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   81896篇
  免费   459篇
  国内免费   397篇
化学   26846篇
晶体学   823篇
力学   6787篇
数学   32495篇
物理学   15801篇
  2022年   52篇
  2021年   77篇
  2020年   131篇
  2019年   100篇
  2018年   10484篇
  2017年   10285篇
  2016年   6155篇
  2015年   923篇
  2014年   380篇
  2013年   532篇
  2012年   4012篇
  2011年   10775篇
  2010年   5741篇
  2009年   6135篇
  2008年   6781篇
  2007年   8939篇
  2006年   425篇
  2005年   1433篇
  2004年   1651篇
  2003年   2082篇
  2002年   1088篇
  2001年   285篇
  2000年   344篇
  1999年   196篇
  1998年   223篇
  1997年   176篇
  1996年   255篇
  1995年   157篇
  1994年   115篇
  1993年   155篇
  1992年   107篇
  1991年   100篇
  1990年   91篇
  1989年   94篇
  1988年   97篇
  1987年   85篇
  1986年   94篇
  1985年   93篇
  1984年   86篇
  1983年   69篇
  1982年   63篇
  1981年   64篇
  1980年   71篇
  1979年   77篇
  1978年   62篇
  1977年   54篇
  1976年   58篇
  1975年   61篇
  1974年   51篇
  1973年   85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.
9.
10.
In the past 6 years changes have occurred in GCE A-levels. Inparticular, there have been several major changes in A-levelMathematics courses. As engineering students are usually requiredto have studied A-level Mathematics, or its equivalent, thesechanges have had an effect on their prior mathematical knowledge.Moreover, engineering students traditionally obtained a goodgrounding in mechanics as part of their A-level Mathematicsqualification. However, mechanics, which was once included inthe core syllabus, is now optional. This article investigatesthe current availability and uptake of mechanics modules withinA-level Mathematics courses in schools. Comparisons are drawnbetween these results and results of a survey of schools in2004 and surveys of first year engineering students conductedin 2004 and 2005. It is found that there is a decline in theavailability of mechanics modules and the uptake of more thanone mechanics module has also decreased. The implications ofthese findings for engineering educators are discussed.  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