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   214746篇
  免费   5522篇
  国内免费   3037篇
化学   122493篇
晶体学   3084篇
力学   9088篇
综合类   191篇
数学   20611篇
物理学   67838篇
  2019年   1917篇
  2018年   1949篇
  2017年   1895篇
  2016年   3246篇
  2015年   2667篇
  2014年   3503篇
  2013年   9347篇
  2012年   7035篇
  2011年   8519篇
  2010年   5669篇
  2009年   5569篇
  2008年   7383篇
  2007年   7424篇
  2006年   7038篇
  2005年   6318篇
  2004年   5673篇
  2003年   5038篇
  2002年   4898篇
  2001年   6194篇
  2000年   4817篇
  1999年   3960篇
  1998年   3140篇
  1997年   3167篇
  1996年   3161篇
  1995年   2861篇
  1994年   2749篇
  1993年   2540篇
  1992年   3023篇
  1991年   2882篇
  1990年   2770篇
  1989年   2762篇
  1988年   2692篇
  1987年   2674篇
  1986年   2492篇
  1985年   3348篇
  1984年   3335篇
  1983年   2761篇
  1982年   2855篇
  1981年   2794篇
  1980年   2680篇
  1979年   2837篇
  1978年   3090篇
  1977年   2902篇
  1976年   2851篇
  1975年   2703篇
  1974年   2651篇
  1973年   2680篇
  1968年   1926篇
  1967年   2128篇
  1966年   1921篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Journal of Thermal Analysis and Calorimetry - In recent decades, the growth of heat transfer using nanomaterials in the conventional base fluid has caught the attention of researchers...  相似文献   
42.
Journal of Thermal Analysis and Calorimetry - Low productivity of single-slope solar still is the main barrier for its worldwide usability. An attempt has been conducted to enhance the distillate...  相似文献   
43.
Human skin is exposed to visible light (VL; 400–700 nm) and long-wavelength ultraviolet A1 (UVA1) radiation (370–400 nm) after the application of organic broad-spectrum sunscreens. The biologic effects of these wavelengths have been demonstrated; however, a dose–response has not been investigated. Ten subjects with Fitzpatrick skin phototype IV-VI were enrolled. Subjects were irradiated with 2 light sources (80–480 J cm−2): one comprising VL with less than 0.5% UVA1 (VL+UVA1) and the other pure VL. Skin responses were evaluated for 2 weeks using clinical and spectroscopic assessments. 4-mm punch biopsies were obtained from nonirradiated skin and sites irradiated with 480 J cm−2 of VL+UVA1 and pure VL 24 h after irradiation. Clinical and spectroscopic assessments demonstrated a robust response at VL+UVA1 sites compared with pure VL. Histology findings demonstrated a statistically significant increase in the marker of inflammation (P < 0.05) and proliferation (P < 0.05) at the irradiated sites compared with nonirradiated control. Threshold doses of VL+UVA1 resulting in biologic responses were calculated. Results indicate that approximately 2 h of sun exposure, which equates to VL+UVA1 dose (~400 J cm−2), is capable of inducing inflammation, immediate erythema and delayed tanning. These findings reinforce the need of photoprotection beyond the UV range.  相似文献   
44.
Embedding endohdedral metallofullerenes (EMFs) into electron donor–acceptor systems is still a challenging task owing to their limited quantities and their still largely unexplored chemical properties. In this study, we have performed a 1,3‐dipolar cycloaddition reaction of a corrole‐based precursor with Sc3N@C80 to regioselectively form a [5,6]‐adduct ( 1 ). The successful attachment of the corrole moiety was confirmed by mass spectrometry. In the electronic ground state, absorption spectra suggest sizeable electronic communications between the electron acceptor and the electron donor. Moreover, the addition pattern occurring at a [5,6]‐bond junction is firmly proven by NMR spectroscopy and electrochemical investigations performed with 1 . In the electronically excited state, which is probed in photophysical assays with 1 , a fast electron‐transfer yields the radical ion pair state consisting of the one‐electron‐reduced Sc3N@C80 and of the one‐electron‐oxidized corrole upon its exclusive photoexcitation. As such, our results shed new light on the practical work utilizing EMFs as building blocks in photovoltaics.  相似文献   
45.
46.
47.
48.
49.
50.
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