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   250359篇
  免费   2760篇
  国内免费   1117篇
化学   118098篇
晶体学   3274篇
力学   14271篇
综合类   7篇
数学   49479篇
物理学   69107篇
  2021年   1023篇
  2020年   1147篇
  2019年   1181篇
  2018年   11374篇
  2017年   11166篇
  2016年   8302篇
  2015年   2809篇
  2014年   2840篇
  2013年   8244篇
  2012年   10110篇
  2011年   18281篇
  2010年   10424篇
  2009年   10972篇
  2008年   13823篇
  2007年   15905篇
  2006年   7402篇
  2005年   8015篇
  2004年   7513篇
  2003年   7162篇
  2002年   6102篇
  2001年   6323篇
  2000年   4882篇
  1999年   3677篇
  1998年   2837篇
  1997年   2810篇
  1996年   2833篇
  1995年   2477篇
  1994年   2309篇
  1993年   2173篇
  1992年   2442篇
  1991年   2424篇
  1990年   2112篇
  1989年   2124篇
  1988年   2151篇
  1987年   2061篇
  1986年   1973篇
  1985年   2891篇
  1984年   2882篇
  1983年   2299篇
  1982年   2513篇
  1981年   2389篇
  1980年   2345篇
  1979年   2278篇
  1978年   2340篇
  1977年   2280篇
  1976年   2207篇
  1975年   2188篇
  1974年   2076篇
  1973年   2160篇
  1972年   1234篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Homogenous amphiphilic crosslinked polymer films comprising of poly(ethylene oxide) and polysiloxane were synthesized utilizing thiol‐ene “ click ” photochemistry. A systematic variation in polymer composition was Carried out to obtain high quality films with varied amount of siloxane and poly(ethylene oxide). These films showed improved gas separation performance with high gas permeabilities with good CO2/N2 selectivity. Furthermore, the resulting films were also tested for its biocompatibility, as a carrier media which allow human adult mesenchymal stem cells to retain their capacity for osteoblastic differentiation after transplantation. The obtained crosslinked films were characterized using differential scanning calorimetry, dynamic mechanical analysis, thermogravimetric analysis, FTIR, Raman‐IR , and small angle X‐ray scattering. The synthesis ease and commercial availability of the starting materials suggests that these new crosslinked polymer networks could find applications in wide range of applications. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1548–1557  相似文献   
62.
63.
π-Extended molecules are key components for the development of materials science. In fact, polyaromatic structures are fundamental for the scientific and technological progress of fields such as organic electronics and bio-applications. Beneficial properties of π-extended structures are absorption in the visible region, often luminescence, high electron mobilities and stability. Common approaches to adjust the properties of polyaromatic structures to functional setups involve changes in shape and size at the molecular level. Recently, incorporating hetero-elements emerged as successful approach. In this regard, organophosphorus conjugated molecules are new materials holding great promise for potential applications. In this review, we comprehensively discuss the design/development of polyaromatic phosphorus materials and their applicability. We establish structure/property/applicability relationships to provide key guidelines for the engineering of newer, future applications. This article thus provides a source of information for the further development of this rapidly evolving field of research.  相似文献   
64.
65.
66.
67.
Li  C.  Zhang  D.  Cheng  G.  Zhu  Y. 《Experimental Mechanics》2020,60(3):329-343
Experimental Mechanics - There have been relatively few studies on mechanical properties of nanomaterials under high strain rates, mainly due to the lack of capable nanomechanical testing devices....  相似文献   
68.
We give the form of the output function in Ginsburg’s machine in which the input and output dictionaries are abelian groups and the transition function is of a special form.  相似文献   
69.
70.
The first immobilized catalyst for Ir‐catalyzed asymmetric allylic aminations is described. The catalyst is a cationic (π‐allyl)Ir complex bound by cation exchange to an anionic silica gel support. Preparation of the catalyst is facile, and the supported catalyst displayed considerably enhanced activity compared with the parent homogeneous catalyst. Up to 43 consecutive amination runs were possible in recycling experiments.  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