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   1352449篇
  免费   29653篇
  国内免费   7723篇
化学   674003篇
晶体学   20463篇
力学   75202篇
综合类   105篇
数学   243210篇
物理学   376842篇
  2021年   13565篇
  2020年   15952篇
  2019年   16085篇
  2018年   13864篇
  2016年   28474篇
  2015年   20915篇
  2014年   30510篇
  2013年   74493篇
  2012年   38680篇
  2011年   36435篇
  2010年   37849篇
  2009年   40186篇
  2008年   35200篇
  2007年   31257篇
  2006年   36115篇
  2005年   29082篇
  2004年   30190篇
  2003年   28327篇
  2002年   29257篇
  2001年   29073篇
  2000年   24980篇
  1999年   22623篇
  1998年   21106篇
  1997年   21110篇
  1996年   21157篇
  1995年   19208篇
  1994年   18676篇
  1993年   18194篇
  1992年   18255篇
  1991年   18522篇
  1990年   17719篇
  1989年   17774篇
  1988年   17334篇
  1987年   17339篇
  1986年   16280篇
  1985年   22707篇
  1984年   23910篇
  1983年   20082篇
  1982年   21712篇
  1981年   20945篇
  1980年   20294篇
  1979年   20539篇
  1978年   21760篇
  1977年   21366篇
  1976年   21075篇
  1975年   19729篇
  1974年   19379篇
  1973年   19829篇
  1972年   14307篇
  1967年   12561篇
排序方式: 共有10000条查询结果,搜索用时 15 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