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   25346篇
  免费   948篇
  国内免费   144篇
化学   16974篇
晶体学   258篇
力学   762篇
数学   2358篇
物理学   6086篇
  2023年   156篇
  2022年   453篇
  2021年   595篇
  2020年   454篇
  2019年   469篇
  2018年   418篇
  2017年   397篇
  2016年   751篇
  2015年   648篇
  2014年   894篇
  2013年   1553篇
  2012年   1881篇
  2011年   2071篇
  2010年   1321篇
  2009年   1139篇
  2008年   1715篇
  2007年   1491篇
  2006年   1527篇
  2005年   1302篇
  2004年   1148篇
  2003年   970篇
  2002年   926篇
  2001年   556篇
  2000年   503篇
  1999年   350篇
  1998年   217篇
  1997年   212篇
  1996年   278篇
  1995年   193篇
  1994年   205篇
  1993年   207篇
  1992年   156篇
  1991年   133篇
  1990年   129篇
  1989年   107篇
  1988年   68篇
  1987年   76篇
  1986年   53篇
  1985年   78篇
  1984年   55篇
  1983年   45篇
  1982年   65篇
  1981年   63篇
  1979年   48篇
  1978年   45篇
  1977年   34篇
  1976年   42篇
  1975年   37篇
  1974年   36篇
  1973年   34篇
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
991.
992.
Journal of the Korean Physical Society - In intensity-modulated radiosurgery (IMRS) treatment, radiation delivery techniques require the ability to accurately verify complex three-dimensional (3D)...  相似文献   
993.
The self-assembly of short peptides gives rise to versatile nanomaterials capable of promoting efficient catalysis. We have shown that short, seven-residue peptides bind hemin to produce functional catalytic materials which display highly efficient peroxidation activity, reaching a catalytic efficiency of 3×105 m −1 s−1. Self-assembly is essential for catalysis as non-assembling controls show no activity. We have also observed peroxidase activity even in the absence of hemin, suggesting the potential to alter redox properties of substrates upon association with the assemblies. These results demonstrate the practical utility of self-assembled peptides in various catalytic applications and further support the evolutionary link between amyloids and modern-day enzymes.  相似文献   
994.
N-substituted anilines react with triethanolamine in the presence of a catalytic amount of a homogeneous ruthenium catalyst to give the corresponding 1-substituted indoles in good yields.  相似文献   
995.
Abstract

Bola-amphiphiles having two aza-18-crown-6 ether rings attached by a covalent spacer (O—O) and an analogous tris (macrocycle) (O—O—O) have been prepared and their cation complexation behavior has been assessed by fast atom bombardment and collisionally activated dissociation tandem mass spectrometry; the key finding is that two cations may simultaneously be complexed by a two- or three-crown system and that this complexation may also involve an anion.  相似文献   
996.
997.
We demonstrate the directional alignment of perpendicular‐lamellae domains in fluorinated three‐armed star block polymer (BP) thin films using solvent vapor annealing with shear stress. The control of orientation and alignment was accomplished without any substrate surface modification. Additionally, three‐armed star poly(methyl methacrylate‐block‐styrene) [PMMA‐PS] and poly(octafluoropentyl methacrylate‐block‐styrene) were compared to their linear analogues to examine the impact of fluorine content and star architecture on self‐assembled BP feature sizes and interdomain density profiles. X‐ray reflectometry results indicated that the star BP molecular architecture increased the effective polymer segregation strength and could possibly facilitate reduced polymer domain spacings, which are useful in next‐generation nanolithographic applications. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1663–1672  相似文献   
998.
999.
To address tremendous needs for developing efficiently heat dissipating materials with lightweights, a series of liquid crystalline epoxy resins (LCEs) are designed and synthesized as thermally conductive matrix. All prepared LCEs possess epoxies at the molecular side positions and cyanobiphenyl mesogenic end groups. Based on several experimental results such as differential scanning calorimetry, polarized optical microscopy, and X‐ray diffraction, it is found that the LCEs exhibited liquid crystalline mesophases. When LCE is cured with a diamine crosslinker, the cured LCE maintains the oriented LC domain formed in the uncured state, ascribing to a presence of dipole–diploe and π–π interactions between cyanobiphenyl mesogenic end groups. Due to the anisotropic molecular orientation, the cured LCE exhibits a high thermal conductivity of 0.46 W m?1 K?1, which is higher than those of commercially available crystalline or amorphous epoxy resins. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 708–715  相似文献   
1000.
Journal of Radioanalytical and Nuclear Chemistry - U chlorination is demonstrated using electrochemical and chemical reactions with ZnCl2 in LiCl–KCl molten salts. Voltammetric studies...  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