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   59024篇
  免费   13671篇
  国内免费   69篇
化学   65192篇
晶体学   106篇
力学   2101篇
数学   3397篇
物理学   1968篇
  2024年   386篇
  2023年   4206篇
  2022年   2499篇
  2021年   4053篇
  2020年   6584篇
  2019年   4222篇
  2018年   2335篇
  2017年   690篇
  2016年   5754篇
  2015年   5667篇
  2014年   5123篇
  2013年   5324篇
  2012年   3567篇
  2011年   1477篇
  2010年   3623篇
  2009年   3506篇
  2008年   1362篇
  2007年   1052篇
  2006年   410篇
  2005年   323篇
  2004年   289篇
  2003年   235篇
  2002年   223篇
  2001年   145篇
  1997年   160篇
  1996年   143篇
  1995年   212篇
  1994年   169篇
  1993年   258篇
  1992年   145篇
  1989年   120篇
  1988年   144篇
  1987年   122篇
  1984年   118篇
  1982年   137篇
  1981年   169篇
  1980年   213篇
  1979年   197篇
  1978年   205篇
  1977年   319篇
  1976年   367篇
  1975年   459篇
  1974年   472篇
  1973年   285篇
  1972年   370篇
  1971年   357篇
  1970年   541篇
  1969年   413篇
  1968年   470篇
  1967年   115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