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   9863篇
  免费   214篇
  国内免费   20篇
化学   5826篇
晶体学   162篇
力学   267篇
数学   733篇
物理学   3109篇
  2023年   94篇
  2022年   211篇
  2021年   162篇
  2020年   177篇
  2019年   240篇
  2018年   207篇
  2017年   232篇
  2016年   317篇
  2015年   212篇
  2014年   400篇
  2013年   781篇
  2012年   548篇
  2011年   655篇
  2010年   417篇
  2009年   405篇
  2008年   460篇
  2007年   440篇
  2006年   335篇
  2005年   281篇
  2004年   229篇
  2003年   163篇
  2002年   183篇
  2001年   117篇
  2000年   125篇
  1999年   86篇
  1998年   56篇
  1997年   56篇
  1996年   92篇
  1995年   104篇
  1994年   98篇
  1993年   92篇
  1992年   120篇
  1991年   86篇
  1990年   79篇
  1989年   92篇
  1988年   87篇
  1987年   90篇
  1986年   74篇
  1985年   104篇
  1984年   119篇
  1983年   82篇
  1982年   98篇
  1981年   97篇
  1980年   102篇
  1979年   90篇
  1978年   102篇
  1977年   84篇
  1976年   56篇
  1975年   61篇
  1974年   74篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
The time integral pertturbed angular correlation (TIPAC) technique is employed to study PAC parameters in aqueous solutions of biomolecules Bovine Serum Albumin (BSA), lysozyme and ethylenediaminetetraacetic acid disodium salt (EDTA), using radioactive147Nd as a probe. The attenuation coefficient (G22) is found to decrease with increasing concentration of BSA The effect of attenuation is more pronounced for protein molecules BSA and lysozyme than in the case of EDTA. The relaxation constant (2) increases with increasing concentration of the solution as well as with the increasing size of the solute molecule.  相似文献   
142.
The kinetics of oxidation of three aldoses (glucose, mannose and galactose) byN-bromoacetamide (NBA) in the presence of an alkaline solution of RuO4 as catalyst and Hg(OAc)2 as co-catalyst and as a scavenger for bromide have been investigated. The main products of the oxidation are the corresponding aldonic acids. The reaction is zero order with respect to aldose and OH. First order dependence of the reaction on both NBA and RuO4 at low concentrations shifts to zero order at higher concentrations. Addition of acetamide decreases the reaction rate, while addition of Hg(OAc)2 has the opposite effect. No significant effect of ionic strength was observed. OBr is postulated as the reactive oxidising species and a mechanism involving co-catalysis by RuO4 and HgII is proposed. TMC 2588  相似文献   
143.
Complete Separation of ternary mixtures of Ca, Mg and Sr or Ba ions with ammonium chloride and less complete but detectable separation of the same mixtures with ammonium nitrate have been achieved, as well as a few binary separations of the type Ca-Ba, Ca-Sr, Ca-Mg, Mg-Sr and Mg-Ba.  相似文献   
144.
Compatibilities of various PVC blends with chlororubber-20 and its graft polyblends have been studied on the basis of our previous findings. It has been found that chlororubber-20 makes compatible blends with PVC, while grafting of styrene, ethyl acrylate or acrylonitrile onto chlororubber-20 generates heterogeneity in their blends with PVC. The behaviour of these blends at the molecular level is reflected in the changes of ultrasonic velocity and absolute viscosity with composition.  相似文献   
145.
Ultrafine -SiC with high surface area (150 m2 g–1) has been synthesized by inflight processing of charred rice husk in a r.f. plasma reactor operating at atmospheric pressure. The plasma-synthesized particles were doped with platinum (1%) and tested as a catalytic support material. The catalyst (1% Pt doped -SiC) showed 100% conversion of CO to CO2 at a temperature as low as 175°C.  相似文献   
146.
Molar excess volumes, VE, for pyridine (A) + α-picoline (B), + β-picoline (B) and + γ-picoline (B) and benzene (A) + toluene (B), + o-xylene (B) and + p-xylene (B) and carbon tetrachloride (A) + n-heptane (B) have been measured dilatometrically as a function of temperature and composition and have been utilized to study B—B and B—B—B interactions in the presence of A via the Mayer—McMillan approach. A model has also been presented to account for these B—B and B—B—B interactions. The VE data at 308.15 K have also been analysed in terms of the “graph theoretical” approach which describes the VE data well for all these mixtures at 308.15 K. The “graph theoretical” approach has further been extended to successfully evaluate VE data for a mixture at any temperature, T2, when the VE data at T1 are known.  相似文献   
147.
The Mössbauer spectrum of ferrous zirconium double sulphate FeZrO(SO4)2·8H2O shows a quadrupole split doublet at room temperature. The results are discussed in terms of high-spin Fe(II) in distorted octahedral symmetry.  相似文献   
148.
Summary Copper(II) or Copper(II) and iron(III) in a mixture are determined by titration with EDTA (disodium salt) solution as complexometric reagent at pH 4.0 using potassium thiocyanate-p-anisidine as an indicator.FeIII is estimated in the mixture by titration with EDTA (disodium salt) solution using potassium thiocyanate-ether as an indicator.CuII present in the mixture is, therefore, equivalent to the difference in amounts of the EDTA (disodium salt) used for the two sets of titrations of the mixture using potassium thiocyanate-p-anisidine and potassium thiocyanate-ether as indicators respectively.Strontium, magnesium, manganese, calcium, barium and mercuric ions do not interfere in these estimations.
Zusammenfassung Kupfer(II) oder Kupfer(II) und Eisen(III) zusammen werden komplexometrisch mit ÄDTA-Lösung bei pH 4,0 unter Verwendung von Kaliumthiocyanat-p-Anisidin als Indicator titriert. Eisen(III) wird in dem Gemisch durch komplexometrische Titration gegen Kaliumthiocyanat-Äther als Indicator bestimmt. Der Kupfer(II)-gehalt ergibt sich aus der Differenz der beiden Titrationen. Strontium, Magnesium, Mangan, Calcium, Barium und Quecksilber(II) stören nicht.
  相似文献   
149.
Z-2-Chlorostilbene undergoes uncatalyzed LiAlH4 reduction giving phenanthrene and Z-stilbene. An electron transfer radical mechanism is proposed. LiAlH4 induced isomerization of Z-stilbene produces E-stilbene.  相似文献   
150.
Summary In this paper we have reported our results on the attempted separation of copper(II), nickel(II), cobalt(II) and iron(III) in mixtures by filter paper strip chromatography, using aqueous ethanol as solvent. The effect of the presence of varying concentrations of citrate ion as a complexing agent in the mixtures has been studied. The complexing agent has been added in the metal solution, and not in the solvent as usually done by previous workers.  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