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   1558篇
  免费   60篇
  国内免费   8篇
化学   916篇
晶体学   8篇
力学   17篇
数学   310篇
物理学   375篇
  2022年   12篇
  2021年   22篇
  2020年   22篇
  2019年   34篇
  2018年   23篇
  2017年   11篇
  2016年   41篇
  2015年   27篇
  2014年   40篇
  2013年   66篇
  2012年   58篇
  2011年   68篇
  2010年   40篇
  2009年   47篇
  2008年   82篇
  2007年   63篇
  2006年   78篇
  2005年   66篇
  2004年   50篇
  2003年   47篇
  2002年   51篇
  2001年   32篇
  2000年   27篇
  1999年   20篇
  1998年   20篇
  1997年   10篇
  1996年   28篇
  1995年   18篇
  1994年   25篇
  1993年   17篇
  1992年   28篇
  1991年   25篇
  1990年   27篇
  1989年   19篇
  1988年   19篇
  1987年   14篇
  1986年   16篇
  1985年   27篇
  1984年   24篇
  1983年   22篇
  1982年   25篇
  1981年   20篇
  1980年   18篇
  1979年   22篇
  1978年   27篇
  1977年   14篇
  1976年   23篇
  1975年   20篇
  1974年   9篇
  1973年   12篇
排序方式: 共有1626条查询结果,搜索用时 15 毫秒
141.
The total hadron multiplicity and the multiplicity in the three-jet events ine + e ?-annihilation are considered. The formula for the total multiplicity (with account for the heavy quark contribution) agrees well with experiment. The value of the multiplicity for three-jet events is predicted.  相似文献   
142.
143.
144.
When 4-nitro-AF4 is treated with nucleophiles such as alkoxides and cyanide, a novel ring opening, cyclophane destroying reaction is observed whereby, via an SNAr mechanism, the nucleophile attacks the bridgehead aryl carbon vicinal to the nitro group with subsequent aryl-CF2 bond cleavage.  相似文献   
145.
146.
147.
148.
Wireless mobile networks from the fifth generation (5G) and beyond serve as platforms for flexible support of heterogeneous traffic types with diverse performance requirements. In particular, the broadband services aim for the traditional rate optimization, while the time-sensitive services aim for the optimization of latency and reliability, and some novel metrics such as Age of Information (AoI). In such settings, the key question is the one of spectrum slicing: how these services share the same chunk of available spectrum while meeting the heterogeneous requirements. In this work we investigated the two canonical frameworks for spectrum sharing, Orthogonal Multiple Access (OMA) and Non-Orthogonal Multiple Access (NOMA), in a simple, but insightful setup with a single time-slotted shared frequency channel, involving one broadband user, aiming to maximize throughput and using packet-level coding to protect its transmissions from noise and interference, and several intermittent users, aiming to either to improve their latency-reliability performance or to minimize their AoI. We analytically assessed the performances of Time Division Multiple Access (TDMA) and ALOHA-based schemes in both OMA and NOMA frameworks by deriving their Pareto regions and the corresponding optimal values of their parameters. Our results show that NOMA can outperform traditional OMA in latency-reliability oriented systems in most conditions, but OMA performs slightly better in age-oriented systems.  相似文献   
149.
We have examined and subjected to analysis an exhaustive number of consumer products, including but not limited to lotions and cosmetics, herbal supplements, household cleaners, food items, and beverages. As a result we describe all those consumer products herein, to our knowledge, that are appropriately labelled as “Chemical free”.  相似文献   
150.
CF3CFBr2 was employed in catalytic olefination reactions of aromatic aldehydes. In situ prepared hydrazones of aldehydes were transformed to β-fluoro-β-(trifluoromethyl)styrenes by reaction with CF3CFBr2 under CuCl catalysis. Based on this reaction, a novel stereoselective approach towards β-fluoro-β-(trifluoromethyl)styrenes was elaborated. Nucleophilic vinylic substitution of fluorine by secondary amines, thiolates and alkoxides in β-fluoro-β-(trifluoromethyl)styrenes was also tested.  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