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   1269篇
  免费   3篇
化学   987篇
晶体学   5篇
力学   24篇
数学   70篇
物理学   186篇
  2021年   11篇
  2020年   12篇
  2019年   17篇
  2018年   25篇
  2017年   36篇
  2016年   27篇
  2015年   20篇
  2014年   34篇
  2013年   63篇
  2012年   46篇
  2011年   53篇
  2010年   54篇
  2009年   57篇
  2008年   48篇
  2007年   44篇
  2006年   30篇
  2005年   40篇
  2004年   37篇
  2003年   39篇
  2002年   43篇
  2001年   42篇
  2000年   31篇
  1999年   18篇
  1998年   11篇
  1997年   16篇
  1996年   12篇
  1992年   12篇
  1991年   18篇
  1990年   14篇
  1989年   17篇
  1988年   11篇
  1987年   20篇
  1986年   12篇
  1985年   16篇
  1984年   15篇
  1983年   17篇
  1982年   20篇
  1981年   15篇
  1980年   14篇
  1979年   16篇
  1978年   15篇
  1977年   19篇
  1976年   13篇
  1975年   18篇
  1973年   12篇
  1972年   8篇
  1971年   15篇
  1970年   9篇
  1969年   15篇
  1967年   12篇
排序方式: 共有1272条查询结果,搜索用时 15 毫秒
61.
62.
4-Methoxybenzyl chloride reacts with elemental (red or white) phosphorus under the conditions of phase-transfer catalysis (concentrated aqueous KOH, dioxane, benzyltriethylammonium chloride, 85-90°C, argon) to give as major product tris(4-methoxybenzyl)phosphine oxide in up to 45% yield. With white phosphorus at lower (70°C) temperature this reaction yields mainly bis(4-methoxybenzyl)phosphine oxide. Phosphine reacts with 4-methoxybenzyl chloride in superbasic KOH-DMSO suspension, and under definite conditions bis(4-methoxybenzyl)phosphine oxide is predominantly formed.  相似文献   
63.
2-(1-Naphthyl)- and 2-(2-naphthyl)pyrroles and their 1-vinyl derivatives were synthesized in 22–64% yields by the reaction of 1- and 2-acetylnaphthalene oximes with acetylene at both atmospheric pressure and elevated pressures in an alkali metal hydroxide-dimethyl sulfoxide system.See [1] for communication 22.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1351–1353, October, 1982.  相似文献   
64.
A new general approach to anionic transformations of acetylenes using superbasic media has been developed. It allows series of new reactions which are not undergone by acetylene under conventional conditions. The triads Se8KOHdimethylsulfoxide (DMSO), Se8KOHDMSO, TeKOH-hexamethyl-phosphorictriamide (HMPA) are proposed as new effective reagents for the preparation of unsaturated compounds of sulfur, selenium and tellerium. A series of reactions of acetylene with sulfur, selenium and tellerium proceeding in DMSO or HMPA in the presence of alkali and water at 80–120° leading to divinyl sulfide, divinyl selenide and divinyl teluride in 25–80% yields have been found. Thiophen, di-1-(1,3-butadienyl) sulfide, 1-vinyl-2-thiabicyclo[3.2.0]hept-3-ene, and dihydrothiophen have been obtained by the reaction of vinylacetate with sulfur. The reaction of vinylacetylene with selenium affords selenophen, di-1-(1,3-butadienyl) selenide, 1-vinyl-2-selenabicyclo[3.2.0]hept-3-ene, methyl (1-(1,3-butadienyl) sulfide, and methylthiomethyl 1-(1,4-butadienyl) selenide, vinyl 1-(1,3-butadienyl) sulfide, and methylthiomethyl 1-(1,3-butadienyl) selenide (the latter two with DMSO participation). The reaction of vinylacetate with tellerium gives mainly di-1-(1,3-butadienyl) telluride. A series of reactions between DMSO and selenium leading to dimethyl sulfide, dimethyl sulfoselenide, and methylthiomethyl selenide have been observed.  相似文献   
65.
66.
The possibility of formation of a basic (stationary) and an additional (moving) high-absorption domain in an optically bistable system, based on high absorption, is demonstrated. A semiconductor with the absorption coefficient dependent on the concentration of free charge carriers in the conduction band is considered as a nonlinear medium. Under certain conditions, an optical beam passing through the stationary high-absorption domain acquires an annular profile and, after traveling a certain distance, transforms into a Gaussian beam with an intensity on the axis sufficient to switch the medium-beam system to the upper state. This moving domain periodically disappears and reappears due to diffusion processes.  相似文献   
67.
68.
69.
70.
The corresponding 2-bromomethyl derivatives of benzofuran and indole were obtained by bromination of 2-methyl-3-carbethoxy-5-methoxybenzofuran and 1,2-dimethyl-3-earbethoxy-5-methoxyindole with N-bromosuccinimide. A number of alkyl(aryl)thiomethyl and dialkylaminomethyl derivatives were obtained by reaction of the 2-bromomethyl derivatives with nucleophilic reagents.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 308–311, March, 1973.  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