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   212608篇
  免费   2767篇
  国内免费   527篇
化学   118121篇
晶体学   3349篇
力学   8387篇
综合类   12篇
数学   20187篇
物理学   65846篇
  2021年   1811篇
  2020年   2128篇
  2019年   2357篇
  2018年   2661篇
  2017年   2736篇
  2016年   4057篇
  2015年   2589篇
  2014年   4168篇
  2013年   10074篇
  2012年   7406篇
  2011年   8935篇
  2010年   6278篇
  2009年   6118篇
  2008年   7710篇
  2007年   7623篇
  2006年   7143篇
  2005年   6442篇
  2004年   5805篇
  2003年   5337篇
  2002年   5043篇
  2001年   6247篇
  2000年   4708篇
  1999年   3589篇
  1998年   2792篇
  1997年   2781篇
  1996年   2667篇
  1995年   2495篇
  1994年   2383篇
  1993年   2235篇
  1992年   2905篇
  1991年   2787篇
  1990年   2727篇
  1989年   2741篇
  1988年   2751篇
  1987年   2753篇
  1986年   2625篇
  1985年   3347篇
  1984年   3277篇
  1983年   2562篇
  1982年   2671篇
  1981年   2724篇
  1980年   2506篇
  1979年   2868篇
  1978年   2857篇
  1977年   2979篇
  1976年   2814篇
  1975年   2554篇
  1974年   2487篇
  1973年   2460篇
  1968年   1704篇
排序方式: 共有10000条查询结果,搜索用时 515 毫秒
41.
42.
43.
In order to investigate the characteristics of force chains in a granular flow system, a parallel plate shear cell is constructed to simulate the shear movement of an infinite parallel plate and observe variations in relevant parameters. The shear dilatancy process is divided into three stages, namely, plastic strain, macroscopic failure, and granular recombination. The stickslip phenomenon is highly connected with the evolution of force chains during the shear dilatancy process. The load–distribution rate curves and patterns of the force chains are utilized to describe the load-carrying behaviors and morphologic changes of force chains separately. Force chains, namely, “diagonal gridding,” “tadpole-shaped,” and “pinnate” are defined according to the form of the force chains in the corresponding three stages.  相似文献   
44.
45.
46.
A facile synthetic strategy towards conformationally stable chiral chromophores based on dimeric porphyrinoids has been established. A peculiar class of face-to-face intramolecularly interlocked corrole dimers were formed by the oxidative C−C coupling linked at the inner carbon sites upon simple treatment of copper(II) ions. Their intrinsic electronic structures were modulated by the peripheral corrole ring annulations, which lead to distinct optical properties and redox profiles. The stereogenic carbon centers implemented in the confused corrole skeleton provided a rationale for designing novel chiral materials.  相似文献   
47.
Journal of Thermal Analysis and Calorimetry - Over the last few decades, tremendous consideration is drawn towards corrugation surfaces because of their advantages over the improvement in thermal...  相似文献   
48.
ABSTRACT

The authors present the results of an investigation in Fe–Ni-Cr austenitic alloys of the low-temperature deformation-induced segregations of nickel that form in the micro regions being (i) located close to grain- and subgrain boundaries and (ii) characteristic of the concentration and magnetic inhomogeneities indicated by the appearance of a dark diffraction contrast at the electron diffraction patterns taken from these regions typical (at the same time) of an enhanced value of Curie temperature. The observed effects were connected with the micro distortions caused by the local change of lattice parameter because of an increase in nickel concentration, as well as in the result of a magnetostriction dilatation. Using methods of the X-ray energy dispersive spectroscopy (XEDS) and atomic-probe body-section radiography (tomography – APT) has made it possible to determine the borders of those regions of austenite that were characteristic of an enhanced concentration of nickel in the fields of the localisation of a deformation-induced segregation of nickel in the vicinity of grain (subgrain) boundaries of austenitic alloys of the types Fe–13Cr–30Ni and Fe–37Ni–3Ti.  相似文献   
49.
50.
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