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   3970篇
  免费   149篇
  国内免费   54篇
化学   2182篇
晶体学   60篇
力学   189篇
综合类   16篇
数学   870篇
物理学   856篇
  2023年   29篇
  2022年   55篇
  2021年   68篇
  2020年   109篇
  2019年   105篇
  2018年   152篇
  2017年   140篇
  2016年   210篇
  2015年   157篇
  2014年   218篇
  2013年   467篇
  2012年   246篇
  2011年   241篇
  2010年   263篇
  2009年   162篇
  2008年   233篇
  2007年   204篇
  2006年   138篇
  2005年   95篇
  2004年   82篇
  2003年   81篇
  2002年   105篇
  2001年   87篇
  2000年   57篇
  1999年   37篇
  1998年   47篇
  1997年   40篇
  1996年   35篇
  1995年   15篇
  1994年   23篇
  1993年   16篇
  1992年   10篇
  1991年   13篇
  1990年   17篇
  1989年   13篇
  1988年   7篇
  1986年   9篇
  1985年   11篇
  1984年   17篇
  1983年   16篇
  1982年   6篇
  1981年   17篇
  1980年   11篇
  1979年   9篇
  1978年   10篇
  1977年   10篇
  1976年   12篇
  1975年   9篇
  1974年   9篇
  1964年   8篇
排序方式: 共有4173条查询结果,搜索用时 0 毫秒
41.
Zusammenfassung Die analytische Bestimmung der Metalle, des Dipyridyls und der Chloride in Oxo-chloro-alkoxo-dipyridyl-Komplexverbindungen des Niobs und Tantals wurde beschrieben. Eine modifizierte Methode der Dipyridylanalyse, wie auch der Chloridbestimmung in Gegenwart von Dipyridyl wurde angegeben. Die radiometrische Metallbestimmung in Extraktionsverbindungen von Niob und Tantal mit Di-oktyl-methylenbis-phosphonsäure wurde dargelegt.
Summary The analytical determination of metals, dipyridyl and chlorides in oxochloro-alkoxo-dipyridyl complex compounds of niobium and tantalum is described. A modified procedure of the dipyridyl analysis and also of the determination of chloride in the presence of dipyridyl is given. The radiometric determination of the metals in extraction compounds of niobium and tantalum with di-octyl-methylene-bis-phosphonic acid is discussed.

Résumé On décrit le dosage des métaux, du dipyridyle et des chlorures dans les composés complexes oxo, chloro, alcoxo, dipyridyle, du niobium et du tantale. On indique une méthode modifiée pour le dosage de dipyridyle ainsi que pour la détermination des chlorures, en présence de dipyridyle. On décrit le dosage radiométrique des métaux dans les produits d'extraction du niobium et du tantale par l'acide di-octyl-méthylène-bis-phosphonique.


Vorgetragen beim Symposium für analytische Chemie in Graz, 29. September bis 1. Oktober 1965.  相似文献   
42.
A new alcohol soluble functionalized vic-dioxime, bis-[(1-hydroxyhexyl)-(8,9-hydroxyimino)-7,10-dithiahexacosane (LH2), and its alcohol-soluble mono and dinuclear complexes (NiII, CuII, CoII, MnII, PdII and UO 2 II ) have been prepared from 6-mercapto-1-hexanol and (E,E)-dichloroglyoxime under high dilution basic conditions. Reactive polyalcohol moieties appended at the periphery of the oxime containing two different heteroatoms (S-, O-), serve as a weak exocyclic binding sites for PdII and AgI metal ions and also provide solubility for the vic-dioxime complexes in low molecular-weight alcohols. Both mono-nuclear (LH)2M and homodinuclear (LH)2(UO2)2(OH)2 and heterotrinuclear (LH)2MM 2 Xn, where M = CoII M′ = PdII, X = Cl, n = 4 and AgI X = NO 3 , n = 2) complexes have been obtained with a 1:2, 2:2, 3:2 metal/ligand ratio, respectively. Electronic spectra of the modified vic-dioximes exhibit monitorable changes in UV. All mono and dinuclear-complexes are soluble in common organic solvents. The elemental analysis, 1H-n.m.r, i.r., u.v–vis, and f.a.b.–m.s data and by cyclic and differential pulse voltammetry measurements are presented.  相似文献   
43.
The separation of isomers and enantiomers of branched C10-C12 phenylalkanes by gas chromatography on fused silica capillary columns coated with some modified β- and γ-cyclodextrins was studied. It was shown that the separation of positional isomers of C10-C12 phynylalkanes on modified cyclodextrin capillary columns is not better than that on a column coated with modified polyethylene glycol. Differences were found in the enantioselectivity of modified β- and γ-cyclodextrins for the separation of C10-C12 secondary phenylalkane enantiomers. While alkylderivatives of β-CDs resolve enantiomers of 3-phenylalkanes, alkyl derivatives of γ-CD resolve enantiomers of 2-phenylalkanes. Since shape selectivity factors of modified cyclodextrins have indicated no inclusion of the considered solutes in cyclodextrin cavities, enantioselective interactions most probably occur on the outer sphere of cyclodextrins.  相似文献   
44.
在许多嵌入式设计中,数据存储器是稀缺资源.如何基于静态分配方案,用最少的内存空间来存储程序数据成为嵌入式设计中一个非常重要的问题.如果两个函数之间不存在直接或者间接的调用关系的话,这两个函数的局部变量的生命期就没有重叠.这样的两个函数的局部变量可以共用存储空间而不会影响程序的正确性.基于这个思路,本文提出一种基于函数调用图的拓扑排序的最优静态分配算法(TBA)并证明了该分配算法的最优性.该分配算法通过静态分析技术,构建函数调用图(FCG),基于FCG的拓扑排序,计算每个函数的私有数据段的全局地址以及段内每个符号的全局地址,并根据重定位表更新对这些符号的引用.实验结果表明该算法优于前人提出的启发式算法.  相似文献   
45.
分析了连续激光辐照ZnSe/MgF2/K9滤光片引起透射特性的变化。在室温条件下,用波长0.632 8μm激光作为探测光束,测量了1.06μm连续激光辐照ZnSe/MgF2/K9滤光片温升引起薄膜折射率的改变,导致探测光束通过干涉滤光片后透过率的热致非线性变化。在光斑直径0.75mm条件下,测量了不同功率激光辐照ZnSe/MgF2/K9滤光片引起温升随时间的变化。在激光功率30W,辐照时间2.52s条件下,实验观测到ZnSe/MgF2/K9滤光片薄膜破坏温度约为90℃,辐照时间10s时干涉滤光片形成的薄膜龟裂形貌。  相似文献   
46.
This paper describes the use of IBC’s AnaLig® Sr-01 molecular recognition technology product to effectively and selectively pre-concentrate, separate, and recover strontium from urine samples. This method uses two-stage columns separation consisting of two different commercial products Eichrom’s Pre-filter Material and AnaLig® Sr-01 column from IBC Advanced Technologies. This method does not involve co-precipitation of strontium as phosphates and oxalates from urine samples. The new rapid method separates strontium-90 with high chemical recovery.  相似文献   
47.
The mechanism of interaction of trypsin with the sulfathiazole was studied through using fluorescence quenching and UV-visible absorption spectra at pH 7.4. The Stern-Volmer quenching constants, binding constants, number of binding sites and the corresponding thermodynamic parameters ΔHo, ΔSo and ΔGo were calculated at different temperatures. The effect of common metal ions on the constants was also discussed. The results suggest that sulfathiazole can interact strongly trypsin and that there is the formation of trypsin-sulfathiazole complex and the interaction can be explained on the basis of hydrogen bonds and van der Waals forces. The binding distance (r) between the donor (trypsin) and acceptor (sulfathiazole) was 3.52 nm based on the Förster’s non-radiative energy transfer theory. The detection and quantification limits of sulfathiazole were calculated as 2.52 and 8.40 μM in the presence of trypsin, respectively. The relative standard deviation (RSD) was 4.086 % for determinations (n?=?7) of a sulfathiazole solution with the concentration of 7.54 μM.  相似文献   
48.
49.
The magnetic filtration theory was evaluated to intensify the filtration of industrial fluids by magnetic filters. Effects of filtration velocity and external magnetic field intensity on filter performance were investigated and the dependence of the logarithmic efficiency coefficient on filtration velocity was questioned. It was concluded that change in the magnetic susceptibility of the dispersion particles, caused by external magnetic field, and change in the flow rate properties of the liquid alongside the filter pores are the most essential factors to be considered in the design, development, and modeling of magnetic filtration systems in various industrial areas.  相似文献   
50.
The results of measurements of the dielectric constant of TlGaSe2 in temperature range of successive phase transitions are presented. An anomaly in the temperature dependence of the real part of dielectric constant in TlGaSe2 has been observed at about 242?K in addition to anomalies at 115, 108, and also near 65?K as reported in previous publications. The presence of temperature hysteresis effects in temperature interval between 115 and 242?K allowed making a conclusion about possible existence of an incommensurate phase in the mentioned temperature range. A model of succession of the structural phase transitions in TlGaSe2 has been suggested.  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