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   78500篇
  免费   342篇
  国内免费   379篇
化学   24557篇
晶体学   797篇
力学   6735篇
数学   31965篇
物理学   15167篇
  2018年   10437篇
  2017年   10257篇
  2016年   6070篇
  2015年   847篇
  2014年   299篇
  2013年   339篇
  2012年   3791篇
  2011年   10529篇
  2010年   5635篇
  2009年   6057篇
  2008年   6617篇
  2007年   8790篇
  2006年   269篇
  2005年   1349篇
  2004年   1569篇
  2003年   2001篇
  2002年   1057篇
  2001年   249篇
  2000年   294篇
  1999年   163篇
  1998年   198篇
  1997年   149篇
  1996年   202篇
  1995年   130篇
  1994年   80篇
  1993年   96篇
  1992年   53篇
  1991年   66篇
  1990年   50篇
  1989年   60篇
  1988年   66篇
  1987年   60篇
  1986年   63篇
  1985年   54篇
  1984年   51篇
  1983年   40篇
  1982年   44篇
  1981年   46篇
  1980年   52篇
  1979年   53篇
  1978年   39篇
  1973年   27篇
  1914年   45篇
  1913年   40篇
  1912年   40篇
  1910年   24篇
  1909年   41篇
  1908年   40篇
  1907年   32篇
  1904年   28篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
5.
6.
Structural hierarchy of rock masses and the mechanisms of its formation   总被引:1,自引:0,他引:1  
The formation mechanisms for the structural hierarchy in geological media are discussed. It is shown that the formation of such a hierarchy is caused by certain external and internal circumstances. The first ones consist in the fact that, because of external actions, the Earth’s poles continuously execute the translational and rotational motions responsible for a regular structure of rock fracture and for the appearance of the scale factor √2. The second ones consist in the fact that, under the action of many random factors and because of external actions, during the formation of geological media there appear dissipative structures and, hence, some self-similar fractal structures are formed.  相似文献   
7.
Nicholas Nathan tries to resist the current version of the causal argument for sense-data in two ways. First he suggests that, on what he considers to be the correct re-construction of the argument, it equivocates on the sense of proximate cause. Second he defends a form of disjunctivism, by claiming that there might be an extra mechanism involved in producing veridical hallucination, that is not present in perception. I argue that Nathan’s reconstruction of the argument is not the appropriate one, and that, properly interpreted, the argument does not equivocate on proximate cause. Furthermore, I claim that his postulation of a modified mechanism for hallucinations is implausibly ad hoc.  相似文献   
8.
The electrophoresis of DNA chains in uncrosslinked polymer solutions with a Brownian dynamics simulation with an anisotropic friction tensor was analyzed. According to the degree of anisotropy, three types of migration behavior are obtained: fluctuation without or with periodicity between U‐shaped and compact conformations, or migration with linear conformation. We found good agreement between our simulation results and the direct observations of DNA by fluorescence microscopy. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1316–1322, 2003  相似文献   
9.
The oscillation of the interfacial tension and electrical potential at a water/nitrobenzene interface was observed with homologous anionic surfactant molecules, sodium-alkyl-sulfates. Concerning small molecules with a short hydrophobic carbon chain, the oscillation period and amplitude decreased with a decrease of the length of the alkyl chain. On the other hand, when surfactant molecules with a long hydrophobic carbon chain were used, no remarkable periodic oscillation occurred after the first oscillation. In all systems, an interfacial flow by Marangoni convection was observed when the oscillation took place. By monitoring the movement of carbon powder scattered on the liquid/liquid interface with a CCD camera, we could observe that the liquid/liquid interface expanded outward from the area on which the surfactant molecules adsorbed when the oscillation occurred. When the small molecule was used, the speed of expansion of the interface (flow speed) was small and shrinkage followed by expansion of the interface repeatedly occurred. However, when the large molecule was used, the flow speed was large and expansion occurred only one time. These results show that hydrodynamic factors and surface activities are important in chemical oscillation systems.  相似文献   
10.
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