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   1602篇
  免费   306篇
  国内免费   145篇
化学   1012篇
晶体学   9篇
力学   86篇
综合类   28篇
数学   216篇
物理学   702篇
  2024年   3篇
  2023年   29篇
  2022年   23篇
  2021年   39篇
  2020年   61篇
  2019年   65篇
  2018年   54篇
  2017年   35篇
  2016年   69篇
  2015年   63篇
  2014年   81篇
  2013年   108篇
  2012年   130篇
  2011年   145篇
  2010年   81篇
  2009年   90篇
  2008年   87篇
  2007年   93篇
  2006年   94篇
  2005年   78篇
  2004年   80篇
  2003年   50篇
  2002年   49篇
  2001年   27篇
  2000年   27篇
  1999年   40篇
  1998年   37篇
  1997年   25篇
  1996年   37篇
  1995年   29篇
  1994年   27篇
  1993年   26篇
  1992年   24篇
  1991年   23篇
  1990年   19篇
  1989年   25篇
  1988年   21篇
  1987年   12篇
  1986年   9篇
  1985年   8篇
  1984年   2篇
  1983年   3篇
  1982年   2篇
  1981年   2篇
  1980年   4篇
  1979年   4篇
  1978年   2篇
  1976年   4篇
  1973年   4篇
  1930年   1篇
排序方式: 共有2053条查询结果,搜索用时 15 毫秒
61.
62.
Nowadays sodium-based energy storage systems (Na-based ESSs) have been widely researched as it possesses the possibility to replace traditional energy storage media to become next generation energy storage system. However, due to the irreversible loss of sodium ions in the first cycle, development of Na-based ESSs is limited. Presodiation, as a strategy of adding excess sodium ions to the system in advance, accomplishes the enhancement of electrochemical performance. In this minireview, different presodiation strategies applied in sodium-based energy storage systems will be summarized in detail, their functions and corresponding mechanisms will be discussed as well. Furthermore, the current novel application of presodiation method in other aspects of Na-based ESSs will be mentioned additionally. At last, in the view of present research status of presodiation, issues that can be mitigated are put forward and guidelines are given on how to deliberate in-depth presodiation technology in the future, dedicating to promote the further development of Na-based ESSs.  相似文献   
63.
64.
65.
66.
Research on Chemical Intermediates - A highly efficient oligomer antimicrobial agent, polyhexamethylene guanidine hydrochloride (PHMGH), is added to mixtures of polyvinylpyrrolidone (PVP)/chitosan...  相似文献   
67.
A selective and effective oxidation of alcohols, except aliphatic alcohols, such as 1‐hexanol or 1‐octyl alcohol, to the corresponding aldehydes and ketones using a new reagent, iron(III) nitrate supported on aluminum silicate, under heterogeneous conditions with reflux with 85–98% yield is described.  相似文献   
68.
After the Higgs discovery, precise measurements of the Higgs properties and the electroweak observables become vital for the experimental particle physics. A powerful Higgs/Z factory, the Circular Electron Positron Collider (CEPC) is proposed. The Particle Flow oriented detector design is proposed to the CEPC and a Particle Flow algorithm, Arbor is optimized accordingly. We summarize the physics object reconstruction performance of the Particle Flow oriented detector design with Arbor algorithm and conclude that this combination fulfills the physics requirement of CEPC.  相似文献   
69.
A simple, rapid, and efficient oxidation of oximes to the corresponding ketones and aldehydes with manganese dioxide catalyzed by kieselguhr under solvent-free conditions at room temperature in the yields between 82 and 98 is described. It seems that kieselguhr in the present procedure can highly expedite the reaction rate. By comparing to other methods described previously, the main advantages of this oxidation are that the oxidations are more efficient, the reaction conditions are milder, the reaction times are shorter, and the work-up is easier. Furthermore, the amount of manganese dioxide used in this oxidation is largely decreased.  相似文献   
70.
Due to the rapid development and growth of computer networks, there have been greater and greater demands for remote password authentication protocols. Recently, the focus has been on protocols for multiserver environments that run on smart cards. These protocols typically count on the nonce or timestamp to provide protection against the replay attack. However, as Tsaur et al. pointed out, these protocols have some security issues such as disturbance in clock synchronization and vulnerability to the man-in-the-middle attack. In order to solve the above problems, Tsaur et al. proposed a multiserver authentication scheme with key agreement in 2012, and they claimed that their scheme could effectively achieve password-authenticated key agreement while getting around the technical difficulty of implementing clock synchronization in multiserver environments. Unfortunately, we found out that Tsaur et al.’s protocol still has the following weaknesses: (1) inability to resist privileged insider attack, (2) inability to resist known-plaintext attack, (3) inability to provide user anonymity, and (4) lack of perfect forward secrecy. To fix these secure flaws of Tsaur et al.’s protocol, in this paper, we shall propose an improved multiserver authentication protocol with key agreement based on extended chaotic maps. We shall also offer formal proof of smooth execution of the improved authenticated key agreement protocol.  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