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   702篇
  免费   6篇
  国内免费   6篇
化学   433篇
晶体学   7篇
力学   14篇
数学   89篇
物理学   171篇
  2021年   6篇
  2020年   19篇
  2019年   20篇
  2018年   19篇
  2017年   15篇
  2016年   34篇
  2015年   8篇
  2014年   17篇
  2013年   29篇
  2012年   33篇
  2011年   24篇
  2010年   15篇
  2009年   22篇
  2008年   35篇
  2007年   29篇
  2006年   26篇
  2005年   27篇
  2004年   19篇
  2003年   29篇
  2002年   33篇
  2001年   17篇
  2000年   7篇
  1999年   11篇
  1997年   6篇
  1995年   8篇
  1994年   5篇
  1993年   8篇
  1992年   5篇
  1991年   4篇
  1990年   6篇
  1989年   9篇
  1987年   8篇
  1986年   8篇
  1985年   11篇
  1984年   8篇
  1983年   6篇
  1982年   10篇
  1981年   6篇
  1980年   7篇
  1979年   6篇
  1978年   6篇
  1977年   6篇
  1976年   6篇
  1975年   6篇
  1974年   7篇
  1973年   9篇
  1972年   6篇
  1971年   4篇
  1969年   4篇
  1967年   10篇
排序方式: 共有714条查询结果,搜索用时 13 毫秒
101.
The reaction of pentaphenylantimony with mercury iodide affords the ionic complex [Ph4Sb] 2 + [Hg2I6]2?·Ph2Hg (I). The [Ph4Sb] 2 + [Hg2I6]2? (II) and [Ph4Sb] 2 + [Cd2I6]2? (III) complexes are synthesized from tetraphenylantimony iodide and mercury and cadmium iodides. The [Ph4Sb] 2 + [Hg4I10]2? complex (IV) is prepared from tetraphenylantimony 2,4-dimethylbenzenesulfonate and mercury iodide. According to the X-ray diffraction data, the Sb atom in the [Ph4Sb]+ cations of complex I has virtually ideal tetrahedral coordination (the CSbC angles are 108.09°–109.64°). In the central square fragment Hg2I2 of the [Hg2I6]2? anion, the Hg-Ibr bond lengths are 2.825 and 3.075 Å, and the terminal iodine atoms are more strongly bonded to the mercury atoms (Hg-Iterm 2.691 and 2.700 Å). The [Cd2I6]2? anion in complex III has a similar structure (the Cd-Ibridg and Cd-Iterm distances are 2.865, 2.872 and 2.723, 2.748 Å, respectively). The anions in complex IV are joined by I…Hg (3.651 Å) and I…I (4.058 Å) interactions into an infinite dimeric network.  相似文献   
102.
Reactions of 5-substituted furan-2(3H)-ones with ethylenediamine, 2-aminoethanol, and o-aminophenol do not stop at the stage of formation of the corresponding 4-oxoalkanoic acid amides but lead to new bi-and tricyclic structures as a result of double intramolecular cyclodehydration.  相似文献   
103.
We investigate the tail behavior of the sojourn-time distribution for a request of a given length in an M/G/1 Processor-Sharing (PS) queue. An exponential asymptote is proven for general service times in two special cases: when the traffic load is sufficiently high and when the request length is sufficiently small. Furthermore, using the branching process technique we derive exact asymptotics of exponential type for the sojourn time in the M/M/1 queue. We obtain an equation for the asymptotic decay rate and an exact expression for the asymptotic constant. The decay rate is studied in detail and is compared to other service disciplines. Finally, using numerical methods, we investigate the accuracy of the exponential asymptote. AMS 2000 Subject Classifications Primary:60K25,Secondary: 60F10,68M20,90B22  相似文献   
104.
The application of micellar electrokinetic capillary chromatography (MECC) to the analysis of illicit drug seizures is presented. Areas investigated include general screening and qualitative and, in some instances, quantitative analysis of various drugs, including heroin, opium, cocaine, amphetamines, LSD and anabolic steroids. Due to its high efficiency, high selectivity and general applicability, MECC is well suited for forensic drug analyses.  相似文献   
105.
Four new complexes of pentavalent bismuth are synthesized: Ph3Bi[OC6H2(Br3-2,4,6)]2, Ph3Bi[OC6H2(Cl3-2,4,6)]2, Ph4BiOC6H2(Br3-2,4,6), and Ph4BiOC6H2(Cl3-2,4,6). Tetraphenylbismuth aroxides are produced by the disproportionation reaction of ligands from pentaphenylbismuth and triphenylbismuth diaroxides in toluene or from pentaphenylbismuth and phenol. Triphenylbismuth diaroxides are synthesized from phenol, triphenylbismuth, and hydrogen peroxide taken at a molar ratio of 2 : 1 : 1, respectively, in diethyl ether. According to the X-ray diffraction data, the bismuth atom surrounding in 2,4,6-tribromophenoxytetraphenylbismuth has the configuration of a trigonal bipyramid with the aroxyl ligand in the axial position. The Bi-C and Bi-O bond lengths are 2,184, 2.190, 2.234, and 2.514 Å, respectively, and the equatorial CSbC angles are equal to 111.4°, 121.3°, and 121.3°.Translated from Koordinatsionnaya Khimiya, Vol. 30, No. 12, 2004, pp. 935–938.Original Russian Text Copyright © 2004 by Sharutin, Egorova, Tsiplukhina, Gerasimenko, Pushilin.  相似文献   
106.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 52, No. 4, pp. 586–592, April, 1990.  相似文献   
107.
108.
109.
Adduct of triphenylphosphine oxide and sulfuric acid was synthesized by reacting arenesulfonic acids with triphenylphosphine oxide (1 : 2) in the presence of the moisture of air. According to the X-ray diffraction data, the phosphorous atom has a distorted tetrahedral coordination. The sulfuric acid molecule is disordered over two sites and is linked with two triphenylphosphine oxide molecules through hydrogen bonds.  相似文献   
110.
The anion radical of 1,2-diphenylcyclobutene was studied by electron spin resonance. The hyperfine splittings were found to be 0·47 and 0·74 G for the meta-positions, 2·23 and 2·69 G for the ortho-positions and 4·21 G for the para-positions of the phenyl rings. The methylene proton splittings were 4·27 G, which would imply that the value of Q is 27 G, much lower than that of other cyclobutene anions. It was also estimated that the angle between the axis of the p-orbitals of the ethylene group and that of the phenyl group is about 30°, in agreement with that found for the tetraphenylethylene anion.  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