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   218969篇
  免费   1853篇
  国内免费   647篇
化学   120313篇
晶体学   3295篇
力学   8501篇
综合类   6篇
数学   23946篇
物理学   65408篇
  2020年   2000篇
  2019年   2294篇
  2018年   3243篇
  2017年   3150篇
  2016年   4323篇
  2015年   2443篇
  2014年   3900篇
  2013年   9484篇
  2012年   7054篇
  2011年   8623篇
  2010年   6191篇
  2009年   6031篇
  2008年   8302篇
  2007年   8362篇
  2006年   7798篇
  2005年   7121篇
  2004年   6318篇
  2003年   5777篇
  2002年   5646篇
  2001年   5994篇
  2000年   4750篇
  1999年   3532篇
  1998年   3047篇
  1997年   3103篇
  1996年   2896篇
  1995年   2380篇
  1994年   2474篇
  1993年   2507篇
  1992年   2643篇
  1991年   2708篇
  1990年   2598篇
  1989年   2577篇
  1988年   2497篇
  1987年   2466篇
  1986年   2380篇
  1985年   3113篇
  1984年   3254篇
  1983年   2604篇
  1982年   2892篇
  1981年   2774篇
  1980年   2556篇
  1979年   2782篇
  1978年   2900篇
  1977年   2929篇
  1976年   2882篇
  1975年   2740篇
  1974年   2712篇
  1973年   2848篇
  1972年   1892篇
  1967年   1846篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
92.
93.
Kim  F. H.  Moylan  S. P.  Phan  T. Q.  Garboczi  E. J. 《Experimental Mechanics》2020,60(7):987-1004
Experimental Mechanics - Insufficient data are available to fully understand the effects of metal additive manufacturing (AM) defects for widespread adoption of the emerging technology....  相似文献   
94.
Journal of Analytical Chemistry - A new liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) method has been developed and validated for alfuzosin quantification in...  相似文献   
95.
π-Extended molecules are key components for the development of materials science. In fact, polyaromatic structures are fundamental for the scientific and technological progress of fields such as organic electronics and bio-applications. Beneficial properties of π-extended structures are absorption in the visible region, often luminescence, high electron mobilities and stability. Common approaches to adjust the properties of polyaromatic structures to functional setups involve changes in shape and size at the molecular level. Recently, incorporating hetero-elements emerged as successful approach. In this regard, organophosphorus conjugated molecules are new materials holding great promise for potential applications. In this review, we comprehensively discuss the design/development of polyaromatic phosphorus materials and their applicability. We establish structure/property/applicability relationships to provide key guidelines for the engineering of newer, future applications. This article thus provides a source of information for the further development of this rapidly evolving field of research.  相似文献   
96.
97.
98.
Optics and Spectroscopy - The population kinetics of a two-level system has been theoretically investigated taking into account the transfer of spontaneous radiation under continuous optical...  相似文献   
99.
We describe the synthesis and the physical properties of polyaromatic hydrocarbons (PAHs) containing a phosphorus atom at the edge. In particular, the impact of the successive addition of aromatic rings on the electronic properties was investigated by experimental (UV/Vis absorption, fluorescence, cyclic voltammetry) and theoretical studies (DFT). The physical properties recorded in solution and in the solid state showed that the P‐containing PAHs exhibit properties expected for an emitter in white organic light‐emitting diodes (WOLEDs).  相似文献   
100.
The highly substituted mono-aryl/alkylthio-(hetero)acenes prepared in this study have been found to be thermally more stable (Tdecomp.=331–354 °C) than the known di-aryl/alkylthio-substituted acenes by an average of 25 °C. They are also much more photostable at 254 and 365 nm (in both argon and air) than the parent anthracene and other reported anthracenes. The most photostable aryl/alkylthio-anthracenes at 254 nm were found to be 60–70 (in air) and 130 (in argon) times more stable in solution than the unsubstituted anthracene, and much more stable than known EDG/EWG-substituted anthracenes (EDG=electron-donating group, EWG=electron-withdrawing group) with an extended aromatic core. Furthermore, the acenes showed significantly higher photostability at 365 nm in both air and argon. The anthracenes were obtained by the novel thio-Friedel–Crafts/Bradsher cyclization reaction of hitherto unknown [o-(1,3-dithian-2-yl)aryl](aryl)methyl thioethers. The developed approach provides a general access to mono-aryl/alkylthio-substituted (hetero)acene frameworks containing at least three fused (hetero)aromatic rings. The characteristic feature of this approach, which leads to highly substituted acenes, is that the substituents, unlike in other methods, may be introduced at an early stage of the synthesis. DFT and TD-DFT calculations confirmed the stabilizing role of the aryl/alkylthio substituent in the mono-aryl/alkylthio-substituted anthracenes, which are the most stable anthracenes prepared to date. Their high photostability is mainly due to the quenching of singlet oxygen by the acene and the quenching of the acene S1 state by molecular oxygen.  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