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   1335329篇
  免费   29625篇
  国内免费   7809篇
化学   665232篇
晶体学   20262篇
力学   74690篇
综合类   105篇
数学   243557篇
物理学   368917篇
  2021年   13549篇
  2020年   15961篇
  2019年   16145篇
  2018年   12438篇
  2016年   27929篇
  2015年   20940篇
  2014年   30616篇
  2013年   74794篇
  2012年   37778篇
  2011年   34337篇
  2010年   36868篇
  2009年   39242篇
  2008年   33647篇
  2007年   29205篇
  2006年   36016篇
  2005年   28003篇
  2004年   29749篇
  2003年   28198篇
  2002年   29210篇
  2001年   27615篇
  2000年   24362篇
  1999年   22368篇
  1998年   21066篇
  1997年   21063篇
  1996年   21214篇
  1995年   19273篇
  1994年   18712篇
  1993年   18280篇
  1992年   18078篇
  1991年   18410篇
  1990年   17605篇
  1989年   17669篇
  1988年   17206篇
  1987年   17165篇
  1986年   16101篇
  1985年   22593篇
  1984年   23856篇
  1983年   20076篇
  1982年   21781篇
  1981年   20988篇
  1980年   20355篇
  1979年   20431篇
  1978年   21792篇
  1977年   21357篇
  1976年   21056篇
  1975年   19747篇
  1974年   19383篇
  1973年   19853篇
  1972年   14334篇
  1967年   12495篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
101.
A new amino‐functionalized strontium–carboxylate‐based metal–organic framework (MOF) has been synthesized that undergoes single crystal to single crystal (SC‐to‐SC) transformation upon desolvation. Both structures have been characterized by single‐crystal X‐ray analysis. The desolvated structure shows an interesting 3D porous structure with pendent ?NH2 groups inside the pore wall, whereas the solvated compound possesses a nonporous structure with DMF molecules on the metal centers. The amino group was postmodified through Schiff base condensation by pyridine‐2‐carboxaldehyde and palladium was anchored on that site. The modified framework has been utilized for the Suzuki cross‐coupling reaction. The compound shows high activity towards the C?C cross‐coupling reaction with good yields and turnover frequencies. Gas adsorption studies showed that the desolvated compound had permanent porosity and was microporous in nature with a BET surface area of 2052 m2 g?1. The material also possesses good CO2 (8 wt %) and H2 (1.87 wt %) adsorption capabilities.  相似文献   
102.
In many organic electronic devices functionality is achieved by blending two or more materials, typically polymers or molecules, with distinctly different optical or electrical properties in a single film. The local scale morphology of such blends is vital for the device performance. Here, a simple approach to study the full 3D morphology of phase‐separated blends, taking advantage of the possibility to selectively dissolve the different components is introduced. This method is applied in combination with AFM to investigate a blend of a semiconducting and ferroelectric polymer typically used as active layer in organic ferroelectric resistive switches. It is found that the blend consists of a ferroelectric matrix with three types of embedded semiconductor domains and a thin wetting layer at the bottom electrode. Statistical analysis of the obtained images excludes the presence of a fourth type of domains. The criteria for the applicability of the presented technique are discussed. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1231–1237  相似文献   
103.
104.
Physics of Atomic Nuclei - We have studied the mechanisms influencing production of cumulative pions and protons in the fragmentation of the incident deuterons into cumulative pions and protons...  相似文献   
105.
106.
Unsteady transitions of separation patterns in single expansion ramp nozzle   总被引:2,自引:0,他引:2  
Y. Yu  J. Xu  K. Yu  J. Mo 《Shock Waves》2015,25(6):623-633
  相似文献   
107.
We have synthesized a series of triarylamine‐cored molecules equipped with an adjacent amide moiety and dendritic peripheral tails in a variety of modes. We show by 1H NMR and UV/Vis spectroscopy that their supramolecular self‐assembly can be promoted in solution upon light stimulation and radical initiation. In addition, we have probed their molecular arrangements and mesomorphic properties in the bulk by integrated studies on their film state by using differential scanning calorimetry (DSC), variable‐temperature polarizing optical microscopy (VT‐POM), variable‐temperature X‐ray diffraction (VT‐XRD), and atomic force microscopy (AFM). Differences in the number and the disposition of the peripheral tails significantly affect their mesomorphic properties associated with their lamellar‐ or columnar‐packed nanostructures, which are based on segregated stacks of the triphenylamine cores and the lipophilic/lipophobic periphery. Such structural tuning is of interest for implementation of these soft self‐assemblies as electroactive materials from solution to mesophases.  相似文献   
108.
109.
110.
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