年   5352篇
  1978年   5491篇
  1977年   5385篇
  1976年   5328篇
  1975年   4914篇
  1974年   4885篇
  1973年   4882篇
  1972年   3455篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
We report on the effect of commercially important polysaccharides (maltodextrins with variable dextrose equivalent (Paselli SA-2, MD-6 and MD-10) on the surface activity at the air–water interface of small-molecule surfactants (sms), possessing different hydrophobic–lipophilic balance ((SSL (Na+), the main component is a sodium salt of stearol–lactoyl lactic acid, and PGE (080), polyglycerol ester of C18 fatty acid), and widely used in food products. A marked change of the surface activity of sms was found in the presence of maltodextrins by tensiometry. The combined data of laser multiangle light scattering and mixing calorimetry have suggested that this result is governed by specific complex formation between maltodextrins and sms in aqueous medium. Measurements have been made of the molar mass, the second virial coefficient and the enthalpy of intermolecular interactions in aqueous solutions. The implication of a degree of polymerization of maltodextrins in this phenomenon was shown. The interrelation between the molecular parameters of the formed complexes and their surface activity at the air–water interface has been revealed and discussed.  相似文献   
112.
We prove new theorems on the justification of the averaging method for multifrequency oscillation systems with pulse influence at fixed times.  相似文献   
113.
A precession mechanism of spin relaxation of conduction electrons in a square quantum well is analyzed. The dependence of the spin relaxation time on the width of a quantum well and the height of its barriers is calculated under the assumption that the electron-electron collisions dominate over other processes of carrier scattering.  相似文献   
114.
115.
A study of the atmospheric pollution by suspended particulate lead in the city of Seville, Spain, was carried out during the period between March 1983 and February 1984. The results obtained from seven sampling stations allowed us to study the site to site variations; there are two locations with average annual concentrations higher than 2 micrograms X m-3. In one station, the meteorological and traffic effects and relationship with other traffic-related pollutants, were investigated. The regression analyses performed on the average monthly data have shown an inverse correlation with wind speed and temperature and a direct correlation with carbon monoxide and smoke concentrations, but no significant correlation was found with the lead deposition levels.  相似文献   
116.
Disordered Sr2FeMoO6 shows a drastic reduction in saturation magnetization compared to highly ordered samples, moreover magnetization as a function of the temperature for different disordered samples shows qualitatively different behaviours. We investigate the origin of such diversity by performing spatially resolved photoemission spectroscopy on various disordered samples. Our results establish that extensive electronic inhomogeneity, arising most probably from an underlying chemical inhomogeneity in disordered samples, is responsible for the observed magnetic inhomogeneity. It is further pointed out that these inhomogeneities are connected with composition fluctuations of the type Sr2Fe1+x Mo1-x O6 with Fe-rich (x > 0) and Mo-rich (x < 0) regions. Dedicated to Prof J Gopalakrishnan on his 62nd birthday.  相似文献   
117.
A simple procedure for the synthesis of an important standard, isotopically enriched methylmercury, which is not commercially available, has been established successfully. The isotopically enriched standard synthesized is utilized in conventional isotope dilution mass spectrometry (IDMS), as well as in speciated IDMS (SIDMS), for determination of the true concentration of methylmercury in environmental samples. The CH3201Hg+ standard has been synthesized from commercially available 201HgO and tetramethyltin. The synthesis time required is 1 h at 60°C. The product is highly pure, yielding more than 90% as 201Hg in CH3201Hg+. Hazardous dimethylmercury does not occur during this synthesis procedure. The product synthesized was analyzed using high‐performance liquid chromatography coupled with inductively coupled plasma mass spectrometry (ICP‐MS) and ICP‐MS alone in order to determine its concentration, isotopic composition and purity. The stability of the product was also evaluated for over 6 months and found to be stable at 4°C in the dark. The isotopically enriched methylmercury synthesized can be used in SIDMS and IDMS analyses as a standard. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   
118.
Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 2, pp. 127–134, March–April, 1991.  相似文献   
119.
120.
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