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   585887篇
  免费   6198篇
  国内免费   1898篇
化学   306643篇
晶体学   8835篇
力学   26229篇
综合类   14篇
数学   71374篇
物理学   180888篇
  2021年   4519篇
  2020年   4955篇
  2019年   5399篇
  2018年   6797篇
  2017年   6902篇
  2016年   10499篇
  2015年   6778篇
  2014年   10509篇
  2013年   27276篇
  2012年   20764篇
  2011年   25280篇
  2010年   17477篇
  2009年   17306篇
  2008年   22829篇
  2007年   23109篇
  2006年   21676篇
  2005年   19221篇
  2004年   17737篇
  2003年   15696篇
  2002年   15544篇
  2001年   17673篇
  2000年   13433篇
  1999年   10704篇
  1998年   8837篇
  1997年   8598篇
  1996年   8375篇
  1995年   7447篇
  1994年   7188篇
  1993年   6985篇
  1992年   7710篇
  1991年   7813篇
  1990年   7411篇
  1989年   7204篇
  1988年   7231篇
  1987年   7055篇
  1986年   6755篇
  1985年   9163篇
  1984年   9297篇
  1983年   7638篇
  1982年   8047篇
  1981年   7837篇
  1980年   7587篇
  1979年   7934篇
  1978年   8016篇
  1977年   7941篇
  1976年   7911篇
  1975年   7635篇
  1974年   7388篇
  1973年   7611篇
  1972年   4922篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
To further evaluate the causality between endogenous pyrogen (EP)-induced fever and cyclic adenosine-3',5'-monophosphate (cyclic AMP) level, the effects of sodium salicylate (SS) on the febrile response and increased levels of cyclic AMP in both cerebrospinal fluid (c.s.f.) and plasma during EP-induced fever in rabbits were observed. The results suggest that cyclic AMP is probably involved in the central mediation of EP-induced fever and that increased concentration of cyclic AMP in c.s.f. associated with EP-induced fever is not the result of temperature elevation but appears to be caused by the increased synthesis in the central nervous system. In addition it is confirmed that blood is impossibly a contributory source of increased cyclic AMP in c.s.f. during EP fever, and that SS may act subsequent to the increase in cyclic AMP.  相似文献   
22.
Crystalline materials that are transparent in the vacuum UV spectral region and currently used have been reviewed. Transmission of crystals of solid solutions with the fluorite structure Ca1?x R xF2+x (R = Sc, Y, La, Yb, Lu) in the UV and vacuum UV spectral regions has been investigated. It is shown that application of different methods of purification of fluorides from some impurities can significantly improve the optical quality of fluoride multicomponent crystals in the short-wavelength spectral region.  相似文献   
23.
24.
25.
26.
27.
A three-dimensional examination of blood vessels is provided using MR data from seven cases. The vascular surfaces are constructed with an algorithm that automatically follows the selected artery or vein and generates a projected three-dimensional gradient shaded image. Fast 3DFT pulse sequences were optimized to enhance the time-of-flight contrast of the intravascular region. By increasing the surface threshold value in a three-dimensional head study, the flesh of a patient's face was peeled away to demonstrate the superfacial temporal artery. Gated cardiac images show the great vessels and cardiac chambers. A three-dimensional view of the aorta shows an irregular surface in the vicinity of an adrenal tumor. 3D MR exams provide a non-invasive technique for assessing vascular morphology in a clinical setting.  相似文献   
28.
Considering the importance of the X-ray production cross sections for the determination of the element concentrations in a given material, we have measured them experimentally for Al Si, Sc, Ti, V, Fe, Co, Ni and Cu bombarded by protons with energies ranging from 40 to 180 keV. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
29.
Summary The adsorption of gaseous molecular iodine on clean silver surfaces proceeds in the first stage by dissociative chemisorption. After the formation of half a monolayer of chemisorbed iodine atoms the formation of silver iodide begins, which forms a very regular overlayer on top of the substrate. Both iodine species can be distinguished due to a difference in chemical shift of the M4N4, 5N4, 5-Auger transitions. After completion of this overlayer further iodine uptake is slowed down significantly. Above an overlayer thickness of about 10 nm a further progress of the reaction cannot be followed anymore due to the limited information depth of XPS.  相似文献   
30.
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