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   87710篇
  免费   693篇
  国内免费   463篇
化学   30923篇
晶体学   872篇
力学   6951篇
综合类   1篇
数学   33528篇
物理学   16591篇
  2023年   83篇
  2022年   130篇
  2021年   204篇
  2020年   213篇
  2019年   255篇
  2018年   10528篇
  2017年   10360篇
  2016年   6410篇
  2015年   1122篇
  2014年   608篇
  2013年   906篇
  2012年   4352篇
  2011年   11075篇
  2010年   6044篇
  2009年   6391篇
  2008年   7108篇
  2007年   9302篇
  2006年   691篇
  2005年   1818篇
  2004年   1941篇
  2003年   2292篇
  2002年   1325篇
  2001年   401篇
  2000年   425篇
  1999年   245篇
  1998年   291篇
  1997年   254篇
  1996年   306篇
  1995年   207篇
  1994年   159篇
  1993年   193篇
  1992年   132篇
  1991年   142篇
  1990年   123篇
  1989年   124篇
  1988年   109篇
  1987年   112篇
  1986年   126篇
  1985年   151篇
  1984年   143篇
  1983年   115篇
  1982年   110篇
  1981年   110篇
  1980年   115篇
  1979年   109篇
  1978年   102篇
  1977年   59篇
  1975年   66篇
  1974年   65篇
  1973年   60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 effects of the size (pseudo‐generation number) and nature of end groups on physical and rheological properties were investigated for a series of hyperbranched polyesters based on an ethoxylated pentaerythritol core and 2,2‐bis‐(hydroxymethyl)propionic acid repeat units. The observed linear dependence of the melt viscosity on the molar mass in the high pseudo‐generation‐number limit indicated that entanglement effects were substantially absent. Moreover, the marked influence of end capping of the end groups on the physical and rheological properties suggested that intermolecular interactions were dominated by contacts between the outer shells of the molecules, in which the end groups were assumed to be concentrated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1218–1225, 2004  相似文献   
9.
10.
Using a monodisperse PMMA dispersion, it was shown that light reflection at the sample cuvette walls may greatly influence the results of both static (SLS) and dynamic (DLS) light scattering experiments. Considering SLS, this reflection phenomenon mostly causes an overestimation of the scattered intensity at high scattering angles, which may give rise to the emergence of an additional, artificial peak in the lower region of the particle size distribution. On the other hand, the influcence of reflection on DLS measurements was shown to be particularly important in the upper region of the particle size distribution. The experimentally observed phenomena were explained from the basic principles of both particle sizing methods. Finally, it was shown that the disturbing effect of reflection could be avoided by modifying either the hardware or the software of the static and dynamic light scattering technique.  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