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   206篇
  免费   12篇
  国内免费   3篇
化学   175篇
晶体学   3篇
力学   4篇
数学   15篇
物理学   24篇
  2021年   4篇
  2020年   9篇
  2019年   7篇
  2018年   2篇
  2017年   4篇
  2016年   10篇
  2015年   6篇
  2014年   9篇
  2013年   14篇
  2012年   12篇
  2011年   8篇
  2010年   10篇
  2009年   9篇
  2008年   12篇
  2007年   8篇
  2006年   7篇
  2005年   3篇
  2004年   8篇
  2003年   4篇
  2002年   7篇
  2001年   6篇
  1999年   1篇
  1998年   3篇
  1996年   4篇
  1995年   1篇
  1994年   2篇
  1993年   1篇
  1992年   2篇
  1991年   4篇
  1990年   2篇
  1989年   5篇
  1988年   4篇
  1987年   2篇
  1986年   3篇
  1985年   1篇
  1984年   1篇
  1983年   1篇
  1982年   3篇
  1981年   1篇
  1979年   3篇
  1978年   2篇
  1977年   2篇
  1976年   1篇
  1975年   2篇
  1974年   1篇
  1972年   2篇
  1971年   1篇
  1970年   2篇
  1968年   2篇
  1967年   2篇
排序方式: 共有221条查询结果,搜索用时 15 毫秒
1.
We answer a question of J. Anderson's by producing infinitely many commensurability classes of fibered hyperbolic 3-manifolds whose fundamental groups contain subgroups that are locally free and not free. These manifolds are obtained by performing 0–surgery on a collection of knots with the same properties.  相似文献   
2.
前报中已证明用三氟化硼-环氧氯丙烷(ECH)引发四氢呋喃(THF)聚合具有较高的引发效率,并对在Ac_2O、水和无水存在下的聚合反应进行了研究。本文报道1,4-丁二醇(BG)对BF_3引发THF聚合反应的影响。通常认为在BG存在下,BF_3是不能引发THF聚合的,但本工作证明BG是有效的分子量调节剂,制备分子量在  相似文献   
3.
The possibility of using horse radish peroxidase as a catalyst for polymerization of monomers (vinylformamide and sodium vinylsulfonate) in the presence of hydrogen peroxide and 2,4-pentanedione in aqueous medium at room temperature was studied.  相似文献   
4.
1.  Stability constants for alkali metal complexes of composition [ML]+ and a copper complex [CuLCl]+, which are formed via treatment of alkali metal 2,4-dinitrophenolate or copper chloride with a series of carbamoyl phosphine oxide derivatives, have been determined in anhydrous solutions.
2.  The most stable complexes are formed by ligands containing an aryl substituent attached to the phosphorus atom.
Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 53–58, January, 1988.  相似文献   
5.
The aminolysis of 5-aryl-3-arylidene-3H-furan-2-ones by the action of aromatic amines leads to the formation of substituted amides of 4-oxo acids, the subsequent azacyclization of which in the presence of acetic anhydride leads to the formation of 1,5-diaryl-substituted 3-arylidene-3H-pyrrol-2-ones. The mechanism of the occurring and alternative transformations is discussed.  相似文献   
6.
Reaction of different anionic S-nucleophiles with 3-R-2-aryl-4,6-dinitroindoles led to a regiospecific nucleophilic substitution of the nitro group in position 4 with 6-NO2 group remaining intact. The representatives of some peri-annulated polycyclic systems were synthesized on the basis of the substitution products. Dedicated to Academician V. A. Tartakovsky in honor of his 75th anniversary. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1543–1547, August, 2007.  相似文献   
7.
聚环硫氯丙烷或环硫氯丙烷与环氧氯丙烷共聚物,在少量二乙烯三胺存在下制得交联预聚物,将交联预聚物分别与硫代硫酸钠,叠氮化钠反应,制得四种侧链带有硫代硫酸根或叠氮基的新型螯合树脂。它们对贵金属离子具有较高的吸附容量和较好的吸附选择性。  相似文献   
8.
The stereochemistry of the successive addition of two different dienophiles, viz., N-phenylmaleinimide and 4-phenyl-1,2,4-triazoline-3,5-dione, to 2-pyrones was studied. The configurations of the mixed adducts (bisimides) obtained were established by PMR and mass spectrometry. It is shown that in all cases the reactions proceed with the formation of mixtures of syn and anti isomers, the ratios of which depend on the positions of the methyl groups in the starting 2-pyrones.See [1] for communication 30.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1471–1476, November, 1982.  相似文献   
9.
The title salt, [Zn(C2N2H8)3]2[CdI4]I2, conventionally abbreviated [Zn(en)3]2[CdI4]I2, where en is ethyl­enediamine, contains discrete [Zn(en)3]2+ cations and [CdI4]2− anions with distorted octa­hedral and nearly tetra­hedral geometries, respectively, as well as uncoordinated I ions. The cation and the free I anion lie on twofold rotation axes and the [CdI4]2− anion lies on a axis in the space group I2d. The structure exhibits numerous weak inter‐ionic hydrogen bonds of two types, viz. N—H⋯I(free ion) and N—H⋯I([CdI4]2−), which support the resulting three‐dimensional framework.  相似文献   
10.
Acylation of 3-ethoxycarbonyl-2,6-dimethyl-5-pyridinecarboxylic acid hydrazide and 2,6-dimethyl-3,5-pyridinedicarboxylic acid dihydrazide using aromatic acid chlorides gave the corresponding N-aroyl hydrazides. It was found that the hydrazinolysis of 3-ethoxycarbonyl-2,6-dimethyl-5-pyridinedicarboxylic acid N-aroyl hydrazides occurred not at the ester group but as a rehydrazinolysis reaction at the dihydrazide fragment. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1834–1845, December, 2005.  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