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   247252篇
  免费   6918篇
  国内免费   5319篇
化学   143007篇
晶体学   3643篇
力学   10174篇
综合类   356篇
数学   27286篇
物理学   75023篇
  2021年   2498篇
  2020年   2803篇
  2019年   3015篇
  2018年   3427篇
  2017年   3511篇
  2016年   4921篇
  2015年   3737篇
  2014年   5174篇
  2013年   10889篇
  2012年   10113篇
  2011年   11876篇
  2010年   8549篇
  2009年   8248篇
  2008年   10696篇
  2007年   10666篇
  2006年   10025篇
  2005年   9019篇
  2004年   7832篇
  2003年   6820篇
  2002年   6710篇
  2001年   7337篇
  2000年   5631篇
  1999年   4141篇
  1998年   3389篇
  1997年   3313篇
  1996年   3271篇
  1995年   2865篇
  1994年   2948篇
  1993年   2749篇
  1992年   2972篇
  1991年   3026篇
  1990年   2819篇
  1989年   2703篇
  1988年   2629篇
  1987年   2549篇
  1986年   2581篇
  1985年   3348篇
  1984年   3378篇
  1983年   2822篇
  1982年   3064篇
  1981年   2814篇
  1980年   2614篇
  1979年   2798篇
  1978年   2999篇
  1977年   3034篇
  1976年   3060篇
  1975年   2793篇
  1974年   2907篇
  1973年   2957篇
  1972年   2318篇
排序方式: 共有10000条查询结果,搜索用时 21 毫秒
81.
82.
83.
84.
85.
A new microscopic model of anomalous muonium for the elemental semiconductors is proposed. The relevant configuration consisting of both a diamagrentic molecule Si−Mu and an unpaired orbital e is contained into a semivacancy of the real lattice. By using the unrestricted Hartree-Fock computational method the principal properties of the system are established. A dynamical version of the model together with a question on the formation of such system are discussed.  相似文献   
86.
87.
Erratum     
  相似文献   
88.
Rate constants have been measured by pulse radiolysis for the reactions of the carbonate radical, CO3·?, with a number of organic and inorganic reactants as a function of temperature, generally over the range 5 to 80°C. The reactants include the substitution-inert cyano complexes of FeII, MoIV, and WIV, the simple inorganic anions SO32?, ClO2?, NO2?, I?, and SCN?, several phenolates, ascorbate, tryptophan, cysteine, cystine, methionine, triethylamine, and allyl alcohol. The measured rate constants ranged from less than 105 to 3 × 109 M?1 s?1, the activation energies ranged from ?11.4 to 18.8 kJ mol?1, and the pre-exponential factors ranged from log A = 6.4 to 10.7. The activation energies for the metal complexes and inorganic anions generally decrease with increasing driving force for the reaction, as expected for an outer sphere electron transfer. For highly exothermic reactions, however, the activation energy appears to increase, probably reflecting the temperature dependence of diffusion. For many of the organic reactants, the activation energies were low and independent of driving force, suggesting that the oxidation is via an inner sphere mechanism.  相似文献   
89.
Peroxyoxalate chemiluminescence may be used for sensitive postcolumn detection of phenothiazine analytes separated by high performance liquid chromatography with appropriate optimization of measurement conditions such as solvent, pH and oxalate ester. Detectability of fluorescent analytes by chemical excitation varies greatly, but analytes with low oxidation potentials are generally more readily detected at low levels, as demonstrated for phenothiazines, an important class of fluorescent drugs. Some improvement in detection limits is observed for fluphenazine when chemiluminescence detection is compared to conventional fluorescence detection. Because of the specificity of chemical excitation, fewer interferences from fluorescent impurities in a urine matrix are observed.  相似文献   
90.
After briefly renewing toxicological data on germanium compounds, the authors report on the subchronic oral toxicity of carboxyethylgermanium sesquioxide in rats. During six months, male and female animals received 1 g kg?1. day?1. No particular toxic symptoms, and no behaviour problems except a small decrease of body weight in male rats, at the end of the six-month experimentation period, were observed. A significant decrease of erythropoiesis and some significant changes in leucocyte ratios were demonstrated. The main marked effect was a moderate renal dysfunction characterized by a tubular disease with the presence of cylinders, swelling of tubulus cells and flocculus deposits. Germanium urinary excretion was constant and linked to the received dose. Six months later, no preferential accumulation in organs was evident.  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