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   912篇
  免费   33篇
  国内免费   1篇
化学   681篇
晶体学   16篇
力学   31篇
数学   52篇
物理学   166篇
  2023年   4篇
  2022年   4篇
  2021年   7篇
  2020年   15篇
  2019年   15篇
  2018年   6篇
  2017年   6篇
  2016年   19篇
  2015年   20篇
  2014年   26篇
  2013年   62篇
  2012年   53篇
  2011年   44篇
  2010年   36篇
  2009年   22篇
  2008年   51篇
  2007年   55篇
  2006年   52篇
  2005年   49篇
  2004年   44篇
  2003年   38篇
  2002年   38篇
  2001年   14篇
  2000年   23篇
  1999年   12篇
  1998年   11篇
  1997年   9篇
  1996年   6篇
  1995年   7篇
  1994年   16篇
  1993年   13篇
  1992年   12篇
  1991年   9篇
  1990年   11篇
  1989年   10篇
  1988年   10篇
  1987年   14篇
  1986年   13篇
  1985年   12篇
  1984年   3篇
  1983年   3篇
  1982年   6篇
  1981年   6篇
  1980年   7篇
  1979年   6篇
  1978年   8篇
  1977年   5篇
  1976年   5篇
  1975年   6篇
  1974年   10篇
排序方式: 共有946条查询结果,搜索用时 15 毫秒
81.
82.
83.
Static light scattering measurements were performed on dilute solutions of monodisperse poly(ethylene oxide) (PEO) in methanol at 25°C. PEOs of five different molecular weights ranging from nominal Mw = 8.6 × 104 to 9.13 × 105 were used. Linear Zimm plots were obtained for all the PEO samples: no downturn was observed at small angles, indicating that no large aggregates of PEO molecules exist in the solution. From the plots, values of the weight-average molecular weight, Mw, the radius gyration, RG, and the second virial coefficient, A2, were successfully determined for respective PEOs. Observed relationship between RG and Mw indicates that methanol is certainly a good solvent for the polymer. © 1996 John Wiley & Sons, Inc.  相似文献   
84.
We have investigated unlignified tension wood and normally lignified wood celluloses inPopulus maximowiczii with particular reference to the composition of two crystalline phases I/I (triclinic/ monoclinic). Four independent techniques, which enable us to detect the two phases, CP/MAS13C NMR, Fourier transform infrared microscopy, selected-area electron diffraction, and X-ray diffraction were applied. Because of the low crystallinity of wood celluloses, particularly in the case of celluloses in the lignified cell wall, no single method was decisive enough to be able to determine the composition of the two phases as one can with highly crystalline materials. The I dominant structure (monoclinic crystal type) was, however, preferred for both tension and normal wood celluloses.  相似文献   
85.
Seasonal changes in diffuse ultraviolet (UV) and visible light attenuations and inherent optical properties in the lake water were monitored at the pelagic and littoral shallow zones of Lake Biwa which features a broad range of optical conditions within a single large water body. We considered the absorption factors that affect UV attenuation, and clarified the contribution of the absorption of suspended particles and chromophoric dissolved organic matter (CDOM) by multiple regression analyses of the monitoring data. The variability of UV attenuations in the lake demonstrated a strong contrast between the pelagic and the shallow zones. The latter were characterized by turbid systems supplying suspended matter as well as CDOM, whereas the former was far from the turbid systems in the littoral zone or the lake bottom. In this lake, the regulation of UV and light attenuations is rendered competitive by the absorption of suspended particles and CDOM in the lake water, hence, the UV penetration has both spatial and temporal variability based on changes in the physical and biological condition of the lake.  相似文献   
86.
87.
88.
89.
A new synthetic approach to quinazolines bearing a carboxy group is described. Reaction of 5-carbonyl substituted 1,3,6-tri-methyluracils (I) with dimethyl acetylenedicarboxylate or electron-deficient olefines affords quinazoline derivatives (III-VI) via pyrimidine(Z)-dienols (II) formed by base-catalyzed isomerization.  相似文献   
90.
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