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   1456篇
  免费   31篇
  国内免费   12篇
化学   935篇
晶体学   19篇
力学   10篇
数学   135篇
物理学   400篇
  2021年   11篇
  2020年   12篇
  2019年   23篇
  2018年   8篇
  2017年   15篇
  2016年   21篇
  2015年   16篇
  2014年   32篇
  2013年   66篇
  2012年   75篇
  2011年   95篇
  2010年   38篇
  2009年   48篇
  2008年   82篇
  2007年   83篇
  2006年   86篇
  2005年   88篇
  2004年   84篇
  2003年   68篇
  2002年   52篇
  2001年   38篇
  2000年   32篇
  1999年   18篇
  1998年   19篇
  1997年   21篇
  1996年   24篇
  1995年   9篇
  1994年   16篇
  1993年   15篇
  1992年   15篇
  1991年   18篇
  1990年   15篇
  1989年   17篇
  1988年   17篇
  1987年   8篇
  1986年   13篇
  1985年   23篇
  1984年   26篇
  1983年   11篇
  1982年   17篇
  1981年   19篇
  1980年   15篇
  1979年   11篇
  1978年   12篇
  1976年   8篇
  1975年   16篇
  1974年   5篇
  1973年   8篇
  1972年   5篇
  1968年   4篇
排序方式: 共有1499条查询结果,搜索用时 15 毫秒
71.
72.
73.
Objective: To investigate the significance of intra-abdominal fat area (IAFA) on new onset of individual components of the metabolic syndrome: high blood pressure, dyslipidemia, or hyperglycemia. Methods: We conducted a longitudinal study using checkup data of a hospital from 1994 to 2010. Of 25,255 subjects, we examined 1,380 Japanese, who underwent computed tomography to measure IAFA and had no metabolic syndrome components at baseline. Results: During 3.6 years of the mean follow-up period, one of metabolic syndrome components occurred in 752 subjects. Of three components, high blood pressure was more prevalent. The multiple Cox regression analysis disclosed that IAFA is significantly associated with onset of metabolic syndrome components (HR: 1.05 per 10 cm2, 95%CI: 1.03–1.07). This finding was independent of BMI, and significant even in non-obese individuals with body mass index <25 kg/m2. Conclusions: MERLOT study demonstrates that IAFA is an independent predictor for new onset of individual components of the metabolic syndrome, even in non-obese healthy Japanese.  相似文献   
74.
Abstract

Ultraviolet photoelectron spectra of potassium dosed higher fullerenes are measured with a synchrotron radiation light source. Potassium dosing to higher fullerenes brings a new structure between the spectral onset of pristine fullerenes and the Fermi level. As the spectral edge of the new structure does not cross the Fermi level, potassium dosed higher fullerenes are not metallic but semiconductive. When the potassium is excessively dosed to the fullerenes, the lower binding energy structures above 5 eV become faint. In contrast to this phenomenon, four distinct structures appear between 5 and 14 eV.  相似文献   
75.
76.
The cyclization reaction of diarylethenes having an azulene ring occurs only via higher excited states. Novel diarylethenes having an azulene ring with a strong donor or acceptor were synthesized and examined in these reactions. A derivative having an electron-donating 1,3-benzodithiol-2-ylidenemethyl group at the 1-position of the azulene ring showed photochromism, whereas neither a derivative having a π-conjugated electron-donating group at the 3-position of the azulene ring nor derivatives having a π-conjugated electron-withdrawing group at the 1- or 3-position of the azulene ring showed any photochromism. The photoreactivities of these compounds were explained by calculating forces and bond orders on the excited states using density functional theory (DFT) and time-dependent (TD)-DFT.  相似文献   
77.
Abstract

Novel metal-carbene complexes (4) with a metallapentalene framework have been obtained from hypervalent diazadiselenathiapentalenes (3) by treating with Pt(PPh3)4, Pd(PPh3)4 and RhCl(PPh3)3. X-Ray investigations revealed that the central hypervalent sulfur atom in 3 was substituted by a metal atom to form M-Se bonds in the resultant metallapentalene framework.  相似文献   
78.
Abstract

The deformation electron-density distributions of 6a-thia-1,3,4,6-tetraazapentalene derivatives (I, II) and bis(phenylthio)dibenzothiophene (III) were investigated by the X-ray diffraction method. For I and II, a structure around the hypervalent S-N bonds is a trigonal bipyramid with equatorial sp2 hybrid of S-C bond and lone-pair electrons and apical polarized S-N bonds. In 111 lone-pair electron densities are observed perpendicular to the thiophene ring and the C-S-C sulfide planes.  相似文献   
79.
80.
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