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   965篇
  免费   38篇
  国内免费   2篇
化学   653篇
晶体学   22篇
力学   15篇
数学   127篇
物理学   188篇
  2023年   15篇
  2022年   20篇
  2021年   15篇
  2020年   37篇
  2019年   30篇
  2018年   28篇
  2017年   16篇
  2016年   29篇
  2015年   20篇
  2014年   28篇
  2013年   57篇
  2012年   52篇
  2011年   78篇
  2010年   35篇
  2009年   28篇
  2008年   51篇
  2007年   56篇
  2006年   36篇
  2005年   43篇
  2004年   26篇
  2003年   24篇
  2002年   24篇
  2001年   13篇
  2000年   13篇
  1999年   7篇
  1998年   9篇
  1997年   7篇
  1996年   6篇
  1995年   7篇
  1994年   14篇
  1993年   10篇
  1991年   7篇
  1987年   5篇
  1986年   6篇
  1981年   6篇
  1980年   7篇
  1978年   8篇
  1977年   7篇
  1976年   5篇
  1975年   4篇
  1971年   6篇
  1970年   6篇
  1969年   8篇
  1968年   8篇
  1964年   4篇
  1963年   6篇
  1962年   8篇
  1961年   11篇
  1958年   7篇
  1955年   5篇
排序方式: 共有1005条查询结果,搜索用时 31 毫秒
941.
Bhattacharya  S.  Tiwari  N.  Mishra  A.  Mitra  S.  Dey  G. K.  Ghorui  S. 《Plasma Chemistry and Plasma Processing》2019,39(4):1019-1048
Plasma Chemistry and Plasma Processing - Plasma temperature, density and arc dynamics have been investigated in underwater arc discharges under different anodic environments. Distinct differences...  相似文献   
942.
Cytochromes c are small water-soluble proteins that catalyze electron transfer in metabolism and energy conversion processes. Hydrogenobacter thermophilus cytochrome c552 presents a curious case in displaying fluxionality of its heme axial methionine ligand; this behavior is altered by single point mutation of the Q64 residue to N64 or V64, which fixes the ligand in a single configuration. The reorganization energy (λ) of these cytochrome c552 variants is experimentally determined using a combination of rotating disc electrochemistry, chronoamperometry and cyclic voltammetry. The differences between the λ determined from these complementary techniques helps to deconvolute the contribution of the active site and its immediate environment to the overall λ (λTotal). The experimentally determined λ values in conjunction with DFT calculations indicate that the differences in λ among the protein variants are mainly due to the differences in contributions from the protein environment and not just inner-sphere λ. DFT calculations indicate that the position of residue 64, responsible for the orientation of the axial methionine, determines the geometric relaxation of the redox active molecular orbital (RAMO). The orientation of the RAMO with respect to the heme is key to determining electron transfer coupling (HAB) which results in higher ET rates in the wild-type protein relative to the Q64V mutant despite a 150 mV higher λTotal in the former.

Efficient delocalization of the redox-active molecular orbital (RAMO) in HtWT results in an increase in HAB value which in turn accelerates the electron transfer (ET) rate in spite of the higher reorganization energy (λ) than the HtQ64V mutant.  相似文献   
943.
Curve reconstruction: Connecting dots with good reason   总被引:1,自引:0,他引:1  
Curve reconstruction algorithms are supposed to reconstruct curves from point samples. Recent papers present algorithms that come with a guarantee: Given a sufficiently dense sample of a closed smooth curve, the algorithms construct the correct polygonal reconstruction. Nothing is claimed about the output of the algorithms, if the input is not a dense sample of a closed smooth curve, e.g., a sample of a curve with endpoints. We present an algorithm that comes with a guarantee for any set P of input points. The algorithm constructs a polygonal reconstruction G and a smooth curve Γ that justifies G as the reconstruction from P.  相似文献   
944.
The time differential as well as time integral perturbed angular correlations of the 486-134 keV cascade in 131Cs have been studied in a polycrystalline BaSO4 powder source using a HPGe-BaF2 detector system. The fundamental quadrupole frequency for the 134 keV level has been found to be ω0= (4.4 ± 0.4) × 107 rad/s. From a comparison of the quadrupole frequencies of this level and that of the 81 keV level in 133Cs, measured earlier in the same crystalline environment of the source, the absolute value of the quadrupole moment of the 134 keV level in 131Cs has been found to be 0.022 ± 0.002 b. This value of the quadrupole moment is reported for the first time and compared with the value predicted theoretically within the unified nuclear model with intermediate coupling. Received: 21 October 1999 / Revised version: 22 December 1999  相似文献   
945.
946.
In the title compound, C6H12O4·H2O, 1,4/2,5‐cyclo­hexane­tetrol and water mol­ecules are seen to possess twofold symmetry. All four hydrox­yl groups of the tetrol participate in extensive inter­molecular O—H⋯O hydrogen bonding to form mol­ecular tapes propagating along the a axis. Translationally related tapes along the c axis are held together by four coordinated water mol­ecules.  相似文献   
947.
Summary On the ageing of thorium hydroxide, there is considerable change in the pH of the system. Increase of pH is a result of release of hydroxyl ions and decrease of pH indicates the release of hydrogen ions from the adsorbent. Ageing before inflexion point especially with larger alkali leads to the coagulation of thorium hydroxide which eventually increases the pH of the medium.
Zusammenfassung Mit Alterung von Thoriumoxid treten betr?chtliche ?nderungen im pH der Systeme auf. Der Anstieg des pH ist ein Ergebnis des Freiwerdens von HydroxylIonen, die Abnahme zeigt das Freiwerden von Wasserstoff-Ionen vom Adsorbenten an. Alterung unterhalb des Inflexionspunktes, besonders mit gr?\erem Alkali-Gehalt, führt zur Koagulation des Thoriumhydroxids, was schlie\lich das pH des Mediums vergr?\ert.
  相似文献   
948.
Samal S  Acharya S  Dey RK  Ray AR 《Talanta》2002,57(6):1075-1083
Two new chelating resins (o-HAP-DDE-HCHO and o-HAP-DDE-FFD), having multiple functional groups are synthesised by condensing the Schiff base of o-hydroxyacetophenone-4,4′-diaminodiphenylether (o-HAP-DDE) with formaldehyde and furfuraldehyde, respectively. The extent of loading of metal ions Cu(II) and Ni(II) was studied in both competitive and non-competitive conditions varying the time of contact, metal ion concentration and the pH of the reaction medium. Both the resins are able to preferentially remove Cu(II) from the mixture of Cu(II) and Ni(II) at a pH 5.89 in the batch operation, maximum % uptake being 76.8 and 84.1, respectively, for o-HAP-DDE-HCHO and o-HAP-DDE-FFD. The furfuraldehyde condensed resin was found to be more effective in removing Cu(II) ions than the formaldehyde condensed resins in batch technique. The resins exhibited little affinity for alkali and alkaline earth metal ions. Further, the furfuraldehyde condensed resin was utilised in column operation for removing Cu(II) ions. Elution study with HCl (>1.0 mol l−1) resulted in removal of nearly 40–50% of loaded Cu(II) from the resin column.  相似文献   
949.
Reactions of one-electron reducing as well as oxidizing radicals with 4-mercaptopyridine (4-MPy) were studied in aqueous solutions at different pH values. One-electron oxidizing radicals such as N3 and Br2 , react with 4-MPy by electron transfer reaction at pH 11 to give 4-pyridylthiyl radical. The reduction potential for the couple 4-PyS /4-PyS was estimated to be 0.93V vs. NHE by equilibrium reaction with I2 /2I couple. At pH 6.8, where the compound is predominantly present in the thione form, the transient species formed is a cation radical. OH radicals react with 4-MPy by addition to the pyridine ring at pH 6.8 and 11. At pH 0, OH radicals as well as one-electron oxidants like Cl2 and Br2 radicals react with 4-MPy to produce the protonated form of 4-pyridylthiyl radical. At pH 6.8 and 11, eaq reaction with 4-MPy gave an initial adducts which reacted with the parent molecule to give dimer radicals. Acetone ketyl radicals were unable to reduce 4-MPy at neutral pH. Reducing radicals like H-atoms and acetone ketyl radicals reacted with 4-MPy at acidic pH by H-abstraction reaction to give the same species as produced by oxidizing radicals.  相似文献   
950.
Summary The filter paper strip Chromatographic separation of the individual members of various groups of the qualitative analysis chart has been described. Use has been made of the ascending method, using 60% aqueous ethanol as solvent. The migrated ions are detected after their separation by the use of organic reagents.
Zusammenfassung Die einzelnen Gruppen des qualitativen Kationentrennungsganges werden mit 60%igem Äthanol als Lösungsmittel papierchromatographisch nach der aufsteigenden Methode getrennt. Zum Nachweis der getrennten Ionen werden organische Reagentien benutzt.
  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