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   54678篇
  免费   13616篇
  国内免费   62篇
化学   62165篇
晶体学   67篇
力学   2057篇
数学   2837篇
物理学   1230篇
  2024年   379篇
  2023年   4183篇
  2022年   2515篇
  2021年   4031篇
  2020年   6484篇
  2019年   4094篇
  2018年   2295篇
  2017年   623篇
  2016年   5615篇
  2015年   5552篇
  2014年   4979篇
  2013年   5189篇
  2012年   3255篇
  2011年   1078篇
  2010年   3440篇
  2009年   3404篇
  2008年   1088篇
  2007年   811篇
  2006年   179篇
  2005年   124篇
  2004年   85篇
  1997年   86篇
  1996年   84篇
  1995年   140篇
  1994年   88篇
  1993年   214篇
  1992年   97篇
  1988年   114篇
  1987年   98篇
  1985年   101篇
  1984年   105篇
  1983年   101篇
  1982年   128篇
  1981年   154篇
  1980年   195篇
  1979年   184篇
  1978年   189篇
  1977年   309篇
  1976年   361篇
  1975年   456篇
  1974年   471篇
  1973年   284篇
  1972年   369篇
  1971年   356篇
  1970年   541篇
  1969年   413篇
  1968年   470篇
  1967年   114篇
  1966年   89篇
  1963年   112篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
An efficient and convenient synthesis of useful linear cyclopentenone‐fused polycyclic compounds has been achieved through a novel gold(I)‐catalyzed transformation of diynes. The method demonstrates high product yields and tolerates of a wide variety of important functional groups. Gold‐vinylidene formation, methoxy group migration, and Nazarov‐type cyclization are proposed to be the key steps in the reaction pathway. The synthetic utility of this method is demonstrated by converting the product to eight‐membered‐ring‐fused compound.  相似文献   
62.
Control of boronic acid speciation is presented as a strategy to achieve nucleophile chemoselectivity in the Suzuki–Miyaura reaction. Combined with simultaneous control of oxidative addition and transmetalation, this enables chemoselective formation of two C? C bonds in a single operation, providing a method for the rapid preparation of highly functionalized carbogenic frameworks.  相似文献   
63.
64.
Gold nanoparticles (AuNPs) are subjects of broad interest in scientific community due to their promising physicochemical properties. Herein we report the facile and controlled light‐mediated preparation of gold nanoparticles through a Norrish type I reaction of photoactive polymers. These carefully designed polymers act as reagents for the photochemical reduction of gold ions, as well as stabilizers for the in situ generated AuNPs. Manipulating the length and composition of the photoactive polymers allows for control of AuNP size. Nanoparticle diameter can be controlled from 1.5 nm to 9.6 nm.  相似文献   
65.
66.
67.
68.
69.
Metagenomic studies suggest that only a small fraction of the viruses that exist in nature have been identified and studied. Characterization of unknown viral genomes is hindered by the many genomes populating any virus sample. A new method is reported that integrates drop‐based microfluidics and computational analysis to enable the purification of any single viral species from a complex mixed virus sample and the retrieval of complete genome sequences. By using this platform, the genome sequence of a 5243 bp dsDNA virus that was spiked into wastewater was retrieved with greater than 96 % sequence coverage and more than 99.8 % sequence identity. This method holds great potential for virus discovery since it allows enrichment and sequencing of previously undescribed viruses as well as known viruses.  相似文献   
70.
A general and efficient access to aryl, heteroaryl, vinyl and alkynyl difluoromethylphosphonates is described. The developed methodology using TMSCF2PO(OEt)2, iodonium salts and a copper salt provided a straightforward manifold to reach these highly relevant products. The reaction proved to be highly functional group tolerant and proceeded under mild conditions, giving the corresponding products in good to excellent yields. This method represents the first general synthetic route to this important class of fluorinated scaffolds, which are well‐recognized as in vivo stable phosphate surrogates.  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