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   633篇
  免费   13篇
  国内免费   9篇
化学   273篇
晶体学   5篇
力学   12篇
数学   273篇
物理学   92篇
  2023年   6篇
  2022年   18篇
  2021年   22篇
  2020年   8篇
  2019年   13篇
  2018年   12篇
  2017年   16篇
  2016年   19篇
  2015年   19篇
  2014年   15篇
  2013年   48篇
  2012年   39篇
  2011年   38篇
  2010年   32篇
  2009年   43篇
  2008年   37篇
  2007年   48篇
  2006年   33篇
  2005年   34篇
  2004年   19篇
  2003年   25篇
  2002年   19篇
  2001年   3篇
  2000年   8篇
  1999年   8篇
  1998年   5篇
  1997年   10篇
  1996年   6篇
  1995年   3篇
  1994年   2篇
  1993年   7篇
  1992年   4篇
  1991年   2篇
  1989年   2篇
  1987年   5篇
  1986年   2篇
  1985年   2篇
  1984年   6篇
  1983年   1篇
  1982年   4篇
  1981年   4篇
  1979年   1篇
  1978年   2篇
  1976年   2篇
  1974年   1篇
  1961年   1篇
  1929年   1篇
排序方式: 共有655条查询结果,搜索用时 171 毫秒
561.
Genera connections between quantifier elimination and decidability for first order theories are studied and exemplified.  相似文献   
562.
563.
Several types of lithium organocuprates (I) e.g. R2CuLi, RR'CuLi, R3CuLi2, R2CuLi2X (X- CN, SCN), were prepared and used as polymerization initiators for methyl methacrylate in THF at temperatures ranging from −30 to +20 *C. Polymerization initiated by a mixed homocuprate, e.g. lithium n-butyl (thien-2-yl)cuprate was studied in more detail. Kinetic measurements indicated an overall large (−4 to −14 kcal) apparent negative activation energy of polymerization in the −30 + +20 *C temperature range. The reaction was shown to have a kinetic order of about 1.5 with respect to initiator concentration. Conductance measurements indicate that the equivalent conductance increases with initiator concentration in the 10−2 + 10−1 M range indicating the formation of multiple ions formed by intermolecular association. The data are consistent with a polymerization involving aggregated ion pairs of as yet undetermined composition. The negative activation energy is tentatively interpreted as due to the exothermic formation of aggregates existing as highly solvated ion pairs.  相似文献   
564.
565.
We introduce a new type of coupling of reflecting Brownian motions in smooth planar domains, called scaling coupling. We apply this to obtain monotonicity properties of antisymmetric second Neumann eigenfunctions of convex planar domains with one line of symmetry. In particular, this gives the proof of the hot spots conjecture for some known types of domains and some new ones.

  相似文献   

566.
Several new coordination polymers of copper(II) with different carboxylate ligands containing siloxane units were synthesized by equilibrium polycoordination reactions of copper(II) acetate with the proper dicarboxylic acid (i.e. 1,3‐bis(3‐carboxypropyl)tetramethyldisiloxane, α,ω‐bis(3‐carboxypropyl)oligodimethylsiloxane, and 1,3‐bis(sebacomethyl)tetramethyldisiloxane) in solution (methanol), at room temperature. Some variations in the feed molar ratios were made. The resulting polymers having a polycoordination degree between 5 and 71 are soluble in a wide range of common organic solvents. The formation of polymers was proved by IR and UV–VIS absorption spectroscopy. The thermal behaviour of the coordination polymers was analysed by thermogravimetry in air. The silicon and copper contents and inherent viscosities were also determined. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   
567.
568.
569.

Zero sets of polynomials: one versus two variables

  相似文献   
570.
The treatment of chromium tanned sheepskins with poly(hydroxyl urethane) and dispersion of chemically synthesized nanosilver showed the best resistance to fungi and bacterial exposure tests. These collagen-based materials containing different amounts of nanosilver were investigated by Atomic Absorption Spectroscopy, Atomic Force Microscopy and Scanning Electron Microscopy coupled with Energy Dispersive X-Ray Spectroscopy. The influence of sheepskins treated with silver nanoparticles on the wound healing process was assessed and the nanoparticles concentration seems to have a positive effect up to 370 ppm and does not influence the inflammatory process above this concentration.  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