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   48275篇
  免费   1376篇
  国内免费   28篇
化学   29420篇
晶体学   243篇
力学   812篇
综合类   1篇
数学   8993篇
物理学   10210篇
  2023年   354篇
  2022年   343篇
  2021年   521篇
  2020年   705篇
  2019年   653篇
  2018年   994篇
  2017年   911篇
  2016年   1754篇
  2015年   1461篇
  2014年   1425篇
  2013年   3171篇
  2012年   2984篇
  2011年   2818篇
  2010年   1883篇
  2009年   1564篇
  2008年   2474篇
  2007年   2251篇
  2006年   1992篇
  2005年   2035篇
  2004年   1767篇
  2003年   1458篇
  2002年   1267篇
  2001年   974篇
  2000年   970篇
  1999年   675篇
  1998年   531篇
  1997年   442篇
  1996年   593篇
  1995年   429篇
  1994年   504篇
  1993年   457篇
  1992年   478篇
  1991年   408篇
  1990年   461篇
  1989年   366篇
  1988年   373篇
  1987年   342篇
  1986年   331篇
  1985年   459篇
  1984年   424篇
  1983年   337篇
  1982年   337篇
  1981年   359篇
  1980年   283篇
  1979年   276篇
  1978年   280篇
  1977年   264篇
  1976年   281篇
  1974年   253篇
  1973年   265篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
A simple model including different processes important for the creation of APS signals formed by electrons is proposed. Mean probabilities of elastic and inelastic interactions of electrons with individual atom layers in the solid are introduced. The contribution of different layers to the DAPS and AEPS signals and the dependence of these signals on the interaction parameters are calculated.I am indebted to dr. J. Pavluch for valuable discussions.  相似文献   
32.
The paper describes the results of investigations of the solar wind ions, carried out on board the high apogee Prognoz 7 and Prognoz 8 Earth's satellites with the aid of an SKS instrument (USSR) and a Monitor instrument (USSR-SSR). Behaviour of proton and that of components on the front of Earth's bow and interplanetary shock waves were compared by means of the energoanalysis and energy-mass analysis techniques. In several long-term periods of observation the solar wind heavy ions — oxygen, silicon and iron were determined. It enabled us to estimate the solar corona chemical composition and electron temperature.Presented at the 5th General Assembly IAGA/IAMAP August 5–17, 1985, Prague, Czechoslovakia.  相似文献   
33.
The main result of this paper is that ifV satisfies GCH andω 1<λ<μ are arbitrary regular cardinals, then in some cardinal preserving forcing extensionW ofV we have λ=λ=2 N 0,μ=2 λ and there are a hereditarily separableX ?2 λ with |X|= \(2^{\aleph _0 } \) =μ and a hereditarily LindelöfY ?2 μ withw(Y)= \(2^{2^\aleph 0} \) =μ. So far similar results have only been obtained under the assumption of CH.  相似文献   
34.
This paper shows the separation and determination of eight compounds containing the OH group (ethanol, pentanol, 3-methyl-1-butanol, hexanol, phenol, benzyl-alcohol, phenylethanol and geraniol) in synthetic wine by gas chromatography using UV-Vis molecular absorption spectrometry as detection system. All the parameters affecting the separation and determination were optimised using some methods of experiment design. The analytical characteristics of each compound were calculated and detection limits ranging from 2.3 to 74 mg l(-1) have been obtained.  相似文献   
35.
The leaching rate of1 3 7Cs from bituminized products was studied by leach tests conducted for two years.  相似文献   
36.
An efficient method was developed for the determination of nanogram levels of lithium in biological samples. Serum samples from human subjects from southeastern Spain, treated or not treated with lithium carbonate, were analyzed by electrothermal atomic absorption spectrometry. The samples were previously treated with a matrix modifier consisting of 0.1% Triton X-100 and injected through a graphite tube with L'vov platform. The Li concentrations measured by the procedure described for the 3 certified reference samples used were not significantly different (p > 0.05) than certified levels. Sample recoveries and variability during several days, with coefficients of variation from 4.00 to 14.8%, demonstrated the reliability and accuracy of this technique. Mean Li concentration determined in the serum of individuals with psychiatric disorders treated with Li (n = 117, 5.077 +/- 1.795 microg Li/mL) was significantly higher (p < 0.001) than that in individuals not treated with Li (n = 24, 1.902 +/- 2.054 ng Li/mL).  相似文献   
37.
A number of ruthenium triphenylphosphine complexes catalyse the reduction of ketones to their corresponding alcohols in the presence of water. The most convenient catalyst precursors are carbonyl containing complexes which do not promote decarbonylation of the substrate. The hydrogenation of acetone with hydridochlorocarbonyltris(triphenylphosphine)ruthenium is first order with respect to the substrate concentration, the catalyst concentration, the hydrogen pressure and the water concentration. Turnover numbers up to 15,000 have been achieved with this catalyst. Other ketones are also reduced by RuHCl(CO)(PPh3)3 and the rate of the reaction is dependent on the nature of the substrate.  相似文献   
38.
2-Deoxy-2-[18F]fluoro-D-glucose ([18F] FDG), the most popular positron emitting radiopharmaceutical, may oxidise by autoradiolysis in aqueous solution. The aim of this work was to use LC-MS for determination of the oxidation products of fluorodeoxyglucose and glucose (Glc) obtained by oxidation with Fenton's reagent. Asahipak NH2P-50 polyamide silica column and acetonitrile-0.025% aqueous ammonium formate (80:20 (v/v)) eluent were utilised with an Agilent 1100 HPLC-MS instrument. Ten major oxidation products of FDG and Glc were separated and identified by mass spectrometry: 2-fluorogluconic acid, 2-fluoroglucuronic acid, 2-oxoerythronic acid, arabinose, arabonic acid, araburonic acid, erythrose, erythrulose, gluconic acid, and glucuronic acid. The most intensive electrospray ionisation signals were found in the negative ion spectra and were due to HCOO- adducts, the other acids being in their lactone forms.  相似文献   
39.
A spectrophotometric method for cyanide based on its inhibition of the colour formation reaction between nickel(II) and 3-(4,5-dimethyl-2-thiazolylazo)-2,6-dihydroxybenzoic acid has been developed, and allows the determination of down to 0.1 g of cyanide. Most of the interferences can be avoided by displacement of the hydrogen cyanide using an arsine generator.  相似文献   
40.
A new reagent for the highly selective extraction of cesium (e-1,7–2,2)4,8–8,4-(bis--o-phenylene)bisdicarbollidocobalt(1–)ate, [(C2B9H9)2(C6H4)2Co], abbreviated as BISPHECOSAN is described in this paper. The choice of organic solvent and solubilizer, dependence of distribution ratio of Cs+ on acidity and other parameters are studied. The extraction mechanism based on selective binding of Cs+ cation between two phenylene rings is presented and factors influencing the chemical stability of the reagent are determined.  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