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   328899篇
  免费   4912篇
  国内免费   1087篇
化学   180628篇
晶体学   4561篇
力学   13284篇
综合类   7篇
数学   39205篇
物理学   97213篇
  2020年   2233篇
  2019年   2219篇
  2018年   2331篇
  2017年   2195篇
  2016年   4495篇
  2015年   3729篇
  2014年   4931篇
  2013年   15037篇
  2012年   11783篇
  2011年   14413篇
  2010年   8861篇
  2009年   8799篇
  2008年   13212篇
  2007年   13472篇
  2006年   13015篇
  2005年   11868篇
  2004年   10696篇
  2003年   9331篇
  2002年   9116篇
  2001年   10357篇
  2000年   7967篇
  1999年   6302篇
  1998年   5022篇
  1997年   4858篇
  1996年   4945篇
  1995年   4507篇
  1994年   4274篇
  1993年   4083篇
  1992年   4565篇
  1991年   4410篇
  1990年   4124篇
  1989年   3936篇
  1988年   4205篇
  1987年   3871篇
  1986年   3768篇
  1985年   5437篇
  1984年   5518篇
  1983年   4447篇
  1982年   4828篇
  1981年   4873篇
  1980年   4634篇
  1979年   4723篇
  1978年   4722篇
  1977年   4709篇
  1976年   4647篇
  1975年   4556篇
  1974年   4392篇
  1973年   4566篇
  1972年   2589篇
  1971年   1901篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Kim  F. H.  Moylan  S. P.  Phan  T. Q.  Garboczi  E. J. 《Experimental Mechanics》2020,60(7):987-1004
Experimental Mechanics - Insufficient data are available to fully understand the effects of metal additive manufacturing (AM) defects for widespread adoption of the emerging technology....  相似文献   
103.
A model is developed for the formation and propagation of cracks in a material sample that is heated at its top surface, pyrolyses, and then thermally degrades to form char. In this work the sample is heated uniformly over its entire top surface by a hypothetical flame (a heat source). The pyrolysis mechanism is described by a one-step overall reaction that is dependent nonlinearly on the temperature (Arrhenius form). Stresses develop in response to the thermal degradation of the material by means of a shrinkage strain caused by local mass loss during pyrolysis. When the principal stress exceeds a prescribed threshold value, the material forms a local crack. Cracks are found to generally originate at the surface in response to heating, but occasionally they form in the bulk, away from ever-changing material boundaries. The resulting cracks evolve and form patterns whose characteristics are described. Quantities examined in detail are: the crack spacing in the pyrolysis zone; the crack length evolution; the formation and nature of crack loops which are defined as individual cracks that have joined to form loops that are disconnected from the remaining material; the formation of enhanced pyrolysis area; and the impact of all of the former quantities on mass flux. It is determined that the mass flux from the sample can be greatly enhanced over its nominal (non-cracking) counterpart. The mass efflux profile qualitatively resembles those observed in Cone Calorimeter tests.  相似文献   
104.
105.
106.
Shi  D.  Feng  J.  Wang  J.  Zhao  W.  Li  X. 《Kinetics and Catalysis》2020,61(5):750-757
Kinetics and Catalysis - A series of Cu-SSZ-13@CeO2 catalysts with surface modification with CeO2 was prepared by the modified self-resemble method based on the one-pot synthesized Cu-SSZ-13...  相似文献   
107.
The current work utilizes three separate techniques to study the physical aging process in amorphous poly(ethylene furanoate) (PEF), which is a recently introduced engineering thermoplastic with enhanced properties compared to petroleum‐sourced poly(ethylene terephthalate). Differential scanning calorimetry aging experiments were conducted at multiple aging temperatures and times, and the resultant enthalpic recovery values compared to the theoretical maximum enthalpy loss evaluated from calculations involving extrapolation of the equilibrium liquid line. Density measurements reveal densification of the matrix for the aged versus unaged samples, and provide an estimate for the reduction in free volume for the aged samples. Complementary oxygen permeation and pressure‐decay sorption experiments provide independent verification of the free volume reduction mechanism for physical aging in glassy polymers. The current work provides the first detailed aging study for PEF. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 389–399  相似文献   
108.
We describe the synthesis and the physical properties of polyaromatic hydrocarbons (PAHs) containing a phosphorus atom at the edge. In particular, the impact of the successive addition of aromatic rings on the electronic properties was investigated by experimental (UV/Vis absorption, fluorescence, cyclic voltammetry) and theoretical studies (DFT). The physical properties recorded in solution and in the solid state showed that the P‐containing PAHs exhibit properties expected for an emitter in white organic light‐emitting diodes (WOLEDs).  相似文献   
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